WO2012161824A1 - Projection system - Google Patents

Projection system Download PDF

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Publication number
WO2012161824A1
WO2012161824A1 PCT/US2012/026768 US2012026768W WO2012161824A1 WO 2012161824 A1 WO2012161824 A1 WO 2012161824A1 US 2012026768 W US2012026768 W US 2012026768W WO 2012161824 A1 WO2012161824 A1 WO 2012161824A1
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WO
WIPO (PCT)
Prior art keywords
polarization state
light
projector
images
projection system
Prior art date
Application number
PCT/US2012/026768
Other languages
French (fr)
Inventor
Yufeng Liu
Original Assignee
3M Innovative Properties Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 3M Innovative Properties Company filed Critical 3M Innovative Properties Company
Publication of WO2012161824A1 publication Critical patent/WO2012161824A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N13/00—Stereoscopic video systems; Multi-view video systems; Details thereof
    • H04N13/30—Image reproducers
    • H04N13/363—Image reproducers using image projection screens
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N13/00—Stereoscopic video systems; Multi-view video systems; Details thereof
    • H04N13/30—Image reproducers
    • H04N13/332—Displays for viewing with the aid of special glasses or head-mounted displays [HMD]
    • H04N13/337—Displays for viewing with the aid of special glasses or head-mounted displays [HMD] using polarisation multiplexing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N13/00—Stereoscopic video systems; Multi-view video systems; Details thereof
    • H04N13/30—Image reproducers
    • H04N13/332—Displays for viewing with the aid of special glasses or head-mounted displays [HMD]
    • H04N13/341—Displays for viewing with the aid of special glasses or head-mounted displays [HMD] using temporal multiplexing
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N13/00—Stereoscopic video systems; Multi-view video systems; Details thereof
    • H04N13/30—Image reproducers
    • H04N13/324—Colour aspects

Definitions

  • This invention generally relates to projection systems.
  • the invention relates to three- dimensional (3D) front projection systems.
  • Projection systems are typically capable of providing large viewing areas by projecting an image onto a large screen.
  • a projection system typically includes a projector that emits an image and projects the image onto a viewing screen.
  • the viewer and the projector are on opposite sides of the projection screen.
  • the viewer and the projector are on the same side of the projection screen.
  • 3D projection systems simulate three-dimensional viewing of images by alternately projecting images for viewing by the left eye and the right eye of a viewer.
  • a projection system includes a projector that sequentially emits first images having a first polarization state for viewing by a left eye and second images having the first polarization state for viewing by a right eye.
  • the projection system further includes a front projection screen that scatters the sequentially emitted first and second images.
  • the front projection screen reflects light having the first polarization state, and absorbs light having a second polarization state perpendicular to the first polarization state.
  • the projection system further includes a viewing device that includes a first shutter that is synchronized with the projector and transmits the first, but not the second, images scattered by the front projection screen; and a second shutter that is synchronized with the projector and transmits the second, but not the first, images scattered by the front projection screen.
  • a viewing device that includes a first shutter that is synchronized with the projector and transmits the first, but not the second, images scattered by the front projection screen; and a second shutter that is synchronized with the projector and transmits the second, but not the first, images scattered by the front projection screen.
  • Each of the first and second shutters has a pass axis along the first polarization axis and a block axis along the second polarization axis.
  • the front projection screen includes a reflective polarizer that reflects light having the first polarization state and transmits light having the second polarization state; and a light absorbing layer that absorbs light that is transmitted by the reflective polarizer.
  • the reflective polarizer specularly reflects light having the first polarization state.
  • the reflective polarizer diffusely reflects light having the first polarization state.
  • the front projection screen includes an absorbing polarizer that transmits light having the first polarization state and absorbs light having the second polarization state; and a reflective layer that reflects light that is transmitted by the absorbing polarizer.
  • the projector includes an LCD projector that emits light having first, second and third color components, the first and second color components having the first polarization state and the third color component having the second polarization state.
  • the projector also includes a color selective filter that rotates the second polarization state of the third color component to the first polarization state without substantially altering the first polarization state of the first and second color components.
  • the projector includes an LCOS projector that emits light having first, second and third color components, each color component having the first polarization state.
  • the first and second shutters are synchronized with the projector via a signal emitted by the projector.
  • the emitted signal includes an IR signal, an RF signal, or a microwave signal.
  • the projector emits each of the first and second images at a frequency that is in a range from about 30 Hz to about 120 Hz.
  • the projection system also includes a pair of active shutter glasses that include the first and second shutters.
  • FIG. 1 is a schematic three-dimensional view of a projection system
  • FIG. 2 is a schematic plot of a projection screen's gain curve
  • FIG. 3 is a schematic side-view of a front projection screen
  • FIG. 4 is a schematic side-view of another front projection screen.
  • the present invention generally relates to projection systems.
  • the invention is particularly related to 3D front projection systems.
  • the disclosed projection systems include a polarized image emitting and projecting projector and a polarization sensitive front projection screen.
  • the projector sequentially projects onto the screen images for viewing by the left and the right eyes of a viewer.
  • the front projection screen is polarization sensitive and scatters the left-eye-images and the right-eye images since they have the desired polarization state and absorbs light having the undesired polarization state, typically in the forms of ambient, such as room, light.
  • the disclosed projection systems further include a viewing device that transmits essentially the entire light received by the viewing device, hence resulting in bright images for viewing by a viewer.
  • Projector 1 is a schematic three-dimensional view of a projection system 100 that includes a projector 1 10, a front projection screen 130 and a viewing device 140.
  • Projector 1 10 is a polarized projector meaning that the projector emits polarized light and images 1 12 that have a desired polarization state, such as, for example, linear, circular, or elliptical polarization state or any polarization state that may be desirable in an application.
  • projector 1 10 emits unpolarized light.
  • projector system may include a polarization control element 1 14 in the path of unpolarized emitted light 1 16 to convert the unpolarized light and images to emitted polarized light and images 1 12.
  • polarization control element 1 14 can be or include one or more elements to produce the desired polarization.
  • polarization control element 1 14 can include a polarizer and/or a retarder.
  • polarization control element 1 14 converts the unpolarized emitted light to polarized light by absorbing the undesired polarization state and transmitting the desired polarization state.
  • the polarization control element 1 14 can be or include an absorbing polarizer and the intensity or brightness of the emitted polarized images can be substantially reduced, for example, by as much as a factor of 2.
  • polarization control element 1 14 converts the unpolarized emitted light to polarized emitted light by converting, such as by rotating or recycling, the undesired polarization state to the desired polarization state.
  • polarization control element 1 14 can include, for example, a polarizer and a polarization rotator, and the unpolarized emitted light and images 1 16 can be converted to polarized light and images 1 12 without significant reduction in the intensity or brightness of the emitted light.
  • Projector 1 10 includes one or more image-forming devices.
  • the image-forming devices can be any suitable type of image forming device.
  • the image-forming devices can be optically transmissive or reflective image-forming devices.
  • the image-forming devices can include transmissive and/or reflective liquid crystal display (LCD) panels.
  • LCD liquid crystal display
  • HTPS high temperature polysilicon
  • LCOS reflective liquid crystal on silicon
  • LCD-based image- forming devices form polarized images. In such cases, projection system 100 may not need polarization control element 1 14 to polarize light 1 16.
  • DMD digital multimirror device
  • a DMD image-forming device uses an array of individually addressable mirrors, which either deflect the illumination light towards or away from the desired optical path.
  • DMD-based image-forming devices form unpolarized images.
  • projection system 100 may include polarization control element 1 14 to polarize light 1 16.
  • all the primary, such as red, green, and blue, colors in emitted light and images 1 16 have the same polarization state.
  • light 1 16 is polarized and there may not be a need for polarization control element 1 14.
  • the polarization state may not be the desired polarization state.
  • the polarization state may be a linear polarization state oriented horizontally or along the y-axis whereas the desired polarization state may be a linear polarization state oriented vertically or along the x-axis.
  • polarization control element 1 14 can be or include one or more quarter- wave retarders and/or half-wave retarders for rotating the polarization.
  • projector 1 10 emits light and images 1 16 where one or more primary colors have a first polarization state and the other primary colors have an orthogonal second polarization state.
  • the green primary color may be horizontally polarized and red and blue primary colors may be polarized linearly along the vertical or x-axis.
  • projection system 100 may include a polarization control element 1 14 for rotating the polarization state of one or more of the primary colors so that all the primary colors have the same desired polarization state.
  • polarization control element 1 14 can include a polarization rotator for rotating the polarization state of the green, but not blue and red, by 90 degrees resulting in all the primary colors being vertically polarized.
  • projector 1 10 includes an LCD projector emitting light having a first such as blue, a second such as red, and a third such as green, color components, where the first and second color components can have first polarization state 122 and the third color component can have second polarization state 125.
  • projection system 100 or projector 110 can also include a color selective filter that rotates second polarization state 125 of the third color component to first polarization state 122 without substantially altering first polarization state 122 of the first and second color components.
  • the color selective filter rotates at least 90%, or at least 95% of the second polarization state of the third color component, and rotates less than 10%, or less than 5%, of the first polarization state of the first and second color components.
  • the color selective filter can include a ColorSelect ® filter for rotating the polarization state of one primary color by 90 degrees without rotating the polarization states of the other primary colors, where ColorSelect ® filters are available from ColorLink Inc., Boulder, Colorado, USA.
  • projector 110 can include an LCOS projector that emits light having a first such as blue, a second such as green, and a third such as red, color components, where each color component has first polarization state 122.
  • Projector 110 and front projection screen 130 are centered on an optical axis 105 that is along the general direction of propagation of light and image beams 1 16 and 1 12, although in general, the projector and the projection screen need not be centered on the same axis.
  • optical axis 105 is along the z-direction of the xyz-coordinate system.
  • the optical axis can be along any suitable direction.
  • the optical axis can be folded or unfolded.
  • the exemplary projection system 100 in FIG. 1 is centered on an unfolded optical axis 105.
  • optical axis 105 can be folded at one or more points or locations along the optical axis by one or more reflecting or redirecting optical elements such as mirrors and/or prisms not shown expressly in FIG. 1. In such cases, the optical axis is folded to, for example, save space and reduce the foot print of projection system 100.
  • Projector 1 10 sequentially emits first images 120 having first polarization state 122 for viewing by the left eye of a viewer 160 and second images 124 having first polarization state 122 for viewing by the right eye of the viewer. Sequentially emitted first and second images 120 and 124 have the same polarization state 122, where in the exemplary projection system 100, polarization state 122 is linear and oriented vertically or along the x-direction. First and second images 120 and 124 are projected along the general direction of optical axis 105 and illuminate front projection screen 130. Front projection screen scatters, by reflection, light having first polarization state 122 and absorbs light having second polarization state 125 that is oriented horizontally or along the y-axis and orthogonal to first polarization state 122.
  • front projection screen 130 scatters an incident light having the first polarization state in different directions.
  • front projection screen 130 is a symmetric screen meaning that the screen scatters light similarly in different directions.
  • front projection screen 130 is an asymmetric screen meaning that the screen scatters light differently in different directions, such as for example, along the horizontal and vertical directions.
  • the scattering properties of the front projection screen can be described in terms of the gain curve of the screen along different directions.
  • front projection screen 130 can have a gain curve 210 as a function of the angle at which the screen is viewed along a direction, such as for example, the horizontal direction (in the yz-plane).
  • Front projection screen 130 has a maximum gain g 0 that corresponds to the on-axis or zero degree viewing angle and a half-maximum gain that defines a horizontal viewing angle A H that is equal to A H i-A H2 where A H i and A H2 may be referred to as the positive and negative horizontal viewing angles, respectively.
  • the positive viewing angle A H i corresponds to the half-brightness viewing angle for positive viewing angles and the negative viewing angle A H2 corresponds to the half-brightness viewing angle for negative viewing angles, and the horizontal viewing angle A H corresponds to the angle between positive and negative viewing angles.
  • Front projection screen 130 has a corresponding gain curve along an orthogonal direction, such as the vertical direction (in the xy-plane) with a maximum on-axis gain g 0 and a vertical viewing angle A V .
  • the horizontal viewing angle A H is substantially equal to the vertical viewing angle A V .
  • the magnitude of the difference between A H and A V is less than 5 degrees, or less than 4 degrees, or less than 3 degrees, or less than 2 degrees, or less than 1 degree.
  • the horizontal viewing angle A H is substantially different than the vertical viewing angle A V .
  • the magnitude of the difference between A H and A V is at least 10 degrees, or at least 15 degrees, or at least 20 degrees, or at least 25 degrees, or at least 30 degrees.
  • the exemplary gain curve 210 in FIG. 2 is symmetric about the on-axis direction or viewing, where the on-axis direction can correspond to optical axis 105 being normal to front projection screen 130.
  • front projection screen 130 can have a gain curve that may or may not be symmetric about the direction normal to the screen.
  • gain curves 210 is symmetric about the on-axis viewing direction as illustrated schematically in FIG. 2.
  • gain curve 210 may not be symmetric about the on-axis direction.
  • the peak gain may occur at an oblique viewing angle.
  • front projection screen 130 diffusely reflects an incident light into a half-brightness cone of reflected light, where the cone has a horizontal cone angle A H and a vertical cone angle A v .
  • front projection screen 130 scatters the sequentially emitted first and second images 120 and 124 towards viewer 160 for viewing by the viewer through viewing device 140.
  • front projection screen 130 diffusely reflects first image 120 having first polarization state 122 as diffusely reflected first image 170 propagating toward viewer 160 and diffusely reflects second image 124 as diffusely reflected second image 172 propagating toward the viewer.
  • front projection screen is substantially polarization preserving, meaning that the incident light and the diffusely reflected light have substantially the same polarization.
  • the diffusely reflected light for light incident on the front projection and having first polarization state 122, at least 80%, or at least 85%, or at least 85%, or at least 90%, or at least 95%, of the diffusely reflected light also has the first polarization state 122.
  • front projection screen is substantially polarization preserving
  • diffusely reflected first and second images 170 and 172 have substantially the first polarization state 122.
  • Viewing device 140 receives first and second images 170 and 172 for viewing by viewer 160.
  • Viewing device 140 is a stereoscopic viewing device allowing viewer 160 to view the images received by the viewing device 140 in three dimensions.
  • Viewing device 140 includes a first shutter 150 and a second shutter 152 where each of the first and second shutters has a pass axis along first polarization axis 122 (along the x-axis or direction) and a block axis along second polarization axis 123 (in the yz-plane).
  • First shutter 150 is synchronized with projector 1 10 in such a way that it transmits first images 170 but not second images 172
  • second shutter 152 is synchronized with projector 1 10 in such a way that is transmits second images 172 but not first images 170.
  • first and second shutters 150 and 152 can be any suitable shutters.
  • each of first and second shutters 150 and 152 includes a liquid-crystal-based shutter.
  • First and second shutters 150 and 152 are mounted on a support 191 and frames 190.
  • viewing device 140 can be a pair of 3D glasses for observing an image with parallax from individual right and left eye viewpoints.
  • support 191 can be a nose piece of the 3D glasses and frames 190 can form the temple and earpiece of the 3D glasses.
  • viewer 160 can wear a pair of active shutter or 3D glasses 140 for 3D viewing of images emitted by projector 1 10 and displayed by front projection 130.
  • Each of first and second optical shutters 150 and 152 has an on-state and an off-state.
  • Viewing device 140 also includes a driver 192 for powering and controlling the on- and off-states of each of first and second optical shutters 150 and 152, and a synchronizing device 194 for synchronizing the on- and off-states of each of first and second optical shutters 150 and 152 with a synchronizing signal 180 that is emitted by polarized projector 1 10 and is reflected by front projection screen 130 as reflected
  • first and second images 120 and 124 are emitted from projector 1 10.
  • projector 1 10 emits each of first and second images 120 and 124 at a frequency that is in a range from about 30 Hz to about 480 Hz, or from about 30 Hz to about 360, or from about 30 Hz to about 240, or from about 30 Hz to about 120.
  • projector 1 10 emits each of first and second images 120 and 124 at a frequency that is at least 60 Hz, or at least 90 Hz, or at least 120 Hz, or at least 150 Hz, or at least 180 Hz, or at least 210 Hz, or at least 240 Hz.
  • first shutter 150 and second shutter 152 are synchronized with projector 1 10 via synchronizing signal 180 that is emitted by projector 1 10.
  • signal 180 can be any type signal that can facilitate synchronization of shutters 150 and 152.
  • signal 180 can be or include an IR (infrared) signal, an RF (radio frequency) signal, or a microwave signal.
  • projector 1 10 sequentially emits first and second images 120 and 124 at a sufficiently high rate that the two images are displayed on front projection screen 130 substantially simultaneously.
  • the image emitting rate is sufficiently high so that for viewing purposes, the two images are projected onto and displayed by front projection screen 130 at the same time.
  • viewer can view the displayed images on front projection screen 130 in 3D.
  • synchronizing signal 180 is emitted by projector 1 10 between first and second images 120 and 124, where synchronizing signal 180 propagates toward front projection screen 130 and is reflected by the projection screen as reflected synchronizing signal 182. Reflected signal 182 propagates toward and is received by synchronizing device 194 of viewing device 140.
  • projector 1 10 can include a synchronization system that is commonly referred to as DLP ® Link TM , developed by and available from Texas Instruments (Texas Instruments, Dallas, Texas, USA).
  • FIG. 3 is a schematic side-view of a front projection screen 300 that can be used as front projection 130 in projection system 100.
  • Front projection screen 300 is substantially polarization preserving and includes a light diffusing layer 310, a reflective polarizer layer 320, a light absorbing layer 330 and an optional support or substrate 340 for providing support to the screen.
  • Light diffusing layer scatters incident light that is reflected by reflective polarizer layer 320.
  • light diffusing layer can be a symmetric diffuser having substantially the same horizontal and vertical viewing angles.
  • light diffusing layer can be an asymmetric diffuser having substantially different horizontal and vertical viewing angles. In such cases, the horizontal viewing angle along the y-direction can be larger than the vertical viewing angle along the x-direction.
  • Reflective polarizer layer 320 substantially reflects light having first polarization state 122 oriented along the x-axis and substantially transmits light having second polarization state 125 oriented along the y-axis.
  • the average reflectance of reflective polarizer layer 320 in the visible for the polarization state that is substantially reflected by the reflective polarizer is at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or at least about 95%.
  • the average transmittance of reflective polarizer layer 320 in the visible for the polarization state that is substantially transmitted by the reflective polarizer is at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or at least about 95%, or at least about 97%, or at least about 98%, or at least about 99%.
  • reflective polarizer layer 320 substantially reflects light having a first linear polarization state (for example, along the x-direction) and substantially transmits light having a second linear polarization state (for example, along the y-direction).
  • reflective polarizer layer 320 Any suitable type of reflective polarizer may be used for reflective polarizer layer 320 such as, for example, a multilayer optical film (MOF) reflective polarizer, a diffusely reflective polarizing film (DRPF) having a continuous phase and a disperse phase, such as a VikuitiTM Diffuse Reflective Polarizer Film (“DRPF”) available from 3M Company, St. Paul, Minnesota, a wire grid reflective polarizer described in, for example, U.S. Patent No. 6,719,426, or a cholesteric reflective polarizer.
  • DRPF VikuitiTM Diffuse Reflective Polarizer Film
  • reflective polarizer layer 320 specularly reflects substantially all light having the first polarization state.
  • At least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is specularly reflected.
  • reflective polarizer layer 320 diffusely reflects substantially all light having the first polarization state.
  • at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is diffusely reflected.
  • reflective polarizer layer 320 can be or include an MOF reflective polarizer, formed of alternating layers of different polymer materials, where one of the sets of alternating layers is formed of a birefringent material, where the refractive indices of the different materials are matched for light polarized in one linear polarization state and unmatched for light in the orthogonal linear polarization state.
  • an incident light in the matched polarization state is substantially transmitted through reflective polarizer layer 320 and an incident light in the unmatched polarization state is substantially reflected by reflective polarizer layer 320.
  • an MOF reflective polarizer layer 320 can include a stack of inorganic dielectric layers.
  • reflective polarizer layer 320 can be or include a partially reflecting layer that has an intermediate on-axis average reflectance in the pass state.
  • the partially reflecting layer can have an on-axis average reflectance of at least about 90% for visible light polarized in a first plane, such as the xz-plane, and an on-axis average reflectance in a range from about 25% to about 90% for visible light polarized in a second plane, such as the yz-plane, perpendicular to the first plane.
  • Such partially reflecting layers are described in, for example, U.S. Patent Publication No. 2008/064133, the disclosure of which is incorporated herein in its entirety by reference.
  • reflective polarizer layer 320 can be or include a circular reflective polarizer, where light circularly polarized in one sense, which may be the clockwise or counterclockwise sense (also referred to as right or left circular polarization), is preferentially transmitted and light polarized in the opposite sense is preferentially reflected.
  • a circular polarizer includes a cholesteric liquid crystal polarizer.
  • reflective polarizer layer 320 can be a multilayer optical film that reflects or transmits light by optical interference, such as those described in Provisional U.S. Patent Application No. 61/116132, filed November 19, 2009; Provisional U.S. Patent Application No. 61/116291, filed November 19, 2008; Provisional U.S. Patent Application No. 61/116294, filed November 19, 2008; Provisional U.S. Patent Application No. 61/116295, filed November 19, 2008; Provisional U.S. Patent Application No.
  • reflective polarizer layer 320 can be or include a diffusely reflective polarizing film (DRPF) having a continuous phase and a disperse phase, such as a DRPF film.
  • DRPF diffusely reflective polarizing film
  • reflective polarizer layer 320 diffusely reflects first and second images 120 and 124 having first polarization state 122.
  • light diffusing layer 310 may be absent from the front projection screen, although in some cases, the front projection screen can include a diffuse reflective polarizer 320 and a light diffusing layer 310 for providing additional light scattering.
  • Light absorbing layer 330 absorbs substantially all light that is transmitted by reflective polarizer 330.
  • light absorbing layer 330 can absorb at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, of light that is transmitted by reflective polarizer layer 320.
  • Light absorbing layer 330 can increase the contrast of images viewed by viewer 160 by absorbing ambient light 350 that is not reflected by reflective polarizer layer 320.
  • Light absorbing layer 330 can include any light absorbing material that may be desirable and/or practical in an application.
  • layer 330 can include carbon black, light absorptive dyes such as black dyes or other dark dyes, light absorptive pigments or other dark pigments, or opaque particles, dispersed in a binder material.
  • Suitable binders include thermoplastics, radiation curable or thermoset acrylates, epoxies, silicone -based materials, or other suitable binder materials.
  • the optical absorption coefficient of light absorbing layer 330 in the visible is at least about 0.1 inverse microns, or at least about 0.2 inverse microns, or at least about 0.4 inverse microns, or at least about 0.6 inverse microns.
  • front projection screen 300 includes an optional substrate 340.
  • substrate 340 can primarily provide support for the other components in the front projection screen. In some cases, substrate 340 can provide one or more additional optical functions.
  • substrate 340 can be or include an optical diffuser, a broadband light absorber, an absorbing polarizer, a reflective polarizer, or any other film with a function that may be desirable in an application.
  • Substrate 340 can be any material that may be suitable and/ or practical in an application, such as polyethylene terapthalate (PET), polyvinyl chloride (PVC), polycarbonates, acrylics, aluminum sheet, and glass, and composites thereof.
  • PET polyethylene terapthalate
  • PVC polyvinyl chloride
  • polycarbonates acrylics, aluminum sheet, and glass, and composites thereof.
  • FIG. 4 is a schematic side-view of a front projection screen 400 that can be used as front projection 130 in projection system 100.
  • Front projection screen 400 includes an absorbing polarizer layer 410, light diffusing layer 310, a reflective layer 420 and optional substrate 340.
  • Light absorbing polarizer layer 410 transmits incident light having first polarization state 122 oriented along the x- direction and absorbs incident light having second polarization state 125 oriented along the y-axis.
  • absorbing polarizer layer 410 can be any suitable light absorbing polarizer.
  • absorbing polarizer layer 410 can be a dichroic absorber.
  • absorbing polarizer layer 410 can be a linear absorbing polarizer or a circular absorbing polarizer, such as a cholesteric polarizer combined with a retarder.
  • Reflective layer 420 reflects substantially all light that is transmitted by absorbing polarizer 410 and diffuser 310. For example, in some cases, reflective layer 420 reflects at least 80%, or at least 85%, or at least 90%, or at least 95%, of light that is transmitted by light diffusing layer 310.
  • reflective layer 420 is primarily a specular reflective layer. For example, in such cases, at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is specularly reflected. In some cases, reflective layer 420 is primarily a diffuse reflective layer. For example, in such cases, at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is diffusely reflected. As a result, in some cases, light diffusing layer 310 may be absent from front projection screen 400, although in some cases, the front projection screen can include a diffuse reflective layer 420 and a light diffusing layer 310 for providing additional light scattering.
  • reflective layer 420 can be any reflector that may be desirable and/or practical in an application.
  • reflective layer 420 can be or include an aluminized film, a multilayer inorganic dielectric film, or a multi-layer polymeric reflective film, such as a Vikuiti ESR film available from 3M Company, St. Paul, Minnesota.
  • a projection system comprising: a projector sequentially emitting first images having a first polarization state for viewing by a left eye and second images having the first polarization state for viewing by a right eye;
  • a front projection screen scattering the sequentially emitted first and second images, reflecting light having the first polarization state, and absorbing light having a second polarization state
  • a viewing device comprising:
  • each of the first and second shutters has a pass axis along the first polarization axis and a block axis along the second polarization axis.
  • Item 2 The projection system of claim 1, wherein the front projection screen comprises:
  • a light absorbing layer absorbing light that is transmitted by the reflective polarizer.
  • Item 3 The projection system of claim 2, wherein the reflective polarizer specularly reflects light having the first polarization state.
  • Item 4 The projection system of claim 2, wherein the reflective polarizer diffusely reflects light having the first polarization state.
  • Item 5 The projection system of claim 1, wherein the front projection screen comprises:
  • a reflective layer reflecting light that is transmitted by the absorbing polarizer.
  • Item 6 The projection system of claim 1, wherein the projector comprises an LCD projector emitting light having first, second and third color components, the first and second color components having the first polarization state and the third color component having the second polarization state.
  • Item 7 The projection system of claim 6, wherein the projector further comprises a color selective filter that rotates the second polarization state of the third color component to the first polarization state without substantially altering the first polarization state of the first and second color components.
  • the projector comprises an LCOS projector emitting light having first, second and third color components, each color component having the first polarization state.
  • the first and second shutters are synchronized with the projector via a signal emitted by the projector.
  • Item 10 The projection system of claim 9, wherein the emitted signal comprises an IR signal. Item 1 1. The projection system of claim 9, wherein the emitted signal comprises an RF signal.
  • Item 12 The projection system of claim 9, wherein the emitted signal comprises a microwave signal.
  • Item 13 The projection system of claim 1, wherein the projector emits each of the first and second images at a frequency that is in a range from about 30 Hz to about 480 Hz.
  • Item 14 The projection system of claim 1, wherein the projector emits each of the first and second images at a frequency that is in a range from about 30 Hz to about 120 Hz.
  • Item 15 The projection system of claim 1 further comprising active shutter glasses comprising the first and second shutters.

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Abstract

A projection system is disclosed. The projection system includes a projector that sequentially emits first images having a first polarization state for viewing by a left eye and second images having the first polarization state for viewing by a right eye. The projection system further includes a front projection screen that scatters the sequentially emitted first and second images. The front projection screen reflects light having the first polarization state, and absorbs light having a second polarization state, where the second polarization state is perpendicular to the first polarization state. The projection system also includes a viewing device that includes a first shutter that is synchronized with the projector and transmits the first, but not the second, images scattered by the front projection screen. The viewing device also includes a second shutter that is synchronized with the projector and transmits the second, but not the first, images scattered by the front projection screen. Each of the first and second shutters has a pass axis that lies along the first polarization axis and a block axis that lies along the second polarization axis.

Description

PROJECTION SYSTEM
FIELD OF THE INVENTION
This invention generally relates to projection systems. In particular, the invention relates to three- dimensional (3D) front projection systems.
BACKGROUND
Projection systems are typically capable of providing large viewing areas by projecting an image onto a large screen. A projection system typically includes a projector that emits an image and projects the image onto a viewing screen. In a rear projection system, the viewer and the projector are on opposite sides of the projection screen. In a front projection system, the viewer and the projector are on the same side of the projection screen. 3D projection systems simulate three-dimensional viewing of images by alternately projecting images for viewing by the left eye and the right eye of a viewer. SUMMARY OF THE INVENTION
Generally, the present invention relates to projection systems. In one embodiment, a projection system includes a projector that sequentially emits first images having a first polarization state for viewing by a left eye and second images having the first polarization state for viewing by a right eye. The projection system further includes a front projection screen that scatters the sequentially emitted first and second images. The front projection screen reflects light having the first polarization state, and absorbs light having a second polarization state perpendicular to the first polarization state. The projection system further includes a viewing device that includes a first shutter that is synchronized with the projector and transmits the first, but not the second, images scattered by the front projection screen; and a second shutter that is synchronized with the projector and transmits the second, but not the first, images scattered by the front projection screen. Each of the first and second shutters has a pass axis along the first polarization axis and a block axis along the second polarization axis.
In some cases, the front projection screen includes a reflective polarizer that reflects light having the first polarization state and transmits light having the second polarization state; and a light absorbing layer that absorbs light that is transmitted by the reflective polarizer. In some cases, the reflective polarizer specularly reflects light having the first polarization state. In some cases, the reflective polarizer diffusely reflects light having the first polarization state.
In some cases, the front projection screen includes an absorbing polarizer that transmits light having the first polarization state and absorbs light having the second polarization state; and a reflective layer that reflects light that is transmitted by the absorbing polarizer.
In some cases, the projector includes an LCD projector that emits light having first, second and third color components, the first and second color components having the first polarization state and the third color component having the second polarization state. In some cases, the projector also includes a color selective filter that rotates the second polarization state of the third color component to the first polarization state without substantially altering the first polarization state of the first and second color components.
In some cases, the projector includes an LCOS projector that emits light having first, second and third color components, each color component having the first polarization state.
In some cases, the first and second shutters are synchronized with the projector via a signal emitted by the projector. In some cases, the emitted signal includes an IR signal, an RF signal, or a microwave signal.
In some cases, the projector emits each of the first and second images at a frequency that is in a range from about 30 Hz to about 120 Hz.
In some cases, the projection system also includes a pair of active shutter glasses that include the first and second shutters. BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be more completely understood and appreciated in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which:
FIG. 1 is a schematic three-dimensional view of a projection system;
FIG. 2 is a schematic plot of a projection screen's gain curve;
FIG. 3 is a schematic side-view of a front projection screen; and
FIG. 4 is a schematic side-view of another front projection screen.
In the specification, a same reference numeral used in multiple figures refers to the same or similar elements having the same or similar properties and functionalities.
DETAILED DESCRIPTION
The present invention generally relates to projection systems. The invention is particularly related to 3D front projection systems. The disclosed projection systems include a polarized image emitting and projecting projector and a polarization sensitive front projection screen. The projector sequentially projects onto the screen images for viewing by the left and the right eyes of a viewer. The front projection screen is polarization sensitive and scatters the left-eye-images and the right-eye images since they have the desired polarization state and absorbs light having the undesired polarization state, typically in the forms of ambient, such as room, light. The disclosed projection systems further include a viewing device that transmits essentially the entire light received by the viewing device, hence resulting in bright images for viewing by a viewer. FIG. 1 is a schematic three-dimensional view of a projection system 100 that includes a projector 1 10, a front projection screen 130 and a viewing device 140. Projector 1 10 is a polarized projector meaning that the projector emits polarized light and images 1 12 that have a desired polarization state, such as, for example, linear, circular, or elliptical polarization state or any polarization state that may be desirable in an application. In some cases, projector 1 10 emits unpolarized light. In such cases, projector system may include a polarization control element 1 14 in the path of unpolarized emitted light 1 16 to convert the unpolarized light and images to emitted polarized light and images 1 12. In general, polarization control element 1 14 can be or include one or more elements to produce the desired polarization. For example, polarization control element 1 14 can include a polarizer and/or a retarder. In some cases, polarization control element 1 14 converts the unpolarized emitted light to polarized light by absorbing the undesired polarization state and transmitting the desired polarization state. In such cases, the polarization control element 1 14 can be or include an absorbing polarizer and the intensity or brightness of the emitted polarized images can be substantially reduced, for example, by as much as a factor of 2. In some cases, polarization control element 1 14 converts the unpolarized emitted light to polarized emitted light by converting, such as by rotating or recycling, the undesired polarization state to the desired polarization state. In such cases, polarization control element 1 14 can include, for example, a polarizer and a polarization rotator, and the unpolarized emitted light and images 1 16 can be converted to polarized light and images 1 12 without significant reduction in the intensity or brightness of the emitted light.
Projector 1 10 includes one or more image-forming devices. In general, the image-forming devices can be any suitable type of image forming device. For example, the image-forming devices can be optically transmissive or reflective image-forming devices. For example, the image-forming devices can include transmissive and/or reflective liquid crystal display (LCD) panels. Another example of an image-forming device is a high temperature polysilicon (HTPS) LCD device. Another example of an image-forming device is reflective liquid crystal on silicon (LCOS) panel. In general, LCD-based image- forming devices form polarized images. In such cases, projection system 100 may not need polarization control element 1 14 to polarize light 1 16. Another type of image-forming device is a digital multimirror device (DMD) supplied by, for example, Texas Instruments, Piano, Texas, under the brand name DLP™. A DMD image-forming device uses an array of individually addressable mirrors, which either deflect the illumination light towards or away from the desired optical path. In general, DMD-based image-forming devices form unpolarized images. In such cases, projection system 100 may include polarization control element 1 14 to polarize light 1 16.
In some cases, all the primary, such as red, green, and blue, colors in emitted light and images 1 16 have the same polarization state. In such cases, light 1 16 is polarized and there may not be a need for polarization control element 1 14. In such cases, however, the polarization state may not be the desired polarization state. For example, the polarization state may be a linear polarization state oriented horizontally or along the y-axis whereas the desired polarization state may be a linear polarization state oriented vertically or along the x-axis. In such cases, there may still be a need for a polarization control element 1 14 for rotating the polarization of light 1 16 from horizontal to vertical resulting in light and image 1 12 being vertically polarized. In such cases, polarization control element 1 14 can be or include one or more quarter- wave retarders and/or half-wave retarders for rotating the polarization.
In some cases, projector 1 10 emits light and images 1 16 where one or more primary colors have a first polarization state and the other primary colors have an orthogonal second polarization state. For example, the green primary color may be horizontally polarized and red and blue primary colors may be polarized linearly along the vertical or x-axis. In such cases, projection system 100 may include a polarization control element 1 14 for rotating the polarization state of one or more of the primary colors so that all the primary colors have the same desired polarization state. For example, polarization control element 1 14 can include a polarization rotator for rotating the polarization state of the green, but not blue and red, by 90 degrees resulting in all the primary colors being vertically polarized.
In some cases, projector 1 10 includes an LCD projector emitting light having a first such as blue, a second such as red, and a third such as green, color components, where the first and second color components can have first polarization state 122 and the third color component can have second polarization state 125. In such cases, projection system 100 or projector 110 can also include a color selective filter that rotates second polarization state 125 of the third color component to first polarization state 122 without substantially altering first polarization state 122 of the first and second color components. For example, in such cases, the color selective filter rotates at least 90%, or at least 95% of the second polarization state of the third color component, and rotates less than 10%, or less than 5%, of the first polarization state of the first and second color components. In some cases, the color selective filter can include a ColorSelect® filter for rotating the polarization state of one primary color by 90 degrees without rotating the polarization states of the other primary colors, where ColorSelect® filters are available from ColorLink Inc., Boulder, Colorado, USA.
In some cases, projector 110 can include an LCOS projector that emits light having a first such as blue, a second such as green, and a third such as red, color components, where each color component has first polarization state 122.
Projector 110 and front projection screen 130 are centered on an optical axis 105 that is along the general direction of propagation of light and image beams 1 16 and 1 12, although in general, the projector and the projection screen need not be centered on the same axis. In the exemplary projection system shown in FIG. 1 , optical axis 105 is along the z-direction of the xyz-coordinate system. In general, the optical axis can be along any suitable direction. Furthermore, the optical axis can be folded or unfolded. For example, the exemplary projection system 100 in FIG. 1 is centered on an unfolded optical axis 105. In some cases, optical axis 105 can be folded at one or more points or locations along the optical axis by one or more reflecting or redirecting optical elements such as mirrors and/or prisms not shown expressly in FIG. 1. In such cases, the optical axis is folded to, for example, save space and reduce the foot print of projection system 100.
Projector 1 10 sequentially emits first images 120 having first polarization state 122 for viewing by the left eye of a viewer 160 and second images 124 having first polarization state 122 for viewing by the right eye of the viewer. Sequentially emitted first and second images 120 and 124 have the same polarization state 122, where in the exemplary projection system 100, polarization state 122 is linear and oriented vertically or along the x-direction. First and second images 120 and 124 are projected along the general direction of optical axis 105 and illuminate front projection screen 130. Front projection screen scatters, by reflection, light having first polarization state 122 and absorbs light having second polarization state 125 that is oriented horizontally or along the y-axis and orthogonal to first polarization state 122.
In general, front projection screen 130 scatters an incident light having the first polarization state in different directions. In some cases, front projection screen 130 is a symmetric screen meaning that the screen scatters light similarly in different directions. In some cases, front projection screen 130 is an asymmetric screen meaning that the screen scatters light differently in different directions, such as for example, along the horizontal and vertical directions. The scattering properties of the front projection screen can be described in terms of the gain curve of the screen along different directions. For example, as schematically illustrated in FIG. 2, front projection screen 130 can have a gain curve 210 as a function of the angle at which the screen is viewed along a direction, such as for example, the horizontal direction (in the yz-plane). Front projection screen 130 has a maximum gain g0 that corresponds to the on-axis or zero degree viewing angle and a half-maximum gain
Figure imgf000007_0001
that defines a horizontal viewing angle AH that is equal to AHi-AH2 where AHi and AH2 may be referred to as the positive and negative horizontal viewing angles, respectively. The positive viewing angle AHi corresponds to the half-brightness viewing angle for positive viewing angles and the negative viewing angle AH2 corresponds to the half-brightness viewing angle for negative viewing angles, and the horizontal viewing angle AH corresponds to the angle between positive and negative viewing angles.
Front projection screen 130 has a corresponding gain curve along an orthogonal direction, such as the vertical direction (in the xy-plane) with a maximum on-axis gain g0 and a vertical viewing angle AV. In the case of a symmetric front projection screen 130, the horizontal viewing angle AH is substantially equal to the vertical viewing angle AV. For example, in such cases, the magnitude of the difference between AH and AV is less than 5 degrees, or less than 4 degrees, or less than 3 degrees, or less than 2 degrees, or less than 1 degree. In the case of an asymmetric front projection screen 130, the horizontal viewing angle AH is substantially different than the vertical viewing angle AV. For example, in such cases, the magnitude of the difference between AH and AV is at least 10 degrees, or at least 15 degrees, or at least 20 degrees, or at least 25 degrees, or at least 30 degrees. The exemplary gain curve 210 in FIG. 2 is symmetric about the on-axis direction or viewing, where the on-axis direction can correspond to optical axis 105 being normal to front projection screen 130. In general, front projection screen 130 can have a gain curve that may or may not be symmetric about the direction normal to the screen. For a symmetric projection screen 130, gain curves 210 is symmetric about the on-axis viewing direction as illustrated schematically in FIG. 2. For an asymmetric front projection screen 130, gain curve 210 may not be symmetric about the on-axis direction. For example, in such cases, the peak gain may occur at an oblique viewing angle. In general, front projection screen 130 diffusely reflects an incident light into a half-brightness cone of reflected light, where the cone has a horizontal cone angle AH and a vertical cone angle Av.
Referring back to FIG. 1, front projection screen 130 scatters the sequentially emitted first and second images 120 and 124 towards viewer 160 for viewing by the viewer through viewing device 140. In particular, front projection screen 130 diffusely reflects first image 120 having first polarization state 122 as diffusely reflected first image 170 propagating toward viewer 160 and diffusely reflects second image 124 as diffusely reflected second image 172 propagating toward the viewer. In some cases, front projection screen is substantially polarization preserving, meaning that the incident light and the diffusely reflected light have substantially the same polarization. For example, in such cases, for light incident on the front projection and having first polarization state 122, at least 80%, or at least 85%, or at least 85%, or at least 90%, or at least 95%, of the diffusely reflected light also has the first polarization state 122. In cases, where front projection screen is substantially polarization preserving, diffusely reflected first and second images 170 and 172 have substantially the first polarization state 122.
Viewing device 140 receives first and second images 170 and 172 for viewing by viewer 160. Viewing device 140 is a stereoscopic viewing device allowing viewer 160 to view the images received by the viewing device 140 in three dimensions. Viewing device 140 includes a first shutter 150 and a second shutter 152 where each of the first and second shutters has a pass axis along first polarization axis 122 (along the x-axis or direction) and a block axis along second polarization axis 123 (in the yz-plane). First shutter 150 is synchronized with projector 1 10 in such a way that it transmits first images 170 but not second images 172, and second shutter 152 is synchronized with projector 1 10 in such a way that is transmits second images 172 but not first images 170. In general, first and second shutters 150 and 152 can be any suitable shutters. For example, in some cases, each of first and second shutters 150 and 152 includes a liquid-crystal-based shutter.
First and second shutters 150 and 152 are mounted on a support 191 and frames 190. In some cases, viewing device 140 can be a pair of 3D glasses for observing an image with parallax from individual right and left eye viewpoints. In such cases, support 191 can be a nose piece of the 3D glasses and frames 190 can form the temple and earpiece of the 3D glasses. In some cases, viewer 160 can wear a pair of active shutter or 3D glasses 140 for 3D viewing of images emitted by projector 1 10 and displayed by front projection 130. Each of first and second optical shutters 150 and 152 has an on-state and an off-state. Viewing device 140 also includes a driver 192 for powering and controlling the on- and off-states of each of first and second optical shutters 150 and 152, and a synchronizing device 194 for synchronizing the on- and off-states of each of first and second optical shutters 150 and 152 with a synchronizing signal 180 that is emitted by polarized projector 1 10 and is reflected by front projection screen 130 as reflected
synchronizing signal 182 propagating toward viewing device 140. The on- and off-states alternate between the two shutters 150 and 152 at a suitable frequency that, in some cases, matches the frequency at which first and second images 120 and 124 are emitted from projector 1 10. In some cases, projector 1 10 emits each of first and second images 120 and 124 at a frequency that is in a range from about 30 Hz to about 480 Hz, or from about 30 Hz to about 360, or from about 30 Hz to about 240, or from about 30 Hz to about 120. In some cases, projector 1 10 emits each of first and second images 120 and 124 at a frequency that is at least 60 Hz, or at least 90 Hz, or at least 120 Hz, or at least 150 Hz, or at least 180 Hz, or at least 210 Hz, or at least 240 Hz.
In general, first shutter 150 and second shutter 152 are synchronized with projector 1 10 via synchronizing signal 180 that is emitted by projector 1 10. In general, signal 180 can be any type signal that can facilitate synchronization of shutters 150 and 152. For example, in some cases, signal 180 can be or include an IR (infrared) signal, an RF (radio frequency) signal, or a microwave signal.
In some cases, projector 1 10 sequentially emits first and second images 120 and 124 at a sufficiently high rate that the two images are displayed on front projection screen 130 substantially simultaneously. For example, the image emitting rate is sufficiently high so that for viewing purposes, the two images are projected onto and displayed by front projection screen 130 at the same time. In such cases, viewer can view the displayed images on front projection screen 130 in 3D. In some cases, synchronizing signal 180 is emitted by projector 1 10 between first and second images 120 and 124, where synchronizing signal 180 propagates toward front projection screen 130 and is reflected by the projection screen as reflected synchronizing signal 182. Reflected signal 182 propagates toward and is received by synchronizing device 194 of viewing device 140. Such active communication between projector 1 10 and viewing device 140 can result in substantially real time 3D viewing of images displayed on the front projection screen. In some cases, projector 1 10 can include a synchronization system that is commonly referred to as DLP® Link™, developed by and available from Texas Instruments (Texas Instruments, Dallas, Texas, USA).
FIG. 3 is a schematic side-view of a front projection screen 300 that can be used as front projection 130 in projection system 100. Front projection screen 300 is substantially polarization preserving and includes a light diffusing layer 310, a reflective polarizer layer 320, a light absorbing layer 330 and an optional support or substrate 340 for providing support to the screen.
Light diffusing layer scatters incident light that is reflected by reflective polarizer layer 320. In some cases, light diffusing layer can be a symmetric diffuser having substantially the same horizontal and vertical viewing angles. In some cases, light diffusing layer can be an asymmetric diffuser having substantially different horizontal and vertical viewing angles. In such cases, the horizontal viewing angle along the y-direction can be larger than the vertical viewing angle along the x-direction.
Reflective polarizer layer 320 substantially reflects light having first polarization state 122 oriented along the x-axis and substantially transmits light having second polarization state 125 oriented along the y-axis. For example, in some cases, the average reflectance of reflective polarizer layer 320 in the visible for the polarization state that is substantially reflected by the reflective polarizer is at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or at least about 95%. As another example, the average transmittance of reflective polarizer layer 320 in the visible for the polarization state that is substantially transmitted by the reflective polarizer is at least about 50%, or at least about 60%, or at least about 70%, or at least about 80%, or at least about 90%, or at least about 95%, or at least about 97%, or at least about 98%, or at least about 99%. In some cases, reflective polarizer layer 320 substantially reflects light having a first linear polarization state (for example, along the x-direction) and substantially transmits light having a second linear polarization state (for example, along the y-direction).
Any suitable type of reflective polarizer may be used for reflective polarizer layer 320 such as, for example, a multilayer optical film (MOF) reflective polarizer, a diffusely reflective polarizing film (DRPF) having a continuous phase and a disperse phase, such as a Vikuiti™ Diffuse Reflective Polarizer Film ("DRPF") available from 3M Company, St. Paul, Minnesota, a wire grid reflective polarizer described in, for example, U.S. Patent No. 6,719,426, or a cholesteric reflective polarizer. In some cases, reflective polarizer layer 320 specularly reflects substantially all light having the first polarization state. For example, in such cases, at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is specularly reflected. In some cases, reflective polarizer layer 320 diffusely reflects substantially all light having the first polarization state. For example, in such cases, at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is diffusely reflected.
In some cases, reflective polarizer layer 320 can be or include an MOF reflective polarizer, formed of alternating layers of different polymer materials, where one of the sets of alternating layers is formed of a birefringent material, where the refractive indices of the different materials are matched for light polarized in one linear polarization state and unmatched for light in the orthogonal linear polarization state. In such cases, an incident light in the matched polarization state is substantially transmitted through reflective polarizer layer 320 and an incident light in the unmatched polarization state is substantially reflected by reflective polarizer layer 320. In some cases, an MOF reflective polarizer layer 320 can include a stack of inorganic dielectric layers.
As another example, reflective polarizer layer 320 can be or include a partially reflecting layer that has an intermediate on-axis average reflectance in the pass state. For example, the partially reflecting layer can have an on-axis average reflectance of at least about 90% for visible light polarized in a first plane, such as the xz-plane, and an on-axis average reflectance in a range from about 25% to about 90% for visible light polarized in a second plane, such as the yz-plane, perpendicular to the first plane. Such partially reflecting layers are described in, for example, U.S. Patent Publication No. 2008/064133, the disclosure of which is incorporated herein in its entirety by reference.
In some cases, reflective polarizer layer 320 can be or include a circular reflective polarizer, where light circularly polarized in one sense, which may be the clockwise or counterclockwise sense (also referred to as right or left circular polarization), is preferentially transmitted and light polarized in the opposite sense is preferentially reflected. One type of circular polarizer includes a cholesteric liquid crystal polarizer.
In some cases, reflective polarizer layer 320 can be a multilayer optical film that reflects or transmits light by optical interference, such as those described in Provisional U.S. Patent Application No. 61/116132, filed November 19, 2009; Provisional U.S. Patent Application No. 61/116291, filed November 19, 2008; Provisional U.S. Patent Application No. 61/116294, filed November 19, 2008; Provisional U.S. Patent Application No. 61/116295, filed November 19, 2008; Provisional U.S. Patent Application No.
61/116295, filed November 19, 2008; and International Patent Application No. PCT/US 2008/06031 1, filed May 19, 2008, claiming priority from Provisional U.S. Patent Application No. 60/939085; all incorporated herein by reference in their entirety.
In some cases, reflective polarizer layer 320 can be or include a diffusely reflective polarizing film (DRPF) having a continuous phase and a disperse phase, such as a DRPF film. In such cases, reflective polarizer layer 320 diffusely reflects first and second images 120 and 124 having first polarization state 122. As a result, in some cases, light diffusing layer 310 may be absent from the front projection screen, although in some cases, the front projection screen can include a diffuse reflective polarizer 320 and a light diffusing layer 310 for providing additional light scattering.
Light absorbing layer 330 absorbs substantially all light that is transmitted by reflective polarizer 330. For example, in some cases, light absorbing layer 330 can absorb at least 70%, or at least 75%, or at least 80%, or at least 85%, or at least 90%, or at least 95%, of light that is transmitted by reflective polarizer layer 320. Light absorbing layer 330 can increase the contrast of images viewed by viewer 160 by absorbing ambient light 350 that is not reflected by reflective polarizer layer 320. Light absorbing layer 330 can include any light absorbing material that may be desirable and/or practical in an application. For example, layer 330 can include carbon black, light absorptive dyes such as black dyes or other dark dyes, light absorptive pigments or other dark pigments, or opaque particles, dispersed in a binder material. Suitable binders include thermoplastics, radiation curable or thermoset acrylates, epoxies, silicone -based materials, or other suitable binder materials. In some cases, the optical absorption coefficient of light absorbing layer 330 in the visible, is at least about 0.1 inverse microns, or at least about 0.2 inverse microns, or at least about 0.4 inverse microns, or at least about 0.6 inverse microns. In some cases, front projection screen 300 includes an optional substrate 340. In some cases, substrate 340 can primarily provide support for the other components in the front projection screen. In some cases, substrate 340 can provide one or more additional optical functions. For example, substrate 340 can be or include an optical diffuser, a broadband light absorber, an absorbing polarizer, a reflective polarizer, or any other film with a function that may be desirable in an application. Substrate 340 can be any material that may be suitable and/ or practical in an application, such as polyethylene terapthalate (PET), polyvinyl chloride (PVC), polycarbonates, acrylics, aluminum sheet, and glass, and composites thereof.
FIG. 4 is a schematic side-view of a front projection screen 400 that can be used as front projection 130 in projection system 100. Front projection screen 400 includes an absorbing polarizer layer 410, light diffusing layer 310, a reflective layer 420 and optional substrate 340. Light absorbing polarizer layer 410 transmits incident light having first polarization state 122 oriented along the x- direction and absorbs incident light having second polarization state 125 oriented along the y-axis. In general, absorbing polarizer layer 410 can be any suitable light absorbing polarizer. For example, absorbing polarizer layer 410 can be a dichroic absorber. As another example, absorbing polarizer layer 410 can be a linear absorbing polarizer or a circular absorbing polarizer, such as a cholesteric polarizer combined with a retarder.
Reflective layer 420 reflects substantially all light that is transmitted by absorbing polarizer 410 and diffuser 310. For example, in some cases, reflective layer 420 reflects at least 80%, or at least 85%, or at least 90%, or at least 95%, of light that is transmitted by light diffusing layer 310.
In some cases, reflective layer 420 is primarily a specular reflective layer. For example, in such cases, at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is specularly reflected. In some cases, reflective layer 420 is primarily a diffuse reflective layer. For example, in such cases, at least 80%, or at least 85%, or at least 90%, or at least 95%, or at least 98%, of reflected light is diffusely reflected. As a result, in some cases, light diffusing layer 310 may be absent from front projection screen 400, although in some cases, the front projection screen can include a diffuse reflective layer 420 and a light diffusing layer 310 for providing additional light scattering. In general, reflective layer 420 can be any reflector that may be desirable and/or practical in an application. For example reflective layer 420 can be or include an aluminized film, a multilayer inorganic dielectric film, or a multi-layer polymeric reflective film, such as a Vikuiti ESR film available from 3M Company, St. Paul, Minnesota.
s used herein, terms such as "vertical", "horizontal", "above", "below", "left" , "right", "upper" and "lower", "clockwise" and "counter clockwise" and other similar terms, refer to relative positions as shown in the figures. In general, a physical embodiment can have a different orientation, and in that case, the terms are intended to refer to relative positions modified to the actual orientation of the device.
Item 1. A projection system comprising: a projector sequentially emitting first images having a first polarization state for viewing by a left eye and second images having the first polarization state for viewing by a right eye;
a front projection screen scattering the sequentially emitted first and second images, reflecting light having the first polarization state, and absorbing light having a second polarization state
perpendicular to the first polarization state; and
a viewing device comprising:
a first shutter synchronized with the projector and transmitting the first, but not the second, images scattered by the front projection screen; and
a second shutter synchronized with the projector and transmitting the second, but not the first, images scattered by the front projection screen, wherein each of the first and second shutters has a pass axis along the first polarization axis and a block axis along the second polarization axis.
Item 2. The projection system of claim 1, wherein the front projection screen comprises:
a reflective polarizer reflecting light having the first polarization state and transmitting light having the second polarization state; and
a light absorbing layer absorbing light that is transmitted by the reflective polarizer.
Item 3. The projection system of claim 2, wherein the reflective polarizer specularly reflects light having the first polarization state.
Item 4. The projection system of claim 2, wherein the reflective polarizer diffusely reflects light having the first polarization state.
Item 5. The projection system of claim 1, wherein the front projection screen comprises:
an absorbing polarizer transmitting light having the first polarization state and absorbing light having the second polarization state; and
a reflective layer reflecting light that is transmitted by the absorbing polarizer.
Item 6. The projection system of claim 1, wherein the projector comprises an LCD projector emitting light having first, second and third color components, the first and second color components having the first polarization state and the third color component having the second polarization state.
Item 7. The projection system of claim 6, wherein the projector further comprises a color selective filter that rotates the second polarization state of the third color component to the first polarization state without substantially altering the first polarization state of the first and second color components. Item 8. The projection system of claim 1, wherein the projector comprises an LCOS projector emitting light having first, second and third color components, each color component having the first polarization state. Item 9. The projection system of claim 1, wherein the first and second shutters are synchronized with the projector via a signal emitted by the projector.
Item 10. The projection system of claim 9, wherein the emitted signal comprises an IR signal. Item 1 1. The projection system of claim 9, wherein the emitted signal comprises an RF signal.
Item 12. The projection system of claim 9, wherein the emitted signal comprises a microwave signal. Item 13. The projection system of claim 1, wherein the projector emits each of the first and second images at a frequency that is in a range from about 30 Hz to about 480 Hz.
Item 14. The projection system of claim 1, wherein the projector emits each of the first and second images at a frequency that is in a range from about 30 Hz to about 120 Hz.
Item 15. The projection system of claim 1 further comprising active shutter glasses comprising the first and second shutters.
All patents, patent applications, and other publications cited above are incorporated by reference into this document as if reproduced in full. While specific examples of the invention are described in detail above to facilitate explanation of various aspects of the invention, it should be understood that the intention is not to limit the invention to the specifics of the examples. Rather, the intention is to cover all modifications, embodiments, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Claims

What is claimed is:
1. A projection system comprising:
a projector sequentially emitting first images having a first polarization state for viewing by a left eye and second images having the first polarization state for viewing by a right eye;
a front projection screen scattering the sequentially emitted first and second images, reflecting light having the first polarization state, and absorbing light having a second polarization state perpendicular to the first polarization state; and
a viewing device comprising:
a first shutter synchronized with the projector and transmitting the first, but not the second, images scattered by the front projection screen; and
a second shutter synchronized with the projector and transmitting the second, but not the first, images scattered by the front projection screen, wherein each of the first and second shutters has a pass axis along the first polarization axis and a block axis along the second polarization axis.
2. The projection system of claim 1, wherein the front projection screen comprises:
a reflective polarizer reflecting light having the first polarization state and transmitting light having the second polarization state; and
a light absorbing layer absorbing light that is transmitted by the reflective polarizer.
3. The projection system of claim 2, wherein the reflective polarizer specularly reflects light having the first polarization state.
4. The projection system of claim 2, wherein the reflective polarizer diffusely reflects light having the first polarization state.
5. The projection system of claim 1, wherein the front projection screen comprises:
an absorbing polarizer transmitting light having the first polarization state and absorbing light having the second polarization state; and
a reflective layer reflecting light that is transmitted by the absorbing polarizer.
6. The projection system of claim 1, wherein the projector comprises an LCD projector emitting light having first, second and third color components, the first and second color components having the first polarization state and the third color component having the second polarization state.
7. The projection system of claim 1, wherein the first and second shutters are synchronized with the projector via a signal emitted by the projector.
8. The projection system of claim I, wherein the projector emits each of the first and second images at a frequency that is in a range from about 30 Hz to about 120 Hz.
PCT/US2012/026768 2011-03-03 2012-02-27 Projection system WO2012161824A1 (en)

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