JP2012189773A - Polarization element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization element which can obtain excellent polarization throughput characteristics.SOLUTION: A polarization element includes a rugged structure arranged with a pitch smaller than the wavelength of light in the use bandwidth on a transparent substrate 10, and in a protrusion 20 of the rugged structure, a high refractive index material 21 composed of a dielectric or a semiconductor, and a low refractive index material 22 having lower refractive index than that of the high refractive index material 21 and composed of a dielectric or a semiconductor, are alternatively laminated. The polarization element has a multi-layer grid structure of a dielectric with no free electron and a semiconductor with little free electron, and therefore excellent polarization throughput characteristics can be obtained.

Description

  The present invention relates to a polarizing element that absorbs one of orthogonal polarization components (so-called P-polarized wave and S-polarized wave) and transmits the other. More specifically, the present invention relates to a polarizing element that utilizes a difference in light transmittance in the in-plane axial direction for light in a use band.

  Conventionally, as a typical structure of a polarizing element, a “MacNeille prism” in which a prism having a polarizing film having a multilayer structure of 20 layers or more is bonded is known (for example, see Patent Document 1). This polarizing element has a high contrast and is used as the most standard polarizing element. However, the polarizing element having this structure has a large angle dependency of incident light. Furthermore, since an organic adhesive is used for bonding the prisms, when used for a light source with high luminance, the deterioration is accelerated by the heat and UV components of the light source, and the characteristics deteriorate.

  As a polarizing element that avoids these problems, a wire grid type polarizing element is known. A wire grid type polarizing element generally has a fine grid structure having a period smaller than the wavelength of light to be used and extending in one direction. Such a wire grid type polarizing element reflects linearly polarized light that oscillates in a direction parallel to the one direction, and passes linearly polarized light that oscillates in an orthogonal direction. For this reason, for example, when non-polarized light is incident, light separated from predetermined polarized light is emitted.

  FIG. 16 is a schematic view showing polarization separation of the polarizing element. Ideally, the polarizing element completely reflects some linearly polarized light and completely transmits orthogonal linearly polarized light when light is incident at an angle of 45 degrees.

  As described in Patent Documents 2 and 3, the conventional wire grid type polarizing element has a structure in which a wire structure using a metal material is formed on a transparent substrate that transmits visible light. Since a metal wire (for example, Al) is provided on an inorganic transparent substrate (for example, a quartz substrate), it has superior heat resistance compared to the prism-type polarizing element described above, and the angle dependency of incident light is relatively ± 10 °. There is an advantage of being small.

  Patent Document 4 describes a polarizing element in which metal wires and dielectric layers are alternately formed. According to this structure, it is possible to improve the polarization performance of the polarizing element by a combination of the photon tunnel and the in-grid resonance effect.

  However, as described in Patent Document 4, when a metal material is used for the wire grid type polarizing element, the light transmittance of the polarized light component perpendicular to the wire is lowered due to the light absorbency of the metal. Specifically, when light is incident at an angle of 45 degrees, the transmittance of p-polarized light (hereinafter referred to as Tp) and the reflectance of s-polarized light (hereinafter referred to as Rs) are limited to about 90%. Yes, the polarization throughput represented by Tp × Rs is as low as 80%. For this reason, the characteristic of the polarizing element with respect to the request | requirement of high brightness in recent projectors etc. is inadequate.

U.S. Pat. No. 2,043,731 JP 2009-139411 A US Pat. No. 6,122,103 Japanese Patent No. 4152645

  The present invention has been proposed in view of such circumstances, and an object of the present invention is to provide a polarizing element capable of obtaining excellent polarization throughput characteristics.

  In order to solve the above-described problems, a polarizing element according to the present invention has a concavo-convex structure arranged on a transparent substrate at a pitch smaller than the wavelength of light in a use band, and the convex portion of the concavo-convex structure is a dielectric. A high refractive index material made of a body or a semiconductor and a low refractive index material made of a dielectric or a semiconductor are alternately laminated.

  In addition, a liquid crystal projector according to the present invention includes the polarizing element described above, a light source, and a liquid crystal panel.

  Since the present invention has a multi-layer grid structure of a dielectric without free electrons and a semiconductor with very few free electrons, compared to a wire grid type polarizing element using a metal that absorbs light and has free electrons. Excellent polarization throughput characteristics can be obtained.

It is a schematic sectional drawing which shows the polarizing element which concerns on one embodiment of this invention. It is a schematic sectional drawing which shows the modification of the polarizing element which concerns on one embodiment of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method (the 1) of the polarizing element which concerns on one embodiment of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method (the 2) of the polarizing element which concerns on one embodiment of this invention. It is a schematic sectional drawing for demonstrating the manufacturing method (the 3) of the polarizing element which concerns on one embodiment of this invention. It is a schematic sectional drawing which shows the structure of the optical engine part of the liquid-crystal projector which concerns on one embodiment of this invention. It is a graph which shows the angle dependence of Tp and Rs with respect to the incident light of the polarizing element of a dielectric multilayer structure. It is a graph which shows the wavelength dependence of Tp, Rs, and Tp * Rs in 45-degree incident light of the polarizing element of a dielectric multilayer structure. It is a graph which shows the wavelength dependence of Tp, Rs, and Tp * Rs of a polarizing element when the grid height of a dielectric multilayer structure is 270 nm and 480 nm. It is a graph which shows the wavelength dependence of Tp, Rs, and Tp * Rs when the grid width of a dielectric multilayer structure is 50 nm and 105 nm. It is a graph which shows the wavelength dependence of Tp, Rs, and Tp * Rs of the polarizing element of a dielectric 7 layer structure. It is a graph which shows the angle dependence of Tp and Rs with respect to the incident light of the polarizing element of a dielectric material / semiconductor multilayer structure. It is a graph which shows the angle dependence of Tp and Rs with respect to the incident light of a polarizing element when the grid height of a dielectric material / semiconductor multilayer structure is 250 nm. It is a graph which shows the wavelength dependence of Tp, Rs, Tp * Rs when the grid height of a dielectric material / semiconductor multilayer structure is 350 nm. It is a graph which shows the wavelength dependence of Tp, Rs, and Tp * Rs when the grid width | variety of a dielectric material / semiconductor multilayer structure is 50 nm and 105 nm. It is the schematic which shows the polarization separation of a polarizing element.

Hereinafter, embodiments of the present invention will be described in detail in the following order with reference to the drawings.
1. 1. Configuration of polarizing element 2. Manufacturing method of polarizing element 3. Configuration example of liquid crystal projector Example

<1. Configuration of polarizing element>
FIG. 1 is a schematic sectional view showing a polarizing element according to an embodiment of the present invention. As shown in FIG. 1, the polarizing element has a concavo-convex structure arranged on a transparent substrate 10 at a pitch smaller than the wavelength of light in the use band. That is, the polarizing element has a one-dimensional lattice-like wire grid structure in which convex portions are arranged on the transparent substrate 10 at regular intervals.

  The transparent substrate 10 is transparent with respect to light in the use band and is made of a material having a refractive index of 1.1 to 2.2, such as glass, sapphire, and quartz. Further, glass, particularly quartz (refractive index 1.46) or soda lime glass (refractive index 1.51) may be used depending on the application of the polarizing element. The component composition of the glass material is not particularly limited. For example, an inexpensive glass material such as silicate glass widely distributed as optical glass can be used, and the manufacturing cost can be reduced.

  The convex portion 20 of the concavo-convex structure has a high refractive index material 21 made of a dielectric or semiconductor and a low refractive index material 22 made of a dielectric or semiconductor having a refractive index smaller than that of the high refractive index material 21 on the transparent substrate 10. They are stacked alternately. Each layer of the high refractive index material 21 and the low refractive index material 22 can be formed by, for example, an oblique vapor deposition method to be described later.

Dielectric materials used for the high refractive index material 21 and the low refractive index material 22 include SiO ₂ (refractive index: 1.46 (near 500 nm)), Al ₂ O ₃ (refractive index: 1.63 (near 550 nm)). TiO ₂ (refractive index: 2.5 (near 550 nm)), Ta ₂ O ₅ (refractive index: 2.16 (near 550 nm)), CeO ₂ (refractive index: 2.2 (near 550 nm)), ZrO ₂ Select an oxide such as (refractive index: 2.05 (near 550 nm)), ZrO (refractive index: 2.1 (near 550 nm)), Nb ₂ O ₅ (refractive index: 2.33 (near 500 nm)). be able to. By using such an oxide, for example, when a dielectric multilayer film is formed by sputtering or the like, film formation in the same chamber is possible, and lead time can be reduced. In addition, the oxide has a high affinity for a reactive ion etching process for forming a grid.

The semiconductor used for the high refractive index material 21 and the low refractive index material 22 may be selected from Si (refractive index: 3.4 (near 400 nm)), an alloy containing the same, or a silicide-based semiconductor material. it can. By using such a Si-based material, the affinity for the reactive ion etching process is high. In addition, when an alternating multilayer film with SiO ₂ is formed, film formation in the same chamber is possible.

In the present embodiment, it is preferable to select the high refractive index material 21 and the low refractive index material 22 having a refractive index difference of 1 or more from the above-described dielectrics or semiconductors. Specific combinations of the high refractive index material 21 and the low refractive index material 22 include TiO ₂ and SiO ₂ , Si and SiO _{2, and the} like. When the refractive index difference between the high refractive index material 21 and the low refractive index material 22 is 1 or more, high reflectance can be obtained, and excellent throughput characteristics can be obtained with a small number of layers.

  In this way, by forming a multi-layer grid structure using a dielectric that does not have free electrons and a refractive index difference of a semiconductor with very few free electrons, a metal layer that has free electrons and absorbs light was used. Compared with a wire grid type polarizing element, excellent polarization throughput characteristics can be obtained.

  In the polarizing element having the above-described configuration, the grid pitch formed by the convex portions 20 and the concave portions 30 may be 200 nm or less, which is half or less of the visible light region when used in the visible light region (400 to 700 nm). preferable.

  Moreover, although the grid width which is the width | variety of the convex part 20 can be designed freely by a use wavelength band, it is preferable that it is 20 to 90% of a grid pitch. A more preferable grid width is 30 to 70% of the grid pitch. When the grid width is less than 20% of the grid pitch, not only the production becomes difficult, but also the band with good polarization throughput becomes narrow. Fabrication is relatively easy when the grid pitch exceeds 90%, but the band with good polarization throughput is also narrow.

  The height of the grid, which is the height of the convex portion of the concavo-convex structure, can be freely designed according to the wavelength band used, but is preferably 500 nm or less. When the grid height exceeds 500 nm, not only is the production difficult, but the strength of the grid structure is reduced.

  Moreover, you may form the support part 31 which supports between convex parts in the recessed part 30 of an uneven structure for the purpose of improving the intensity | strength of the grid structure of a polarizing element. The height of the support portion 31 is preferably equal to or less than the height of the convex portion 20 that contributes to preventing the wire grid from falling down.

  FIG. 2A shows an example of a polarizing element in which a grid 32 having a period larger than the use wavelength intersecting a wire grid having a period smaller than the use wavelength is formed. By forming such a grid, the wire grid can be prevented from falling. The method for producing the orthogonal grid can be obtained by patterning so as to intersect by interference exposure described later. Note that the intersecting angle does not necessarily have to be orthogonal as shown in FIG. 2A, and it is only necessary to maintain a period longer than the used wavelength.

FIG. 2B shows an example of a polarizing element in which an extremely low refractive index material 33 having a refractive index lower than that of the low refractive index material 22 is inserted into the concave portion 30 having a concavo-convex structure. Thus, by inserting the ultra-low refractive index material 33 into the gap of the concave portion 30, it is possible to prevent the wire grid from falling. As the ultra-low refractive index material 33, for example, MgF ₂ can be used. As a method for inserting an ultra-low refractive index material, a spin coating method can be used in which a sol is dropped onto a substrate that rotates at high speed.

Further, for the purpose of improving reliability such as moisture resistance, a protective film such as SiO ₂ may be deposited on the top as long as the change in optical characteristics does not affect the application.

  In the polarizing element having such a configuration, since the grid is formed of a multilayer structure made of a dielectric or a semiconductor that does not contain a metal material, the polarization throughput (in a desired wavelength band) can be changed by arbitrarily changing the shape of the grid. Tp × Rs) can be 90% or more. Moreover, since it is comprised only with the inorganic material, high heat resistance can be acquired. Further, when used in a liquid crystal projector, it is possible to cope with a high light density, so that the optical unit portion can be downsized.

<2. Manufacturing method of polarizing element>
Next, the manufacturing method of the polarizing element in this Embodiment is demonstrated with reference to FIG. First, the high refractive index material 21 and the low refractive index material 22 are alternately laminated on the transparent substrate 10 so as to have a predetermined number of layers and a predetermined grid height. Each layer can be formed by a general vacuum film formation method such as a sputtering method, a vapor phase growth method, or an evaporation method, or a sol-gel method (for example, a method in which a sol is coated by spin coating and gelled by thermal curing). .

Next, as shown in FIG. 3A, an antireflection film (BRAC) 41 is formed on the laminate, and a lattice is formed by nanoimprint, photolithography, or the like so that the resist 42 has a predetermined grid pitch and grid width. A mask pattern is formed. Then, as shown in FIGS. 3B and 3C, the antireflection film 41 is removed by dry etching, and the high refractive index material 21 and the low refractive index material 22 are etched. Examples of the dry etching gas include Ar / O ₂ for the antireflection film, Cl ₂ / BCl _{3 for} AlSi, SiO ₂ , Si, and Ta for CF ₄ / Ar. Further, by optimizing the etching conditions (gas flow, gas pressure, power, substrate cooling temperature), a highly perpendicular lattice shape is realized. Thereby, a concavo-convex structure having a predetermined number of layers, a predetermined grid height, a predetermined grid pitch, and a grid width can be formed, and a polarizing element can be manufactured.

  In addition, when the inorganic fine particle layer is formed by oblique vapor deposition as shown in FIG. 4, a one-dimensional lattice is formed on the transparent substrate 10, and in the direction of the vapor deposition angle α with respect to the normal direction of the substrate surface of the transparent substrate 10. A high refractive index material 21 and a low refractive index material 22 are installed.

  When the xy plane in the x, y, z orthogonal coordinates is the substrate surface, the dielectric material is obliquely deposited from two directions different by 180 ° in the xy plane. For example, after the high refractive index material 21 is obliquely vapor-deposited from one direction, the transparent substrate 10 is rotated 180 °, and the low refractive index material 22 is obliquely vapor-deposited from the other direction. A membrane can be obtained.

  The method for forming the mask pattern is not limited to the above-described method, and the fine periodic structure pattern may be formed by interference exposure as shown in FIG. As the exposure substrate, a high refractive index material 21 and a low refractive index material 22 (not shown) are alternately stacked on the transparent substrate 10, and a light shielding film 40 and a resist 42 are provided on the exposed substrate so as not to transmit light to the back surface of the crystal substrate. And an antireflection film 41 resist 42 for removing reflection from the lower interface is laminated in this order. Then, exposure from two directions at an angle θ with respect to the normal direction of the substrate surface generates interference fringes. The relationship between the pitch p and the exposure wavelength λ is as follows.

  In addition, interference exposure can also be used in the case where the support portion 31 that supports the convex portion is formed in the concave portion 30 of the concavo-convex structure. In this case, first, exposure is performed at a cycle shorter than the wavelength used, a mask pattern for structural birefringence is formed, and exposure is performed at a cycle longer than the wavelength used by rotating the substrate or the interference exposure optical system in a predetermined direction. Then, a mask pattern for the support portion 41 is formed. Then, through the development process, for example, a polarizing element in which a grid 32 intersecting with the wire grid shown in FIG.

<3. Example of LCD projector configuration>
Next, a liquid crystal projector according to an embodiment of the present invention will be described. The liquid crystal projector 100 includes a lamp serving as a light source, a liquid crystal panel, and the polarizing element described above.

  FIG. 6 shows a configuration example of the optical engine portion of the liquid crystal projector according to the present invention. The optical engine portion of the liquid crystal projector 100 includes an incident side polarizing element 10A for the red light LR, a liquid crystal panel 50, an outgoing pre-polarizing element 10B, an outgoing main polarizing element 10C, and an incident side polarizing element 10A for the green light LG, the liquid crystal panel 50, Outgoing pre-polarizing element 10B, outgoing main polarizing element 10C, incident side polarizing element 10A for blue light LB, liquid crystal panel 50, outgoing pre-polarizing element 10B, outgoing main polarizing element 10C, and outgoing main polarizing element 10C And a cross dichroic prism 60 for synthesizing the incoming light and emitting it to the projection lens. Here, the polarizing element described above is applied to each of the incident side polarizing element 10A, the outgoing pre-polarizing element 10B, and the outgoing main polarizing element 10C.

  In the liquid crystal projector 100, light emitted from a light source lamp (not shown) is separated into red light LR, green light LG, and blue light LB by a dichroic mirror (not shown), and incident side polarization elements corresponding to the respective lights. The light LR, LG, and LB incident on 10A and then polarized by the respective incident-side polarizing elements 10A are spatially modulated by the liquid crystal panel 50 and emitted, and pass through the outgoing pre-polarizing element 10B and the outgoing main polarizing element 10C. Thereafter, the image is synthesized by the cross dichroic prism 60 and projected from a projection lens (not shown). Even if the light source lamp has a high output, since the polarizing element 1 having excellent light resistance against strong light is used, a highly reliable liquid crystal projector can be realized.

  The polarizing element of the present invention is not limited to application to the liquid crystal projector, but is suitable as a polarizing element that receives heat as a use environment. For example, the present invention can be applied as a polarizing element for a car navigation system of an automobile or a liquid crystal display of an instrument panel.

<4. Example>
Examples of the present invention will be described below. Here, a polarizing element in which a dielectric is laminated and a polarizing element in which a dielectric and a semiconductor are laminated are manufactured, and the transmittance of P-polarized light (hereinafter referred to as Tp) and the reflectance of S-polarized light (hereinafter referred to as Rs). ) And polarization throughput (hereinafter referred to as Tp × Rs). The present invention is not limited to these examples.

Example 1: Dielectric Lamination
First, TiO ₂ and SiO ₂ were alternately laminated on a glass substrate so as to have a predetermined number of layers and a predetermined grid height. An antireflection film (BRAC) was formed on the laminate, and a lattice-like mask pattern was formed with a resist so as to have a predetermined grid pitch and grid width.

Next, the antireflection film was removed by scum treatment with Ar / O ₂ gas, and TiO ₂ and SiO ₂ were etched with CF ₄ / Ar gas. Then, the resist and the antireflection film were removed by O ₂ ashing to form a concavo-convex structure having a predetermined number of layers, a predetermined grid height, a predetermined grid pitch, and a grid width, and a polarizing element was manufactured.

FIGS. 7A and 7B are graphs showing the angle dependence of Tp and Rs with respect to the incident light of the polarizing element having a dielectric multilayer structure, respectively. The polarizing element used for the measurement has a dielectric five-layer structure in which convex portions of the concavo-convex structure are laminated in the order of TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂ from the glass substrate side. The polarizing element has a grid height of 400 nm, a grid pitch of 150 nm, and a grid width of 75 nm. In addition, as a comparative example, a calculated value in a wire grid type polarizing element having the same structural dimensions made of a commercially available Al single metal layer is shown.

  The values of Tp shown in FIG. 7A and Rs shown in FIG. 7B were both higher in the dielectric multilayer structure polarizing element than in the metal single layer structure polarizing element. In the polarizing element having a metal single layer structure, the maximum Tp × Rs is about 85%, whereas in the polarizing element having a dielectric multilayer structure, Tp × Rs shows a value of 90% or more. In addition, the polarizing element having the dielectric multilayer structure also has good incident angle dependency, and Tp × Rs is 90% or more in the range of the incident light angle of 35 to 65 °.

  FIG. 8 is a graph showing the wavelength dependence of Tp, Rs, Tp × Rs at 45 ° incident light of a polarizing element having a dielectric multilayer structure. As described above, the polarizing element used for the measurement has a five-layer structure in which the protrusions of the concavo-convex structure are dielectric materials, the grid height is 400 nm, the grid pitch is 150 nm, and the grid width is 75 nm.

  This polarizing element having a dielectric multilayer structure had a Tp × Rs of 90% or more in the wavelength band of 500 to 600 nm and exhibited good characteristics in the green light band.

  FIGS. 9A and 9B are graphs showing the wavelength dependence of Tp, Rs, and Tp × Rs of the polarizing element when the grid height of the dielectric multilayer structure is 270 nm and 480 nm, respectively. As described above, the polarizing element used for the measurement has a five-layer structure in which the protrusions of the concavo-convex structure are dielectric, the grid pitch is 150 nm, and the grid width is 75 nm. The wavelength dependence of the polarizing element was measured with the angle of incident light being 45 °.

  From the results shown in FIG. 9A, it was found that a polarizing element having a grid height of 270 nm has a Tp × Rs of 90% or more in the wavelength band of 400 to 480 nm and exhibits good characteristics in the blue light band. . Further, from the result shown in FIG. 9B, the polarizing element having a grid height of 480 nm has a Tp × Rs of 90% or more in the wavelength band of 580 to 700 nm and exhibits good characteristics in the red light band. I understood. Further, from the result shown in FIG. 8 described above, the polarizing element having a grid height of 400 nm showed Tp × Rs of 90% or more in the wavelength band of 500 to 600 nm, and showed good characteristics in the green light band. Thus, it has been found that by designing the grid height so that Tp, Rs, and Tp × Rs are high, it is possible to easily obtain good characteristics for light in a desired wavelength band.

  FIGS. 10A and 10B are graphs showing the wavelength dependence of Tp, Rs, and Tp × Rs when the grid width of the dielectric multilayer structure is 50 nm and 105 nm, respectively. As described above, the polarizing element used for the measurement has a five-layer structure in which the projections of the concavo-convex structure are dielectric, the grid height is 270 nm, and the grid pitch is 150 nm. The wavelength dependence of the polarizing element was measured with the angle of incident light being 45 °.

  From the comparison between the graph shown in FIG. 10A and the graph shown in FIG. 9A, the polarizing element with a grid width of 50 nm has a better wavelength range of Tp × Rs than the polarizing element with a grid width of 75 nm. Was found to move to the short wavelength region. Conversely, from a comparison between the graph shown in FIG. 10B and the graph shown in FIG. 9A, the polarizing element with a grid width of 105 nm has a better Tp × Rs than the polarizing element with a grid width of 75 nm. It was found that the wavelength range moves to the long wavelength range, but the wavelength range becomes narrower. Therefore, for example, it was found that the polarizing element for the blue light band preferably has a grid width of 30 to 70% of the grid pitch.

FIG. 11 is a graph showing the wavelength dependence of Tp, Rs, Tp × Rs of a dielectric 7-layer polarizing element. The polarizing element used for the measurement has a dielectric seven-layer structure in which convex portions of the concavo-convex structure are laminated in the order of TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂ from the glass substrate side. Have. The polarizing element has a grid height of 400 nm, a grid pitch of 150 nm, and a grid width of 75 nm. The wavelength dependence of the polarizing element was measured with the angle of incident light being 45 °.

  This polarizing element having a dielectric multilayer structure has a Tp × Rs of 90% or more in the wavelength band of 400 to 500 nm, and has been found to exhibit good characteristics in the blue light band. In addition, the wavelength dependence graph of the polarizing element having the same structural dimensions consisting of five layers shown in FIG. 8 shows good characteristics in the green light band of 500 to 600 nm. It was found that bandwidth design is possible.

Example 2 Dielectric / Semiconductor Lamination
First, Si and SiO ₂ were alternately laminated on a glass substrate so as to have a predetermined number of layers and a predetermined grid height. An antireflection film (BRAC) was formed on the laminate, and a lattice-like mask pattern was formed with a resist so as to have a predetermined grid pitch and grid width.

Next, the antireflection film was removed by scum treatment with Ar / O ₂ gas, and Si and SiO ₂ were etched with CF ₄ / Ar gas. Then, the resist and the antireflection film were removed by O ₂ ashing to form a concavo-convex structure having a predetermined number of layers, a predetermined grid height, a predetermined grid pitch, and a grid width, and a polarizing element was manufactured.

FIGS. 12A and 12B are graphs showing the angle dependency of Tp and Rs with respect to incident light of a polarizing element having a dielectric / semiconductor multilayer structure, respectively. The polarizing element used for the measurement has a five-layer structure of a dielectric and a semiconductor in which convex portions of the concavo-convex structure are laminated in the order of Si / SiO ₂ / Si / SiO ₂ / Si from the glass substrate side. The polarizing element has a grid height of 280 nm, a grid pitch of 150 nm, and a grid width of 75 nm. In addition, as a comparative example, a calculated value in a wire grid type polarizing element having the same structural dimensions made of a commercially available Al single metal layer is shown.

  Tp shown in FIG. 12A and Rs shown in FIG. 12B were both higher in the dielectric / semiconductor multilayer polarizing element than in the metal single-layer polarizing element. The dielectric / semiconductor multilayer polarizing element also has good incident angle dependency, and Tp × Rs is 90% or more in a wide range of incident light angles of 0 to 65 °.

  FIG. 13 is a graph showing the angle dependency of Tp and Rs with respect to the incident light of the polarizing element when the grid height of the dielectric / semiconductor multilayer structure is 250 nm. The polarizing element used for the measurement is the same as described above except that the grid height is 250 nm, the convex portion of the concavo-convex structure has a five-layer structure of dielectric and semiconductor, the grid pitch is 150 nm, and the grid width is 75 nm. The wavelength dependence of the polarizing element was measured with the angle of incident light being 45 °.

  From the graph shown in FIG. 13, it was found that the polarizing element having a grid height of 250 nm has Tp × Rs of 90% or more in the wavelength band of 500 to 580 nm and exhibits good characteristics in the green light band.

  FIG. 14 is a graph showing the wavelength dependence of Tp, Rs, Tp × Rs of the polarizing element when the grid height of the dielectric / semiconductor multilayer structure is 350 nm. In the polarizing element used for the measurement, as described above, the convex portion of the concavo-convex structure has a five-layer structure of dielectric and semiconductor, the grid pitch is 150 nm, and the grid width is 75 nm. The wavelength dependence of the polarizing element was measured with the angle of incident light being 45 °.

  From the graph shown in FIG. 14, it was found that the polarizing element having a grid height of 350 nm has Tp × Rs of 90% or more in the wavelength band of 580 to 700 nm and exhibits good characteristics in the red light band.

  FIGS. 15A and 15B are graphs showing the wavelength dependence of Tp, Rs, and Tp × Rs of the polarizing element when the grid width of the dielectric / semiconductor multilayer structure is 50 nm and 105 nm, respectively. In the polarizing element used for the measurement, as described above, the convex portion of the concavo-convex structure has a five-layer structure of dielectric and semiconductor, the grid height is 250 nm, and the grid pitch is 150 nm. The wavelength dependence of the polarizing element was measured with the angle of incident light being 45 °.

  From the comparison between the graph shown in FIG. 15A and the graph shown in FIG. 13, the polarizing element with a grid width of 50 nm has a shorter wavelength range where Tp × Rs is better than the polarizing element with a grid width of 75 nm. It turns out to move to. From the comparison between the graph shown in FIG. 15B and the graph shown in FIG. 13, the polarizing element with a grid width of 105 nm has a longer wavelength range where Tp × Rs is better than the polarizing element with a grid width of 75 nm. Although it moved to the wavelength range, it was found that the wavelength range narrowed. Therefore, for example, it has been found that the polarizing element for the green light band preferably has a grid width of 30 to 70% of the grid pitch.

[Example 3: Formation of support part]
First, TiO ₂ and SiO ₂ were alternately laminated on a glass substrate so as to have a predetermined number of layers and a predetermined grid height. An antireflection film (BRAC) was formed on the laminate, and a lattice-like mask pattern was formed with a resist so as to have a predetermined grid pitch and grid width. In addition, a mask pattern having a period longer than the wavelength of the use band intersecting with the lattice mask pattern was formed. Specifically, using interference exposure, exposure is performed at a cycle of 150 nm to form a lattice-like mask pattern, and the substrate is rotated in a predetermined direction to perform exposure at a cycle of 1000 nm to form a mask pattern for a support grid. did.

Next, the antireflection film was removed by scum treatment with Ar / O ₂ gas, and TiO ₂ and SiO ₂ were etched with CF ₄ / Ar gas. Then, the resist and the antireflection film were removed by O ₂ ashing to produce a polarizing element in which a support grid having a height of 400 nm and a width of 40 nm was formed with a period of 1000 nm. This polarizing element has a five-layer structure of a dielectric in which convex portions of a concavo-convex structure are laminated in the order of TiO ₂ / SiO ₂ / TiO ₂ / SiO ₂ / TiO ₂ from the glass substrate side, and the grid height is 400 nm, The grid pitch was 150 nm and the grid width was 75 nm.

  When measuring the wavelength dependency of Tp, Rs, Tp × Rs of the polarizing element in which the support grid is formed, the wavelength dependency of 500 to 600 nm is obtained as in the wavelength dependency of the polarizing element in which the support grid is not shown in FIG. Tp × Rs was 90% or more in the wavelength band, and good characteristics were shown in the green light band.

  DESCRIPTION OF SYMBOLS 10 Transparent substrate, 20 Convex part, 21 High refractive index material, 22 Low refractive index material, 30 Concave part, 31 Support part, 32 Orthogonal grid, 33 Super low refractive index material, 40 Light shielding film, 41 Antireflection film, 42 Resist, 50 liquid crystal panel, 60 cross dichroic prism, 100 liquid crystal projector,

Claims (9)

Having a concavo-convex structure arranged on a transparent substrate at a pitch smaller than the wavelength of light in the use band,
The convex part of the concavo-convex structure is a polarizing element in which a high refractive index material made of a dielectric or a semiconductor and a low refractive index material made of a dielectric or a semiconductor having a smaller refractive index than the high refractive index material are alternately stacked.   The polarizing element according to claim 1, wherein a difference in refractive index between the high refractive index material and the low refractive index material is 1 or more. The pitch is 200 nm or less,
The polarizing element according to claim 1, wherein a width of the convex portion is 20 to 90% of the pitch. 4. The polarized light according to claim 1, wherein the high refractive index material is TiO ₂ , the low refractive index material is SiO ₂ , or the high refractive index material is Si, and the low refractive index material is SiO _2. element.   The polarizing element according to any one of claims 1 to 4, wherein a height of the convex portion of the concavo-convex structure is 500 nm or less.   The polarizing element according to claim 1, wherein a support portion that supports the space between the convex portions is formed in the concave portion of the concavo-convex structure.   The polarizing element according to claim 6, wherein the support portion is formed in a part of the concave portion with a pitch larger than a wavelength of light in the use band.   The polarizing element according to claim 7, wherein the support portion is formed of a material having a refractive index lower than that of the low refractive index material.   A liquid crystal projector comprising the polarizing element according to claim 1, a light source, and a liquid crystal panel.

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