Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3141—Constructional details thereof
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3102—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators
  • H04N9/3105—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators for displaying all colours simultaneously, e.g. by using two or more electronic spatial light modulators
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
  • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
  • G02F1/1333—Constructional arrangements; Manufacturing methods
  • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
  • G02F1/13363—Birefringent elements, e.g. for optical compensation

Definitions

• Disclosed embodiments herein generally relate to optical devices for use in liquid crystal (LC) display systems, and more in particular to reflective liquid crystal on silicon (LCoS) projection architectures using compensators to enhance contrast.
• the compensators are configured to compensate for residual in-plane and out-of-plane retardation present in the OFF-state of an LC panel and also to compensate for non-ideal optical effects present in other optical components.
• compensators act first to remove residual in-plane OFF- state retardance of the panel, and second to reduce OFF-state light leakage due to the out-of-plane retardance which relates to field-of-view (FOV) performance of the LC layer.
• Removing the in-plane retardance is important since it corresponds to the extent to which the LC molecules are not aligned normal to the substrate or not balanced in their orientations when projected onto the panel plane.
• the substantial out-of-plane retardance alters the polarization state of off-axis rays, and acts to reduce the panel's field-of-view and in non-collimated systems leads again to OFF-state leakage.
• both in-plane and out-of-plane compensation is desired.
• an optical projection system for projecting modulated light from an LC panel along a light path.
• the projection system includes an LC panel and a compensator.
• the LC panel is positioned in the light path, and the LC panel is substantially planar and operable to receive polarized input light on an illumination portion of the light path.
• the LC panel is further operable to modulate the input light to form a modulated light that travels along a modulated light portion of the light path, thus imparting a first polarization upon certain portions of the input light, and imparting a second polarization upon other portions of the input light.
• a substantially planar compensator is positioned along the light path.
• the compensator has an optic axis tilted relative to the plane of the LC panel.
• FIGURE 1 is a schematic diagram of an exemplary optical three- panel LCoS projection system using a wire grid polarization beam splitter in accordance with the present disclosure
• FIGURE I A is a schematic diagram of an exemplary subsystem that may be used with the three-panel LCoS projection system of FIGURE 1 ;
• FIGURE 2 is a schematic perspective representation of the birefringence of a retardation film as an index ellipsoid.
• FIGURE 3 is a schematic perspective diagram illustrating an exemplary compensator component in accordance with the present disclosure
• FIGURE 4 is a graph showing an exemplary relationship of compensator orientation as a function of in-plane retardance for an LC display panel in accordance with the present disclosure
• FIGURE 5 is a schematic diagram illustrating the structure of an exemplary wire grid polarizing beam splitter in accordance with the present disclosure
• FIGURE 6 is a schematic diagram showing the application and positioning of a wire grid polarizer in an exemplary modulation subsystem in accordance with the present disclosure
• FIGURE 7 is a schematic diagram of an exemplary optical three- panel LCoS projection system using polarization beam splitter cubes in accordance with the present disclosure
• FIGURE 8A is a schematic perspective diagram illustrating another exemplary compensator component in accordance with the present disclosure.
• FIGURE 8B is a schematic diagram illustrating a cross-sectional view of the compensator component shown in FIGURE 8A.
• FIGURE 1 is a schematic diagram of an exemplary optical three- panel LCoS projection system 100.
• Projection system 1 00 may include an illumination subsystem 101 , which may distribute light to the modulation subsystems 1 30, 140, 1 50 via beam splitters 1 1 2, 1 20, and mirrors 1 14, 1 16, 1 1 8, arranged as shown.
• Beam splitters 1 12 and 1 20 split light into two beams of differing wavelength (color), that selectively reflect or transmit light depending on the light's wavelength.
• Beam splitters 1 1 2 and 120 may be dichroic beam splitters, such as dichroic mirrors or prisms.
• Projection system 100 may further include projection lens 170 for outputting modulated light, typically to a screen for viewing an image.
• Modulation subsystems 1 30, 140, and 1 50 are adapted to modulate blue, green, and red wavelength portions of the visual light spectrum respectively. A more detailed description of modulation subsystems 1 30, 140, 1 50 is provided with reference to FIGURE I A below.
• Illumination subsystem 101 may include a light source 102, lens arrays 104, 106, polarization beam splitter (PBS) array 108, and combining lens 1 10. Illumination subsystem 101 provides homogenized, telecentric polarized illumination to the modulation subsystems 1 30, 140, 1 50. As will be appreciated by a person of ordinary skill in the art, various illumination subsystems and variations thereof may be used to provide these functions and others, for example, illumination subsystems shown and described in MICHAEL G.
• FIGURE I A is a schematic diagram of an exemplary modulation subsystem 1 40 that may be used with the three-panel LCoS projection system 100 of FIGURE 1 .
• Modulation subsystem 140 includes a wire grid PBS (WGP) 142, a modulating panel 144, and a biaxial compensator 146.
• WGP wire grid PBS
• modulation subsystem 140 is illustrated, which modulates green light, this description also applies to modulation subsystems 1 30 and 1 50, which are of substantially similar structure and function, except they are adapted to modulate blue and red light respectively.
• modulation subsystem 1 30 (for blue light) includes a WGP 1 32, a modulating panel 1 34, and a biaxial compensator 1 36.
• modulation subsystem 1 50 (for red light) includes a WGP 1 52, a modulating panel 1 54, and a biaxial compensator 1 56. It should be appreciated that each modulation subsystem may comprise components having variations in optical characteristics to optimize the performance of each respective subsystem for a particular wavelength, or range of wavelengths.
• each modulation subsystem may comprise components having variations in optical characteristics to optimize the performance of each respective subsystem for a particular wavelength, or range of wavelengths.
• the light from the projection lamp 102 is transmitted through a fly's eye lens array (104-106) and PBS array 1 08 to homogenize the light, and a series of dichroic mirrors 1 1 2, 1 20 is used to separate incoming white light from the projection lamp 102 into red, green, and blue components.
• Absorption polarizers 1 22, 124, 1 26, may be used at each stage (for each color) to polarize the incoming light so at each modulation subsystem 130, 140, 1 50, the light can be modulated and reflected by the ensuing modulating panel 1 34, 144, 1 54, and wire-grid polarizer 1 32, 142, 1 52, respectively.
• both the modulating panel (e.g., 1 34, 144, 1 54) and wire-grid polarizers ⁇ e.g., 132, 142, 1 52) for each modulation subsystem 1 30, 140, 1 50, respectively may introduce nonideal polarization effects, such as skew-ray or off-axis polarization effects.
• a biaxial compensator 136, 146, 1 56 can be positioned at one or more of the modulation subsystems 1 30, 140, 1 50, in order to compensate for these nonideal polarization effects.
• Affecting system contrast is the reflection of light off the compensator and panel. For instance, light passing though the compensator 1 36, 146, 1 56 and back without encountering the LC will exhibit mixed polarization and contribute to off-state leakage. Although reducing interface reflection (e.g., by using anti-reflective coatings on the compensator component) can reduce this effect, negating it altogether is not practical.
• the proposed compensation techniques include tilting the compensators 1 36, 1 46, 1 56 to reduce this effect, thereby improving system contrast. Unwanted reflected light off the proposed tilted compensator/air interfaces would be at a bias angle away from the system's optic axis, thereby desirably minimizing its capture and projection onto the display screen.
• tilting one or more of compensators 1 36, 146, 1 56 relative to the plane of the respective modulating panel 1 34, 144, 1 54 provides improvements to system contrast.
• the biaxial compensators 1 36, 146, 1 56 (or compound compensating films having the same polarization effect) within the system may be oriented about, and may be tilted with respect to, the projection system's 100 optic axis, specifically including tilting them relative to the plane of the respective modulating panels 1 34, 144, 1 54 and relative to the usual 45-degree orientation of the PBS surface.
• an embodiment employs a compensating element of less than 0.5 mm to allow reasonable tilting (e.g., approximately 5 degrees, or less than about 5 degrees, or less than about 10 degrees) of up to ten degrees without significant image defocus ( ⁇ 0.5 pixel).
• a planar compensator with a tilted optic axis may be used such as a biaxial material sandwiched between oppositely wedged glass substrates. Although this does not reduce the surface reflection contribution to the contrast, it does act to further compensate the WGP 1 32, 142, 1 52.
• An exemplary embodiment of such a compensator component 800 is illustrated later with reference to FIGURES 8A and 8B.
• Each modulating panel 1 34, 144, 1 54 is operable to modulate light by imparting a first polarization state upon certain portions of the light ⁇ e.g., in an ON-state), and imparting a second polarization state upon other portions of the light ⁇ e.g., in an OFF-state).
• the modulated light from each modulation subsystem 1 30, 140, 1 50 then passes through clean-up polarizers 162, 1 64, 1 66, respectively, prior to being recombined by dichroic x-cube 1 60, and being directed to a screen by projector lens 1 70.
• FIGURE 2 is a three dimensional schematic representation of the birefringence of a retardation film as an index ellipsoid 200.
• One or more retardation films may be combined to make a compensator, such as compensator 1 36, 146, or 1 56 of FIGURE 1 .
• Any retardation film can be characterized uniquely by three refractive indexes n x , n y and n z , where n x , n y and n z are defined for orthogonal polarization axes.
• a representation of the three axes is shown by the index ellipsoid 200. It is known that with simple one-dimensional stretching, substantially uniaxial birefringence is formed with associated optical properties.
• Liquid crystal molecules in LCoS panels are positive uniaxial with their x-axis (optic axis) parallel to the molecular alignment direction.
• PC polycarbonate
• Such retarders may be appropriate to address LCD contrast and FOV enhancement requirements.
• the more complex 2D stretching, which includes shearing, can form layers that exhibit biaxiality.
• improvements in off-axis performance can be achieved.
• the extent to which off-axis performance is improved can be readily calculated for varying degrees of biaxiality in a viewing plane containing two of the film's three orthogonal optic axes (n x , n z ).
• N z (n x - n z ) / (n x - n y ).
• FIGURE 3 is a schematic diagram illustrating a possible construction of the elements of an exemplary compensator component 300.
• Stretched polymer retarders are typically manufactured by coating resin on a metal casting belt.
• the optical properties ⁇ e.g., transmitted wavefront distortion) of a polymer retarder can adversely affect the image quality when incorporated into a projection system.
• One solution is to mount the polymer film 302 between optically flat substrates 304 (such as glass) using a conforming, index matched optical adhesive 306.
• An anti-reflective coating 308 may be provided on the optically flat substrates 304.
• Film casting is followed by stretching. The stretching is accomplished in a continuous fashion via an accurately controlled oven with a pair of rollers turning at different rotation speeds.
• Stretched polymer retarders are low-cost birefringent elements that can be manufactured with large apertures, good cosmetic quality, high durability, and with varying, prescribed retardances.
• a single birefringent layer can be approximated by compound structures comprising combinations of retarder films.
• a combination of an a- and c-plate can, properly designed, yield for certain performance characteristics substantially the same performance as a single biaxial film.
• the terms "compensator” or "biaxial compensator” includes single or compound retarders performing in this way.
• the compensators described herein may, in other embodiments, be made from any equivalent suitable material such as solid crystals, liquid crystal polymers, or another material exhibiting optical properties in which the R 0 and Rth values of the compensator's retardance (defined below) can be configured consistent with the teachings of the present application.
• the liquid crystal polymer can have dual homogeneous alignment, splay alignment
• the present application discloses various embodiments of compensators for an LC panel where the projected indices of the LC panel are compensated by the in-plane retardance component (Ro) and out-of-plane retardance component (Rth) of the film using a biaxial compensator.
• Ro in-plane retardance component
• Rth out-of-plane retardance component
• a value of Ro is chosen to be greater than 10 nm more than the residual of the panel such that its x-axis is close ( ⁇ 1 0°) to the input polarization direction.
• the compensator ⁇ e.g., 136, 146, 1 56
• the compensator may then be rotated by ⁇ 5° about an axis parallel to the wire grid metal stripes such that the compensator is at an angle of about 40° relative to the PBS plate 142.
• the five-degree rotation is merely exemplary and other advantageous compensator plate tilting can be employed according to system design needs, including tilted about axes other than that defined by the wire grid stripes.
• FIGURE 4 is a graph showing an exemplary relationship of compensator orientation as a function of in-plane retardance for an LC display panel.
• FIGURE 4 illustrates a resulting 1 C 1 curve 400 of optimal compensator orientation (y-axis) as a function of its in-plane retardance (x-axis) when the residual retardance of an LC panel is 3 nm at an input wavelength of 550 nm ⁇ i.e., at point 405).
• the solution equation from which this C-curve is generated is set forth and described in commonly- assigned U.S. Pat. App. No. 10/908,671 , which is incorporated by reference, and provides definition and application of that formula in the LC compensating context.
• the compensators described in this application may also be used to compensate for other components in an optical projection system, and in particular may be used to compensate for birefringent effects induced by other optical components, including wire grid, MacNeille, form birefringent ⁇ e.g., VikuitiTM PBS manufactured by 3M, Inc.) or other types of polarizing beam splitters.
• birefringent effects induced by other optical components including wire grid, MacNeille, form birefringent ⁇ e.g., VikuitiTM PBS manufactured by 3M, Inc.
• FIGURE 7 An illustration of an exemplary projection system with a cube PBS is shown later with reference to FIGURE 7].
• a wire-grid PBS plate for example, is an important component found in many optical projection systems, and in particular in many LCoS projection systems, and the compensators disclosed by this application may be used to compensate for nonideal polarization effects introduced by these types of component, as well.
• the overall optimum compensation solution for system contrast in an exemplary optical projection system 1 00 should also take into account imperfections in polarization handling of this beam splitting component.
• the plate PBS is a tilted wire-grid polarizer, and in effect can be thought of as a periodic ordering of one-dimensional metal gratings, ideally with a pitch ⁇ 1 /10 of the shortest illuminating wavelength.
• the performance of a high aspect ratio (a '/a >>1 ) wire grid PBS can be modeled as a form-birefringence element comprising alternate metal/air layers normal to the substrate.
• FIGURE 6 is a perspective schematic diagram showing the application and positioning of a wire grid polarizer in an exemplary modulation subsystem.
• sheet polarizers 602 and 604 are located on the entrance and exit ports.
• Exit polarizer 604 may be the absorptive type.
• Wire grid polarizer 606 may be positioned along the modulated light portion of the light path and operable to direct a first polarization light in a first direction and to direct a second polarization light in a second direction.
• geometrical considerations dictate that the wire orientation of wire-grip polarizer 606 should be substantially normal to the system optic axis since the component tends to behave predominantly as an o- type polarizer with its axis along the wires.
• the compensator 608 may be tilted about an axis that is substantially parallel to the wires of the wire-grid polarizer.
• FIGURE 7 is a schematic diagram of an exemplary optical three- panel LCoS projection system using a polarization beam splitter cube.
• Projection system 700 shows an exemplary MacNeille 3xPBS/x-cube architecture employing tilted PBS cubes. Collimated light from illumination subsystem 702 is directed toward red, green, and blue modulating subsystems 704, 706, 708, respectively. Each of modulating subsystems 704, 706, 708 respectively includes a MacNeille PBS 710, 712, 714, an LCoS panel 722, 724, 726, and a compensator disposed between the LCoS panel and the PBS, with the elements arranged as shown. As previously described with respect to other embodiments, the compensators 716, 71 8, 720 may be tilted relative to the plane of the respective LCoS panel 722, 724, 726.
• a further technique includes using a quarter wave plate in addition to a compensator, the QWP is aligned to the PBS's s-polarization axis.
• a MacNeille type PBS is shown in this exemplary embodiment, it should be appreciated that this is used for illustration only, and other types of PBS may be used. For instance, a multilayer or a form- birefringent PBS may be substituted for the MacNeille type.
• form- birefringent PBSs generally do not suffer from the geometrical skew ray polarization mixing that MacNeille type PBSs incur.
• the Rth value of the compensator in embodiments using form-birefringent PBSs may be selected to be substantially matched to the total retardance of the respective LCoS panel 722, 724, 726.
• FIGURE 8A is a schematic perspective diagram illustrating another exemplary compensator component 800.
• a planar compensator with a tilted optic axis may be used such as a biaxial material 802 sandwiched between oppositely wedged glass substrates 804.
• an anti-reflective coating 808 may be applied to the glass substrates 804.
• Biaxial material 802 may be bonded to the glass substrates 804 using a conforming index-matched adhesive 806.
• An exemplary orientation axis for the biaxial material 802 is shown by arrow 810 at ⁇ ° relative to the horizontal.
• FIGURE 8B is a schematic diagram illustrating a cross-sectional view of the compensator component 800. This view illustrates that the wedged glass substrates 804 keep the biaxial material 802 at a tilt angle to the surface of compensator component 800. It should thus be appreciated that when compensator compenent 800 is used with projection systems, such as those illustrated in FIGURES 1 and 7, that the plane of the component 800 is parallel to the LC panel, although the plane biaxial material 802 is tilted relative to the plane of the LC panel, and the optic axis of the compensator is also tilted with respect to the LC panel.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Liquid Crystal (AREA)
• Polarising Elements (AREA)

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• 2006
  • 2006-08-11 WO PCT/US2006/031456 patent/WO2007021981A2/en active Application Filing
  • 2006-08-11 JP JP2008526245A patent/JP2009505141A/ja active Pending

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