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WO2000007061A1 - Systemes de projection a trois dimensions fondes sur un dispositif optique holographique commutable - Google Patents

Systemes de projection a trois dimensions fondes sur un dispositif optique holographique commutable Download PDF

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Publication number
WO2000007061A1
WO2000007061A1 PCT/US1999/017343 US9917343W WO0007061A1 WO 2000007061 A1 WO2000007061 A1 WO 2000007061A1 US 9917343 W US9917343 W US 9917343W WO 0007061 A1 WO0007061 A1 WO 0007061A1
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Prior art keywords
image
switchable
dimensional
dimensional image
plane
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PCT/US1999/017343
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English (en)
Inventor
Milan M. Popovich
Jonathan D. Waldern
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DigiLens Inc
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DigiLens Inc
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Priority to AU52469/99A priority Critical patent/AU5246999A/en
Publication of WO2000007061A1 publication Critical patent/WO2000007061A1/fr
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    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03H—HOLOGRAPHIC PROCESSES OR APPARATUS
    • G03H1/00—Holographic processes or apparatus using light, infrared or ultraviolet waves for obtaining holograms or for obtaining an image from them; Details peculiar thereto
    • G03H1/26—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique
    • G03H1/30—Processes or apparatus specially adapted to produce multiple sub- holograms or to obtain images from them, e.g. multicolour technique discrete holograms only
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B30/00—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images
    • G02B30/50—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images the image being built up from image elements distributed over a 3D volume, e.g. voxels
    • G02B30/52—Optical systems or apparatus for producing three-dimensional [3D] effects, e.g. stereoscopic images the image being built up from image elements distributed over a 3D volume, e.g. voxels the 3D volume being constructed from a stack or sequence of 2D planes, e.g. depth sampling systems
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/32—Holograms used as optical elements
    • 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
    • G02F1/1334—Constructional arrangements; Manufacturing methods based on polymer dispersed liquid crystals, e.g. microencapsulated liquid crystals
    • G02F1/13342—Holographic polymer dispersed liquid crystals
    • 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
    • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
    • G02F2201/30—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 grating
    • G02F2201/305—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 grating diffraction grating

Definitions

  • TITLE THREE DIMENSIONAL PROJECTION SYSTEMS BASED ON SWITCHABLE HOLOGRAPHIC OPTICS
  • the invention relates generally to image projection systems, and particularly to three-dimensional projection systems
  • Video display and projection systems are ubiquitous devices with applications in many settings Simple TV's are a major tool m the communication of images for entertainment, news, and advertising
  • Computer monitors are an indispensable tool for displaying text, images, video, and other graphics
  • video displays have hitherto been inherently two-dimensional devices They display information on a flat surface, with any three-dimensional structure compressed into a single plane of view
  • Efforts have been made on a number of fronts to present 3-D structures on 2-D media
  • One class of techniques mvolves stereo imaging, which uses the binocular aspect of the human visual system to simulate 3-D imagery
  • the viewer's eyes are presented with two separate 2-D views of a 3-D object Each eye is provided with the picture that would been seen from a point m space where that eye would be located while viewing the 3-D object
  • parallax effects create the illusion of an image with depth
  • 3-D motion pictures are a common application of stereo imaging
  • two images are simultaneously projected onto a single movie screen using polarized light
  • the polarizations used in generating the two images are orthogonal to each other
  • the screen shows a blurred combination of two separate images
  • polarized "3-D glasses” however, each of the viewer's eyes sees only one of the two images The viewer can then naturally combme the two images into a single fused 3-D image
  • Stereo imaging is also used in "random-dot stereograms" These are pictures that initially appear to be a random collection of dots When a viewer appropriately aligns his eyes, two separate collections of dots m the stereogram overlap, fusing into a single 3-D image
  • Another technique used to present 3-D images is to combine several views of the same 3-D object into parallel st ⁇ ps on a single flat picture, and then to cover the picture with a lenticular screen so that each of the views is only visible when the picture is seen from a particular angle While this technique does not rely on binocular vision, it is similar to stereo imaging in that the number of different views available to an observer is strongly limited The observer can only view the 3-D object from those angles corresponding to the views that were combmed into the single flat picture
  • the lenticular screen technique has been used in cameras that take 3-
  • True holograms are lnterferomet ⁇ c recordmgs of three-dimensional objects onto a holographic recording medium Unlike standard photographs, which record only the intensity of incident light, holograms record the phase as well as the intensity of the light that illuminates them When appropriately illuminated by coherent light scattered from a three-dimensional object, a hologram records the wave fronts created by the object During subsequent viewing, the hologram is approp ⁇ ately illuminated by a light source It functions as a diffraction grating, scattering the light m various directions The hologram scatters the light in such a way as to recreate the originally recorded wavefronts The result is a real or virtual image of the original three- dimensional object Unlike the images generated by stereo images, lenticular stereographic images, wire-grid drawings, and other 2-D images, holograms provide a 3-D image that can be mspected from a number of different viewpoints selected by the observer
  • Holograms tend to be largely monochromatic, smce the interference effects used to record and display a hologram are highly wavelength-specific They are also limited to the recording of static objects Thus, holograms have not found widespread practical applications in video display technology
  • a hologram may be used as a diffraction grating that reproduces the effects of a particular optical element, such as a lens or a mirror
  • HOEs holographic optical elements
  • HOEs may be far easier and less expensive to produce than then glass counterparts, especially when the optical element is complicated or must meet stringent tolerances
  • HOEs may generally be employed m any place where the corresponding glass optical element is used HOEs have found applications in video projection systems, where large-dimension (wide) optical elements are required They take the place of large lenses and other beam-shaping elements that can be expensive to produce in glass
  • Described herein are systems and methods for projecting images that use switchable holographic optical elements (HOEs) These systems and methods can be used to project three-dimensional images or to project two-dimensional tiled images with increased size and/or resolution
  • HOEs switchable holographic optical elements
  • a method for projectmg three-dimensional images includes steps of (a) displaying, in an object plane, a two-dimensional image that is a cross-section of a three-dimensional image, (b) activating a switchable holographic optical element and focussmg the two dimensional image onto an image plane with the activated switchable HOE, (c) deactivating the switchable HOE, (d) displaying a second two-dimensional image (which is a different cross-section of the 3-D image) at the object plane, and (e) activatmg a second switchable HOE and focussmg the second two dimensional image onto a second image plane with the activated second switchable HOE The second image plane is adjacent to the first image plane
  • the method for projectmg three-dimensional images includes (a) displaying, at an object plane, a two-dimensional image that is a cross-section of a three-dimensional image, (b) activatmg a switchable holographic optical element (HOE) to focus one color component
  • Step (c) in which the various color components are projected onto the various image planes, is performed quickly, within a time less than the integration tune of the human eye This allows the different projected images to be perceived as a smgle 3-D image
  • Each frame - a complete cycle through the various color components and image planes - is preferably completed in a tune interval short enough to allow frame rates of 25, 30, 50, 60, 70, 72, 75, or more frames per second
  • the method projects monochrome 3-D images through the steps of (a) displaying, at an object plane, a two-dimensional image that is a cross-section of a three-dimensional image, (b) activatmg a switchable HOE to focus the two dimensional image onto an appropnate image plane, and (c) repeating steps (a)-(b) for different cross-sections of the three-dimensional image Each of the cross sections is focussed onto a different image plane Steps (a)-(c) are then repeated to create a continuously displayed 3-D image
  • the method includes steps of sequentially displaying two-dimensional images
  • a three-dimensional projection system This system includes a two-dimensional display configured to sequentially display a se ⁇ es of cross-sections of a three-dimensional image, and a switchable HOE configured to focus the two-dimensional display onto a sequence of image planes at a plurality of distances from the two-dimensional display
  • the two-dimensional display is preferably a reflective LCD display
  • the switchable HOE is preferably configured to sequentially focus a se ⁇ es of three colors for each image plane
  • the system also includes a combmer lens configured to direct beams from the switchable HOE onto overlapping positions on the image planes
  • the switchable HOE preferably includes a senes of switchable HOEs, each of which can be made to either diffract light (m an "on" state) or to transmit light (in an "off state) By approp ⁇ ately switching the lenses on and off, the switchable HOE can be controlled to focus the two-dimensional display onto an appropnate object plane
  • the switchable HOEs may be arranged
  • the switchable HOEs are also used in image projection method and system that projects an image composed of an a ⁇ ay of "tiles " Each tile is a smgle image displayed on a display device, such as a reflective
  • the display device is configured to sequentially display tile elements of the image
  • the image projection system also includes a switchable HOE configured to focus the two-dimensional display onto a sequence of positions on an image plane
  • the display device and the switchable HOE are synchronized so that tile elements are focussed onto their appropriate corresponding array positions m the image plane
  • the system sequences through the plurality of tile elements rapidly, displaying an entire image in less than 100 ms
  • the displayed image appears as a single, continuous image BRIEF DESCRIPTION OF THE DRAWINGS
  • FIG 1 is a cross-sectional view of an electrically switchable hologram made of an exposed polymer- dispersed liquid crystal (PDLC) matenal
  • FIG 2 is a graph of the normalized net transmittance and normalized net diffraction efficiency of a hologram (without the addition of a surfactant) versus the rms voltage applied across the hologram
  • FIG 3 is a graph of both the threshold and complete switching rms voltages needed for switching a hologram to minimum diffraction efficiency versus the frequency of the rms voltage
  • FIG 4 is a graph of the normalized diffraction efficiency as a function of the applied elect ⁇ c field for a PDLC matenal formed with 34% by weight liquid crystal surfactant present and a PDLC material formed with 29% by weight liquid crystal and 4% by weight surfactant
  • FIG 5 is a graph showmg the switchmg response time
  • FIG 8a and with an electric field applied (FIG 8b) wherem the liquid-crystal utilized m the formation of the gratmg has a positive dielectric amsotropy
  • FIG 9a and FIG 9b are elevational views of a reflection gratmg havmg pe ⁇ odic planes of polymer channels and PDLC channels disposed parallel to the front surface of the gratmg m the absence of an electnc field (FIG 9a) and with an electric field applied (FIG 9b) wherem the liquid crystal utilized in the formation of the gratmg has a negative dielectric amsotropy
  • FIG 10a is an elevational view of a reflection grating disposed withm a magnetic field generated by Helmholtz coils
  • FIG 10b and FIG 10c are elevational views of the reflection gratmg of FIG 10a in the absence of an electnc field (FIG 10b) and with an electnc field applied (FIG 10c)
  • FIG 11a and FIG l ib are representative side views of a slanted transmission gratmg (FIG 11a) and a slanted reflection grating (FIG 1 lb) showing the orientation of the grating vector G
  • FIG 13 is an elevational view of a subwavelength grating having periodic planes of polymer channels and PDLC channels disposed perpendicular to the front surface of the gratmg
  • FIG 14a is an elevational view of a switchable subwavelength wherem the subwavelength gratmg functions as a half wave plate whereby the polarization of the incident radiation is rotated by 90 :
  • FIG 14b is an elevational view of the switchable half wave plate shown m FIG 14a disposed between crossed polarizers whereby the mcident light is transmitted
  • FIG 14c and FIG 14d are side views of the switchable half wave plate and crossed polarizes shown in FIG 14b and showing the effect of the application of a voltage to the plate whereby the polarization of the light is no longer rotated and thus blocked by the second polarizer
  • FIG 15a is a side view of a switchable subwavelength grating wherem the subwavelength grating functions as a quarter wave plate whereby plane pola ⁇ zed light is transmitted through the subwavelength gratmg, retroreflected by a minor and reflected by the beam splitter,
  • FIG 15b is a side view of the switchable subwavelength gratmg of FIG 15a and showmg the effect of the application of a voltage to the plate whereby the polarization of the light is no longer modified, thereby permitting the reflected light to pass through he beam splitter,
  • FIG 16a and FIG 16b are elevational views of a transmission grating havmg pe ⁇ odic planes of polymer channels and PDLC channels disposed perpendicular to the front face of the gratmg m the absence of an elect ⁇ c field (FIG 16a) and with an electric field applied (FIG 16b) wherem the liquid crystal utilized m formation of the gratmg has a positive dielectric amsotropy
  • FIG 17 is a side view of five subwavelength gratings wherem the gratmgs are stacked and connected electrically m parallel thereby reducing the switchmg voltage of the subwavelength gratmg
  • FIG 18 shows a system for projectmg 3-D objects that uses switchable holographic elements
  • FIG 19 shows an embodiment of the system from FIG 18 that uses a stack of holographic elements that can be selectively made transparent
  • FIG 20 shows another embodiment of the system that uses an anay of switchable holographic optical elements
  • FIG 21 shows a system for projecting a tiled-
  • switchable (or "reconfigurable”) holographic optical elements enables the construction of several types of video projection systems These systems may be configured to project true 3-D images They may also be configured to project large 2-D images by projectmg a se ⁇ es of tiles that make up the large image
  • the switchable HOEs can be switched by an applied electric field from a state in which they diffract light to a state in which they merely transmit light without substantial alteration
  • an optical system of several switchable HOEs may be switched between a number of states m which the optical system operates as one of several distinct optical elements Figs. 1-17: Switchable Hologram Materials And Devices
  • Holographic optical elements are formed, m one embodiment, from a polymer dispersed liquid crystal (PDLC) matenal compnsmg a monomer, a dispersed liquid crystal, a cross-linking monomer, a coimtiator and a photoimtiator dye
  • PDLC polymer dispersed liquid crystal
  • the PDLC matenals used in the holographic optical elements may be formed in a single step
  • the holographic optical elements may also use a unique photopolymenzable prepolymer material that permits in situ control over characteristics of resulting gratmgs, such as domam size, shape, density, orde ⁇ ng and the like
  • methods and materials taught herem can be used to prepare PDLC materials for optical elements compnsmg switchable transmission or reflection type holographic gratmgs
  • the process of forming a hologram is controlled primarily by the choice of components used to prepare the homogeneous starting mixture, and to a lesser extent by the intensity of the mcident light pattern
  • the polymer dispersed liquid crystal (PDLC) matenal employed m the present mvention creates a switchable hologram in a smgle step
  • a feature of one embodiment of PDLC matenal is that illumination by an inhomogeneous, coherent light pattern initiates a patterned, amsotropic diffusion (or counter diffusion) of polymenzable monomer and second phase matenal, particularly liquid crystal (LC)
  • LC liquid crystal
  • the features of the PDLC material are influenced by the components used in the preparation of the homogeneous starting mixture and, to a lesser extent, by the intensity of the mcident light pattern
  • the prepolymer matenal comprises a mixture of a photopolymenzable monomer, a second phase matenal, a photoinitiator dye, a co nitiator, a cham extender (or cross-linker), and, optionally, a surfactant
  • two major components of the prepolymer mixture are the polyme ⁇ zable monomer and the second phase material, which are preferably completely miscible Highly functionalized monomers may be preferred because they form densely cross-linked networks which shrink to some extent and to tend to squeeze out the second phase matenal As a result, the second phase matenal is moved amsotropically out of the polymer region and, thereby, separated mto well-defined polymer-poor, second phase-rich regions or domams Highly functionalized monomers may also be prefened because the extensive cross-linking associated with such monomers yields fast kmetics, allowing the hologram to form relatively quickly, whereby the second phase matenal will exist in domains of less than approximately 0 1 ⁇ m
  • the second phase material of choice is a liquid crystal (LC)
  • LC liquid crystal
  • concentration of LC employed should be large enough to allow a significant phase separation to occur in the cured sample, but not so large as to make the sample opaque or very hazy Below about 20% by weight very little phase separation occurs and diffraction efficiencies are low Above about 35% by weight, the sample becomes highly scattering, reducmg both diffraction efficiency and transmission Samples fabricated with approximately 25% by weight typically yield good diffraction efficiency and optical clarity In prepolymer mixtures utilizing a surfactant, the concentration of LC may be mcreased to
  • Suitable liquid crystals contemplated for use in the practice of the present invention may include the mixture of cyanobiphenyls marketed as E7 by Merck, 4'-n-pentyl-4-cyanob ⁇ phenyl, 4'-n-heptyl-4-cyanob ⁇ phenyl, 4'-octaoxy-4- cyanobiphenyl, 4'-pentyl-4-cyanoterphenyl, cc-methoxybenzyl ⁇ dene-4'-butylan ⁇ hne, and the like Other second phase components are also possible
  • the polymer dispersed liquid crystal material employed in the practice of the present invention may be formed from a prepolymer material that is a homogeneous mixture of a polymenzable monomer compnsmg dipentaerythntol hydroxypentacrylate (available, for example, from Polysciences, Inc , Warnngton, Pennsylvania), approximately 10-40 wt% of the
  • the mixture of liquid crystal and prepolymer matenal are homogenized to a viscous solution by suitable means (e g , ultrasomfication) and spread between indium-tin-oxide (ITO) coated glass sides with spacers of nominally 15-100 ⁇ m thickness and, preferably, 10-20 ⁇ m thickness
  • ITO indium-tin-oxide
  • the ITO is electrically conductive and serves as an optically transparent electrode
  • Preparation, mixing and transfer of the prepolymer matenal onto the glass slides are preferably done m the dark as the mixture is extremely sensitive to light
  • the switchmg voltage for PDLC materials containmg a surfactant are significantly lower than those of a PDLC matenal made without the surfactant While not wishing to be bound by any particular theory, it is believed that these results may be attributed to the weakening of the anchoring forces between the polymer and the phase-separated LC droplets SEM studies have shown that droplet sizes in PDLC materials including surfactants are reduced to the range of 30-50nm and the distribution is more homogeneous Random scatte ⁇ ng m such matenals is reduced due to the dommance of smaller droplets, thereby increasing the diffraction efficiency Thus, it is believed that the shape of the droplets becomes more sphencal in the presence of surfactant, thereby contnbunng to the decrease m switchmg voltage
  • VN VN
  • N-vinylpyrrolidinone N-vinylpyrrolidinone
  • surfactant octanoic acid 6 5% by weight
  • VN VN also acts as a chain extender due to the presence of the reactive acrylate monomer group
  • high optical quality samples were obtamed with about 70% diffraction efficiency, and the resulting gratings could be electrically switched by an applied field of 6V/ m
  • PDLC mate ⁇ als may also be formed usmg a liquid crystalline bifunctional acrylate as the monomer (“LC monomer”)
  • LC monomers have an advantage over conventional acrylate monomers due to then high compatibility with the low molecular weight nematic LC materials, thereby facilitating formation of high concentrations of low molecular weight LC and yieldmg a sample with high optical quality
  • the presence of higher concentrations of low molecular weight LCD in the PDLC material greatly lowers the switching voltages (e g , to ⁇ 2V//jm)
  • Another advantage of using LC monomers is that it is possible to apply low AC or DC fields while recording holograms to pre-ahgn the host LC monomers and low molecular weight LC so that a desired o ⁇ entation and configuration of the nematic directors can be obtamed m the LC droplets
  • the chemical formulate of several suitable LC monomers are as follows
  • Semifluormated polymers are known to show weaker anchormg properties and also significantly reduced switchmg fields Thus, it is believed that semifluormated acrylate monomers which are bifimctional and liquid crystalline may find suitable application in the formulation of holograms
  • FIG 1 there is shown a cross-sectional view of an electncally switchable hologram 10 made of an exposed polymer dispersed liquid crystal matenal made accordmg to the teachmgs of this descnption
  • a layer 12 of the polymer dispersed liquid crystal material is sandwiched between a pair of lndium- tin-oxide coated glass slides 14 and spacers 16
  • the mtenor of hologram 10 shows Bragg transmission gratmgs
  • Liquid crystal domam size can be controlled by varymg the concentrations of photomitiator, coinitiator and chain-extending (or cross-linking) agent
  • the onentahon of the nematic directors can be controlled while the gratmgs are bemg recorded by application of an external electnc field across the ITO electrodes
  • the scanning electron micrograph shown in FIG 2 of the referenced Applied Physics Letters article and incorporated herem by reference is of the surface of a gratmg which was recorded m a sample with a 36 wt% loading of liquid crystal using the 488 nm lme of an argon ion laser at an intensity of 95 mW/cm "
  • the size of the liquid crystal domains is about 0 2 ⁇ m and the gratmg spacmg is about 0 54 ⁇ m
  • FIG 2 is a graph of the normalized net transmittance and normalized net diffraction efficiency of a hologram made accordmg to the teachmgs of his disclosure versus the root mean square voltage ("Vrms") applied across the hologram ⁇ is the change m first order Bragg diffraction efficiency ⁇ T is the change in zero order transmittance
  • FIG 2 shows that energy is transfened from the first order beam to the zero-order beam as the voltage is increased
  • the peak diffraction efficiency can approach 100%, dependmg on the wavelength and polarization of the probe beam, by approp ⁇ ate adjustment of the sample thickness
  • the minimum diffraction efficiency can be made to approach 0% by slight adjustment of the parameters of the PDLC material to force the refractive index of the cured polymer to be equal to the ordinary refractive index of the liquid crystal
  • FIG 3 is a graph of both the threshold rms voltage 20 and the complete switchmg rms voltage 22 needed for switchmg a hologram made accordmg to the teachmgs of this disclosure to minimum diffraction efficiency versus the frequency of the rms voltage
  • the threshold and complete switching rms voltages are reduced to 20 Vrms and 60 Vrms, respectively, at 10 kHz Lower values are expected at even higher frequencies
  • FIG 5 is a graph of the normalized net transmittance and normalized net diffraction efficiency of a hologram made according to the teachmgs of this disclosure versus temperature
  • the polymer dispersed liquid crystal materials descnbed herein successfully demonstrate the utility for recordmg volume holograms of a particular composition for such polymer dispersed liquid crystal systems
  • a PDLC reflection gratmg is prepared by placmg several drops of the mixture of prepolymer material 112 on an indium- tin oxide coated glass slide 114a A second indium- tin oxide coated slide 114b is then pressed agamst the first, thereby causmg the prepolymer matenal 112 to fill the region between the slides 114a and 114b
  • the separation of the slides is mamtamed at approximately 20 ⁇ m by utilizing uniform spacers 118
  • Preparation, mixing and transfer of the prepolymer material is preferably done in the dark
  • a mirror 116 may be placed directly behmd the glass plate 114b The distance of the mirror from the sample is preferably substantially shorter than the coherence length of the laser
  • the PDLC matenal is preferably exposed to the 488 nm lme of an argon-ion laser, expanded to fill the entire plane of the glass plate, with an intensity of approximately 0 1-100 mWat
  • the prepolymer material utilized to make a reflection gratmg comprises a monomer, a liquid crystal, a cross-linking monomer, a coinitiator, and a photomitiator dye
  • the reflection gratmg may be formed from prepolymer matenal compnsmg by total weight of the monomer dipentaerythntol hydroxypentacrylate (DPHA), 35% by total weight of a liquid crystal compnsmg a mixture of cyano biphenyls (known commercially as "E7"), 10% by total weight of a cross-linking monomer compnsmg N- vmylpyrrohdmone (“NVP”), 2 5% by weight of the coinitiator N-phenylglycme (“NPG”),and 10 5 to 10 "6 gram moles of a photomitiator dye compnsmg rose bengal ester
  • the addition of surfactants is expected to facilitate the same advantageous properties
  • gratmg 130 includes periodic planes of polymer channels 130a and PDLC channels 130b which run parallel to the front surface 134
  • the grating spacing associated with these periodic planes remains relatively constant throughout the full thickness of the sample from the air/film to the film/substrate interface
  • the morphology of the reflection grating differs significantly In particular, it has been determined that, unlike transmission gratings with similar liquid crystal concentrations, very little coalescence of individual droplets was evident Further more, the droplets that were present m the matenal were significantly smaller havmg diameters between 50 and 100 nm Furthermore, unlike transmission gratmgs where the liquid crystal-nch regions typically comprise less than 40% of the grating, the liquid crystal-nch component of a reflection gratmg is significantly larger Due to the much smaller periodicity associated with reflection gratings, I e , a narrower grating spacmg
  • the absorbance spectrum supports the conclusion that a penodic refractive mdex modulation is disposed through the thickness of the film
  • the reflection notch typically has a reflection wavelength at approximately 472 nm for normal incidence and a relatively narrow bandwidth
  • the small difference between the writing wavelength and the reflection wavelength (approximately 5%) mdicates that shrinkage of the film is not a significant problem Moreover, it has been found that the performance of such gratmgs is stable over pe ⁇ ods of many
  • suitable PDLC matenals could be prepared utilizing monomers such as tnethyleneglycol diacrylate, tnmethylolpropanet ⁇ acrylate, pentaerythntol tnacrylate, pentaerythntol tetracrylate, pentaerythntol pentacrylate, and the like Similarly, other coinitiators such as tnethylamine, tnethanolamme, N.N-dunethyl-
  • 2,6-dnso ⁇ ropylan ⁇ l ⁇ ne, and the like could be used instead of N-phenylglycme
  • the photomitiator dyes rose bengal sodium salt, eosm, eosm sodium salt, fluorescein sodium salt and the like will give favorable results
  • the 633 nm lme is utilized, methylene blue will find ready application
  • other liquid crystals such as 4'-pentyl-4-cyanob ⁇ phenyl or 4'-heptyl-4-cyanob ⁇ phenyl, can be utilized
  • FIG 8a there is shown an elevational view of a reflection gratmg 130 made in accordance with this disclosure having periodic planes of polymer channels 130a and PDLC channels 130b disposed parallel to the front surface 134 of the grating 130
  • the symmetry axis 136 of the liquid crystal domams is formed in a direction perpendicular to the penodic channels 130a and 130b of the grating 130 and perpendicular to the front surface 134 of the gratmg 130
  • a reflection grating tends to reflect a narrow wavelength band, such that the grating can be used as a reflection filter
  • the reflection gratmg is formed so that it will be switchable
  • switchable reflection gratmgs can be made utilizing negative dielect ⁇ c amsotropy LCs (or LCs with a low cross-over frequency), an applied magnetic field, an applied shear stress field, or slanted gratings
  • Liquid crystals can be found m nature (or synthesized) with either positive or negative ⁇
  • a LC which has a positive ⁇ at low frequencies, but becomes negative at high frequencies
  • the frequency (of the applied voltage) at which ⁇ changes sign is called the cross-over frequency
  • the cross-over frequency will vary with LC composition, and typical values range from 1-10 kHz
  • the reflection gratmg may be switched
  • low crossover frequency matenals can be prepared from a combination of positive and negative dielectric amsotropy liquid crystals
  • a suitable positive dielectric liquid crystal for use m such a combination contains four nng esters as shown below
  • a strongly negative dielect ⁇ c liquid crystal suitable for use such a combmation is made up of py ⁇ dazines as shown below
  • switchable reflection gratmgs can be formed usmg positive ⁇ liquid crystals As shown m FIG 10a, such gratmgs are formed by exposmg the PDLC starting material to a magnetic field during the curing process
  • the magnetic field can be generated by the use of Helmholtz coils (as shown in FIG 10a), the use of a permanent magnet, or other suitable means
  • the magnetic field M is oriented parallel to the front surface of the glass plates (not shown) that are used to form the grating 140
  • the symmetry axis 146 of the liquid crystals will orient along the field while the mixture is fluid
  • the field may be removed and the alignment of the symmetry axis of the liquid crystals will remam unchanged (See FIG 10b )
  • an electric field is applied, as shown m FIG 10c the positive ⁇ liquid crystal will reorient m the direction of the field, which is perpendicular to the front surface of gratmg and to the periodic
  • FIG 11a depicts a slanted transmission gratmg 148 and FIG 1 lb depicts a slanted reflection gratmg 150
  • a holographic transmission gratmg is considered slanted if the direction of the grating vector G is not parallel to the grating surface
  • the gratmg is said to be slanted if the gratmg vector G is not perpendicular to the gratmg surface
  • Slanted gratings have many of the same uses as nonslanted gratmg such as visual displays, minors, lme filters, optical switches, and the like
  • slanted holographic gratings are used to control the direction of a diffracted beam
  • a slanted gratmg is used to separate the specular reflection of the film from the diffracted beam
  • a slanted grating has an even more useful advantage
  • the slant allows the modulation depth of the grating to be controlled by an electric field when using either tangential or homeotropic aligned liquid crystals This is because the slant provides components of the electric field in the directions both tangent and perpendicular to the gratmg vector
  • the LC domain symmetry axis will be oriented along the grating vector G and can be switched to a direction perpendicular to the film plane by a longitudinally applied field E This is the typical geometry for switching of the diffraction efficiency of the slanted reflection grating
  • switchable reflection gratmgs may be formed in the presence of an applied shear stress field
  • a shear stress would be applied along the direction of a magnetic field M
  • This shear stress would distort the LC domains m the direction of the stress, and the resultant LC domam symmetry axis will be preferentially along the direction of the stress, parallel to the PDLC planes and perpendicular to the direction of the applied elect ⁇ c field for switchmg
  • Reflection gratmg prepared in accordance with this descnption may find application m color reflective displays, switchable wavelength filters for laser protection, reflective optical elements and the like
  • PDLC materials can be made that exhibit a property known as form birefringence whereby polarized light that is transmitted through the gratmg will have its pola ⁇ zation modified
  • Such gratmgs are known as subwavelength gratings, and they behave like a negative umaxial crystal, such as calcite, potassium dihydrogen phosphate, or lithium niobate, with an optic axis perpendicular to the PDLC planes Refemng now to FIG 13, there is shown an elevational view of a transmission gratmg 200 made in accordance with this descnption having periodic planes of polymer planes 200a and PDLC planes 200b disposed perpendicular to the front surface 204 of the gratmg 200 The optic axis 206 is disposed perpendicular to polymer planes 200a and the PDLC planes 200b Each polymer plane 200a has a thickness t p and refractive index n p , and each PDLC plane 200b has
  • FIG 16a there is shown an elevational view of a subwavelength gratmg 230 recorded in accordance with the above-described methods and having pe ⁇ odic planes of polymer channels 230a and PDLC channels 230b disposed perpendicular to the front surface 234 of gratmg 230
  • the symmetry axis 232 of the liquid crystal domams is disposed m a direction parallel to the front surface 234 of the gratmg and perpendicular to the periodic channels 230a and 230b of the grating 230
  • the symmetry axis 232 distorts and reo ⁇ ents m a direction along the field E, which is perpendicular to the front surface 234 of the gratmg and parallel to the penodic channels 230a and 230b of the gratmg 230
  • subwavelength gratmg subwavelength gratmg
  • n o the ordinary index of refraction of the subwavelength grating
  • n,. the extraordinary mdex of refraction
  • n PDLC the refractive mdex of the PDLC plane
  • n p the refractive index of the polymer plane
  • n L c the effective refractive index of the liquid crystal seen by an incident optical wave.
  • the effective refractive index of the liquid crystal, n LC is a function of the applied electric field, having a maximum when the field is zero and value equal to that of the polymer, n P , at some value of the electric field, E MA ⁇
  • n PDL c (t + rio) /2
  • NPDLC n P + f LC [n LC - n P ]
  • f C is the volume fraction of liquid crystal dispersed in the polymer withm the PDLC plane
  • f LC [V LC / (V LC + V P )]
  • n C 1 7
  • n P , 1 5
  • the net birefringence, ⁇ n, of the subwavelength grating is approximately 0 008
  • the length of the subwavelength grating should be 50 ⁇ m for a half-wave plate and a 25 ⁇ m for a quarter-wave plate
  • the refractive index of the liquid crystal can be matched to the refractive mdex of the polymer and the birefringence of the subwavelength grat
  • Subwavelength gratmgs in accordance with the this descnption are expected to find suitable application in the areas of polarization optics and optical switches for displays and laser optics, as well as tunable filters for telecommunications, colorimetry, spectroscopy, laser protection, and the like
  • electrically switchable transmission gratings have many applications for which beams of light must be deflected or holographic images switched Among these applications are Fiber optic switches, reprogrammable NxN optical interconnects for optical computmg, beam steermg for laser surgery, beam steermg for laser radar, holographic image storage and retneval, digital zoom optics (switchable holographic lenses), graphic arts and entertainment, and the like
  • a switchable hologram is one for which the diffraction efficiency of the hologram may be modulated by the application of an elect ⁇ c field, and can be switched from a fully on state (high diffraction efficiency) to a fully off state (low or zero diffraction efficiency)
  • a static hologram is one whose properties remain fixed independent of an applied field
  • a high contrast status hologram can also be created
  • the holograms are recorded as descnbed previously
  • the cured polymer film is then soaked m a suitable solvent at room temperature for a short duration and finally dried
  • methanol has shown satisfactory application
  • Other potential solvents include alcohols such as ethanol, hydrocarbons such as hexane and heptane, and the like
  • a high birefringence static sub-wavelength wave-plate can also be formed Due to the fact that the refractive index for air is significantly lower than for most liquid crystals, the conespondmg thickness of the half-wave plate would be reduced accordingly Synthesized wave- plates m accordance with this description can be used in many applications employmg polarization optics, particularly where a material of the appropriate birefringence that the appropriate wavelength is unavailable, too costly, or too bulky
  • the term polymer dispersed liquid crystals and polymer dispersed liquid crystal material m cludes, as may be appropriate, solutions m which none of the monomers have yet polymerized or cured, solutions in which some polymerization has occuned, and solutions which have undergone complete polymerization Those of skill in the art will clearly understand that the use herein of the standard term used m the art, polymer dispersed liquid crystals (which grammatically refers to liquid crystals dispersed in a fully polymerized matrix) is meant to include all
  • FIG. 18 illustrates the operation of one embodiment of a 3-D projection system.
  • the system comprises a flat display unit 305, such as an LCD display that can display a sequence of images, and a switchable holographic optical system 320.
  • a viewer may observe a projected 3-D image by looking toward switchable holographic optical system 320; the 3-D image appears in an image volume 330, between the viewer and switchable holographic optical system 320.
  • Display unit 305 displays a series of images 306-308 in sequence. These images are cross-sectional views through a solid 3-D object.
  • Display unit 305 is preferably an LCD display, such as a reflective display mounted on a silicon substrate. In another embodiment, the LCD display is a transmissive display. Other types of displays may also be used for display unit 305, such as standard cathode ray tubes.
  • Display unit 305 is mounted at the object plane 310 of the projection system.
  • Switchable holographic optical system 320 can be switched among several operating modes. In each operating mode, system 320 behaves as one of several conventional optical elements, including lenses with various focal lengths. As the successive cross-sections are displayed on display unit 305, switchable holographic optical system 320 is successively switched between different modes of operation so that it focuses object plane 310 onto a series of image planes 331-334. This switching of focal lengths is synchronized with the switching of cross-sections displayed on display unit 305, and is performed at a rate that is fast in comparison with the integration time of the human eye (approximately 100 milliseconds). The result is that the several cross-sections displayed on display unit 305 are imaged onto an "image volume" 330 that is made up of image planes 331-334.
  • the image 335 cast onto image volume 330 by this system is a real image.
  • a viewer may directly observe image 335 as a reconstructed three-dimensional image that appear to float in the image volume 330.
  • a "viewing screen" can be placed at image volume 330 to facilitate observation of 3-D image 335.
  • This viewing screen may be composed of a volumetric semi-transparent diffuser.
  • the diffuser is a stack of planar diffusers.
  • the 3-D diffuser is made of one or a few vibrating planar diffusers.
  • the cross-sections used in images 306-308 are line drawings of the outline of 3-D object. When these cross sections are projected onto image volume 330, the result is an image 335 showing the surfaces of the original 3-D object.
  • the line drawings in images 306-308 are filled, resulting in an apparently solid image 335.
  • the cross sections in images 306-308 are created with hidden-line / hidden-surface removal to eliminate some of the extraneous lines and surfaces from the displayed image 335.
  • Switchable holographic optical system 320 is an optical element whose optical properties are controlled by an applied control signal.
  • switchable optical system 320 is a single switchable holographic optical element whose optical properties can be rapidly switched among several operating modes.
  • switchable optical system 320 comprises several switchable holographic optical elements, each of which can be switched between a diffracting state and a substantially transparent state.
  • FIG. 19 illustrates one embodiment of the 3-D projection system comprising several switchable holographic optical elements (HOEs).
  • the switchable holographic optical system 320A is made out of switchable HOEs 321-324, each of which can be switched between a diffracting state and a substantially transparent state.
  • One or more of the switchable HOEs 321 -324 may include an exposed PDLC material such as, for example, the material presented in FIG 1
  • the PDLC material undergoes phase separation dunng the exposure process (1 e , during the hologram recording process), creatmg regions densely populated by liquid crystal droplets, interspersed by regions of clear photopolymer
  • an electric field is applied to the exposed PDLC and changes the natural orientation of the liquid crystal droplets therein which, m turn, causes the refractive index modulation of the frmges to reduce and the hologram diffraction efficiency to drop to very low levels, effectively erasing the hologram recorded therem
  • No electnc field is applied m the diffracting state, in which the exposed PDLC material exhibits its very high diffraction efficiency
  • the exposed PDLC switches between the diffracting state and the substantially transparent state very quickly (e g , the exposed material can be switched in tens of microseconds, which is very fast when compared with conventional liquid
  • the switchable HOEs 321-324 are, m one embodiment, Bragg-type elements that provide a high diffraction efficiency.
  • switchable thm-phase HOEs (sometimes referred to as Raman-Nath type) may also be employed, although thin phase HOEs may not provide a high level of diffraction efficiency when compared to Bragg type HOEs
  • the switchable HOEs descnbed herein are transmissive type, it bemg understood that reflective type switchable HOEs may be employed in addition or instead In a projection system employing switchable reflective HOEs 321-324 m the optical system 320, the image planes would be on the same side of the optical system 320 as the object plane
  • a display unit (such as 305 from FIG. 18) is placed at object plane 310 m FIG. 19 and is imaged onto an image volume 330 composed of several image planes
  • switchable HOEs 321- 324 are used to focus object plane 310 onto the image planes 331-334, respectively, m image volume 330
  • Switchable HOEs 321-324 are placed next to each other in a holographic optical system 320A
  • the number of switchable HOEs in holographic optical system 320A is equal to the number of desired image planes in image volume 330
  • FIG 19 shows holographic optical system 320A with four switchable HOEs, 321-324, each of which is configured to focus object plane 310 onto one of four image planes 331-334
  • the switchable HOEs preferably operate m sequence: at any given time, only one of them is active The active HOE diffracts light so that object plane 310 is focused onto the conespondmg image plane Meanwhile, the remainder of the switchable HOEs are inactive, that is, they are substantially transparent and do not further modify the light transmitted from object plane 310 to image volume 330
  • holographic optical system 320A compnses four groups of HOEs 321a-c, 322a-c, 323a-c, and 324a-c, where HOEs 321a, 322a, 323a, and 324a diffract a first color component of image light when active, HOEs 321b, 322b, 323b, and 324b diffract a second color component of image light when active, and HOEs 321c, 322c, 323c, and 324c diffract a third color component of image light when active
  • the three color components are preferably red, green, and blue (RGB) components
  • the color image may be composed of cyan, yellow, and magenta (CYM) components or other sets of three basis colors appropriate for spanning the range of sensitivity of the human eye
  • the projection system rapidly cycles through a series of display modes In each mode, one color component for one cross-section of three-dimensional object 335 is imaged at one image plane of image volume 330 via one activated HOE element 321a-c, 322a-c, 323a-c, or 324a-c
  • the projection system sequentially images all three color components of a cross section at an image plane before sequentially imaging the three color components of the next cross section at the next image plane
  • the cycle is restarted
  • the cycle time of imaging all image planes w ith the three color components is smaller than an eye integration time
  • the color components and image planes may be addressed in some other order
  • holographic optical system 320A may be controlled so that one color component is projected onto all of the image planes before holographic optical system 320A switches to another color component
  • Each cycle effectively comprises one frame in a continuous display It
  • Fig. 20 Three-dimensional projection with a switchable holographic array
  • the switchable HOEs may be ananged m a planar a ⁇ ay A system usmg such a switchable holographic lens anay 420 is shown in
  • FIG 20 The system also includes an LCD display 405, a planar anay of conventional lenses 450, shutter anay 460, and a combiner lens system 470
  • Switchable holographic lens anay 420 comprises, m one embodiment, a series of switchable HOEs arranged side-by-side m a plane
  • lens anay 420 comprises a stack of three switchable HOEs, one for transmitting each of three basis colors (such as RGB or CYM)
  • the lens anay 420 may comprise a stack of conventional static HOEs (to achieve a monochrome display)
  • FIG 20 will be descnbed with lens anay 420 comprising switchable HOEs formed from PDLC material described above
  • the beam path in this embodiment is less susceptible to attenuation and abenations that may be introduced by the inactive holographic optical elements
  • LCD display 405 is preferably a reflective LCD display illuminated by a high-intensity light source
  • LCD display 405 is preferably an active display that uses TFT (thin-film transistor) elements to mamtam the on/off status of the pixels between each refresh of the screen LCD display 405 is preferably configured for fast refresh rates, high reflection efficiency, and high contrast
  • TFT thin-film transistor
  • micro-mirror anays such as the devices manufactured by Texaas Instruments Inc
  • LCD display 405 is placed at the object plane of the display system, and is preferably illuminated by one or more bnght light sources, such as high-power mcoherent sources (incandescent lamps, fluorescent lamps, halogen lamps, induction lamps, or LEDs, among others) or lasers
  • bnght light sources such as high-power mcoherent sources (incandescent lamps, fluorescent lamps, halogen lamps, induction lamps, or LEDs, among others) or lasers
  • LCD display 405 is placed at the object plane of the display system, and is preferably illuminated by one or more bnght light sources, such as high-power mcoherent sources (incandescent lamps, fluorescent lamps, halogen lamps, induction lamps, or LEDs, among others) or lasers
  • LCD display 405 is placed at the object plane of the display system, and is preferably illuminated by one or more bnght light sources, such as high-power mcoherent sources (incandescent lamps, fluorescent lamps,
  • Each of the elements or series of three elements m switchable holographic lens array 420 is configured to focus light from LCD display 405 onto one of several planes 431-434 m an image volume 430
  • combiner lens system 470 directs the light from different elements in lens anay 420 onto the compact image volume 430
  • Light from LCD display 405 is selectively passed to anay 420 via shutter array
  • the shutter can rapidly switch so that a different element is unblocked, thereby allowing the light from LCD display 405 to reach image volume 430 by another beam path, such as the one mdicated by 482
  • the HOEs m holographic lens anay 420 are constructed with different focal lengths conespondmg to the different focal planes m image volume 430
  • beam path 482 When beam path 482 is open, light from LCD display 405 is imaged onto image plane 433
  • Combmer lens 470 redirects the different beam paths from lens anay 420 so that they overlap m image volume 430 Each beam path selected by shutter anay 460 goes through a different lens element in lens array 420 Thus the va ⁇ ous beams emergmg from lens anay 420 do not share a common optical axis Combmer lens
  • combiner lens 470 is a system of conventional optical elements
  • combmer lens 470 may be constructed from switchable holographic optical elements, or from a combmation of conventional optics and switchable HOEs Switchable HOEs m combiner lens 470 would preferably be used for conectmg chromatic abenations introduced by holographic lens anay 420
  • Holographic lens anay 420 preferably mcludes, for example, a stack of separated red-, green-, and blue-sensitive hologram anays that are switched sequentially at a rate synchronized with the refresh rate of LCD display 405
  • HOEs of holographic lens anay 420 m FIG 20 are represented as smgle lenses, m practice more HOEs may be added m order to optimize the beam characte ⁇ stics and to conect abenations Therefore, prefened embodmients of holographic lens anay 420 would have multi-layer configurations m many situations
  • the HOEs in holographic lens anay 420 are preferably configured so that light reflected from each LCD element of display 405 fills the entire aperture of each HOE Design considerations for lens anay 420 preferably include the efficient collection of light from display 405
  • stacks of anays are used in holographic lens anay 420, further increasing the number of image planes can be generated
  • shutter anay 460 can be replaced by Bragg-type holograms whose angular selectivity perform the same function as the shutter anay Additional functionality can also be added by incorporating additional hologram layers to perform specific optical operations
  • holographic lens anav 420 mcludes a hologram stack with elements having different optical powers This configuration of the lens anay provides the system with rapidly switchable variable magnification (zoom)
  • FIG 21 shows a system that projects a 2-D image onto a flat screen 510 The image is made of an anay of image tiles, each of which is projected onto screen 510 by a pro j ector 501
  • Projector 501 time-multiplexes its projection angle It has a display that sequentially generates the images intended for display on the different tiles
  • the display is preferably a smgle reflective LCD display, although other types and numbers of displays may also be used
  • one or more switchable HOEs in projector 501 focus the display onto a particular image tile 520
  • the switchable HOEs work in synchrony with the display so that when the display switches to displaying an image for a new tile 525, the switchable HOEs switch to a mode in which they direct the image onto the new tile
  • the pro j ector generates an apparently continuous image over the entire screen 510
  • the display and the switchable HOEs must have a sufficiently fast update rate to provide a smooth flicker-free image
  • the update rate is preferably 25, 30, 50, 60, or 72 frames per second
  • the tiling technique may be used to increase the size or the resolution of a display, or both, as shown by the following examples
  • an image from a 1024 x 768 LCD display is projected onto a 10 x 10 anay of tiles
  • the focussmg optics are configured so that each tile has the dimensions of a 12" video monitor
  • the pixel size of the display is comparable to that of a standard video monitor, but the overall size of the display is much larger a factor of 100 greater m area This configuration allows the generation of a large viewmg area with adequate resolution for viewing at close range
  • a 3 x 3 anay of tiles is generated from an LCD display havmg a resolution of 800 x 600 pixels
  • the 9 tiles are projected onto a 24" monitor, thereby providmg a high resolution monitor (2400 x 1800 pixels) readily usable in a graphics workstation
  • the projection system when displaying a scene m which most of the motion is restncted to one portion of the screen, one embodiment of the projection system would update the data used for the other tiles less frequently than the data used for the central tiles While each tile is preferably re-projected once in each frame period, the data used to make up that tile may not be updated for several frame penods if little no motion occurs in that tile Thus, the motion in the active portion of the screen would appear fluid, and digital video-processing power would not be expended on unnecessarily updating other portions of the screen In one embodiment of the projection svstem, the video-processing power may be reduced by using decreased resolutions in some portions of the screen One embodiment of such a system is depicted m FIG 22
  • FIG 22 shows a user 550 who is looking at tiled video screen 510
  • Video screen 510 is preferably sufficiently large that only a portion 511 of video screen 510 is in the center of the viewer's field of view
  • a gaze-tracking system such as one incorporating cameras 551 and 552, monitors the user's head position and/or eye position to determine which part of screen 510 is centered in the user's field of view
  • This central portion 511 is then projected with high resolution by projector 501, smce it is this portion of the screen that is viewed by the fovea, the most sensitive portion of the user's eye
  • Other regions of screen 510 may be projected with lower resolution to reduce the amount of video-processmg power required by the system
  • the projection system considers the foveal characteristics of user 550 m determining how to allocate video data processmg resources
  • the gaze-tracking system may use additional layers of HOE optics m projector 501 to perform the optical functions necessary for head tracking
  • projector 501 may mclude elements for projectmg infrared (IR) radiation (or suitable visible-band light) onto the feature to be tracked and additional elements for imaging the back-scattered IR onto some imagmg sensor inside the projector

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Abstract

On utilise des éléments optiques holographiques (EOH) (320) commutables qui peuvent être mis en oeuvre ou arrêtés, dans des systèmes et des procédés de projection d'images 3D, ou de projection d'images 2D en mosaïque avec une taille agrandie et/ou une meilleure résolution. Dans une forme de réalisation, le procédé assure la projection d'images 3D monochromes et comprend les étapes suivantes: (a) l'affichage au niveau d'un plan objet (310), d'une image 2D (306; 307; 308) qui est une coupe transversale d'une image 3D; (b) l'activation d'un EOH (320) pour focaliser l'image 2D sur un plan image approprié (331; 332; 333; 334); et (c) la répétition des étapes (a)- (b) pour différentes coupes transversales de l'image 3D. Chacune des coupes transversales est focalisée sur un plan image différent, de sorte que les images résultantes semblent apparaître sous forme d'une 'image en volume' (330) telle qu'une image 3D. Les étapes (a)- (c) sont ensuite rapidement répétées à vitesse rapide (telle que 60 séquences par seconde) pour créer une image 3D (335) affichée en continu. L'image 3D peut être une image statique ou une image mobile. Dans une autre forme de réalisation, le procédé comprend les étapes suivantes: l'affichage séquentiel d'images en coupe transversales 2D, et, exactement dans le même temps, l'activation séquentielle des EOH commutables qui rendent en image les coupes transversales sur différents plans image. Un système de projection 3D comprend (a) un affichage 2D configuré pour afficher séquentiellement une série de coupes transversales et (b) un EOH configuré pour focaliser l'affichage 2D sur une série de plans image à des distances différentes par rapport à l'affichage 2D. Les EOH commutables sont également utilisés dans un système de projection d'images qui projette une image constituée d'un réseau de 'pavés'.
PCT/US1999/017343 1998-07-29 1999-07-28 Systemes de projection a trois dimensions fondes sur un dispositif optique holographique commutable Ceased WO2000007061A1 (fr)

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WO2017173994A1 (fr) * 2016-04-07 2017-10-12 中山大学 Système et procédé d'affichage tridimensionnel à vues multiples
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