EP1766462A4 - Optical switching device using holographic polymer dispersed liquid crystals - Google Patents
Optical switching device using holographic polymer dispersed liquid crystalsInfo
- Publication number
- EP1766462A4 EP1766462A4 EP05754190A EP05754190A EP1766462A4 EP 1766462 A4 EP1766462 A4 EP 1766462A4 EP 05754190 A EP05754190 A EP 05754190A EP 05754190 A EP05754190 A EP 05754190A EP 1766462 A4 EP1766462 A4 EP 1766462A4
- Authority
- EP
- European Patent Office
- Prior art keywords
- liquid crystal
- optical switch
- light
- electrodes
- hpdlc
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
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
- This invention is related generally to an optical device that can switch the direction of impinging light. More particularly, the present invention is related to a holographic optical switch containing polymer dispersed liquid crystals in liquid crystal displays and other electronics.
- LCDs have many advantages over other types of displays. LCDs provide high picture quality in a small volume and are lightweight. In addition, LCDs have comparatively low power consumption, which is dependent on the type of LCD. This has caused the portable electronic market to focus on LCD use for such applications as small portable televisions, mobile telephones and other communication products, video recording units, notebook computers, and desktop monitors.
- 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.
- an intrinsic light source generally called a backlight is added to the liquid guide panel.
- the backlight is supplied to the liquid crystal layer from a fluorescent lamp, light emitting diode (LED), or electroluminescent diode (EL).
- the backlight is located behind the display requiring the material used for the pixel electrodes has to be a transparent conductive material such as indium tin oxide (ITO).
- ITO indium tin oxide
- the backlight also consumes the most power in the LCD, severely decreasing battery life if constantly used.
- the pixel electrodes are usually a combination of aluminum in one location and ITO in another location. This permits external light to be used as the light source when the external light is of high enough intensity to provide a good image and the backlight to be used as the light source when the external light is not of high enough intensity. However, the area in which images can be displayed is reduced in both the transmittance and reflectance modes in a transflective LCD.
- 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.
- the PDLC layer is placed directly below the liquid crystal panel between the backlight and the liquid crystal panel so that, in the reflectance mode when no voltage is applied to the PDLC layer external light is scattered and the liquid crystal display is illuminated and, in the transmission mode when a voltage is applied to the PDLC layer, the PDLC is transparent and allows light from the backlight (which extends over the surface area) directly there beneath to illuminate the liquid crystal layer.
- the backlight In other transflective LCDs, however, the backlight not directly below the liquid crystal panel. Instead, the backlight is adjacent to a light guide layer beneath the liquid crystal layer. The light guide layer guides light into the liquid crystal layer. PDLC layers have not been used with these structures.
- PDLC layers have not been used with these structures.
- One readily apparent example is the use of an internal light source to illuminate an area in front of the electronic device without the need for an additional light source. More particularly, for cellular telephones having cameras, the backlight can be used, for example, to illuminate a subject to be photographed and enable a viable picture or series of pictures to be taken.
- no structure or optical switch exists that provides this ability within the required tolerances of the small electronics, e.g. cost, size, weight, ruggedness, and minimal power consumption.
- the present embodiments provide an optical switch that may be preferable to use in small electronic devices, in addition to being used elsewhere.
- the optical switch transmits light from a wideband light source such as a light emitting diode (LED) through the optical switch without application of a voltage to the switch without substantial attenuation over the entire wavelength range of the light source.
- the switch is compact enough to fit in a camera cellular phone, for example, without adding appreciable size and is light enough to not add noticeable weight.
- the switch is polarization independent, transmitting and diffracting light of both s and p polarizations without substantial loss.
- the switch is also non- mechanical inasmuch as no shutters or other components need be used, thereby affording application of a rugged component that is not easily misaligned or broken if the electronic device is dropped or otherwise subject to a physical shock.
- the optical switch of one embodiment includes opposing substrates, electrodes disposed between the substrates, and a Bragg grating disposed between the electrodes.
- the Bragg grating contains regions of polymerized photopolymers and liquid crystal aggregates. Refractive indexes of the photopolymers and liquid crystals are substantially the same when the electrodes have the same potential.
- a liquid crystal display device that includes the optical switch of one of the embodiments of the present invention also contains a liquid crystal display having opposing substrates, electrodes on the substrates, a liquid crystal layer between the electrodes, polarizers disposed on opposite sides of the substrates as the liquid crystal layer and a light guide disposed on one of the polarizers.
- An optical switch is disposed between the light guide and a light source.
- the optical switch contains opposing optical switch substrates, optical switch electrodes disposed between the optical switch substrates, and a Bragg grating disposed between the electrodes.
- the Bragg grating has regions of a polymerized photopolymer and liquid crystal aggregates and is substantially polarization independent.
- a method of manufacturing the liquid crystal device includes both placing an LED and a holographic polymer dispersed liquid crystal (HPDLC) adjacent to each other, and adjusting the HPDLC such that light from the light source that has entered the HPDLC is transmitted directly through the HPDLC without being substantially diffracted without a voltage being applied to the HPDLC.
- HPDLC holographic polymer dispersed liquid crystal
- 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.
- FIG. 1 illustrates an embodiment of the present invention.
- FIG. 2 shows a schematic of the optic experimental setup for fabrication of an HPDLC according to the embodiment, in which mirrors are mounted on rotation stages.
- FIG. 3 shows a close up view of the crossing area of the split beams on the grating structure of FIG. 2.
- FIGS. 4(a) and 4(b) show detailed grating structures and design parameters.
- 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.
- FIGS. 8(a) and 8(b) show an LCD according to an embodiment of the present invention with different voltages applied.
- FIGS. 9(a), 9(b), and 9(c) show diffraction efficiencies vs. applied voltages for a conventional HPDLC, and HPDLCs according to embodiments of the present invention.
- 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.
- HPDLCs may be integrated in the device to provide switching and alleviate a number of problems.
- the present HPDLCs dramatically decrease the response time of the switch: a mechanical switch has a typical response time of 10-20 milliseconds, whereas the present HPDLC has a response time of 10 ⁇ s to 1-2 milliseconds, i.e. one to three orders of magnitude faster.
- time-to- failure is also much longer.
- a HPDLC can be placed between the light source and light guide so that the liquid crystal display includes the liquid crystal panel, light guide, HPDLC, light source and opaque reflector below the light source to reflect light from the light source back towards the HPDLC
- other embodiments may be more suitable for miniaturized electronics.
- 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.
- an optical switch that is mechanically stable and uses low power can be formed.
- the holographic optical switch is ideal for use in portable electronics or other devices in which a thin, low power switch is desired.
- such an optical switch may be used to provide an additional light source for a camera cell phone, thereby enabling relatively short distance pictures to be taken without using an external light source.
- Appropriate selection of the photopolymer matrix and liquid crystals enclosed therein as well as the grating dimensions, permit the transmission through the switch to be maximized without applying a voltage to the structure while simultaneously affording a substantially polarization independent switch. This permits light from a wideband light source such as an LED to be used in the liquid crystal display.
- Light may be coupled into the light panel relatively easily in the edge structure disclosed.
- the gratings disclosed herein are relatively thin, being under 10 ⁇ m thick, and more typically 2-4 ⁇ to provide a relatively wide passband (enough to adequately transmit light from the light source without substantial attenuation, e.g. of at least about 100 ⁇ m at 10% of the maximum transmission) while having a significant diffraction efficiency at the desired applied voltage.
- HPDLCs Holographic polymer dispersed liquid crystals
- a HPDLC device 100 is fabricated by taking two parallel substrates 102 whose sides are sealed and filling the cavity formed by the combination with a mixture of photopolymers and liquid crystal materials 106, similar to a fabrication process for the liquid crystal panel in a liquid crystal display.
- the substrates 102 may be uniformly spaced using spacers (not shown) such as spherical insertions or prismatic projections.
- the substrates 102 can be formed of glass or other material that is substantially transparent to a particular wavelength range, such as the visible wavelength range from about 400 nm to about 800 nm.
- the substrates 102 may be coated with an anti-reflection coating to improve transmittance to greater than 99% at the particular wavelength range of interest.
- Examples of one or more glasses that may form the substrates 102 include BK7, FK51, LAK6, with the particular glass having very little effect on the results of the switching.
- Other materials that may be used as a substitute for or in addition to glass, for example, include quartz or plastic.
- Types of plastic substrates include, for example, polyester, such as polyethyleneterephthalate (PET), or of polyvinylalcohol (PVA), polycarbonate (PC) or triacetylcellulose (TAC).
- PET polyethyleneterephthalate
- PVA polyvinylalcohol
- PC polycarbonate
- TAC triacetylcellulose
- a birefringent substrate for example, a uniaxially stretched plastic film can also be used.
- the substrate may be covered with a rubbed polyimide.
- a birefringent substrate or rubbed polyimide may decrease the polarization dependence of the optical switch. If using a polymerizable material as the thin layer 106, the substrate may or may not be removed after polymerization. If the substrate is not removed from the polymerized film after polymerization, an isotropic substrate may be used.
- One or both substrates support transparent electrodes 104.
- the electrodes 104 may be formed from any of a wide variety of transparent films, such as indium tin oxide or indium zinc oxide films. A voltage may be supplied across the electrodes 104 to apply an electric field across the HPDLC layer 106.
- a polymerizable liquid crystal material 106 is filled into the space between two substrates containing the transparent electrode 104 and the liquid crystal material is aligned into a uniform orientation. The orientation of liquid crystal material can then be permanently fixed by the formed solid polymer structure.
- 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.
- one or more photo-initiators can be used that decomposes under UV irradiation to produce free radicals or ions that start the polymerization reaction.
- photo-initiators include Irgacure 651, Irgacure 184, Darocure 1173 or Darocure 4265 (all from Ciba Geigy AG) or UVI 6974 (Union Carbide).
- the total composition of the mixture usually includes about 0.01 to 10% by weight of the photo-initiator.
- the curing time depends on the reactivity of the polymerizable material, the thickness of the coated layer, the type of polymerization initiator and the power of the radiation source. The curing time may be as short as possible if a high throughput process is desired. Generally, the curing time is no longer than several minutes.
- the polymerizable material may also comprise one or more other suitable components, for example, catalysts, stabilizers, chain-transfer agents or co-reacting monomers.
- stabilizers may prevent undesired spontaneous polymerization of the polymerizable material, for example, during storage.
- stabilizers all compounds can be used that are known to the skilled in the art for this purpose. These compounds are commercially available in a broad variety. Typical examples for stabilizers are 4-ethoxyphenol or butylated hydroxytoluene (BHT).
- chain transfer agents can also be added to the polymerizable material in order to modify the physical properties of the polymer film.
- a chain transfer agent such as a monofunctional thiol compound like dodecane thiol, or a multifunctional thiol compound like trimethylpropane tri(3-mercaptopropionate)
- the length of the free polymer chains and/or the length of the polymer chains between two crosslinks in the inventive polymer film can be controlled.
- the amount of the chain transfer agent is increased, the polymer chain length in the obtained polymer film decreases.
- the general fabrication apparatus 200 includes a UV laser 202 that emits a laser beam 201 of a wavelength of lower than about 400 nm.
- the laser beam 201 is controlled by a shutter 204, which opens or closes according to whether or not the presence of the laser beam 201 is desired.
- the shutter(s) 204 can be placed essentially anywhere along the path of the laser beam(s) before the beams impinge on the grating structure containing the liquid material 214.
- the laser beam 201 then impinges on a polarizer 206 and the polarized laser beam 201 is then incident on a beam expander 208.
- the beam expander 208 increases the radius of the laser beam 201 to form an expanded beam 203.
- 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 Bragg grating 214 is formed through the interference between the split expanded laser beams 203 at the crossing area of the beams. A close up of the object beam and reference beam impinging on the crossing area is shown in Fig. 3.
- the diffraction grating 214 is a result of the interference pattern produced by the interaction of the polarized beams in the photopolymer dispersed in the liquid crystal. When the photopolymer is exposed to the interference pattern it itself is patterned in a like manner so that in effect the interference pattern is embedded in the cell.
- 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.
- HPDLC gratings can switch between two states as the directors of the liquid crystal molecule align with the electric field.
- the natural orientation of the liquid crystal droplets is changed from a random orientation when no electric field is applied to being aligned with an applied electric field.
- the whole composites exhibits a well-defined 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.
- the grating can switch between two states as the liquid crystal molecule align with application of an external electric field.
- the whole composite exhibits a well-defined grating.
- the refractive index of the liquid crystal droplets having an orientation perpendicular to LC-polymer interface is different from that of the polymer regions, thereby causing a modulation in the refractive index of the structure.
- the liquid crystal droplets become uniformly oriented in the same direction and, the indices of refraction of the liquid crystal droplets and polymer regions eventually become equal.
- the refractive index of the polymer regions and the average index of the liquid crystal droplets are matched only when a specific non-zero electric field is applied to the structure (hereinafter called the maximal voltage).
- an electrically switchable grating is basically a volume phase grating with diffraction properties well predicted using Kogelnik model. The diffraction properties can be modeled by assuming an index modulation given by:
- n 0 is the average refractive index
- K is the grating vector
- r is a position coordinate.
- n is the index modulation amplitude given by:
- 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.
- R is the peak reflection
- d is the grating length
- 0 is the Bragg wavelength
- the refractive index modulation typically ranges from 0.01 to 0.2 for achieving high diffraction efficiency (about 100%).
- HPDLC cell thickness (interaction length) is in the range from 1 to 25 microns.
- An optimized fabrication process uses a balanced rate of diffusion and polymerization.
- 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.
- Nematic liquid crystals which are arranged with parallel but not lateral order and thus have a constant director, cannot be used alone as the index of refraction is dependent on the focus of the major axis ae.
- Cholesteric liquid crystals are arranged at a slight angle relative to each other (rather than parallel as in the nematic). Each consecutive molecule is rotated slightly relative to the adjacent molecule, thereby having a director that rotates helically and causing the index of refraction to be dependent on the average of the focus of the major axis and semi-major axes (2 ao + ae)/3.
- adding chiral dopants to the nematic liquid crystals to twist the director of the nematic liquid crystals may permit the combination to be used.
- Photopolymers with different refractive index were formulated from many different commercially available monomers, oligomers, photo-initiators, and optionally adhesion promoters, surfactants etc.
- photopolymerization kinetics directly affect the phase separation of liquid crystals from the polymer matrix, one consideration is using a photopolymer formulation with reasonable curing speed.
- acrylate photopolymers may be preferred since they have superior curing speed compared to other photopolymers such as epoxies and vinyl ethers.
- High refractive index monomers and/or oligomers useful for this invention may comprise one or sulfur elements, bromine elements, or bisphenol A derivatives.
- Photopolymer 1 2-Ethylhexyl acrylate 52%, Ethoxylated bisphenol A diacrylate 2%, polyester tetraacrylate 17%, Phenylthioethyl acrylate 10%, Octafluoropentyl acrylate 16%, Diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide 1%, Daracure 1173 1%, Methacryoyl trimethoxysilane 1%.
- Photopolymer 2 Ethoxylated bisphenol A diacrylate 16.5%, Phenylthioethyl acrylate 64.5%, Octafluoropentyl acrylate 16%, Diphenyl(2,4,6- trimethylbenzoyl)phosphine oxide 1%, Daracure 1 173 1%, Methacryoyl trimethoxysilane 1%.
- Cholesteric liquid crystals are suited for making HPDLC devices.
- Merck offers a broad range of Cholesteric liquid crystals for HPDLC applications which may be used in the present HPDLC device when combined with the right photopolymers.
- Examples of commercially available Cholesteric liquid crystals are Merck BL112, BL118 or BL126, available from EM Industries of Hawthorne, N.Y. Adding chiral dopants into nematic liquid crystals can also make Cholesteric liquid crystals.
- 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.
- Thicknesses of as low as about 2 to about 4 ⁇ m permit sufficient wavelength ranges (see Equation (4)) to be used.
- the diffraction efficiency as a function of applied voltage of an HPDLC of Example 2 (in which chiral agents are added) is shown in Fig. 9(b).
- Fig. 9(a) shows Example 1.
- the diffraction efficiency for both s and p polarized light of laser light at 442 nm is somewhat the same.
- the diffraction efficiency essentially monotomically decreases with increasing voltage.
- the diffraction efficiency of a HPDLC of Example 3 is shown in Fig. 9(c).
- Figs. 8(a) and 8(b) illustrate an LCD display in one embodiment without a voltage applied to the optical switch and with the maximal voltage applied.
- the LCD display 800 contains a light source 802.
- 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 light from the LED 802 is transmitted through the holographic optical switch 804 when no voltage exists between the electrodes of the holographic optical switch 804 (the OFF state) and is diffracted when the voltage is applied between the electrodes of the holographic optical switch 804 (the ON state). When in the ON state, the diffracted light does not impinge on the LCD. Although not shown, the non-diffracted light, if it exists, can be transmitted to the LCD for display or other purposes. [0071]
- the LED 802 and holographic optical switch 804 are laterally aligned with a light guide 806 of the LCD such that light transmitted through the holographic optical switch 804 is transmitted towards the light guide 806 and at least some of this light eventually impinges on the light guide 806.
- 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).
- a power supply 812 such as a battery is contained within the LCD display 800.
- the power supply 812 provides power to the LED 802, the electrical driver of the optical switch 804 (thereby supplying voltage across the electrodes of the optical switch) and the LCD panel.
- This power supply may be adjustable to vary the voltage supplied, e.g. to vary the electric field in across the grating.
- power may be supplied to the various components of the LCD display 800 through an external supply.
- the LCD display 800 or other portable electronic device also contains a casing (or housing) 814 that encloses the LED 802, the optical switch 804 and the LCD among other components of the LCD display 800.
- the casing 814 has a viewing portion (not shown) that permits the LCD to be viewed by a user and a lighting portion (not shown) through which the diffracted light exits the casing 814 to the outside. This is to say that the light from the optical switch is directed to illuminate outside the casing.
- a lens can be added within the casing 814 and/or at the lighting portion of the casing 814 to collimate or focus the diffracted light within the casing 814 and/or outside of the casing 814.
- the light source 802, optical switch 804 and liquid crystal display are arranged such that when a potential difference between the electrodes of the optical switch is substantially different from zero, light from the light source 802 in the optical switch is directed substantially away from the liquid crystal display.
- the angle of the optical switch is adjusted such that when non-zero voltage at which the light from the light source is maximally refracted is applied to the optical switch, the light from the light source that has exited from the optical switch is directed adjacent to the liquid crystal panel without impinging on the liquid crystal panel.
- multiple gratings may be disposed between the light source and the light guide panel.
- These gratings may be wholly physically separate optical switches with different properties or may be multiple layers that are integrated either side-by-side or in a thickness direction in the same optical switch. If the optical switches are separate, the physical position of the grating and other grating characteristics including physical tilt angles or spatial frequencies, for example, can be different.
- the materials used in the HPDLC layers may be the same or different if the optical switches are separate or may be different if the layers are integrated into a single optical switch. This permits one or more beams of light to be deflected to different positions, if desired. No matter whether the optical switches are separate or integrated, either the same or different voltages may be applied to the HPDLC layers. For example, in an integrated optical switch, one or more of the transparent electrodes may be connected at different potentials using, say, voltage dividers.
- light sources may be used. These light sources may impinge on the same grating or different gratings, interact with the same or different light guides, and may be disposed adjacent to each other, on the same side of the liquid crystal display, or on opposing sides of the liquid crystal display.
- the liquid crystal display device includes a liquid crystal display, a light source, and the optical switch.
- the liquid crystal display has opposing substrates, electrodes on the substrates, a liquid crystal layer between the electrodes, polarizers disposed on opposite sides of the substrates as the liquid crystal layer, and a light guide disposed on one of the polarizers.
- the optical switch is disposed between the light guide and the light source.
- the optical switch contains opposing optical switch substrates, optical switch electrodes disposed between the optical switch substrates, and a diffraction grating disposed between the electrodes.
- This diffraction grating includes regions of a polymerized photopolymer having a refractive index and liquid crystal aggregates having an effective refractive index substantially the same as the refractive index of the polymerized photopolymer when the electrodes have the same potential.
- a power supply is connected to the electrodes of the optical switch.
- the grating may be substantially polarization independent.
- the light source, optical switch and liquid crystal display may be arranged such that when substantially no potential difference exists between the electrodes of the optical switch, light from the light source is transmitted through the optical switch towards the light guide.
- the light source, optical switch and liquid crystal display may be arranged such that when a potential difference between the electrodes of the optical switch is substantially different from zero, light from the light source in the optical switch is directed substantially away from the liquid crystal display.
- the light source and light guide are planar with each other.
Landscapes
- Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Chemical & Material Sciences (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Liquid Crystal (AREA)
- Dispersion Chemistry (AREA)
- Mathematical Physics (AREA)
- Crystallography & Structural Chemistry (AREA)
Abstract
Description
Claims
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/850,713 US20050259216A1 (en) | 2004-05-20 | 2004-05-20 | Optical switching device using holographic polymer dispersed liquid crystals |
US10/850,714 US7301601B2 (en) | 2004-05-20 | 2004-05-20 | Optical switching device using holographic polymer dispersed liquid crystals |
PCT/US2005/017994 WO2005114310A2 (en) | 2004-05-20 | 2005-05-19 | Optical switching device using holographic polymer dispersed liquid crystals |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1766462A2 EP1766462A2 (en) | 2007-03-28 |
EP1766462A4 true EP1766462A4 (en) | 2008-08-13 |
Family
ID=35429017
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP05754190A Withdrawn EP1766462A4 (en) | 2004-05-20 | 2005-05-19 | Optical switching device using holographic polymer dispersed liquid crystals |
Country Status (3)
Country | Link |
---|---|
EP (1) | EP1766462A4 (en) |
JP (1) | JP4889643B2 (en) |
WO (1) | WO2005114310A2 (en) |
Families Citing this family (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
KR101718370B1 (en) * | 2010-09-29 | 2017-03-22 | 동우 화인켐 주식회사 | Solid polymer electrolyte composition and electrochromic device using the same |
KR101716799B1 (en) * | 2010-09-29 | 2017-03-16 | 동우 화인켐 주식회사 | Gel polymer electrolyte composition and electrochromic device using the same |
WO2013027004A1 (en) * | 2011-08-24 | 2013-02-28 | Milan Momcilo Popovich | Wearable data display |
TWI776898B (en) * | 2018-05-18 | 2022-09-11 | 揚明光學股份有限公司 | Manufacturing method of a pattern generating device, and the pattern generating device manufactured thereby |
CN109633918A (en) * | 2019-01-11 | 2019-04-16 | 浙江大学 | Time division multiplexing 3D glasses based on holographic polymer dispersed liquid crystal grating |
CN111381395B (en) * | 2020-01-21 | 2023-11-28 | 奥提赞光晶(山东)显示科技有限公司 | Electric control continuous zoom lens, preparation method and exposure system |
Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP1211869A1 (en) * | 2000-11-30 | 2002-06-05 | Siemens Aktiengesellschaft | Videocamera with integrated illumination system for a videophone |
JP2002311435A (en) * | 2001-04-18 | 2002-10-23 | Matsushita Electric Ind Co Ltd | Liquid crystal display and imaging system |
US20030058400A1 (en) * | 2001-09-26 | 2003-03-27 | Songlin Zhuang | Liquid crystal based optical switch utilizing diffraction |
US6646772B1 (en) * | 1999-09-14 | 2003-11-11 | Digilens, Inc. | Holographic illumination system |
JP2004140436A (en) * | 2002-10-15 | 2004-05-13 | Kyocera Corp | Portable terminal with camera |
Family Cites Families (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US5594560A (en) * | 1994-03-07 | 1997-01-14 | Motorola, Inc. | Display device comprising fluorescent enhanced reflective holographic illumination |
JPH1048605A (en) * | 1996-08-07 | 1998-02-20 | Fuji Xerox Co Ltd | Light control element and its production |
US6172792B1 (en) * | 1997-01-31 | 2001-01-09 | Mary Lou Jepsen | Method and apparatus for forming optical gratings |
US6317228B2 (en) * | 1999-09-14 | 2001-11-13 | Digilens, Inc. | Holographic illumination system |
US6574487B1 (en) * | 2000-02-23 | 2003-06-03 | Motorola, Inc. | Communication device with a dual-sided liquid crystal display |
JP2001324322A (en) * | 2000-05-15 | 2001-11-22 | Olympus Optical Co Ltd | Range finder |
KR100490816B1 (en) * | 2001-06-15 | 2005-05-24 | 샤프 가부시키가이샤 | Micro corner cube array, method of making the micro corner cube array and reflective type display device |
US6861015B2 (en) * | 2001-07-20 | 2005-03-01 | Au Optronics Corporation | Method of integrally forming light-guide and polarizer |
-
2005
- 2005-05-19 EP EP05754190A patent/EP1766462A4/en not_active Withdrawn
- 2005-05-19 JP JP2007527537A patent/JP4889643B2/en not_active Expired - Fee Related
- 2005-05-19 WO PCT/US2005/017994 patent/WO2005114310A2/en active Application Filing
Patent Citations (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US6646772B1 (en) * | 1999-09-14 | 2003-11-11 | Digilens, Inc. | Holographic illumination system |
EP1211869A1 (en) * | 2000-11-30 | 2002-06-05 | Siemens Aktiengesellschaft | Videocamera with integrated illumination system for a videophone |
JP2002311435A (en) * | 2001-04-18 | 2002-10-23 | Matsushita Electric Ind Co Ltd | Liquid crystal display and imaging system |
US20030058400A1 (en) * | 2001-09-26 | 2003-03-27 | Songlin Zhuang | Liquid crystal based optical switch utilizing diffraction |
JP2004140436A (en) * | 2002-10-15 | 2004-05-13 | Kyocera Corp | Portable terminal with camera |
Also Published As
Publication number | Publication date |
---|---|
EP1766462A2 (en) | 2007-03-28 |
JP2007538293A (en) | 2007-12-27 |
WO2005114310A3 (en) | 2006-08-03 |
JP4889643B2 (en) | 2012-03-07 |
WO2005114310A2 (en) | 2005-12-01 |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US7301601B2 (en) | Optical switching device using holographic polymer dispersed liquid crystals | |
US6317189B1 (en) | High-efficiency reflective liquid crystal display | |
TWI637200B (en) | Illumination apparatus for a liquid-crystal display | |
US6211976B1 (en) | Holographic projection system | |
US6657700B2 (en) | Reflection-type and transmission-type liquid crystal display devices | |
US5748272A (en) | Method for making an optical device using a laser beam interference pattern | |
US6646772B1 (en) | Holographic illumination system | |
US6661495B1 (en) | Pancake window display system employing one or more switchable holographic optical elements | |
US7515232B2 (en) | Arrangements in a transflective liquid crystal display with patterned optical foil | |
KR101625089B1 (en) | Transflective display apparatus | |
US6678078B1 (en) | Optical filter employing holographic optical elements and image generating system incorporating the optical filter | |
JP3506978B2 (en) | Reflective liquid crystal display | |
WO2005114310A2 (en) | Optical switching device using holographic polymer dispersed liquid crystals | |
US20060216434A1 (en) | Polymer dispersed liquid crystal device and method of manufacturing the same | |
US20050259216A1 (en) | Optical switching device using holographic polymer dispersed liquid crystals | |
US6339486B1 (en) | Holographic technique for illumination of image displays using ambient illumination | |
Sutherland et al. | Switchable holograms for displays and other applications | |
JP3162762B2 (en) | Display element | |
US20020005930A1 (en) | A liquid crystal layer including a dichroic dye | |
Yuan et al. | HPDLC color reflective displays | |
KR20040052451A (en) | Substrate with cholesteric layer and display having the substrate | |
US20050237589A1 (en) | Optical filter employing holographic optical elements and image generating system incorporating the optical filter | |
JP3717016B2 (en) | Reflective liquid crystal display device using hologram | |
JP3506405B2 (en) | Optical element and display device | |
JP2001181316A (en) | Photopolymerizable composition, optically functional film using same, and method for producing optically functional film |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
17P | Request for examination filed |
Effective date: 20061218 |
|
AK | Designated contracting states |
Kind code of ref document: A2 Designated state(s): AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IS IT LI LT LU MC NL PL PT RO SE SI SK TR |
|
DAX | Request for extension of the european patent (deleted) | ||
A4 | Supplementary search report drawn up and despatched |
Effective date: 20080715 |
|
RIC1 | Information provided on ipc code assigned before grant |
Ipc: H04M 1/02 20060101ALI20080710BHEP Ipc: G02F 1/13 20060101AFI20070124BHEP Ipc: G02F 1/1335 20060101ALI20080710BHEP |
|
17Q | First examination report despatched |
Effective date: 20081106 |
|
STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN |
|
18D | Application deemed to be withdrawn |
Effective date: 20090519 |