Patent Application
20100103380
The present invention relates generally to an illumination module and more particularly to an optical projection system that provides a substantially uniform illumination over a projected area.
Illumination modules have a wide range of applications in a variety of fields, including projection displays, sun simulators, backlights for liquid crystal displays (LCDs), and others. Projection systems usually include a source of radiative energy, illumination optics, an image-forming device, projection optics, and a projection screen. The illumination optics collect light from a light source and direct it to one or more image-forming devices in a predetermined manner. The image-forming device(s), controlled by an electronically conditioned and processed digital video signal, produces an image corresponding to the video signal. Projection optics then magnify the image and project it onto the projection screen.
Modern projector systems predominately utilize light emitting diodes (LEDs) as an illumination source. Light emitting diodes are semiconductor devices (e.g., semiconducting p-n diodes) that emit radiative energy when an electrical current is applied to the device. The emitted radiative energy is incoherent and has a wavelength corresponding to the band gap of the semiconductor device used to form the LED. Accordingly, the emitted radiative energy is a narrow-spectrum light emitted from the p-n junction.
LEDs offer a number of advantages over other illumination sources (e.g., white light sources such as arc lamps) including longer lifetime, higher efficiency, and superior thermal characteristics.
One example of an image-forming device frequently used in digital light processing systems is a digital micro-mirror device (DMD). The main feature of a DMD is an array of rotatable micro-mirrors. The tilt of each mirror is independently controlled by the data loaded into a memory cell associated with each mirror, to steer reflected light and spatially map a pixel of video data to a pixel on a projection screen. Light reflected by a mirror in an “on” state passes through the projection optics and is projected onto the projection screen to create a bright field (e.g., pixel). Alternatively, light reflected by a mirror in an “off” state misses the projection optics, resulting in a dark field (e.g., pixel). A color image also may be produced using a DMD by utilizing color sequencing, or, alternatively, using three DMDs, one for each primary color.
Other examples of image-forming devices include liquid crystal panels, such as a liquid crystal on silicon device (LCOS), which are typically rectangular. In liquid crystal panels, the alignment of the liquid crystal material is controlled incrementally (pixel-to-pixel) according to the data corresponding to a video signal. Depending on the alignment of the liquid crystal material, polarization of the incident light may be altered by the liquid crystal structure. Thus, with appropriate use of polarizers or polarizing beam splitters, dark and light regions may be created, which correspond to the input video data. Color images have been formed using liquid crystal panels in the manner similar to the DMDs.
The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary presents one or more concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later and is not an extensive overview of the invention. In this regard, the summary is not intended to identify key or critical elements of the invention, nor does the summary delineate the scope of the invention.
The present invention relates to an optical projection illumination module that projects highly uniform radiative energy (e.g., visible light, ultraviolet radiation, infrared radiation, etc.) onto a target area. More particularly, the illumination module comprises a radiative energy source (e.g., a LED) configured to provide divergent radiative energy (e.g., a non-uniform illumination) directly to a reflective tunnel (e.g., Total Internal Reflection (TIR) tunnel), separated from the radiative energy source by a small gap and optically in contact (e.g., physically coupled) to a front optical element (e.g., collimator lens). The reflective tunnel mixes the divergent radiative energy, and outputs a substantially uniform radiative energy to a front optical element. One or more downstream optical elements image the output of the reflective tunnel directly to the target area (e.g., the object imaged on to the target area is located on an image plane embedded between the reflective tunnel and the front optical element).
The following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed.
The present invention will now be described with reference to the attached drawing figures, wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures and devices are not necessarily drawn to scale.
For digital projectors to produce high quality projected images it is desirable to display a uniform (i.e., homogeneous) illumination over the area of the projected image. Often it is difficult to project illumination sources in a uniform manner, because the illumination sources have non-uniform emitting areas that do not provide a uniform emission profile. For example, a light emitting diode (LED), which is commonly used as a projector illumination source, may have wiring bonding connections which, when projected, are visible with a high contrast or may exhibit current density non-uniformity providing different emission profiles between the center of the LED and the corners. To compensate for the lack of uniformity in illumination sources, optical engines comprised within the digital projectors will often utilize special techniques to achieve uniform illumination over the area of a projected image. For example, a fly eyes array (i.e., a two dimensional array comprising individual optical elements assembled into a single optical element) may be placed between the illumination source and a projection area to improve the uniformity of projected irradiance onto a projection screen. However, such conventional techniques add size and complexity to an optical projection illumination module design. Therefore, there is a need for an optical projection illumination module which provides a uniform illumination without increasing the size or complexity of the module.
The present invention relates to an optical projection illumination module that projects highly uniform radiative energy (e.g., visible light, ultraviolet radiation, infrared radiation, etc.) onto a target area (e.g., a SLM, DMD). More particularly, the illumination module comprises a radiative energy source (e.g., a LED) configured to provide divergent radiative energy (e.g., a non-uniform illumination) directly to a reflective tunnel (e.g., total internal reflection tunnel (TIR) tunnel), separated from the radiative energy source by a small gap and optically in contact (e.g., physically coupled) to a front optical element (e.g., collimator lens). The reflective tunnel mixes the divergent radiative energy, and outputs a substantially uniform radiative energy to a front optical element. One or more downstream optical elements image the output of the reflective tunnel directly to the target area (e.g., the object imaged on to the target area is located on an image plane embedded between the reflective tunnel and the front optical element).
Referring to
It will be appreciated the term reflective tunnel, as used in relation to
The light engine 200 comprises an illumination source 202 configured to provide a divergent (e.g., non-uniform) illumination (e.g., visible light) to a total internal reflection tunnel (TIR tunnel) 204 that is optically in contact (e.g., physically cemented) with a front optical element 206 (e.g., collimator lens). The TIR tunnel 204 receives the divergent illumination at its proximal surface (e.g., surface situated closest to the illumination source), mixes the received illumination, and outputs a substantially uniform illumination through its distal surface (e.g., surface situated furthest from the illumination source) to the front optical element 206. The front optical element 206 relays the uniform illumination to one or more downstream optical elements 208 (e.g., a field lens, TIR prism) configured to image the output of the TIR tunnel directly a focal point located at the SLM 210 (i.e., the object imaged on to the DMD is located on an image plane embedded between the TIR tunnel 204 and the front optical element 206).
The TIR tunnel 204, the front optical element 206, and the one or more downstream optical elements 208 comprise an optical system that provides an Abbe configuration, the illumination of the uniform illumination output by the TIR tunnel 204 directly onto the SLM 210. The SLM 210 selectively reflects the received illumination to projection optics 212 located downstream that provide an image to a projection screen 214.
In one embodiment, the optical elements (e.g., 206, 208, etc.) of the light engine 200 are configured to have their center of curvature substantially aligned with the optical axis 216 of the light engine. However, it will be appreciated that although the optical elements (e.g., 206, 208, etc.) of the light engine shown in
The illumination source and TIR tunnel are illustrated in more detail in
As illustrated in
In one embodiment, the proximal surface of the TIR tunnel 204 is configured to have the same aspect ratio as the illumination source 202, thereby improving coupling between the illumination source 202 and TIR tunnel 204. For example, an illumination source 202 having an emitting aspect ratio of 9×16 will be matched to a TIR tunnel 204 having a proximal surface with a substantially equal aspect ratio.
In another embodiment, the DMD has a different aspect ratio than the TIR tunnel or the illumination source. In such an embodiment, one or more optical elements having an anamorphic power (e.g., one or more cylindrical lens or anamorphic prism) are used in the optical relay (e.g., downstream from the TIR tunnel) to provide an image to the DMD having a proper aspect ratio. For example, one or more cylindrical lenses can be used to image an illumination source having a first aspect ratio (e.g., a square aspect ratio) onto a DMD having a second aspect ratio (e.g., a rectangular aspect ratio; the first aspect ratio stretched in the vertical direction), wherein the first and second aspect ratios are not equal.
The TIR tunnel 204 is comprised of an optical material that allows transmission of visible light. For example, the TIR tunnel 204 may be made of acrylic, polycarbonate or another suitable material, the internal surfaces of which operate as simple reflectors for the light emanating from the emitting surface of the LED at angles that are sufficiently large to result in internal reflection (e.g., total internal reflection) of such light within the tunnel. It will be appreciated that light collection efficiency will be improved by forming the TIR tunnel 204 of materials with higher refractive indexes or by providing highly polished internal surfaces so long as the index of refraction difference between the TIR tunnel 204 and front lens is greater than 0.2 (e.g., preferably 0.3 or 0.5 and higher).
Furthermore, if the TIR tunnel 204 offers a high acceptance angle for TIR propagation, then in embodiments where the illumination source provides a highly divergent illumination the length of the TIR tunnel 204 can be kept small (e.g., 0.3 mm) while still providing a high degree of mixing as will be explained below.
Furthermore, in one embodiment the short TIR tunnel acts as a low pass spatial filter, which “erases” high frequency details or defects of the source such as dark spots and wire shadows without having to reduce the low frequency details. This property offers an advantage that the illumination source could be composed of sub illumination sources in an array that would be modulated depending on the spatial color content of the image to be generated by the DMD to be imaged on the screen.
The configuration of the illumination module in
Furthermore, coupling of the TIR tunnel 204 with the front optical element 206 (e.g., lens) improves efficiency of the illumination module by effectively forming a single optical element (e.g., lens) having two different indices of refraction. This configuration allows the position of the TIR tunnel 204 to vary with respect to the front optical element 206 (i.e., precise positioning of the TIR tunnel with the front lens or LED is not required since the tunnel is part of the lens) without reducing the system efficiency, so long as the TIR tunnel 204 remains in contact with the front optical element 206. Therefore, a robust optical system is provided that can accept misalignment in the process without negative effects on performance of the illumination module.
Illumination (illustrated by the light ray) is output from the LED 202 and is received by the TIR tunnel 204. As illustrated in
The front lens 402 relays the substantially uniform illumination to the rear optical element 404 which is configured to image the object from the image plane 114 directly onto the DMD 406 (i.e., the new object which is imaged onto the DMD is embedded between the end of the TIR tunnel and the front lens).
As shown in
In another embodiment, the LED 202 (i.e., the illumination source) is highly divergent. In such an embodiment the light output from the LED will enter into the TIR tunnel 204 at an angle, a, relative to the optical axis 216. An increase in the divergence will result in faster mixing of the light (i.e., the relative mixing efficiency is proportional to n and the tunnel length is proportional to 1/n, where maximum efficiency of 1 is for a mirrored hollow tunnel). Therefore, a highly divergent source (e.g., a source having light incident upon the TIR at an angle α>60°) will provide increased mixing of the output illumination from the TIR tunnel 204 relative to an illumination source with lower divergence (e.g., a source providing light incident upon the TIR at an angle α=20°). The increased mixing of illumination from a highly divergent source will improve the uniformity of the light output from the TIR tunnel 204 resulting in a more uniform illumination being relayed to the DMD 406 and projection screen. Furthermore, the use of a highly divergent illumination source allows for a high degree of mixing over a short TIR tunnel distance (e.g., by a TIR tunnel having a length of 0.3 mm).
In alternative embodiments, the index of refraction break between the front lens 402 and the TIR tunnel 204 may vary. For example, the front lens may be comprised of materials having an index of refraction greater than 2 or slightly less than 2. Accordingly the resultant difference in refractive index between the front optical element and the TIR tunnel can vary slightly (e.g., Δn=0.4, 0.5, 0.6, 0.7, etc.). However, it will be appreciated that the resultant difference in index of refraction values between the TIR tunnel and the front lens should remain large enough so that illumination divergence is reduced and an image is provided to the DMD. If a large enough index of refraction difference is not provided, illumination from the LED will be highly divergent and it will be difficult to get light onto the DMD with the desired uniformity and smooth illumination profile.
The illumination source 202 is separated from a front window 702 by a gap 302. The size of the gap 302 is important to the operation of the illumination module 700 as the larger the size of the gap 302 the less light collected by the TIR tunnel 204.
In one embodiment the gap 302 has a size that can be minimized by providing an LED 202 (i.e., illumination source) that utilizes a flip chip structure. An LED utilizing flip chip structure will not have connections on the emitting surface of the LED (e.g., the surface facing the proximal surface of the front window 702) but instead will have connections on the back side of the LED. This removes wire bonding on the side of the LED facing the front window, thereby allowing the LED to get very close to the front window and thereby increasing the coupling efficiency of the illumination module.
Referring to
In one embodiment, the TIR tunnel 204 comprises a shape having parallel faces which provide a highly symmetric TIR tunnel shape (e.g., a simple plate having polished edges to increase internal reflection along the TIR tunnel). It can be formed using a BK7 material (e.g., a crown glass produced from alkali-lime silicates comprising approximately 10% potassium oxide and having a low refractive index (≈1.52) and low dispersion (with Abbe numbers around 60)). In alternative embodiments other equivalent materials may also be used to form the TIR tunnel 204. In one example the TIR tunnel may comprise a length of approximately 0.3 mm, for example. In alternative embodiments the TIR tunnel comprises a length of approximately 1.0-2.0 mm, thereby avoiding edge effects on TIR propagation.
The piano-convex lens 902 provides illumination to an additional lens 904 configured to reduce divergence of the LED illumination by focusing illumination to a rear lens 906. In one embodiment the rear lens 906 has an aspheric prescription. In alternative embodiments, the rear lens 906 may be comprise a group of lenses configured to project the received image onto the image plane of the DMD or an aspheric condenser lens configured to provide a telecentric beam with a low level of aberration that prevents etendue degradation
In one embodiment, a TIR prism 908 is configured between the rear lens 906 (e.g., aspheric rear lens) and the DMD 406. The TIR prism 908 receives illumination from the rear lens 906 and conveys it to the DMD 406. Placement of the TIR prism 908 requires that the rear lens 906 have a sufficiently large back focal length (BFL) such that the light path can extend to the DMD 406 with the TIR prism 908 in place (e.g., twice the diagonal of a DMD being projected onto). In one embodiment, the TIR prism is replaced by an airgap. In alternative embodiments, the TIR prism is replaced by one of a Polarization Beam splitter, an Xprism, or any other optical elements with substantial glass thickness.
In one embodiment of the light engine 900, the piano-convex lens 902 is comprised of glass and the additional lens 904 and the rear lens 906 comprise aspheric plastic lens (e.g., molded acrylic). The piano-convex glass lens 902 filters the UV spectrum of Blue LED light, thereby avoiding darkening on that channel. The aspheric plastic lenses (904, 906) provide a light weight aspheric surface that is low cost and weight with easier aberration correction than glass spherical lenses.
In one particular embodiment, the light engine of
It will be appreciated that the system of optical elements included in the light engine 900 of
The light engine 900 provides improved performance over traditional light engine optical systems. For example, the performance of an optical system, such as illumination optics of a projection system, may be characterized by a number of parameters, one of them being etendue. The etendue, ε, is a function of the area of the receiver or emitter and the solid angle of emission or acceptance (i.e., Etendue(θ, A)=π*A*sin2(θ), where θ is the maximum source divergence angle A is the area).
If the etendue of a certain element of an optical system is more than the etendue of an upstream optical element, the mismatch may result in loss of light, which reduces the efficiency of the optical system. Therefore, performance of an optical system is usually limited by an optical element in the system that has the smallest etendue. For example, in the projector optical system if the etendue of the illumination source is more than the etendue of the DMD, the performance of the system will be limited by the etendue of the DMD. Therefore, it is important for the source to match the DMD etendue and that the optical system of
The rear group of lenses 1020 will convey light from the LEDs (1004, 1006, 1008) to the DMD 1022. Often the front lens (1010, 1012, 1014), dichroic plates (1016, 1018), a rear group of lenses 1020 are comprised within a lens barrel. The DMD 1022 uses an array of microscopic mirrors that build an image by rapidly switching the DMD “on” and “off” in response to the image data received by the graphics driver. The DMD comprises mirror elements that are fabricated over a semiconductor substrate, which has a memory cell associated with each mirror element. The mirrors of the mirror elements of the DMD operate such that they are in either an on or an off position for each image. Rotation of the mirrors is accomplished with electrostatic attraction produced by voltage differences developed between the mirror and the underlying memory cell. For example, one mirror position may be tilted at an angle of +10 degrees while the other mirror position is tilted at an angle of −10 degrees. The light incident of the face of each mirror complies with optical geometry so as to direct the light from the one mirrors to a projection lens, such as the lens of
At 1102 an illumination source is provided. The illumination source is specifically configured in one embodiment to provide a high degree of etendue matching between the illumination source and a DMD comprised within the light engine. In alternative embodiments the illumination source also provides illumination having a high degree of divergence.
A TIR tunnel is positioned to receive non-uniform illumination from the illumination source at 1104. The TIR tunnel mixes the non-uniform illumination over the course of transmission along the length of the tunnel resulting in an output illumination having a smooth, substantially uniform illumination profile.
At 1106 first optical element is physically coupled to the TIR tunnel. The first optical element is coupled downstream from the LED. The first optical element relays uniform illumination from an image plane located at the distal edge of the TIR tunnel to additional optical elements downstream. In one embodiment the first optical element is coupled to the TIR tunnel, having an index of refraction 0.5 lower, using an optical image matching gel with an index of refraction substantially equal to the TIR tunnel, thereby reducing loss between the TIR tunnel and the first optical element.
It will be appreciated that the optical projection illumination module and optical engines provided herein can be utilized in a variety of front projection (e.g., front projection movie projector) applications, rear projection (e.g., rear projection television) applications, or any other application where a target is to be illuminated with radiation in high uniformity conditions. For example,
Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”.
