Polarizing plate, method for manufacturing the same, and optical apparatus

Abstract

The polarizing plate (100) of the present application is a polarizing plate having a wire grid structure. The polarizing plate (100) has a transparent substrate (10) and a plurality of projections (20) formed on a first surface (10a) of the transparent substrate (10) and extending in a first direction, and periodically arranged at intervals shorter than the wavelength of light used, each of the plurality of projections (20) having, in order from the transparent substrate (10) side, a reflection layer (21), a dielectric layer (22), and an absorption layer (23), the top surface (20aa) and the side surface (20ab) of each of the plurality of projections (20) being further covered with a protective film (40A) composed of a dielectric, and the area of the protective film (40A) gradually increasing from the top surface (20aa) side to the transparent substrate (10) side when viewed from a cross section that cuts the projections (20) in a plane orthogonal to the surface (10a) of the transparent substrate (10) and orthogonal to the first direction.

Description

TECHNICAL FIELD

[0001] The present application relates to a polarizing plate and a manufacturing method thereof, and an optical apparatus.

[0002] This application claims priority based on Japanese Patent Application No. 2020-090347 filed on May 25, 2020, the contents of which are hereby incorporated by reference. BACKGROUND

[0003] A polarizing plate is an optical element that absorbs a polarized light in one direction and transmits a polarized light in a direction orthogonal thereto. In a liquid crystal display device, a polarizing plate is required in principle. In particular, a liquid crystal display device using a light source with a large amount of light such as a transmission-type liquid crystal projector requires excellent heat resistance and light resistance because a polarizing plate receives strong radiation, and control of a size of several centimeters or less, a high extinction ratio, and reflectance characteristics are required. In order to meet these requirements, a wire grid-type inorganic polarizing plate has been proposed.

[0004] A wire grid-type polarizing plate has a structure in which a plurality of wires extending in one direction are arranged at a pitch (several tens of nm to several hundreds of nm) narrower than a wavelength band of a light to be used on a substrate. When light is incident on the polarizing plate, a polarized wave (TE wave (S wave)) parallel to the extension direction of the wires cannot be transmitted, and a polarized wave (TM wave (P wave)) perpendicular to the extension direction of the wires is directly transmitted.

[0005] The wire grid-type polarizing plate has excellent heat resistance and light resistance, can be used to manufacture a relatively large element, and has a high extinction ratio. Furthermore, by adopting a multilayer structure, the reflectance characteristics can be controlled, and degradation of image quality caused by ghosting or the like due to reflection of return light reflected by the surface of the polarizing plate within the device of the liquid crystal projector can be reduced, so the wire grid-type polarizing plate is suitable for use in a liquid crystal projector or the like.

[0006] In view of the above, the present application proposes various polarizing plates as wire grid-type polarizing plates.

[0007] PRIOR ART DOCUMENTS

[0008] Patent Document 1: Japanese Patent Publication No. 2016-536651

[0009] Patent Document 2: Japanese Patent Publication No. 2019-536074

[0010] TECHNICAL PROBLEM

[0011] Patent Document 1 discloses a polarizing plate in which side walls of wire grid polarizers (polarizing plates) are formed with side bars that can assist each other. It is described that durability of the wire grid polarizers can be improved and good polarizing characteristics in the visible spectrum can be exhibited. However, since the durability of the wire grid polarizers with high aspect ratio is improved only by the side bars, the width of the side bars is necessarily thick, and thus good polarizing characteristics such as reduction in transmittance or increase in reflectance cannot be obtained. Also, in the case where the wire grid polarizers are filled, although the durability of the wire grid polarizers is improved to the extent that they can be touched, good polarizing characteristics such as further reduction in transmittance or increase in reflectance cannot be obtained.

[0012] Patent Document 2 discloses a polarizing plate in which an outer coating layer is formed from the front end to the side wall of a wire grid polarizer (polarizing plate), and a polarizing plate in which an anti-reflection layer is formed on the outer coating layer. It is described that the wire grid polarizer can have durability and high performance. However, even if the wire grid polarizer is supported by the outer coating layer to avoid collapse, since an air layer is included, good polarizing characteristics such as reduction in transmittance or increase in reflectance cannot be obtained. Also, the anti-reflection layer is provided on this basis, and although the polarizing characteristics are recovered, since the process is increased, the cost is also increased without doubt.

[0013] In recent years, light sources of illuminations / displayers have evolved from bulbs to LEDs and lasers, and even in liquid crystal projectors, high luminance is sought by using several semiconductor laser diodes (LDs) to become high luminous flux. Thus, polarizing plates are required to have durability in an environment of strong light with high luminance, while high transmittance characteristics can be achieved. For this reason, a polarizing plate with an optimized grid structure including a protective film needs to be proposed.

[0014] The present application was completed in view of the above-described circumstances, and aims to provide a polarizing plate and a manufacturing method thereof, and an optical device provided with the polarizing plate, in which light transmission characteristics in the transmittance axis direction are improved while durability is maintained by optimizing a grid structure including a protective film. SUMMARY

[0015] The present application provides the following means in order to solve the above-described problems.

[0016] (1) The polarizing plate of one embodiment of the present application is a polarizing plate having a wire grid structure, and includes a transparent substrate and a plurality of protrusions formed on a first surface of the transparent substrate and extending in a first direction, and periodically arranged at a pitch shorter than the wavelength of light used, each of the plurality of protrusions including, in order from the transparent substrate side, a reflection layer, a dielectric layer, and an absorption layer, the top surface and side surface of each of the plurality of protrusions being covered with a protective film made of a dielectric, and the area of the protective film gradually increasing from the top surface side to the transparent substrate side when the protrusions are viewed in a cross section orthogonal to the surface of the transparent substrate and taken along a plane orthogonal to the first direction.

[0017] (2) In the above embodiment, the protective film can be approximately left-right symmetrical with the center between adjacent protrusions as a reference.

[0018] (3) In the above embodiment, the bottom surface of the protective film can be on the transparent substrate.

[0019] (4) In the above embodiment, the transparent substrate can be engraved along a plane extending from the outer peripheral surface of the protective film covering the side surface of the protrusions.

[0020] (5) The method for manufacturing a polarizing plate of another embodiment of the present application is a method for manufacturing a polarizing plate having a wire grid structure, including the steps of: forming a reflection layer, a dielectric layer, and an absorption layer in order on a first surface of a transparent substrate to manufacture a layered body made of the reflection layer, the dielectric layer, and the absorption layer; forming a plurality of protrusions extending in a first direction and periodically arranged at a pitch shorter than the wavelength of light used, by selectively etching the layered body; and forming a protective film made of the dielectric layer covering the surface of each of the plurality of protrusions, wherein the step of forming the protective film includes a step of etching the protective film so that the area of the protective film gradually increases from the top surface side to the transparent substrate side when the protrusions are viewed in a cross section orthogonal to the surface of the transparent substrate and taken along a plane orthogonal to the first direction.

[0021] (6) An optical device of another embodiment of the present application includes the polarizing plate of the above embodiment.

[0022] According to the present application, a polarizing plate in which the light transmission characteristics in the transmission axis direction are improved while the durability is maintained can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A schematic view of a polarizing plate according to one embodiment of the present application.

[0024] Figure 2Cross-sectional view of a polarizing plate related to an embodiment of the present invention.

[0025] Figure 3 Cross-sectional view of a polarizing plate related to another embodiment of the present invention. Figure 2

[0026] Figure 4 Cross-sectional view of a polarizing plate related to another embodiment of the present invention.

[0027] Figure 5 Cross-sectional view of a polarizing plate related to another embodiment of the present invention. Figure 4

[0028] Figure 6 Cross-sectional view of a polarizing plate related to another embodiment of the present invention.

[0029] Figure 7 Cross-sectional view of a polarizing plate related to another embodiment of the present invention. Figure 6

[0030] Figure 8 Cross-sectional view of a model of a protective film shape before processing.

[0031] Figure 9 Cross-sectional view of a model of a conventional structure without a protective film.

[0032] Figure 10 Graph showing the transmittance of the transmission axis in the optical characteristics of a polarizing plate related to an embodiment of the present invention, obtained by simulation calculation.

[0033] Figure 11 Graph showing the average transmittance of the transmission axis per wavelength band in the transmittance of the transmission axis obtained by simulation calculation for a polarizing plate related to an embodiment of the present invention.

[0034] Explanation of symbols

[0035] 10, 11: transparent substrate

[0036] 10a, 11a: first surface

[0037] 10b, 11b: second surface

[0038] 20: convex portion

[0039] 21: reflection layer

[0040] 22: dielectric layer

[0041] 23: absorption layer

[0042] 40A, 41A, 42A: protective film

[0043] ​​​100, 200, 300: Polarizing plate

[0044] 100a, 200a, 300a: Surface of polarizing plate DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be described clearly and completely below with appropriate reference to the accompanying drawings. In the description of the present application, it should be understood that, because the features are easy to understand, in the accompanying drawings used in the following description, the size ratio of each constituent element may be different from the actual one because of the magnified representation of the features. The materials, dimensions, and the like exemplified in the following description are only some of the embodiments of the present application, and not all the embodiments. All other embodiments obtained by those skilled in the art without creative labor based on the embodiments in the present application fall within the scope of protection of the present application.

[0046] [Polarizing plate (first embodiment)]

[0047] Figure 1 A schematic view of a polarizing plate according to an embodiment of the present application.

[0048] Figure 1 The polarizing plate 100 shown is a polarizing plate having a wire grid structure, and has a transparent substrate 10 and a plurality of convex portions 20 formed on a first surface 10a of the transparent substrate 10 and extending in a first direction (Y direction) to be arranged at a pitch shorter than the wavelength of light used. Figure 1 In the drawing, a protective film covering the convex portions 20 is not shown.

[0049] Here, as shown in Figure 1 the drawing, the extending direction (first direction) of the plurality of convex portions 20 is referred to as the Y-axis direction. The direction orthogonal to the Y-axis direction and along which the plurality of convex portions 20 are arranged along the main surface of the transparent substrate 10 is referred to as the X-axis direction. The direction orthogonal to the Y-axis direction and the X-axis direction and perpendicular to the main surface of the transparent substrate 10 is referred to as the Z-axis direction. In addition, light incident on the polarizing plate 100 can be incident from the first surface 10a side or the second surface 10b side of the transparent substrate 10, and is preferably incident from the first surface side (grid surface side) of the transparent substrate 10 on which the plurality of convex portions 20 are formed, as shown in Figure 1 the drawing, from the Z-axis direction orthogonal to the X-axis direction and the Y-axis direction.

[0050] The polarizing plate having a wire grid structure attenuates a polarized wave having an electric field component in the Y-axis direction (TE wave (S wave)) by utilizing four effects of transmission, reflection, interference, and selective light absorption of a polarized wave due to optical anisotropy, and transmits a polarized wave having an electric field component in the X-axis direction (TM wave (P wave)). Thus, in the present embodiment, the Y-axis direction is the direction of the absorption axis of the polarizing plate 100, and the X-axis direction is the direction of the transmission axis of the polarizing plate 100. Figure 1

[0051] Figure 2 A cross-sectional view of a polarizing plate related to the first embodiment of the present application.

[0052] Figure 2 The polarizing plate 100 shown in the drawing has a transparent substrate 10 and a plurality of convex portions 20 formed on the first surface 10a of the transparent substrate 10 and extending in the first direction, and periodically arranged at a pitch shorter than the wavelength of light used. The plurality of convex portions 20 have, in order from the side of the transparent substrate 10, a reflection layer 21, a dielectric layer 22, and an absorption layer 23. The top surface 20aa and the side surface 20ab of each of the plurality of convex portions 20 are also covered with a protective film 40A composed of a dielectric. From a cross section obtained by cutting the convex portions 20 with a plane orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction, the area of the protective film 40A gradually increases from the side of the top surface 20aa to the side of the transparent substrate 10.

[0053] In addition, the polarizing plate 100 of the present embodiment can also have the transparent substrate 10, the reflection layer 21, the dielectric layer 22, the absorption layer 23, the protective film 40A, and layers other than these, within the range where the effects of the present application are achieved.

[0054] From the side of the plurality of convex portions 20 (the side of the grid surface) of the polarizing plate 100 shown in the drawing, light is incident, and a part of the light is attenuated by being absorbed when passing through the absorption layer 23 and the dielectric layer 22. Among the light transmitted through the absorption layer 23 and the dielectric layer 22, the polarized wave (TM wave (P wave)) is transmitted through the reflection layer 21 with high transmittance. On the other hand, among the light transmitted through the absorption layer 23 and the dielectric layer 22, the polarized wave (TE wave (S wave)) is reflected by the reflection layer 21. The TE wave reflected by the reflection layer 21 is partly absorbed and partly reflected back to the reflection layer 21 when passing through the absorption layer 23 and the dielectric layer 22. Also, the TE wave reflected by the reflection layer 21 is attenuated by interference when passing through the absorption layer 23 and the dielectric layer 22. As described above, by performing selective attenuation of the TE wave, the polarizing plate 100 can obtain the desired polarizing properties. Figure 2 Here, the use of the reflection layer 21, the dielectric layer 22, and the absorption layer 23 is not limited to the above-described configuration. For example, the reflection layer 21 can be omitted, and the dielectric layer 22 and the absorption layer 23 can be formed in a single layer.

[0055] Figure 2 Figure 3 ​​​The size of the polarizing plate 100 in the present specification will be described. The height h of the lattice refers to the size in the Z-axis direction perpendicular to the main surface of the transparent substrate 10 in Figure 3 the height of the convex portions 20 and the height of the protective film 40A (the thickness of the upper protective film 40Aa covering the top surface 20aa of the convex portions 20) h1. The width w refers to the size in the X-axis direction of the top surface 40Aaaa of the protective film 40A as viewed in the Y-axis direction along the direction in which the plurality of convex portions 20 extend. Also, the repeating interval in the X-axis direction of the plurality of convex portions 20 as viewed in the Y-axis direction along the direction in which the plurality of convex portions 20 extend is referred to as the pitch p.

[0056] In the polarizing plate 100 of the present embodiment, the pitch p of the plurality of convex portions 20 is not particularly limited as long as it is shorter than the wavelength of the light of the used wavelength band. From the viewpoint of ease of production and stability, the pitch p of the plurality of convex portions 20 is preferably, for example, 100 nm to 200 nm. The pitch p of the plurality of convex portions 20 can be measured by observation using a scanning electron microscope or a transmission electron microscope. For example, the pitch p can be measured at any four points using a scanning electron microscope or a transmission electron microscope, and the arithmetic mean of the measured values can be taken as the pitch p of the plurality of convex portions 20. Hereinafter, this measurement method is referred to as the electron microscope method.

[0057] The polarizing plate 100 of the present embodiment is characterized in that the shape of the protective film from the front end of the lattice to between the lattices is optimized. Thereby, it is possible to improve the light transmission properties in the transmission axis direction while maintaining the durability.

[0058] [Transparent Substrate]

[0059] As the transparent substrate 10, any substrate having light transmittance with respect to the light of the used wavelength band can be used, and there is no particular limitation, and the substrate can be appropriately selected according to the purpose. The "light transmittance with respect to the light of the used wavelength band" does not mean that the transmittance of the light of the used wavelength band is 100%, but means that the light transmittance can be maintained as a function of the polarizing plate. As the light of the used wavelength band, for example, visible light having a wavelength of about 380 nm to 810 nm can be used. The shape of the main surface of the transparent substrate 10 is not particularly limited, and the shape (for example, a rectangular shape) can be appropriately selected according to the purpose. The average thickness of the transparent substrate 10 is preferably, for example, 0.3 mm to 1 mm.

[0060] As the material constituting the transparent substrate 10, a material having a refractive index of 1.1 to 2.2 is preferable, and can be glass, water crystal, quartz, sapphire, or the like. From the viewpoint of cost and light transmittance, glass is preferably used, and quartz glass (refractive index 1.46) or soda lime glass (refractive index 1.51) is particularly preferable. The composition of the glass material is not particularly limited, and inexpensive glass materials such as silicate glass, which is widely available as optical glass, can be used.

[0061] Further, from the viewpoint of thermal conductivity, water crystal or sapphire, which have high thermal conductivity, are preferably used. Thus, high light resistance against strong light can be obtained, and the polarizing plate used for the optical engine of a projector, which generates a large amount of heat, is preferably used.

[0062] In addition, when the transparent substrate 10 is constituted by an optically active crystal such as water crystal or sapphire, a plurality of convex portions 20 are preferably arranged in the parallel direction or the perpendicular direction with respect to the optical axis of the crystal. Thus, excellent optical characteristics can be obtained. The optical axis here refers to the direction axis in which the difference between the refractive indices of O (ordinary ray) and E (extraordinary ray) of light advancing in that direction is the smallest.

[0063] [Reflection layer]

[0064] The reflection layer 21 is formed on the transparent substrate 10, and a metal film extending in a band shape is arranged in the Y-axis direction as the absorption axis.

[0065] The reflection layer 21 has the function of a wire grid type polarizer, attenuates a polarized wave (TE wave (S wave)) having an electric field component in the direction parallel to the length direction of the reflection layer 21, and transmits a polarized wave (TM wave (P wave)) having an electric field component in the direction orthogonal to the length direction of the reflection layer 21. The film thickness of the reflection layer 21 is not particularly limited, and is preferably, for example, 100 nm to 300 nm. In addition, the film thickness of the reflection layer 21 can be measured by the electron microscope method described above, for example.

[0066] As the material constituting the reflection layer 21, a material having reflectivity with respect to the light of the wavelength band used is sufficient, and is not particularly limited, and can be, for example, a single element selected from Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Ge, Te, and the like, or an alloy including one or more of these elements. Among them, from the viewpoint of suppressing the absorption loss of the wire grid to be small in the visible light region and the viewpoint of cost, the reflection layer 21 is preferably constituted by aluminum or an aluminum alloy. In addition, in addition to these metal materials, for example, it can be constituted by an inorganic film or a resin film other than metal having high surface reflectivity formed by coloring or the like.

[0067] Further, the reflective layer 21 can be formed as a high-density film by, for example, an evaporation method or a sputtering method. Also, the reflective layer 21 can be formed of two or more layers of different materials.

[0068] [Dielectric layer]

[0069] The dielectric layer 22 is formed on the reflective layer 21 and has dielectric films arranged in a strip shape extending in the Y-axis direction as an absorption axis. The film thickness of the dielectric layer 22 is set to a range in which a polarized wave reflected by the reflective layer 21 is phase-shifted by half a wavelength with respect to a polarized wave transmitted through the absorption layer 23. Specifically, the film thickness of the dielectric layer 22 is set to a range of 1 nm to 500 nm in which the phase of the polarized wave is adjusted to improve the interference effect. The film thickness of the dielectric layer 22 can be measured by, for example, the electron microscope method described above. Further, the dielectric layer 22b is formed as a barrier layer that suppresses the diffusion of constituent elements of the reflective layer 21 and the absorption layer 23 described later.

[0070] As a material constituting the dielectric layer 22, a general material such as one or a combination of Si oxides selected from SiO2and the like, metal oxides such as Al2O3, beryllium oxide, bismuth oxide, and the like, MgF2, cryolite, germanium, titanium dioxide, silicon, magnesium fluoride, boron nitride, boron oxide, tantalum oxide, and carbon can be used.

[0071] Among them, the dielectric layer 22 is preferably composed of one or more oxides selected from the group of Si oxides, Ti oxides, Zr oxides, Al oxides, Nb oxides, and Ta oxides from the viewpoint of the transmittance and the function of the barrier layer.

[0072] The refractive index of the dielectric layer 22 is preferably 1.0 to 2.5. Since the optical properties of the reflective layer 21 are also affected by the refractive index of the surrounding, the optical properties of the polarizing plate 100 can be controlled by selecting the material of the dielectric layer 22. Also, by appropriately adjusting the film thickness and the refractive index of the dielectric layer 22, for the TE wave reflected by the reflective layer 21, a part of the TE wave can be reflected at the absorption layer 23 to return to the reflective layer 21, and the light transmitted through the absorption layer 23 is attenuated by interference. In this way, by performing selective attenuation of the TE wave, the desired polarized wave properties can be obtained.

[0073] Further, the dielectric layer 22 can be formed as a high-density film by, for example, an evaporation method or a sputtering method, a chemical vapor deposition (CVD) method, or an atomic layer deposition (ALD) method. Also, the dielectric layer 22 can be formed of two or more layers of different materials.

[0074] [absorption layer]

[0075] The absorption layer 23 has an absorption effect on the light wavelength of the used wavelength band, and is formed on the dielectric layer 22 so as to extend in a strip shape in the Y-axis direction as an absorption axis. The film thickness of the absorption layer 23 is not particularly limited, and is preferably, for example, 5 nm to 50 nm. The film thickness of the absorption layer 23 can be measured by the electron microscope method described above, for example.

[0076] The absorption layer 23 is preferably composed of any one or more materials selected from the group consisting of a metal, an alloy material, and a semiconductor material.

[0077] As the material constituting the absorption layer 23, an appropriate material can be selected according to the range of the applied light wavelength.

[0078] As the metal material, it can be a single element selected from Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Sn, and the like, or an alloy including one or more of these elements. Also, as the semiconductor material, it can be one or more selected from Si, Ge, Te, ZnO, and silicide materials (β-FeSi2, MgSi2, NiSi2, BaSi2, CrSi2, CoSi2, or TaSi, and the like). By using these materials, the polarizing plate 100 can obtain a high extinction ratio with respect to the applied visible light region. Among them, the absorption layer 23 is preferably composed of Fe or Ta, and includes Si.

[0079] When a semiconductor material is used as the absorption layer 23, the band gap energy of the semiconductor participates in the absorption effect, and needs to be below the used wavelength band.

[0080] For example, when used for visible light, it is necessary to absorb a wavelength of 400 nm or more, that is, it is necessary to use a material having a band gap of 3.1 eV or less.

[0081] In addition, the absorption layer 23 can be formed into a high-density film by using, for example, an evaporation method or a sputtering method. Also, the absorption layer 23 can be composed of two or more layers having different materials.

[0082] [protective film]

[0083] The top surface 20aa and the side surface 20ab of each of the plurality of convex portions 20 are covered with a protective film 40A composed of a material capable of constituting the dielectric layer 22 described above. By being covered with the protective film 40A, the durability of the polarizing plate 100 can be improved.

[0084] In addition, the top surface 20aa of the convex portion 20 is also the top surface of the absorbing layer 23, the side surface 20ab of the convex portion 20 is composed of the side surface 21b of the reflecting layer 21, the side surface 22b of the dielectric layer 22, and the side surface 23b of the absorbing layer 23, and the protective film 40A is composed of the upper protective film 40Aa covering the top surface 20aa of the convex portion 20 and the side protective film 40Ab covering the side surface 20ab of the convex portion 20.

[0085] The protective film has a shape in which, when viewed from a cross section obtained by cutting the convex portion with a plane orthogonal to the surface of the transparent substrate and orthogonal to the first direction, the area of the protective film gradually increases from the top surface side to the transparent substrate side (in the Z direction). Here, as the "shape in which the area gradually increases", the inclined surface of the cross section view can be linear or curved. The curve of the shape of the curved inclined surface may, for example, follow the equation of a parabola (Z = aX 2 ; a is a coefficient) or the equation of a hyperbola (Z = b / X; b is a coefficient).

[0086] The protective film can have a substantially left-right symmetrical structure when viewed from a cross section obtained by cutting the convex portion with a plane orthogonal to the surface of the transparent substrate and orthogonal to the first direction.

[0087] The surface 40Aaa of the upper protective film 40Aa is composed of a top surface 40Aaaa and an inclined surface 40Aaab. The inclined surface 40Aaab is a linear inclined surface when viewed from a cross section obtained by cutting the convex portion 20 with a plane orthogonal to the surface 10a of the transparent substrate 10 and from a plane orthogonal to the first direction. The protective film 40A has a substantially conical portion structure.

[0088] The surface 40Aba of the side protective film 40Ab is composed of an inclined surface. The inclined surface 40Aba is also a linear inclined surface when viewed from a cross section obtained by cutting the convex portion 20 with a plane orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction, and is continuous with the inclined surface 40Aaab of the upper protective film 40Aa.

[0089] The inclined surface of the protective film 40A is composed of the inclined surface 40Aaab and the inclined surface 40Aba, and is a linear inclined surface when viewed from a cross section obtained by cutting the convex portion 20 with a plane orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction.

[0090] Figure 2 The polarizing plate 100 shown is a structure in which the inclined surface 40Aaab and the inclined surface 40Aba, which are linear inclined surfaces, are continuously connected at the same angle of inclination, but can also be a structure in which the inclined surface 40Aaab and the inclined surface 40Aba, which are linear inclined surfaces, are each continuously connected at different angles of inclination.

[0091] The width wO (refer to Figure 3 ) of the bottom surface of the upper protective film 40Aa is wider than the width w of the top surface 20aa of the convex portion 20. Therefore, the both ends 20aae (refer to Figure 3 ) of the top surface 20aa of the convex portion 20 are not in contact with the inclined surface of the protective film 40A. In other words, the inclined surface of the protective film 40A is separated from the both ends 20aae of the top surface 20aa of the convex portion 20. By the above configuration, the convex portion 20 becomes a structure completely covered with the protective film 40A.

[0092] The bottom surfaces (the bottom surfaces of the side protective films 40Ab) of the adjacent protective films 40A are in contact with each other (refer to xO in Figure 3 ), and the first surface 10a of the transparent substrate 10 is not exposed.

[0093] Figure 2 The polarizing plate 100 shown in FIG. 6 is a structure in which the bottom surfaces (the bottom surfaces of the side protective films 40Ab) of the adjacent protective films 40A are in contact with each other, but can also be a structure in which the bottom surfaces (the bottom surfaces of the side protective films 40Ab) of the adjacent protective films 40A overlap each other to have a thickness.

[0094] When the protective film 40A is formed, it is preferable to use the ALD (Atomic Layer Deposition) method which is dense, uniform, and excellent in film thickness controllability. Also, like the dielectric layer 22 described above, it can also be configured by two or more layers of different constituent materials.

[0095] In addition, in the shape of the protective film 40A, the upper protective film 40Aa does not necessarily need to be flat, and the change in the side surface shape of the side protective film 40Ab is not limited to the case where there is no inflection point. For example, as a cross-sectional shape in which the convex portion 20 is buried, a shape in which the surface 40Aaa of the upper protective film 40Aa is drawn as a curved surface and the side surface 40Aba of the side protective film 40Ab has a plurality of inflection points can be used, and the protective film 40A can also have a height distribution.

[0096] In addition, when the protective film 40A completely fills the spaces between the convex portions 20 or fills part of the spaces between the convex portions 20, in addition to the method of forming the dielectric layer 22 described above, the SOG (Spin on Glass) method can be used. By the SOG method, planarization without an air layer can be achieved.

[0097] As the material of the protective film, a publicly known metal oxide or metal nitride or the like can be used, but from the viewpoint of heat resistance, Al2O3 is particularly preferable.

[0098] (1) In the protective film 40A, the thickness (height) hi of the upper protective film 40Aa can be set to, for example, 0 < hi < 50 nm, preferably 0 < hi < 25 nm, in consideration of the influence of the characteristics caused by the change in the grid height h.

[0099] (2) Also, the protective film 40A needs to completely cover the convex portion 20. Therefore, the width wO of the protective film 40A at the same height position as the height (h - hi) of the convex portion is larger than the width w of the convex portion (wO > w).

[0100] (3) The intersection points of the side inclined surfaces 40Aba of the adjacent convex portions (X = xO in the figure) Figure 3 Although it is preferable to be located at the middle (center) between the adjacent convex portions 20 in terms of optical characteristics (i.e., the shape of the protective film is bilaterally symmetrical with respect to X = xO), it can be shifted to either the convex portion side.

[0101] The features of (1) to (3) are also the same features in the examples described later.

[0102] [Antireflection Layer]

[0103] An antireflection layer can also be formed on the second surface 10b of the transparent substrate 10. The antireflection layer can be formed of a known antireflection material, for example, a multilayer film of at least two layers or more formed of a material capable of constituting the dielectric layer 22. The same applies to the polarizing plate 200 or the polarizing plate 300 described later.

[0104] As one example of the multilayer film, by alternately laminating a low-refractive-index layer and a high-refractive-index layer having different refractive indexes, light reflected at the interface can be attenuated by interference. The film thickness of the antireflection layer is not particularly limited, and is appropriately set to be within the range of 1 nm to 500 nm for each layer constituting the dielectric layer 22. The film thickness of the antireflection layer can be measured, for example, by the electron microscope method described above.

[0105] The low-refractive-index layer is a layer having SiO2 (oxide of Si) or the like as a main component. The refractive index of the low-refractive-index layer is preferably 1.20 to 1.60, and particularly preferably 1.30 to 1.50.

[0106] The refractive index of the high-refractive-index layer is preferably 2.00 to 2.60, and particularly preferably 2.10 to 2.45. As such a high-refractive-index dielectric, there can be used niobium pentoxide (Nb2O5, refractive index 2.33), titanium oxide (TiO2, refractive index 2.33 to 2.55), tungsten oxide (WO3, refractive index 2.2), cerium oxide (CeO2, refractive index 2.2), tantalum pentoxide (Ta2O5, refractive index 2.16), zinc oxide (ZnO, refractive index 2.1), or indium tin oxide (ITO, refractive index 2.06), or the like.

[0107] In addition, the antireflection layer 30 can be formed as a high-density film by using the same film formation method as the dielectric layer 22 described above. It is preferable to use an ion-beam assisted deposition (IAD) method or an ion beam sputtering (IBS) method, which can form a higher-density film.

[0108] Further, in consideration of the formation of the protective film 40A thereafter, the material or film thickness, etc. are preferably designed so that the antireflection layer does not decrease in optical properties.

[0109] [Water-repellent film]

[0110] Further, in the polarizing plate of the present embodiment, at least one of the surfaces 100a, 100b of the polarizing plate 100 can also be covered with an organic water-repellent film (not shown). When the antireflection layer is provided on the second surface 10b of the transparent substrate 10, the antireflection layer can also be covered with the organic water-repellent film. Similarly with respect to the polarizing plate 200 or the polarizing plate 300 described later, at least one of the surfaces 200a, 200b of the polarizing plate 200 or at least one of the surfaces 300a, 300b of the polarizing plate 300 can also be covered with the organic water-repellent film.

[0111] The organic water-repellent film is composed of, for example, a fluorine-based silane compound such as perfluorodecyltriethoxysilane (FDTS) or the like, and can be formed by the CVD method or the ALD method described above, for example. Thus, the reliability of the polarizing plate in terms of moisture resistance, etc. can be improved.

[0112] [Polarizing plate (second embodiment)]

[0113] Figure 4 A cross-sectional view of a polarizing plate related to the second embodiment of the present application.

[0114] Figure 4 The polarizing plate 200 shown has a transparent substrate 10 and a plurality of convex portions 20 formed on the first surface 10a of the transparent substrate 10 and extending in the first direction to be periodically arranged at a pitch shorter than the wavelength of light of the wavelength band used, and sequentially has a reflection layer 21, a dielectric layer 22, and an absorption layer 23 from the side of the transparent substrate 10, and the top surface 20aa and the side surface 20ab of each of the plurality of convex portions 20 are also covered with a protective film 41A composed of a dielectric, and the protective film 41A has a feature that the area from the top surface 20aa side to the transparent substrate 10 side gradually increases when viewed from a cross section that cuts the convex portions 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction, and Figure 2 The polarizing plate 100 shown is the same as the polarizing plate 200 shown.

[0115] In another aspect, Figure 4 The polarizing plate 200 shown in FIG. 2 is different from the polarizing plate 100 shown in FIG. 1 in that the inclined surface of the protective film 40A is a linear inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction, and in that the inclined surface of the protective film 41A is a curved inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction. Figure 2 The polarizing plate 100 shown in FIG. 1 is different from the polarizing plate 200 shown in FIG. 2 in that the inclined surface of the protective film 40A is a linear inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction, and in that the inclined surface of the protective film 41A is a curved inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction. Figure 2 In the polarizing plate 100 shown in FIG. 1, the inclined surface of the protective film 40A is a linear inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction. In the polarizing plate 100 shown in FIG. 1, the inclined surface of the protective film 41A is a curved inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction. Figure 4 In the polarizing plate 200 shown in FIG. 2, the inclined surface of the protective film 41A is a curved inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction. In the polarizing plate 200 shown in FIG. 2, the inclined surface of the protective film 40A is a linear inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction. Figure 4 The shape of the curved inclined surface in the polarizing plate 200 shown in FIG. 2 is an example in which the curved line is substantially a parabolic equation (Z = aX 2 ). The protective film 41A has a substantially parabolic portion.

[0116] The protective film 41A is composed of an upper protective film 41Aa that covers the top surface 20aa of the convex portion 20 and a side protective film 41Ab that covers the side surface 20ab of the convex portion 20.

[0117] The surface 41Aaa of the upper protective film 41Aa is composed of a top surface 41Aaaa and an inclined surface 41Aaab. The inclined surface 41Aaab is a curved inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction.

[0118] The surface 41Aba of the side protective film 41Ab is composed of an inclined surface. The inclined surface 41Aba is also a curved inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction, and is continuous with the inclined surface 41Aaab of the upper protective film 41Aa.

[0119] The inclined surface of the protective film 41A is composed of the inclined surface 41Aaab and the inclined surface 41Aba, and is a curved inclined surface as viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction.

[0120] Figure 4 The polarizing plate 200 shown in FIG. 2 is a structure in which the inclined surface 41Aaab and the inclined surface 41Aba of the curved inclined surface are continuously connected, but can also be a structure in which they are discontinuously connected.

[0121] Also, in the polarizing plate 200 shown in FIG. 2, the inclined surface of the protective film 40A is a curved inclined surface that is recessed toward the convex portion 20 side, but can also be a curved inclined surface that is expanded toward the outside. Figure 4

[0122] ​The width w1 (see Figure 5 ) of the bottom surface of the upper protective film 41Aa is wider than the width w of the top surface 20aa of the convex portion 20. Therefore, the both ends 20aae (see Figure 5 ) of the top surface 20aa of the convex portion 20 are not in contact with the inclined surface of the protective film 41A. In other words, the inclined surface of the protective film 41A is separated from the both ends 20aae of the top surface 20aa of the convex portion 20. With the above configuration, the convex portion 20 becomes a structure completely covered by the protective film 41A.

[0123] The bottom surfaces (the bottom surfaces of the side protective films 41Ab) of the adjacent protective films 41A are in contact with each other, and the first surface 10a of the transparent substrate 10 is not exposed.

[0124] Figure 4 The polarizing plate 200 illustrated in the drawing is a structure in which the bottom surfaces (the bottom surfaces of the side protective films 41Ab) of the adjacent protective films 41A are in contact with each other, but can also be a structure in which the bottom surfaces of the adjacent protective films 41A overlap each other to have a thickness.

[0125] [Polarizing plate (third embodiment)]

[0126] Figure 6 A cross-sectional view of a polarizing plate related to the third embodiment of the present application is illustrated.

[0127] Figure 6 The polarizing plate 300 illustrated in the drawing has a transparent substrate 11 and a plurality of convex portions 20 formed on the first surface 10a of the transparent substrate 11 and extending in the first direction to be periodically arranged at a pitch shorter than the wavelength of light used, and the plurality of convex portions 20 have, in order from the transparent substrate 11 side, a reflection layer 21, a dielectric layer 22, and an absorption layer 23, and the top surface 20aa and the side surface 20ab of each of the plurality of convex portions 20 are also covered by a protective film 42A composed of a dielectric, and the area from the top surface 20aa side to the transparent substrate 11 side gradually increases when viewed from a cross section that cuts the convex portion 20 with a plane orthogonal to the surface 11a of the transparent substrate 11 and orthogonal to the first direction, and the polarizing plate 300 has the same features as the polarizing plate 100 illustrated in the drawing. Figure 2 The polarizing plate 300 illustrated in the drawing is the same as the polarizing plate 100 illustrated in the drawing except for the following point.

[0128] On the other hand, Figure 6 The polarizing plate 300 illustrated in the drawing is the same as the polarizing plate 100 illustrated in the drawing except for the following point. Figure 2 The polarizing plate 300 illustrated in the drawing is the same as the polarizing plate 100 illustrated in the drawing except for the following point. Figure 2 In the polarizing plate 100 illustrated in the drawing, the inclined surface of the protective film 40A is a straight inclined surface when viewed from a cross section that cuts the convex portion 20 with a plane orthogonal to the surface 10a of the transparent substrate 10 and orthogonal to the first direction; and in the polarizing plate 300 illustrated in the drawing, the inclined surface of the protective film 42A is a curved inclined surface when viewed from a cross section that cuts the convex portion 20 with a plane orthogonal to the surface 11a of the transparent substrate 11 and orthogonal to the first direction. Figure 6In the polarizing plate 300 shown, the inclined surface of the protective film 42A is a curved inclined surface when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 11a of the transparent substrate 11 and orthogonal to the first direction. In the polarizing plate 300 shown, the convex portion 20 is formed on the surface 11a of the transparent substrate 11. Figure 6 In the polarizing plate 300 shown, the shape of the curved inclined surface is an example in which the curve is a parabolic equation (Z = bX 2 ). The protective film 42A has a substantially parabolic portion.

[0129] Also, the polarizing plate 300 shown has a common point with the polarizing plate 200 shown in that the inclined surface is curved when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface of the transparent substrate and orthogonal to the first direction. On the other hand, the polarizing plate 300 shown has a difference from the polarizing plate 200 shown in that Figure 6 the transparent substrate is engraved in the polarizing plate 300 shown, and the transparent substrate is not engraved in the polarizing plate 200 shown. Figure 4 the polarizing plate 300 shown has a common point with the polarizing plate 200 shown in that the inclined surface is curved when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface of the transparent substrate and orthogonal to the first direction. On the other hand, the polarizing plate 300 shown has a difference from the polarizing plate 200 shown in that Figure 6 the transparent substrate is engraved in the polarizing plate 300 shown, and the transparent substrate is not engraved in the polarizing plate 200 shown. Figure 4 the polarizing plate 300 shown has a common point with the polarizing plate 200 shown in that the inclined surface is curved when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface of the transparent substrate and orthogonal to the first direction. On the other hand, the polarizing plate 300 shown has a difference from the polarizing plate 200 shown in that Figure 6 the transparent substrate is engraved in the polarizing plate 300 shown, and the transparent substrate is not engraved in the polarizing plate 200 shown. Figure 4 the polarizing plate 300 shown has a common point with the polarizing plate 200 shown in that the inclined surface is curved when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface of the transparent substrate and orthogonal to the first direction. On the other hand, the polarizing plate 300 shown has a difference from the polarizing plate 200 shown in that Figure 6 the polarizing plate 300 shown can be a variation of the polarizing plate 200 shown. Figure 4 the polarizing plate 300 shown can be a variation of the polarizing plate 200 shown.

[0130] The protective film 42A is composed of an upper protective film 42Aa that covers the top surface 20aa of the convex portion 20 and a side protective film 42Ab that covers the side surface 20ab of the convex portion 20.

[0131] The surface 42Aaa of the upper protective film 42Aa is composed of a top surface 42Aaaa and an inclined surface 42Aaab. The inclined surface 42Aaab is a curved inclined surface when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 11a of the transparent substrate 11 and orthogonal to the first direction.

[0132] The surface 42Aba of the side protective film 42Ab is composed of an inclined surface. The inclined surface 42Aba is also a curved inclined surface when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 11a of the transparent substrate 11 and orthogonal to the first direction, and is continuous with the inclined surface 42Aaab of the upper protective film 42Aa.

[0133] The inclined surface of the protective film 42A is composed of the inclined surface 42Aaab and the inclined surface 42Aba, and is a curved inclined surface when viewed from a cross section that cuts the convex portion 20 with a surface orthogonal to the surface 11a of the transparent substrate 11 and orthogonal to the first direction.

[0134] The transparent substrate 11 has an engraved portion 12a engraved from the first surface 11a of the transparent substrate 11 in a manner continuous with the inclined surface 42Aba of the side protective film 42Ab. The engraved portion 12a is formed in a depth d (refer to Figure 7 ) and in a manner continuous with the respective inclined surfaces 42Aba of the adjacent side protective films 42Ab.

[0135] The engraved portion 12a is configured with a surface extending along the inclined surface 42Aba of the side protective film 42Ab.

[0136] In the polarizing plate 300 shown in FIG. 1, the engraved portion 12a is formed in a structure continuous with the respective inclined surfaces 42Aba of the adjacent side protective films 42Ab, but can also be in a structure discontinuous with the respective inclined surfaces 42Aba of the adjacent side protective films 42Ab. Figure 6 Also, in the polarizing plate 300 shown in FIG. 1, the inclined surface of the protective film 42A is a curved inclined surface recessed toward the convex portion 20 side, but can also be a curved inclined surface bulging outward.

[0137] Figure 6 In the polarizing plate 300 shown in FIG. 1, the width w2 (refer to ) of the bottom surface of the upper protective film 42Aa is a structure wider than the width w of the top surface 20aa of the convex portion 20. Therefore, the both ends 20aae (refer to

[0138] ) of the top surface 20aa of the convex portion 20 are not in contact with the inclined surface of the protective film 42A. In other words, the inclined surface of the protective film 42A is separated from the both ends 20aae of the top surface 20aa of the convex portion 20. By the above configuration, the convex portion 20 becomes a structure completely covered by the protective film 42A. Figure 7 Figure 7 The polarizing plate 300 shown in FIG. 1 is different from the polarizing plate 100 shown in FIG. 2 and the polarizing plate 200 shown in FIG. 3,

[0139] in that the polarizing plate 300 shown in FIG. 1 is a structure in which the bottom surfaces (the bottom surfaces of the side protective films 42Ab) of the adjacent protective films 42A are in contact with each other. Figure 6 Figure 2 [Method for manufacturing a polarizing plate] Figure 4 Figure 6

[0140] [Method for manufacturing a polarizing plate]

[0141] ​​​The manufacturing method of the polarizing plate of the present embodiment is a manufacturing method of a polarizing plate having a wire grid structure, including the following steps: a step of forming a reflection layer, a dielectric layer, and an absorption layer in this order on a first surface of a transparent substrate, and producing a laminate composed of the reflection layer, the dielectric layer, and the absorption layer; a step of forming a plurality of convex portions extending in a first direction and periodically arranged at a pitch shorter than the wavelength of light of the used wavelength band and separated from each other by selectively etching the laminate; and a step of forming a protective film composed of the dielectric layer so as to cover the surface of each of the plurality of convex portions; wherein the step of forming the protective film includes a step of etching so that the protective film gradually increases in area from the top surface side to the transparent substrate side when viewed from a cross section that cuts the convex portions in a plane orthogonal to the surface of the transparent substrate and orthogonal to the first direction.

[0142] Regarding the formation of the plurality of convex portions, a one-dimensional grid-like mask pattern is formed on the laminate film formed on one surface of the transparent substrate, for example, by photolithography, nanoimprint method, or the like, using a resist. By selectively etching the portion where the mask pattern is not formed, the plurality of convex portions periodically arranged at a pitch shorter than the wavelength of light of the used wavelength band and separated from each other are formed on the transparent substrate. As the etching method, for example, dry etching using an etching gas corresponding to the etching object can be used.

[0143] Regarding the formation of the protective film, the space between the grids is completely filled and planarized, for example, by the SOG method using methyl silicate or methyl siloxane as a raw material, in a manner so as to cover the surface of the convex portions. Next, a one-dimensional grid-like mask pattern is formed at the position overlapping with the convex portions described above, using a resist formed on the protective film, by photolithography, nanoimprint method, or the like. Next, by selectively etching the protective film, the shape of the protective film can be processed. For example, it can also be processed to depict a substantially tapered or substantially parabolic shape.

[0144] CVD (Chemical Vapor Deposition) method and ALD (Atomic Layer Deposition) method, when filling the space between the convex portions, fill the space between the convex portions in a form where molecules are stacked on the convex portions, which can form an air layer, and thus is not recommended because it becomes a cause of unnecessary reflection due to the formation of an interface with the protective film.

[0145] As described above, the polarizing plate shown in FIG. 1 is manufactured. Figures 1-7 In addition, the manufacturing method of the polarizing plate of the present embodiment can also have a step of forming an antireflection film, and a step of covering the surface of the polarizing plate with an organic waterproof film.

[0146] [Optical instrument]

[0147] The optical device of this embodiment includes the polarizing plates 100, 200, and 300 described above. The polarizing plates 100, 200, and 300 of this embodiment can be used for various applications. Suitable optical devices include, for example, liquid crystal displays, liquid crystal projectors, head-up displays, and vehicle headlights. In particular, since the polarizing plates 100, 200, and 300 of this embodiment have high transmittance, they can achieve high brightness with excellent heat resistance and high transmittance even in environments with high-brightness, strong light using multiple semiconductor lasers (LDs). Therefore, they are suitable for applications such as liquid crystal projectors.

[0148] In the case where the optical device related to this embodiment has a plurality of polarizing plates, at least one of the plurality of polarizing plates only needs to be the polarizing plate 100, 200, or 300 related to this embodiment. For example, when the optical device related to this embodiment is a liquid crystal projector, at least one of the polarizing plates disposed on the incident side and the emission side of the liquid crystal panel needs to be the polarizing plate 100, 200, or 300 related to this embodiment.

[0149] Example

[0150] Next, embodiments of the present invention will be described. However, the present invention is not limited to these embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0151] [simulation]

[0152] As the polarizing plate of the present invention, Figure 2 The polarizing plate shown Figure 4 The polarizing plate shown, and Figure 6 The polarizing plates shown were simulated for the model. Specifically, the optical properties of these polarizing plates were verified using electromagnetic field simulations based on the RCWA (Rigorous Coupled Wave Analysis) method. The grating simulator GSolver from Grating Solver Development was used in the simulation.

[0153] For comparison, for Figure 8 The model shown depicts a structure where the protrusions are filled with a protective film that has not been etched. Figure 9 The model shown was also simulated before the protective film was formed (without the protective film). Figure 8 and Figure 9 In the middle, used with Figure 2 , Figure 4 and Figure 6 The same component symbol represents the same Figure 2 , Figure 4 and Figure 6The same element's material or parameter.

[0154] In Figure 8 , the element symbol 140 is a layer composed of the same material as the protective film 40A, 41A, 42A, and is a layer indicating a state before the protective film 40A, 41A, 42A is processed, and the thickness (height) h1 thereof is the same as the height of the protective film 40A, 41A, 42A. Figure 2 , Figure 4 and Figure 6 .

[0155] In Figure 2 , the polarizing plate (protective film with a tapered portion) shown in Figure 4 , the polarizing plate (parabolic portion) shown in Figure 6 , and the polarizing plate (parabolic portion + engraved portion) shown in , the same parameters and materials are as follows.

[0156] Transparent substrate: material (alkali-free glass), thickness (0.7 mm);

[0157] Reflective layer: material (Al), thickness (250 nm), width w (35 nm);

[0158] Dielectric layer: material (SiO2), thickness (5 nm), width w (35 nm);

[0159] Absorbing layer: material (FeSi), thickness (25 nm), width w (35 nm);

[0160] Protective film: material (SiO2), height h1 (15 nm);

[0161] Grid: height (sum of convex portion and protective film) h (295 nm), pitch p (141 nm).

[0162] Figure 2 In Figure 4 , the polarizing plate shown in Figure 6 , and the polarizing plate shown in Figure 3 , the shape of the protective film is bilaterally symmetrical with the center between adjacent convex portions (for example, X = x0 of ) as a reference.

[0163] Figure 2 Also, in the model of the polarizing plate shown in Figure 3 , the width of the top surface 40Aaaa is the same as the width W of the convex portion, and the width w0 of the protective film 40A at the same height position as the height (h - h1) of the convex portion (refer to ) is 40.39 nm.

[0164] Figure 4In the model of the polarizing plate shown, the shape of the curved inclined surface, when viewed from a cross-section where the protrusion is truncated by a plane orthogonal to the surface of the transparent substrate and to the first direction, can be expressed by the formula of a parabola (Z = aX). 2 The width of the top surface 41Aaaa is the same as the width W of the protrusion, and the width w1 of the protective film 41A at a height equal to the height (h-h1) of the protrusion is (see reference). Figure 5 The wavelength is 37.73 nm.

[0165] Furthermore, in Figure 6 In the model of the polarizing plate shown, the shape of the curved inclined surface, when viewed from a cross-section where the protrusion is truncated by a plane orthogonal to the surface of the transparent substrate and to the first direction, can be expressed by the formula of a parabola (Z = bX). 2 The width of the top surface 42Aaaa is the same as the width W of the protrusion, and the width w2 of the protective film 42A at a height equal to the height (h-h1) of the protrusion is (see reference). Figure 7 The wavelength is 37.55nm.

[0166] Furthermore, in Figure 6 In the model of the polarizing plate shown, the depth d of the engraved part (refer to...) Figure 7 The wavelength is 20nm.

[0167] Figure 10 This is a graph showing the beam splitting waveforms of the transmission axis transmittance in the visible light region (red band: wavelength λ = 600–680 nm, green band: wavelength λ = 520 nm–590 nm, blue band: λ = 430 nm–510 nm) obtained through simulation. The horizontal axis represents wavelength λ (nm), and the vertical axis represents transmission axis transmittance (%). Here, transmission axis transmittance refers to the transmittance of polarized light waves (TM waves) incident on the polarizing plate along the transmission axis direction (X-axis direction).

[0168] Figure 2 The polarizing plate shown Figure 4 The polarizing plate shown and Figure 6 Any one of the polarizing plates shown, with the protrusions filled by a protective film that has not been etched ( Figure 8 Compared to the previous method, the transmittance of the transmission axis is improved across the entire wavelength range (400nm~700nm).

[0169] Comparing these three structures, we can see that the transmittance of the transmission axis is according to Figure 6 The polarizing plate shown (conical part + engraved part) Figure 4 The polarizing plate shown Figure 2 The order of the polarizing plates shown has been improved.

[0170] Figure 6 The polarizing plate shown is relative toFigure 4 The polarizing plate shown is only slightly engraved in the transparent substrate, and the transmittance of the transmission axis is increased to the same level as the structure before the protective film is formed (without the protective film). Figure 9 ).

[0171] This can be considered to be due to the fact that in the region below the visible light, the shape of the protective film expands toward the substrate direction (-Z direction), and the refractive index difference between the air layer adjacent to the protective film and the protective film gradually decreases, thereby improving the reflection suppression effect.

[0172] Figure 11 is a graph showing the average value of the transmittance of the transmission axis in each wavelength band obtained by simulation.

[0173] Figure 2 Any one of the polarizing plates shown, Figure 4 the polarizing plate shown, and Figure 6 the polarizing plate shown, the average value of the transmittance of the transmission axis in the full wavelength band is improved compared to the structure in which the convex portion is filled with the protective film of the unetched film.

[0174] Furthermore, in the full wavelength band, the average value of the transmittance of the transmission axis is improved in the order of Figure 6 the polarizing plate shown, Figure 4 the polarizing plate shown, Figure 2 the polarizing plate shown.

[0175] Figure 6 The polarizing plate shown is improved in the average value of the transmittance of the transmission axis relative to Figure 4 The polarizing plate shown is only slightly engraved in the transparent substrate, and the average value of the transmittance of the transmission axis is increased to the same level as the structure before the protective film is formed (without the protective film). Figure 9 ).

[0176] From the disclosure thus far, it will be apparent to those of ordinary skill in the art that embodiments herein can be varied in a number of ways. Such variations should not be considered a departure from the spirit and scope of the disclosure, and it will be apparent to one of ordinary skill in the art that all such modifications are intended to be included within the scope of the claims.

Claims

1. A polarizing plate having a wire grid structure, comprising: a transparent substrate; and a plurality of protrusions formed on a first surface of the transparent substrate and extending in a first direction, and periodically arranged at a pitch shorter than a wavelength of light used; wherein each of the plurality of protrusions has, in order from the transparent substrate side, a reflection layer, a dielectric layer, and an absorption layer, a top surface and a side surface of each of the plurality of protrusions are covered with a protective film composed of a dielectric, and from a cross section obtained by cutting the protrusions with a plane orthogonal to a surface of the transparent substrate and orthogonal to the first direction, an area of the protective film gradually increases from the top surface side to the transparent substrate side. The protective film is symmetric about a center between adjacent protrusions. A bottom surface of the protective film is on the transparent substrate. The transparent substrate is engraved along a plane extending from an outer peripheral surface of the protective film covering the side surface of the protrusion.

5. A method of manufacturing a polarizing plate having a wire grid structure, comprising: a step of forming, in order, a reflection layer, a dielectric layer, and an absorption layer on a first surface of a transparent substrate to produce a laminate composed of the reflection layer, the dielectric layer, and the absorption layer; a step of forming a plurality of protrusions extending in a first direction and periodically arranged at a pitch shorter than a wavelength of light used by selectively etching the laminate; and a step of forming a protective film composed of the dielectric layer covering a surface of each of the plurality of protrusions; wherein the step of forming the protective film includes a step of etching so that the protective film has a shape in which, from a cross section obtained by cutting the protrusions with a plane orthogonal to a surface of the transparent substrate and orthogonal to the first direction, an area of the protective film gradually increases from a top surface side to a transparent substrate side.

6. An optical device comprising the polarizing plate according to any one of claims 1 to 4.

2. The polarizing plate of claim 1, wherein ​ 3. The polarizing plate according to claim 1 or 2, wherein ​ 4. The polarizing plate of Claim 1 or 2, wherein ​ ​ ​ ​ ​ ​ ​

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