Abstract:
An optical module includes a light source and a reflective substrate. A first optical medium is disposed such that the first optical medium in combination with the reflective substrate substantially envelops the light source. A second optical medium is disposed to contact the first optical medium, defining a boundary therebetween. Reflective sidewalls bound a lateral portion of the second optical medium. A lens has a lower surface in contact with the second optical medium and spaced from the first optical medium. Light from the source passing through the lens follows a first and a second optical path, the first including refraction at the boundary followed by refraction at the lens; and the second including refraction at the boundary followed by reflection from a sidewall followed by refraction at the lens. An alternative embodiment uses the reflective sidewalls to bound the first optical medium, and the second path differs.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This Application claims priority to U.S. Provisional Patent Application Ser. No. 60/638,911 filed on Dec. 23, 2004. This application is also related to co-pending and co-owned U.S. patent application Ser. No. 10/622,296 filed on Jul. 17, 2003 and entitled “2D/3D Data Projector”; and No. 11/051,652 filed on Feb. 4, 2005 and entitled “Method for Manufacturing Three Dimensional Optical Components”. 
     
    
     TECHNICAL FIELD  
       [0002]     The present invention relates to optical collection and distribution systems such as imaging projectors or beam shaping systems using a non-lasing light source.  
       BACKGROUND  
       [0003]     There is an increasing demand for optical collection and distribution systems on the micro scale, parallel to the demand for digital cameras on a micro scale that are now deployed in mobile telephones and common security systems. The intrinsic challenges in a micro-device approach is to collect light from the optical source (e.g., LED, filament, arc) in a small physical space with little loss. Optical efficiency is important for example in projector applications. Merely increasing power leads to prohibitive power consumption when the optical system is disposed in a battery-operated appliance, and increases problems with managing heat dissipation.  
         [0004]     As an additional figure of merit, it is often desirable for an optical system to provide uniform illumination at a rectilinear imaging surface. This is because people expect to view a rectilinear image rather than an elliptical one. It is considerably difficult task to provide that uniform illumination, and it is achieved at the cost of efficiency. For example in data projectors, the resulting non-uniformities are evident in darker screen corners. Resolving these non-uniformities becomes more difficult with smaller projecting devices.  
         [0005]     In general, prior art collection optics collect light emanating from the source to a spatially larger beam with a smaller opening angle, for example by using a cylindrically symmetrical collimator. The related beam forming components such as lenses, lightpipes, or micro-optical “top-hat” components, shape the beam to better fit an optical engine input. An optical engine is an optical component that manipulates light between the collecting/distributing apparatus and the target surface/viewing screen. Because the light source generates light from a smaller physical area than that needed for the input filed at the optical engine, these prior art approaches require physical space to propagate light intensity to the proper position. To the inventors&#39; knowledge, prior art light collection and beam shaping systems are efficient and small in size only for cylindrically symmetric systems, or systems in which the light emanating from the collimator defines a circular cross-section. Further, the prior art appears to accept relatively large losses of light in that not all light from the source is collected. The prior art solutions are large in physical size, and some of them are not amenable to a heat sinking mechanism by which to draw off heat from the light source.  
         [0006]     Some specific prior art approaches to beam-shaping are now broadly presented. In a first conventional approach depicted in prior art  FIG. 1A , light from a source  12  is gathered in a collimator  14  and directed to a condenser lens  16 , which then focuses its incident light into a lightpipe  18 . In this approach, illumination from the lightpipe  18  exit may be substantially uniform if the lightpipe  18  is sufficiently long. However, the exiting light is generally not optimized for input into an optical engine (detailed in the context of the present invention below). More fundamentally, this approach is necessarily large in size due to the length of the optical path from the collimator  14  to the lightpipe  18 , and to the length of the lightpipe  18  itself. Further, the lightpipe  18  increases losses, increasing the need for a more intense light source  12 .  
         [0007]     A second conventional approach is shown at  FIG. 1B . A LED chip  12  is disposed within a cone or well defined by reflecting concave surfaces of a lighting case  20 , in such a way that the light is leaving the case only upwards and mostly inside a smaller cone. This is sometimes referred to as a surface emitting LED. The case constrains the emitted light to a circular cross section, and those light rays are directed toward a beam shaper  22 , which redirects the rays towards the optical engine. The beam shaper may also convert the cross section of its incident light to more resemble a rectilinear cross section. The second conventional approach imposes difficulties also. Because the light incident to the beam shaper must be collected and at least partially collimated, the problems with the first conventional approach are not overcome but merely shifted in space to within the surface emitting LED (the source  12 /case  20  combination). Currently available surface-emitting LEDs fail to preserve etendue (described in the Detailed Description section) of their internal LED chip. In other words the brightness of the surface emitting LED is smaller than the brightness of the LED chip inside it or the total output power of the surface emitting LED is smaller than the total output power of the LED chip inside it.  
         [0008]      FIG. 1C  shows a third conventional approach where a cylindrically symmetric collimator  14  is used to collect the light from the source  12 . The first micro-optical beam shaper  24  is used to convert the cylindrically symmetric intensity distribution into rectilinear distribution onto the second micro-optical beam shaper  28 , which turns the rays into the proper angular distribution for an optical engine  19 . Because light is first collected by a cylindrically symmetric component and then converted to a rectilinear field, a gap  26  is needed between the first and second beam shaping components for transporting the intensity to the correct position. This gap together with the relatively large size of the collimator  14 , which is needed for decreasing the beam numerical aperture enough for the beam shapers, means that the solution is large in size.  
         [0009]      FIG. 1D  shows a fourth conventional approach where a cylindrically symmetric collimator  14  is used to collect the light from the source  12  into a rectangular lightpipe  18  placed directly after the collimator  14 . In order to obtain a sufficient degree of collimation, the collimator  14  is lengthened. Similarly, in order to obtain sufficient uniformity at the output of the lightpipe  30 , the lightpipe  18  is lengthened. This results in a large apparatus. Additionally, the light field at the lightpipe  18  output is generally not optimized to the optical engine of projectors, which results in excess losses from the optical engine. Further, light coupling from the circular collimator  14  to the generally rectangular lightpipe  18  causes etendue to increase, which results in decreased illumination brightness.  
         [0010]     The present invention seeks to overcome at least some of the above difficulties and undesirable tradeoffs.  
       SUMMARY  
       [0011]     The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings.  
         [0012]     In accordance with one embodiment, the invention is a method for manipulating light. In the method, light is emitted from a multi-directional source. The light is collected and spatially distributed using at least one patterned optical surface while substantially preserving etendue of the emitted light. The collected light is distributed angularly using at least one second optical surface while substantially preserving the etendue of the collected light.  
         [0013]     In accordance with another aspect, the invention is an optical module that includes a multi-directional light source and a substrate that has a reflective surface facing the light source. A first optical medium defining a refractive index greater than unity is disposed such that the first optical medium in combination with the reflective substrate substantially envelops the light source. A second optical medium is disposed to be in contact with the first optical medium, and a boundary is defined between the first and second optical mediums. The optical module further includes reflective sidewalls that bound a lateral portion of the second optical medium, and a lens having a lower surface in contact with the second optical medium and spaced from the first optical medium. The above recited components are arranged such that light from the source passing through the lens follows a first and a second optical path. The first optical path includes refraction at the boundary followed by refraction at the lens. The second optical path includes refraction at the boundary followed by reflection from a sidewall followed by refraction at the lens.  
         [0014]     In accordance with another embodiment, the invention is an optical module that also includes a multi-directional light source and a substrate having a reflective surface facing the light source. A first optical medium defining a refractive index greater than unity is disposed such that the first optical medium in combination with the reflective substrate substantially envelops the light source. A second optical medium is disposed to be in contact with the first optical medium, and a boundary is defined between the first and second optical mediums. The optical module further includes reflective sidewalls that bound a lateral portion of the first optical medium, and a lens having a lower surface in contact with the second optical medium and spaced from the first optical medium. The above recited components are arranged such that light from the source passing through the lens follows a first and a second optical path. The first optical path includes refraction at the boundary followed by refraction at the lens. The second optical path includes reflection from a sidewall followed by refraction at the boundary followed by refraction at the lens. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein:  
         [0016]      FIG. 1A  is a schematic diagram of a first prior art conventional approach to beam collection and distribution.  
         [0017]      FIG. 1B  is a schematic diagram of a second prior art conventional approach to beam collection and distribution.  
         [0018]      FIG. 1C  is a schematic diagram of a third prior art conventional approach to beam collection and distribution.  
         [0019]      FIG. 1D  is a schematic diagram of a fourth prior art conventional approach to beam collection and distribution.  
         [0020]      FIG. 2A  is a cut-away plan view of an optical module  30  according to the preferred embodiment of the present invention.  
         [0021]      FIG. 2B  is an exploded view of the embodiment of  FIG. 2A .  
         [0022]      FIG. 3A  is a cut-away plan view of an optical module  30 ′ according to an alternative embodiment of the present invention, absent the substrate  34  of  FIG. 2A  to better delineate the distinctions.  
         [0023]      FIG. 3B  is an exploded view of the embodiment of  FIG. 3A .  
         [0024]      FIG. 4  is a schematic block diagram of an optical module arranged with a micro-display and imaging unit.  
         [0025]      FIG. 5  is a schematic block diagram of three different color optical modules whose output is combined prior to passing through a micro-display and imaging unit.  
         [0026]      FIG. 6  is similar to  FIG. 5  but with the light passing through micro-displays prior to being combined.  
         [0027]      FIG. 7  is a schematic block diagram showing a polarizing beam splitter disposed between the optical module and the imaging unit.  
         [0028]      FIG. 8  is a hybrid combination of  FIGS. 5 and 7 .  
         [0029]      FIG. 9  is a schematic diagram showing a total internal reflecting prism for off axis orientation of components.  
         [0030]      FIG. 10  is a hybrid combination of  FIGS. 5 and 9 .  
         [0031]      FIG. 11  is a schematic diagram showing relative dimensions of the optical module and optical engine.  
         [0032]      FIG. 12  are some representative rectilinear cross sections over which the present invention may uniformly illuminate. 
     
    
     DETAILED DESCRIPTION  
       [0033]     The inventors have reviewed the prior art approaches and found several inherent shortfalls that the present invention seeks to overcome. Specifically, the fact that prior art approaches use separate mechanisms for collection and distribution (beam forming) results in apparatus that do not lend themselves to easy miniaturization. The present invention performs both light collection from a source and distribution to the desired input field (i.e., for input to an optical engine) in a single unit which is inherently small and substantially smaller than prior art approaches. The present invention further considers the need to minimize losses within the collecting/distribution device and provides for heat sinking the light source. The preferred embodiment is detailed at  FIGS. 2A-2B .  
         [0034]      FIG. 2A  is a cut-away plan view of an optical module  30  according to the preferred embodiment of the present invention.  FIG. 2B  is an exploded view of the same embodiment as shown in  FIG. 2A . A multi-directional light source  32  such as an LED is disposed on a substrate  34 . Light emanating from the source  32  passes through a first optical medium or material  36  having a first refractive index and is refracted at a boundary layer  38  into a second optical medium or material  40 . The first and second optical mediums  36 ,  40  are optically transparent or substantially so at least to the intended wavelengths. The boundary layer  38  includes an upper surface  38 A and side surfaces  38 B, each of which are preferably planar. The boundary layer  38  consists of microstructure optics/features as described in the incorporated reference. The second optical medium  40  is bounded by the boundary layer surfaces  38 A-B, by a series of reflective sidewall surfaces  42 A of sidewalls  42 , and by a lower refractive surface  44 A of a lens  44 . The reflective sidewall surfaces  42 A preferably also include microstructure optics/features as described in the incorporated reference. Preferably, an opposed upper surface  44 B of the lens  44  is planar and parallel to the upper surface  38 A of the boundary layer. The lens  44  preferably defines a periphery that contacts the sidewalls  42  or at least very nearly so. An apex  44 C of the lens defined by symmetrical lower lens surfaces  44 A is preferably spaced from the upper surface  38 A of the boundary layer, at least some minimal amount so that the apex  44 C does not contact the boundary layer  38 .  
         [0035]     The substrate  34  may be heat sunk to draw heat from the source  32 . Preferably, the substrate  34  has a high thermal conductivity, and is coupled to one or more cooling elements as known in the art. Importantly, a surface  32 A of the substrate facing the source  32  is highly reflective to minimize losses through absorption and scattering of the multi-directional light emanating from the source  32  toward the surface  32 A.  
         [0036]     The first optical medium has a refractive index greater than one, preferably between 1.3 and 1.7. When LED&#39;s are used as a light source, this refractive index raises the external efficiency of LED. The second optical medium may be air with a refractive index essentially one, or may be some other material optically matched to the refractive index of the first optical medium to direct light as desired toward the lens  44 , as particularly described below with respect to the preferred embodiment.  
         [0037]     The optical pathways are now described. In the preferred embodiment of  FIGS. 2A-2B , three distinct optical pathways are defined. Rays that pass through the upper surface  38 A of the boundary  38  follow a first optical path and are represented in  FIG. 2A  by a first exemplary ray  46 , rays that pass though a side surface  38 B of the boundary  38  and reflect from the sidewall surface  42 A follow a third optical path and are represented in  FIG. 2A  by a third exemplary ray  50 , and all other rays follow a second optical path and are represented in  FIG. 2A  by a second exemplary ray  48 .  
         [0038]     Rays along the first optical path  46  pass from the source through the first optical medium  36  and are refracted at the upper surface  38 A of the boundary  38 , pass through the second optical medium  40 , and are refracted at the lower surface  44 A of the lens. Rays along the second optical path  48  propagate similarly to those of the first path  46 , except they pass through a side surface  38 B of the boundary  38  rather than the upper surface  38 A. Rays along the third optical path  50  pass from the source through the first optical medium  36  and are refracted at a side surface  38 B of the boundary  38  and pass through the second optical medium  40 . There, they are reflected from the sidewall surface  42 A, pass again through the second optical medium  40 , and are finally refracted at the lower surface  44 A of the lens just as the other two rays  46 ,  48 . The upper  38 A and side  38 B surfaces of the boundary  38  determine the first optical surface, which forms the desired spatial intensity distribution of light onto the second optical surface. The sidewall surfaces  42 A determine the second optical surface for the rays along the third optical path and the lower lens surfaces  44 A determine the second optical surface for the rays along the first and the second optical path, which surface forms the angular distribution of light to the desired input field to an optical engine (discussed below).  
         [0039]      FIG. 3A  is a cut-away plan view of an optical module  30 ′ according to an alternative embodiment of the present invention.  FIG. 3B  is an exploded view of the same embodiment as shown in  FIG. 3A . Like components and surfaces are represented by like reference numbers and not further detailed except to explain differences in operation. An important distinction in this embodiment as compared to the preferred embodiment is that in  FIGS. 3A-3B , the sidewall surfaces  42 A′ are contacted by the first optical medium  36  rather than the second, and because of that the boundary is extended by surfaces  38 C′ to meet the sidewall surfaces  42 A′ (or the lens  44 ′) near the lens lower surface  44 A′. In this alternative embodiment  30 ′ the boundary also defines an upper surface  38 A′ and side surfaces  38 B′. The extension surface  38 C′ extends approximately parallel to a ray traced from the source  32  (though not necessarily co-linear with that parallel ray). The other distinction in this alternative embodiment  30 ′ as compared to the preferred embodiment  30  is that the upper surface  38 A′ of the boundary and the sidewall surfaces  42 A′ are circumferentially arcuate rather than a series of planar surfaces. This is shown generally in  FIG. 3B . While either embodiment  30 ,  30 ′ may be made either planar or with varying degrees of curvature in the described and distinguished surfaces, the illustrated embodiments are deemed the best mode for the different embodiments given practical manufacturing considerations. In this alternative embodiment  30 ′, the boundary does not consist of microstructured optics/features, but in order to facilitate similar operation, the lens  44 ′ includes microstructured optics/features in either it&#39;s lower  44 A or upper  44 B surfaces and is because of that termed a micro-optical lens  44 ′.  
         [0040]     In this alternative embodiment  30 ′, there are two distinct optical paths, termed herein a direct path represented by the ray  52  of  FIG. 3A  and an indirect path represented by the ray  54  of  FIG. 3A . These terms are used only to avoid confusion with previously described first/second/third optical paths detailed with respect to the preferred embodiment. The direct optical path  52  is similar in principle to the first optical path  46  previously discussed: a light ray emanating from the source  32  passes through the first optical medium  36  and is refracted at the upper surface  38 A′ or at the side surface  38 B′ of the boundary, passes through the second optical medium  40  and is again refracted at the lower surface  44 A of the micro-optical lens  44 ′. Rays following the indirect optical path  54  differ from any previously discussed, in that they pass through the first optical medium  36  and are reflected from the mirrored sidewall surface  42 A′ back into the first optical medium  36 . They are then refracted at the extended surface  38 C′ of the boundary  38 , pass through the second optical medium  40 , and are again refracted at the lower surface  44 A of the micro-optical lens  44 . In this alternative embodiment, the boundary surfaces  38 A′ and  38 B′ and the sidewall reflective surfaces  42 A′ determine the spatial intensity distribution of light to the micro-optical lens  44 ′, and the micro-optical lens  44 ′ modifies the angular distribution of the light to match any related optical engine. The microstructured optics/features previously noted as being along the lower surface  44 A of the micro-optical lens  44 ′ may instead be on the upper surface  44 B or both surfaces  44 A-B.  
         [0041]     The present invention collects multi-directional light from a small source, preferably a point source such as an LED or even an incandescent filament or arc lamp, and shapes the light (e.g., directs the rays) into a certain angular and spatial distribution. Uniform rectangular illumination is needed in many different applications, for example in micro-projectors. The present invention may achieve uniform rectangular illumination at aspect ratios of 3:4, 16:9, 16:10, and 1:2. Further, the present invention is not constrained to uniform illumination over a shape defined by right angles but may yield uniform illumination over a trapezoid or parallelogram as shown in  FIG. 12 , as well as the illustrated square and rectangle.  
         [0042]     One important aspect of the present invention is the management of lighting efficiency in the design of the optical module  30 ,  30 ′. Heat sinking the source  32  to the substrate  34  as noted above is an important feature in order to keep the junction temperature of the LED within the efficient working region. A more fundamental tool is to use of microstructured optics/features in order to precisely manage etendue of the system. Etendue is a figure of merit for optical efficiency, and conservation of etendue provides that in any optical system, etendue cannot decrease but can at best remain unchanged in a lossless system. The present invention is designed to actively manage etendue throughout the optical pathways.  
         [0043]     Etendue is a term that has been conceptualized as optical throughput. There are many etendue critical applications, where, to achieve a desired result, it is important that the etendue of the source is near to the etendue of the illumination field to be formed. In etendue critical applications, conservation of etendue requires that increases in etendue during the collection (over etendue of the light source) results in etendue losses later in the optical system. Because the surface emitting LED of the second conventional approach shown in  FIG. 2B  has larger etendue in comparison to the etendue of the LED chip inside it, losses are inherently high in the optical engine, when that system is used in etendue critical applications (detailed below). Further, the single beam shaper offers but one surface to shape the beam, and the spatial light distribution at the beam shaper is defined by the LED component, generally circular.  
         [0044]     For a surface of arbitrary shape and light coming from a material with a refractive index n l , the etendue in its general form is defined as  
               E   =         n   1   2       n   2   2       ⁢     ∫     ∫       ⅆ   A     ⁢         e   ^     A     ·     ⅆ   Ω       ⁢           ⁢       e   ^     Ω               ,           (   1   )             
 
 where n 1  and n 2  are the refractive indices of the optical mediums or materials; dA is the differential area element on the surface; ê A  is the surface normal vector corresponding to dA; dΩ is the differential solid angle element, and ê Ω  is the centroid direction vector corresponding to dΩ. Because etendue cannot be decreased through optical means, any losses in any component of an optical system carry through the entire system. That is, the etendue of a system is driven by the smallest of the etendues of its components. 
 
         [0045]     Define an etendue critical system as one wherein the etendue of the system E system  and the etendue of the source E source  have the following relation:  
                   E   source     2     &lt;     E   system     &lt;     2   *     E   source         ,           (   2   )             
 
 A micro-projector using a small microdisplay (approximately 0.55″ diagonal) and a LED source (approximately 1 mm×1 mm×0.1 mm in its size) is a good example of an etendue critical system. 
 
         [0046]     In micro-projection systems, for example, the micro-display has a certain spatial extent and acceptance angle. The projection lens has similar limitations. Together, these limitations, along with other etendue limiting factors from other system components such as cross-dichroic prisms (X-cubes), cause the etendue of the system to be limited. To obtain high efficiency, the inventors have chosen the course of preserving etendue of the light beam in its original value of source etendue through the optical system until the etendue limiting factors are passed.  
         [0047]     Etendue management may be practiced in simpler cases such as fiber to lens coupling, light collection from a fiber to a detector, or object illumination in a microscope. These are relatively simple as the source is emitting only into a certain numerical aperture, or all of the light emitted need not be collected (which is management of etendue for only a portion of the emitted light). Etendue management becomes increasingly difficult for more complex tasks, such as low power micro-projectors, in which all light that is emitted by the source (over a hemisphere with a reflective substrate) must be collected and delivered to the optical engine with a certain spatial and angular distribution. [The term “all light” is understood not to exclude real-world devices where losses may arise from the practical limitations of manufacturing, but to exclude devices whose design purposefully fails to collect a non-negligible amount of emitted light.] This distribution is a complex function of space, especially where uniform illumination is not cylindrically symmetric. Contributing to complexity of etendue management is that when the source is emitting into a very wide angle (e.g., 180° LED with a reflective substrate, 360° incandescent filament or arc lamp), the source cannot be mathematically approximated by a point source, and that the illumination is not cylindrically symmetric but illumination needs to be rectilinearly uniform. Most pressing for broad applications of any solution, beam shaping must be done in a small space to facilitate miniaturization.  
         [0048]     The present invention effectively manages etendue along the entire optical pathway(s) through the optical module  30 ,  30 ′. The reflective substrate surface  34 A limits losses that occur from the light source  32  emanating over a wide cone, and the reflective sidewall surfaces  42 A,  42 A′ also similarly limit losses. The preservation of the etendue of the source through this component itself and the use of microstructured optics/features enable the matching of the beam precisely to the input field of the optical engine, which prevent losses happening later in the optical engine. These are areas where large losses traditionally occur in the prior art approaches described above. The present invention limits optical losses to a maximum of about 30%, generally to about 20%, and typically about 10%, whereas losses in the prior art are generally on the order of about 70% in the same size. This enables the present invention to use LEDs as the light source  32  in such applications where traditional solutions need to use brighter and more inefficient sources. The particular arrangement of reflective and refractive surfaces enables the present optical module  30 ,  30 ′ to be made on the miniature-scale.  
         [0049]      FIGS. 4-10  are schematic diagrams of one or more of the described optical modules may be disposed relative to an optical engine for completing an optical projector. In all instances, rays emanating from the optical module form the desired input field to the optical engine, which then forms a cross section that is preferably rectilinear rather than circular symmetric at the microdisplay, and further forms the desired uniform rectilinear image on the target. Examples of some but not all potential rectilinear cross sections of the beam at the microdisplay and at the screen are shown in  FIG. 12 .  
         [0050]     In  FIG. 4 , the optical module  30 ,  30 ′ is positioned so that the rays emanate to a transmissive micro-display  56 , which transmits the rays to an imaging unit  58  such as a series of focusing lenses as traditionally arranged in a projector having one optical axis. A transmissive micro-display  56  may be a LCD (liquid crystal display) or a MEMS (micro electro-mechanical system), to name but two. In a preferred embodiment, the light source  32  includes a white LED, and the micro-display  56  includes a color LCD panel, which together results in a color image at the screen/target (not shown). An alternative embodiment is to make a one-color image by using a monochromatic light source  32  (for example, a red LED) together with a non-color micro-display  56 , such as monochromatic LCD. Of course embodiments between these two are also possible: a light source  32  exhibiting a spectrum anywhere between a full visible spectrum and a single color, and/or a micro-display  56  that may be any number of colors.  
         [0051]      FIG. 5  depicts the same relative arrangement of transmissive micro-display  56  and imaging unit  58 , but with three optical modules  30 -R,  30 -G,  30 -B arranged about sides of an X-cube  60  and the transmissive micro-display  56  aligned with an optical axis at the output side of the X-cube  60 . Preferably, the modules each include a source  32  emanating in a different portion of the visible light spectrum, or at least emanating over a spectrum range having different center wavelengths (where the sources are not mono-chromatic). Indicated are red, green, and blue LED sources. The optical module  30 -G with the green LED source is oriented similar to that described in  FIG. 4 ; the green emanating rays pass undeflected through two filters  62 ,  64  that each bisect the X-cube  60 . Most preferably, the filters  62 ,  64  are dichroic mirrors that operate to reflect light of a desired wavelength (or range) and pass light of other wavelengths. The optical module  30 -R with the red LED source is oriented perpendicular to the module  30 -G with the green LED, and its red emanating rays are at least partially reflected by one of the dichroic mirrors  62  to align with the system optical axis defined by the transmissive micro-display  56  and imaging unit  58 . Similarly, the optical module  30 -B with the blue LED source is also oriented perpendicular to that with the green LED and facing the red module  30 -R, and its blue emanating rays are at least partially reflected by the other of the dichroic mirrors  64  to align with the system optical axis. Either a monochromatic or a color micro-display  56  can be used. If a monochromatic micro-display  56  is used, light sources  32  with different colors may illuminate the micro-display  56  sequentially in time. The micro-display  56  then need to be sufficiently fast for a flicker-free screen image as viewed by the human eye. The X-Cube  60  is typically made of glass, by securing/adhering four glass prisms together with thin film dichroic coatings. Alternatively, the X-cube  60  can be made by arranging glass sheets with thin film coatings in an X-form.  
         [0052]      FIG. 6  is similar to the arrangement of  FIG. 5 , except a transmissive micro-display  56  is disposed between each optical module  30  and the X-cube  60  rather than between the X-cube  60  and the imaging unit  58 . In this arrangement, the system optical axis is defined by the imaging unit  58 , which is also the same as that defined by the optical module  30 -G whose rays are not reflected by the X-cube  60 .  
         [0053]     The three abovementioned optical engine configurations of  FIGS. 4-6 . which use transmissive micro-displays  56 , enable very small projector sizes, starting from below 1 cc up to 10 cc, including the lens.  
         [0054]      FIG. 7  illustrates an embodiment where rays emanating from the optical module  30  enter into a polarizing beam splitter  66  where a splitter plate  68  divides the beam into different polarization components. One such component is reflected back from one reflective micro-display  70  and the other such component is reflected back from another reflective micro-display  70  oriented at an angle (preferably perpendicular) to the first. The separate polarized components are re-joined along the system optical axis and transmitted to the imaging unit  58 . Examples of reflective micro-displays  70  include reflective LCDs, and LCoS (liquid crystal on silicon). It is possible to use a white light source  32  and a color micro-display  70  if a color image is desired. It is also possible to use only one micro-display  70 , in which case the other polarization component is lost. If two micro-displays  70  are used, it is possible to present 3D-images by modulating different micro-displays  70  with different images (right eye and left eye images) and then using a polarization preserving screen (such as a metallized reflection screen or rear-projection screen) and polarizing glasses in viewing.  
         [0055]      FIG. 8  is essentially a combination of  FIGS. 5 and 7 , but without the transmissive micro-display  56  of  FIG. 5 . The polarizing beam splitter (PBS)  66  and reflective micro-displays  70  are as described with reference to  FIG. 7 , but in the embodiment of  FIG. 8 , the input to the PBS  66  is from an X-cube  60  that aligns rays from three chromatic optical modules  30  as described with reference to  FIG. 5 . In  FIG. 8 , light from different sources are combined, then the combination is separated by polarization and recombined as it is re-directed toward the imaging unit  58 .  
         [0056]      FIG. 9  shows that the various optical pathways between the optical module  30  and the imaging unit  58  are not limited to normal angles to one another. Light from the optical module  30  enters into a total internal reflection (TIR) prism  72  and is reflected by total internal reflection at a surface  74  toward a reflective micro-display  70 . From there, light is reflected back toward the surface  74 , which it passes through, and to the imaging unit  58 . This configuration is especially beneficial with DMD-microdisplay because the same microdisplay can be used for both polarization components.  
         [0057]      FIG. 10  is a schematic diagram of a combination of  FIGS. 5 and 9 , but without the transmissive micro-display  56  of  FIG. 5 . Light from the various optical modules  30 -R,  30 -G,  30 -B are combined into a single path as described with reference to  FIG. 5  and input into a TIR prism  72  as described with reference to  FIG. 9 . Within the TIR prism  72 , light is reflected by total internal reflection as described above from the surface  74  and then reflected again from the reflecting micro-display  70 , where it aligns with the optical axis defined by the imaging unit  58  and is directed toward it.  
         [0058]     In the abovementioned optical engine configurations for micro-projection, other performance enhancing components can be used also, as known in the field of projector optics. For example, additional polarizers can be used to enhance image contrast and quarter wavelength plates can be used in enhancing uniformity, in LCD and LCoS engines. Thin film antireflection coatings can be used in optically transmissive surfaces to eliminate unwanted reflections. PBS and X-Cubes can be made of glass blocks glued together or they can be air-spaced consisting glass sheets with functional coatings. It is preferable for etendue management that the optical modules  30 ,  30 ′ are disposed immediately adjacent to the optical engine (X-cube  60 , polarizing beam splitter PBS  66 , or TIR prism  72 ) so that the lens  44 ,  44 ′ of the module  30 ,  30 ′ faces an input side of the optical engine. However, variations of the illustrated embodiments may impose a space or even additional components between the modules  30 ,  30 ′ and the optical engine so long as they remain optically coupled to one another, wherein the output of the optical modules  30 ,  30 ′ is directed to an input of the optical engine, regardless of whether the optical axis between them is a straight line or reflected/redirected by the other intervening components.  
         [0059]      FIG. 111  is a schematic diagram showing dimensions of the optical module  30  relative to the optical engine  76 . The optical engine may be any of the various arrangements of optical components described in  FIGS. 4-10 , excluding the optical module  30 ,  30 ′ and including the X-cube  60 , the PBS  66 , and the TIR prism  72 . Where the width of the optical input field of the optical engine  76  is denoted as WOE, the width of the optical module  30 ,  30 ′ is denoted as WM, and the depth of the optical module is denoted as DM, the following relations preferably hold for any of the various embodiments of the present invention: 
 W M &lt;2*W OE   (2)  D M &lt;2*W OE   (3)  
         [0060]     Preferably, D M &lt;W M  also. In the preferred embodiment, the width of the optical module W M  is less than about 1.1 times the width of the optical engine input field W OE , and the depth of the optical module D M  is about one half the width of the optical engine input field W OE . The present invention is deemed particularly adapted to the micro-optics regime, defined as having diffractive optical structures/feature sizes between about 0.01 μm and about 100 μm, and/or refractive micro-optical structures/feature sizes between about 0.5 μm and about 1000 μm, and/or micro-prism arrays and/or micro-lens arrays. Preferably, the optical module  30 ,  30 ′ is less than about 2.5 cm on each width and length side and has a depth of about less than 1.5 centimeters.  
         [0061]     Whereas the above description has primarily assumed a LED as the light source  32 , any multi-directional light source may be used, such as an incandescent bulb or filament, a gas discharge lamp, etc. The present invention has been designed assuming that the source emits into a wider angle than that defined and limited by the parallaxial region.  
         [0062]     Although described in the context of particular embodiments, it will be apparent to those skilled in the art that a number of modifications and various changes to these teachings may occur. Thus, while the invention has been particularly shown and described with respect to one or more preferred embodiments thereof, it will be understood by those skilled in the art that certain modifications or changes may be made therein without departing from the scope and spirit of the invention as set forth above, or from the scope of the ensuing claims.