Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
  • G03B21/00—Projectors or projection-type viewers; Accessories therefor
  • G03B21/14—Details
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/04—Prisms
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
  • G02B27/62—Optical apparatus specially adapted for adjusting optical elements during the assembly of optical systems
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
  • G02B7/18—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors
  • G02B7/1805—Mountings, adjusting means, or light-tight connections, for optical elements for prisms; for mirrors for prisms

Definitions

• This invention relates to methods and apparatus for accurately positioning one or more optical prisms in an optical assembly. More particularly, the invention relates to accurately positioning the diagonal of an optical prism where the diagonal divides (or is adapted to divide) incident light into a transmitted portion and a reflected portion. Accurate positioning of such a light-dividing diagonal is of importance since misalignment of the diagonal causes misdirection of reflected light and the introduction of parallax into transmitted light. BACKGROUND OF THE INVENTION
• Optical prisms having light-dividing diagonals are used in a variety of optical systems.
• a particularly important application for such prisms has been in projection systems which employ Liquid- Cry stal- On-Silicon (LCoS) panels.
• LCDoS Liquid- Cry stal- On-Silicon
• the above COLORQUADTM prism assembly suffers from two major problems.
• the assembly consists of four polarization beam splitters (PBSs) and five COLORSELECTTM polarization filters (Colorlink Inc., Boulder, Colorado). All of these components are optically cemented to each other. Optical cementing is a non-reversible process, which means that if something is wrong with any of the cemented components (scratched, displaced, tilted, etc.), the entire assembly must be rejected. Accordingly, the COLORQUADTM assembly suffers from low yields and high assembly costs.
• the second major problem with the COLORQUADTM assembly relates to its manner of use.
• three LCoS panels are used with one COLORQUADTM assembly to create a color image on a screen.
• all three images red, green and blue
• the panels are fixed in space. Simultaneously, red, green and blue light patches from the illuminator should overlap the corresponding panels.
• any misalignment in the COLORQUADTM assembly cannot be compensated for by moving the panels themselves (they are fixed as described in the previous paragraph) and will require increasing the light patch from the illumination system to provide complete illumination of all three panels. This significantly reduces the throughput of the optical engine from its theoretical maximum value.
• the overlapping of images through the illumination path of the COLORQUADTM assembly depends on the accuracy with which the assembly is constructed and cannot be compensated for once the assembly process has been completed. In the other words, the COLORQUADTM assembly must be assembled with very high accuracy, which requires active alignment of the components during the process of cementing. Like the problem of rejecting an entire assembly due to damage of any one component, active alignment during cementing increases the final cost of the COLORQUADTM assembly.
• the invention provides an optical assembly comprising:
• the invention provides a prism which has a top, a bottom, a plurality of sides, and a diagonal which has a top and a bottom, said prism comprising:
• first and second sub-prisms each of which has a surface that is parallel to the diagonal
• first and second sub-prisms each of which has a surface that is parallel to the diagonal
• second sub-prism a first mechanical reference surface for the top of the diagonal which comprises an extension of the parallel-to-the-diagonal surface of the first sub-prism above the parallel-to-the- diagonal surface of the second sub-prism
• C a second mechanical reference surface for the bottom of the diagonal which comprises an extension of the parallel-to-the- diagonal surface of the first sub-prism below the parallel-to- the-diagonal surface of the second sub-prism.
• the invention provides a method for positioning a prism, said prism having a diagonal which has a top and a bottom, said method comprising:
• the invention provides a method for positioning a prism, said prism (i) having a diagonal which has a top and a bottom and (ii) comprising first and second sub-prisms, each of which has a surface that is parallel to the diagonal, said method comprising:
• Figure 1 is a schematic diagram illustrating the four components of a "Separate Quad" constructed in accordance with the invention.
• Figure 2 is a perspective drawing of a prism, specifically, a polarization beam splitter (PBS), constructed in accordance with the invention.
• PBS polarization beam splitter
• Figure 3 is a schematic diagram illustrating the position of mechanical bases and locking elements, e.g., spring-loaded lockers, for use with the Separate Quad of Figure 1.
• Figure 4 is a schematic diagram illustrating another embodiment of the invention employing three prisms and a wire grid polarizer.
• FIG. 5 is a schematic diagram illustrating a further embodiment of the invention employing two prisms and two wire grid polarizers.
• the reference numbers used in the drawings correspond to the following:
• locking elements represented by open arrows in Figure 3 with the point of the arrow engaging a side of the prism
• fixed mechanical references represented by closed arrowheads in Figure 3 with the point of the arrowhead engaging either a mechanical reference surface or a side of the prism
• the present invention provides an opto- mechanical assembly 11 (also referred to herein as a "subassembly") of four prisms or prism units 15, which together form a "Quad” or “Separate Quad” for use in a reflective LCoS projection system.
• the prism subassembly 11 consists of four pre-assembled components 15A, 15B, 15C, and 15D.
• Components 15A, 15B, 15C, and 15D are each a polarization beam splitter (PBS) with components 15A, 15B, and 15C having one optically cemented polarization filter, while component 15D has two cemented filters.
• PBS polarization beam splitter
• the polarization filters can be COLORSELECTTM filters produced by Colorlink Inc., of Boulder, Colorado. These four components are assembled in the mechanical housing for the light engine to the required accuracy without any additional alignment.
• the most critical optical elements of the Quad from a positioning point of view are the diagonals 13 of the four polarization beam splitters.
• the PBS preferably has the shape shown in Figure 2.
• Each PBS consists of two cemented right angle prisms or sub-prisms (17A,17B), with a polarization coating on the PBS's diagonal.
• the polarization coating can, for example, be a multilayer structure as used in the MacNeille polarizing cube (see E. Stupp, M. Brennesholtz, Projection Displays, 1999, p. 130-133) or a polarization birefringence film such as that manufactured by 3M under the tradename 3M CARTESIAN POLARIZER (see Private Line Report on Projection Display, Volume 7, No. 11, July 20, 2001, pages 6-8).
• one sub-prism 17A is taller (longer) than the other sub-prism 17B, which allows the open or extended sections of the diagonal surface of the longer sub-prism to be used as mechanical reference surfaces 19A and 19B for positioning.
• the housing for the Separate Quad subassembly preferably consists of a top plate, bottom plate and four locking elements 21 (e.g., spring-loaded lockers), one per each PBS.
• the top and bottom plates have four sets of three pads (mechanical references), with each set forming a base for its respective prism 15A, 15B, 15C, and 15D. In each set, two pads are in contact with the PBS's diagonal and one in contact with a side surface of the PBS, as shown in Figure 3 (pads or mechanical basis shown in the drawing as black triangles/arrowheads).
• each PBS is placed against its own set of pads as shown in Figure 3.
• the spring-loaded locker forces the PBS to slide along the diagonal until full contact between the glass and the mount is achieved.
• the position of each PBS is determined by the position of the mechanical pads which can be fabricated to the required accuracy.
• Figures 4 and 5 show variations of the system of Figure 1 wherein a wire grid polarizer has been substituted for one ( Figure 4) or two (Figure 5) of the polarization beam splitters.
• the remaining PBS's (15B, 15C, and 15D in Figure 4; 15C and 15D in Figure 5) will have a construction of the type shown in Figure 2 and the housing for these PBS's will have appropriate fixed mechanical references and locking elements like those shown in Figure 3, adjusted to take account of the reduced number of PBSs.
• the housing will also include suitable fixtures for mounting the wire grid polarizers.
• the wire grid polarizers can be of the type manufactured by MOXTEK (Orem, UT, USA) under the PROFLUX trademark. See also U.S. Patent No. 6,122,103.
• the prism positioning system of the invention has the following benefits:
• the system provides a drop-in assembly method which does not require alignment.
• the accuracy of a diagonal's positioning does not depend on the PBS geometry or the accuracy of the filters (e.g., COLORSELECTTM filters) mounted on the PBS. Rather, it depends on the accuracy of the pad positioning and spacer geometry, which can be provided by fabricated mechanical components.
• each prism and its associated light- dividing diagonal is positioned independently of all other prisms in an assembly, the invention can be employed for only a subset of the prisms of an assembly (including only one prism of an assembly), with the remaining prisms being cemented together and positioned as one or more groups.
• the invention has been illustrated in terms of a prism diagonal which divides incident light based on polarization, the invention can be used with prism diagonals that divide light based on color, e.g., prisms whose diagonals comprise a dichroic coating.
• dichroic prisms can have the same geometrical configuration as shown in Figure 2 or can comprise two sub-prisms and a plane parallel plate between the sub-prisms which constitutes the prism's light- dividing diagonal.
• the plane parallel plate can extend above and below the sub -prisms to form the top and bottom mechanical reference surfaces which engage the fixed mechanical references of the prism's housing.
• the number of fixed mechanical references used for an individual prism can differ from that shown in Figure 3.
• the number of fixed mechanical references used for an individual prism can differ from that shown in Figure 3.
• the minimum number of fixed mechanical references needed to define the position of the light-dividing diagonal is four -- three which engage the diagonal and one which engages a side of the prism, with the locking element being appropriately located to effectively press the prism against the four fixed references.
• locking elements although spring loaded lockers are preferred because of their low cost and ready availability, other force applying locking elements can be used if desired.
• lockers which employ a resilient polymeric material which is compressed during positioning of the prism can be used, rather than a metallic spring.
• a turn screw or similar mechanical force generator, e.g., a cam mechanism can also be used for this purpose if desired.
• Additional variations include using prisms of differing heights with the housing and its associated fixed mechanical references being adjusted to accommodate those heights, e.g., the housing can have a stepped configuration.
• the housing can, and typically will, comprise multiple components connected to one another.
• the heights of mechanical reference surfaces 19A and 19B can vary both between prisms and/or for a given prism, e.g., mechanical reference surface 19A can be longer than (or shorter than) reference surface 19B for a given prism and the dimensions of the reference surfaces can be different for different prisms in an assembly.
• mechanical reference surface 19A can be longer than (or shorter than) reference surface 19B for a given prism and the dimensions of the reference surfaces can be different for different prisms in an assembly.
• two sub-prisms of different heights is the preferred approach for producing the mechanical reference surfaces, other approaches can be used if desired, e.g., one of the sub-prisms can be formed with or machined to have projecting portions at its top and bottom which will serve as mechanical reference surfaces or projections can be attached to a sub-prism using a suitable cement or other fixation technique.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Elements Other Than Lenses (AREA)
• Mounting And Adjusting Of Optical Elements (AREA)
• Optical Head (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

Country Status (7)

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• 2002
  • 2002-04-15 EP EP02717808A patent/EP1379899A2/en not_active Withdrawn
  • 2002-04-15 WO PCT/US2002/011660 patent/WO2002086549A2/en not_active Ceased
  • 2002-04-15 CN CNA028085515A patent/CN1503915A/zh active Pending
  • 2002-04-15 US US10/122,558 patent/US6643077B2/en not_active Expired - Fee Related
  • 2002-04-15 JP JP2002584020A patent/JP2004527791A/ja not_active Abandoned
  • 2002-04-15 AU AU2002248784A patent/AU2002248784A1/en not_active Abandoned
  • 2002-04-15 KR KR10-2003-7013638A patent/KR20030088142A/ko not_active Ceased

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