WO2000062104A1 - Systeme et procede de modulation de l'intensite de la lumiere - Google Patents

Systeme et procede de modulation de l'intensite de la lumiere Download PDF

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Publication number
WO2000062104A1
WO2000062104A1 PCT/US1999/024250 US9924250W WO0062104A1 WO 2000062104 A1 WO2000062104 A1 WO 2000062104A1 US 9924250 W US9924250 W US 9924250W WO 0062104 A1 WO0062104 A1 WO 0062104A1
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WIPO (PCT)
Prior art keywords
wherem
light
hologram
optical element
holographic optical
Prior art date
Application number
PCT/US1999/024250
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English (en)
Inventor
Milan M. Popovich
John J. Storey
Jonathan D. Waldern
Michael D. Walshe
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Digilens, Inc.
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Publication date
Application filed by Digilens, Inc. filed Critical Digilens, Inc.
Priority to AU12092/00A priority Critical patent/AU1209200A/en
Publication of WO2000062104A1 publication Critical patent/WO2000062104A1/fr

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Classifications

    • 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
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133621—Illuminating devices providing coloured light
    • 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
    • G02F1/1347—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells
    • G02F1/13476—Arrangement of liquid crystal layers or cells in which the final condition of one light beam is achieved by the addition of the effects of two or more layers or cells in which at least one liquid crystal cell or layer assumes a scattering state

Definitions

  • TITLE SYSTEM AND METHOD FOR MODULATING LIGHT INTENSITY
  • the present mvention relates generally to light intensity modulators, and more particularly to light intensity modulators employing holograms
  • Spatial light modulators SLMs
  • light intensity modulators LIMs
  • SLMs Spatial light modulators
  • LIMs light intensity modulators
  • electromechanical shutters typically use an electric motor or actuator to move an opaque member in or out of the light's path
  • the acousto-optic modulator diffracts light using a sound wave travelling through a transparent solid
  • the electro- optic modulators use the effect of electrically mduced refractive index changes to modulate polarized light
  • electromechanical modulators have perfect optical characteristics, passmg all incident light without alteration in their open state, and completely stopping all incident light m their closed state They have the disadvantages of relatively slow switchmg time (typically not faster than a few milliseconds) and high switchmg energy Further, electro-mechanical modulators capable of independently controlling selected parts of their aperture are possible m principle, but difficult m practice because of their complexity and poor reliability
  • the acousto-optic modulators are much faster (typical bandwidths of many MHz) and more reliable than mechanical modulators, but they also require high power requirements (typically 1 watt) to operate
  • the electro-optic modulators can also be quite fast, while consuming less power when compared to acousto-optic modulators
  • Electro-optic modulators are often constructed by placing electrode adjacent to a liquid crystal matenal This principle is used to make the well-known liquid crystal displays Liquid crystal displays rely on the bulk properties of the liquid crystal material to achieve light
  • liquid crystal displays relying on the bulk properties of liquid crystals are limited m their ability to produce modulated light of acceptable intensity
  • Liquid crystal displays employing liquid crystal droplets embedded in a polymer matrix modulate light by means of a diffraction pattern comprising alternate bands of clear polymer and polymer populated by liquid crystal droplets
  • the diffraction efficiency suitable for image display purposes generally require the LIM to be relatively thick enough that the incident light encounters a sufficient number of randomly oriented liquid crystal droplets
  • the speed at which the LIM can be switched lowers as the LIMs thickness increases
  • LIMs find application in a variety of systems
  • LIMs can be employed in communication systems to encode information by light intensity modulation
  • a light intensity level is assigned to, for example, a digital value
  • the LIM receives a data signal having a particular digital value
  • the LIM then converts the data signal into a corresponding light of assigned intensity
  • the light is transmitted over an optical medium (e g , fiber optical cable) to a destination where a decoder receives and decodes the intensity of the transmitted light to produce the original data signal
  • LIMs can be used in illumination systems where it is important to control the intensity of light illuminating objects such as dynamic and static image display panels
  • LIMs find use in medical or scientific applications where it is also important to control the intensity of light over time
  • LIMs can also be employed as picture elements in image displays, as noted above, where it is important to generate gray levels SLM arrays, also referred to as light- valve arrays are used m projection displays, optical interconnects, holographic storage, and other
  • the present invention relates to a light intensity modulator that employs a hologram
  • the light intensity modulator includes an electrical circuit and a holographic optical element containing the hologram
  • the holographic optical element is electrically coupled to and receives a va ⁇ able voltage generated by the electnc circuit
  • the holographic optical element receives an mput light from a light source
  • the holographic optical element receives and diffracts the mput light to produce first and second output lights
  • An intensity of the first output light varies directly with the magnitude of the voltage
  • the first and second output lights define a non-zero angle therebetween
  • the holog ⁇ am operates m an active state or an inactive state In the active state, the hologram diffracts the input light In the inactive state, the hologram transmits the input light without diffraction
  • the hologram operating m the inactive state, transmits the input light as though the hologram was
  • a second holographic optical element is added The second holographic optical element mcludes a second hologram
  • the electrical circuit generates a second voltage that varies m magnitude
  • the second holographic optical element is coupled to the electrical circuit receives the second voltage
  • the second holographic optical element also receives a second input light
  • the second holographic optical element produces third and forth output lights in response to receiving the second input light and the second voltage
  • An intensity of the third output light vanes directly with the magnitude of the second voltage while an intensity of the fourth output light varies indirectly with the magnitude of the second voltage
  • a second non-zero angle is defined between the third and fourth output lights, wherein
  • the hologram is formed by exposing an interference pattern inside a polymer- dispersed liquid crystal mate ⁇ al
  • This material includes, in one embodiment, a polymenzable monomer, a liquid crystal, a cross-linking monomer, and a coinitiator 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) material made in accordance with the teachmgs of the descnption herein,
  • PDLC polymer dispersed liquid crystal
  • Fig. 2 is a graph of the normalized net transmittance and normalized net diffraction efficiency of a hologram made in accordance with the teachings of the description herein (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 switchmg rms voltages needed for switching a hologram made in accordance with the teachmgs of the description herem 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 electnc field for a PDLC matenal formed with 34% by weight liquid crystal surfactant present and a PDLC matenal formed with 29% by weight liquid crystal and 4% by weight surfactant,
  • Fig 5 is a graph showing the switching response time data for the diffracted beam m the surfactant- containing PDLC matenal in Fig 4,
  • Fig. 6 is a graph of the normalized net transmittance and the normalized net diffraction efficiency of a hologram
  • Fig. 7 is an elevational view of typical expenmental arrangement for recordmg reflection gratings
  • Figs. 8a and 8b are elevational views of a reflection grating, made m accordance with the teachmgs of the descnption herem, having periodic planes of polymer channels and PDLC channels disposed parallel to the front surface m the absence of a field (Fig 8a) and with an electnc field applied (Fig. 8b) wherein the liquid- crystal utilized m the formation of the grating has a positive dielectnc anisotropy; Figs.
  • FIG. 9a and 9b are elevational views of a reflection gratmg, made m accordance with the teachings of the descnption herem, havmg periodic planes of polymer channels and PDLC channels disposed parallel to the front surface of the gratmg in the absence of an electnc field (Fig. 9a) and with an electnc field applied (Fig 9b) wherein the liquid crystal utilized in the formation of the gratmg has a negative dielectric anisotropy,
  • Figs. 9c and 9d depict chemical formulas of vanous types of liquid crystal matenals
  • Fig. 10a is an elevational view of a reflection gratmg, made m accordance with the teachings of the descnption herem, disposed with a magnetic field generated by Helmholtz coils,
  • Figs. 10b and 10c are elevational views of the reflection gratmg of Fig. 10a in the absence of an electnc field (Fig 10b) and with an electric field applied (Fig 10c),
  • Figs. 11a and l ib are representative side views of a slanted transmission grating (Fig 1 1a) and a slanted reflection grating (Fig l ib) showing the orientation of the grating vector G of the periodic planes of polymer channels and PDLC channels,
  • Fig. 12 is an elevational view of a reflection grating, made in accordance with the teachings of the descnption herem, when a shear stress field is applied thereto
  • Fig 13 is an elevational view of a subwavelength grating, made in accordance with the teachings of the description herein, having periodic planes of polymer channels and PDLC charmels disposed perpendicular to the front surface of the grating,
  • Fig 14a is an elevational view of a switchable subwavelength, made in accordance with the teachings of the description herein, wherein the subwavelength grating 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 in Fig 14a disposed between crossed polarizers whereby the incident light is transmitted,
  • Figs 14c and 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 gratmg, made in accordance with the teachings of the descnption herein, wherem the subwavelength gratmg functions as a quarter wave plate whereby plane polarized light is transmitted through the subwavelength grating, retroreflected by a mirror and reflected by the beam splitter,
  • Fig 15b is a side view of the switchable subwavelength grating of Fig 15a and showing the effect of the application of a voltage to the plate whereby the polanzation of the light is no longer modified, thereby permitting the reflected light to pass through the beam splitter,
  • Figs 16a and 16b are elevational views of a transmission gratmg, made m accordance with the teachmgs of the descnption herein, havmg penodic planes of polymer channels and PDLC channels disposed perpendicular to the front face of the grating in the absence of an electnc field (Fig 16a) and with an electric field applied (Fig 16b) wherem the liquid crystal utilized m formation of the grating has a positive dielectnc anisotropy,
  • Fig 17 is a side view of five subwavelength gratings wherem the gratmgs are stacked and connected electrically m parallel thereby reducmg the switchmg voltage of the subwavelength grating,
  • Fig 18 is a block diagram of a LIM system employmg the present invention.
  • Fig 19a illustrates operational aspects of one type of switchable holographic optical element employable in the system shown in Fig 18,
  • Fig 19b illustrates operational aspects of another type of switchable holographic optical element employable in the system shown in Fig 18,
  • Fig 20a-c illustrates operational aspects of the switchable holographic optical element illustrated in Fig 19a
  • Fig 21 is a cross sectional view of one embodiment of a monochromatic switchable holographic optical element employable m the system of Fig 18,
  • Fig 22 is a cross sectional view of one embodiment of a polychromatic switchable holographic optical element employable in system of Fig 18,
  • Fig 23 is a cross sectional view of another embodiment of a polychromatic switchable holographic optical element employable in the system of Fig 18,
  • Fig 24a is a cross sectional view of one embodiment of a monochromatic switchable holographic optical element employable as a diffractive display in the system of Fig 18,
  • Fig 24b is an elevational view of the monochromatic switchable holographic optical element shown in Fig 24b
  • Fig 25 is a cross sectional view of one embodiment of a polychromatic switchable holographic optical element employable as a diffractive display in the system of Fig 18,
  • Fig 26 is a cross sectional view of another embodiment of a polychromatic switchable holographic optical element employable as a diffractive display m the system of Fig 18,
  • Fig 27 is a plan view of a portion or pixel of a polychromatic switchable holographic optical element employable as a diffractive display m the system of Fig 18,
  • Fig 28a is a plan view of an electrode which may be used to modulate the refractive mdex of polychromatic switchable holographic optical element pixel of Fig 27,
  • Fig 28b is a plan view of an electrode havmg sub-electrodes that may be used to modulate sub-areas of the refractive mdex of polychromatic switchable holographic optical element pixel of Fig 27
  • the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be desc ⁇ bed in detail It should be understood, however, that the drawing and detailed descnption thereto are not mtended to limit the mvention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling withm the spi ⁇ t and scope of the present invention as defined by the appended claims
  • the present invention employs holographic optical elements formed, in one embodiment, from a polymer dispersed liquid crystal (PDLC) matenal including a monomer, a dispersed liquid crystal, a cross- linking monomer, a coinitiator and a photoinitiator dye These PDLC matenals exhibit clear and orderly separation of the liquid crystal and cured polymer, whereby the PDLC material advantageously provides high quality optical elements
  • PDLC materials used m the holographic optical elements may be formed m a smgle step
  • the holographic optical elements may also use a unique photopolyme ⁇ zable prepolymer matenal that permits in situ control over charactenstics of resulting gratings, such as domain size, shape, density, ordering and the like
  • methods and materials taught herein may be used to prepare PDLC materials for optical elements mcludmg switchable transmission or reflection type holographic gratmgs
  • a hologram may be formed 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
  • PDLC polymer dispersed liquid crystal
  • a feature of one embodiment of PDLC material is that illumination by an inhomogeneous, coherent light pattern initiates a patterned, anisottopic diffusion (or counter diffusion) of polyme ⁇ zable monomer and second phase material, particularly liquid crystal (LC)
  • LC liquid crystal
  • the resulting PDLC material may have an amsotropic spatial distribution of phase-separated LC droplets within the photochemically cured polymer matnx
  • Pnor art PDLC materials made by a single-step process may achieve at best only regions of larger LC bubbles and smaller LC bubbles in a polymer matnx
  • the large bubble sizes are highly scattering which produces a hazy appearance and multiple ordermg diffractions, in contrast to the well-defined first order diffraction and zero order diffraction made possible by the small LC bubbles of one embodiment of PDLC material
  • m well-defined channels of LC-nch matenal Reasonably well-defined alternately LC- ⁇ ch channels and nearly pure polymer channels m a PDLC matenal are possible by multi-step processes, but such processes do not achieve the precise morphology control over LC droplet size and distnbution of sizes and widths of the polymer and LC- ⁇ ch channels made possible by one embodiment of PDLC matenal
  • the same may be prepared by coating the mixture between two mdium-tin-oxide (ITO) coated glass slides separated by spacers of nominally 10-20 ⁇ r_ thickness
  • ITO mdium-tin-oxide
  • the sample is placed m a conventional holographic recordmg setup
  • Gratmgs are typically recorded using the 488 nm line of an Argon ion laser with intensities of between about 0 1-100 mW/cm 2 and typical exposure times of 30-120 seconds
  • the angle between the two beams is vaned to vary the spacing of the intensity peaks, and hence the resulting gratmg spacing of the hologram Photopolyme ⁇ zation is induced by the optical intensity pattern
  • SPIE Society of Photo-Optical Instrumentation Engineers
  • the features of the PDLC matenal are influenced by the components used in the preparation of the homogeneous starting mixture and, to a lesser extent, by the intensity of the incident light pattern
  • the prepolymer matenal compnses a mixture of a photopolyme ⁇ zable monomer, a second phase matenal, a photoinitiator dye, a coinitiator, a chain 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 prefened because they form densely cross-linked networks which shrink to some extent and to tend to squeeze out the second phase material As a result, the second phase material is moved amsotropically out of the polymer region and, thereby, separated into well-defined polymer-poor, second phase-rich regions or domains Highly functionalized monomers may also be preferred because the extensive cross-linking associated with such monomers yields fast kinetics, allowing the hologram to form relatively quickly, whereby the second phase matenal will exist in domains of less than approximately 0 1 ⁇ m
  • a mixture of penta-acrylates in combmation with di-, tn-, and/or tetra-acrylates may be used m order to optimize both the functionality and viscosity of the prepolymer matenal
  • Suitable acrylates such as tnethyleneglycol diacrylate, t ⁇ methylolpropane t ⁇ acrylate, pentaerythntol t ⁇ acrylate, pentaerythntol tetracrylate, pentaerythntol pentacrylate, and the like may be used.
  • tnethyleneglycol diacrylate t ⁇ methylolpropane t ⁇ acrylate
  • pentaerythntol t ⁇ acrylate pentaerythntol tetracrylate
  • pentaerythntol pentacrylate and the like
  • it has been found that an approximately 1 4 mixture of tn- to penta-acrylate facilitates homogeneous mixing while providmg a favorable
  • the second phase matenal of choice is a liquid crystal (LC)
  • LC liquid crystal
  • the 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 fab ⁇ cated with approximately 25% by weight typically yield good diffraction efficiency and optical clanty
  • the concentration of LC may be mcreased to 35% by weight without loss m optical performance by adjusting the quantity of surfactant
  • Suitable liquid crystals contemplated for use m the practice of the present mvention may mclude the mixture of cyanobiphenyls marketed as E7 by Merck, 4'-n-pentyl-4-cyanob ⁇ phenyl, 4'-n-h
  • the mixture of liquid crystal and prepolymer material 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 in the dark as the mixture is extremely sensitive to light
  • photoinitiator dyes that may be useful m generating PDLC materials are rose bengal ester (2,4,5,7-tetra ⁇ odo-3 , ,4',5',6'- tetrachlorofluoresce ⁇ n-6-acetate ester), rose bengal sodium salt, eosm, eosm sodium salt, 4,5-duodosucc ⁇ nyl fluorescein, camphorquinon
  • Suitable surfactants include octanoic acid, heptanoic acid, hexanoic acid, dodecanoic acid, decanoic acid, and the like
  • LC monomers liquid crystalline bifunctional acrylate as the monomer
  • LC monomers have an advantage over conventional acrylate monomers due to their high compatibility with the low molecular weight nematic LC matenals, thereby facilitating formation of high concentrations of low molecular weight LC and yielding a sample with high optical quality
  • the presence of higher concentrations of low molecular weight LCs in the PDLC matenal greatly lowers the switchmg voltages (e g , to ⁇ 2V//-m)
  • Another advantage of using LC monomers is that it is possible to apply low AC or DC fields while recordmg holograms to pre-align the host LC monomers and low molecular weight LC so that a desired onentation and configuration of the nematic directors may be obtained m the LC droplets
  • the chemical formulate of several suitable LC monomers are as follows
  • FIG 1 there is shown a cross-sectional view of an electrically switchable hologram 10 made of an exposed polymer dispersed liquid crystal material made according to the teachmgs of this descnption
  • a layer 12 of the polymer dispersed liquid crystal matenal is sandwiched between a pair of indium-tin-oxide coated glass slides 14 and spacers 16
  • the interior of hologram 10 shows Bragg transmission gratmgs 18 formed when layer 12 was exposed to an interference pattern from two intersectmg beams of coherent laser light
  • the exposure times and intensities may be varied dependmg on the diffraction efficiency and liquid crystal domam size desired Liquid crystal domam size may be controlled by varymg the concentrations of photoinitiator, coinitiator and chain-extending (or cross-linking) agent
  • the onentation of the nematic directors may be controlled while the gratings are being recorded by application of an external electric 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 in a sample with a 36 wt% loadmg of liquid crystal usmg the 488 nm line of an argon ion laser at an intensity of 95 mW/cm 2
  • the size of the liquid crystal domains is about 0 2 ⁇ m and the grating spacmg is about 0 54 ⁇ m
  • This sample which is approximately 20 ⁇ m thick, diffracts light m the Bragg regime
  • 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 m zero order transmittance
  • FIG 2 shows that energy is transferred from the first order beam to the zero-order beam as the voltage is mcreased
  • the peak diffraction efficiency may approach 100%, dependmg on the wavelength and polarization of the probe beam, by appropnate adjustment of the sample thickness
  • the minimum diffraction efficiency may be made to approach 0% by slight adjustment of the parameters of the PDLC matenal to force the refractive mdex 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 switching rms voltage 22 needed for switching a hologram made accordmg to the teachmgs of this disclosure to mmimum 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
  • a PDLC reflection grating is prepared by placing several drops of the mixture of prepolymer matenal 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 causing the prepolymer matenal 112 to fill the region between the slides 114a and 114b
  • the separation of the slides is maintained at approximately 20 ⁇ m by utilizing uniform spacers 118
  • Preparation, mixing and transfer of the prepolymer matenal is preferably done m 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
  • the prepolymer material utilized to make a reflection gratmg comp ⁇ ses a monomer, a liquid crystal, a cross-linking monomer, a coinitiator, and a photoinitiator dye
  • the reflection gratmg may be formed from prepolymer matenal including by total weight of the monomer dipentaerythntol hydroxypentacrylate (DPHA), 35% by total weight of a liquid crystal including a mixture of cyano biphenyls (known commercially as "E7"), 10% by total weight of a cross-linking monomer mcludmg N- vinylpyrro dinone ("NVP"), 2 5% by weight of the coinitiator N-phenylglycme (“NPG”),and 10 5 to 10 " * gram moles of a photoinitiator dye mcludmg rose bengal ester
  • DPHA monomer dipentaerythntol hydroxypentacrylate
  • E7 cyano biphenyls
  • gratmg 130 mcludes penodic planes of polymer channels 130a and PDLC channels 130b which run parallel to the front surface 134
  • the gratmg spacmg associated with these periodic planes remains relatively constant throughout the full thickness of the sample from the air/film to the film/substrate mterface
  • the morphology of the reflection gratmg 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 in the material were significantly smaller having diameters between 50 and 100 nm. Furthermore, unlike transmission gratings where the liquid crystal-rich regions typically comprise less than 40% of the gratmg, the liquid crystal-rich component of a reflection grating is significantly larger. Due to the much smaller periodicity associated with reflection gratings, i.e., a narrower grating spacing (-0.2 microns), it is believed that the time difference between completion of curing in high intensity versus low intensity regions is much smaller. It is also believed that the fast polymerization, as evidenced by small droplet diameters, traps a significant percentage of the liquid crystal in the matrix during gelation and precludes any substantial growth of large droplets or diffusion of small droplets into larger domains.
  • the reflection notch In PDLC materials that are formed with the 488 nm line of an argon ion laser, 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%) indicates that shrinkage of the film is not a significant problem. Moreover, it has been found that the performance of such gratings is stable over periods of many months.
  • suitable PDLC materials could be prepared utilizing monomers such as triethyleneglycol diacrylate, trimethylolpropanetriacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, pentaerythritol pentacrylate, and the like.
  • monomers such as triethyleneglycol diacrylate, trimethylolpropanetriacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, pentaerythritol pentacrylate, and the like.
  • other coinitiators such as triethylamine, triethanolamine, N,N-dimethyl- 2,6-diisopropylaniline, and the like could be used instead of N-phenylglycine.
  • the photoinitiator dyes rose bengal sodium salt, eosin, eosin sodium salt, fluorescein sodium salt and the like will give favorable results.
  • the 633 nm line is utilized, methylene blue will find ready application.
  • other liquid crystals such as 4'-pentyl-4-cyanobiphenyl or 4'-heptyl-4-cyanobiphenyl, may be utilized.
  • FIG. 8a there is shown an elevational view of a reflection grating 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 domains is formed in a direction perpendicular to the periodic channels 130a and 130b of the grating 130 and perpendicular to the front surface 134 of the grating 130.
  • the symmetry axis 136 is already in a low energy state in alignment with the field E and will reorient.
  • reflection gratings formed in accordance with the procedure described above will not normally be switchable.
  • a reflection grating tends to reflect a narrow wavelength band, such that the grating may be used as a reflection filter.
  • the reflection grating is formed so that it will be switchable. More particularly, switchable reflection gratmgs may be made utilizing negative dielectric anisotropy LCs (or LCs with a low cross-over frequency), an applied magnetic field, an applied shear stress field, or slanted gratings.
  • Liquid crystals may be found in 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 may be prepared from a combmation of positive and negative dielectric anisotropy liquid crystals
  • a suitable positive dielectnc liquid crystal for use in such a combmation contains four ring esters as shown m
  • FIG 9D A strongly negative dielectnc liquid crystal suitable for use m such a combmation is made up of pyndazmes as shown m FIG 9D
  • Both liquid crystal matenals are available from LaRoche & Co , Switzerland By varymg the proportion of the positive and negative liquid crystals m the
  • switchable reflection gratmgs may be formed using positive ⁇ liquid crystals As shown in FIG 10a, such gratmgs are formed by exposmg the PDLC starting matenal to a magnetic field dunng the cunng process
  • the magnetic field may 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 o ⁇ ented parallel to the front surface of the glass plates (not shown) that are used to form the gratmg 140
  • the symmetry axis 146 of the liquid crystals will onent 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 )
  • FIG 10c When an electric field is applied, as shown in FIG 10c the positive ⁇ liquid crystal will reonent in the direction of the field, which is perpendicular to the front surface of grating
  • FIG 11a depicts a slanted transmission grating 148 and FIG l ib depicts a slanted reflection grating 150
  • a holographic transmission grating is considered slanted if the direction of the gratmg vector G is not parallel to the gratmg surface
  • the grating is said to be slanted if the gratmg vector G is not perpendicular to the grating surface
  • Slanted gratmgs 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 grating is used to separate the specular reflection of the film from the diffracted beam
  • a slanted gratmg has an even more useful advantage
  • the slant allows the modulation depth of the gratmg to be controlled by an electnc field when using either tangential or homeotropic aligned liquid crystals This is because the slant provides components of the electnc field m the directions both tangent and perpendicular to the grating vector
  • the LC domam symmetry axis will be o ⁇ ented along the grating vector G and may be switched to a direction perpendicular to the film plane by a longitudinally applied field E This is the typical geometry for switchmg of the diffraction efficiency of the slanted reflection gratmg
  • Reflection gratmg prepared m accordance with this description may find application in color reflective displays, switchable wavelength filters for laser protection, reflective optical elements and the like
  • PDLC matenals may 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 gratings are known as subwavelength gratmgs, and they behave like a negative uniaxial crystal, such as calcite, potassium dihydrogen phosphate, or lithium niobate, with an optic axis perpendicular to the PDLC planes
  • FIG 13 there is shown an elevational view of a transmission gratmg 200 made in accordance with this descnption having penodic planes of polymer planes 200a and PDLC planes 200b disposed perpendicular to the front surface 204 of the grating 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-, and refractive mdex ri p , and each
  • the gratmg will exhibit form birefringence
  • the magnitude of the shift in polarization is proportional to the length of the gratmg
  • the length of the subwavelength gratmg should be selected so that
  • the length of the subwavelength gratmg should be selected so that
  • the polarization of the mcident light is at an angle of 45° with respect to the optic axis 210 of a half-wave plate 212, as shown m FIG 14a, the plane polarization will be preserved, but the polarization of the wave exiting the plate will be shifted by 90°
  • the half- wave plate 212 is placed between cross polarizers 214 and 216, the mcident light will be transmitted If an approp ⁇ ate switchmg voltage is applied, as shown in FIG 14d, the pola ⁇ zation of the light is not rotated and the light will be blocked by the second polarizer
  • FIG 16a there is shown an elevational view of a subwavelength gratmg 230 recorded m accordance with the above-descnbed methods and havmg penodic 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 domains is disposed in a direction parallel to the front surface 234 of the gratmg and perpendicular to the penodic channels 230a and 230b of the grating 230
  • the symmetry axis 232 distorts and reonents 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 grating 230
  • subwavelength gratmg 230 recorded m accordance with the above-descnbed methods and havmg penodic planes of polymer channels 230a and
  • n. 2 - n 0 2 -[(f PDLC ) (f p ) (n PDLC 2 - n, 2 )] / [f PDLC n PDLC 2 + f-n, 2 ]
  • n 0 the ordinary mdex of refraction of the subwavelength gratmg
  • n. the extraordinary mdex of refraction
  • n PD ix me refractive mdex of the PDLC plane
  • ri p the refractive mdex of the polymer plane
  • n LC the effective refractive mdex of the liquid crystal seen by an mcident optical wave
  • fp D i t PDLC / (t PDLC + t P )
  • f P V (t PDLC + t P )
  • the effective refractive mdex of the liquid crystal, n LC is a function of the applied electnc field, havmg a maximum when the field is zero and value equal to that of the polymer, n P , at some value of the electnc field, E MAX
  • ⁇ n -[(fp DL c) (f p ) (n PDLC 2 - n_ 2 )] / [2n AVG (f PDLC n PDLC 2 + f ⁇ 2 )]
  • n AVG (n. + n.) 12
  • N PDLC n P + f LC [n LC - n p ]
  • f LC [V LC /
  • n LC 1
  • n P , 1 5
  • the net birefringence, ⁇ n, of the subwavelength grating is approximately 0008
  • 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 mdex of the liquid crystal may be matched to the refractive mdex of the polymer and the birefnngence of the
  • the plates may be switched between the on and off (zero retardance) states on the order of microseconds
  • current Pockels cell technology may be switched m nanoseconds with voltages of approximately 1000-2000 volts, and bulk nematic liquid crystals may be switched on the order of milliseconds with voltages of approximately 5 volts
  • the switchmg voltage of the subwavelength gratmg may be reduced by stacking several subwavelength gratings 220a-220e together, and connecting them electncally m parallel
  • the length of the sample is somewhat greater than 50 ⁇ m, because each gratmg mcludes an mdium-tm-oxide coatmg which acts as a transparent electrode
  • the switching voltage for such a stack of plates is only 50 volts
  • Subwavelength gratings m accordance with the this descnption are expected to find suitable application m the areas of pola ⁇ zation optics and optical switches for displays and laser optics, as well as tunable filters for telecommunications, colonmetry, spectroscopy, laser protection, and the like
  • electncally switchable transmission gratmgs 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 computing, beam steering for laser surgery, beam steenng for laser radar holographic image storage and ret ⁇ eval, 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 electnc field, and may 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 rema fixed mdependent of an applied field In accordance with this description, a high contrast static hologram may also be created In this vanation of this description, the holograms are recorded as described previously The cured polymer film is then soaked in a suitable solvent at room temperature for a short duration and finally dned For the liquid crystal E7, methanol has shown satisfactory application Other potential solvents include alcohols such as ethanol, hydrocarbons such as hexane and heptane, and the like When the matenal is dned, a high contrast status hologram with high diffraction efficiency results The high diffraction efficiency is a consequence of the large mdex modulation
  • a high birefringence static sub-wavelength wave-plate may also be formed Due to the fact that the refractive mdex 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 descnption may be used m many applications employmg polanzation optics, particularly where a material of the appropnate birefnngence that the appropriate wavelength is unavailable, too costly, or too bulky
  • the term polymer dispersed liquid crystals and polymer dispersed liquid crystal matenal m cludes, as may be appropnate, solutions in which none of the monomers have yet polymerized or cured, solutions m which some polymerization has occuned, and solutions which have undergone complete polymerization Those of skill m the art will clearly understand that the use herem of the standard term used in the art, polymer dispersed liquid crystals (which gramm
  • Fig 18 is a block diagram showmg a light intensity modulator system 300 employmg the present mvention System 300 m Fig 18 mcludes a switchable holographic optical element (SHOE), 302, a control circuit 304, and a light source 306 SHOE 302 is electncally coupled to control circuit 204, and receives therefrom one or more vanable control voltages SHOE 302 is also positioned to receive an mput light 310 from light source 306
  • SHOE switchable holographic optical element
  • Light source 306 may or may not be electncally coupled to receive controlling signals from control circuit 304 Fig 18 shows light source 306 electncally coupled to control circuit 304, it bemg understood that coupling between light source 306 and control circuit 304, is not necessary in several embodiments of the present mvention
  • SHOE 302 m cludes one or more switchable holograms recorded in a medium descnbed above
  • the switchable hologram may be either a thick phase or a thin phase switchable hologram
  • Thick phase holograms are often refe ⁇ ed to as Bragg or volume type holograms
  • Thin phase holograms are often referred to the holograms that conform to the Raman Nath regime
  • SHOE 302 may be either a reflective or a transmissive type hologram Reflective type holograms receive mput light at one surface and produce refracted light at a second opposite facmg surface
  • a switchable hologram operates in either an active state or an inactive state, depending upon the magnitude of the vanable control voltage supplied thereto
  • a switchable hologram diffracts an mput light
  • a switchable hologram transmits the input light substantially unaltered and without diffraction such that the switchable hologram resembles a transparent medium such as glass
  • the switchable hologram may diffract one of the p ⁇ mary colors of the visible bandwidth (e g , red, green, blue) while transmitting the remaining pnmary colors without diffraction or blockmg the remammg primary colors from further transmission
  • Fig 19a illustrates operational aspects of SHOE 302 havmg a thick phase switchable hologram recorded therein
  • Fig 19b shows operational aspects of SHOE 302 having a thin phase switchable hologram recorded therein
  • the switchable holograms recorded m SHOE 302 of Figs 19a and 19b are shown operating m the active state More particularly, the thick phase hologram recorded in SHOE 302 of Fig 19a receives and diffracts mput light 310 to produce a zero order diffracted output light 312 and a first order diffracted output light 314
  • Zero order diffracted output light 312 may be referred to as first output light 312, while first order diffracted output light 314 may be referred to as second output light 314
  • Output lights 312 and 314 define a non-zero angle 316 therebetween
  • the thm phase switchable hologram of SHOE 302 m Fig 19b receives and diffracts input light 310 to produce zero order diffracted output
  • the emerging light will have two main components, zero order diffracted output light 312, which propagates m the direction of mput light 310 and first order diffracted light 314 which satisfies the Bragg diffraction relation, and will normally carry the bulk of the diffracted light energy There may be higher order diffraction output components, representing a small proportion of the total diffracted light energy If the thick phase hologram has close to maximum theoretical efficiency, the problem of dealing with zero order output light is largely eliminated At lower efficiencies, the zero order output light 312 will be present Thick phase holograms offer higher diffractive efficiencies up to a theoretical maximum of 100% There are stray light considerations, which pomt to the use of thick phase holograms Thm phase holograms, as noted above with respect to Fig 19b, give nse to the positive and negative diffracted orders in addition to the zero order The maximum diffraction efficiency in the first order for thm phase holograms is 33 8%
  • switchable holograms operate m either the active or inactive state m response to the magnitude of the vanable control voltage supplied thereto
  • Figs 20a-20c illustrate operational aspects of the thick phase transmissive type switchable hologram recorded m the SHOE 302 of Fig 19a
  • SHOE 302 operates m the inactive state and transmits mput light 302 without substantial alteration and diffraction
  • Figs 20b and 20c SHOE 302 operates m the active state
  • SHOE 302 modulates the intensity of output lights 312 and 314 as a function of the vanable control voltage magnitude generated by control circuit 304
  • the intensity of first output light 312 is directly related to the magnitude of the vanable control voltage while the intensity of the second output light 314 is indirectly related to the magnitude of the vanable control voltage
  • SHOE 302 receives a first vanable control voltage havmg a first magnitude and m Fig 20c
  • SHOE 302 receives a second variable control
  • Fig 21 shows a cross-sectional view of one embodiment of a monochromatic SHOE 302 shown m Fig 18 SHOE 302 m Fig 21 mcludes a pair of substantially transparent and electncally nonconductive layers 332, a pair of substantially transparent and electncally conductive layers 334, and a switchable hologram layer or medium 336 formed, m one embodiment, from a polymer dispersed liquid crystal matenal desc ⁇ bed above
  • the switchable holographic layer or medium 336 records the switchable hologram
  • substantially transparent, electncally nonconductive layers 332 are formed from glass while the electncally conductive, substantially transparent layers 334 are formed from mdium tin oxide (ITO)
  • ITO mdium tin oxide
  • An anti-reflection coating may be applied to selected surfaces of the layered SHOE 302 mcludmg the example ITO and glass layers, to improve the overall transmission efficiency of the optical element and to reduce stray light
  • all layers 332-336 are
  • Layers 332-336 of SHOE 302 shown in Fig 21 may have substantially thm cross-sectional widths thereby providmg a substantially thm aggregate m cross section More particularly, switchable holographic layer 336 may have a cross-sectional width of 5 - 12 microns (the precise width dependmg on the spectral bandwidth and required diffraction efficiency) The glass layers 332 may have a cross-sectional width of 4 - 8 millimeters Obviously, ITO layer 334 must be substantially thm to be transparent
  • ITO layers 334 are coupled to the control circuit 304 and receive the vanable control voltage provided therefrom
  • the switchable hologram recorded m layer 336 is activated or deactivated dependmg upon the magnitude of the vanable control voltage applied between ITO layers 334
  • the switchable hologram established therein is said to operate m the inactive state
  • the switchable hologram recorded in layer 336 is eventually activated such that it diffracts mput light that satisfies the Bragg diffraction angle of the recorded switchable hologram
  • a continued decrease m the magnitude of the vanable control voltage changes the diffractive mdex modulation of the recorded hologram which, m turn, gives nse to the vanable diffraction efficiency desc ⁇ bed above
  • the SHOE 302 illustrated in Fig 21 is used in a system 300 for modulatmg the intensity of a monochromatic light
  • the SHOE 302 shown in Fig 21 may find application m systems used for illuminating displays with vanable intensity output light 312 or 314 as shown in Fig 18
  • the SHOE 302 shown m Fig 21 could be used m a communication system for modulating the intensity of light transmitted over an optical medium where the intensity of the transmitted light relates to data signals received by the control circuit 304
  • Figs 22 and 23 show embodiments of a polychromatic SHOE 302 employable in the system of Fig 18
  • the SHOE 302 shown m Fig 22 m cludes several substantially transparent and electncally nonconductive layers 332a-332d, several substantially transparent and electrically conductive layers 334r-334b, and several switchable hologram layers 336r-336b formed, in one embodiment, from the polymer dispersed liquid matenal desc ⁇ bed above
  • the electncally nonconductive layers 332a-332b may be formed from glass while the electncally conductive, substantially transparent layers 334r-334b may be formed from ITO
  • An anti-reflection coating (not shown) may be applied to selected surfaces to improve the overall transmission efficiency and to reduce stray light
  • the switchable holographic layers 336r-336b each record a switchable hologram configured to diffract a distinct band of visible light when activated When inactive, each of the switchable holograms transmits all bands of visible light without alteration or diffraction
  • the switchable hologram recorded in layers 336r-336b are optimized to diffract red, green, and blue bandwidth visible light, respectively, when activated
  • Each of the switchable layers 336r-336b is sandwiched between a pair of ITO layers In the configuration shown m Fig 22, any one or all of the holographic layers 336r-336b can be activated with one or several vanable control voltages provided by control circuit 304
  • SHOE 302 of Fig 22 When SHOE 302 of Fig 22 is used m the system shown m Fig 18, hght source 306 may be defined as a white light source capable of simultaneously producmg red, green, and blue bandwidth hght System 300 shown m Fig 18 usmg such a white light source 306 and the SHOE 302 shown m Fig 22, is capable of outputtmg first and second lights 312 and 314 of one of the pnmary visible bandwidths (e g , red, green, or blue)
  • the SHOE 302 shown m Fig 22 operating m the system shown in Fig 18 with a white light source 306, is capable of outputtmg first and second output lights 312 and 314
  • SHOE 302 shown m Fig 23 is likewise capable of producmg first and second modulated output lights 312 and 314 which contam one or more of the primary colors of the visible bandwidth
  • the SHOE shown in Fig 23 finds application m the system 300 shown in Fig 18 with light source 306 defined as three light sources, each one of which is capable of generatmg one of the primary colors of visible light (e g , red, blue, or green)
  • the SHOE 302 shown m Fig 23 m cludes three switchable holographic layers 336r-336b, each one of which is configured to diffract a distinct pnmary color of visible light when activated
  • layers 336r-336b record switchable holograms which, when operating m the inactive state, transmits substantially all visible light without substantial alteration and diffraction
  • the SHOE 302 shown m Fig 23 m cludes four substantially transparent and electncally non-conductive layers 332a-332d (e g , glass)
  • Figs 24a and 24b show an example of a monochromatic SHOE 302 which can be employed the system 300 shown in Fig 18 as a diffractive display
  • Fig 24a is a cross-sectional view of the SHOE 304 shown in Fig 24b
  • SHOE 302 mcludes a parr of substantially transparent and electncally nonconductive layers 342, a transparent and electrical conductive layer 344, a switchable holographic layer 346 formed, m one embodiment, from a polymer dispersed liquid crystal matenal descnbed above, and a layer 348 which mcludes an array of substantially transparent and electncally conductive electrodes 350 electncally isolated by an electncally nonconductive isolator 352
  • the substantially transparent, electncally nonconductive layers 342 are formed from glass while the electncally conductive, substantially transparent layer 344 and electrodes 350 of layer 348 are formed from ITO Anti-reflection coatmgs may be provided on selected surfaces
  • each ITO electrode is isolated and capable of receivmg an mdividual vanable control voltage from control circuit 304 of Fig 18 via a thm conductive lme 360
  • control circuit 304 is capable of activating or deactivating any subarea of the switchable hologram recorded m layer 346 directly underneath an mdividual electrode 350
  • control circuit 304 is capable of modulating the refractive index of the switchable hologram subarea directly underneath an individual electrode 350
  • the vanable control signals generated by circuit 304 may be produced m response to control circuit 304 receivmg a frame of image signals
  • Fig 24b shows a 4 x 4 anay of ITO electrodes 350 with a substantial distance between each field filled by electncally nonconductive isolator It is to be noted that the SHOE 302 shown in Fig 24b could be implemented with an anay havmg a greater number of rows and columns of ITO electrodes 350 Further, Fig 24b shows a large spacmg between ITO conductors such that conductive lmes 360 can be easily identified In practice, the spacing between ITO electrodes 350 will not be so large
  • ITO layer 344 is generally coupled to one terminal (l e , ground) of the control circuit 304 Accordingly, when one of the ITO electrodes 350 is activated by a vanable control voltage from control circuit 304, a conespondmg electnc field is established within the subarea of switchable holographic layer 356 underlymg the electrode If the field is great enough, the hologram withm the subarea will be deactivated
  • Switchable holographic layer 346 (and 336 of Figs 21-23) record holograms, in one embodiment, usmg the techniques described above
  • a high diffraction efficiency and fast rate at which the optical elements can be switched between active and inactive states characterize the resulting hologram
  • the resultmg holograms are characterized by a fast change in refractive index when the holograms are operating m the active state
  • PDLC polymer dispersed liquid crystal
  • the SHOE 302 descnbed m Figs 24a and 24b enable, for example, a diffractive display capable of generatmg a monochromatic image
  • the SHOE 302 shown m Fig 24a and 24b is capable of generatmg the monochromatic image as a function of vanable control voltages provided by control circuit 304 which operates, m turn, m response to receivmg a frame of image signals
  • control circuit 304 which operates, m turn, m response to receivmg a frame of image signals
  • the SHOE shown in Figs 25-28 are capable of generatmg such colored images
  • Fig 25 shows three switchable holographic layers 346r -346b, each one of which records a switchable hologram that operates to diffract a distinct pnmary color of the visible bandwidth when activated and which transmits all visible light without alteration or diffraction when operating in the inactive state
  • the SHOE 302 in Fig 25 also mcludes several substantially transparent and electncally nonconductive layers 342a-342d, several substantially transparent and electncally conductive layers 344r-344b, and layers 348r-348b, each of which compnses an anay of substantially transparent and electrically conductive electrodes 350 electncally isolated by an electncal nonconductor 352
  • layers 342 may be formed from glass while layers 344 and electrodes 350 may be formed from ITO
  • Each ITO electrode 350 m each layer 348r-348b, receives a vanable control voltage from control circuit 304
  • Control circuit 304 generates the vanable control voltages m response to receivmg a frame
  • SHOE 302 shown m Fig 25 can be employed as a diffractive display in the system shown in Fig 18
  • light source 306 may be defined as white light source capable of simultaneously generatmg the three pnmary colors of visible light
  • the operation of such a system is similar to the system descnbed with reference to Fig 22
  • White light 310 inputted to SHOE 302 of Fig 22 is diffracted by one or more subareas of a smgle switchable hologram recorded in layers 336r, 336g, or 336b, which is adjacent to one or more activated electrodes 350 m layers 448r, 448g, or 448b
  • one or more subareas of switchable holograms recorded in two of the three layers 346r-346b may be activated by corresponding electrodes 350
  • only one set of electrodes associated with each of the holograms is enabled at any given time With the electrodes enabled, a selected amount of mput light can be diffracted mto the first output light and towards a user, while light diffracted into the second output light is directed such that it cannot be seen by the user
  • the electrodes conespondmg to each of the three holograms are sequentially enabled such that a selected amount of red, green and blue light is directed towards a user for each electrode location
  • the rate at which the holograms are sequentially enabled is faster than the response time of a human eye, a color image will be created in the viewer's eye due to the integration of the red, green and blue monochrome images created by each of the switchable holograms recorded m the holographic layers
  • Fig 26 shows yet another embodiment of a SHOE 302 which can be employed as a diffractive display m system 300
  • the SHOE 302 shown m Fig 26 mcludes three switchable holographic layers 346r-346b each of which records a switchable hologram that m the active mode diffracts a distinctive bandwidth of visible light
  • the switchable hologram recorded m layer 346r diffracts red bandwidth light when active
  • the switchable hologram recorded n layer 346g diffracts green bandwidth light when activated
  • a switchable hologram recorded in 346b diffracts blue bandwidth light when active
  • each subarea of the switchable holograms recorded in 346r-346b is defined by a refractive mdex which can be modulated quickly m response to a change m voltage on an individual electrode 350
  • the SHOE 302 shown m Fig 26 also mcludes substantially transparent and electncally nonconductive layers 342a-342b,
  • Each of the electrodes 350 m the anay shown in Fig 26 is electncally coupled and configured to receive an mdividual vanable control voltage from the control circuit 304 shown in Fig 18
  • Control circuit 304 generates the variable control voltages m response to receiving a frame of image signals
  • the control circuit 304 may include a digital-to-analog converter that allows a processor (not shown) to w ⁇ te a digital value to each electrode location and to have that digital value converted to a conespondmg analog vanable control voltage that controls the amount of light diffracted mto the first or second output light
  • the control circuit may be designed to simultaneously address all the electrodes or may w ⁇ te to the electrodes m a raster fashion
  • the light source 306 shown in Fig 18, when used in connection with the SHOE 302 shown m Fig 26, ideally contains three distinct light sources, each one of which emits a primary color, (e g , red, green, or blue), of the
  • all three superimposed switchable holograms may be recorded in a smgle holographic layer
  • three separate frmge patterns are provided for the supenmposed holograms conespondmg to red, green and blue wavelengths
  • the separate fringe patterns have distinct angular acceptance charactenstics, such that a ray of light which is diffracted by one set of fringes does not also satisfy the diffraction condition for the other two fringe patterns
  • Fig 27 shows a plam view of a portion of a composite hologram which has three distinct switchable holograms 362r , 362g, and 362b recorded therein
  • the portion shown m Fig 27 represents one of the two- dimensional anay of portions of the composite and define one pixel m a polychromatic diffractive display employable m the system shown m Fig 18
  • Each sub-hologram 362r, 362g, and 362b has a different gratmg pitch such that light of distinct visible bandwidths (e g , red, green, and blue) are defined by a unique range of diffraction angles Red hght would have the largest pitch and blue the nanowest
  • Figs 28a and 28b each represent electrodes formed of visibly transparent and electncally conductive matenal, such as ITO, which are sized to fit over the holographic layer portion 360 set forth m Fig 27
  • Electrode 364 shown in Fig 28a receives a vanable control voltage from control circuit 304 shown m Fig 18 The voltage operates to activate or deactivate all three of the switchable hologram portions shown m Fig 27
  • the electrodes 364r-364b m Fig 28b are also sized to fit over aligned with the holograms 362r, 362g, and 362b, respectively, of the switchable holographic layer portion shown m Fig. 27
  • Each of the electrodes 364r-364b receives a vanable control voltage from control circuit 304 to activate or deactivate the conespondmg switchable holograms 362r-362b shown m Fig 27
  • control circuit 304 provides vanable control voltages to electrodes which causes an underlying one or more switchable electrodes to diffract one or more primary colors of the visible bandwidth
  • the diffracted light is outputted m first and second output lights 312 and 314
  • a viewer who is lme with one of the first and second output lights views the diffracted light
  • An anay of selectively diffracting subareas of one or more switchable holograms presents an image to the viewer
  • the variable control voltage for each electrode in the diffractive display can be individually controlled thereby enabling a two-dimensional image to be created by controlling the amount of light or bnghtness produced by output lights 312 or 314

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Abstract

L'invention concerne un modulateur de l'intensité de la lumière (300) qui utilise un hologramme. Selon un mode de réalisation, le modulateur de l'intensité de lumière (300) comprend un circuit électrique (304) et un élément optique holographique (302) renfermant l'hologramme. Cet élément reçoit une tension variable et est couplé électriquement à cette dernière qui est générée par le circuit électrique. En outre, l'élément optique holographique reçoit une lumière d'entrée (310) provenant d'une source de lumière (306). Ledit élément reçoit et diffracte la lumière d'entrée pour produire des première (312) et seconde (314) lumières de sortie. Une intensité de la première lumière de sortie varie directement avec l'ampleur de la tension. Une intensité de la seconde lumière de sortie varie indirectement avec l'ampleur de la tension. Les première et seconde lumières de sortie définissent un angle non nul (316) entre elles.
PCT/US1999/024250 1998-10-16 1999-10-15 Systeme et procede de modulation de l'intensite de la lumiere WO2000062104A1 (fr)

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AU12092/00A AU1209200A (en) 1998-10-16 1999-10-15 System and method for modulating light intensity

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US10461698P 1998-10-16 1998-10-16
US60/104,616 1998-10-16
US31291199A 1999-05-17 1999-05-17
US09/312,911 1999-05-17

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PCT/US1999/024250 WO2000062104A1 (fr) 1998-10-16 1999-10-15 Systeme et procede de modulation de l'intensite de la lumiere

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002084384A1 (fr) * 2001-04-13 2002-10-24 Ut-Battelle, Llc Modulateur spatial de lumiere a reflexion monochromatique
DE102008020769B3 (de) * 2008-04-21 2009-06-25 Bundesdruckerei Gmbh Sicherheitselement mit einem elektrisch stimulierbaren Volumenhologramm sowie ein Verfahren zu seiner Herstellung
DE102008020770B3 (de) * 2008-04-21 2009-10-29 Bundesdruckerei Gmbh Sicherheitselement mit einem elektrisch stimulierbaren polarisationsabhängigen Volumenhologramm und Verfahren zu dessen Herstellung
US20220283376A1 (en) * 2021-03-05 2022-09-08 Digilens Inc. Evacuated Periodic Structures and Methods of Manufacturing
US11899238B2 (en) 2019-08-29 2024-02-13 Digilens Inc. Evacuated gratings and methods of manufacturing

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WO1991010926A1 (fr) * 1990-01-12 1991-07-25 Polaroid Corporation Hologramme en phase volume avec cristal liquide dans des microcavites entre des franges
EP0664495A1 (fr) * 1994-01-21 1995-07-26 Sharp Kabushiki Kaisha Dispositif holographique commutable
WO1998004650A1 (fr) * 1996-07-12 1998-02-05 Science Applications International Corporation Matieres d'hologrammes volumiques commutables et dispositifs
US5748272A (en) * 1993-02-22 1998-05-05 Nippon Telegraph And Telephone Corporation Method for making an optical device using a laser beam interference pattern

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Publication number Priority date Publication date Assignee Title
WO1991010926A1 (fr) * 1990-01-12 1991-07-25 Polaroid Corporation Hologramme en phase volume avec cristal liquide dans des microcavites entre des franges
US5748272A (en) * 1993-02-22 1998-05-05 Nippon Telegraph And Telephone Corporation Method for making an optical device using a laser beam interference pattern
EP0664495A1 (fr) * 1994-01-21 1995-07-26 Sharp Kabushiki Kaisha Dispositif holographique commutable
WO1998004650A1 (fr) * 1996-07-12 1998-02-05 Science Applications International Corporation Matieres d'hologrammes volumiques commutables et dispositifs

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002084384A1 (fr) * 2001-04-13 2002-10-24 Ut-Battelle, Llc Modulateur spatial de lumiere a reflexion monochromatique
US6552842B2 (en) 2001-04-13 2003-04-22 Ut-Battelle, Llc Reflective coherent spatial light modulator
DE102008020769B3 (de) * 2008-04-21 2009-06-25 Bundesdruckerei Gmbh Sicherheitselement mit einem elektrisch stimulierbaren Volumenhologramm sowie ein Verfahren zu seiner Herstellung
DE102008020770B3 (de) * 2008-04-21 2009-10-29 Bundesdruckerei Gmbh Sicherheitselement mit einem elektrisch stimulierbaren polarisationsabhängigen Volumenhologramm und Verfahren zu dessen Herstellung
US11899238B2 (en) 2019-08-29 2024-02-13 Digilens Inc. Evacuated gratings and methods of manufacturing
US20220283376A1 (en) * 2021-03-05 2022-09-08 Digilens Inc. Evacuated Periodic Structures and Methods of Manufacturing

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