JP2008139684A - Polarization converting element and polarization conversion device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin inexpensive polarization conversion element and a polarization conversion device capable of controlling polarization conversion. <P>SOLUTION: The polarization conversion element includes a lens array layer 7 having a function of splitting incident light into a first polarization component and a second polarization component and a function of condensing at least one polarization component among the above polarization components, and a polarization conversion layer 6 in which a polarization rotating region and a polarization non-rotating region are periodically formed, wherein the lens array layer 7 comprises a pair of substrates, an electrode disposed on at least one of the pair of substrates and capable of applying an electric field between the pair of substrates, and a liquid crystal 8 disposed between the pair of substrates and capable of controlling the distribution of refractive index by the electric field applied by the electrode. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a polarization conversion element and a polarization conversion device.

A conventional polarization conversion element will be described.
In general, in a light valve that displays an image by light modulation of specific polarization like a liquid crystal panel, illumination light other than the specific polarization is absorbed by the polarizing plate on the incident side. Half of the light is lost. In order to solve this problem and improve the light utilization efficiency, various illumination optical systems that perform polarization conversion by polarization separation and polarization rotation have been proposed. Optical elements used for polarization separation include PBS (Polarizing Beam Splitter) prism, PBS array, microprism array, birefringent DOE (Diffractive Optical Element), etc., and optical elements used for polarization rotation are ½ wavelength. Examples thereof include a plate and a TN (Twisted Nematic) liquid crystal.

  Random polarized light is separated into two types of linearly polarized light whose polarization planes (that is, vibration planes of electric vectors) are orthogonal to each other in polarization separation. It becomes a polarization state. By this polarization conversion, only linearly polarized light having a uniform polarization plane can be made incident on the incident side polarizing plate. Therefore, there is almost no light loss due to the incident side polarizing plate, and illumination with high light utilization efficiency can be achieved for the light valve.

The following prior art examples are known for the polarization conversion element.
Patent Document 1 discloses a “polarization conversion element and a display device using the polarization conversion element”. As shown in FIG. 1 of Patent Document 1, the present invention has a microlens array for converging incident light, a birefringent film having birefringence composed of an alignment liquid crystal layer, and a stripe-shaped wavelength in the liquid crystal layer. It is characterized by having a liquid crystal wave plate in which portions having no plate function and wave plate function are alternately arranged at a constant pitch.
However, in the polarization conversion element of Patent Document 1, since a birefringent layer is used for the polarization separation portion, it is not necessary to form a fine structure like a diffraction grating, but the cost can be increased due to the fine structure. There is sex.

With respect to the liquid crystal lens, the following prior art examples are disclosed.
Non-Patent Document 1 discloses a “liquid crystal microlens” that can move the focal point in a direction other than the optical axis direction by using a liquid crystal microlens having an electrode division structure to make the electric field distribution asymmetric. .

  In Patent Document 2, a polymer by photopolymerization is formed in a nematic liquid crystal. A “liquid crystal microlens” having a memory property and having variable lens characteristics is disclosed.

  In Patent Documents 3 and 4, a liquid crystal microlens in which circular hole-patterned electrodes are arranged in an array is used to make a lens having a variable focal length, and the light coupling efficiency of the optical interconnection element is made variable and divided. An “optical coupler” is disclosed in which the focal position can be controlled by an electrode.

However, in each of the related art examples relating to the above-described liquid crystal lens (Non-patent Document 1, Patent Documents 2 to 4), there is no configuration that adds a polarization conversion function.
JP 2000-171633 A Japanese Patent No. 3016744 JP-A-11-109303 JP-A-11-109304 “O plus E, October 1998 issue, published by New Technology Communications Inc., Susumu Sato“ Liquid Crystal Microlens ””

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a thin and low-cost polarization conversion element and a polarization conversion device capable of controlling polarization conversion.

  In order to achieve such an object, the invention described in claim 1 is characterized in that incident light is separated into a first polarization component and a second polarization component, and at least one of the polarization components is condensed. In a polarization conversion element having a lens array layer having a function to perform and a polarization conversion layer that periodically forms a polarization rotation region and a polarization non-rotation region, the lens array layer includes a pair of substrates and a pair of substrates. An electrode provided on at least one of the substrates and capable of applying an electric field between the pair of substrates, and a liquid crystal provided between the pair of substrates and capable of controlling the refractive index distribution by the electric field applied by the electrodes, It is characterized by having.

  The invention according to claim 2 is the second place of the invention according to claim 1, wherein the polarization conversion layer includes at least a liquid crystal composition comprising a pair of substrates, a polymerizable liquid crystal, and a photopolymerization initiator, and a pair of An alignment film provided on each of the substrates and for aligning the liquid crystal composition between the pair of substrates.

  A third aspect of the invention is characterized in that, in the first aspect of the invention, the polarization conversion layer has a periodic structure of a birefringent region and an isotropic region.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the liquid crystal of the lens array layer is a liquid crystal composition containing at least a polymerizable liquid crystal.

  According to a fifth aspect of the present invention, there is provided an electric field capable of switching an electric field application direction or an electric field application timing of the polarization conversion element according to any one of the first to fourth aspects and an electrode provided in the polarization conversion element. And an application control means.

  The invention described in claim 6 includes the polarization conversion element according to any one of claims 1 to 4 and a polarization separation layer provided between the lens array layer and the polarization conversion layer of the polarization conversion element. The polarization separation layer includes a pair of substrates, an electrode capable of applying an electric field between the pair of substrates, and an electric field application control unit capable of switching an electric field application direction or an electric field application timing of the electrodes. It is characterized by.

  The invention according to claim 7 is the invention according to claim 6, wherein the polarization separation layer comprises a composition comprising at least a non-polymerizable liquid crystal, a polymerizable monomer or a prepolymer, and a photopolymerization initiator. A holographic polymer-dispersed liquid crystal layer in which a periodic phase separation structure of a layer mainly composed of a polymer and a layer mainly composed of a non-polymerizable liquid crystal is formed by subjecting an object to two-beam interference exposure. To do.

  According to the present invention, it is possible to provide a thin and low-cost polarization conversion element and a polarization conversion device capable of controlling polarization conversion.

  The best mode for carrying out the present invention will be described below in detail with reference to the accompanying drawings.

[First Embodiment]
First, a first embodiment of the present invention will be described.
The first embodiment aims to provide a thin and low-cost polarization conversion element. In order to achieve this object, the configuration of the first embodiment has a function of separating incident light into a first polarization component and a second polarization component, and condenses at least one of these polarization components. In a polarization conversion element having a lens array layer having a function and a polarization conversion layer that periodically forms a polarization rotation region and a polarization non-rotation region, the lens array layer includes a pair of transparent substrates and these transparent substrates. A stripe-shaped electrode array provided on at least one of the substrates, and a liquid crystal capable of controlling the refractive index distribution by an electric field applied between the pair of transparent substrates by the electrode array. It is characterized by that. Therefore, in the conventional polarization conversion element, a condensing unit, a polarization separation unit, and a polarization conversion unit are required. In the first embodiment, the lens array layer having the functions of the condensing unit and the polarization separation unit. Is realized by using the refractive index distribution of the liquid crystal, so that the polarization conversion function can be realized with a configuration having a smaller number of parts than in the past, so that a thin or small-sized and low-cost polarization conversion element can be realized.

  In addition, the first embodiment aims to provide a polarization conversion element having high environmental resistance (thermal stability). In order to achieve this object, in the configuration of the first embodiment, in the polarization conversion element, the liquid crystal whose refractive index distribution of the lens array layer can be controlled is a liquid crystal composition containing at least a polymerizable liquid crystal. It is characterized by being. Therefore, in the first embodiment, since the liquid crystal used in the polarization conversion element is a liquid crystal composition containing at least a polymerizable liquid crystal, the lens array layer using the liquid crystal whose refractive index distribution can be controlled is an electric field or the like. The focal position can be set by the external field and the film thickness, and the liquid crystal composition can be cured at a desired focal position. By curing in this way, the focal position is not affected by heat or the like, and a polarization conversion element with high environmental resistance can be realized.

  FIG. 1 shows a schematic cross section of the polarization conversion element according to the first embodiment. In FIG. 1, a lens array layer 7 for condensing incident light and a portion including the polarization conversion layer 6 are laminated from the light incident side. The lens array layer 7 and the polarization conversion layer 6 are sandwiched between transparent substrates 1, 2 and 3, respectively. Alternatively, in order to reduce the thickness, the substrate portion (transparent substrate 2) between the lens array layer 7 and the polarization conversion layer 6 may be shared by a single substrate.

  Here, the lens array layer 7 includes two transparent substrates 2 and 3, a striped transparent electrode array 5 formed on at least one substrate (on the transparent substrate 2 in FIG. 1), and two transparent substrates 2 and 2. 3 has a liquid crystal 8 capable of controlling the refractive index distribution by applying an electric field. FIG. 1 schematically shows an example of the alignment state of the liquid crystal 8 in the lens array layer 7. At this time, in an initial state where no electric field is applied between the substrates 2 and 3, the homogeneous alignment treatment is performed so that the liquid crystal molecules 8 are parallel along the transparent substrates 2 and 3, as shown in FIG.

  In FIG. 2, an alignment process is assumed in which the major axis of the liquid crystal molecules 8 is in the horizontal direction of the paper. Transparent electrode lines are formed in an array on the upper transparent substrate 2, and the pitch of the transparent electrode array 5 is such that the polarization rotation region 9 and the polarization non-rotation region 10 of the polarization conversion layer 6 are as shown in FIG. It is preferable to correspond to the pitch. Although the lower transparent electrode 4 is formed on the entire surface, the lower transparent electrode 4 may be an array electrode symmetrical to the upper transparent substrate 2.

  As the material of the transparent substrates 1, 2, 3, glass, plastic or the like can be used, and as the material of the transparent electrodes 4, 5, ITO can be used. The electrode need not be transparent, and may be any material that exhibits conductivity such as Al and Cr. The transparent electrode is installed on the liquid crystal layer side. When the substrate itself to be used has conductivity, the substrate can also be used as an electrode. As a material of the liquid crystal 8, general nematic liquid crystals (non-polymerizable and polymerizable liquid crystals) can be used, and it is preferable that the birefringence Δn and the dielectric anisotropy Δε are large. In particular, the birefringence is preferably such that the ordinary light refractive index of the liquid crystal material is about 1.5 to 1.6, which is close to the refractive index of the glass substrate, and the extraordinary light refractive index is as large as about 1.7 to 1.8.

  An operation function for focusing the lens array layer 7 will be described with reference to FIG. FIG. 3 shows a case where a voltage equal to or higher than the threshold value of the liquid crystal alignment change is applied only to a predetermined transparent electrode line (a portion indicated by coloring in the transparent electrode array 5 in the figure) in the transparent electrode array 5. The electrode portion to which voltage is applied is oriented vertically by the electric field, and the electrode portion to which no voltage is applied remains horizontally oriented. Due to the distribution of the alignment direction due to the non-uniform electric field inside the liquid crystal cell, a refractive index distribution for extraordinary light is generated. When linearly polarized light having a plane of polarization parallel to the plane of the paper is incident, the effective refractive index decreases as the liquid crystal molecule long axis is oriented perpendicular to the substrate, and the influence of the refractive index distribution as shown by the solid line in FIG. receive. This refractive index distribution has a relatively large convex lens shape corresponding to the electrode pitch in FIG. 3, and a light condensing function for focusing light is generated by this refractive index distribution.

  Here, the thickness of the layer of the liquid crystal 8 can be set as appropriate depending on the thickness of a spacer member (not shown) between the substrates. The applied electric field and the refractive index distribution generated by this thickness have a desired focal point. Optimized for position. Further, when a polymerizable liquid crystal is used as the material of the liquid crystal 8, it is necessary to polymerize (harden) in a state where a desired light condensing position as described above can be obtained. By polymerization, a stable state can be maintained even thermally.

  As described above, according to the first embodiment, the lens array layer using the refractive index distribution of the liquid crystal has both a condensing function and a polarization separation function. Therefore, compared with the conventional polarization conversion element, the number of parts is small and a thin polarization conversion element can be realized.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.
The second embodiment aims to provide a low-cost and thin polarization conversion element. In order to achieve this object, the configuration of the second embodiment is the polarization conversion element of the first embodiment, wherein the polarization conversion layer includes at least a pair of substrates, a polymerizable liquid crystal, and a photopolymerization initiator. And a liquid crystal composition formed on the pair of substrates and an alignment film for aligning the liquid crystal composition between the pair of substrates. Therefore, the polarization conversion in the conventional polarization conversion element is performed by attaching a half-wave plate to the polarization separation layer (polarization beam splitter) at a predetermined position, but the polarization conversion according to the second embodiment. Is made of only a polarization conversion layer, and therefore a step of attaching a half-wave plate is not required, and can be manufactured more easily than in the past. This polarization separation layer is composed of a liquid crystal composition comprising a polymerizable liquid crystal and a photopolymerization initiator and an alignment film for aligning the liquid crystal composition between a pair of substrates. The periodic structure of the polarization rotation region and the polarization non-rotation region can be formed.

  FIG. 5 illustrates an example of a portion including the polarization conversion layer and the transparent substrate according to the second embodiment. In FIG. 5, the polarization conversion layer 6 holds a liquid crystal composition composed of a polymerizable liquid crystal and a photopolymerization initiator between the transparent substrates 1 and 2, and includes a polarization rotation region 9 and a polarization non-rotation region 10 formed by light irradiation. Arranged periodically. FIG. 5 shows an example in which twisted nematic alignment described later is used, but the alignment state is not limited to this alignment state, and may be an alignment state of a half-wave plate by horizontal alignment. If the substrates 1 and 2 are optically isotropic and transparent, glass, plastic or film can be used.

  In FIG. 5, a spacer member may be disposed between the two substrates 1 and 2. As the spacer member, a spherical spacer, a fiber spacer, a film or the like used in a liquid crystal display device can be used. Further, the protrusion shape may be processed on the substrate surface by photolithography and etching or molding technique. The spacer member is preferably formed outside the effective area of the polarization conversion layer 6. The height of the spacer member is preferably in the range of several μm to several tens of μm, and is appropriately set so that the retardation or optical rotation of the liquid crystal layer exhibits a desired value.

  As the polymerizable liquid crystal, a monofunctional liquid crystal acrylate monomer, a liquid crystal methacrylate monomer, a bifunctional liquid crystal diacrylate monomer, a liquid crystal dimethacrylate monomer, or the like is used. These materials may have a methylene chain between the acryloyloxy group which is a functional group and the liquid crystal skeleton. As a specific example, a liquid crystal acrylate monomer UCL001 manufactured by Dainippon Ink & Chemicals, Inc. can be used.

  As the photopolymerization initiator, known materials can be used, for example, biacetyl, acetophenone, benzophenone, Michler ketone, benzyl, benzoin alkyl ether, benzyl dimethyl ketal, 1-hydroxy-2-methyl-1-phenylpropane-1- ON, 2-chlorothioxanthone, methylbenzoyl formate, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, diethoxyacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy Examples include -1,2-diphenylethane-1-one, α-aminoalkylphenone, bisacylphosphine oxide, and metallocene. The addition amount of the photopolymerization initiator varies depending on the absorbance of each material with respect to the wavelength of light to be irradiated, but is preferably 0.1% by weight or more and 10% by weight or less based on the total amount of the monomer or prepolymer. More preferably, it is at least 3% by weight. As a specific example, in the case of exposing with blue light, about 0.5 parts by weight of a metallocene photopolymerization initiator (Irgacure 784 manufactured by Ciba Geigy) can be added.

  Alignment films 11 and 12 for aligning the liquid crystal composition between the two transparent substrates 1 and 2 are used on the surfaces of the transparent substrates 1 and 2, respectively. The alignment state in which the polarization plane of the incident polarization component rotates and exits is set by tilting the alignment direction of the horizontally aligned liquid crystal at a desired angle with respect to the polarization plane, and setting the retardation of the liquid crystal layer to ½ wavelength. It is preferable to use either the case of using or the case of utilizing the optical rotation of twisted nematic orientation.

  In the case of a liquid crystal phase difference plate with retardation set to ½ wavelength, alignment films 11 and 12 for parallel alignment of the liquid crystal composition between the two substrates 1 and 2 are provided on the surfaces of the transparent substrates 1 and 2. ing. As the alignment films 11 and 12, polyimide or the like can be used, and as an alignment treatment method for the alignment films 11 and 12, a photo-alignment method such as a rubbing method or irradiation with polarized ultraviolet rays can be used. By setting the alignment processing directions of the upper and lower transparent substrates 1 and 2 in parallel and setting the alignment direction of the liquid crystal to be inclined by about 45 degrees with respect to the polarization plane, the polarization plane of the emitted light can be rotated by 90 degrees. In this case, since the thickness of the liquid crystal layer is set according to the wavelength of the light used and the birefringence of the liquid crystal material, it is necessary to set a dedicated liquid crystal thickness for each wavelength.

  On the other hand, when the optical rotation of twisted nematic alignment is used, alignment films 11 and 12 for twisting nematic (TN) alignment of the liquid crystal composition between the two transparent substrates 1 and 2 are formed on the surfaces of the transparent substrates 1 and 2. Is provided. As the alignment films 11 and 12, polyimide or the like can be used, and as an alignment treatment method for the alignment films 11 and 12, a photo-alignment method such as a rubbing method or irradiation with polarized ultraviolet rays can be used. By making the alignment treatment directions of the upper and lower transparent substrates 1 and 2 orthogonal, a TN alignment liquid crystal layer can be formed. At this time, a chiral agent may be added to the liquid crystal composition in order to stabilize the TN alignment. The alignment treatment direction of the alignment films 11 and 12 is set to be parallel or orthogonal to the direction of the stripe structure of the diffraction grating of the polarization separation layer, that is, the P-polarized component incident on the polarization rotation layer or It is set to be orthogonal to the S polarization component. In the case of twisted nematic alignment, the polarization rotation action is optical rotation, and the polarization plane can be rotated in a relatively wide wavelength range.

  In this manner, a TN-aligned liquid crystal composition (TN liquid crystal layer 13) is formed as shown in FIG. Next, as shown in FIG. 7, a desired region is irradiated with light to polymerize and solidify the TN alignment state, and the polarization rotation region 9 is formed. At this time, only an area with a desired pitch is exposed using an aperture mask or the like corresponding to the pitch of the lens array. For example, exposure is performed with blue light sensitive to the above-described photopolymerization initiator. Thereafter, in the uncured portion of the liquid crystal composition, the polarization plane of the incident polarized light component is transferred to an alignment state in which it does not rotate, and is solidified by full or partial light irradiation to form a polarization non-rotation region. . The state in which the polarization plane of the incident polarization component is changed to the alignment state in which the polarization plane does not rotate includes, for example, a vertical alignment state as shown in FIG. 5, a horizontal alignment state without twisting, and an isotropic state. These states can be obtained by applying an electric field or a magnetic field or heating.

  In the polarization conversion layer 6 as shown in FIG. 5, when only P-polarized light is incident on the polarization rotation region 9, it is emitted in the same polarization direction as the S-polarization component due to the optical rotation of the liquid crystal polymer portion fixed in the TN alignment. To do. On the other hand, when only the S-polarized light is incident on the polarization non-rotating region 10, the S-polarized light is emitted as it is. The lens array portion, the portion including the polarization separation layer, and the portion including the polarization rotation layer are aligned and bonded so that the position of the polarization rotation region 9 of the polarization rotation layer corresponds to the center position of each lens of the lens array. .

  In addition, it is also possible to carry out polarization conversion of natural light so that the P-polarized component increases by changing the condensing position of the lens array layer and the setting of the characteristics of the polarization conversion layer. In the second embodiment, the alignment process of the lens array and the polarization rotation layer is necessary, but the entire surface after the mask exposure and the orientation change process using the same material for the periodic structure of the polarization rotation region and the polarization non-rotation region. It can be produced by a relatively simple process such as exposure.

  As a specific example, two substrates: a soda glass (with single-sided AR coating), an outer shape of 30 × 40 mm, and a thickness of 1.1 mm were bonded together, and the cell gap was controlled with a 6 μm spacer between the substrates. Before pasting, 1000 mm of polyimide alignment film (AL3046: made by JSR) was applied to both substrates and rubbed. The rubbing direction was set to be vertical when pasting. The liquid crystal materials are mother liquid crystal (UV curable): UCL-001-K0 (manufactured by DIC), double liquid crystal (Δε induction): E7 (5 wt% with respect to mother liquid crystal) (manufactured by Merck) and chiral agent: S-811 (A setting of TN 90 °) and a photopolymerization initiator: IRG819 (base liquid crystal + 1 wt% with respect to double liquid crystal) were mixed and injected into the cell by capillary action in a dark room.

  Next, the mask pattern was closely exposed using a UV spot irradiator (manufactured by Oak). The mask pattern is (L / S: 500/500 or 50/50 [μm]), and the exposure conditions are UV irradiation (365 nm): 5 mW / cm ^ 2, irradiation time: 2 seconds before electric field application / 5 seconds after electric field application, Electric field application: 35 V / μm, 100 Hz, exposure temperature: RT, and a periodic structure of a polarization rotation region by a TN liquid crystal region and a polarization non-rotation region by a vertical alignment region was formed. The focal position was set in each of the polarization rotation region and the polarization non-rotation region using a blue laser (He-Cd), an objective lens (× 50), and an achromatic lens. The polarization plane of the incident light was the arrangement direction of the periodic structure. When the direction of polarization transmitted through the cell was confirmed using a polarizing plate, the direction of polarization was the same as that upon incidence when it was incident on the polarization non-rotating region. In addition, when entering the polarization rotation region, the polarization direction was a polarization direction rotated 90 degrees from the incident polarization direction.

[Third Embodiment]
Next, a third embodiment of the present invention will be described.
The third embodiment aims to provide a low-cost and thin polarization conversion element. In order to achieve this object, the configuration of the third embodiment is that in the polarization conversion element of the first embodiment, the polarization conversion layer includes a birefringent region and an isotropic region. It is characterized by comprising a periodic structure. Therefore, the polarization conversion layer is composed of a periodic structure of a birefringent region and an isotropic region. The region exhibiting birefringence is formed of liquid crystal, and the polarization refraction region (liquid crystal region) and polarization are optimized by optimizing the birefringence obtained in the liquid crystal region and its film thickness (cell gap) to ½ wavelength conditions. A periodic structure of a non-rotating region (isotropic region) can be formed. As described above, this does not require a step of attaching a half-wave plate, and can be easily manufactured as compared with the prior art.

  FIG. 8 shows a schematic configuration of a cross section of a polarization conversion layer as an example of the third embodiment. FIG. 8A shows a configuration in which a grating shape is formed in a birefringent medium and grating grooves are filled with an isotropic medium, whereas FIG. 8B shows an isotropic structure. A configuration is shown in which a lattice shape is formed on a medium, and lattice grooves are filled with a birefringent medium.

  For example, as a functional operation of the polarization conversion layer shown in FIG. 8, as shown in FIG. 9, the polarization direction incident on the isotropic region is transmitted as it is, and the polarization direction incident on the birefringence region. Transmits with the polarization direction rotated by 90 degrees. Here, the retardation Δnd of the birefringent region and the film thickness d is set to satisfy the condition Δnd = λ / 2. In this way, the polarization conversion layer is composed of a periodic structure of a birefringent region and an isotropic region, so that the condensing position of the lens array layer is rotated as shown in FIG. The polarization conversion function can be realized by setting the area or the polarization non-rotation area.

  Here, the lattice shape can be formed by photolithography and etching, cutting, forming technique, or the like. As the isotropic medium, a transparent resin such as a photopolymer, or an optical glass material such as quartz or BK7 can be used. However, the isotropic medium is not limited to this as long as it does not have birefringence. As the birefringent medium, lithium niobate crystal, tantalum niobate crystal, titanium oxide crystal, polymer birefringent film (polymer film), liquid crystal, and the like can be used. In particular, polymer birefringent films and liquid crystals are excellent in productivity.

  A polymer birefringent film is a polymer film having birefringence by stretching a polymer film and orienting a polymer chain, and can be easily mass-produced, and can be produced at a low cost. There is an advantage that it can be manufactured. As the polymer material of the polymer film to be stretched, for example, polyolefin, polyacrylate, polycarbonate (PC), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), polystyrene, and the like can be used. Is not to be done. Liquid crystals are also widely used in display devices and the like, and are low in cost and mass-productive in terms of manufacturing. Moreover, since birefringence (refractive index anisotropy) is large, there is an advantage that it is suitable for thinning. As the liquid crystal, general liquid crystal types such as nematic, cholesteric and smectic in non-polymerizable liquid crystal can be used. At the time of production, in order to efficiently use the birefringence, it is preferable to perform alignment treatment such as alignment film, rubbing, and photo-alignment.

  In the above description, the lattice shape is formed by a processing technique. However, the isotropic region and the birefringent region may be formed in a self-organized manner by interference exposure as described later (see the fifth embodiment). Although it depends on the size of the element, the self-organized formation method is superior in productivity because the manufacturing time can be shortened compared to the processing method. In addition, it is preferable to provide an overcoat layer (not shown) for resistance to moist heat and durability in the element structure, and the material for forming the overcoat layer is an ordinary ray direction refractive index and an extraordinary ray direction refractive index. It is preferable to use a transparent resin or the like having the same refractive index as either one.

  As a specific example, a SiON film having a thickness of about 3 μm is formed on the surface of a BK7 glass substrate having a thickness of 0.5 mm, and a resist pattern is formed by electron beam drawing and etched to form a pitch of 100 μm on the SiON film and a width of the recess of about 50 μm. A shape having a convex portion width of about 50 μm and a concave portion depth of about 1.5 μm was produced. Using BK7 having a thickness of 0.5 mm as the counter substrate, a polyimide-based alignment film having a thickness of 800 angstroms was formed and rubbed. An empty cell was prepared so as to coincide with the rubbing direction of the groove of the concavo-convex substrate, and a liquid crystal material (ZLI2248 manufactured by Merck) was injected using a vacuum injection method. The focal position was set for each of the concave and convex shapes using a blue laser (He-Cd), an objective lens (x50), and an achromatic lens. The polarization plane of the incident light was a direction rotated 45 degrees with the rubbing direction. When the direction of polarization transmitted through the cell was confirmed using a polarizing plate, the direction of polarization was the same as that upon incidence when incident on the convex portion. Further, when entering the concave portion, the polarization direction was a polarization direction rotated by 90 degrees from the incident polarization direction.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described.
The fourth embodiment aims to provide a polarization conversion device capable of controlling polarization conversion by an electric field. In order to achieve this object, the configuration of the fourth embodiment is the electric field application direction of the polarization conversion element of the first to third embodiments and the electrodes installed in the lens array layer of the polarization conversion element. Alternatively, an electric field application control means capable of switching the electric field application timing is provided. Therefore, since the electric field application control means for applying an electric field to the lens array layer is provided, the focal position can be changed according to the switching of the electric field application. By selecting the polarization rotation region and the non-polarization rotation region as the focal position, the polarization conversion function can be controlled by the electric field.

  A feature of the fourth embodiment is that, as shown in FIG. 10, an electric field application control means 20 is provided in the lens array layer 7, and the polarization conversion can be actively controlled by the electric field application control means 20.

  Here, FIG. 11 shows an operation of polarization conversion by electric field control. As in the first embodiment, in the upper part of FIG. 11 (state 1), only a predetermined transparent electrode line in the transparent electrode array 5 (a portion indicated by a color in the transparent electrode array 5 in the figure) is shown. The case where the voltage more than a threshold value is applied is shown. The electrode portion to which voltage is applied is oriented vertically by the electric field, and the electrode portion to which no voltage is applied remains horizontally oriented. Due to the distribution of the alignment direction due to the non-uniform electric field inside the liquid crystal cell, a refractive index distribution for extraordinary light is generated. When linearly polarized light having a plane of polarization parallel to the plane of the paper is incident, the effective refractive index decreases as the liquid crystal molecule major axis is oriented perpendicular to the substrate, and refraction as shown by the solid line (state 1) shown in FIG. Influenced by rate distribution. This refractive index distribution has a relatively large convex lens shape corresponding to the electrode pitch in FIG. 11, and a condensing function is generated for one polarization component.

  Next, as shown in the lower diagram (state 2) of FIG. 11 by the electric field application control means 20, when the electrode to which the electric field is applied is switched, the alignment state of the liquid crystal molecules also changes, and the broken line (state) shown in FIG. The refractive index distribution changes as in 2).

  Thus, the focal position can be shifted by condensing by applying an electric field to the electrode array and switching the position of the applied electrode. That is, by setting the focal position to one of the polarization rotation region and the polarization non-rotation region of the polarization rotation layer, the direction of the polarization plane to be emitted can be controlled by electric field control.

  As described above, this focal position changes depending on the refractive index distribution resulting from the alignment of the liquid crystal. Since the orientation of the liquid crystal changes depending on the applied electric field strength, the focal position can be varied by having the electric field application control means 20 that can adjust the applied electric field strength. That is, it can be adjusted when the focal position changes for some reason. For example, there is an influence of temperature as one cause of changing the focal position. This is because the characteristics of the liquid crystal material are temperature dependent. For example, the threshold voltage increases as the temperature decreases due to the temperature characteristics of the elastic constant and dielectric constant of the liquid crystal material. That is, when the electric field applied to the liquid crystal layer is constant, the focal position changes as the temperature changes. Therefore, it is preferable to have a temperature detection unit and control the focal position by adjusting the electric field applied by the electric field application control unit corresponding to the temperature detected by the temperature detection unit.

  As a specific example, two transparent glass substrates (3 cm × 4 cm, thickness 1.1 mm) were used, and a Cr line electrode was formed on one substrate. The line electrodes are provided with comb electrodes A and B so that the same voltage can be applied alternately. The other substrate was formed as a solid electrode by forming ITO on the entire surface of one side of the substrate. A polyimide alignment material (AL3046-R31, JSR) was spin coated on the ITO side of the glass substrate to form an alignment film of about 0.3 μm. After annealing the glass substrate, a rubbing process was performed in a direction perpendicular to the Cr line. A 3 μm spacer (true ball) was sandwiched between the two glass substrates, the upper and lower substrates were bonded together (the electrode surfaces were opposed) and pressurized, and then sealed with a UV curable adhesive to produce an empty cell. A nematic liquid crystal having a positive dielectric anisotropy (ZLI-2471, Merck) was injected into the empty cell by a capillary method to produce a liquid crystal cell. Since the upper and lower substrates are rubbed in the same direction, the liquid crystal molecules are all parallel to the substrate and aligned in the same direction (homogeneous alignment).

  The cell produced here was operated by applying a voltage. As the applied voltage, three function generators were used, and one was used as a trigger to alternately apply voltages to the comb electrodes A and B. The input frequency was 100 Hz, the voltage input waveform was a triangular wave, and the voltage value was confirmed with an oscilloscope and a tester. For the incident light to the cell, an aperture (1.5 mm) is attached to a white lamp, collimated by a collimating lens, and the polarization direction is set by using a polarizing plate so that it is perpendicular to the stripe shape of the comb electrode. The transmitted light was observed with a microscope [objective lens (40 ×) + relay lens + CCD (“1/3]]. The microscope position was moved parallel to the optical axis and fixed at the most focused position. The observation image position was shifted by switching the applied voltage of 16 V to the comb electrodes A and B.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described.
The fifth embodiment provides a polarization conversion device in which polarization conversion can be controlled by an external field. In order to achieve this object, the polarization conversion element of the first to third embodiments is provided, and a polarization separation layer is provided between the lens array layer and the polarization conversion layer of the polarization conversion element. Has a pair of transparent substrates, an electrode capable of applying an electric field between the pair of transparent substrates, and an electric field application control means capable of switching the electric field application direction or electric field application timing of the electrodes. To do. Therefore, by providing a deflection separation layer between the lens array layer and the polarization conversion layer and selecting the polarization rotation region and the non-polarization rotation region as the light deflection direction of the polarization separation layer, Thus, even when the focal position of the lens array layer is fixed, polarization conversion can be controlled by an electric field.

  The fifth embodiment is intended to provide a polarization conversion device capable of controlling polarization conversion at high speed by an external field. In order to achieve this object, the configuration of the fifth embodiment is that, in the polarization conversion device of the present embodiment, the polarization separation layer includes at least a non-polymerizable liquid crystal, a polymerizable monomer or a prepolymer, and photopolymerization. The composition was composed of an initiator, and this composition was subjected to two-beam interference exposure to form a periodic phase separation structure of a layer composed mainly of a polymer and a layer composed mainly of a non-polymerizable liquid crystal. It is a holographic polymer dispersed liquid crystal layer. Therefore, since the polarization separation layer is composed of a holographic polymer-dispersed liquid crystal layer, the switching speed of polarization conversion can be switched at high speed on the order of several tens of μsec by electric field control.

  A feature of the fifth embodiment is that a polarization separation layer 14 having an electric field application control means 20 is provided between the lens array layer 7 and the polarization conversion layer 6 as shown in FIG. Actually, electrodes for applying an electric field are provided on the transparent substrates 2a and 2b sandwiching the polarization separation layer 14, but they are omitted in FIG.

  In FIG. 13, for example, the polarization separation layer 14 is composed of a composition comprising at least a non-polymerizable liquid crystal, a polymerizable monomer or prepolymer, and a photopolymerization initiator, and the composition is subjected to two-beam interference exposure. A holographic polymer dispersed liquid crystal layer in which a periodic phase separation structure of a layer mainly made of polymer and a layer mainly made of non-polymerizable liquid crystal is formed. In this case, a volume hologram having a desired pitch can be produced by adjusting the angle and wavelength of the two light beams. Further, by adjusting the direction of the interference fringes and the arrangement angle of the element, the structure of the hologram tilted inside the element can be freely produced.

  As the non-polymerizable liquid crystal, a general liquid crystal having refractive index anisotropy can be used. When selecting a liquid crystal material, a liquid crystal material having a refractive index equal to the refractive index of the cured layer of the polymerizable monomer or prepolymer may be selected in an orientation state of a certain order parameter. Then, the polymerizable monomer or the prepolymer may be selected so that the refractive index becomes the same as the refractive index in the orientation state of the liquid crystal in a certain order parameter.

  As the non-polymerizable liquid crystal, any of nematic, cholesteric, and smectic types may be used, and conventionally known biphenyl, terphenyl, phenylcyclohexane, biphenylcyclohexane, benzoic acid phenyl ester, cyclohexanecarboxylic acid phenyl ester, phenylpyrimidine, phenyldioxane, Tran, 1-phenyl-2-cyclohexylethane, 1-phenyl-2-biphenylethane, 1-cyclohexyl-2-biphenylethane, biphenylcarboxylic acid phenylester, 4-cyclohexylbenzoic acid phenylester, etc. A liquid crystal having a cyano group, a halogen group, or the like as a substituent as a polar group for imparting an alkoxy group or dielectric anisotropy can be used. The non-polymerizable liquid crystal material is preferably used in a proportion of 20 to 500 parts by weight with respect to 100 parts by weight of the total amount of polymerizable monomers or prepolymers.

  It is preferable to use a polymerizable monomer or a prepolymer thereof that has a large cure shrinkage due to polymerization. As such a polymerizable monomer, a photopolymerizable compound having an ethylenically unsaturated bond, a photopolymerization having at least one ethylenically unsaturated double bond in one molecule, a photocrosslinkable monomer, Examples of monomers and copolymers thereof include unsaturated carboxylic acids and salts thereof, esters of unsaturated carboxylic acids and aliphatic polyhydric alcohol compounds, unsaturated carboxylic acids and Examples thereof include amides with aliphatic polyvalent amine compounds. Particularly, bifunctional or higher polyfunctional monomers have large curing shrinkage and can be suitably used. Examples of unsaturated carboxylic acid monomers include acrylic acid, methacrylic acid, itaconic acid, crotonic acid, isocrotonic acid, maleic acid, and halogen-substituted unsaturated carboxylic acids such as chlorinated unsaturated carboxylic acids and brominated unsaturated carboxylic acids. And fluorinated unsaturated carboxylic acid. Examples of unsaturated carboxylic acid salts include sodium and potassium salts of the aforementioned acids. Moreover, polyfunctional acrylates and methacrylates such as urethane acrylates, polyester acrylates, epoxy resins and (meth) acrylic acid can be mentioned. In addition to the above, a thermal polymerization inhibitor, a plasticizer, and the like may be added.

  As the photopolymerization initiator, known materials can be used as described above. The addition amount of the photopolymerization initiator varies depending on the absorbance of each material with respect to the wavelength of light to be irradiated, but is preferably 0.1% by weight or more and 10% by weight or less based on the total amount of the monomer or prepolymer. More preferably, it is at least 3% by weight. When the amount of the photopolymerization initiator added is too small, phase separation between the polymer and the liquid crystal hardly occurs, and the necessary exposure time becomes long. On the other hand, if there are too many photopolymerization initiators, the polymer and liquid crystal are cured with insufficient phase separation, so that many liquid crystal molecules are taken into the polymer and the polarization selectivity deteriorates. There is. Here, the polarization selectivity is the ratio between the diffraction efficiency in the polarization direction substantially parallel to the arrangement direction of the periodic structure and the diffraction efficiency in the polarization direction rotated by 90 degrees with respect to the polarization direction. The selectivity is assumed to be good.

  Next, a hologram forming process by phase separation will be described with reference to FIG. In FIG. 14, when the composition is exposed using a two-beam interference exposure system with a laser light source having a desired wavelength (not shown), the photopolymerization reaction of the polymerizable monomer or prepolymer starts in the bright part of the interference fringes. At this time, curing shrinkage occurs, resulting in a density difference, the adjacent polymerizable monomer or prepolymer moves to the bright part, and further polymerization proceeds. At the same time, phase separation occurs when the non-polymerizable liquid crystal present in the bright part is driven out toward the dark part. At this time, it is considered that when the liquid crystal molecules move, a force to align the major axis of the liquid crystal molecules in the moving direction by the interaction with the monomer or polymer chain is considered to work. That is, it is considered that a force for orienting liquid crystal molecules in the direction of the interference fringe acts in the phase separation process. Finally, as shown in FIG. 15, a periodic structure of a polymer layer and a non-polymerizable liquid crystal layer is formed corresponding to the bright and dark pitches of the interference fringes, and the orientation vector of the liquid crystal layer portion indicates the interval direction of the interference fringes. It is thought that the state which turned suitable is obtained. In this interference exposure and phase separation process, the sample is preferably heated and held at an appropriate temperature. It is considered that the phase separation speed changes depending on the temperature and affects the orientation of the liquid crystal molecules. The optimum heating temperature varies depending on the material used, but is preferably about 40 ° C to 100 ° C.

  Strictly speaking, it is difficult for the periodic structure of the polymer layer and the non-polymerizable liquid crystal layer by phase separation to completely separate the polymer and the non-polymerizable liquid crystal periodically, and the polymer layer here has many polymer components. The region may contain liquid crystal molecules. The non-polymerizable liquid crystal layer is a region having a large amount of non-polymerizable liquid crystal components and may contain a polymer component. Actually, the interface between the polymer layer and the liquid crystal layer is assumed to be uneven, not an ideal plane, so the variation in the major axis direction of the liquid crystal molecules at the interface is large and the order parameter of the liquid crystal layer is relatively small. It becomes. Therefore, the birefringence of the liquid crystal layer portion is relatively small.

The pitch of the periodic structure to be produced varies depending on the desired diffraction angle and wavelength, but is generally in the range of 0.2 μm to 1000 μm. For example, in order to obtain a 20 ° diffraction angle with respect to 405 nm incident light, a pitch of about 1.1 μm and a pitch of about 2.3 μm with respect to 650 nm incident light are required. The inclination angle between the polymer layer and the liquid crystal layer interface is preferably about 0 ° to 20 °. The exposure amount varies depending on the addition concentration of the photopolymerization initiator and the temperature at the time of exposure, but is preferably 0.5 J / cm ² to 30 J / cm ^2, more preferably 1 J / cm ² to 15 J / cm ² .

  In the fifth embodiment, the combination of the type of liquid crystal and the type of polymer is appropriately set so that the ordinary light refractive index no of the entire liquid crystal part and the refractive index np of the polymer part substantially coincide with each other. It does not diffract for polarized incident light because it does not feel the difference between the ordinary refractive index no of the whole liquid crystal part and the refractive index np of the polymer part, and for the incident light of P polarized light, the extraordinary light refractive index of the whole liquid crystal part. A polarization-selective hologram composed of a holographic polymer-dispersed liquid crystal layer that diffracts by feeling the refractive difference between ne and the polymer portion can be produced at a relatively low cost.

  Since such a holographic polymer-dispersed liquid crystal layer has a periodic structure of non-polymerizable liquid crystal regions and polymer regions, the orientation of the liquid crystal in the liquid crystal regions can be controlled by the electric field by applying an electric field in the layer. Here, the operation function by the electric field control is shown in FIG. As shown in FIG. 16A, when no electric field is applied, the orientation of the liquid crystal is oriented in the arrangement direction of the periodic structure, and light is diffracted with respect to the P-polarized light. Here, when an electric field is applied as shown in FIG. 16B, the orientation of the liquid crystal is oriented in the direction of the electric field (direction perpendicular to the substrate surface), and light is transmitted through the P-polarized light. (S-polarized light is transmitted in either case), that is, the diffraction angle determined by the holographic polymer dispersed liquid crystal layer is set so as to correspond to the polarization rotation region and the polarization non-rotation region of the polarization conversion layer. As described above, the focal position of the light (P-polarized light) transmitted through the lens array layer can be varied.

  In general, polymer-dispersed liquid crystals are strongly regulated by the polymer interface, so that the alignment regulating power of the liquid crystals is large. Therefore, the response speed of the liquid crystal is multiplied by the regulation force, and a high-speed response of several tens of microseconds can be obtained.

As a specific example, an antireflection film for blue light was formed on one side of a glass substrate having a thickness of 0.15 mm, and then ITO was deposited on the opposite side to a thickness of 1500 mm. Spacer particles with a particle size of 4 μm are dispersed in an adhesive, applied outside the effective area, and bonded to a glass substrate. The width of the effective area was about 10 mm square. Next, a composition composed of a mixture of the following five types of materials was injected into the cell by the capillary method while heating to about 60 ° C. to form a composition layer having a thickness of about 4 μm. In addition, since this composition was reactive to light having a shorter wavelength than green, it was handled in a dark room using red light.
<1> Nematic liquid crystal (ZLI-4850, Merck ZLI-4850, Δε <0) 30 parts by weight <2> Phenylglycidyl ether acrylate hexamethylene diisocyanate urethane prepolymer (AH600, manufactured by Kyoeisha Chemical Co., Ltd.) 75 parts by weight <3> Dimethylol tricyclodecandi Acrylate (DCP-A manufactured by Kyoeisha Chemical Co., Ltd.) 10 parts by weight <4> 2-hydroxyethyl methacrylate (HO manufactured by Kyoeisha Chemical Co., Ltd.) 5 parts by weight <5> Metallocene photopolymerization initiator (Irgacure 784 manufactured by Ciba-Geigy) 0.5 part by weight Cell After pouring in, the composition was isotropic at room temperature.

  Next, a two-beam interference exposure system using a He—Cd laser having a wavelength of 442 nm and an output of 80 mW was prepared. The laser beam was divided and expanded so that one light beam was parallel light of about 11 mW / cm 2, and the crossing angle of the two light beams was set to 26 degrees. At this wavelength and crossing angle, interference fringes with a period of about 1 μm are generated in the crossing region of the two light beams.

  With the cell substrate attached to a heating device and heated to about 60 ° C., two-beam interference exposure was performed for about 5 minutes to produce a hologram element. At this time, two light beams were set to enter from directions of +13 degrees and -13 degrees with respect to the direction perpendicular to the substrate surface.

  A linearly polarized laser beam having a wavelength of 442 nm was irradiated from a direction with an angle of 13 degrees to the substrate surface of the produced hologram element, and the + 1st order diffracted light intensity with respect to the incident light intensity was measured. The incident light intensity was adjusted using an ND filter so as to be about 5 mW. By arranging a linearly polarizing plate and a half-wave plate in the incident optical path and rotating the optical axis of the half-wave plate by 45 degrees, the polarization direction (P-polarized light, S-polarized light) incident on the hologram element can be switched, The polarization of incident light was set to P polarization. The light transmitted through the element was almost diffracted, and the + 1st order diffraction efficiency was 80%.

  When a rectangular wave of 1 kHz and ± 20 V / μm was applied between the substrates using a function generator and an amplifier for the hologram element, and the optical characteristics of the element were measured in the same manner, the transmission quality of the 0th order light was 95%. . When the light transmitted through the element was received by a high-speed camera and the response speed was measured, a high-speed response of 100 μsec was obtained. The outgoing angle of the + 1st order diffracted light with respect to the incident light is 26 degrees, and polarization conversion is possible by electric field control by making it correspond to the polarization rotation region or polarization non-rotation region of the polarization conversion layer.

  The embodiment of the present invention has been described above, but the present invention is not limited to the description of the embodiment, and various modifications can be made without departing from the scope of the invention.

  The present invention can be applied to illumination optical systems such as liquid crystal displays and liquid crystal projectors.

It is sectional drawing which shows typically the structure of the polarization conversion element which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows typically an example of the state of the liquid crystal in the polarization conversion element concerning the 1st Embodiment of this invention. It is sectional drawing which shows typically an example of the state of the liquid crystal in the polarization conversion element concerning the 1st Embodiment of this invention. It is a graph which shows the influence of the refractive index distribution in the polarization conversion element concerning the 1st Embodiment of this invention. It is sectional drawing which shows typically the structure of the polarization conversion element which concerns on the 2nd Embodiment of this invention. It is sectional drawing which shows typically an example of the state of the liquid crystal in the polarization conversion element concerning the 2nd Embodiment of this invention. It is sectional drawing which shows typically an example of the state of the liquid crystal in the polarization conversion element concerning the 2nd Embodiment of this invention. It is sectional drawing which shows typically the structure of the polarization converting layer which concerns on the 3rd Embodiment of this invention. It is sectional drawing for demonstrating the function operation | movement of the polarization converting layer which concerns on the 3rd Embodiment of this invention. It is sectional drawing which shows typically the structure of the polarization converting apparatus which concerns on the 4th Embodiment of this invention. It is sectional drawing for demonstrating the operation | movement of the polarization conversion by the electric field control of the polarization converter which concerns on the 4th Embodiment of this invention. It is a graph which shows the influence of the refractive index distribution in the polarization conversion element concerning the 4th Embodiment of this invention. It is sectional drawing which shows typically the structure of the polarization converting apparatus which concerns on the 5th Embodiment of this invention. It is a figure for demonstrating the hologram formation process by phase separation. It is sectional drawing which shows the orientation state of the liquid crystal in the hologram formation process by phase separation. It is sectional drawing for demonstrating the operation | movement function by the electric field control of the polarization converter which concerns on the 5th Embodiment of this invention.

Explanation of symbols

1, 2, 2a, 2b, 3 Transparent substrate 4 Transparent electrode 5 Transparent electrode array 6 Polarization conversion layer 7 Lens array layer 8 Liquid crystal (liquid crystal component)
DESCRIPTION OF SYMBOLS 9 Polarization rotation area | region 10 Polarization non-rotation area | region 11, 12 Alignment film 13 TN liquid crystal layer 14 Polarization separation layer 20 Electric field application control means

Claims (7)

A lens array layer having a function of separating incident light into a first polarization component and a second polarization component, and a function of condensing at least one polarization component of the polarization components, a polarization rotation region, and polarization In a polarization conversion element having a polarization conversion layer that periodically forms a non-rotating region,
The lens array layer is
A pair of substrates;
An electrode provided on at least one of the pair of substrates and capable of applying an electric field between the pair of substrates;
A liquid crystal provided between the pair of substrates and capable of controlling a refractive index distribution by an electric field applied by the electrodes;
A polarization conversion element comprising: The polarization conversion layer is at least
A pair of substrates;
A liquid crystal composition comprising a polymerizable liquid crystal and a photopolymerization initiator;
An alignment film provided on each of the pair of substrates, for aligning the liquid crystal composition between the pair of substrates;
The polarization conversion element according to claim 1, comprising:   The polarization conversion element according to claim 1, wherein the polarization conversion layer has a periodic structure including a birefringent region and an isotropic region.   4. The polarization conversion element according to claim 1, wherein the liquid crystal of the lens array layer is a liquid crystal composition containing at least a polymerizable liquid crystal. 5. The polarization conversion element according to any one of claims 1 to 4,
An electric field application control means capable of switching an electric field application direction or an electric field application timing of an electrode provided in the polarization conversion element;
A polarization conversion device comprising: The polarization conversion element according to any one of claims 1 to 4,
A polarization separation layer provided between the lens array layer and the polarization conversion layer of the polarization conversion element,
The polarization separation layer is
A pair of substrates;
An electrode capable of applying an electric field between the pair of substrates;
Electric field application control means capable of switching the direction of electric field application of the electrode or the timing of electric field application;
A polarization conversion device comprising: The polarization separation layer is at least
A composition comprising a non-polymerizable liquid crystal, a polymerizable monomer or prepolymer, and a photopolymerization initiator,
It is a holographic polymer dispersed liquid crystal layer in which a periodic phase separation structure of a layer mainly composed of a polymer and a layer mainly composed of a non-polymerizable liquid crystal is formed by two-beam interference exposure of the composition. The polarization conversion device according to claim 6, characterized in that:

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