Classifications

• • 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
  • G02F1/29—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 position or the direction of light beams, i.e. deflection
  • G02F1/31—Digital deflection, i.e. optical switching
• • 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
  • 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
  • G02F1/133615—Edge-illuminating devices, i.e. illuminating from the side
• • 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
  • G02F2203/00—Function characteristic
  • G02F2203/06—Polarisation independent

Definitions

• Active LCDs which are the most common LCDs in use, contain substrates, a liquid crystal layer through which light passes, and a pixel electrode on one of the substrates that supplies an electric field to liquid crystal layer to form a light guide panel.
• the metal used to fabricate the pixel electrode depends on the type of LCD used. Reflective LCDs use a natural or artificial light source located outside the LCD and thus the material used for the pixel electrodes has to be a reflective conductive material such as metal aluminum. However, if the external light intensity is not strong enough, the image displayed by the reflective LCD is poor.
• PDLC Polymer dispersed liquid crystal
• PDLC is a photoelectric material that transmits light through the material when a voltage is applied to the structure and renders the structure relatively opaque by scattering the incident light when no voltage is applied.
• PDLC is a mixture of monomers or oligomers with liquid crystal molecules, and then polymerizing the monomers/oligomers to form a polymer.
• the liquid crystal molecules aggregate to form micro-droplets and are dispersed in the polymer matrix under certain conditions.
• a method of manufacturing a holographic polymer dispersed liquid crystal includes: blending monomers and liquid crystals to form a mixture; filling the mixture into a cavity between two joined glass substrates; exposing the joined substrates to intersecting coherent radiation beams of sufficient intensity and for a sufficient amount of time to initiate polymerization in high intensity regions of an interference pattern and permit the liquid crystal to diffuse to the low intensity regions, saturate and precipitate aggregates, the phase separation, depending upon the concentration of liquid crystal and polymer; and flooding the exposed mixture with a beam of uniform radiation to surround the liquid crystal aggregates with a cured polymer matrix in which a refractive index of the aggregates is equal to a refractive index of the matrix without a voltage being applied to the flooded mixture.
• FIGS. 5(a) and 5(b) show a transmission and reflection optical switches, respectively.
• FIGS. 6(a) and 6(b) show a conventional optical switch with different voltages applied.
• FIGS. 7(a) and 7(b) show an optical switch according to an embodiment of the present invention with different voltages applied.
• the light from the light source is supplied to the LCD through the light guide layer and the transparent substrate of the LCD.
• no switch is provided between the light source and the liquid crystal panel.
• a mechanical switch could be used, such a switch is relatively bulky and adds considerable weight to the device in which the LCD and switch is housed.
• the HPDLC is disposed adjacent to the light guide as shown and described below in Fig. 4.
• the HPDLC is disposed laterally near an end of the light guide rather than under the light guide.
• the former arrangement will be referred to hereinafter as an end mounted HPDLC while the latter arrangement will be referred to as a surface mounted HPDLC.
• This decreases the thickness of the structure and permits a HPDLC to be used without substantially (if at all) increasing the size of the overall device due to other electronic components being placed in a similar fashion nearby. Such a structure also permits the diverted light to be used elsewhere if desired.
• using conventional HPDLCs still engender the polarization problem above.
• FIG. 9(a) One example of such a conventional HPDLC is shown in Fig. 9(a), in which the response of the grating is dependent on the polarization.
• the diffraction efficiency decreases from about 15% to under 5% for s polarized laser light of 442 nm as the applied voltage increases from 0V to 40 V.
• the diffraction efficiency for p polarized light decreases from close to 100% to almost 0%.
• the transmission efficiency for the conventional HPDLC increases from 85% to over 95% and from 0% to almost 100% for s and p polarized light, respectively, and thus requires a relatively large voltage to be applied for transmission of both polarizations.
• Polymerization of the polymerizable liquid crystal material is achieved, for example, by exposure to coherent radiation.
• Lasers are commonly used as the irradiation source.
• UV, visible or IR wavelengths may be used, as may X-rays, gamma rays or other high energy particles, for example, ions or electrons.
• the radiation may be photolithography radiation, i.e. radiation used in standard photolithographic processes, which may include exposure through a phase mask.
• the mixture may additionally include photo-initiators, surfactants, and other components. If a photo-initiator is present, the photo-initiator will absorb at the wavelength of the radiation when polymerizing.
• Expanding the laser beam 201 permits the entire area of the grating structure 214 to be covered by the expanded laser beam 203 giving a column with cross-sectional area of about 100 cm 2 in one embodiment.
• the large exposure area brings additional benefits, such as more precise control over the power density of the exposure and thus loose fabrication tolerance and high efficiency.
• a beam splitter 210 then splits the expanded laser beam 203 into two mutually coherent beams, which are then directed by mirrors 212 onto the grating structure 214.
• the two beams may or may not be identical.
• High quality front-surface mirrors may be used.
• a typical laser power used to produce the present HPDLC structures is about 10 W to about 500 mW when the wavelength is in the UV region. Typical curing times for the present HPDLC structures are about 1 second to about 300 seconds.
• the polymer syrup cell containing homogeneous mix of liquid crystals and monomers and/or oligomers, as well as photo-initiators and surfactants, is put in the center of interference area.
• the photopolymers polymerize and the mixture undergoes a phase separation, creating regions densely populated by liquid crystal droplets, interspersed with regions of clear polymer.
• the electrically switchable gratings are formed by a microphase separation of small-molecule liquid crystals from a polymerizing organic matrix with a holographically defined periodic pattern.
• the polymerization is initiated by photo exposure in the high light intensity areas of the interference pattern.
• liquid crystal droplet refers merely to an aggregate of liquid crystals rather than a particular shape such as a teardrop or spherical shape.
• the interference of the two plane waves in the medium can be described as a sum of two electric fields.
• the optical intensity square of field amplitude
• the intensity is quadrupled in the high light intensity areas. This is to say that the intensity is 4I 0 when constructive interference occurs and the intensity is zero when destructive interference occurs.
• constructive interference occurs when the wave amplitudes add to produce a maximum in the high light intensity areas
• destructive interference occurs when the wave amplitudes cancel each other to produce a minimum in the low light intensity areas.
• the monomers In the high light intensity areas, the monomers begin linking with one another to form polymer chains. There is little polymerization at the low light intensity areas. Other monomers or oligomers diffuse into these bright regions to link up with the rapidly forming polymers chains.
• the liquid crystal diffuses to the low light intensity areas, which saturate and precipitate droplets that grow in size as the diffusion process continues.
• a time shutter is used to remotely control exposure time.
• the whole mixture is flooded with uniform light to completely surround the liquid crystal droplets with fully cured polymer matrix, resulting in a solid grating layer.
• the alternating liquid crystal-rich and liquid crystal-depleted regions form the fringe planes of the grating.
• Typical sources of the uniform light include lasers or conventional UV lights.
• the Bragg grating exhibits very high diffraction efficiency, which is then controlled by the magnitude of the electric field applied across the HPDLC layer.
• the clouds of droplets are "seen” as a homogenous region with an effective index (n LCM ) different from that of the interspersed polymer regions (n p ).
• the basic parameters are shown in the examples of Figs. 4(a) and 4(b): grating period A (also called grating pitch), refractive index modulation, slant angle ⁇ , and grating vector K, which will be described later.
• the HPDLCs created may be categorized into two types: transmission holograms and reflection holograms, which are illustrated in Figs. 5(a) and 5(b), respectively.
• transmission holograms the incident and diffracted beams are disposed at opposite sides of the grating.
• reflection grating the incident and diffracted beams are disposed on the same side of the grating.
• the grating is shown as containing a single layer of material that includes polymerized photopolymers and liquid crystal aggregates, multiple layers containing different materials may be used. Such layers may contain either or both different polymerized photopolymers and liquid crystal aggregates, each of which may be formed from materials and/or compositions different from one or more of the other layers.
• n, (2f c / ⁇ )(n LCM -n p )sin( ⁇ ) (2)
• f c is the volume fraction of phase-separated liquid crystal in the grating
• n p is the polymer index
• n LCM is the average index of liquid crystal droplets
• ⁇ is the fraction of grating period A occupied by the liquid crystal droplets.
• the passband width of the filter may be calculated according to following equation:
• the passband frequency is about 300 nm, broad enough to pass light from an LED without substantial attenuation.
• the refractive index of the polymer regions can be matched to the average index of the liquid crystal droplets without the application of an external electric field across the matrix.
• the polarization sensitivities may be compensated.
• the grating structure is picked to get close diffraction angle for both polarizations, and then the materials are chosen to compensate.
• a polymer having a relatively high refractive index and the ability to polymerize well is selected before the liquid crystal material is chosen.
• Relatively high refractive index polymers used here have a refractive index of larger than about 1.55, and preferably larger than about 1.58.
• the relatively high index of refraction of the polymerized photopolymer is sufficient to match the effective refractive index of the liquid crystal aggregates when the electrodes have the same potential.
• Cholesteric liquid crystals are generally selected for the optical switch rather than nematic liquid crystals due to the polarization-insensitive refractive index.
• Examples of chiral dopants are Merck C15, CB15, ZLI-811, ZLI 3786, ZLI-4571, ZLI-4572, MLC-6247, and MLC-6248, also available from EM Industries of Hawthorne, N.Y.
• HPDLC syrups were obtained by mixing the photopolymer formulations with liquid crystals. The liquid crystal level as a weight percentage of the total syrup range from about 35-75%, and more particularly from about 45-60%.
• Materials formulations and performance data are listed below in Table 1 where example 1 is a traditional HPDLC cell and example 2 is a traditional HPDLC cell based on commercially available Cholesteric liquid crystals BL 118.
• Example 3 is a HPDLC cell of the present application based on commercially available BL118.
• the light source was a 460 nm laser for the measurements.
• Table 1 Examples of HPDLC samples and the resulting diffraction characteristics [0067] As shown in Table 1 , using the third syrup, a simple holographic optical switch may be obtained without increasing the cost of materials or fabrication from conventional HPDLC gratings.
• the third syrup contains two types of liquid crystals of different weight percentages, although more could be used and the weight percentages equal, as desired.
• the holographic cell is 6 ⁇ m thick and exhibits substantially uniform transmission and diffraction for both the S and P polarizations at the same voltage. Note that as the thickness of the grating is reduced, the index of refraction increases, resulting in a larger usable wavelength range.
• the light source 802 may be any backlight used in LCD displays, such as an LED, EL or fluorescent lamp. LEDs are generally used as they are efficient in terms of power and size.
• a wideband light source such as a white LED, covers at least about 400 to 800 nm, i.e. the visible wavelength regime. This permits a color LCD to be used (color filters are present but not shown in the figures) and simultaneous allows white light to be used externally if desired. Either single LEDs such as red, blue, or green LEDs, or combinations of LEDs may be used. If a blue (or perhaps green) LED is used, phosphor may be disposed on one or more surfaces of the optical switch, or inside the optical switch, to absorb the light and emit light with other colors such as yellow.
• the LED light passes through the polymer matrix and liquid crystal droplets, either being transmitted or diffracted, before impinging upon the phosphor.
• the gratings may be designed to transmit and/or diffract from about 190 nm to about 2 ⁇ m.
• Light from the LED 802 impinges on the holographic optical switch 804 disposed adjacent to the LED 802.
• a reflector, focusing lens or housing (not shown) of some type can surround the LED 802 and reflect or focus light from the LED 802 directed away from the holographic optical switch 804 back towards the holographic optical switch 804.
• the LED 802, holographic optical switch 804, and light guide 806 are substantially planar with each other.
• the arrangements shown in Fig. 8 permit easy coupling of light into the LCD.
• the light guide 806 may be formed from plastic or any other material used in LCDs and may be formed using any known light guide structure.
• the LED 802 and LCD are shown as being separate, they may be attached to each other.
• Light entering the light guide 806 enters the LCD panel from the underside of the LCD panel in contact with the top of the light guide 806. As shown, light in the light guide 806 may be reflected numerous times before being completely introduced to the LCD panel.
• the LCD panel includes polarizers 808, a liquid crystal layer 810 and numerous other known layers not shown.
• These layers include, but are not limited to, transparent substrates on which the polarizers 808 are disposed and between which the liquid crystal layer 810 is disposed, transparent and reflective electrodes that serve to apply an electric field to the liquid crystal layer 810 for example, layers to form and protect thin film transistors, and color filter layers that divide unit cells of the LCD into pixels of multiple colors (usually red, green, blue and perhaps white).

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• Nonlinear Science (AREA)
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• Dispersion Chemistry (AREA)
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• Crystallography & Structural Chemistry (AREA)

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• 2005
  • 2005-05-19 JP JP2007527537A patent/JP4889643B2/ja not_active Expired - Fee Related
  • 2005-05-19 WO PCT/US2005/017994 patent/WO2005114310A2/en not_active Ceased
  • 2005-05-19 EP EP05754190A patent/EP1766462A4/en not_active Withdrawn

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