Patent Grant
6999237
A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has not objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
1. Field of Invention
The invention relates to Light Management Systems (LMSs). The invention is more particularly related to improvements to LMS and their applications to reflective microdisplay based video projectors.
2. Discussion of Background
Light Management Systems (LMSs) are utilized in optical devices, particularly projection video devices and generally comprises a light source, condenser, kernel, projection lens, and a display screen, and related electronics. The function of the components of a video projector 100 is explained with reference to
Commercially available prism assemblies include:
In the prism assembly, pathlengths are precisely matched. That is, the optical distance [] from each of the three microdisplays to an exit face (or output face) 155 of the prism assembly is essentially identical. This allows the microdisplays to be simultaneously in focus at the projection lens. In most currently available prism assemblies, the configuration of the prism assembly consists of precisely formed optical components that have been bonded together. The specific construction techniques by which this is accomplished provides differing advantages and disadvantages.
In some prism assembly configurations, an air gap is introduced between the microdisplays and a face on the prism assembly where the microdisplays are mounted. The air gap is a legitimate approach to accomplish pathlength matching, but has substantial disadvantages. For example, anti-reflection (AR) coatings are needed on the outer surfaces of the microdisplays and the prism assembly faces. The three microdisplays are aligned with respect to each other along all 6 axes of the microdisplay (x, y, z, roll, pitch, and yaw). Alignment is generally performed using mechanical positioners. Once alignment has been accomplished, the problem of maintaining the required precise alignment during the mechanical shock of appliance transport and during the thermal expansion/contraction that occurs while the video projector is in use still remains. In addition, the AR surfaces are exposed to dust, moisture and other atmospheric contaminates that may cause them to degrade. All of these factors reduce video projector performance.
In other prism assembly configurations the microdisplays are bonded to the faces of the prism assembly. Pathlength matching is accomplished by making the prism assembly have “perfect” (very precise) dimensions. Technologies currently being considered for producing these “perfect” dimensions include:
1. Tight Tolerance Component Fabrication
Source components may be fabricated to an extremely tight tolerance. However, such components are not currently available in high volume from vendors within the optics industry. When available, they will be very expensive.
2. Sort Components By Size
Measuring each component in an inventory and matching similarly sized components. The matched components are then used to construct a prism assembly. However, this requires an increased inventory of components from which to select matched sets of components.
3. Utilize Automated Assembly Equipment
The equipment measures the dimensions of each optical component and then actively adjusts their position during the assembly process. Such equipment must be custom designed and is expected to be quite expensive and inflexible.
In all three cases, extremely tight tolerances must be applied to the process used to assemble the optical components into the prism assembly. In all three cases, the outside dimensions of the resulting prism assembly, although having matched pathlengths, can still fall within a wide range. This requires that provisions be made within the video projector to mechanically adjust the position of the prism assembly with respect to the projection lens. Although bonding the microdisplays makes fabrication of the prism assembly more difficult, it has the advantage of eliminating the possibility of eventual misalignment of the microdisplays. In addition, the monolithic construction eliminates exposed surfaces and possible modes of degradation.
The prism assembly configurations each include several different types of plastic and/or glass materials. These disparate materials are bonded together. However, a difficulty arises because each material will have a different coefficient of thermal expansion. Since the prism assembly and its components will inevitably heat and cool during operation, the resulting expansion/contraction of the materials will generate stress (in fact, the process of assembly itself can build mechanical stresses into the prism assembly). Mechanical stress generates optical birefringence. Birefringence effects the polarization of the light beams traveling through the prism assembly and can be visualized on the screen as an undesirable artifact. It is, therefore, important to minimize the occurrence of stress within the prism assembly. One approach to minimize stress is to utilize glass that, in addition to meeting a long list of optical requirements, also has the lowest possible coefficient of stress induced birefringence. An example of one such glass is Schott's SF-57. The use of such a glass improves the situation but does not eliminate the problem.
Based on the considerations discussed above, it should be understood that there are many benefits to mounting the microdisplays directly onto the faces of the prism assembly. However, other various difficulties arise, including the expense of accomplishing the matching of the pathlengths and preparing microdisplays suitable for direct mounting. Furthermore, manufacturers of LMSs have had difficulties with attempts to implement such approaches in high volume manufacturing of any prism assembly configurations. The invention disclosed in this document consists of a prism assembly and construction techniques that can be applied to the construction of most prism assembly configurations (including all of those listed above). It enables inexpensive, high volume manufacturing of pathlength matched prism assemblies allowing the benefits of subsequent attachment of the microdisplays directly onto the faces of the prism assembly.
The present inventors have realized the need for cost effective pathlength matching and manufacturing techniques of Light Management Systems (LMSs) and particularly the construction of prism assemblies and microdisplay mounting on the prism assembly. The present invention describes a new approach to configuring the prism assembly, one that minimizes the undesirable optical consequences of mechanical stresses that arise within the prism assembly as a result of known construction techniques. The invention includes an inexpensive arrangement and method of constructing a pathlength matched prism assembly. The arrangement and method utilize less expensive, readily available optical components. Optically, the prism assemblies produced by this method are essentially identical and, therefore, can be used in a video projector with little need for mechanical adjustment. The invention can be applied to a wide range of prism assembly configurations and does not compromise other desirable mechanical or optical aspects of prism assembly performance.
In one embodiment, the present invention provides a prism assembly, comprising, a set of optical components arranged in pathlength matched positions, optical coupling fluid in contact with and between each of the optical components, and a frame affixed to each optical component and arranged so as to prevent optical coupling fluid leakage from between the optical components.
In another embodiment the present invention provides a prism assembly comprising, at least two optical components having imprecise dimensions configured to at least one of polarize, beam split, beam reflection and beam combine, said optical components fixed in a position such that pathlengths of beams directed through various paths in the prism assembly and to a focal point are matched, and an optical coupling fluid arranged in said pathlengths so as to contact at least two of the optical components.
In yet another embodiment, the present invention provides a prism assembly, comprising, a set of optical components, a baseplate attached to at least one of the optical components, a seal affixed to at least two of the optical components, and an optical coupling fluid disposed between the sealed optical components.
The present invention also includes a method of constructing a prism assembly, comprising the steps of, fixing a set of optical components to a baseplate, sealing spaces between the optical components, and filling spaces between the optical components with an optical coupling fluid. Various other methods and configurations will become apparent upon a detailed review of the disclosure and drawings as discussed below.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
Referring again to the drawings, wherein like reference numerals designate identical or corresponding parts, and more particularly to
The prism assembly 201 comprises a set of optical components, films, and matching elements making a single prism assembly unit. A white light 205 is directed at a Polarizing Beam Splitter (PBS) 210. A polarizing beam splitter thin film 215 perpendicularly polarizes and splits the white light into two beams of polarized light 220 and 240. The lightpaths through the prism assembly are each labeled to indicate the color and polarization of each light path. For example, incoming white light 205 is labeled W S+P (meaning White S and P polarized); light beam 220 is initially labeled WS (meaning white, s-polarized). The s-polarized white light 220 passes through a green dichroic filter 221 (passing green light, making beam 220 a green s-polarized beam (and labeled GS)), and enters a second Beam Splitter 212. A polarizing beam splitter thin film 217 reflects the s-polarized green light to “green” microdisplay 230.
The green microdisplay 230 manipulates the polarized green light according to green content of an image to be displayed. The “green” microdisplay modulates the polarization of the green light on a pixel-by-pixel basis. For example, a no green content pixel of the image to be displayed will be left unaltered, a strong green content pixel of the image to be displayed will have its polarization rotated 90°, and other pixels having varying levels of green content will have their polarization rotated in varying amounts in proportion to the amount of green content. The microdisplay also reflects (reflection or other polarization effects on the light are accounted for by the polarization manipulation of the microdisplay) the green light (now modulated) back toward the polarizing beam splitter thin film 217.
The polarizing beam splitter thin film 217 then reflects some portions and passes other portions of the green light. The amount of light reflected versus passing is based on the amount of modulation performed on the reflected green light. Light with the same polarization as was reflected into the green microdisplay is again reflected. Light that is oppositely polarized (or at least different from a polarization sensitivity of the polarizing beam splitter thin film 217) is passed. Amounts of green light less than the full amount of original green light and more than 0 depend on the amount of modulation (modulation in this example is the amount of polarization rotation).
Beam 235 represents the modulated green light that passes back through the polarizing beam splitter thin film 217 (e.g. green light sufficiently modulated to pass through the polarizing beam splitter thin film 217). Beam 235 enters final Beam Splitter 216 and is reflected off polarizing beam splitter thin film 213. Each of the red and blue components are similarly modulated and passed or reflected from corresponding polarization sensitive materials, to produce beam 250. After reflecting off polarizing beam splitter thin film 213, the modulated green light beam 235 is combined with the red and blue components of beam 250 and then exits the prism assembly through output face 275 as white light 280 containing the image to be displayed.
PBSs 210, 212, 214, and 216 are constructed similarly. In this configuration, each PBS contains 2 optical components (e.g., prisms 208 and 206) and a polarizing beam splitter thin film (e.g. 215). The polarizing beam splitter thin film is, for example, a coating that reflects s-polarized light and passes p-polarized light. Optical elements (e.g., retarders, rotators, etc) are utilized to change the polarization so that desired light beams are either reflected or passed by the polarizing beam splitter thin film so that subsequent polarizing beam splitter thin films may pass or reflect the desired light beams depending on the configuration of optical components and the desired path of each light beam (
The configuration of
Optical components are combined to create the beam splitters. For example, individual prisms 206 and 208 are optical components that are combined to produce the Polarizing Beam Splitter (PBS) 210. Before manufacture of the prism assembly, the beam splitting optical components are built. Prism assembly 201 illustrates four beam splitting optical components, polarizing beam splitters (PBSs) 210, 212, 214, and 216. Each of the polarizing beam splitters (hereinafter referred to as PBSs) contains a polarizing beam splitter thin film (e.g., 215, 217, 219, and 213). Preferably, the polarizing beam splitter thin films are at the diagonal of the beam splitters and extend through the corner as defined by the outside surfaces of the PBS. For example, the polarizing beam splitter thin film 215 extends along the diagonal of 206 and 208 through corners 202 and 204 of the PBS 210. The PBSs may be constructed so that the polarizing beam splitter thin film is on a plane of the diagonal and need not extend through the corners, particularly if light does not pass through the entire range of the diagonal.
The assembly of such PBS is accomplished by the use of optical pathlength matching. Referring to PBS 210, it can be noted that the two optical components (prisms) 206 and 208 need not be exactly the same size (and, consequently, the outside dimensions of the PBS need not meet any specific dimensional requirement). Since there are no specific dimensional requirements for the PBS, optical components with a “loose” mechanical tolerance may be utilized. Such optical components (and prisms used to construct those components) can be produced at modest cost and in high volume by existing vendors of optical components.
The optical components are assembled from the “outside in”. As shown in
Assembly tool includes an assembly tool base plate 315 to which the precision alignment corners 300 are fixed. Construction of the alignment corners 300A, 300B, 300C, and 300D can be performed using mechanical tooling. The alignment corners are constructed to a tolerance and positioned on the assembly tool base plate such that they precisely fix the outside dimensions of each PBS. Each alignment corner includes a device for securing the PBS in position during assembly. For example, PBS 210 is held tight in alignment corner 300A via vacuum holders 330 and 335. The vacuum holders are connected to vacuum pump 330 via vacuum tube 325. In one embodiment, there is a single vacuum holder in the corner of the alignment corner.
The alignment corners provide the precise dimensional accuracy required to achieve pathlength matching and is accomplished by mechanical tooling rather than expensive tightly toleranced optical components. However, pathlength matching alone does not produce an acceptable prism assembly. Although pathlength matched, because the optical components are of varying non-precise tolerances (different sizes), the PBS do not fit precisely together (e.g., intersection of PBS 210 and 214, and any dichroics or filters placed therebetween, do not fit exactly) and an air gap is introduced between the internal optical surfaces of the PBSs. The air gap itself introduces other problems including refraction and other optical variations that need to be reduced or eliminated.
The present invention reduces the undesirable effects from the imprecisely fit PBSs by coupling the PBSs with a liquid. In one embodiment, all internal optical surfaces of the prism assembly are coupled using a liquid.
In one embodiment, a frame, glued to the external surfaces of the prism assembly, is used to contain the liquid and hold the components in place.
Using the adhesive between the frame and PBSs to fix the matched pathlengths is performed by determining the matched pathlength positions of the prism assembly components (e.g., using a tool having corner pieces or other positioning devices to assure the correct optical pathlengths), and then gluing the components (e.g., PBSs) to one or more parts of the frame at those matched pathlength positions. Additional optical elements are then positioned in the joints (e.g., optical elements 410 and 420), the joints are then at least partly filled with optical coupling fluid (liquid coupling fluid), the joints are then capped with a top frame piece, and then the coupling fluid is topped off (except for the air bubble or other expansion air space), and then the fill hole is capped.
The present invention includes various methods and devices to fill the prism assembly with the coupling liquid. For example,
Recognize that, if the components within the prism assembly were to directly touch (e.g., optical element 410 directly touching either optical element 420 or PBS 212), the result could be a visible artifact in an image projected by the prism assembly. The solution to this problem is to assure that a thin layer of liquid exists between the components and or elements of the optical assembly. Many different methods and/or devices may be implemented to assure that a layer of liquid exists between components. For example, the optical elements may be physically separated during filling of the coupling fluid, spacers may be affixed to portions of the frame to separate the elements and PBSs. In one embodiment, spacers are applied between the optical surfaces.
The present invention includes various methods and devices for application of the spacers. In one set of embodiments, the spacers are applied directly to the optical surfaces of the PBSs and/or optical elements. In one embodiment, the spacers are sprayed onto the optical surfaces. Spraying spacers onto optical surfaces may be performed using liquid crystal display manufacturing techniques and machinery. Either wet or dry spacer application may be utilized. In other embodiments, the spacers are suspended in the liquid coupling fluid at least during manufacture. After manufacture of the prism assembly, suspended spaces remain lodged between the optical surfaces and/or settle to a bottom portion of the prism assembly out of the viewing area.
The liquid coupling fluid is an optical coupling fluid selected to have an index of refraction that matches (or closely matches) the index of refraction of the PBSs and any optical elements spaced within the fluid. In one embodiment, the optical coupling fluid is at least one of mineral oil and other fluid having an index of refraction within 25% of the index of refraction of the optical components.
The index of refraction changes depending on wavelength, and is different for each of the components and elements in the prism assembly. Typical values are 1.52 for plastic elements, and 1.71 for glass components. The optical coupling fluid generally preferred to have an index of refraction in the 1.50–1.85 range. A 1.6 index of refraction optical coupling fluid has worked well in experiments carried out by the inventors. Similarly, in the embodiments using spacers, the optical coupling fluid is chosen to have an index of refraction preferably matching each of the PBSs, optical elements, and spacers as closely as possible. Matching the index of refraction can be done by splitting the difference between the index of refraction of the optical components and elements. Another method would be to perform an impedance matching type of arithmetic (e.g., taking the square root of the sum of the squares of the index of refraction of each optical component/element). However, the present inventors note that selection of any index of refraction between the high and low index of refraction of the optical components and elements provides better matching than any other embodiments of the pathlength matched prism assembly, including the gel, cured epoxy, and air filled embodiments discussed elsewhere herein. The chosen index of refraction of the coupling fluid may also be weighted toward matching component interfaces that occur more frequently in the prism assembly. In one embodiment, the index of refraction of the coupling fluid matches the index of refraction of the spacers.
Important properties for the coupling fluid are toxicity, flammability, yellowing propensity, chemical properties, and cost. Toxicity and flammability are safety considerations, the product is preferably non-toxic and non-flammable. Also, the optical coupling fluid, to be practical, needs to be resistant to yellowing, particularly under intense light and heat conditions. The optical coupling fluid has to have chemical properties that do not react with other optical elements, components, and parts of the prism assembly. And, to be commercially practical, the optical coupling fluid needs to be relatively inexpensive and readily available. In one embodiment, the optical coupling fluid is, for example, mineral oil. Many different types and properties of optical coupling fluid are commercially available (e.g., Cargille Corp makes many different types of index matching fluid).
In one embodiment, the optical coupling fluid is a UV curing adhesive, which, when cured, makes a solid prism assembly, the cured adhesive coupling the optical elements/components without fluids. However, the liquid filled embodiments have better index of refraction matching than commercially practical UV curing adhesive, so the liquid filled embodiments are preferred. In another embodiment, optical coupling is performed by inserting an optical coupling gel between the various components/elements of the prism assembly. NYE corporation makes one such gel (matching gel). In yet another embodiment, the coupling material is air, or another gas is utilized as a coupler between the optical components and elements. In the air-filled embodiment, anti-reflection coating are places on the surfaces of the optical elements and components to eliminate or reduce reflections.
Note that variations of the assembly techniques described herein can be applied to any of the prism assembly configurations discussed in this document.
There are several other advantages offered by the configuration and manufacturing method described above. These include the following:
Several prism assembly configurations include polarization-rotating component(s) (rotators) (e.g., rotating beam 235 after being passed by polarizing beam splitter thin film 217 so it is then reflected by polarizing beam splitter thin film 213). Rotators are generally constructed of layers of polycarbonate plastic bonded together. In prior systems, the adhesive needs to be able to bond the polycarbonate plastic of the rotator to the glass of the prism assembly components. The common solution to this problem is to purchase the polarizing rotator from the vendor in the form of a “sandwich”. In “sandwich” form, the rotator has been bonded between two cover glasses. The cover glasses make it easier for the prism assembly manufacturer to bond the rotator into the prism assembly (e.g., bonding between surfaces of adjacent cover glasses). However, compared to the polycarbonate rotator itself, the sandwich may be available only in limited supply and is more expensive. In contrast, in the present invention, The liquid coupling method allows the direct use of the inexpensive, readily available polycarbonate component. Since with liquid coupling the polycarbonate is not bonded with adhesive, this class of problems is eliminated.
The precise outside dimensions of the prism assembly obtained using the new manufacturing method not only allow direct mounting of the microdisplays onto the prism assembly, but also allows for the use of precision (or fixed) mounting points for mounting the completed kernel (prism assembly with microdisplays attached) into the device in which it is to be used (e.g., light engine). The use of precision or fixed mounting points reduces or eliminates the need for a physical adjustment mechanism and procedure when mounting the kernel into the light engine.
Conventional prism assemblies generally utilize a series of glue cure steps. As the prism assembly grows in size and complexity, it becomes progressively more difficult to cure the adhesives due to the absorption of light by the glass and/or the optical properties of the components. Liquid coupling as provided by the present invention eliminates this problem and can greatly reduce the time required for prism assembly.
The present invention includes a device and method to hold the optical elements (e.g., optical elements 410 and 420) in place. The optical elements are also generally referred to as flat components because they are generally rectangular in shape and flat (having a thin width). However, the present invention may be practiced using different shapes and widths of the optical components.
One concern at any time, including manufacture, shipping, storage, and/or during actual use is the potential movement of optical components in the coupling fluid. Movement towards the central fill hole 700 could potentially leave the moved component (or parts of the moved component) out of the optical path. The present invention provides for placing a spacer device in the central fill hole 700 to hold the flat components in a stable general location.
As previously discussed an air bubble may be left inside the prism assembly to account for expansion of the various components. One problem with expansion of the components is that the components expand at different rates. As the optical coupling fluid expands, so does the optical components of the prism assembly. however, the expansion of the liquid and optical components is at different rates (differential expansion). In most cases, the optical coupling fluid expands at a higher rate than the optical components. Without the air bubble, an amount of stress is applied against the optical components by the expanding fluid. Without the air bubble, this stress can cause an undesirable amount of stress induced birefringence effecting the various light beams passing through the optical components of the prism assembly as the liquid coupling fluid expand.
Referring back to
In the example embodiment of
The air filled bladder 1000 is inserted into the fill channel (central fill hole 700). The volume of the bladder can increase or decrease to accommodate volumetric changes in the coupling liquid. In alternative embodiments, the bladder may be filled with any suitably compressible material (e.g., gas, liquid, solid, or combination thereof). The bladder 1000 can also serve to assist in holding those components in place that are not glued to the frame (e.g., the “flat” components (e.g., 410, 420) located between the polarized beamsplitting cubes). When configured to assist in holding the “flat” components in place, spacers such as polycarbonate roll 800 are not needed.
Each of the above embodiments have an external frame (e.g., frame 500—external to the optical components of the prism assembly) that seals the prism assembly and contains the optical coupling fluid (and include any necessary attachments for any of the stress relief features discussed above). The frame also provides structural strength to the prism assembly. However, the present inventors have also realized the need for a compact arrangement for sealing the optical coupling fluid. The compact arrange then allows for the prism assembly to be utilized in a wider variety of optical applications, including different LCoS based video projection systems.
Furthermore, any newly designed and/or previously existing light engine systems can be fitted with a fluid coupled prism assembly. In new designs, fitting the liquid coupled prism assembly may be performed by fitting mounts within the projection system to accommodate one or more liquid coupled prism assembly sizes. However, in the case of retrofit systems (fitting liquid filled prism assemblies to previously sold projection systems and/or fitting liquid coupled prism assemblies to new projection system of a previous design), physical accommodation of the liquid coupled prism assemblies may not be so easily accomplished. That is, the physical size and shape of a fluid coupled prism assembly may not allow it to directly fit into the position provided for a conventional prism assembly within an existing light engine. The modifications of the light engine required to accommodate a fluid coupled prism assembly may be difficult, expensive or, in an extreme case, not possible. Therefore, by providing a fluid coupled prism assembly that is sealed and provides structural strength and has external dimensions that are similar to that of an equivalent conventional prism assembly, that prism assembly could be used as a drop in replacement for a conventional prism assembly in any light engine design. The invention disclosed in this document is such a means.
For these reasons, the present inventors have also developed an internally sealed prism assembly that seals and provides structural integrity to a liquid filled prism assembly.
Alternatively, the adhesive seal may be a pliant adhesive such as silicone based adhesives. However, flexing of the prism assembly can become an issue if non-hardened sealant is utilized. While the bottom plate of the frame provides enough rigidity that pliant adhesives may be acceptable in some applications, a top plate (on the side of the prism assembly opposite the base plate) in addition to the base plate adds enough rigidity that pliant adhesives are fully acceptable in most all applications.
As explained above, the principle advantages of the disclosed liquid coupled prism assembly techniques and configurations include the ability to use less expensive, low tolerance glass components, and the ability to fabricate a prism assembly with “perfect” outside dimensions and in so doing, enabling the attachment of microdisplays directly to the prism assembly. In turn, the latter provides several advantages the foremost being that the resulting monolithic assembly will remain in a alignment under a wide range of conditions.
An alternative means by which these advantages can be obtained is to utilize the “build from the outside in” procedure described previously but, rather than filling the prism assembly with an optical coupling liquid, leaving the assembly empty therefore “filling” with air. However, in this approach, it will be necessary to coat all surfaces now exposed with an anti-reflection thin film (AR coatings) to suppress reflections. The expansion port is not required in this configuration. In some applications it may be possible to also omit the side rails of the frame (e.g., 500B) and possibly the top (500C).
In yet another alternative, the prism assembly is filled with an epoxy that cures. Preferably the cured epoxy has an index of refraction that closely matches the index of refraction of the PBSs and optical elements utilized. In still yet another embodiment, a gel substance may also be used to fill the joints between adjacent PBSs. Again, preferably, the gel has an index of refraction that approximates that of the other parts of the prism assembly. An example gel that could be utilized is manufactured by NYE Corporation.
In describing preferred embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the present invention is not intended to be limited to the specific terminology so selected, and it is to be understood that each specific element includes all technical equivalents which operate in a similar manner. For example, when describing a spacer device constructed of rolled polycarbonate, any other equivalent device, such as a geometrically shaped (square, triangle, pentagon, hexagon, etc) or other shape roll of polycarbonate or any other material or any other device having an equivalent function or capability, whether or not listed herein, may be substituted therewith. Furthermore, the inventors recognize that newly developed technologies not now known may also be substituted for the described parts and still not depart from the scope of the present invention.
The present invention is mainly described in conjunction with a LMS that utilizes a microdisplay that operates by rotating polarization of individual pixels. However, based on the description provided herein, it should be understood that the present invention may be practiced in devices with other types of microdisplays (e.g., scattering, absorption, diffraction based microdisplays), or in optical devices constructed without microdisplays.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
This invention claims priority to the following co-pending U.S. provisional patent applications, which are incorporated herein by reference, in its entirety: Detro et al., U.S. Provisional Patent Application Ser. No. 60/322,490, entitled “An Improved Configuration and Means of Assembling the Light Management System used in a Microdisplay Based Video Projector,”, filed Sep. 12, 2001; Detro et al., U.S. Provisional Patent Application Ser. No. 60/356,207, entitled “Means to Accommodate Expansion in Liquid Coupled Prism Assemblies,”, filed Feb. 11, 2002; and Detro et al., U.S. Provisional Patent Application Ser. No. 60/362,970, entitled “A Compact Means to Seal a Fluid Coupled Prism Assembly,”, filed Mar. 07, 2002.
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