JP7553226B2 - Polarizing plate and optical device equipped with same - Google Patents

Description

The present invention relates to a polarizing plate and an optical device equipped with the same.

A polarizing plate is an optical element that absorbs light polarized in one direction and transmits light polarized in the direction perpendicular to the direction. In principle, polarizing plates are necessary in LCD displays. In particular, in LCD displays that use a light source with a large amount of light, such as a transmissive LCD projector, the polarizing plate is exposed to strong radiation, so it needs to have excellent heat and light resistance, as well as a size of several centimeters and high control over the extinction ratio and reflectance characteristics. To meet these requirements, wire-grid inorganic polarizing plates have been proposed.

A wire grid polarizer has a structure in which a large number of conductive wires extending in one direction are arranged on a substrate with a pitch (tens to hundreds of nm) narrower than the wavelength band of the light used. When light is incident on this polarizer, polarized light parallel to the extension direction of the wires (TE waves (S waves)) cannot be transmitted, and polarized light perpendicular to the extension direction of the wires (TM waves (P waves)) is transmitted as is. Wire grid polarizers have excellent heat and light resistance, can be made into relatively large elements, and have a high extinction ratio. In addition, the multi-layer structure makes it possible to control the reflectance characteristics, and reduces the deterioration of image quality caused by ghosts, etc., which occurs when light reflected on the surface of the polarizer is reflected again inside the LCD projector device, making them suitable for applications such as LCD projectors.

In response to this, various types of wire grid type polarizers have been proposed.

Patent No. 5184624 Patent No. 5359128

For example, Patent Document 1 discloses a polarizing plate having a wire grid layer formed on a substrate and consisting of an array of extended metal elements having a length longer than the wavelength of incident light and a period shorter than half the wavelength of the incident light.

Patent Document 2 also discloses a polarizing plate having a diffraction grating-shaped concave-convex portion on a substrate that is transparent to visible light, and an inorganic fine particle layer on some of the convex portions.

However, although these polarizing plates are described in terms of grid structure, their specific optical properties are not described, nor is the grid shape required to obtain those optical properties. In recent years, with the increasing brightness of liquid crystal projectors, polarizing plates are required to withstand strong light conditions and have high transmittance. To achieve this, it is necessary to optimize the grid shape taking into account the material.
In recent years, lighting and display light sources have evolved from lamps to LEDs and then to lasers, and liquid crystal projectors also use multiple semiconductor lasers (LDs) to achieve high luminous flux and brightness. This requires polarizing plates to have high transmittance while also being able to withstand environments with high luminosity and strong light. To achieve this, it is necessary to optimize the grid shape taking into account the material.

The present invention was made in consideration of the above problems, and aims to provide a polarizing plate with improved light transmission characteristics in the transmission axis direction by optimizing the grid shape, and an optical device equipped with the polarizing plate.

To solve the above problems, the present invention provides the following means.

(1) A polarizing plate according to one aspect of the present invention is a polarizing plate having a wire grid structure, and includes a transparent substrate and a plurality of protrusions extending in a first direction on the transparent substrate and arranged periodically at a distance from one another at a pitch shorter than the wavelength of light in the band of use, each of the protrusions including a base shape portion formed so that the width of a cross section perpendicular to the first direction becomes narrower toward the tip, and a protrusion portion protruding from the base shape portion and absorbing the wavelength of light in the band of use.

(2) In the aspect described in (1) above, the base shape portion may be substantially triangular in a cross section perpendicular to the first direction.

(3) In the aspect described in (2) above, when the height of the approximately triangular base shape portion is a and the width of the approximately triangular shape is b, (a/b) may be greater than 1/2.

(4) In the aspect described in (3) above, when the height of the approximately triangular base shape portion is a and the width of the approximately triangular shape is b, 13/10 ≧ (a/b) ≧ 7/10 may be satisfied.

(5) In any of the aspects (1) to (4) above, the transparent substrate may be a laminate of a first substrate made of a first material and a second substrate made of a second material, the first substrate of the laminate being disposed on the base shape portion side, and the first material may be the same material as the material of the base shape portion.

(6) In the aspect described in (5) above, the second substrate may be made of sapphire.

(7) In the aspect described in either (5) or (6) above, a phase difference compensation element may be provided on the surface of the second substrate opposite to the surface on which the first substrate is arranged.

(8) In any of the aspects (1) to (7) above, the protrusion may be made of a material selected from the group consisting of metals, alloys, and semiconductors that is absorbent for the wavelength of light in the band of use.

(9) In any of the above aspects (1) to (8), the surface of the polarizing plate facing the convex portion may be covered with a protective film made of a dielectric.

(10) In any of the above aspects (1) to (9), the surface of the polarizing plate on the side of the convex portion may be covered with an organic water-repellent film.

(11) An optical device according to another aspect of the present invention includes a polarizing plate according to any one of the aspects (1) to (10) above.

The present invention provides a polarizing plate with improved light transmission characteristics in the transmission axis direction.

1 is a schematic cross-sectional view of a polarizing plate according to a first embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of a polarizing plate according to a second embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of a polarizing plate of Comparative Example 1. 1 is a graph showing the average value of the transmission axis transmittance for each wavelength band in the polarizing plates of Examples 1-1 to 1-4 and Comparative Example 1. 1 is a graph showing the average value of the transmission axis transmittance for each wavelength band in the polarizing plates of Examples 2-1 to 2-5. 1 is a graph showing the average value of the transmission axis transmittance for each wavelength band in the polarizing plates of Examples 3-1 to 3-5. 1 is a graph showing the average value of the transmission axis transmittance for each wavelength band in the polarizing plates of Examples 4-1 to 4-5. FIG. 11 is a schematic cross-sectional view of a polarizing plate according to a third embodiment of the present invention. FIG. 11 is a schematic cross-sectional view of another example of a polarizing plate according to the third embodiment of the present invention. 1 is a graph showing the average value of the transmission axis transmittance for each wavelength band in the polarizing plates of Examples 5-1 to 5-5. 1 is a schematic perspective view showing an example of an optical system including a polarizing plate according to an embodiment of the present invention.

The present embodiment will be described in detail below with reference to the drawings as appropriate. The drawings used in the following description may show characteristic parts in an enlarged scale for the sake of convenience in order to make the features easier to understand, and the dimensional ratios of each component may differ from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited to them. Appropriate changes can be made within the scope of the effects of the present invention.

[Polarizing Plate (First Embodiment)]
FIG. 1 is a schematic cross-sectional view of a polarizing plate according to a first embodiment of the present invention.
The polarizing plate 100 shown in Figure 1 is a polarizing plate having a wire grid structure, and comprises a transparent substrate 10, and a plurality of convex portions 20 extending in a first direction (y direction) on the transparent substrate 10 and periodically arranged at a distance from one another at a pitch P shorter than the wavelength of light in the band of use, and each of the convex portions 20 comprises a base shape portion 21 formed so that the width of a cross section perpendicular to the first direction (y direction) becomes thinner towards the tip, and a protrusion portion 22 protruding from the base shape portion 21 and having absorptivity for the wavelength of light in the band of use.
The polarizing plate of the present invention may include layers other than the transparent substrate and the convex portions as long as the effects of the present invention are achieved.

As shown in FIG. 1, the plane on which the main surface 10a of the transparent substrate 10 extends is defined as the xy plane, the direction in which the convex portions extend (first direction) is defined as the y direction, and the direction perpendicular to the y direction and in which the convex portions are arranged is defined as the x direction. The direction perpendicular to the xy plane is defined as the z direction. In FIG. 1, an example is shown in which the light incident on the polarizing plate is incident from the z direction on the side of the transparent substrate on which the convex portions are formed (grid surface side), but the light incident on the polarizing plate may also be incident from the transparent substrate side.

A polarizing plate with a wire grid structure utilizes four actions: transmission, reflection, interference, and selective optical absorption of polarized waves due to optical anisotropy, to attenuate polarized waves with electric field components parallel to the y direction (TE waves (S waves)) and transmit polarized waves with electric field components parallel to the x direction (TM waves (P waves)). Therefore, in Figure 1, the y direction is the direction of the absorption axis of the polarizing plate, and the x direction is the direction of the transmission axis of the polarizing plate.

Light incident on the side of the polarizing plate 100 shown in FIG. 1 on which the convex portions 20 are formed (grid surface side) is partially absorbed and attenuated as it passes through the protrusions 22. Of the light that passes through the protrusions 22, TM waves (P waves) pass through the transparent substrate 10 with high transmittance. On the other hand, of the light that passes through the protrusions 22, TE waves (S waves) are reflected by the transparent substrate 10. The TE waves reflected by the transparent substrate 10 interfere and are attenuated as they pass through the protrusions 22. By selectively attenuating the TE waves as described above, the polarizing plate 100 can obtain the desired polarization characteristics.

<Transparent substrate>
The transparent substrate 10 is not particularly limited as long as it is a substrate that is transparent to light of a wavelength in the band used by the polarizing plate 100, and can be appropriately selected according to the purpose. "Having transparency" does not mean that 100% of the light of the wavelength in the band used can be transmitted, but it is sufficient that the light can be transmitted to an extent that the function of the polarizing plate can be maintained. The average thickness of the transparent substrate 10 is preferably 0.3 mm or more and 1 mm or less. Examples of light in the band used include visible light with a wavelength of about 380 nm to 810 nm.

The transparent substrate 10 is preferably made of a material having a refractive index of 1.1 to 2.2, such as glass, quartz, or sapphire. From the standpoint of cost and light transmittance, it is preferable to use glass, particularly quartz glass (refractive index 1.46) or soda-lime glass (refractive index 1.51). There are no particular limitations on the composition of the glass material, and it is possible to use inexpensive glass materials such as silicate glass, which is widely available as optical glass.

In addition, from the viewpoint of thermal conductivity, it is preferable to use quartz crystal or sapphire, which have high thermal conductivity. This provides high light resistance to strong light, and is preferably used as a polarizing plate for the optical engine of a projector that generates a lot of heat.

When using a transparent substrate made of an optically active crystal such as quartz, it is preferable to arrange the convex portions parallel or perpendicular to the optical axis of the crystal. This results in excellent optical properties. Here, the optical axis is the directional axis in which the difference in refractive index between the O (ordinary ray) and E (extraordinary ray) of light traveling in that direction is the smallest.

<Convex part>
The protrusions 20 extend in the y direction on the transparent substrate 10 and are periodically arranged in the x direction at a pitch P that is shorter than the wavelength of light in the used band.

The convex portion 20 is composed of a base shape portion 21 formed so that the width of the xz cross section perpendicular to the y direction becomes narrower toward the tip, and a protrusion portion 22 protruding from the base shape portion 21 and absorbing the wavelengths of light in the band of use.

The pitch (repeated interval in the x-direction) of the convex portions 20, indicated by the symbol P in FIG. 1, is not particularly limited as long as it is shorter than the wavelength of light in the band used. From the viewpoint of ease of fabrication and stability, the pitch of the convex portions is preferably, for example, 100 nm to 200 nm. This pitch of the convex portions can be measured by observation with a scanning electron microscope or a transmission electron microscope. For example, the pitch can be measured at any four locations using a scanning electron microscope or a transmission electron microscope, and the arithmetic average value can be taken as the pitch of the convex portions. Hereinafter, this measurement method is referred to as the electron microscopy method.

(Base shape part)
The base shape portion 21 is formed so that the width of the xz cross section perpendicular to the y direction becomes thinner toward the tip side. There are various ways in which the width of the xz cross section becomes thinner toward the tip side.

The base shape portion 21 may have a substantially triangular shape in an xz cross section perpendicular to the y direction.
The approximately triangular shape is preferably an approximately isosceles triangle (see FIG. 1).
Here, the substantially triangular shape does not have to be a strict triangular shape, but may be an approximately triangular shape as long as the effects of the present invention are achieved. For example, it may be a trapezoid with a missing tip.
Furthermore, since the convex portion has a very fine structure, the tapered shape may have a certain degree of roundness due to manufacturing reasons, and in this case, it is also included in the above-mentioned approximately triangular shape.
Furthermore, the generally triangular inclined surface (reference numeral 21a in FIG. 1) of the protrusion may have some curvature, and this case is also included in the generally triangular shape.

The dimensions of the base shape portion 21 in this specification will now be described with reference to FIG. 1. The height of the base shape portion 21 is the dimension in the z direction from the bottom surface 21b (main surface 10a of the transparent substrate 10) of the base shape portion 21 to the tip 21c, and is the dimension indicated by the symbol a in FIG. 1. The width of the base shape portion 21 is the dimension in the x direction of the bottom surface 21b of the base shape portion 21 in the xz cross section, and is the dimension indicated by the symbol b in FIG. 1.

The height a of the base shape portion 21 is appropriately set in the range of several tens of nm to several hundreds of nm. The height of the base shape portion 21 can be measured, for example, by the above-mentioned electron microscope method.
The height a of the base shape portion 21 is preferably in the range of 50 to 130 nm, for example.

In terms of the relationship between the height a and the width b of the base shape portion 21, from the viewpoint of improving transmittance, it is preferable that (a/b)>1/2, more preferably that 13/10≧(a/b)≧7/10, and even more preferably that 13/10≧(a/b)≧9/10.

The width b of the base shape portion 21 is appropriately set in the range of several tens of nm to several hundreds of nm. The width of the base shape portion 21 can be measured, for example, by the above-mentioned electron microscope method.
The width b of the base shape portion 21 is preferably in the range of 80 to 120 nm, for example.

In terms of the relationship between the width b of the base shape portion 21 and the height a, from the viewpoint of improving transmittance, it is preferable that (a/b)>1/2, more preferably that 13/10≧(a/b)≧7/10, and even more preferably that 13/10≧(a/b)≧9/10.

The base shape portion 21 may be made of the same material as the transparent substrate 10 .
The base shape portion 21 and the transparent substrate 10 may be formed integrally, or the base shape portion 21 made of the same material as the transparent substrate 10 may be formed on the transparent substrate 10. In the former case, the base shape portion 21 is formed on the main surface 10a of the transparent substrate 10 by processing (e.g., selective etching) the main surface of a transparent original plate (a substrate before being processed into the transparent substrate 10 is referred to as the transparent original plate).

The ratio of the width b of the base shape portion 21 to the area "P-b" where the base shape portion 21 is not formed is preferably, for example, 6/1 ≧ (b/P-b) ≧ 4/3.

The base shape portion 21 may be made of a dielectric material different from that of the transparent substrate 10 .
In this case, the thickness of the dielectric film (height a of the base shape portion 21) is appropriately set in the range of several tens of nm to several hundreds of nm. The thickness of the dielectric film can be measured, for example, by the above-mentioned electron microscope method.
In terms of the relationship between the film thickness of the dielectric (height a of the base shape portion 21) and the width b, from the viewpoint of improving transmittance, it is preferable that (a/b)>1/2, it is more preferable that 13/10≧(a/b)≧7/10, and it is even more preferable that 13/10≧(a/b)≧9/10.
Examples of materials constituting the dielectric include common materials such as silicon oxides such as _SiO2 , metal oxides such as _{Al2O3 ,} beryllium oxide, and bismuth oxide, _MgF2 , cryolite, germanium, titanium dioxide, silicon, magnesium fluoride, boron nitride, boron oxide, tantalum oxide, carbon, and combinations thereof. Among these, it is preferable that the dielectric is composed of silicon oxide.
The refractive index of the dielectric material is preferably greater than 1.0 and equal to or less than 2.5. Since the optical characteristics of the protrusions are also affected by the refractive index of the surroundings, the characteristics of the polarizing plate can be controlled by selecting the material of the dielectric material.
The base shape portion 21 made of a dielectric material can be formed as a high-density film by utilizing a deposition method, a sputtering method, a CVD (Chemical Vapor Deposition) method, or an ALD (Atomic Layer Deposition) method.

(Protrusion)
The protrusion 22 protrudes from the base shape portion 21 and has absorptivity for the wavelength of light in the used band. Protruding from the base shape portion 21 means, with reference to FIG. 1, that the protrusion is formed so as to protrude from the inclined surface 21 a or the tip (apex) 21 c of the base shape portion 21.

The protrusions 22 may be in the form of fine particles in the xz cross section.

The protrusions 22 can be arranged to extend in the y direction, which is the absorption axis. In this case, the protrusions 22 form a wire grid structure and function as a wire grid polarizer, attenuating polarized waves (TE waves (S waves)) that have an electric field component in a direction parallel to the longitudinal direction of the protrusions 22, and transmitting polarized waves (TM waves (P waves)) that have an electric field component in a direction perpendicular to the longitudinal direction of the protrusions 22.

The constituent material of the protrusion 22 includes one or more substances having a non-zero extinction constant of the optical constant, such as a metal material or a semiconductor material, and has a light absorbing effect, and is appropriately selected according to the wavelength range of the light to be applied. Examples of the metal material include simple elements such as Ta, Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, and Sn, or alloys containing one or more of these elements. Examples of the semiconductor material include Si, Ge, Te, ZnO, and silicide materials (β-FeSi ₂ , MgSi ₂ , NiSi ₂ , BaSi ₂ , CrSi ₂ , CoSi ₂ , TaSi, etc.). By using these materials, the polarizing plate can obtain a high extinction ratio for the visible light range to which it is applied.

When using a semiconductor material as the constituent material of the protrusion 22, the band gap energy of the semiconductor is involved in the absorption action, so the band gap energy must be equal to or lower than the band of use. For example, when used with visible light, it is necessary to use a material that absorbs at wavelengths of 400 nm or more, i.e., has a band gap of 3.1 eV or less.

When the protrusion 22 has a substantially circular shape in the xz cross section, the radius is appropriately set in the range of several nm to several hundred nm. The radius of the protrusion 22 can be measured, for example, by the above-mentioned electron microscope method.
In the case of the protrusion 22 having a substantially circular shape, the radius is preferably in the range of 5 nm to 100 nm, for example.

The film thickness of the protrusions 22 (the thickness protruding from the base shape portion 21) is not particularly limited, and is preferably, for example, 5 nm to 100 nm. The film thickness of the protrusions 22 can be measured, for example, by the electron microscope method described above.

There is no particular limitation on the position of the protrusion 22 on the base shape portion 21 , and it may be on the inclined surface or the tip of the base shape portion 21 .
The position of the protrusion 22 on the base shape portion 21 is preferably within 3/4 of the distance from the tip to the bottom surface of the base shape portion 21, and more preferably within 1/2 of the distance from the tip to the bottom surface of the base shape portion 21. This is because if the protrusion 22 is located closer to the bottom surface of the base shape portion 21, there is a risk that it may also be located on the main surface of the transparent substrate during the manufacturing process.

The protrusions 22 can be formed by a known dry method such as a vapor deposition method or a sputtering method.
In this case, protrusions 22 can also be formed on one inclined surface of base shape portion 21 by performing vapor deposition or sputtering from an oblique angle. After forming protrusions 22 on one inclined surface of base shape portion 21, protrusions 22 can also be formed on the other inclined surface. In the former case, protrusions 22 are formed in an asymmetrical position with respect to base shape portion 21 when viewed in a plan view from the z direction. In the latter case, protrusions 22 can be formed in a symmetrical position with respect to base shape portion 21 when viewed in a plan view from the z direction.

The protrusions 22 may be formed by known wet techniques.

The protrusion 22 may be made up of two or more layers made of different materials.

<Protective film>
Furthermore, the polarizing plate of this embodiment may have a surface on the light incident side covered with a protective film made of a dielectric material, as long as this does not affect changes in the optical properties.

<Water-repellent film>
Furthermore, the polarizing plate of this embodiment may have a surface on the light incident side covered with an organic water-repellent film. The organic water-repellent film is made of a fluorine-based silane compound such as perfluorodecyltriethoxysilane (FDTS) and can be formed by using the above-mentioned CVD method or ALD method. This can improve the reliability of the polarizing plate, such as its moisture resistance.

The polarizing plate of the present invention can also be used as a pre-polarizing plate installed before the exit polarizing plate in liquid crystal projectors, which are becoming increasingly bright. This distributes the amount of light received by the exit polarizing plate, thereby reducing the thermal load on the exit polarizing plate and achieving high transmittance.

[Polarizing Plate (Second Embodiment)]
Fig. 2 is a schematic cross-sectional view of a polarizing plate according to a second embodiment of the present invention. In Fig. 2, the same reference numerals as those in Fig. 1 are the same in Fig. 2 and will not be described. Fig. 2 shows an example in which light incident on the polarizing plate is incident from the z direction on the side (grid surface side) on which the convex portions of the transparent substrate are formed, but light incident on the polarizing plate may be incident from the transparent substrate side.
The polarizing plate 200 shown in Figure 2 is a polarizing plate having a wire grid structure, and includes a transparent substrate 10, and a plurality of convex portions 30 extending in a first direction (y direction) on the transparent substrate 10 and periodically arranged at a pitch P shorter than the wavelength of light in the band of use, and each of the convex portions 30 includes a base shape portion 31 formed so that the width of a cross section perpendicular to the first direction (y direction) becomes thinner toward the tip, and a protrusion portion 32 protruding from the base shape portion 31 and having absorptivity for the wavelength of light in the band of use.
A polarizing plate 200 shown in Fig. 2 has a different shape of a base shape portion from the polarizing plate 100 shown in Fig. 1. Specifically, the xz cross section of the base shape portion 21 shown in Fig. 1 is triangular, whereas the xz cross section of the base shape portion 31 shown in Fig. 2 is trapezoidal.

The base shape portion 31 may be substantially trapezoidal in an xz cross section perpendicular to the y direction.
The substantially trapezoidal shape is preferably one in which two inclined surfaces 31a connecting the upper surface 31c and the lower surface (bottom surface) 31b have equal lengths and the angles θ formed by the inclined surfaces 31a and the lower surface 31b are equal (see FIG. 2). This shape is a trapezoid symmetrical with respect to an axis parallel to the z-axis.
Here, the substantially trapezoidal shape does not necessarily have to be a strict trapezoidal shape, but may be an approximately trapezoidal shape as long as the effects of the present invention are achieved.
Furthermore, since the convex portion has a very fine structure, the tapered shape may have a certain degree of roundness due to manufacturing reasons, and this case is also included in the above-mentioned approximate trapezoidal shape.
Furthermore, the generally trapezoidal inclined surface (reference numeral 31a in FIG. 2) of the convex portion may have some curvature, and in this case too, it can be said to be generally trapezoidal.

The dimensions of the base shape portion 31 in this specification will be explained with reference to Figure 2. The height of the base shape portion 31 is the dimension in the z direction from the bottom surface 31b (main surface 10a of the transparent substrate 10) of the base shape portion 31 to the top surface 31c, and is the dimension indicated by the symbol a in Figure 2. The width of the base shape portion 31 is the dimension in the x direction of the bottom surface 31b of the base shape portion 31 in the xz cross section, and is the dimension indicated by the symbol b in Figure 2.

The shape and material of the base shape portion 31 can be the same as those described for the base shape portion 21.

[Polarizing Plate (Third Embodiment)]
8 is a schematic cross-sectional view of a polarizing plate according to a third embodiment of the present invention. Members using the same reference numerals as those in the above embodiment have the same configurations, and their descriptions will be omitted. In addition, descriptions of members having the same functions as those in the above embodiment, even if the reference numerals are different, may be omitted.

The polarizing plate 300 shown in Figure 8 is a polarizing plate having a wire grid structure, and comprises a transparent substrate 110, and a plurality of convex portions 20 extending in a first direction (y direction) on the transparent substrate 110 and arranged periodically at a distance from each other at a pitch P shorter than the wavelength of light in the band used, each of the convex portions 20 comprising a base shape portion 21 formed so that the width of a cross section perpendicular to the first direction (y direction) becomes thinner toward the tip, and a protrusion portion 22 protruding from the base shape portion 21 and absorbing the wavelength of light in the band used, the transparent substrate 110 being a laminate of a first substrate 110A made of a first material and a second substrate 110B made of a second material, one substrate 110A of the laminate being disposed on the base shape portion 21 side, and the first material being the same material as the material of the base shape portion 21.
The polarizing plate of this embodiment can be used such that light enters the polarizing plate from the back surface 110b side (-z direction) of the transparent substrate 110, but it can also be used such that light enters the polarizing plate from the front surface 110a side (+z direction) of the transparent substrate 110.

<Transparent substrate>
The transparent substrate 110 is a laminate of a first substrate 110A made of a first material and a second substrate 110B made of a second material.

As the material of the second substrate 110B, the same materials as those described above as the material of the transparent substrate 10 can be used.
The second substrate 110B is preferably a sapphire substrate or quartz. This is because sapphire and quartz have high thermal conductivity (heat dissipation). Therefore, since high light resistance can be obtained by dissipating heat even against high-intensity light, they are preferably used as a polarizing element for the optical engine of a projector that generates a large amount of heat. Examples of light in the usable band include visible light with a wavelength of about 380 nm to 810 nm. The average thickness of the sapphire substrate or quartz substrate is preferably, for example, 0.3 mm to 1.5 mm.

The material of the first substrate 110A is different from the material of the second substrate 110B, and can be the same as that described above as the material of the base shape portion 21.

<Protective film>
Furthermore, in the polarizing plate of this embodiment, the surface on the light exit side may be covered with a protective film made of a dielectric material, as in the above embodiment, to the extent that it does not affect changes in the optical properties.

<Water-repellent film>
Furthermore, the surface of the polarizing plate of this embodiment on the light exit side may be covered with an organic water-repellent film, similar to the above embodiment.

<Retardation Compensation Layer>
Furthermore, the polarizing element of this embodiment may have a retardation compensation layer 120 formed on the surface on the light incident side, as shown in Fig. 9. The retardation compensation layer is made of a multilayer film using an inorganic material having optical anisotropy, for example, and can be formed by, for example, oblique deposition or sputtering. This makes it possible to correct the disturbance of the polarization after passing through the liquid crystal panel.

[Method of manufacturing polarizing plate (first embodiment and second embodiment)]
An example of a method for producing the polarizing plate according to the first or second embodiment of the present invention will be described below.
When manufacturing a polarizing plate having a transparent substrate and a base shape portion formed by processing the main surface of a transparent original plate, the method for manufacturing the polarizing plate of the present invention includes an etching step of selectively etching the main surface of the transparent original plate to form convex portions arranged on the transparent substrate at a pitch shorter than the wavelength of light in the band of use, and a step of forming protrusions on the base shape portion of the convex portions that are absorbent for the wavelength of light in the band of use, and in the etching step, the convex portions are formed so that the width of a cross section perpendicular to the direction in which the convex portions extend becomes narrower toward the tip.

The base shape portion can be formed by known methods such as photolithography and nanoimprinting. Specifically, a one-dimensional lattice-shaped mask pattern is formed using resist formed on a transparent original plate. The transparent substrate surface on which the mask pattern is not formed is selectively etched to form base shape portions arranged on the transparent substrate at a pitch shorter than the wavelength of light in the band being used. Examples of etching methods include dry etching using an etching gas that corresponds to the etching target.

In particular, in the present invention, by optimizing the etching conditions (gas flow rate, gas pressure, output, cooling temperature of the transparent substrate), it is possible to form the base shape portion into a tapered shape in which the sides are inclined in the direction in which the width becomes narrower toward the tip.

The protrusions can be formed on the tapered shape of the base shape by, for example, vapor deposition or sputtering from an oblique angle.

This is how the polarizing plate, an example of which is shown in Figures 1 and 2, is manufactured.

When manufacturing a polarizing plate in which a base shape portion made of a material different from the material of the transparent substrate is formed on the main surface of the transparent substrate, the manufacturing method of the polarizing plate of the present invention includes a step of forming a base shape portion made of a material different from the material of the transparent substrate on the main surface of the transparent substrate instead of the above-mentioned etching step.

The method for producing a polarizing plate of the present invention may include a step of coating the surface with a protective film made of a dielectric material. The method for producing a polarizing plate of the present invention may further include a step of coating the surface with an organic water-repellent film.

[Method of manufacturing polarizing plate (third embodiment)]
The method for producing a polarizing plate according to the third embodiment of the present invention will be described mainly with respect to steps different from those of the above-described embodiments.
A second substrate (e.g., a sapphire substrate) is prepared, and a film of the material for the first substrate and the base shape portion (e.g., _SiO2 ) is formed thereon. The surface of the film of the material is then selectively etched to form convex portions arranged on the first substrate at a pitch shorter than the wavelength of light in the band of use, while leaving the portion that will become the first substrate. Other steps can be performed in the same manner as in the manufacturing method for the polarizing plate of the above embodiment.

[Optical equipment]
The optical device of the present invention includes the polarizing plate of the present invention. In the optical device of the present invention including the polarizing plate of the present invention, the light source may be a semiconductor laser.
The polarizing plate according to the present invention can be used for various purposes, such as optical devices including liquid crystal displays, liquid crystal projectors, head-up displays, and digital cameras.
In particular, since the polarizing plate according to the present invention is an inorganic polarizing plate having excellent heat resistance, it can be suitably used in applications requiring heat resistance such as liquid crystal projectors and head-up displays, as compared with organic polarizing plates made of organic materials.
In addition, since the polarizing plate according to the present invention has high transmittance and high heat dissipation, it can achieve high brightness with excellent heat resistance and high transmittance even in an environment of high-intensity light using multiple semiconductor lasers (LDs). This makes it suitable for use in applications such as liquid crystal projectors. The polarizing plate according to the present invention is particularly suitable for optical devices (projectors, etc.) with high brightness that use semiconductor lasers as light sources.

When the optical device according to the present invention includes a plurality of polarizing plates, at least one of the plurality of polarizing plates may be the polarizing plate according to the present invention. For example, when the optical device according to the present invention is a liquid crystal projector, at least one of the polarizing plates arranged on the entrance side and the exit side of the liquid crystal panel may be the polarizing plate according to the present invention.
The optical device of the present invention can preferably improve the durability of the exit side polarizing plate by arranging the polarizing plate of the present invention in front of the polarizing plate arranged on the exit side, as shown in Figure 11, for example, so that a certain percentage of the high-intensity light received by the exit side polarizing plate can be borne and dissipated with high heat dissipation.
As shown in FIG. 11, the optical device according to the present invention can include a light source, an incident-side polarizing plate, a liquid crystal optical element, an exit-side polarizing plate (the polarizing plate of the present invention), and an exit-side polarizing plate.

Next, examples of the present invention will be described, but the present invention is not limited to these examples.

The polarizing plate according to the present invention was simulated to verify its effectiveness. More specifically, the optical properties of these polarizing plates were verified by electromagnetic field simulation using the RCWA (Rigorous Coupled Wave Analysis) method. For the simulation, a grating simulator, Gsolver, from Grating Solver Development, Inc. was used.

(Examples 1-1 to 1-4)
The shape of the polarizing plate in Example 1-1 is as shown in FIG. 1, and the shapes of the polarizing plates in Examples 1-2 to 1-4 are as shown in FIG.
Regarding the materials of the polarizing plates in Examples 1-1 to 1-4, the transparent substrate 10 and the base shape portion 21 are both made of quartz, and the protrusion portion 22 is made of Ge.
The shape of the base shape portion 21 in each of Examples 1-1 to 1-4 is such that the height a is 70 nm, the width b is 100 nm, the pitch P is 141 nm, and the inclination angles θ are 54°, 63°, 72°, and 81°, respectively. Since the height a and the width b are fixed, the xz cross section of Example 1-1 (θ=54°) is triangular, and the xz cross sections of Examples 1-2 (θ=63°), 1-3 (θ=72°), and 1-4 (θ=81°) are trapezoidal. In addition, the shape of the protrusions 22 in each of Examples 1-1 to 1-4 is a circle in cross section, with a radius of 15 nm. As shown in FIG. 1, the position of the protrusions 22 in the base shape portion 21 is such that the outermost circumference of the circle is the same as the height a, and is in contact with the inclined surface 21a.

(Comparative Example 1)
The shape of the xz cross section of the polarizing plate of Comparative Example 1 is as shown in FIG.
The materials of the polarizing plate 1000 in Comparative Example 1 are the transparent substrate 10 and the base shape portion 121, both of which are made of quartz, and the protrusion portion 22 is made of Ge, which is common to Examples 1-1 to 1-4. However, it differs from Examples 1-1 to 1-4 in that the xz cross section is rectangular.
The shape of base shape portion 121 in Comparative Example 1 has a height a of 70 nm, a width b of 100 nm, a pitch P of 141 nm, and an inclination angle θ of 90°. The shape of protrusion portion 22 in Comparative Example 1 has a circular cross section with a radius of 15 nm. As shown in FIG. 3, protrusion portion 22 is positioned on base shape portion 21 such that the outermost circumference of the circle is the same as height a and is in contact with inclined surface 121a.

4 is a graph showing the average value of the transmission axis transmittance for each wavelength band in the polarizing plates of Examples 1-1 to 1-4 and Comparative Example 1. The horizontal axis indicates the wavelength λ (nm), and the vertical axis indicates the transmission axis transmittance Tp (%). Here, the transmission axis transmittance Tp means the transmittance of the polarized wave (TM wave) in the transmission axis direction (X direction) that is incident on the polarizing plate.
As shown in FIG. 4, the polarizing plate according to the present invention has a smaller inclination angle θ than the polarizing plate of Comparative Example 1, and thereby the transmission axis transmittance is improved in all of the visible light range (red band: wavelength λ=600 to 680 nm, green band: wavelength λ=520 nm to 590 nm, blue band: λ=430 nm to 510 nm).
It was found that, when the height a and width b are the same, the base shape portion 121 has better optical properties when it is tapered than when it is rectangular. It was also found that, when the height a and width b are the same, the optical properties are better when the xz cross section is triangular than when it is trapezoidal. It was also found that, when the height a and width b are the same and the xz cross section is trapezoidal, the optical properties are better when the inclination angle θ is smaller.

(Examples 2-1 to 2-5)
The shapes of the polarizing plates in Examples 2-1 to 2-5 are as shown in FIG.
In the polarizing plates of Examples 2-1 to 2-5, the transparent substrate 10 and the base shape portion 21 are both made of quartz, and the protrusions 22 are made of Ge.
The polarizing plates in Examples 2-1 to 2-5 all have the same shape, with a width b of 100 nm and a pitch P of 141 nm, but the heights a of 50 nm, 70 nm, 90 nm, 110 nm, and 130 nm, respectively (as a result, the inclination angles θ of 54°, 45°, 61°, 66°, and 69°, respectively). The shape of the protrusions 22 in Examples 1-1 to 1-4 is all a circle in cross section with a radius of 15 nm. The position of the protrusions 22 on the base shape portion 21 is such that the outermost circumference of the circle is the same as the height a and is in contact with the inclined surface 21a, as shown in FIG. 1.

5 is a graph showing the average transmission axis transmittance for each wavelength band in the polarizing plates of Examples 2-1 to 2-5, where the horizontal axis represents the wavelength λ (nm) and the vertical axis represents the transmission axis transmittance Tp (%).
Based on FIG. 5, the ratio of height a to width b (a/b) is preferably greater than 1/2, more preferably 7/10 or greater, with 9/10, 11/10, and 13/10 being more preferable than 7/10.

(Examples 3-1 to 3-5)
The shapes of the polarizing plates in Examples 3-1 to 3-5 are as shown in FIG.
The polarizing plates of Examples 3-1 to 3-5 were made of a transparent substrate 10 and a base shape portion 21 both made of sapphire, and the protrusions 22 were made of Ge.
The polarizing plates in Examples 3-1 to 3-5 all have the same shape, with a width b of 100 nm and a pitch P of 141 nm, but the heights a of 50 nm, 70 nm, 90 nm, 110 nm, and 130 nm, respectively (as a result, the inclination angles θ are 54°, 45°, 61°, 66°, and 69°, respectively). The shape of the protrusions 22 in Examples 3-1 to 3-5 all has a circular cross section with a radius of 15 nm. As for the position of the protrusions 22 in the base shape portion 21, as shown in FIG. 1, the outermost circumference of the circle is the same as the height a, and is in contact with the inclined surface 21a.

6 is a graph showing the average transmission axis transmittance for each wavelength band in the polarizing plates of Examples 3-1 to 3-5, where the horizontal axis represents the wavelength λ (nm) and the vertical axis represents the transmission axis transmittance Tp (%).
6, the ratio of height a to width b (a/b) is preferably more than 1/2, more preferably 7/10 or more, and 9/10, 11/10, and 13/10 are more preferable than 7/10. This is similar to the polarizing plates of Examples 2-1 to 2-5, and it was found that this characteristic does not change even if the material of the transparent substrate and base shape portion is changed from quartz to sapphire.

(Examples 4-1 to 4-5)
The shapes of the polarizing plates in Examples 4-1 to 4-5 are as shown in FIG.
The polarizing plates of Examples 4-1 to 4-5 were made of materials in which the transparent substrate 10 was made of sapphire, the base shape portion 21 was made of SiO ₂ , and the protrusions 22 were made of Ge.
The polarizing plates in Examples 4-1 to 4-5 all have the same shape, with a width b of 100 nm and a pitch P of 141 nm, but the heights a of 50 nm, 70 nm, 90 nm, 110 nm, and 130 nm, respectively (as a result, the inclination angles θ are 54°, 45°, 61°, 66°, and 69°, respectively). The shape of the protrusions 22 in Examples 4-1 to 4-5 all has a circular cross section with a radius of 15 nm. As for the position of the protrusions 22 in the base shape portion 21, as shown in FIG. 1, the outermost circumference of the circle is the same as the height a, and is in contact with the inclined surface 21a.

7 is a graph showing the average transmission axis transmittance for each wavelength band in the polarizing plates of Examples 4-1 to 4-5, where the horizontal axis represents the wavelength λ (nm) and the vertical axis represents the transmission axis transmittance Tp (%).
Based on FIG. 7, for the entire visible light region (red band: wavelength λ=600 to 680 nm, green band: wavelength λ=520 nm to 590 nm, blue band: λ=430 nm to 510 nm), it is preferable to make the ratio of height a to width b (a/b) to exceed 1/2, since this improves the transmission axis transmittance.
Moreover, it is more preferable to set the a/b ratio to 7/10 or more over the entire visible light region, since this improves the transmission axis transmittance.
Also, for the entire visible light region, configurations in which a/b is 9/10 and 11/10 are preferable to configurations in which a/b is 7/10.
Also, for the green band (wavelength λ=520 nm to 590 nm) and the blue band (λ=430 nm to 510 nm), a configuration in which a/b is 13/10 is preferable to a configuration in which a/b is 7/10.

(Examples 5-1 to 5-5)
The polarizing plates of Examples 5-1 to 5-3 have shapes as shown in Fig. 8, with the first substrate 110A and base shape portion 21 made of _SiO2 , the second substrate 110B made of sapphire, and the protrusions 22 made of Ge. In addition, the polarizing plates of Examples 5-1 to 5-3 have first substrate thicknesses d1 of 35 nm, 70 nm, and 105 nm, respectively, and second substrate thicknesses d2 of 0.7 mm.
The shape of the polarizing plate of Example 5-4 is as shown in Fig. 1, the transparent substrate 10 is made of sapphire, the base shape portion 21 is made of _SiO2 , and the protrusion portion 22 is made of Ge. The thickness of the transparent substrate 10 is 0.7 mm.
1, the transparent substrate 10 and the base shape portion 21 are both made of sapphire, and the protrusions 22 are made of Ge. The transparent substrate 10 has a thickness of 0.7 mm.
In addition, the shape of protrusion 22 in Examples 5-1 to 5-5 all had a circular cross section with a radius of 15 nm. As for the position of protrusion 22 on base shape portion 21, as shown in FIG. 8 or FIG. 1, the outermost circumference of the circle was the same as height a, and protrusion 22 was in contact with inclined surface 21 a.
In the simulation, the incident light was incident from the direction shown in FIG.

10 is a graph showing the average value of the transmission axis transmittance for each wavelength band in the polarizing plates of Examples 5-1 to 5-5, where the horizontal axis represents the wavelength λ (nm) and the vertical axis represents the transmission axis transmittance Tp (%).
10, the polarizing plates of Examples 5-1 and 5-2, in which the transparent substrate is a two-layer laminate and the first substrate on the base shape portion side is made of the same material as the base shape portion, have improved transmission axis transmittance in all wavelength ranges in the visible light region (red band: wavelength λ = 600 to 680 nm, green band: wavelength λ = 520 nm to 590 nm, blue band: λ = 430 nm to 510 nm)) than the polarizing plates of Examples 5-4 and 5-5, in which the transparent substrate is a single layer. Also, the polarizing plate of Example 5-3 has improved transmission axis transmittance in the green band and blue band compared to the polarizing plates of Examples 5-4 and 5-5, in which the transparent substrate is a single layer.
Therefore, from the viewpoint of improving the transmission axis transmittance, it is preferable to use a transparent substrate that is a two-layer laminate in which the first substrate on the base shape portion side is made of the same material as the base shape portion.

REFERENCE SIGNS LIST 10 transparent substrate 10a main surface 20 convex portion 21 base shape portion 22 protrusion portion 30 convex portion 31 base shape portion 32 protrusion portion 100, 200, 300 polarizing plate 110 transparent substrate 110A first substrate 110B second substrate

Claims (9)

A polarizing plate having a wire grid structure,
A transparent substrate;
a plurality of protrusions extending in a first direction on the transparent substrate and periodically arranged at intervals shorter than the wavelength of light in a used band;
Each of the convex portions includes a base shape portion formed so that a width of a cross section perpendicular to the first direction becomes narrower toward a tip side, and a protrusion portion protruding from the base shape portion and having absorptivity for wavelengths of light in a usage band,
the transparent substrate is a laminate of a first substrate made of a first material and a second substrate made of a second material,
The first substrate of the laminate is disposed on the base shape portion side, and the first material is the same material as the material of the base shape portion;
The base shape portion has a substantially triangular shape in a cross section perpendicular to the first direction . 2. The polarizing plate according to claim 1 , wherein, in the substantially triangular base shape portion, when the height of the substantially triangular shape is a and the width of the substantially triangular shape is b, (a/b)>1/2. 2. The polarizing plate according to claim 1, wherein, in the substantially triangular base shape portion, when the height of the substantially triangular shape is a and the width of the substantially triangular shape is b, 13/10≧(a/b)≧7/10. The polarizing plate according to any one of claims 1 to 3 , wherein the second substrate is made of sapphire. 5. The polarizing plate according to claim 1, further comprising a retardation compensation element provided on a surface of the second substrate opposite to a surface on which the first substrate is disposed. 6. The polarizing plate according to claim 1 , wherein the protrusions are made of a material selected from the group consisting of metals, alloys, and semiconductors, which has an absorptivity for the wavelength of light in the used band. The polarizing plate according to claim 1 , wherein a surface of the polarizing plate on the side of the convex portions is covered with a protective film made of a dielectric material. The polarizing plate according to any one of claims 1 to 7 , wherein a surface of the polarizing plate on the side of the convex portions is covered with an organic water-repellent film. An optical device comprising the polarizing plate according to any one of claims 1 to 8 .

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