Patent Application
20090103054
1. Field of the Invention
The present invention relates generally to the system configuration and methods for controlling and operating a projection apparatus comprising a spatial light modulator. More particularly, this invention related to an image projection apparatus implemented with a spatial light modulator and joinder prisms for separating and synthesizing lights transmitted in different wavelengths for projecting images of a plurality of colors.
2. Description of the Related Art
Even though there have been significant advances made in recent years on the technologies of implementing electromechanical micromirror devices as spatial light modulator, there are still limitations and difficulties when these devices are employed to provide high quality image displays. Specifically, when the display images are digitally controlled, the image qualities are adversely affected due to the fact that the image is not displayed with a sufficient number of gray scales.
Electromechanical micromirror devices have drawn considerable interest because of their application as spatial light modulators (SLMs). A spatial light modulator requires an array of a relatively large number of micromirror devices. In general, the number of devices required ranges from 60,000 to several million for each SLM.
The on-and-off states of the micromirror control scheme, as that implemented in the U.S. Pat. No. 5,214,420 and by most of the conventional display systems, impose a limitation on the quality of the display. Specifically, in a conventional configuration of the control circuit, the gray scale (PWM between ON and OFF states) is limited by the LSB (least significant bit, or the least pulse width). Due to the ON-OFF states implemented in conventional systems, there is no way to provide a shorter pulse width than LSB. The least amount of controllable light intensity, which determines gray scale, is the light reflected during the least pulse width. The limited gray scales lead to degradations of image display.
Specifically,
The dual states switching, as illustrated by the control circuit, controls the micromirrors to position either at an ON or an OFF angular orientation, as that shown in
When adjacent image pixels are shown with a great degree of difference in the gray scales due to a very coarse scale of controllable gray scale, artifacts are shown between these adjacent image pixels. That leads to image degradations. The image degradations are especially pronounced in bright areas of display where there are “bigger gaps” between gray scales of adjacent image pixels. In bright areas of the display, the adjacent pixels are displayed with visible gaps of light intensities.
As the micromirrors are controlled to have a fully on and fully off position, the light intensity is determined by the length of time the micromirror is at the fully on position. In order to increase the number of gray scales of a display, the speed of the micromirror must be increased such that the digital control signals can be increased to a higher number of bits. However, when the speed of the micromirrors is increased, a stronger hinge is necessary for the micromirror to sustain the required number of operational cycles for a designated lifetime of operation, In order to drive micromirrors supported on a stronger hinge, a higher voltage is required. In this case, the voltage may exceed twenty volts, and may even be as high as thirty volts. Micromirrors manufactured by applying the CMOS technologies would probably not be suitable for operation this higher range of voltages, and therefore, DMOS micromirror devices may be required. In order to achieve higher degree of gray scale control, more complicated manufacturing processes and larger device areas are necessary when DMOS micromirrors are implemented. Conventional modes of micromirror control are therefore facing a technical challenge due to the difficulties that the accuracy of gray scale has to be sacrificed for the benefit of smaller and more cost effective micromirror displays, due to the operational voltage limitations.
There are many patents related to light intensity control. These patents include U.S. Pat. Nos. 5,589,852, 6,232,963, 6,592,227, 6,648,476, and 6,819,064. There are further patents and patent applications related to the different shapes of light sources. These patents includes U.S. Pat. Nos. 5,442,414, 6,036,318, and Application 20030147052. U.S. Pat. No. 6,746,123 discloses special polarized light sources for preventing light loss. However, these patents and patent application do not provide an effective solution to overcome the limitations caused by insufficient gray scales in the digitally controlled image display systems.
Furthermore, there are many patents related to spatial light modulation including U.S. Pat. Nos. 2,025,143, 2,682,010, 2,681,423, 4,087,810, 4,292,732, 4,405,209, 4,454,541, 4,592,628, 4,767,192, 4,842,396, 4,907,862, 5,214,420, 5,287,096, 5,506,597, and 5,489,952. However, these inventions have provided a direct resolution to overcome the limitations and difficulties discussed above.
Therefore, a need still exists in the art of image display systems, applying digital control of a micromirror array as a spatial light modulator, for new and improved systems such that the difficulties and limitations discussed above can be resolved.
Therefore, one aspect of the present invention is to decrease the size of a spatial light modulator (SLM) and to implement a spatial light modulator of a reduced size in a projection apparatus.
A first exemplary embodiment of the present invention provides a projection apparatus, comprising a light source, a plurality of spatial light modulators each comprising a mirror capable of deflecting an incident light emitted from the light source in an intermediate direction between two mutually different first and second directions, along with the first and second directions, a projection optical system for projecting a modulation light modulated by the spatial light modulator, a first joinder prism comprising a first optical surface to which at least two of the incident lights with mutually different frequencies are incident, a second optical surface which ejects the incident light incident from the first optical surface and to which the modulation light is incident, and a selective reflection surface for reflecting the incident light incident from the first optical surface and transmitting the modulation light, and a second joinder prism comprising a third optical surface to which the modulation light ejected from the first joinder prism is incident, a synthesis surface for synthesizing, in the same light path, the modulation lights with different frequencies incident from the third optical surface, and an ejection surface which is equipped at a position approximately opposite to the projection optical system and which ejects a synthesized light synthesized on the synthesis surface, wherein the first optical surface is approximately perpendicular to the synthesis surface.
A second exemplary embodiment of the present invention provides the projection apparatus according to the first exemplary embodiment, further comprising a third joinder prism which is placed in a light path of the incident light and between the light source and first joinder prism and which is in a similar form to the second joinder prism.
A third exemplary embodiment of the present invention provides the projection apparatus according to the second exemplary embodiment, wherein the third joinder film comprises an incidence surface to which the incident light is incident, a separation surface for separating the incident light incident from the incidence surface, and a fourth optical surface for ejecting the incident light separated on the separation surface to the first optical surface, wherein the fourth optical surface is placed opposite to the first optical surface.
A fourth exemplary embodiment of the present invention provides the projection apparatus according to the first exemplary embodiment, wherein the second joinder prism comprises a fifth optical surface, which is approximately perpendicular to the synthesis surface and to which a portion of the modulation light is incident, wherein the modulation light is incident to the fifth optical surface at an angle smaller than the critical angle.
A fifth exemplary embodiment of the present invention provides the projection apparatus according to the first exemplary embodiment, wherein the second joinder prism comprises a fifth optical surface which is approximately perpendicular to the synthesis surface and to which a portion of the modulation light is incident, and the projection apparatus further comprises a prism joined to the second joinder prism on the fifth optical surface, wherein the prism comprises a first flat surface, which is the joinder surface between the present prism and second joinder prism, and to which the modulation light ejected from the second joinder prism is incident at an angle smaller than the critical angle, and a second flat surface to which the modulation light incident from elsewhere other than the joinder surface is incident at an angle no smaller than the critical angle.
A sixth exemplary embodiment of the present invention provides the projection apparatus according to the second exemplary embodiment, wherein the width of the second joinder prism in a direction parallel to the third optical surface and parallel to the deflection locus formed by the modulation light is approximately equal to the diameter of the entrance pupil of the projection optical system.
A seventh exemplary embodiment of the present invention provides the projection apparatus according to the second exemplary embodiment, wherein the direction in which the incident light is incident to the third joinder prism is approximately the same as the direction of the synthesized light ejected from the second joinder prism.
An eighth exemplary embodiment of the present invention provides the projection apparatus according to the fourth exemplary embodiment, further comprising a light absorption member that is placed in the extended optical axis of the modulation light incident to the fifth optical surface and outside of the second joinder prism or in the proximity of the fifth optical surface.
A ninth exemplary embodiment of the present invention provides the projection apparatus according to the fourth exemplary embodiment, further comprising heat dissipation member that is placed in the extended optical axis of the modulation light incident to the fifth optical surface and outside of the second joinder prism or in the proximity of the fifth optical surface.
A tenth exemplary embodiment of the present invention provides a projection apparatus, comprising a light source, a plurality of spatial light modulators each comprising a micromirror capable of deflecting an incident light emitted from the light source in an intermediate direction between two mutually different first and second directions, along with the first and second directions, a separation-use prism for separating the illumination light into lights with different wavelengths and ejecting the separated illumination lights to the micromirror, and a synthesis-use prism which is formed similarly to the separation-use prism and which is placed in inclination to the present separation-use prism by a predetermined angle and which comprises a synthesis surface for synthesizing, in the same light path, the modulation lights modulated by the micromirror.
An eleventh exemplary embodiment of the present invention provides the projection apparatus according to the tenth exemplary embodiment, further comprising a projection optical system, wherein the synthesis-use prism ejects the synthesized light synthesized on the synthesis surface toward the projection optical system.
A twelfth exemplary embodiment of the present invention provides the projection apparatus according to the tenth exemplary embodiment, wherein the predetermined angle is approximately 90 degrees.
A thirteenth exemplary embodiment of the present invention provides the projection apparatus according to the tenth exemplary embodiment, wherein the predetermined angle is two times the maximum deflection angle of the micromirror relative to the horizontal state thereof.
A fourteenth exemplary embodiment of the present invention provides the projection apparatus according to the tenth exemplary embodiment, further comprising a projection optical system, wherein the modulation light deflected in the first direction is incident to the synthesis-use prism and then is incident to a surface of the synthesis-use prism, the surface opposite to the projection optical system, and the modulation light deflected in the second direction is incident to the synthesis-use prism and then is incident to an optical surface of the synthesis-use prism, the optical surface approximately perpendicular to the synthesis surface at an angle smaller than the critical angle.
The present invention is described in detail below with reference to the following Figures.
First is a description of an outline of an example of a mirror device according to a preferred embodiment of the present invention.
Image projection apparatuses implemented with a spatial light modulator (SLM), such as a transmissive liquid crystal, a reflective liquid crystal, a mirror array and other similar image modulation devices, are widely known.
A spatial light modulator is formed as a two-dimensional array of optical elements, ranging in number from tens of thousands to millions of miniature modulation elements, with the individual elements enlarged and displayed, as the individual pixels corresponding to an image to be displayed, onto a screen by way of a projection lens.
Spatial light modulators generally used for projection apparatuses primarily include two types: 1.) a liquid crystal device, formed by sealing a liquid crystal between transparent substrate, for modulating the polarizing direction of incident light and providing them with a potential and 2.) a mirror device deflects miniature micro electro mechanical systems (MEMS) mirrors with electrostatic force and controls the reflecting direction of illumination light.
One embodiment of the above described mirror device is disclosed in U.S. Pat. No. 4,229,732, in which a drive circuit using MOSFET and deflectable metallic mirrors are formed on a semiconductor wafer substrate. The mirror can be deformed by electrostatic force supplied from the drive circuit and is capable of changing the reflecting direction of the incident light.
Meanwhile, U.S. Pat. No. 4,662,746 has disclosed an embodiment in which one or two elastic hinges retain a mirror. If the mirror is retained by one elastic hinge, the elastic hinge functions as a bending spring. In a mirror supported by two elastic hinges, these two elastic hinges function as torsion springs to incline the mirror, and thereby deflecting the reflecting direction of the incident light.
The following is an outline description of the configuration of the mirror device.
The size of a mirror for implemented in such a mirror device is between 4 μm and 10 μm on each side. The mirrors are placed on a semiconductor wafer substrate to have a configuration for minimizing the gap between adjacent mirrors. Smaller gaps reduce random and interfering reflection lights from the gap to prevent such reflections from degrading the contrast of the displayed images.
Furthermore, the ratio (referred to as “aperture ratio” hereinafter) of the effective reflection surface to the pixel placement region is commonly set at approximately no less than 80%, with the reflection ratio approximately designated at no lower than 80%. The gap between adjacent mirrors is preferably reduced to a range between 0.15 μm and 0.55 μm, while avoiding physical interference with adjacent mirror elements. A mirror device with improved aperture also has an advantage to reduce the energy irradiated on the device substrate through the gap between adjacent mirrors and accordingly decrease operational failures caused by extraneous heating and a photoelectric effect.
The mirror device is formed on a substrate that includes an appropriate number of mirror elements. Each mirror element is applied to modulate a corresponding image display element known as a pixel. The number of image display elements appropriate for displaying image of specific resolution is determined according to image display standards in compliance to the resolution requirements of a display specified by the Video Electronics Standards Association (VESA) and to the television-broadcasting standard. For example, in the case of configuring a mirror device in compliance with the WXGA (with the resolution of 1280×768) as specified by VESA and in which the size of each mirror is 10 μm, the diagonal length of the display area will be about 0.61 inches, thus producing a sufficiently small mirror device
In the projection apparatus implemented with a reflective spatial light modulator configured as the above-described mirror device, there is a close relationship among the numerical aperture (NA) NA1 of an illumination light path, the numerical aperture NA2 of a projection light path, and the tilt angle α of a mirror.
The following discussion assumes that the tilt angle α of a mirror 4003 is 12 degrees. When a modulated light reflected by the mirror 4003 and incident to the pupil of the projection light path is set perpendicular to a device substrate 4004, the illumination light is incident at an angle inclined by 2α, that is, 24 degrees, relative to the perpendicular axis of the device substrate 4004. For the light beam reflected by the mirror to be most efficiently incident to the pupil of the projection lens, it is advantageous for the numerical aperture of the projection light path to be equal to the numerical aperture of the illumination light path. If the numerical aperture of the projection light path is smaller than that of the illumination light path, the illumination light cannot be sufficiently transmitted into the projection light path. On the other hand, if the numerical aperture of the projection light path is larger than that of the illumination light path, the illumination light can be entirely transmitted onto the projection lens becomes excessively large, which increases the inconvenience in terms of configuring the projection apparatus. Furthermore, in this case, the light fluxes of the illumination light and projection light must be directed apart from each other because the optical members of the illumination system and those of the projection system must be physically placed in separate locations in an image display system. As shown in
NA1=NA2=sin α=sin 12°
Letting the F-number of the illumination light path be F1 and the F-number of the projection light path be F2, the numerical aperture can be converted into an F-number as follows:
F1=F2=1/(2*NA)=1/(2*sin 12°)=2.4
In order to maximize the transmission of illumination light emitted from a light source with non-directivity in the emission direction of light, such as a high-pressure mercury lamp or xenon lamp, which are generally used for a projection apparatus, it is necessary to maximize the projection angle of light on the illumination light path side. Since the numerical aperture of the illumination light path is determined by the specific tilt angle of a mirror to be used, the tilt angle of the mirror needs to be large in order to increase the numerical aperture of the illumination light path.
Increasing of the tilt angle of mirror, however, requires a higher drive voltage and a larger distance between the mirror and the electrode for driving the mirror because a greater physical space needs to be secured for tilting the mirror. The electrostatic force F generated between the mirror and electrode is derived by the following equation:
F=(ε*S*V2)/(2*d2),
where “S” is the area size of the electrode, “V” is the voltage, “d” is the distance between the electrode and mirror, and “ε” is the permittivity of vacuum.
The equation clearly illustrates that the drive force is decreased in proportion to the second power of the distance d between the electrode and mirror. Conventionally, the drive voltage may be increased to compensate for the decrease in the drive force associated with the increase in the distance. However, the drive voltage is about 5 to 10 volts in the drive circuit, by means of a CMOS process used for driving a mirror, and therefore a relatively special process such as a DMOS process is required if a drive voltage in excess of about 10 volts is needed. A DMOS process would be disadvantageous for manufacturing the mirror device due to the cost increase in manufacturing the mirror device.
Furthermore, for the purpose of cost reduction, it is advantageous to obtain as many mirror devices as possible from a single semiconductor wafer substrate in order to improve the productivity. That is, shrinking the pitch between mirror elements reduces the size of the mirror device overall. However, it is clear that the area size of an electrode is reduced in association with a size reduction of the mirror, which also leads to less driving power.
Along with these requirements for miniaturizing a mirror device, there is a design tradeoff for further consideration because of the fact that the larger a mirror device, the brighter the display image when a conventional light lamp is used as the light source. Attributable to an optical functional relationship generally known as etendue, the efficiency of the non-polarized light projected from the conventional lamp may be substantially reduced. The adverse effects must be taken into consideration as an important factor for designing and configuring an image projection system, particularly for designing the light sources.
Let “y” represent the size of a light source 4150 and “u” represent the angle of light with which an optical lens imports the light from the light source. Further, let “u′” be the converging angle on the image side converged by using the optical lens 4106, and “y′” be the size of an image projected onto a screen 4109, by way of a projection lens 4108 after using an optical device 4107 for the converged light. Specifically, there is a relationship known as the etendue among the size y of the light source 4150, the import angle u of light, the converging angle u′ on the image side, and the size y′ of an image, as follows:
y*u=y′*u′
Based on this relationship, the smaller the optical device 4107 attempting to image the light source 4150, the smaller the import angle u of light becomes. Because of this, when the optical device 4107 is made smaller, the image becomes darker as a result of limiting the import angle u of light. Therefore, when using an arc discharge lamp with low directivity, the import angle u of light needs to be appropriately large in order to maintain the brightness of an image.
The larger the optical lens used in this case, the higher the converging capacity and the better the usage efficiency of light. However, increasing the size of the optical device 4107 is contradictory to the demand for shrinking the spatial light modulator or making the projection apparatus more compact.
In contrast, a laser light source has a higher directivity of light and a smaller expansion of light flux than those of a discharge lamp light source. Therefore, a projected image can be made sufficiently bright without the need to increase the size of the optical lens or optical device. Further, if the projected image is not sufficiently bright, adjustment of the output of the laser light source can increase the brightness of the projected images. Also in this case, because of the high directivity of laser light, the light intensity can be increased without allowing a substantial expansion of light flux.
In this case, the usage efficiency of light for the optical lens 4106 and optical device 4107 is improved by taking advantage of the high directivity of the laser light. A projected image can be made brighter without a need to increase the size of the optical lens 4106 or optical device 4107. This eliminates the problem of etendue, making it possible to miniaturize the optical lens 4106 and optical device 4107, leading to a more compact projection apparatus.
The following is an outline description of a resolution limit.
An examination of the limit value of the aperture ratio of a projection lens used for a projection apparatus, which displays the display surface of a mirror device in enlargement, in view of the resolution of an image to be projected, leads to the following.
Where “Rp” is the pixel pitch of the mirror device, “NA” is the aperture ratio of a projection lens, “F” is an F-number, and “λ” is the wavelength of light, the limit “Rp” with which any adjacent pixels on the projection surface are separately observed is derived by the following equation:
Rp=0.61*λ/NA=1.22*λ*F
When the pitch between mirror elements is decreased by using a miniaturized mirror, the relationship among the aperture ratio NA, which is theoretically required for resolving individual mirrors, the F-number for the projection lens, and the corresponding deflection angle of the mirror, is given by the following tables for the wavelength of light at λ=400 nm, the green light (at λ=650 nm) and the red light (at λ=800 nm), respectively.
The NA required for resolving, in the projected image, adjacent mirror elements and the tilt angle of a mirror for separating the illumination light and projection light with the respective
Based on the above tables, it is clear that a sufficient F-number for a projection lens required for resolving, in the projected image, individual pixels with, for example, 10 μm pixel pitch is theoretically F=20.5. The projection lens has an extremely small aperture when the wavelength of illumination light is λ=400 nm. In the meantime, the mirror would have a sufficient deflection angle of mere 1.4 degrees to provide the required resolution. The mirror device can be controlled and the mirror elements may be driven with a very low drive voltage.
However, as discussed above, the image brightness would be significantly reduced when a conventional non-coherent lamp used as a light source is implemented with an illumination lens matched with such a projection lens. Accordingly, a laser light source is implemented to circumvent the above-described problem attributable to the etendue. The implementation of the laser light source makes it possible to increase the F-number for the illumination and projection optical systems to the number indicated in the table and to reduce the deflection angle of a mirror element as a result, thus enabling the configuration of a compact mirror device with a low drive voltage.
Furthermore, the introduction of a laser light source provides the benefit of lowering the drive voltage by introducing the laser light source, making it possible to further reduce the thickness of the circuit-wiring pattern of the control circuit controlling the mirror. It is possible to further reduce power consumption by setting the deflection angle of the mirror at a minimum for each frequency of light as the target of modulation. That is, the deflection angle of the mirror can be reduced for a mirror device modulating, for example, blue light as compared to the deflection angle of a mirror modulating red light. It is thus possible for a projection apparatus to be configured without increasing the sizes of the optical components used in the apparatus when, for example, single color laser light sources are used for light sources, the respective illumination light paths are individually provided, and the optimal NAs are set for the respective illumination light paths.
It is also possible to cause the laser light source to perform pulse emission by configuring a circuit that alternately emits the pulse emission of the ON and OFF lights for a predetermined period. Controlling the pulse emission of the light source makes it possible to adjust intensity in accordance with the image signal (that is, in accordance with the brightness and hue of the entire projection image) and to express the finer gradations of the display image. Further, lowering the output of the laser light makes it possible to vary the dynamic range of an image and to darken the entire screen in response to a dark image.
Furthermore, performing a pulse control makes it possible to turn OFF a laser light source as appropriate during a period where no image is displayed or during a period of changing the colors of a display image in one frame. As a result, a temperature rise due to the irradiation of extraneous light onto a mirror device can be alleviated.
The following is a detail description of a first preferred embodiment of the present invention, taking into consideration of the configuration of the above described mirror device.
The following is a description, in detail, of a mirror device according to the present embodiment with reference to the accompanying drawings.
In the mirror element shown in
The mirror 4003 is formed in the approximate shape of a square, with the length of a side, ranging between 4 μm and 10 μm in an exemplary embodiment. Further, the mirror pitch may be between 4 μm and 10 μm. The deflection axis 4005 of the mirror 4003 is on the diagonal line thereof.
The light emitted from a light source may be a coherent light such as a laser light source, to project onto the mirror 4003 along an orthogonal or diagonal direction relative to the deflection axis 4005.
The following is a description of the reason for placing the deflection axis of the mirror 4003 on the diagonal line thereof.
As shown in the figures, the diffracted light is generated as a result of irradiating the light onto a mirror shown in the center of the diagrams, and the diffracted light 4110 spreads in directions perpendicular to the four sides of the mirror 4003 as the primary diffracted light 4111, the secondary diffracted light 4112, the tertiary diffracted light 4113, and so on. As shown in
The mirror device 4000 shown in
As a result, the diffracted light 4110 does not enter the projection optical system, and thereby the contrast of a projected image is improved. It is also possible to enhance the contrast by setting the deflecting angle of the mirror 4003 at a large angle relative to the incidence pupil of the projection lens and by maintaining the numerical aperture of the illumination light at a lower value, thereby separating the OFF light from the incidence pupil of the projection lens by a greater distance. This is the reason for placing the deflection axis of the mirror 4003 on the diagonal line thereof.
The lower end of the elastic hinge 4007 is connected to the device substrate 4004 that includes a circuit for driving the mirror 4003. The upper end of the elastic hinge 4007 is connected to the bottom surface of the mirror 4003. In the exemplary embodiment, an electrode for securing an electrical continuity and an intermediate member for improving the strength of a member and improving the strength of connection may be placed between the elastic hinge 4007 and the device substrate 4004, or between the elastic hinge 4007 and the mirror 4003.
Further, in the exemplary embodiment shown in
Note that a plurality of elastic hinges (refer to 4007a and 4007b) may be placed along the deflection axis 4005 of the mirror 4003, as shown in
As shown in
As shown in
Furthermore, the individual memory cells 4010a and 4010b are connected to the respective address electrodes 4008a and 4008b to receive signals from a COLUMN line 1, a COLUMN line 2, and a ROW line.
In the first memory cell 4010a, an FET-1 is connected to the address electrode 4008a to a COLUMN line 1 and ROW line, respectively, and a capacitance Cap-1 is connected between the address electrode 4008a and GND (i.e., the ground). Likewise, in the second memory cell 4010b, an FET-2 is connected to the address electrode 4008b, to COLUMN line 2 and ROW line, respectively, and a capacitance Cap-2 is connected between the address electrode 4008b and GND.
Controlling the signals on the COLUMN line 1 and ROW line applies a predetermined voltage to the address electrode 4008a, thereby making it possible to tilt the mirror 4003 towards the address electrode 4008a. Likewise, controlling the signals on the COLUMN line 2 and ROW line applies a predetermined voltage to the address electrode 4008b, thereby making it possible to tilt the mirror 4003 towards the address electrode 4008b.
Note that a drive circuit for each of the memory cells 4010a and 4010b is generally formed inside the device substrate 4004. Controlling the respective memory cells 4010a and 4010b, in accordance with the signal of image data, enables control of the deflection angle of the mirror 4003 and carries out the modulation and reflection of the incident light.
The following is a description of the address electrode comprised in a mirror element according to the present embodiment.
The present embodiment is configured such that the address electrode also functions as a stopper for determining the deflection angle of the mirror. The deflection angle of the mirror is the angle determined by the aperture ratio of a projection lens that satisfies a theoretical resolution determined by the pitch of adjacent mirrors on the basis of the equation below:
Rp=0.61*λ/NA=1.22*λ*F
In other words, the deflection angle of a mirror may not be set at a lower angle than the determined angle. Since a laser light is transmitted with a uniform phase, the diffracted light has a higher light intensity than the light emitted from a mercury lamp. Therefore, the adverse effects of the diffracted light from a coherent light projected from a laser light source can be prevented by setting the deflection angle of mirror at a larger angle than the appropriate angle calculated from the numerical aperture NA of the light flux of a laser light source and the F-number for a projection lens, thereby preventing the diffracted light from being reflected towards the projection lens. In an exemplary embodiment, the deflection angle of a mirror may be 10 to 14 degrees, or 2 to 10 degrees, relative to the horizontal state of the mirror 4003. In a configuration in which the address electrode also serves as a stopper, the space available for the electrode is significantly increased compared to a conventional configuration with the address electrode formed separately from the stopper. The mirror device implemented with such mirror element can therefore be further miniaturized.
“Stiction” is a well-known phenomenon in which a mirror 4003 sticks to the contact surface between the mirror 4003 and address electrode (i.e., also a stopper) due to surface tension or intermolecular force when the mirror is deflected. Accordingly, part of the address electrode may be configured as a circular arc, as shown in
Further, a part of the address electrode, including at least the part contacting the mirror 4003, may be provided with an inactive surface material, such as halide, in order to reduce the occurrence of stiction between the mirror 4003 and address electrode. Moreover, an elastic member formed as an integral part of the electrode may be used as a stopper.
The address electrode is configured to have a shape of a trapezoid includes a top and a bottom side, which are approximately parallel to the deflection axis 4005. The trapezoid further includes sloped sides approximately parallel to the contour line of the mirror 4003 of the mirror device, in which the deflection axis 4005 of the mirror 4003 is matched with the diagonal line thereof, as shown in
A difference in potentials needs to be generated between the mirror and the address electrode to drive the mirror by electrostatic force. The present embodiment using the electrode also as stopper is configured to provide the surface of the electrode and/or the rear surface of the mirror with an insulation layer(s) in order to prevent an electrical shorting at the point of mirror contact with the electrode. If the surface of the address electrode is provided with an insulation layer, the configuration may also be such that the insulation layer is provided to only a part of the electrode, including the part in contact with the mirror.
The following description is for an exemplary embodiment to show the size and shape of an address electrode.
Referring to
The exemplary embodiment as shown in
d1>(L1*d2)/L2
This configuration provides an efficient space utilization of the space under the mirror and maintains a stable deflection angle of the mirror. Note that, while in the example shown in
Furthermore, it is possible to configure the address electrode so that the deflection angle of the mirror 4003, when it comes into contact with the address electrode on one side, is the same as the deflection angle of the mirror 4003, when it comes in contacts with the address electrode on the other side, as shown in
When the electrode is configured so that d1=d2, the point on the electrode determining the deflection angle of the mirror is P2, and the configuration is determined to satisfy the following equation:
cot θ=d2/L2
The following is an outline description of the circuit implemented in the mirror device according to the present embodiment. As shown in
The external interface unit 5140 includes a timing controller 5141 and a selector 5142. The timing controller 5141 controls the ROW line decoder 5130 on the basis of a timing signal from the SLM controller (shown in drawing). The selector 5142 supplies the column driver 5120 with digital signal incoming from the SLM controller.
In the mirror element array 5110, a plurality of mirror elements 4001 is arranged in arrays at the positions where individual bit lines, which are vertically extended respectively from the column drivers 5120, crosses individual word lines which are horizontally extended respectively from the ROW decoders 5130.
An electrical voltage is applied to the address electrodes 4008 (i.e., the address electrodes 4008a and 4008b) in each mirror element 4001. The electrical voltage is applied to the address electrodes 4008) through the memory cells (i.e., the first memory cell 4010a and the second memory cell 4010b) shown as shown in
Another method of driving a mirror to display an image with higher levels of gray scale resolution with a reduced drive voltage is disclosed in US Patent Application 20050190429. In this disclosure, a mirror is controlled to freely oscillate in an oscillation state. The oscillation has an inherent oscillation frequency. The mirror operated in oscillating state projects an intensity of light that is about 25% to 37% of the emission light intensity when a mirror is controlled under a constant ON state.
According to such a control, it is no longer required to drive the mirror at a high speed to achieve a higher resolution of gray scale. A high level of gray scale resolution is achievable with a hinge of a low spring constant for supporting the mirror. The drive voltage may be reduced. This method, combined with the method of decreasing the drive voltage by decreasing the deflection angle of a mirror, as described above, would produce an even greater improvement.
As described above, the use of a laser light source makes it possible to decrease the deflection angle of a mirror and to shrink the mirror device without causing a degradation of brightness, and further, the use of the above described oscillation control enables a higher level of gradation without causing an increase in the drive voltage.
Giving a signal (0, 1) to the memory cells 4010a and 4010b (which are not shown here) described in
Note that the present patent application defines the deflection angles of the mirror 4003 as “+” (positive) for clockwise (CW) direction and “−” (negative) for counterclockwise (CCW) direction, with “0” degrees as the initial state of the mirror 4003. Further, an insulation layer 4006 is provided on the device substrate 4004, and a hinge electrode 4009 connected to the elastic hinge 4007 is grounded through the insulation layer 4006.
Giving a signal (1, 0) to the memory cells 4010a and 4010b (which are not shown here) described in
In either of the states shown in
The total intensity of light reflected by means of the free oscillation toward the projection optical system is certainly lower than the intensity when the mirror 4003 is continuously in the ON light state and higher than the intensity when it is continuously in the OFF light state. That is, it is possible to make an intermediate intensity between those of the ON light state and OFF light state. Therefore, a higher gradation image can be projected than with the conventional technique by finely adjusting the intensity as described above.
Although not shown in the drawing, an alternative configuration may be such that only a portion of light is made to enter the projection optical system by reflecting an incident light in the initial state of a mirror 4003. Configuring as such, a reflection light enters the projection optical system in higher intensity than that when the mirror 4003 is continuously in the OFF light state and lower intensity than that when the mirror 4003 is continuously in the ON light state (which is called an intermediate light state).
The following description outlines the natural oscillation frequency of the oscillation system of a mirror device according to the present embodiment.
The reduction of the drive voltage to achieve a higher resolution of gray scales by controlling the mirrors in a free oscillation is already described above. For a mirror device controlled by a pulse width modulator to operate with a free oscillation intermediate state by applying a control word with a LSB, there is a functional relationship between the length of time represented by the LSB and the natural frequency of the oscillation for a mirror supported on a hinge. The natural oscillation cycle T of an oscillation system=2*π*√(I/K)=LSB time/X [%]; where:
I: the rotation moment of an oscillation system,
K: the spring constant of an elastic hinge,
LSB time: the LSB cycle at displaying n bits, and
X [%]: the ratio of the light intensity obtained by one oscillation cycle to the Full-ON light intensity of the same cycle
Note that:
“I” is determined by the weight of a mirror and the distance between the center of gravity and the center of rotation;
“K” is determined from the thickness, width, length, material and cross-sectional shape of an elastic hinge; and
“LSB time” is determined from one frame time, or one frame time and the number of reproduction bits, in the case of a single-panel projection method.
“X” is determined as described above, particularly from the F-number of a projection lens and the intensity distribution of an illumination light. For example, when a single-panel color sequential method is employed, the ratio of emission intensity by one oscillation is assumed to be 32%, and the minimum emission intensity in a 10-bit grayscale is to be obtained by an oscillation, then “I” and “K” are designed so as to have a natural oscillation cycle as follows:
T=1/(60*3*210*0.32)≈17.0 μsec.
In contrast, when a conventional PWM control is employed to make the changeover transition time tM of a mirror approximately equal to the natural oscillation frequency of the oscillation system of the mirror and the LSB is regulated so that a shortage of the light intensity in the interim can be sufficiently ignored, the gray scale reproducible with the above described hinge is about 8-bit, even if the LSB is set at five times the changeover transition time tM. Specifically, the control process of this invention when implemented with the elastic hinge is able to display an image of a 10-bit grayscale in contrast to the projection apparatuses applying conventional control process would be able to display an image of only about an 8-bit grayscale.
In the single-panel projection apparatus described above, an example configuration attempting to obtain, for example, 13-bit grayscale is as follows:
LSB time=( 1/60)*(⅓)*(½13)=0.68 μsec
If a configuration is such that the light intensity obtained in one cycle for the optical projection system is 38% of the intensity obtained from controlling a mirror in a constant ON state for the same cycle, the oscillation cycle T is as follows:
T=0.68/0.38=1.8 μsec
In contrast, when attempting to obtain an 8-bit grayscale in the multi-panel projection apparatus described above, an example comprisal is as follows:
LSB time=( 1/60)*(⅓)*( 1/28)=21.7 μsec
If a configuration is such that the light intensity obtained in one cycle for the optical projection system is 20% of the intensity obtained from controlling a mirror in a constant ON state for the same cycle, the oscillation cycle T is as follows:
T=21.7/0.20=108.5 μsec.
As described above, the present embodiment is configured to set the natural oscillation cycle of the oscillation system, which includes an elastic hinge, between 1.8 μsec and 110 μsec; and to use three deflection state, i.e., a first deflection state (ON state), in which the light modulated by the mirror element is reflected towards the projection light path, a second deflection state (OFF state), in which the light is reflected in a direction away from the projection light path, and a third deflection state (oscillation state), in which the mirror oscillates between the first and second deflection states. A higher resolution of gray scales is achievable without increasing the drive voltage of the mirror element.
The mirror element 4011 shown in
Note that the area sizes of the address electrode 4013 exposed above the device substrate 4004 are configured to be different between the left side and right side of the deflection axis of the elastic hinge 4007, or mirror 4003, with the area size of the exposed part of the address electrode 4013 on the left side of the elastic hinge 4007 being larger than the area size on the right side, in
Specifically, the mirror 4003 is deflected by the electrical control of one address electrode 4013 and drive circuit. Further, the deflected mirror 4003 is retained at a specific deflection angle by contacting with stopper 4012a or 4012b, which are formed in the vicinity of the exposed parts on the left and right sides of the address electrode 4013.
More specifically, an alternative configuration may eliminate the stopper for allow more areas to form the electrode as described above with the mirror contacting the address electrode directly.
Furthermore, a hinge electrode 4009 connected to the elastic hinge 4007 is grounded through the insulation layer 4006 as part of the mirror element 4011.
The present patent application calls the part, which is exposed above the device substrate 4004, of the address electrode 4013 of
As such, the applying of a voltage by configuring the address electrode 4013 to be asymmetrical, that is, the area size of the left side is different from that of the right side, in relation to the deflection axis of the elastic hinge 4007 or mirror 4003, generates the difference in coulomb force between (a) and (b), where (a): a coulomb force generated between the first electrode part and mirror 4003, and (b): a coulomb force generated between the second electrode part and mirror 4003. The mirror 4003 can be deflected by differentiating the Coulomb force between the left and right sides of the deflection axis of the elastic hinge 4007 or mirror 4003.
Meanwhile,
Other comprisals are similar to the configuration described for
The following is a description, in detail, of a single address electrode 4013 controlling the deflection of a mirror with reference to
Mirror elements 4011a and 4011b respectively shown in
In contrast,
The following is a description of the control for the deflecting operation of a mirror in the mirror element 4011a or 4011b, each respectively shown in
Referring to
The following description refers to the control of only the mirror element 4011a shown in
The vertical axis of the “mirror angle” of
Note that the deflection angle is designated at 13 degrees as an example; the deflection angle is not limited to that particular angle.
Furthermore, the horizontal axis of
When the deflecting operation of the mirror 4003 is performed in the configuration of
Referring to
At the time t1, a voltage of 4 volts is applied to the address electrode 4013a or 4013b, causing the mirror 4003 to be attracted by a coulomb force generated between the mirror 4003 and address electrode 4013a or 4013b toward the first electrode part having a large area size so that the mirror 4003 shifts from the 0-degree deflection angle at the time t1 to a −13-degree deflection angle at time t2. Then, the mirror 4003 is retained on the stopper 4012a on the first electrode part side.
The distance G1 between the mirror 4003 and the first electrode part and the distance G2 between the mirror 4003 and the second electrode part, when the mirror 4003 is in the initial state, are the same, and the first electrode part has a larger area size than the second electrode part, and therefore the first electrode part can retain a larger amount of charge. As a result, a larger coulomb force is generated for the first electrode part.
Between the time t2 and t3, continuously applying a voltage of 4 volts to the address electrode 4013a or 4013b in accordance with the period in response to the data input causes the mirror 4003 to be retained on the stopper 4012a on the first electrode part side.
Then, at the time t3, stopping the data input applies a voltage of “0” volts to the address electrode 4013a or 4013b. As a result, the Coulomb force generated between the address electrode 4013a or 4013b and mirror 4003 is withdrawn. This causes the mirror 4003 retained on the first electrode part side to be shifted to a free oscillation due to the restoring force of the elastic hinge 4007.
Furthermore, the deflection angle of the mirror 4003 becomes θ>0 degrees, and when a voltage of 4 volts is applied to the address electrode 4013a or 4013b at the time t4 when a coulomb force F1, generated between the mirror 4003 and first electrode part, and a coulomb force F2, generated between the mirror 4003 and second electrode part, constitutes the relationship of F1<F2, and thereby the mirror 4003 is attracted to the second electrode part. Further, the mirror 4003 is retained onto the stopper 4012b of the second electrode part at the time t5.
The reason is that the second power of a distance has a greater effect on a Coulomb force F than the difference in electrical voltages, according to the equation noted above. Therefore, with an appropriate adjustment of the area sizes of the first and second electrode parts, a coulomb force F acts more strongly on the smaller distance G2 of the distance between the address electrode 4013a or 4013b and mirror 4003, despite the fact that the area S2 of the second electrode part is smaller than the area S1 of the first electrode part. As a result, the mirror 4003 can be deflected to the second electrode part.
Note that the transition time of the mirror 4003 between the time t3 and t4 is preferably performed in about 4.5 μsec in order to obtain a high grade of gradation. Further, a control can possibly be performed to turn off the illumination light synchronously with a transition of the mirror 4003, so as to not let the illumination light be reflected and incident to the projection light path during a data rewrite, that is, during the transition of the mirror 4003, between the time t3 and t4.
Continuously applying a voltage to the address electrode 4013a or 4013b between the time t5 and t6 causes the mirror 4003 to be continuously retained to the stopper 4012b of the second electrode part. In this event, no data is input and therefore no image is projected.
Then, at the time t6, a new data input is carried out. The voltage of 4 volts, which has been applied to the address electrode 4013a or 4013b, is changed over to “0” volts at the time t6 in accordance with the data input. This operation withdraws the Coulomb force generated between the mirror 4003 retained onto the second electrode part and the address electrode 4013a or 4013b, similar to the process at time t3, so that the mirror 4003 shifts to a free oscillation state due to the restoring force of the elastic hinge 4007.
A voltage of 4 volts is again applied to the address electrode 4013a or 4013b at the time t7 when a coulomb force F1, which is generated between the mirror 4003 and first electrode part, and a coulomb force F2, which is generated between the mirror 4003 and second electrode part, constitutes the relationship of F1>F2 when the deflection angle of the mirror 4003 becomes θ<0 degrees, and thereby the mirror 4003 is attracted to the first electrode part. Then the mirror 4003 is retained onto the second electrode part at the time t8.
This principle is understood from the description of the action of a coulomb force between the above described time t3 and t5. Also in this event, the transition time of the mirror 4003 between the time t3 and t4 is preferably performed in about 4.5 μsec, and the control is performed in such a manner as to turn off the illumination light synchronously with a transition of the mirror 4003, so as to not let the illumination light be reflected and incident to the projection light path during the transition of the mirror 4003.
Then, continuously applying a voltage of 4 volts to the address electrode 4013a or 4013b between the time t8 and t9 causes the mirror 4003 to be continuously retained on the stopper 4012a of the first electrode part. In this event, data is continuously inputted and images are projected.
Then, the voltage applied to the address electrode 4013a or 4013b is changed from 4 volts to “0” volts as the data input is stopped at time t9. This operation puts the mirror 4003 into the free oscillation state. Then, at the time t10, a voltage is applied to the address electrode 4013a or 4013b, according to the same principle as the period from t3 to t5 and from the time t6 to t8, and thereby the mirror 4003 can be retained onto the stopper 4012b of the second electrode part at the time t11. A repetition of the similar operation enables the control for deflecting the mirror 4003.
The following is a description of the control for returning, to the initial state, the mirror 4003 retained onto the stopper 4012a of the first electrode part or onto the stopper 4012b of the second electrode part.
In order to return to the initial state, the mirror 4003 retained onto the stopper 4012a of the first electrode part or onto the stopper 4012b of the second electrode part in the state in which a voltage is applied to the address electrode 4013a or 4013b, an appropriate pulse voltage is applied.
As an example, the mirror 4003 is shifted to a free oscillation state by changing the voltage applied to the address electrode 4013a or 4013b to “0” volts in the state in which the mirror 4003 is retained onto the stopper 4012a of the first electrode part or onto the stopper 4012b of the second electrode part. When the mirror is performing a free oscillation, the mirror 4003 can be returned to the initial state by temporarily applying an appropriate voltage to the address electrode 4013a or 4013b, thereby generating a coulomb force pulling the mirror 4003 back towards the first electrode part or the second electrode part, either of which the mirror 4003 has been retained onto. That is, the coulomb force generates an acceleration in a direction reverse to the direction in which the mirror 4003 was heading when the distance between the address electrode 4013a or 4013b and the mirror 4003 reaches an appropriate distance as the mirror 4003 tilts from the first electrode part side to the second electrode part side, or vice versa.
Considering the principle of the coulomb force between the mirror and address electrode 4013a or 4013b as described above, the applying of a voltage to the address electrode 4013a or 4013b at an appropriate distance between the mirror 4003 and address electrode 4013a or 4013b also makes it possible to retain the mirror 4003 at the deflection angle of the ON light state by returning the mirror 4003 from the ON light state, or at the deflection angle of the OFF light state by returning the mirror 4003 from the OFF light state.
Note that the control of the mirror 4003 of the mirror elements 4011a and 4011b shown in
That is, the configuration of
In the case of the mirror element 4011c shown in
Note that the deflection angle of the mirror 4003 is retained by using the stoppers 4012a and 4012b in
Further, while the present embodiment is configured to set the control voltages at 4-volt and 0-volt applied to the address electrode 4013a, 4013b or 4013c, such control voltages are arbitrary and other appropriate voltages may be used to control the mirror 4003.
Furthermore, the mirror can be controlled with multi-step voltages to be applied to the address electrode 4013a, 4013b or 4013c. As an example, if the distance between the mirror 4003 and address electrode 4013a, 4013b or 4013c, increasing a coulomb force, the mirror 4003 can be controlled with a lower voltage than that when the mirror 4003 is in the initial state.
As described above, even with the configuration in which each mirror element comprises only one address electrode, the use of three deflection states, i.e. the first deflection state (the ON state) in which the light modulated by the mirror element is headed towards a projection light path, the second deflection state (the OFF state) in which the deflected light is headed away from the projection light path and the third deflection state (the oscillation state) in which the mirror element oscillates between the first and second deflection states, makes it possible to display an image with a high level of gradation without requiring an increase in the drive voltage for the mirror element.
Accordingly, each mirror element of the mirror device according to the present embodiment is configured to change the deflection states of the mirror in accordance with the voltage applied to the electrode, deflecting the light incident to the mirror 4003 to specific directions as shown in the example of
The illumination light ejected from the light source 4002 is incident to the mirror 4003 as depicted by an optical axis 4121. Then, the illumination light is reflected as depicted by an optical axis 4122 in the ON state of the mirror 4003, is reflected as depicted by an optical axis 4124 in the OFF state of the mirror 4003 and is reflected as depicted by an optical axis 4123 in the initial state of the mirror 4003. The configuring as such makes it possible to not allow more securely the diffraction light and scattered light generated by the mirror in the OFF light state or OFF angle to enter a projection optical system 4125.
The following is an outline description of a package used for a mirror device according to the present embodiment.
Further, an intermediate member 2009 for joining the individual constituent members includes a support part 2007, for determining the height of the cover glass 2010, and a joinder member made of fritted glass, solder, epoxy resin, or the like.
The cover glass may further be provided with a light shield layer 2006, to shield the device from extraneous light, and an anti-reflection (AR) coating 2011, to prevent extraneous reflection of incident light. The anti-reflection coating 2011 is a coating made of magnesium fluoride or a nano-structure no wider than the wavelength applied to a glass surface. The light shield layer 2006 is composed of a thin black film layer containing carbon, or a multi-layer structure consisting of a thin black film layer and a metallic layer.
Furthermore, the control circuit 2017 inside the package with the circuit wiring-pattern 2005 formed with a very large number of lines is formed on a single package substrate. The floating capacity of the circuit wiring-pattern 2005 is therefore reduced. Furthermore, the control circuit 2017 controlled in higher speed than a video signal can be placed at a position equally distanced from the respective mirror devices 2030 and 2040, and the differences of resistance and floating capacity of the respective circuit wiring-patterns 2005 connected to the individual mirror devices 2030 and 2040 are reduced. This enables the use of a mirror device comprising many mirror elements and a mirror device for which a data processing volume is large and which is capable of control in higher number of gray scales. This accordingly enables an image in a high level of gradation and high resolution. Further, the shortening of the circuit wirings to the respective mirror devices makes it easy to synchronize the timing, for controlling the mirror devices, between the respective mirror devices.
Furthermore, the thermal environments of the plural mirror devices placed on a single package substrate are the same and thereby the positional shifts due to thermal expansion of mirror elements of the respective mirror devices become approximately the same. Therefore, the projection conditions can be made to be identical. Further, the controls for the respective mirror devices can also be handled as for same environment so that the control conditions, such as an analogous control of the mirror and the voltage value of memory, can be made the same for the mirror devices.
Furthermore, the projection apparatus 2500 shown in
Note that the mirror devices 2030 and 2040 and the device substrates 2031 and 2041, which are shown in
As described above, the mirror device according to the present embodiment is configured with the electrode also carries out a function of a stopper for regulating the deflection angle of a mirror, and thereby, the space utilization efficiency is improved when a mirror element is miniaturized, enabling an increase in the area size of the electrode. Therefore, a parallel application of an oscillation control for a mirror makes it possible to enable both a miniaturization of the mirror device and an enhancement of gradations.
Note that the mirror pitch, mirror gap, deflection angle, and drive voltage of the mirror device according to the present embodiment are not limited to the values shown in the above description. Preferably, they should be within the following ranges (including the values at each end of the range): the mirror pitch is between 4 μm and 10 μm; the mirror gap is between 0.15 μm and 0.55 μm; the maximum deflection angle of mirror is between 2 degrees and 14 degrees; and the drive voltage of mirror is between 3 volts and 15 volts.
With reference to the accompanying drawings, the following is a description of a projection apparatus according to the second embodiment comprising a mirror device described in detail for the first embodiment.
First is a description of the configuration of a single-panel projection apparatus comprising a single spatial light modulator and performing color displays by temporarily changing the frequencies of the projection light, with reference to
Note that the spatial light modulator according to the present embodiment is specifically the mirror device 4000 described in detain for the first embodiment.
A projection apparatus 5010, according to the present embodiment, is a commonly referred to as a single-panel projection apparatus 5010 comprising a single spatial light modulator (SLM) 5100, a control unit 5500, a Total Internal Reflection (TIR) prism 5300, a projection optical system 5400, and a light source optical system 5200, as shown in
The projection optical system 5400 includes the spatial light modulator 5100 and TIR prism 5300 in the optical axis of the projection optical system 5400, and the light source optical system 5200 is positioned in such a manner that the optical axis thereof matches that of the projection optical system 5400.
The TIR prism 5300 directs the illumination light 5600, which is incoming from the light source optical system 5200 placed on the side towards the spatial light modulator 5100 at a prescribed inclination angle as incident light 5601 and transmits a reflection light 5602, reflected by the spatial light modulator 5100, to the projection optical system 5400.
The projection optical system 5400 projects the reflection light 5602, coming in from the spatial light modulator 5100 and TIR prism 5300, onto a screen 5900 as projection light 5603.
The light source optical system 5200 includes a variable light source 5210 for generating the illumination light 5600. The light source system further includes a condenser lens 5220 for focusing the illumination light 5600, a rod type condenser body 5230, and a condenser lens 5240.
The variable light source 5210, condenser lens 5220, rod type condenser body 5230, and condenser lens 5240 are sequentially placed in the aforementioned order on the optical axis of the illumination light 5600 projected from the variable light source 5210 into the side face of the TIR prism 5300.
The projection apparatus 5010 employs a single spatial light modulator 5100 for projecting a color display on the screen 5900 by applying a sequential color display method. That is, the variable light source 5210, comprising a red laser light source 5211, a green laser light source 5212, and a blue laser light source 5213 (not shown in drawing) that allows independent controls for the light emission states, divides one frame of display data into multiple sub-fields (in this case, three sub-fields: red (R), green (G) and blue (B)) and makes each of the light sources emit each respective light in a time series at the time band corresponding to the sub-field of each color. This process will be described in greater detail later. Note that the red laser light source 5211, green laser light source 5212 and blue laser light source 5213 may alternatively be replaced with light emitting diodes (LEDs), respectively.
The following is a description of a multi-panel projection apparatus using a plurality of spatial light modulators to continuously modulate the illumination lights with respectively different frequencies using the individual spatial light modulators and carrying out a color display by synthesizing the modulated illumination lights, with reference to
The projection apparatus 5020 is a commonly known as multiple-plate projection apparatus comprising a plurality of spatial light modulators 5100, which is the main difference from projection apparatus 5010 described above. Further, the projection apparatus 5020 includes a control unit 5502 in place of the control unit 5500.
The projection apparatus 5020 includes a plurality of spatial light modulators 5100, and further includes a light separation/synthesis optical system 5310 disposed between the projection optical system 5400 and each of the spatial light modulators 5100.
The light separation/synthesis optical system 5310 includes a TIR prism 5311, a prism 5312 and a prism 5313.
The TIR prism 5311 directs the illumination light 5600, incident from the side of the optical axis of the projection optical system 5400, to the spatial light modulator 5100 as incident light 5601.
The prism 5312 has separates the red (R) light from an incident light 5601, incident by way of the TIR prism 5311 and, making the red light incident to the red light-use spatial light modulators 5100, directs the reflection light 5602 of the red light to the TIR prism 5311.
Likewise, the prism 5313 separates the blue (B) and green (G) lights from the incident light 5601, passing through the TIR prism 5311 to project onto the blue color-use spatial light modulators 5100 and green color-use spatial light modulators 5100, directs the reflection light 5602 of the green light and blue light to the TIR prism 5311.
Therefore, the spatial light modulations of the three color lights R, G and B are carried out simultaneously at three spatial light modulators 5100, respectively, and the reflection lights resulting from the respective modulations are projected onto the screen 5900 as the projection light 5603, by way of the projection optical system 5400; thus a color display is carried out.
Note that various modifications are possible for a light separation/synthesis optical system and are not limited to the light separation/synthesis optical system 5310.
The alternate embodiment includes a light separation/synthesis optical system 5320 in place of the above described light separation/synthesis optical system 5310. The light separation/synthesis optical system 5320 includes a TIR prism 5321 and a cross-dichroic mirror 5322.
The TIR prism 5321 directs an illumination light 5600, projected from the lateral direction of the optical axis of the projection optical system 5400, to the spatial light modulators 5100 as incident light 5601.
The cross dichroic mirror 5322 separates red, blue and green lights from the incident light 5601, incoming from the TIR prism 5321, making the incident lights 5601 of the three colors enter the red-use, blue-use and green-use spatial light modulators 5100, respectively, and also converging the reflection lights 5602, reflected by the respective color-use spatial light modulators 5100, and directing the light towards the projection optical system 5400.
The projection apparatus 5040 is configured, in contrast from the above described projection apparatuses 5020 and 5030, to place, so as to be adjacent to one another in the same plane, a plurality of spatial light modulators 5100 corresponding to the three colors R, G and B on one side of a light separation/synthesis optical system 5330. This configuration makes it possible to consolidate the multiple spatial light modulators 5100 into the same packaging unit, and thereby saving space.
The light separation/synthesis optical system 5330 includes a TIR prism 5331, a prism 5332 and a prism 5333. The TIR prism 5331 has the function of directing, to spatial light modulators 5100, the illumination light 5600, incident in the lateral direction of the optical axis of the projection optical system 5400, as incident light.
The prism 5332 serves the functions of separating a red color light from the incident light 5601 and directing it towards the red color-use spatial light modulator 5100, and of capturing the reflection light 5602 and directing it to the projection optical system 5400.
Likewise, the prism 5333 serves the functions of separating the green and blue incident lights from the incident light 5601, making them incident to the individual spatial light modulators 5100 implemented for the respective colors, and of capturing the green and blue reflection lights 5602 and directing them towards the projection optical system 5400.
Unlike the above described single-panel projection apparatus, a visual problem such as a color break usually does not occur in a multi-panel projection apparatus since the individual primary colors are constantly projected. Furthermore, a bright image can be obtained because the light emitted from the light source can be effectively utilized. On the other hand, there are other challenges, such as a more complicated adjustment for the positioning of the spatial light modulator corresponding to the lights of individual colors and an increase in the size of the apparatus.
The above description has described a three-panel projection apparatus comprising three spatial light modulators as an example of a multi-panel projection apparatus.
The following is a description of a two-panel projection apparatus comprising two spatial light modulators (i.e., mirror devices) as an example of a multi-panel projection apparatus.
The two-panel projection apparatus 2500 does not project only one color of three colors R, G and B in sequence, nor does it project the R, G and B colors continuously and simultaneously, as in the case of a three-panel projection apparatus. A two-panel projection apparatus projects an image by continuously projecting, for example, a green light source possessing high visibility, a red light source, and a blue light source in sequence.
The two-panel projection apparatus 2500 is capable of changing over colors in high speed by means of pulse emission in 180 kHz to 720 kHz by comprising laser light sources, thereby making it possible to obscure flickers caused by changing over among the light sources of the respective colors. It may be alternatively configured to use a light emitting diode (LED) light source in place of the laser light source.
Note that the present configuration using laser light sources emitting the colors red (R), green (G) and blue (B), is arbitrary. Laser lights of colors cyan (C), magenta (M) and yellow (Y) may be also used. Further an R light closer to the wavelength of G, in place of a pure R, a G light closer to the wavelength of R or B, in place of a pure Q and a B light closer to the wavelength of G, in place of a pure B may be used. Further, laser lights of four wavelengths or more, obtained by combining the aforementioned colors, may be used.
Further, a projection method of continuously projecting the brightest color and changing over among the other colors in sequence on the basis of the image signals can also be adopted. Such a projection method can also be applied to a configuration that makes R, G and B lights correspond to the respective mirror devices, as in the three-panel projection method.
The following is a description of the optical comprisal and principle of projection of the two-panel projection apparatus 2500 shown in
The projection apparatus 2500 shown in
The two triangular prisms 2056 and 2059 are joined together to constitute one color synthesis prism 2060. Further, the joined part (i.e., a surface of synthesis 2055a) between the two triangular prisms 2056 and 2059 is provided with a polarization beam splitter film 2055 or coating. The color synthesis prism 2060 primarily carries out a function of synthesizing the light reflected by the two mirror devices 2030 and 2040.
The polarization beam splitter film 2055 is a filter for transmitting only an S-polarized light and reflecting P-polarized light.
A slope face of the right-angle triangle cone light guide prism 2064 is adhesively attached to the front surface of the color synthesis prism 2060, with the bottom of the light guide prism 2064 facing upward. The green laser light source 2051, the illumination optical system 2054a corresponding to the green laser light source 2051, the red laser light source 2052, the blue laser light source 2053, and the illumination optical system 2054d corresponding to the red laser light source 2052 and blue laser light source 2053 are disposed beyond the bottom surface 2064a of the light guide prism 2064, with the respective optical axes of the green laser light source 2051, red laser light source 2052, blue laser light source 2053 being aligned perpendicularly to the bottom surface of the light guide prism 2064.
Specifically, the light guide prism 2064 is implemented for causing the respective lights of the green laser light source 2051, red laser light source 2052 and blue laser light source 2053 to perpendicularly enter the color synthesis prism 2060. Such a light guide prism 2064 makes it possible to reduce the amount of the reflection light caused by the color synthesis prism 2060 when the laser light enters the color synthesis prism 2060.
Further, ¼ wavelength plates 2057a and 2057b are implemented on the bottom surface of the color synthesis prism 2060, on which a light shield layer 2063 (i.e., a light absorption member) is applied to the regions other than the areas where the light is irradiated on the individual mirror devices 2030 and 2040. Because of this, the light shield layer 2063 is also applied between the mirror device 2030 and mirror device 2040. Note that the ¼ wavelength plates 2057a and 2057b may alternatively be implemented on the cover glass of the package.
Furthermore, a light shield layer 2063 is formed also on the rear surface of the color synthesis prism 2060.
Further, the two mirror devices 2030 and 2040, which are accommodated in a single package, are disposed under the ¼ wavelength plates 2057a and 2057b. That is, the configuration is such that the two mirror devices are sealed by the bottom surface (i.e., the principal surface) of the optical member constituted by the light guide prism 2064, color synthesis prism 2060 and ¼ wavelength plates 2057a and 2057b.
The cover glass of the package is joined to the color synthesis prism 2060 with a thermal conduction member 2062 functions as a joinder layer. This joinder layer transmits heat from the cover glass of the package to the color synthesis prism 2060 through the thermal conduction member 2062. Furthermore, the circuit boards 2058, comprising a control circuit(s) for controlling the individual mirror devices 2030 and 2040, are formed on both sides of the package.
Further, the mirror devices 2030 and 2040 are respectively placed to form a 45-degree angle relative to the four sides of the outer circumference of the package on the same horizontal plane. That is, the placement the mirror devices 2030 and 2040 is such that the deflecting direction of each mirror element of the mirror devices 2030 and 2040 is approximately orthogonal to the slope face forming the color synthesis prism 2060 and to the plane on which the reflection lights are synthesized. It is very important that a high degree of precision be used in positioning the mirror devices 2030 and 2040 within the package, in relation to the color synthesis prism 2060, by means of the positioning pattern 2016.
Incidentally, the illumination optical systems 2054a and 2054b each includes a convex lens, a concave lens and other components, and the projection lens 2070 includes a plurality of lenses and other components.
The following is the principle of projection of the projection apparatus 2500 shown in
In the projection apparatus 2500, the individual laser lights 2065, 2066 and 2067 are incident from the front direction and are reflected by the two mirror devices 2030 and 2040 toward the rear direction, and then an image is projected by way of the projection lens 2070 located in the rear.
The following is a description of the projection principle starting from the incidence of the individual laser lights 2065, 2066 and 2067 to the reflection of the respective laser lights 2065, 2066 and 2067 at the two mirror devices 2030 and 2040 toward the rear direction, with reference to the front view diagram of the two-panel projection apparatus shown in
The respective laser lights 2065, 2066 and 2067 emitted from the S-polarized green laser light source 2051, and the P-polarized red laser light source 2052 and blue laser light source 2053 are made to be incident to the color synthesis prism 2060 by way of the illumination optical systems 2054a and 2054b, respectively corresponding to the laser lights 2065, and 2066 and 2067, and by way of the light guide prism 2064. Then, having transmitted through the color synthesis prism 2060, the S-polarized green laser light 2065 and the P-polarized red and blue laser lights 2066 and 2067 are incident to the ¼ wavelength plates 2057a and 2057b, which are placed on the bottom surface of the color synthesis prism 2060. Having passed through the ¼ wavelength plates 2057a and 2057b, the individual laser lights 2065, 2066 and 2067 respectively change the polarization by the amount of ¼ wavelength to become a circular polarized light state.
Then, having passed through the ¼ wavelength plates 2057a and 2057b, the circular polarized green laser light 2065 and the circular polarized red and blue laser lights 2066 and 2067 are respectively incident to the two mirror devices 2030 and 2040 that are accommodated in a single package. The individual laser lights 2065, 2066 and 2067 are modulated and reflected by the corresponding mirror devices so that the rotation directions of the circular polarization are reversed.
Specifically, the red laser light 2066 and blue laser light 2067 are incident to the mirror device 2040; the assumption is that the mirror device 2040 is configured to perform modulation on the basis of a video image signal corresponding to either wavelength.
Note that at least portions of the individual light fluxes of the red laser light 2066 and blue laser light 2067 overlap with each other and mix in the illumination light paths between the red laser light source 2052 and mirror device 2040 and between the blue laser light source 2053 and mirror device 2040. The mixed light is incident to the mirror device 2040.
Further in this event, an alternative configuration may be such that the incidence angle of the green laser light 2065, incident to the mirror device 2030, is different from that of the red laser light 2066 and blue laser light 2067, which are incident to the mirror device 2040. In such a case, each mirror device causing the above described deflection angle to be decreased to a minimum angle, which is determined by the frequency of the light as the target of modulation, makes it possible to reduce the power consumption of the mirror device and enhance the contrast of a projection image. The deflection angle may be decreased when deflecting light of a shorter wavelength versus with light of a longer wavelength.
The following is a description of the projection principle starting from the reflection of individual laser lights 2065, and 2066 and 2067 to the projection of an image with reference to the rear view diagram of the two-panel projection apparatus shown in
The ON light 2068 of the circular polarized green laser and the mixed ON light 2069 of the circular polarized red and blue lasers, which are reflected by the respective mirror devices 2030 and 2040, passes through the ¼ wavelength plates 2057a and 2057b again and enter the color synthesis prism 2060. In this event, the polarization of the green laser ON light 2068 and that of the mixed red and blue laser ON light 2069 are respectively changed by the amount of ¼ wavelengths to become a linear polarized state with 90-degree different polarization axes. That is, the green laser ON light 2068 is changed to a P-polarized light, while the mixed red and blue laser ON light 2069 is changed to an S-polarized light.
Then, the green laser ON light 2068 and the mixed red and blue laser ON light 2069 are respectively reflected by the outer side surface (i.e., a reflection surface) of the color synthesis prism 2060, and the P-polarized green laser ON light 2068 is reflected again by the polarization beam splitter film 2055. Meanwhile, the S-polarized mixed red and blue laser ON light 2069 passes through the polarization beam splitter film 2055. Then, the green laser ON light 2068 and red and blue laser mixed ON light 2069 are incident to the projection lens 2070, and thereby a color image is projected. Note that the optical axes of the respective lights incident to the projection lens 2070 from the color synthesis prism 2060 are desired to be orthogonal to the ejection surface of the color synthesis prism 2060. Alternatively, there is also a viable configuration that does not use the ¼ wavelength plates 2057a and 2057b.
With the configuration and the principle of projection as described above, an image can be projected in the two-panel projection apparatus 2500 comprising the assembly body 2400 that packages the two mirror devices 2030 and 2040, which are accommodated in a single package. Note that the assembly body 2400 in this configuration is a mirror device in a broad sense.
The green laser light 2065 emitted from the green laser light source 2051 orthogonally enters the light guide prism 2064 via the illumination optical system 2054a. With such configuration, by controlling the laser light 2065 to enter into the light guide prism 2064 along an orthogonal direction can minimize the reflection of the laser light 2065.
Then, having passed through the light guide prism 2064, the laser light 2065 passes through the color synthesis prism 2060 and ¼ wavelength plates 2057a and 2057b, which are joined to the light guide prism 2064, and then enters the mirror array 2032 of the mirror device 2030.
In this event, having been reflected by the cover glass, a light shield layer 2063 applied to a surface (i.e., an opposite surface) opposite to the incidence surface before entering the mirror array 2032 of the mirror device 2030 absorbs the laser light 2065.
The mirror array 2032 reflects the laser light 2065 with the deflection angle of a mirror that puts the reflected light in any of the states, i.e., an ON light state in which the entirety of the reflection light is incident to the projection lens 2070, an intermediate light state in which a portion of the reflection light is incident to the projection lens 2070 and an OFF light state in which no portion of the reflection light is incident to the projection lens 2070.
The reflection light of a laser light (i.e., ON light) 2071, from which the ON light state is selected, is reflected by the mirror array 2032 and will be incident to the projection lens 2070.
Meanwhile, a portion of the reflection light of a laser light (i.e., intermediate light) 2072, from which the intermediate state is selected, is reflected by the mirror array 2032 and will be incident to the projection lens 2070.
Furthermore, the mirror array 2032 is controlled to reflect the laser light (i.e., OFF light) 2073 toward the light shield layer 2063 and the reflection light is absorbed.
In this projection apparatus, the light shield layer 2063 may be placed at a position closely adjacent to the rear surface of the color synthesis prism 2060 or placed outside of the color synthesis prism 2060. Either of these locations is on the extended optical axis of the laser light (i.e., the OFF light) 2073. It is also preferable to connect the light shield layer 2063 to a heat dissipation member in order to reduce a temperature rise of the light shield layer 2063 due to the incident light. Also, a configuration may be such that the light shield layer 2063 also functions as the heat dissipation member.
Meanwhile, the configuration is such that the laser light (i.e., the OFF light) 2073 enters the rear surface of the color synthesis prism 2060 at an angle smaller than the critical angle. For example, when the color synthesis prism 2060 is constituted by BK-7 (at the refraction index of 1.51467), the critical angle θ is given by:
θ=sin−1(1/1.51467)□41.3 degrees,
and therefore, in this case, the configuration is such that the incident angle is smaller than 41.3 degrees. This configuration prevents the internal reflection of an extraneous modulation light within the color synthesis prism 2060, thus making it possible to eject the extraneous modulation light to the outside. This in turns enables an enhancement in the contrast of a projection image. It is an easy solution to extraneous modulation light because the light is externally ejected.
With this configuration, the laser light enters the projection lens 2070 at the maximum light intensity of the ON light, at an intermediate intensity between the ON light and OFF light of the intermediate light, and at the zero intensity of the OFF light. This configuration makes it possible to project an image in a high level of gradation. Note that the intermediate light state produces a reflection light reflected by a mirror in which the deflection angle is regulated between the ON light state and OFF light state.
Meanwhile, making the mirror perform a free oscillation causes it to cycle through the three deflection angles, producing the ON light, the intermediate light and the OFF light. Specifically, controlling the number of free oscillations makes it possible to adjust the light intensity and obtain an image in higher level of gradation.
The mirror devices 2030 and 2040 are placed in the package, forming an approximately 45-degree angle, on the same horizontal plane, in relation to the four sides of the outer circumference of the package, as shown in
Further, the heat generated inside of the package is conducted to the color synthesis prism 2060 by way of the thermal conduction member 2062 and is radiated to the outside from there. As such, the conduction of the heat generated in the mirror device to the color synthesis prism 2060 improves the radiation efficiency. Further, the heat generated by absorbing light is radiated to the outside instantly because the light shield layer 2063 is exposed to the outside.
When a mirror element reflects the incident light toward a projection lens 2070 at an intermediate light intensity (i.e., an intermediate state), that is, the intensity between the ON light and OFF light states, an effective reflection plane needs to be conventionally taken widely in the longitudinal direction of the slope face of a prism.
In contrast, the projection apparatus 2500 is enabled to provide a wide effective reflection plane in the thickness direction of the color synthesis prism 2060 even when the mirror element as described above has an intermediate state. With this configuration, the total reflection condition with which the reflection light from the mirror element is reflected by the slope face of the color synthesis prism 2060 can be alleviated.
Note that the locus of the optical axis of the modulation light modulated by the mirror (i.e. laser lights corresponding to the ON light state, OFF light state and intermediate light state), is preferred to be configured to be parallel to the synthesis surface 2055a, as indicated by a deflection locus 8404 shown in
Furthermore, it is also preferred to form the bottom surface 2064a of the light guide prism 2064 approximately orthogonal to the synthesis surface 2055a. In such a case, the color synthesis prism 2060 can also be miniaturized.
A projection apparatus according to the present embodiment is an exemplary modification of the embodiment 2-2. The projection apparatus according to the present embodiment is configured to further join a right-angle triangle columnar prism 8430 to the color synthesis prism 2060 and also covered with a light shield layer 2063 (i.e., a light absorption member) along the slope surface of the prism 8430, as illustrated in
The present embodiment is configured to cause the light shield layer 2063 to absorb extraneous modulation light after the light enters the joinder surface between the color synthesis prism 2060 and prism 8430, and then enters the slope surface thereof at an angle smaller than the critical angle. In this case, if the refraction index of the color synthesis prism 2060 and that of the prism 8430 are configured to be the same, the incidence angle to the prism 8430 may be set at any value and is not limited by the critical angle.
Therefore, neither
A projection apparatus according to the present embodiment is yet another exemplary modification of the embodiment 2-2.
The light source, the configuration between the light source and optical prism, and a part of the optical prism are what distinguishes the exemplary configuration illustrated in
In the exemplary configuration illustrated in
The light emitted from the light source 8411 passes through an illumination optical system 8415 then transmitting to a dichroic filter 8416. The dichroic filter 8416 reflects the red light (i.e., the light of red frequency component) as part of the lights projected to the dichroic filter 8416 while the green and blue lights (i.e., the lights of green and blue frequency components) transmit through the present dichroic filter 8416.
The red light reflected by the dichroic filter 8416 is then reflected by a retention mirror 8417, is incident to the bottom surface of a light guide prism (not shown in drawing), is then ejected from the bottom surface of the color synthesis prism 5340 and is incident to the spatial light modulators (SLM 1) 5100. The path of the light after entering the spatial light modulator (SLM1) 5100 is basically the same as in the exemplary configuration shown in
Meanwhile, the green and blue lights transmitted through the dichroic filter 8416 are then polarized by a PS integrator 8419 as a linear polarized light, i.e., a P-polarization state in the present embodiment) and transmitted through a micro lens 8420 and lens 8421 and reflected by a retention mirror 8422 for projecting to a polarization conversion member 8423.
The polarization conversion member 8423 selectively rotates the polarizing direction of the light of a specific frequency component. The polarization conversion member 8423 can be implemented by using a color switch, a Faraday rotator, a photo-elastic modulator, or a wave plate that is inserted into a light path.
The polarization conversion member 8423 of the present embodiment changes the lights transmitted in different frequencies by rotating the polarizing direction. The polarizing directions of the green or blue lights are rotated by 90 degrees. The lights are converted into a S-polarization state for transmitting as output lights from the polarization conversion member 823. Specifically, the green light in the P-polarization state and the blue light in the S-polarization state are output from the polarization conversion member 8423, or the green light in the S-polarization state and the blue light in the P-polarization state are output therefrom.
The P-polarized light and S-polarized light projecting from the polarization conversion member 8423 are then reflected by a retention mirror 8424, are incident to the bottom surface of the light guide prism, are then ejected from the bottom surface of the color synthesis prism and are incident to the spatial light modulator (SLM 2) 5100.
The optical paths of the lights after entering the spatial light modulator (SLM 2) 5100 are basically the same as the optical paths shown in the exemplary configuration as depicted in
Specifically, the lights incident to the spatial light modulator (SLM 2) 5100 are reflected vertically upward by the mirror, are re-incident to the bottom surface of the color synthesis prism, are reflected by the slope surface of the right-angle triangle columnar prism 5341 and are then incident to the PBS 8425. Then, of the lights incident to the PBS 8425, the P-polarized light transmits through the present PBS 8425, while the S-polarized light is reflected by the present PBS 8425 to be absorbed by a light absorption member 8426.
The P-polarized light (i.e., green or blue light) transmitting through the PBS 8425, further transmits through the joinder surface 5340c to pass through a dichroic color filter 8418 and synthesized with the above-described red light. The synthesized light is ejected from the ejection surface 5340d of the prism 5342 and is incident to the projection optical system 5400.
As described above, the projection apparatus shown in
A projection apparatus according to the present embodiment comprises a light source, a plurality of spatial light modulators each comprising a mirror capable of deflecting an incident light emitted from the light source in an intermediate direction between two mutually different first and second directions, along with the first and second directions, a first joinder prism comprising a first optical surface to which at least two lights with mutually different frequencies are incident, a second optical surface from which the light from the first optical surface is ejected and to which the light modulated by a spatial light modulator is incident and a selective reflection surface reflecting the light from the first optical surface and transmitting a modulation light, a second joinder prism comprising a third optical surface to which a modulation light ejected from the first joinder prism is incident, a synthesis surface for synthesizing a plurality of lights incident to the third optical surface into the same light path and an ejection surface which is placed at a position approximately opposite to a projection lens and which is used for ejecting the synthesized light, wherein the first optical surface of the first joinder prism is approximately perpendicular to the synthesis surface of the second joinder prism.
Specifically, the first direction is defined as the direction in which the light emitted from a light source is deflected when the mirror is in an ON state. In contrast, the second direction is defined as the direction in which the light emitted from a light source is deflected when the mirror is in an OFF state.
The joinder surface with or opposite surface to the third joinder prism 8449 the first joinder prism 8443 is a first optical surface 8450 to receive a plurality of lights with individually different frequencies. Specifically, the first optical surface 8450 is perpendicular to the synthesis surface of the second joinder prism 8446 (which is described later). Further, an optical surface 8451 on the first joinder prism 8443 is the second optical surface (noted as “second optical surface 8451” hereinafter), which ejects the light from the first optical surface 8450. Furthermore, the modulation lights modulated by two spatial light modulators 5100 disposed immediately under the first joinder prism 8443 are also projected to the second optical surface 8451. Furthermore, an optical surface 8452 is a selective reflection surface (noted as “selective reflection surface 8452” hereinafter) to serve the function of reflecting the light from the first optical surface 8450 and transmitting a modulation light.
Furthermore, the joinder surface with, or opposite surface to, the first joinder prism 8443 on the second joinder prism 8446 is the third optical surface 8453 to receive the modulation light ejected from the first joinder prism 8443. Furthermore, the joinder surface between the prisms 8444 and 8445 is the synthesis surface 8454 for synthesizing a plurality of lights incident to the third optical surface 8453 into the same light path. Furthermore, the joinder surface between the prisms 8444 and 8445 is configured with a dichroic filter for reflecting the lights of red and blue frequency components and transmitting the light of green frequency component. Furthermore, an optical surface 8455 is the ejection surface (noted as “ejection surface 8455” hereinafter) disposed at a position approximately opposite to a projection lens (i.e., a projection optical system 5400; not shown in a drawing herein) for ejecting the synthesized light and that ejects the synthesized light. That is, the synthesized light synthesized on the synthesis surface 8454 is ejected toward the projection lens (i.e., the projection optical system 5400).
Note that the second joinder prism 8446 corresponds to the color synthesis prism 2060 of the projection apparatus according to the embodiment 2-2.
Further, the third joinder prism 8449 is placed in the optical path of the light between the light source and first joinder prism 8443. On the third joinder prism 8449, the prisms 8447 and 8448 are joined together on the joinder surface 8456. The dichroic filter reflects the light of the green frequency component and transmits the lights of the blue and red frequency components therethrough. The third joinder prism 8449 is thus capable of separating the incident light into lights having different frequencies.
Meanwhile, the exemplary configuration shown in
The incidence surface of the illumination light is placed on the right side of the third joinder prism 8449 when viewed from the direction of the z-axis in
In a projection apparatus according to the present embodiment configured as described above, when an illumination light is incident to the slope surface (i.e., the incidence surface) of the prism 8447 of the third joinder prism 8449, the green light is reflected by the joinder surface 8456 (i.e., the separation surface) while the red or blue light is transmitted through the joinder surface 8456 (i.e., the separation surface).
The green light reflected by the joinder surface 8456 is reflected by the slope surface of the prism 8447 and is projected from the fourth optical surface opposite to the first optical surface. The green light projected from the fourth optical surface of the third joinder prism 8449 is orthogonally incident to the first optical surface 8450 of the first joinder prism 8443, is reflected by the selective reflection surface 8452, is projected from the second optical surface and is incident to one spatial light modulator 5100. Then, when the mirror 5112 is in the ON state, the incident light is reflected vertically upward, is incident orthogonally to the second optical surface 8451, is transmitted through the selective reflection surface 8452 and is incident to the third optical surface 8453 of the second joinder prism 8446. The path of the green light thereafter, similar to the case of the projection apparatus according to the embodiment 2-2, in which the green light is reflected by the slope surface of the prism 8444, is transmitted through the synthesis surface 8454, and is synthesized with the red or blue light (which is described later) so that the synthesized light is ejected from the ejection surface 8455 to be incident to a projection optical system (which is not shown here).
Meanwhile, having transmitted through the joinder surface 8456 of the third joinder prism 8449, the red or blue light is reflected by the slope surface of the prism 8448, is incident orthogonally to the first optical surface 8450 of the first joinder prism 8443, then is reflected by the selective reflection surface 8452, is ejected from the second optical surface and is incident to the other spatial light modulator 5100, likewise the case of the above description. Then, when the mirror 5112 is in the ON state, the incident light is reflected vertically upward, is incident vertically relative to the second optical surface 8451, is transmitted through the selective reflection surface 8452 and is incident to the third optical surface 8453 of the second joinder prism 8446. The path of the red or blue light thereafter, similar to the case of the projection apparatus according to the embodiment 2-2, in which the red or blue light is reflected by the slope surface of the prism 8445, is reflected by the synthesis surface 8454, then is synthesized with the green light (which is described above) so that the synthesized light is ejected from the ejection surface 8455 to be incident to a projection optical system (which is not shown).
The above description is an exemplary configuration of the projection apparatus according to the present embodiment.
Note that the projection apparatus according to the present embodiment can also be configured to eliminate the third joinder prism 8449. In this case, however, a light source corresponding to the first optical surface 8450 of the first joinder prism 8443 is disposed oppositely to the first optical surface 8450, likewise the case of the projection apparatus according to the embodiment shown in the above described
Further, in the projection apparatus according to the present embodiment, a portion of the modulation light modulated by the spatial light modulator 5100 is also incident to the structure surface 8446a (i.e., the fifth optical surface) (not shown in the drawing here) that is one side surface the second joinder prism 8446. In this case, the structure surface 8446a (i.e., the fifth optical surface) is preferred to be configured to cause the modulation light to be incident to the structure surface 8446a at an angle smaller than the critical angle.
The modulation light incident to the structure surface 8446a (i.e., the fifth optical surface) is a modulation light when the mirror is, for example, in the intermediate state. The modulation light incident to the structure surface 8446a may alternatively be a modulation light when the mirror is in the OFF state.
Such a configuration causes the modulation light incident to the structure surface 8446a (i.e., the fifth optical surface) to be transmitted through the structure surface 8446a (i.e., the fifth optical surface) without being totally reflected therein, thereby making it possible to remove an extraneous modulation light from within the optical system.
Although not shown in a drawing here, a light shield layer (i.e., light absorption member) may be implemented on the extended optical axis of the modulation light incident to the structure surface 8446a (i.e., the fifth optical surface) and on the outside of the second joinder prism or close to the structure surface 8446a (i.e., the fifth optical surface). This configuration makes it possible to process extraneous modulation light ejected from within the optical system. Specifically, a further preferable configuration is to connect the light shield layer to a heat dissipation member (i.e., heat radiator or heat sink) so as to reduce a temperature rise in the light shield layer due to a modulation light. A further alternative configuration may be to have the light shield layer per se function as heat dissipation member (i.e., heat radiator or heat sink).
Further, the projection apparatus according to the present embodiment can also be configured to further join a triangle columnar prism 8461 to the structure surface 8446a (i.e., the fifth optical surface) of the second joinder prism 8446 as illustrated in
If the refractive index of the prism 8461 is different from that of the second joinder prism 8446, however, the prism 8461 comprises a flat surface 8461a (i.e., a first flat surface) which is the joinder surface between the prism 8461 and the second joinder prism and to which a modulation light incident to the second joinder prism 8446, the reflection light as a portion of the modulation light when the mirror is in an intermediate state, is incident at an angle no larger than a critical angle; and comprises a flat surface 8461b (i.e., a second flat surface) on which a reflection light not incident to the second joinder prism 8446, the reflection light as a portion of the reflection light when the mirror is in an intermediate state, is incident at an angle no smaller than the critical angle.
Therefore, the modulation light incident to the flat surface 8461a at an angle no larger than the critical angle is transmitted through the prism 8461 as is, also is transmitted through a flat surface 8461c, to which an extraneous light is incident at an angle no larger than the critical angle, and is ejected to the outside. A reflection light irradiated on the flat surface 8461b at an angle no smaller than the critical angle is reflected by the flat surface 8461b to the outside.
With this configuration, the extraneous light when the mirror is in an intermediate state is ejected or reflected by the prism 8461 to the outside in early stage, and thereby the extraneous modulation light is eliminated from inside of the second joinder prism 8446 and accordingly the contrast of a projection image can be enhanced. If the refractive index of the prism 8461 is the same as that of the second joinder prism 8446, the condition for the incidence angle of extraneous light relative to the flat surface 8461a will be relaxed.
Further, if the refractive index of the prism 8462 is different from that of the joinder prism 8442, the prism 8462 comprises a flat surface 8462a to which a modulation light not incident to the second joinder prism 8446, the reflection light as a portion of the reflection light when the mirror is in an intermediate state, is incident at an angle no larger than the critical angle.
Therefore, the reflection light incident to the flat surface 8462a at an angle no larger than the critical angle is transmitted through the prism 8462 as is and is ejected to the outside.
With this configuration, the extraneous modulation light when the mirror is in the intermediate state is ejected to the outside also by the prism 8462, and thereby the extraneous modulation light is eliminated from the first joinder prism 8443 and second joinder prism 8446 and the contrast of a projection image can further be enhanced.
Note that an example in which the modulation light when the mirror is in the OFF state is not incident to the second joinder prism 8446 has been shown here, such case is arbitrary. An alternative configuration may be such that the modulation light when the mirror is in the OFF state is incident to the structure surface 8446a (i.e., the fifth optical surface). In such a case, a preferable configuration is such that the modulation light when the mirror is in the OFF state is incident to the structure surface 8446a (i.e., the fifth optical surface) at an angle smaller than the critical angle.
As shown in
Further as shown in
Note that a preferable configuration is such that the first optical surface 8450 is placed approximately orthogonally to the synthesis surface of the second joinder prism in either cases of
Further, the projection apparatus according to the present embodiment may be configured to eliminate the first joinder prism 8443 as shown in
In such a case, the illumination light emitted from the third joinder prism 8449 will actually be incident directly to the spatial light modulator 5100. Further, the modulation light modulated by the spatial light modulator 5100 will be incident directly to the second joinder prism.
Therefore, the third joinder prism 8449 is placed at a position where the illumination light ejected from the present third joinder prism 8449 is modulated and reflected to an approximately vertical direction by the spatial light modulator 5100. Further specifically, the third joinder prism 8449 is placed in the axis inclined by an angle that is two times the maximum deflection angle of the mirror, with the axis orthogonally to the bottom surface of the second joinder prism as reference. That is, the third joinder prism 8449 is placed, relative to the second joinder prism, by inclining two times the maximum deflection angle of the mirror, the angle relative to the horizontal state of the mirror comprised in the spatial light modulator 5100.
As such, the configuration eliminating the first joinder prism 8443 contributes to a reduction of cost associated with the optical components and a miniaturization of the projection apparatus.
Further, the exemplary configuration shown in
The exemplary configuration shown in
The second joinder prism 8446A is configured to replace a part of the second joinder prism 8446 shown in
Further, the third joinder prism 8449A is a joinder prism similar to the second joinder prism 8446A, and is configured to replace a part of the third joinder prism 8449 with a fifth joinder prism 8476 that is structured by joining together two right-angle triangle columnar prisms 8474 and 8475 of the same form. Note that prism 8447A and prism 8448A are the respective remaining parts of the prism 8447 and prism 8448, both of which are parts of the third joinder prism 8449 shown in
Note that the exemplary configuration shown in
Meanwhile, the exemplary configuration shown in
In the projection apparatus according to the present embodiment configured as described above, when an illumination light enters the slope surface of the prism 8447A of the third joinder prism 8449A, the green light is reflected by the joinder surface 8456, and the red and blue lights are transmitted through the joinder surface 8456. Then, having transmitted through the joinder surface 8456, when the red and blue lights enters the slope surface of the prism 8474, the blue light is reflected by the joinder surface 8478, while the red light is transmitted through the joinder surface 8478.
The green light reflected by the joinder surface 8456 is reflected by the slope surface of the prism 8447A, is orthogonally incident to the first optical surface 8450 of the first joinder prism 8443, is reflected by the selective reflection surface 8452, is ejected from the second optical surface 8451 and is incident to the spatial light modulators 5100 (G). Then, when the mirror is in the ON state, the incident light is reflected vertically upward, is incident orthogonally to the second optical surface 8451, is transmitted through the selective reflection surface 8452 and is incident to the third optical surface 8453 of the second joinder prism 8446A. Having entered the third optical surface 8453, the green light is reflected by the slope surface of the prism 8472, is transmitted through the synthesis surface 8477 and is then synthesized with the blue light (which is described later) so that the synthesized light is ejected from the slope surface of the prism 8471 and is incident to the prism 8444A. Having entered the prism 8444A, the synthesized green and blue light transmits through the synthesis surface 8454, and is then synthesized with the red light (which is described later) so that the synthesized light is ejected from the ejection surface 8455 and is incident to a projection optical system (not shown here).
Having been reflected by the joinder surface 8478 of the fifth joinder prism 8476, the blue light is reflected by the slope surface of the prism 8474, is incident orthogonally to the first optical surface 8450 of the first joinder prism 8443, is reflected by the selective reflection surface 8452, is ejected from the second optical surface 8451 and is incident to the spatial light modulators 5100 (B). Then, when the mirror is in the ON state, the incident light is reflected vertically upward, is incident orthogonally to the second optical surface 8451, is transmitted through the selective reflection surface 8452 and is incident to the third optical surface 8453 of the second joinder prism 8446A. Having entered the third optical surface 8453, the blue light is reflected by the slope surface of the prism 8471, is further reflected by the synthesis surface 8477 and is synthesized with the above described green light so that the synthesized light is ejected from the slope surface of the prism 8471 and is incident to the prism 8444A. Having entered the prism 8444A, the green and blue synthesized light is transmitted through the synthesis surface 8454, and is then synthesized with the red light (which is described later) so that the synthesized light is ejected from the ejection surface 8455 and is incident to a projection optical system (not shown in a drawing herein).
Having been transmitted through the joinder surface 8478 of the fifth joinder prism 8476, the red light is reflected by the slope surface of the prism 8475, is incident orthogonally to the first optical surface 8450 of the first joinder prism 8443, is reflected by the selective reflection surface 8452, is ejected from the second optical surface 8451 and is incident to the spatial light modulators 5100 (R). Then, when the mirror is in the ON state, the incident light is reflected vertically upward, is incident orthogonally to the second optical surface 8451, is transmitted through the selective reflection surface 8452 and is incident to the third optical surface 8453 of the second joinder prism 8446. Having entered the third optical surface 8453, the red light is reflected by the slope surface of the prism 8445A, is further reflected by the synthesis surface 8454 and is then synthesized with the above described blue/green synthesized light so that the synthesized light is ejected from the ejection surface 8455 and is incident to a projection optical system (not shown in a drawing herein).
The above description is another exemplary configuration of the projection apparatus according to the present embodiment.
Note that the exemplary configuration shown in
Further, in this case, an alternative configuration may be such as to use the red laser light source 5211, green laser light source 5212 and blue laser light source 5213, as the light sources of the respective colors, and place these light sources, the optical system made by joining the first joinder prism 8443 and second joinder prism 8446A together, three spatial light modulators 5100 and a controller 8481 used for controlling the aforementioned components on the same board 8482, as illustrated in
Further, the configuration shown in
As described above, the projection apparatuses implemented with a plurality of spatial light modulators according to the embodiments 2-2 through 2-6 achieves improved contrast of a projection image with a more compact projection apparatus.
Note that the projection apparatuses according to the present embodiments may be implemented with alternate embodiments and changed in various manners possible within the scope of the present embodiment.
The following is a description of a suitable projection lens when the mirror device comprised in the projection apparatus according to the present embodiment is miniaturized.
If a mirror device with a diagonal size of 0.95 inches is used for a rear projection system with about 65-inch screen size, the required projection magnification ratio is about 68. If a mirror array with a diagonal size of 0.55 inches is used, the required projection magnification ratio is about 118. As such, the projection magnification increases in association with the miniaturization of the mirror array. This ushers in the problem of color aberration caused by a projection lens.
The focal distance of the lens needs to be shortened to increase the projection magnification. Accordingly, the F-number for the projection lens is set at 5 or higher by comprising a laser light source. With this, it is possible to use a projection lens with the F-number at 2 times, and the focal distance at a half, as included in a configuration of a mercury lamp and a focal distance is 15 mm with the F-number at about 2.4 for the projection lens. The usage of a projection lens with a large F-number makes it possible to reduce the outer size of the projection lens. This in turn reduces the image size with which a light flux passes through the illumination optical system, thereby making it possible to suppress a color aberration caused by the projection lens.
Therefore, in the case of using a laser light source with a mirror device miniaturized to between 0.4 inches and 0.87 inches, the deflection angle of mirror can be reduced to between +7 degrees and ±5 degrees, and the F-number for a projection lens can be increased. Alternatively, the setting of the numerical aperture NA of an illumination light flux between 0.1 and 0.04 with the deflection angle of mirror maintained at +13 degrees makes it possible to reflect the OFF light to a large distance from the projection lens, improving the contrast of the projection image.
As described above, the projection magnification of a projection lens can be set at 75× to 120× by reducing the numerical aperture NA of the light flux emitted from a laser light source, using a miniaturized mirror device (diagonal size of 0.4 inches to 0.87 inches) with which the deflection angle of mirror is reduced to between ±7 degrees and ±5, and thereby the F-number for a projection lens is increased.
Meanwhile, when a mirror device is moved forward or backward relative to the optical axis of projection, the distance at which a blur (i.e., becomes out of focus) of a projected image is permissible is called a focal depth. When an image is projected with a permissible blur in a degree of the mirror size by an optical setup of the same focal distance, projection magnification and mirror size, a depth of focus is approximated as follows:
Depth of focus Z=2*(permissible blur)*(F number)
Specifically, the depth of focus Z is proportional to the F-number of a projection lens. That is, the permissible distance of the shift in positions of a placed mirror device, relative to the optical axis of projection, increases with F-number. This factor is represented by the relationship between a permissible circle of confusion and a depth of focus. As an example, where the F number of a projection lens is “8” and the permissible blur is equivalent to a 10 μm mirror size in the above described approximation equation, the depth of focus is:
Z=2*10*8=160 [μm]
Further, where a mirror size is 5 μm and an F-number is 2.4, the depth of focus is 24 μm. Specifically, considering the errors of a projection lens and other components of the optical system, the depth of focus is preferred to be no larger than 20 μm or several micrometers or less. With this in mind, when the top or bottom surface of a package substrate is taken as reference, the difference in heights of the reflection on the surface of mirrors placed respectively on both ends of a mirror array is preferred to be no more than 20 μm.
Further, a blurred image of dust, on the surface of a cover glass, can be made invisible by providing a distance between the mirror surface and the bottom surface of the cover glass of no less than the value of the depth of focus. It is therefore preferable to configure the distance between the top surface of the mirror and the bottom surface of the cover glass with a distance of at least 20 times, or more, of the mirror size.
The following is description, in detail, of the configuration of the control unit of the projection apparatus described for the second embodiment with reference to the accompanying drawings.
The control unit 5500 comprises a frame memory 5520, an SLM controller 5530, a sequencer 5540, a light source control unit 5560 and a light source drive circuit 5570.
The sequencer 5540, constituted by a microprocessor, controls the operation timing of the entirety of the control unit 5500 and spatial light modulators 5100.
The frame memory 5520 retains the amount of one frame of input digital video data 5700 incoming from an external device (not shown in drawing) that is connected to a video signal input unit 5510. The input digital video data 5700 is updated every time the display of one frame is completed in real time.
In the case of the single-panel (1×SLM) projection apparatus 5010, one frame (i.e., a frame 6700-1) of the input digital video data 5700 is constituted by a plurality of subfields 6701, 6702 and 6703, in a time sequence, corresponding to the respective colors R, G and B as shown in
The SLM controller 5530 separates the input digital video data 5700 read from the frame memory 5520 into a plurality of subfields 6701, 6702 and 6703, then converts them into mirror profiles (i.e., mirror control profiles 6710 and 6720) that are drives signals for implementing the ON/OFF control and oscillation control for the mirror of the spatial light modulator 5100 for each sub-field and outputs the converted mirror profiles to the spatial light modulator 5100.
Note that the mirror control profile 6710 is a mirror control profile consisting of binary data. Specifically, the binary data means the data in which each bit has a different weighting factor and which includes a pulse width in accordance with the weighting factor of each bit. Meanwhile, the mirror control profile 6720 is a mirror control profile consisting of non-binary data. Specifically, the non-binary data means the data in which each bit has an equal weighting factor and which includes a pulse width in accordance with the number of continuous bits of “1”.
The mirror control profile generated by the SLM controller 5530 is also inputted to the sequencer 5540, which in turn transmits a light source profile control signal 5800 to the light source control unit 5560 on the basis of the mirror control profile input from the SLM controller 5530.
The light source control unit 5560 instructs the light source drive circuit 5570 regarding the emission timing and light intensity of an illumination light 5600 required of the variable light source 5210 corresponding to the driving of the spatial light modulator 5100. The variable light source 5210 performs emission so as to emit the illumination light 5600 at the timing and light intensity driven by the light source drive circuit 5570.
With this control, it is possible to change the brightness of a displayed pixel through a continuous adjustment of the emission light intensity of the variable light source 5210 and to control the characteristics of the gradations of the display image in the midst of driving the spatial light modulator 5100, that is, in the midst of displaying an image onto the screen 5900. The emission light intensity of the variable light source 5210 is adjusted by using a mirror control profile used for driving the spatial light modulator 5100, and therefore no extraneous irradiation occurs, making it possible to reduce the heat from and the power consumption of the variable light source 5210.
The description above is based on the example of the control unit 5500 comprised in the single-panel projection apparatus. In the case of a multi-panel projection apparatus, however, a configuration may be such that the SLM controller 5530 and sequencer 5540 control a plurality of spatial light modulators 5100. An alternative configuration may be to equip an apparatus with multiple SLM controllers, in place of the SLM controller 5530, so as to control the respective spatial light modulators 5100.
In the case of a multi-panel projection apparatus, the structure of the input digital video data 5700 is also different. In the case of, for example, the above described multi-panel (3×SLM) projection apparatuses 5020, 5030 and 5040, the input digital video data 5700 corresponding to one frame (i.e., the frame 6700-1) display period is constituted by a plurality of fields 6700-2 (i.e., which are equivalent to the subfields 6701, 6702 and 6703) corresponding to the respective colors R, G and B, and the fields of the respective colors are outputted to the respective of spatial light modulators 5100 simultaneously, as shown in
The following is a description, in detail, of the embodiment of controlling the variable light source 5210 with the light source profile control signal 5800 corresponding to the mirror control profile.
In this case, one frame of the mirror control profile 6720 includes the combination of a mirror ON/OFF control 6721 in the early stage of the frame and a mirror oscillation control 6722 in the later stage of the frame and is used for controlling the tilting operation of the mirror corresponding to the gray scale of the present frame.
The mirror ON/OFF control signal 6721 controls the mirror under either of the ON state or OFF states, and the mirror oscillation control signal 6722 controls the mirror 5112 under an oscillation state in which it oscillates between the ON state and OFF state.
The light source control unit 5560 changes the frequencies of the pulse emission of the variable light source 5210 in accordance with the signal (i.e., mirror control profile 6720) driving the spatial light modulator 5100. The spatial light modulator 5100 is the above described mirror device 4000 and performs a spatial light modulation of the illumination light 5600 by means of a large number of mirrors corresponding to pixels to be displayed and of the tilting operation of the mirrors.
In controlling the mirror element with the mirror oscillation control signal 6722, the pulse emission frequency fp of the variable light source 5210 emitting the illumination light 5600 is preferably either higher (in the case of the light source pulse pattern 6801 shown in
Based on what is shown in
As described above, adjustment of the light intensity of the illumination light 5600 emitted from the variable light source 5210 is achievable by changing the frequencies of the pulse emission of the variable light source 5210. Note that the present invention may be changed in various manners possible within the scope of the present invention, and is not limited to the configurations shown in the above-described embodiments.
Although the present invention has been described in terms of the presently preferred embodiment, it is to be understood that such disclosure is not to be interpreted as limiting. Various alternations and modifications will no doubt become apparent to those skilled in the art after reading the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alternations and modifications as fall within the true spirit and scope of the invention.
This application is a Non-provisional Application claiming a Priority date of Oct. 2, 2007 based on a previously filed Provisional Application 60/997,436 and a Non-provisional patent application Ser. No. 11/121,543 filed on May 3, 2005 issued into U.S. Pat. No. 7,268,932. The application Ser. No. 11/121,543 is a Continuation In Part (CIP) Application of three previously filed Applications. These three Applications are Ser. No. 10/698,620 filed on Nov. 1, 2003, Ser. No. 10/699,140 filed on Nov. 1, 2003 now issued into U.S. Pat. No. 6,862,127, and 10/699,143 filed on Nov. 1, 2003 now issued into U.S. Pat. No. 6,903,860 by the Applicant of this patent applications. The disclosures made in these patent applications are hereby incorporated by reference in this patent application.
| Number | Date | Country | |
|---|---|---|---|
| 60997436 | Oct 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11121543 | May 2005 | US |
| Child | 12286806 | US | |
| Parent | 10698620 | Nov 2003 | US |
| Child | 11121543 | US | |
| Parent | 10699140 | Nov 2003 | US |
| Child | 10698620 | US | |
| Parent | 10699143 | Nov 2003 | US |
| Child | 10699140 | US |
