The present invention relates generally to a system and method for displaying images, and more particularly to a system and method for increasing display brightness in laser illuminated display systems.
In a microdisplay-based projection display system, light from a light source may be modulated by the microdisplay as the light reflects off the surface of the microdisplay or passes through the microdisplay. Examples of commonly used microdisplays may include digital micromirror devices (DMD), deformable micromirror devices, transmissive or reflective liquid crystal, liquid crystal on silicon, ferroelectric liquid crystal on silicon, and so forth. In a digital micromirror device (DMD)-based projection system, where large numbers of positional micromirrors may change state (position) depending on an image being displayed, light from the light source may be reflected onto or away from a display plane.
For image quality reasons, it may be desirous to maximize the brightness of the images being displayed. In general, the brighter the images, the better the perceived image quality. Therefore, there have been many techniques utilized to help improve image brightness. Some of the techniques may include increasing the brightness of the light source, using multiple light sources, and so forth.
In a laser illuminated, microdisplay-based projection display system, it may be possible to maximize image brightness by increasing the duty cycle of the laser(s) used to illuminate the microdisplay. Scanning the light produced by the laser(s) so that more than one color of light may simultaneously illuminate the microdisplay may be performed to increase the duty cycle of the laser(s). That is, if only one color of light may illuminate the entire microdisplay at a time, then all of the other lasers must be turned off. However, if scanning permits the light from a red colored laser and the light from a green colored laser to illuminate different portions of the microdisplay, then the on-time of the two lasers may be increased, thereby increasing the duty cycle of the lasers.
These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of a system and a method for increasing display brightness in laser illuminated display systems.
In accordance with an embodiment, an illumination source is provided. The illumination source includes a light source to produce light, a disk having a first set of lens elements arranged in a first circular ring around a center of the disk, each lens element periodically optically coupled to the light source, a motor coupled to the disk, and an external optical element positioned in a light path of the light source after the disk. The disk moves the lens elements in the first set of lens elements sequentially through the light, the motor rotates the disk, and the external optical element converts an angular refraction of the light into a spatial deflection.
In accordance with another embodiment, a display system is provided. The display system includes an illumination source, a microdisplay optically coupled to the illumination source and positioned in a light path of the illumination source after the illumination source, and a controller electronically coupled to the microdisplay and to the illumination source. The illumination source includes a light source to produce light, a rotatable disk having a set of lens elements arranged in a circumference around a center of the disk with each lens element equidistant from a center of the disk, the circumference in a light path of the light source, an optical element positioned in a light path of the light source after the light source, and an external lens positioned in a light path of the light source after the disk. The disk moves the lens elements in the set of lens elements through the light, the optical element expands the light along an axis perpendicular to the light path, and the external lens converts an angular refraction of the coherent light by the lens elements into a spatial deflection. The microdisplay produces images by modulating light from the illumination source based on image data, and the controller load image data into the microdisplay.
In accordance with another embodiment, a method of manufacturing a display system is provided. The method includes installing a light source configured to generate coherent light, installing a microdisplay in a light path of the display system after the light source, installing a controller configured to control the light source and the microdisplay, and installing a display plane in the light path of the display system after the microdisplay. The light source installing includes installing a coherent light source, installing a rotatable disk having a set of lens elements arranged along a circumference around a center of the disk, a light path of the coherent light source intersecting the circumference, installing a motor to rotate the disk, and installing an external lens in the light path after the disk.
An advantage of an embodiment is that little additional hardware is required. Furthermore, the additional hardware may be implemented inexpensively. Therefore, increased display brightness may be achieved with a small monetary investment.
A further advantage of an embodiment is that little noise is generated. Therefore, there is no source of distracting noise that may detract from the user's viewing enjoyment.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the embodiments that follow may be better understood. Additional features and advantages of the embodiments will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.
For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
a is a diagram of a side-view of a light source illuminating a microdisplay;
b is a diagram of a sequence of colored light produced by a light source;
a is a diagram of an exemplary microdisplay-based projection display system;
b is a diagram of a portion of an illumination system of the microdisplay-based projection display system;
c is a diagram of an isometric view of a disk;
d is a diagram of the refractive operation of an external lens;
e is a diagram of the reflective operation of an external lens;
f and 2g are diagrams of cross-sectional views of a disk;
a is a diagram of top view of a portion of a disk;
b and 3c are diagrams of cross-sectional views of a disk with a cylindrical and parabolic lens elements;
a is a diagram of a scanning of beams of light in a projection display system;
b is a diagram of the deflection of beams of lights by a lens element;
c is a diagram of a scanning of a microdisplay's surface;
a through 5c are diagrams of alternate embodiments of a disk;
a through 6c are diagrams of different types of disks;
a is a diagram of a cross-section of a disk with a powered lens element;
b is a diagram of a cross-section of a disk with a concave lens element;
c is a diagram of a cross-section of a disk with lens elements on both sides of the disk;
a and 8b are diagrams of a disk with multiple sets of lens elements and an illumination system with such a disk;
The making and using of the embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.
The embodiments will be described in a specific context, namely a laser illuminated, microdisplay-based projection display system, wherein the microdisplay is a DMD. The invention may also be applied, however, to other laser illuminated, microdisplay-based projection display systems, such as projection display systems utilizing deformable micromirror devices, transmissive or reflective liquid crystal displays, liquid crystal on silicon displays, ferroelectric liquid crystal on silicon displays, and so forth.
a illustrates a portion of a microdisplay-based projection display system 100. The microdisplay-based projection display system 100 includes a light source 105 and a microdisplay 110. The light source 105 may be used to provide light that illuminates the microdisplay 110. The light source 105 produces light one color at a time.
Although shown in
a illustrates an exemplary laser illuminated DMD-based projection display system 200. The DMD-based projection display system 200 includes a DMD 205 that modulates light produced by a light source 210. The light source 210 may make use of multiple lasers to produce the desired colors of light. Although the discussion focuses on solid-state lasers, other sources of coherent light, including filtered non-coherent light, free-electron lasers, and so forth, may be used in place of the solid-state lasers. Therefore, the discussion should not be construed as being limited to the present embodiments.
The DMD 205 is an example of a microdisplay or an array of light modulators. Other examples of microdisplays may include transmissive or reflective liquid crystal, liquid crystal on silicon, ferroelectric liquid-crystal-on-silicon, deformable micromirrors, and so forth. In a microdisplay, a number of light modulators may be arranged in a rectangular, square, diamond shaped, and so forth, array. Each light modulator in the microdisplay may operate in conjunction with the other light modulators in the microdisplay to modulate the light produced by the light source 210. The light modulated by the DMD 205 may be used to create images on a display plane 215. The DMD-based projection display system 200 also includes an optics system 220, which may be used to collimate the light produced by the light source 210 as well as to collect stray light. The DMD-based projection display system 200 may also include a lens system 225, which may be used to manipulate (for example, focus) the light reflecting off the DMD 205.
Also included in an optical path of the DMD-based projection display system 200 may be a light steering unit 222. The light steering unit 222 may be used to steer light from the light source 210 onto different portions of the DMD 205 and away from other portions of the DMD 205. This may allow for the simultaneous illumination of the DMD 205 by light of different colors. For example, a red colored light may illuminate a top third of the DMD 205, while a green colored light may illuminate a middle third of the DMD 205, and a blue colored light may illuminate a bottom third of the DMD 205. This may enable a higher duty cycle for the lasers used in the light source 210, thereby increasing the brightness of the images produced by the DMD-based projection display system 200. The light steering unit 222 will be discussed in greater detail below.
The DMD 205 may be coupled to a controller 230, which may be responsible for loading image data into the DMD 205, controlling the operation of the DMD 205, providing micromirror control commands to the DMD 205, controlling the light produced by the light source 210, and so forth. A memory 235, which may be coupled to the DMD 205 and the controller 230, may be used to store the image data, as well as configuration data, color correction data, and so forth.
b illustrates an isometric view of the light steering unit 222. The light steering unit 222 includes a disk 250 with disk body 252 and a plurality of lens elements 255. The plurality of lens elements 255 may be arranged along a periphery of the disk body 252. The lens elements 255 also may be evenly spaced about the periphery of the disk body 252. The disk 250 may be arranged so that light produced by the light source 210 may be incident on the disk 250 and the plurality of lens elements 255 with an angle of incidence less than or equal to an acceptance angle of the lens elements 255. Preferably, the light from the light source 210 should be orthogonal to the disk 250 and the lens elements 255. Furthermore, the disk 250 may be arranged so that the light from the light source 210 is incident mainly on the lens elements 255 and not the disk body 252 nor should a significant amount of the light miss the disk 250.
Although shown in
The individual colored beams of light from the lasers of the light source 210 should be focused to a small spot or a line running along the radial direction of the disk 250. The individual colored beams of light may be arranged so that they are focused on spots that are all substantially equidistant from a center of the disk 250. The individual colored beams of light also may be separated along the circumference of an individual lens element 255. The separation between the focusing spots of the individual colored beams of light may be dependent on a desired phase difference between the light produced by the disk 250. To mitigate far field limitations, the focusing spots of the individual colored beams of light generally should be as close together as possible while meeting desired phase differences. For example, to produce a 120 degree phase difference between the light produced by the disk 250 in a projection display system utilizing three individual colored beams of light, the focusing spots should be separated by about ⅓ of the width of an individual lens element 255. If all of the lens elements 255 are about the same size, then the separation between the focusing spots may be +/− the width of an individual lens element 255. For example, if each lens element is one (1) unit length in width, then the focusing spots may be located at [0, 1/3, and 2/3] so that all three focusing spots may fit within a single lens element 255. Alternatively, the focusing spots may be located at [0, 4/3, 8/3] so that a first focusing spot is on a first lens element, a second focusing spot is on a second lens element, and a third focusing spot is on a third lens element, i.e., no two individual beams of colored light are incident on a single lens element.
The disk 250, including the disk body 252 and the lens elements 255, may be molded from a plastic, such as polymethylmethacrylate (PMMA), polycarbonate, polystyrene, cyclic olefin copolymer, cyclic olefin polymer, and so forth, a glass, or so on. The disk body 252 and the lens elements 255 may be formed in a single molding step or they may be molded separately and then attached to each other using an adhesive, glue, heat, sound waves, or so forth. Generally, care should be provided to ensure that significant light loss at an interface between the disk body 252 and the lens elements 255 is not incurred. Alternatively, the disk 250 may be roughly molded or machined and then receive final machining and polishing to a final state.
The disk 250 may be rotated by a motor 260 with the motor 260 coupled to the disk body 252. As the motor 260 rotates the disk body 252, the lens elements 255 may also be rotated. As a beam of colored light passes through the lens elements 255, it may be refracted by differing degrees, thereby producing a scan line of colored light. Refraction due to the lens elements 255 may cause each of the multiple beams of colored light to deflect up and down along an axis, tracing out (generating) a saw tooth pattern, for example.
In order to scan an entirety of a two-dimensional surface, such as the DMD 205, it may be necessary to scan a line of light over the surface of the DMD 205, producing a three-dimensional surface of light, rather than scanning a beam of light which results in a two-dimensional line of light. Therefore, it may be necessary to include a refractive optical element to convert the beam of colored light into a line of colored light. An optical element 262 positioned in an optical path of the light steering unit 222 after the disk 250 may operate as a refractive optical element and may be used to convert the scanned line of light into a scanned three-dimensional surface of light. The optical element 262 may be a lenticular array or a diffractive optical element, for example. Although shown positioned after the disk 250 in the light path of the light steering unit 222, the optical element 262 may be positioned prior to the disk 250. Furthermore, the optical element 262 may be placed after other optical elements in the light path of the light steering unit 222 after the disk 250.
It may also be desirable to linearize the saw tooth pattern created by the lens elements 255. An external lens (or lenses) 265 may then be used to 1) convert the angular refraction of the multiple beams of colored light into a spatial deflection, 2) correct for a defocusing of the individual beams of colored light along one axis of the lens elements 255 of the disk 250, and 3) correct for a non-linearity of the scanning created by the disk 250. The external lens 265 may typically be implemented with one or more aspherical lenses. For example, the external lens 265 may be implemented with an F-Theta lens with a reverse photolens architecture.
As discussed above, an F-Theta lens may have the architecture of a reverse photolens comprising two lens, a divergent lens 266 followed by a convergent lens 267. The divergent lens 266 and the convergent lens 267 may have circular revolution surfaces and may be aspheric if the scan angle is large. The divergent lens 266 and the convergent lens 267 may also be replaced with similarly shaped mirrored surfaces. The negative distortion of the F-Theta lens may be used to correct for scan non-linearity. It may also be possible to add an additional lens to the external lens 265 with an orthogonal power axis (for example, power along an X axis) to correct for uni-dimension power induced by the lens elements 255.
With reference back to
The disk 250 may also have an index mark 270. The index mark 270 may be positioned at some known location on the surface of the disk 250, such as in the arrangement of lens elements 255. The index mark 270 may then be read by a sensor to signal an orientation of the disk 250 and may be used for synchronization with the controller 230 and the DMD 205. The index mark 270 may be optical in nature or it may be magnetic, for example. Alternatively a sensor may be included in the light path of the DMD-based projection display system to detect light beam position to provide synchronization information to the controller 230 and the DMD 205.
f and 2g illustrate an edge on view of a portion of the disk 250 and a cross-sectional view of one-half of the disk 250.
a illustrates a top view of a portion of the disk 250. Preferably, each lens element 255 has a cross-section of a cylindrical lens. However, since the lens elements 255 are arranged around the periphery of the disk body 252, the shape of the lens elements 255 may not match exactly with that of a cylindrical lens. For example, a first edge 305 of the lens element 255 may be shorter (shown as span 307) than a second edge 310 of the lens element 255 (shown as span 312). Additionally, a third edge 320 of the lens element 255 and the fourth edge 325 of the lens element 255 may not be parallel and may converge at the center of the disk 250. Therefore, each lens element 255 may be best described as an acylindrical lens, which is a cylindrical lens with high-order corrections.
Alternatively, rather than having an acylindrical cross-section, the lens elements 255 may have a parabolic cross-section along an axis orthogonal to a radial axis of the disk 250. A parabolic cross-section may yield a linear scan angle through an illumination system of a projection display system. Furthermore, the parabolic cross-section may not significantly distort the focus of the beam of light produced by the light source.
The surface of the lens elements 255 with a parabolic cross-section may be described as Z=A+B*Y2, where Y is a Cartesian coordinate that is tangential to the circumference of the disk 250, and A and B are coefficients. The parabolic cross-section of the lens elements 255 may vary along a radial coordinate (X) and may be described as Z=A+B*Y2+C*X*Y2, where C is a coefficient. If coefficient C is set to be about equal to −B/Rcenter, where Rcenter is the radius of a beam center, e.g., a radius from the center of the disk 250 to the center of the lens elements 255, then the scan angle range may be independent of radius. Furthermore, if coefficient C is set to be about equal to 2*(−B/Rcenter), then a scan direction of the center beam may be kept constant, independent of angle of the disk 250. A preferred range of values for the magnitude of the coefficient C is from about zero (0) to about 3*B/Rcenter.
a illustrates a view of a portion of an illumination system of a microdisplay-based projection display system, such as the DMD-based projection display system 200. The illumination system includes the light source 210 and the disk 250. The disk 250 may be rotated at a desired rate by a motor. The light source 210 may simultaneously produce multiple beams of colored light that may be focused on the lens elements 255 of the disk 250. For example, in a four color system with the light source 210 may have two lasers producing different wavelengths of a single color or in a seven-color (RGBCYMW) projection display system, the light source 210 may simultaneously produce two or more of the seven available colors. For some colors, such as R, G, and B, a single light source producing a single wavelength of light may be needed, while for other colors, multiple light sources with each light source producing a single wavelength of light may be needed.
With the disk 250 rotating, the multiple beams of colored light will pass through the individual lens elements 255 as the lens elements 255 rotate under the multiple beams of colored light. Refraction due to the lens elements 255 may cause the multiple beams of colored light deflect up and down along an axis, generating a saw tooth pattern. The external lens (or lenses) 265 may then be used to convert the angular refraction of the multiple beams of colored light into a spatial deflection. The spatial deflection may then result in the multiple beams of colored light to scan over the surface of the microdisplay 110, for example, a DMD. For example, a first beam of colored light 405 may be incident to a lens element before a second beam of colored light 410 and a third beam of colored light 415 due to an arrangement of the multiple beams of colored light and a direction of rotation of the disk 250.
As the first beam of colored light 405 passes through the lens element 255, a first refracted light beam 406 may be scanned over the surface of the microdisplay 110. Similarly, the second beam of colored light 410 becomes a second refracted light beam 411 and the third beam of colored light 415 becomes a third refracted light beam 416 after passing through the lens element 255. Since the second beam of colored light 410 and the third beam of colored light 415 are incident on the lens element 255 after the first beam of colored light 405, their respective refracted beams scan over the surface of the microdisplay 110 after the first refracted light beam 406. A spacing between the first, second, and third refracted light beams 406, 411, and 416 may be dependent upon factors such as a spacing between the first, second, and third beam of colored light 405, 410, and 415, as well as the optical properties of the lens elements 255.
b provides a detailed view of the scanning properties of the lens element 255. As the lens element 255 moves through a beam of colored light, such as the first beam of colored light 405, a degree to which the lens element 255 refracts the light depends on the location of the first beam of colored light 405 on the lens element 255.
As a beam of colored light passes through a lens element 255, the beam of colored light is refracted by varying degrees depending on the location of the beam of colored light on the lens element 255 so that the refracted beam of colored light is scanned over the surface of the microdisplay 110. After the lens element 255 is moved through the beam of colored light, another lens element 255 begins its rotation through the beam of colored light. Therefore, as each lens element 255 moves through the beam of colored light, a refracted beam of colored light is scanned over the surface of the microdisplay 110, with the rate of the scan being dependent on the rotational velocity of the disk 250.
c illustrates a diagram of a top-view of the microdisplay 110 with several refracted beams of colored light 406, 411, and 416. As shown in
The number of refracted beams of colored light simultaneously illuminating the surface of the microdisplay 110 may be dependent on the rotation speed of the disk 250, the number of lens elements 255 on the disk 250, the size of the individual lens elements 255, the data movement restrictions of the microdisplay, and so forth. For example, if the rotation speed of the disk 250 is high and the number of lens elements 255 is high, then the scan rate of the refracted beams of colored light may also be high, implying a large number of refracted beams of light illuminating the surface of the microdisplay 110. However, there are limitations on how rapidly image data can be moved into the microdisplay 110, and the scan rate may need to be reduced to ensure that proper image data is loaded into the microdisplay 110 prior to the microdisplay 110 being illuminated by a respective refracted beam of colored light. However, if the microdisplay 110 may be illuminated by two or more refracted beams of light, a net improvement in the brightness of the images generated may be realized.
Some or all of the lens elements 255 of the disk 250 may be modified to adjust performance as needed.
It may be useful to purposefully increase the light loss of some or all of the lens elements 255 of the disk 250. Increased light loss may help to reduce a minimum amount of displayable light, potentially darkening a darkest displayable grayscale. This may result in an increase in the bit-depth of displayed images.
a illustrates a cross-sectional view of the disk 250 along an axis orthogonal to a radial axis of a lens element 255, wherein the disk 250 and the lens element 255 are refractive in nature. Being refractive, the disk 250 and the lens element 255 may pass a light beam 605 incident to the disk 250. As the light beam 605 passes through the lens element 255, the light beam 605 may be refracted (bent) prior to exiting the lens element 255.
The lens elements 255 may also have more power along a first axis than a second axis.
In addition to having a convex cross-section as shown in earlier figures, the lens element 255 may have a concave cross-section.
c illustrates a cross-sectional view of the disk 250 along a radial axis of a lens element 255. However, rather than having optical power on one side of the disk 250, the lens element 255 may have optical power on both sides of the disk 250. Having optical power on both sides of the disk 250 may enable the use of lens elements 255 with smaller profiles, thereby potentially enabling a thinner disk 250.
a illustrates a top-view of a disk 800. Rather than having a single ring of lens elements, such as lens elements 255 of the disk 250 that may be shared by all beams of colored light, each beam of colored light may have its own set of lens elements.
The separation between sets of lens elements may be dependent on factors such as proximity of the beams of colored light, the size of the light source producing the beams of colored light, the size of the lens elements, the size of the light beams, and so forth. For example, if individual beams of colored light may not be closer than a minimum distance apart, then their respective sets of lens elements may need to be similarly separated. Again, to mitigate far field limitations, the sets of lens elements 810, 815, and 820 should be positioned as closely together as possible.
Although the discussion focuses on an embodiment wherein each beam of colored light has its own set of lens elements, it may be possible to use a single set of lens elements with more than one beam of colored light, but not all of the beams of colored light. For example, two distinct beams of colored light may share a first set of lens elements, one beam of colored light may use a second set of lens elements, and finally, two distinct beams of colored light may share a third set of lens elements.
b illustrates an isometric view of a portion of an illumination system of a projection display system. The illumination system of a projection display system may include the disk 800, a light source 830, and an external lens 835. The external lens 835 may be used to convert the angular refraction of the multiple beams of colored light into a spatial deflection. It may also be possible to use a different external lens 835 for each set of lens elements. There may be one or more external lenses 835, with a number potentially being dependent on factors such as the wavelength of the beams of colored light being deflected, the separation between beams of colored light using a single set of lens elements, and so forth.
The manufacture may continue with installing a microdisplay, such as a DMD, in the light path of the multiple colors of light produced by the light source (block 1010). After installing the microdisplay, a lens system may be installed in between the light source and the microdisplay (block 1015). A controller for the microdisplay-based projection display system may then be installed (block 1020). With the controller installed, the manufacture may continue with installing a display plane (block 1025). The order of the events in this sequence may be changed, the sequence may be performed in a different order, or some of the steps may be performed at the same time to meet particular manufacturing requirements of the various embodiments of the DMD, for example.
Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.