Polarization cancellation element, method for manufacturing the same, and low-pass filter including the polarization cancellation element

Abstract

To provide a depolarization element which is simple and low-cost, and has superior optical characteristics, and a low-pass filter using the same.SOLUTION: A depolarization element consists of a depolarization diffraction grating that has an anisotropic structure which has a film made of a liquid crystal material and having its optical axis rotating continuously toward a grating vector direction, and birefringence in a plane of the film is uniform in level, wherein two depolarization elements are arranged having grating vectors orthogonally, and a low-pass filter is constituted therebetween across a birefringent optical element.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a polarization cancellation element using a polarization diffraction grating and a method for manufacturing the same, and further relates to an optical low-pass filter including the polarization cancellation element.

Background Art

[0002] In a projector using a polarized laser as a light source, in a light source unit that excites a phosphor, the light quantity distribution of the projected image is biased in the illumination optical system, which may cause luminance unevenness and color unevenness. To improve such a bias in the light quantity distribution and color unevenness, a polarization cancellation element is used.

[0003] For example, in Patent Document 1 (Japanese Patent No. 6288739), as a polarization cancellation element used in a projector, two wedge-shaped crystal plates are bonded together so that the optical axes form an angle of 45 degrees, thereby changing the polarization state of the incident light and creating light with a randomly changing vibration direction. A polarization cancellation unit is described.

[0004] In Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2018-205431), a polarization cancellation plate is proposed that uses quarter-wave plates with different slow axis settings and two-dimensionally alternately or irregularly arranges minute regions that give different polarization actions.

[0005] It has also been proposed to form regions with different polarization actions by controlling the alignment of liquid crystal molecules. Patent Document 3 (Japanese Patent No. 4333914) describes manufacturing a polarization diffraction element by irradiating a birefringence-induced material polymer with light containing a linearly polarized component to impart a periodic molecular alignment structure with a 90° difference in the molecular alignment direction.

[0006] One application of the polarization cancellation element is a low-pass filter. In solid-state imaging devices such as CCD sensors and CMOS sensors, and imaging devices such as digital cameras using them, an optical low-pass filter is used to attenuate moire-like pseudo signals derived from high spatial frequency components.

[0007] Such optical low-pass filters include those in which multiple crystal birefringent plates are adhered to each other with an adhesive, or those in which multiple crystal birefringent plates and crystal phase plates are adhered together with an adhesive. Patent Document 4 (Japanese Patent Application Laid-Open No. 2016-45432) describes an optical low-pass filter having a configuration in which a quarter-wave plate is sandwiched between two birefringent plates made of crystal or the like.

[0008] A phase grating type low-pass filter that utilizes the diffraction phenomenon of a diffraction grating has also been proposed. For example, Patent Document 5 (Japanese Patent Application Laid-Open No. 2006-184890) describes an optical low-pass filter formed by processing the inside of a transparent material with pulsed laser light and arranging regions having different refractive indices two-dimensionally or three-dimensionally.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0010] In the configuration of the depolarizing element described in Patent Document 1, it is necessary to process quartz into a wedge shape and bond them. Therefore, the manufacturing process is complicated, and it is difficult to suppress the manufacturing cost. In the element described in Patent Document 2, the depolarizing function is exhibited by patterning the retardation. Also, in the element described in Patent Document 3, although the molecular orientation direction changes discontinuously, in these cases, since a difference in refractive index occurs between two (discontinuous) regions near the pattern boundary, optical problems such as scattering occur.

[0011] In the optical low-pass filter using a quartz plate described in Patent Document 4, it is necessary to bond a plurality of accurately polished quartz birefringent plates and retardation plates. Therefore, it is difficult to obtain a thin element, and it is also difficult to suppress the manufacturing cost. Further, in the optical low-pass filter using a conventional diffraction grating as described in Patent Document 5, since higher-order diffracted light is generated, the low-pass effect is reduced, and there are problems such as a decrease in resolution as a whole.

[0012] An object of the present invention is to provide a depolarizing element that can be manufactured by a simple method, has no refractive index discontinuity that causes scattering, is easily thinned, a method for manufacturing the same, and an optical low-pass filter using such a depolarizing element.

Means for Solving the Problems

[0013] A first configuration of the present invention is a depolarizing element, having a film made of a liquid crystalline material, having an anisotropic structure in which the optical axis of the film continuously rotates toward the lattice vector direction, the magnitude of birefringence being uniform in the plane of the film, and consisting of a polarization diffraction grating, which is a depolarizing element.

[0014] Since the polarization cancellation element having the above configuration uses a film made of a liquid crystalline material, it can be easily thinned, and in a film having a uniform birefringence magnitude, since it has an optical structure in which the optical axis continuously rotates, problems such as scattering due to the presence of a discontinuous interface of optical characteristics do not occur.

[0015] A second configuration of the present invention is an optical low-pass filter, comprising a first element and a second element made of the above polarization cancellation element, and a third element having a constant azimuth of the optical axis and having birefringence. The first element and the second element are arranged such that the grating vectors of the polarization diffraction grating are orthogonal to each other, and the third element is arranged between the first element and the second element. It is an optical low-pass filter.

[0016] Since the optical low-pass filter having the above configuration uses the polarization cancellation element of the present invention, it is easy to thin, and can suppress the intensity of zero-order (non-diffracted) and higher-order diffracted light, and can obtain excellent effects such as moire cancellation.

[0017] A third configuration of the present invention is a method for manufacturing the above polarization cancellation element. A step of applying a liquid crystalline material having photo-orientability onto a substrate to form a coating film. A step of irradiating the coating film with left-circularly polarized light and right-circularly polarized light for interference exposure. A method for manufacturing a polarization cancellation element, including a step of heating and cooling the coating film after exposure to induce alignment of the liquid crystalline material. By the above method, the polarization cancellation element of the present invention can be manufactured by a simple process.

[0018] A fourth configuration of the present invention is a method for manufacturing the above polarization cancellation element. A step of applying a liquid crystalline material having photo-orientability onto a substrate to form a first coating film. A step of irradiating the first coating film with left-circularly polarized light and right-circularly polarized light for interference exposure to impart a liquid crystal alignment property in which the optical axis of the first coating film continuously rotates toward the grating vector direction. A step of applying a polymerizable liquid crystal compound to the first coating film after interference exposure to form a second coating film; After heating and cooling the first coating film and the second coating film, irradiating non-polarized ultraviolet rays to polymerize the polymerizable liquid crystal compound and impart the same liquid crystal alignment as the first coating film to the second coating film; A method for manufacturing a depolarizer. According to the above method, the depolarizer of the present invention can be further manufactured while suppressing costs.

Effect of the Invention

[0019] According to the present invention, a depolarization function can be imparted to a film-like optical element by a simple method. Further, an optical low-pass filter having a thin thickness and excellent optical characteristics can be formed using this.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3A

Figure 3B

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0021] First Embodiment [Polarization cancellation element] FIG. 1 is a conceptual diagram for explaining the distribution of the direction of the optical axis of the optical element 1 according to an embodiment of the present invention. The optical element 1 has an anisotropic structure in which the optical axis continuously rotates in the direction of the lattice vector. That is, in the optical element 1 of the present invention, substantially linear portions where the optical axis is in a certain direction are arranged periodically at equal intervals in a lattice-like optical structure, and in the portions therebetween, the optical axis continuously rotates in the direction of the lattice vector of the lattice-like structure. The optical element 1 having such an optical structure functions as a polarization diffraction grating that emits incident light as right-circularly polarized light and left-circularly polarized light.

[0022] FIG. 2 is a cross-Nicol image of the optical element 1 fabricated in Example 1 taken with a polarization microscope. Due to the above-described lattice-like optical structure, portions that become extinction positions (dark portions) appear periodically (in stripes). Since the directions of the optical axes orthogonal to each other become extinction positions, the extinction positions in the same optical axis direction appear as dark portions every other one. With respect to the extinction positions, the portions where the optical axis is rotating appear bright in the cross-Nicol image. The optical element 1 having such an optical structure functions as a diffraction grating having a polarization cancellation function. Hereinafter, this will be described as the polarization cancellation element 1.

[0023] The above-mentioned polarization extinction element 1 can be realized by orienting a material having liquid crystallinity on a substrate such that portions having the same optical axis direction appear periodically and at equal intervals in a lattice pattern, and the optical axis rotates continuously in the direction of the lattice vector, and fixing the orientation (hereinafter referred to as periodic orientation). The polarization extinction element formed by such a manufacturing method has the same refractive index in the entire region. That is, since no region with a discontinuous refractive index occurs, no optical problems such as scattering occur.

[0024] [Manufacturing Method of Polarization Extinction Element] The polarization extinction element having the above optical structure can be manufactured, for example, by the following method. [Method 1] A method of producing a polarization extinction element having an optically anisotropic structure in which the optical axis rotates continuously in the direction of the lattice vector by applying a liquid crystalline material having photo-orientability on a substrate, irradiating the coating film with right-handed circularly polarized light and left-handed circularly polarized light, and fixing the orientation generated by the interference exposure of the two light beams. [Method 2] A method of producing a polarization extinction element having an optically anisotropic structure in which the optical axis rotates continuously in the direction of the lattice vector by applying a liquid crystalline material having photo-orientability on a substrate, irradiating the coating film with right-handed circularly polarized light and left-handed circularly polarized light, forming an alignment film by interference exposure of the two light beams, applying a polymerizable liquid crystal composition or the like on the alignment film and orienting it according to the orientation of the alignment film, and fixing the orientation.

[0025] Figs. 3A and 3B are schematic cross-sectional views of the polarization extinction element 1 manufactured according to the above method. Note that the thickness ratios of the respective layers in these figures do not limit the actual thickness ratios. When manufactured by Method 1, as shown in Fig. 3A, the polarization extinction element 1 has a layer 1b in which a photo-orientable liquid crystalline material exhibits periodic orientation formed on a substrate 1a. When manufactured by Method 2, as shown in Fig. 3B, an alignment film 1c in which a photo-orientable liquid crystalline material exhibits periodic orientation is formed on a substrate 1a, and a layer 1d in which a polymerizable liquid crystal composition exhibits periodic orientation according to the orientation of the alignment film is formed thereon.

[0026] The depolarizer 1 may be used in a state where it includes a substrate 1a. In that case, the substrate 1a may be an optically isotropic body, or may be another optical member combined with the depolarizer 1. If necessary, the substrate 1a peeled off may be used as the depolarizer 1. The thickness of the depolarizer 1 of the present invention is not particularly limited, but it is easy to make it thinner. For example, even if the film thickness of the film on the substrate 1a is 1 mm or less, preferably 50 μm or less, it can be used as the depolarizer 1. For example, in the depolarizer 1 shown in FIG. 3A, the layer 1b may have a thickness of about 1 to 30 μm, and in the depolarizer 1 shown in FIG. 3B, the layer 1c may have a thickness of about 0.06 to 10 μm and the layer 1d may have a thickness of about 1 to 30 μm. The thickness of the substrate 1a is not particularly limited and may be appropriately selected according to the application.

[0027] [Interference exposure apparatus] FIG. 4 is a top view showing an optical system of an apparatus that can be used for interference exposure in the above manufacturing method. In the figure, M1 to M4 are total reflection mirrors provided for adjusting the direction of the optical path, and descriptions thereof are omitted for simplicity. The light emitted from the light source 10 is separated by a polarization beam splitter 20 into a p-wave passing through the first optical path P1 and an s-wave passing through the second optical path P2.

[0028] The p-wave passes through a half-wave plate 30 and a quarter-wave plate 40 arranged in the first optical path P1 and is converted into left-handed circularly polarized light, which is expanded by an enlarging optical system 50 and irradiated onto the sample S. The s-wave passes through a half-wave plate 60 and a quarter-wave plate 70 arranged in the second optical path P2 and is converted into right-handed circularly polarized light, which is expanded by an enlarging optical system 80 and irradiated onto the sample S. With respect to the interference exposure of this left-handed circularly polarized light LCP and right-handed circularly polarized light RCP, the liquid crystal molecules showing photo-orientation property are periodically arranged while changing their orientation as schematically shown in FIG. 5, and the optical characteristics of the depolarizer 1 of the present invention are obtained.

[0029] As the light source 10, for example, an ultraviolet laser light source may be used. The dimensions of the optical system are not particularly limited. By appropriately adjusting the optical system, the interval of the interference fringes formed by interference exposure can be adjusted, and the magnitude of the lattice vector in the polarization extinction element can be adjusted. For example, when performing interference exposure, the magnitude of the lattice vector can be changed by changing the distances between the total reflection mirrors M3, M4 and the sample S.

[0030] In addition, any method other than the above can be used as long as it is a method for imparting periodic orientation to the liquid crystalline material exhibiting photo-orientation. For example, the layer 1b shown in FIG. 3A or the layer 1c shown in FIG. 3B may be formed by a method of scanning while changing the polarization direction using linearly polarized laser light, or by a method of performing mask exposure of linearly polarized light while changing the polarization direction and the mask position.

[0031] [Liquid crystalline material exhibiting photo-orientation] As the liquid crystalline material exhibiting photo-orientation used in the above manufacturing method, for example, a liquid crystalline material at least composed of a polymer having a photosensitive group in at least a part of the side chains and having a side chain represented by any one of the following chemical formulas 1 to 3 can be used. [Chemical formula] [Chemical formula] [Chemical formula] In each of the above chemical formulas 1 and 2, independently, n represents an integer from 1 to 12, m represents an integer from 1 to 12, X and Y each represent none, -COO, -OCO-, -N=N-, -C=C- or -C6H4-, W1 and W2 each represent a cinnamoyloxy group, a chalcone group, a cinnamylidene group, a biphenylacryloyloxy group, a furylacryloyloxy group, a naphthylacryloyloxy group or a derivative thereof, or -H, -OH, or -CN, and in the above chemical formula 3, s represents 0 or 1, t represents an integer from 1 to 3, and R represents H, an alkyl group, an alkyloxy group or a halogen.

[0032] When the above liquid crystalline material is used, the side chain having a photosensitive group is oriented while periodically changing the orientation direction as shown in FIG. 5 by the interference exposure of left circularly polarized LCP and right circularly polarized light RCP. Even if the liquid crystalline material contains a side chain without a photosensitive group, these are oriented according to the neighboring oriented side chains during the heating and cooling processes, and the periodic orientation property is fixed to the sample. The specific process can be carried out under the following conditions.

[0033] [Formation of coating film] A liquid crystalline polymer formed from monomer units having side chains represented by the above chemical formulas 1 to 3, and if necessary, a low molecular compound and other components (such as a polymerization catalyst) are added to the above liquid crystalline polymer, and a coating solution prepared by dissolving these in an appropriate solvent is applied onto a substrate, and a liquid crystalline polymer layer can be formed on the substrate by removing the solvent.

[0034] Examples of the solvent include dioxane, dichloroethane, cyclohexanone, toluene, tetrahydrofuran, o-dichlorobenzene, methyl ethyl ketone, methyl isobutyl ketone, etc., and these solvents are used alone or in combination.

[0035] The support is appropriately selected and used from various polymer films in addition to the glass substrate. For example, polyester films such as polyethylene terephthalate films, cellulose films such as diacetyl cellulose and triacetyl cellulose, polycarbonate films such as bisphenol A-carbonate copolymers, linear or branched polyolefin films such as polyethylene, polypropylene, and ethylene-propylene copolymers, polyamide films, imide polymer films, sulfone polymer films, and the like can be mentioned.

[0036] [Interference exposure] After applying the coating solution onto the support and drying it to the extent that the solvent is removed, a periodic alignment layer can be formed by imaging left-circularly polarized light and right-circularly polarized light on the coating film using, for example, the apparatus described in FIG. 4.

[0037] Interference exposure may be performed during drying (before complete drying). After interference exposure, it is preferable to heat the sample to 80 to 130 ° C, preferably 100 to 120 ° C, and then cool it.

[0038] (Formation of a periodic alignment layer using a polymerizable liquid crystalline material) In some cases, after inducing periodic alignment by subjecting the liquid crystalline material having photoalignment properties represented by the above chemical formulas 1 to 3 to interference exposure with left-circularly polarized light and right-circularly polarized light, this may be used as an underlying alignment film (layer 1c in FIG. 3B), and a periodic alignment layer (layer 1d in FIG. 3B) made of a polymerizable liquid crystalline material may be formed thereon. In the description of the present invention, the polymerizable liquid crystalline material shall not include a liquid crystalline material having photoalignment properties per se. This periodic alignment layer can be formed by dissolving a polymerizable liquid crystalline material in a solvent to form a solution, applying it onto the alignment film, drying it after application, inducing the alignment of the polymerizable liquid crystalline material by performing a heat treatment, and then irradiating it with non-polarized ultraviolet light to fix this alignment.

[0039] [Polymerizable liquid crystalline material] In the present invention, the polymerizable liquid crystalline material to be aligned on the alignment film may be composed of a liquid crystalline polymer or a liquid crystalline monomer. It may also be a liquid crystalline polymer or a liquid crystalline monomer in which a crosslinked structure is introduced to such an extent that the liquid crystallinity is not impaired by a polymerizable liquid crystalline material having a functional group polymerizable by light or heat, or a crosslinking agent such as an isocyanate material or an epoxy material. Further, a bifunctional low molecular material described below may be added as a low molecular material, applied, and after aligning the polymerizable liquid crystalline material, polymerization may be carried out so as to contain a crosslinkable polymer. If necessary, a photopolymerization initiator, a thermal polymerization initiator, or a sensitizer may be mixed. By aligning such a liquid crystallizable material on the alignment film and fixing the alignment, an optically anisotropic layer having the characteristics of a polarization diffraction grating can be formed on the alignment film.

[0040] Examples of the polymerizable liquid crystal include Schiff base type, biphenyl type, terphenyl type, ester type, thioester type, stilbene type, trans type, azoxy type, azo type, phenylcyclohexane type, pyrimidine type, cyclohexylcyclohexane type, trimesic acid type, triphenylene type, torquene type, phthalocyanine type, porphyrin type liquid crystal compounds having a molecular skeleton, or mixtures of these compounds. Those that can be orientation-fixed by means such as thermal crosslinking or photo-crosslinking in a liquid crystal state or in a state cooled below the liquid crystal transition temperature by introducing a crosslinkable group or blending an appropriate crosslinking agent are included. As the polymerizable liquid crystal, it is preferable to use a compound showing a nematic liquid crystal phase.

[0041] Further, the polymerizable liquid crystal may be a liquid crystal polymer that can be orientation-fixed by means such as thermal crosslinking or photo-crosslinking in a liquid crystal state or in a state cooled below the liquid crystal transition temperature by introducing a crosslinkable group or blending an appropriate crosslinking agent, and is not particularly limited as long as it has a unit composed of a mesogen-forming group. The unit may be in the main chain or the side chain of the liquid crystal polymer. Examples of the main chain type liquid crystal polymer include polyester type, polyamide type, polycarbonate type, polyimide type, polyurethane type, polybenzimidazole type, poly Examples include liquid crystal polymers of the benzoxazole type, polybenzothiazole type, polyazomethine type, polyester amide type, polyester carbonate type, polyester imide type, or mixtures thereof. Examples of side-chain liquid crystalline polymers include liquid crystal polymers in which a mesogenic group is bonded as a side chain to a polymer having a linear or cyclic skeletal chain of a polyacrylate type, polymethacrylate type, polyvinyl type, polysiloxane type, polyether type, polymalonate type, or the like, or mixtures thereof. As the liquid crystal polymer, it is preferable to use a polymer exhibiting a nematic liquid crystal phase.

[0042] Examples of the crosslinkable group include a vinyl group, a vinyloxy group, a 1-chlorovinyl group, an isopropenyl group, a 4-vinylphenyl group, an acryloyloxy group, a methacryloyloxy group, an oxiranyl group, an oxetanyl group, and the like. Among them, an acryloyloxy group, a methacryloyloxy group, a vinyloxy group, an oxiranyl group, and an oxetanyl group are preferable, and an acryloyloxy group is more preferable.

[0043] As the polymerizable liquid crystal, commercially available liquid crystalline compounds can be used. For example, LC242 of BASF may be used. Since these liquid crystal compounds are less expensive than the liquid crystal compounds having photoalignment properties represented by Chemical Formulas 1 to 3, the cost of manufacturing the depolarization element can be reduced as compared with the case where the depolarization element is formed using only the liquid crystal compounds having photoalignment properties.

[0044] As the photoinitiator, commercially available photoinitiators such as Irgacure 907, Irgacure 184, Irgacure 651, Irgacure 819, Irgacure 250, Irgacure 369 (all of the above are manufactured by Ciba Japan Co., Ltd.), Seikol BZ, Seikol Z, Seikol BEE (all of the above are manufactured by Seiko Chemical Co., Ltd.), Kayacure BP100 (manufactured by Nippon Kayaku Co., Ltd.), Kayacure UVI-6992 (manufactured by Dow), Adeka Optomer SP-152 or Adeka Optomer SP-170 (all of the above are manufactured by Adeka Corporation), TAZ-A, TAZ-PP (both are manufactured by Nippon Sieber Hegner Co., Ltd.) and TAZ-104 (manufactured by Sanwa Chemical Co., Ltd.) can also be used.

[0045] As the thermal initiator, azo compounds such as azobisisobutyronitrile; peroxides such as hydrogen peroxide, persulfates, benzoyl peroxide, etc. can be mentioned. The content of the polymerization initiator is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 0.5 to 8 parts by mass with respect to 100 parts by mass of the polymerizable liquid crystal compound (or polymerizable liquid crystal polymer). Within the above range, polymerization can be carried out without disturbing the alignment of the polymerizable liquid crystal compound.

[0046] When a photoinitiator is used as the polymerization initiator, a photosensitizer may be used in combination. Examples of the photosensitizer include xanthone compounds such as xanthone and thioxanthone (for example, 2,4-diethylthioxanthone, 2-isopropylthioxanthone, etc.); anthracene compounds such as anthracene and alkoxy group-containing anthracene (for example, dibutoxyanthracene, etc.); phenothiazine; rubrene, etc.

[0047] If necessary, a compound having photosensitivity may be added to the polymerizable liquid crystalline material used to form the alignment layer in an amount that does not disrupt the liquid crystallinity of the polymerizable liquid crystalline material. In this case, it is preferable to use a photosensitive group having the same or similar chemical structure as the photosensitive group of the liquid crystalline material having a photosensitive group for forming the underlying alignment film. For example, a liquid crystalline material having photoalignment properties represented by the above chemical formulas 1 to 3 may be mixed in an amount of about 0.5 to 10 parts by mass with respect to 100 parts by mass of the polymerizable liquid crystal compound (or polymerizable liquid crystal polymer).

[0048] [Formation of Alignment Film] The formation of the alignment film can be carried out in the same manner as the process for forming a periodic alignment layer using the above-described liquid crystalline material having photoalignment properties. That is, a liquid crystalline polymer formed from monomer units having side chains represented by the above chemical formulas 1 to 3, and if necessary, a low molecular compound and other components (such as a polymerization catalyst) are added to the above liquid crystalline polymer, and a coating solution prepared by dissolving these in an appropriate solvent is applied onto a substrate, and the solvent is removed to form a liquid crystalline polymer layer on the substrate. Here, the solvents and the substrate described above can be used. Next, for example, by using the apparatus described in FIG. 4 to perform interference exposure of left circularly polarized light and right circularly polarized light on the coating film, periodic alignment properties are imparted to the coating film. After the interference exposure, the sample may be heated to 80 to 130 ° C., preferably 100 to 120 ° C., and then cooled. However, the heating and cooling of the sample may be performed after applying the polymerizable liquid crystalline material.

[0049] [Formation of Polymerizable Liquid Crystalline Material Layer] After forming an alignment film on the substrate, the above-described polymerizable liquid crystalline material is applied and dried on the alignment film, whereby the polymerizable liquid crystalline material is induced to have alignment properties according to the alignment properties of the underlying alignment film.

[0050] [Irradiation with Non-Polarized Ultraviolet Light] It is preferable to apply a polymerizable liquid crystalline material onto an alignment film, align it according to the alignment property of the alignment film, and then irradiate it with non-polarized ultraviolet light. When irradiated with non-polarized ultraviolet light, the polymerizable groups in the polymerizable liquid crystalline material react to fix the alignment, forming a stable periodic alignment layer and also fixing the alignment property of the alignment film. Further, at the interface between the alignment film and the polymerizable liquid crystalline material layer, a photoreaction occurs between the photosensitive groups of the liquid crystalline material forming the alignment film and the photosensitive groups contained in the polymerizable liquid crystalline material, which is considered to contribute to the high adhesion between the two layers.

[0051] As described above, by using an alignment film and aligning the polymerizable liquid crystalline material directly laminated thereon, the polarization extinction element of the present invention can be formed.

[0052] Second Embodiment [Low-pass Filter] An optical low-pass filter according to an embodiment of the present invention can be formed by using the polarization extinction element (polarization diffraction grating) 1 of the present invention. As shown in FIG. 1, the polarization extinction element 1 of the present invention shows a lattice-like structure in which portions having the same direction of the optical axis appear periodically at equal intervals, and has an anisotropic structure in which the optical axis continuously rotates in the direction of the lattice vector. This element functions as a polarization diffraction grating and can diffract incident light in two directions as right-handed circularly polarized light and left-handed circularly polarized light. FIG. 6 is an example of an optical low-pass filter 100 using this element, and has a structure in which a third element 2 (for example, a quarter-wave plate) having birefringence is sandwiched between a first element 11 and a second element 12 each composed of the polarization extinction element of the present invention, and the second element 12 is arranged such that the direction of the lattice vector is rotated by 90 degrees with respect to the direction of the lattice vector of the first element 11. When light is incident on the optical element laminate having this structure, as shown in the examples described later, the point image can be separated into four, and it can be used as the optical low-pass filter 100. At that time, since the elements 11 and 12 can be formed by fixing the alignment property of the liquid crystalline material constituting the coating film on the substrate as described above, it is easy to reduce the thickness and the manufacturing process can be made simple.

Examples

[0053] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited in any way by these examples.

[0054] (Monomer 1) p-Coumaric acid and 6-chloro-1-hexanol were heated under alkaline conditions to synthesize 4-(6-hydroxyhexyloxy)cinnamic acid. Methacrylic acid was added in a large excess in the presence of p-toluenesulfonic acid to this product for an esterification reaction to synthesize Monomer 1 represented by the following chemical formula.

[0055] [Chemical formula]

[0056] (Monomer 2) 4-Hydroxybenzoic acid and 6-chloro-1-hexanol were heated under alkaline conditions to synthesize 4-(6-hydroxyhexyloxy)benzoic acid. Then, methacrylic acid was added in a large excess in the presence of p-toluenesulfonic acid to this product for an esterification reaction to synthesize Monomer 2 represented by the following chemical formula.

[0057] [Chemical formula]

[0058] (Copolymer 1) Monomer 1 and Monomer 2 were dissolved in dioxane such that the molar ratio of Monomer 1:Monomer 2 was 3:7, and AIBN (azobisisobutyronitrile) was added as a reaction initiator, followed by polymerization at 70°C for 24 hours to obtain Copolymer 1. This Copolymer 1 exhibited liquid crystallinity.

[0059] (Copolymer 1) Monomer 1 and Monomer 2 were dissolved in dioxane such that the molar ratio of Monomer 1 to Monomer 2 was Monomer 1:Monomer 2 = 3:7. AIBN (azobisisobutyronitrile) was added as a reaction initiator, and polymerization was carried out at 70 °C for 24 hours to obtain Copolymer 1. This Copolymer 1 exhibited liquid crystallinity.

[0060] (Copolymer 2) Monomer 1 and 2-hydroxyethyl methacrylate (HEMA) were dissolved in dioxane such that the molar ratio of Monomer 1 to HEMA was Monomer 1:HEMA = 75:25. AIBN (azobisisobutyronitrile) was added as a reaction initiator, and polymerization was carried out at 70 °C for 24 hours to obtain Copolymer 2.

[0061] (Example 1) Copolymer 1 and cinnamic acid were dissolved in tetrahydrofuran (THF) at a weight ratio of 95:5 to prepare a solution. This solution was applied onto a cover glass substrate using a spin coater to a thickness of 3 μm and dried at 25 °C. To the dried coating film, using the interference exposure optical system shown in Fig. 4, ultraviolet laser light of 360 nm emitted from the DPSS laser used as the light source was subjected to interference exposure (irradiation dose 200 mJ / cm 2 ) as left circularly polarized light and right circularly polarized light. Subsequently, heating was carried out at 130 °C for 3 minutes and then cooled to room temperature to induce orientation. This orientation was due to the formation of side chains that underwent axis-selective photoreaction in the coating film according to the polarization direction of the light exposed to each region by interference exposure, and then, by the molecular motion during subsequent heating, the unreacted side chains aligned along the reacted side chains. The coating film thus obtained was an oriented coating film in which the optical axis continuously rotated in the direction of the lattice vector. By this method, the optical element of the present invention was obtained.

[0062] (Example 2) The copolymer 2 was dissolved in tetrahydrofuran (THF) to prepare a solution. This solution was applied onto a cover glass substrate using a spin coater to a thickness of 0.5 μm and dried at 25°C. To the dried coating film, using the interference exposure optical system shown in Fig. 4, ultraviolet laser light with a wavelength of 360 nm emitted from the DPSS laser used as the light source was subjected to interference exposure (exposure dose: 20 mJ / cm 2 ) as left circularly polarized light and right circularly polarized light, to form a coating film imparted with a liquid crystal alignment property in which the optical axis continuously rotates in the lattice vector direction.

[0063] Subsequently, a polymerizable liquid crystal compound (manufactured by BASF, LC-242) and 5 parts by weight of a photopolymerization initiator (manufactured by Ciba Specialty Chemicals, Irgacure 907) were mixed and dissolved in toluene to prepare a solution. This solution was applied onto the aforementioned coating film using a spin coater to a thickness of 2 μm, heated to 70°C, cooled to room temperature, and further irradiated with non-polarized ultraviolet light (exposure dose: 280 mJ / cm 2 ) to polymerize the polymerizable liquid crystal compound, thereby forming an optically anisotropic layer in which the optical axis continuously rotates in the lattice vector direction. By this method, the optical element of the present invention was obtained.

[0064] (Example 3) To evaluate the depolarization effect, a simple imaging optical system was assembled. As shown in Fig. 7, in order from the light source L, a pattern (metal mask) 3, a first polarizing plate 4, an enlarging lens 5, a projection lens 6, a second polarizing plate 7, and a screen 8 were provided. Here, the first polarizing plate 4 and the second polarizing plate 7 were arranged in a cross Nicol configuration. Therefore, it was confirmed that when the depolarizing element 1 of the invention was not inserted, the light transmitted through the first polarizing plate 4 was absorbed by the second polarizing plate 7 and no pattern was projected on the screen.

[0065] The polarization cancellation element 1 of the present invention prepared in the same manner as in Example 1 was inserted into the imaging optical system of FIG. 7 to confirm the degree of polarization cancellation. The insertion positions were selected from three locations: position S1 close to pattern 3 between the magnifying lens 5 and the first polarizing plate, position S2 between the magnifying lens 5 and the projection lens 6, and position S3 between the projection lens 6 and the screen 8. When using an element with a narrow periodic pitch of the anisotropic structure as the polarization cancellation plate 1, it was inserted near pattern 3, and when using an element with a large periodic pitch, it was inserted on the distal side from pattern 3. Note that elements with different periodic pitches were fabricated by changing the distance from the total reflection mirrors M3 and M4 to the sample installation position during interference exposure.

[0066] By inserting a sample of the polarization cancellation element 1 of the present invention, it was confirmed that a pattern was projected onto the screen. Furthermore, it was confirmed that the pattern projected onto the screen did not disappear even when the sample was rotated 360° or when the polarizing plate 2 was rotated 360°, indicating that the polarization was cancelled.

[0067] (Example 4) Two polarization cancellation elements prepared in the same manner as in Example 1 were prepared. The first element and the second element showed retardation values of 276.5 nm and 281.1 nm, respectively, for light with a wavelength of 550 nm. As shown in FIG. 6, the first element 11 and the second element 12 were arranged such that the directions of their lattice vectors were different by 90 degrees, and a third optical element (quarter-wave plate) 2 having birefringence with a retardation of 137 nm for light with a wavelength of 550 nm was arranged therebetween.

[0068] The stacked body of these three optical elements was irradiated with polarized laser light with a wavelength of 532 nm, and the intensity distribution of the emitted light was measured. FIG. 8 shows the observation results of the emitted light distribution, and FIG. 9 shows the measurement data of the intensity distribution. From these results, it was confirmed that the point image could be separated into four points of ±first-order diffracted light. On the other hand, it was confirmed that the emission of the zero-order light and the suppression of higher-order diffracted light such as second-order light were suppressed.

[0069] From the above results, it was confirmed that in the optical low-pass filter of the present invention, a low-pass effect can be obtained while avoiding a decrease in the low-pass effect due to zero-order light and a decrease in resolution due to higher-order diffracted light.

Industrial Applicability

[0070] The depolarizing element of the present invention and the low-pass filter using the same can be provided as a thin optical element and an optical member with excellent optical characteristics and a simple manufacturing method that suppresses costs compared to the prior art, so they have high industrial applicability.

Explanation of Reference Numerals

[0071] 1, 11, 12 Depolarizing element 1a Substrate 1b Photo-alignment liquid crystalline material layer 1c Alignment film 1d Polymerizable liquid crystalline material layer 2 Element having birefringence 3 Pattern 4 First polarizing plate 5 Magnifying lens 6 Projection lens 7 Second polarizing plate 8 Screen 10 Light source 30, 60 Beam splitter 40, 70 Quarter-wave plate 50, 80 Magnifying system 100 Low-pass filter L Light source M1, M2, M3, M4 Total reflection mirror

Claims

1. A film made of a liquid crystalline material, having an anisotropic structure in which the optical axis of the film continuously rotates toward the lattice vector direction, wherein the birefringence magnitude is uniform in the plane of the film, using a polarization diffraction grating, a polarization cancellation element.

2. A film made of a liquid crystalline material exhibiting photoalignment, having an anisotropic structure in which the optical axis of the film continuously rotates toward the lattice vector direction, wherein the birefringence magnitude is uniform in the plane of the film, a polarization diffraction grating comprising a first element and a second element, and a third element having a constant azimuth of the optical axis and having birefringence, wherein the first element, the second element, and the third element are each formed as individual members, wherein the first element and the second element are arranged such that the lattice vectors of the polarization diffraction gratings are orthogonal to each other, and the third element is arranged between the first element and the second element, an optical low-pass filter.

3. In the optical low-pass filter according to claim 2, in the first element and the second element composed of the polarization diffraction grating, linear portions where the optical axis becomes a constant direction are periodically arranged at intervals corresponding to interference fringes formed by the interference of left-circularly polarized light and right-circularly polarized light. an optical low-pass filter.

4. A method for manufacturing a polarization diffraction grating according to any one of claims 1 to 3, comprising a step of applying a liquid crystalline material having photoalignment onto a substrate to form a coating film, a step of irradiating the coating film with left-circularly polarized light and right-circularly polarized light for interference exposure, and a step of heating and cooling the coating film after exposure to induce the alignment of the liquid crystalline material.

5. A method for manufacturing a polarization diffraction grating according to claim 1, comprising a step of applying a liquid crystalline material having photoalignment onto a substrate to form a first coating film, a step of irradiating the first coating film with left-circularly polarized light and right-circularly polarized light for interference exposure to impart a liquid crystal alignment property in which the optical axis of the first coating film continuously rotates toward the lattice vector direction, a step of applying a polymerizable liquid crystal compound onto the first coating film after interference exposure to form a second coating film, and a step of polymerizing the polymerizable liquid crystal compound by irradiating the first coating film and the second coating film with non-polarized ultraviolet light after heating and cooling to impart the same liquid crystal alignment property as the first coating film to the second coating film. a method for manufacturing a polarization diffraction grating.

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