JP2013214019A - Polarizing element and image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing element, which is excellent in heat resistance and light resistance and capable of maintaining transmittance and extinction ratio characteristics even in a simple configuration, and which has low reflectance and enlarges an allowable incident angle.SOLUTION: A polarizing element includes a metal structure layer 6 comprising island-like metal structures 12 stretched in one direction and two-dimensionally arranged, formed on an upper surface of a transparent first support; and the metal structure layer 6 is coated with a transparent second support 8. Each island-like metal structure has a wide part and a narrow part. Light incident to the metal structure layer 6 side exits to the outside of the polarizing element as superposed light including a component of the light reflected by the metal structure layer 6, a component of the light once transmitting through the metal structure layer 6, reflected by a metal thin line structure layer 10 and then again transmitting through the metal structure layer 6, and a component of the light by multipath reflection.

Description

  The present invention relates to a polarizing element having a polarization selection function used for a projection type image display apparatus and the like, and an image display apparatus having the polarizing element.

In a projection-type image display device such as a liquid crystal projector, in order to switch on and off the light to be projected using polarized light, a polarization selection element (polarized light) that transmits one of two orthogonal polarization components and blocks the other. Plate, polarizer) is required.
In recent image display apparatuses, it is required to project a high-contrast image using a high-luminance light source. A polarization selection element used in such an image display device is required to have a high extinction ratio (polarization selection performance), high light resistance and high heat resistance, and it is already known that a wire grid polarizer meets this requirement. It has been.

However, since conventional wire grid polarizers obtain a high extinction ratio by reflecting polarized light on the blocking side with a metal line pattern, this reflected light returns to the optical system of the image display device again, and an image is displayed. There was a problem of deteriorating.
In addition, an optical system that reduces reflected light by using a plurality of polarizing elements, such as a combined use of a polarizing selection element made of an absorbing organic material and a wire grid polarizer, or using a multilayer film configuration is employed. There are problems that the number of optical elements increases, the configuration of the polarizing element is complicated, and the allowable incident angle is limited.
In addition, in connection with these problems, there are problems that it is difficult to reduce the price, the load on the exhaust heat / cooling mechanism is increased, and it is difficult to reduce the size of the apparatus.

  Patent Document 1 discloses a polarizing element in which a thin line structure is arranged on a substrate for the purpose of reducing the reflectance of the polarizing element. This fine wire structure has a structure in which a metal material, a non-dielectric inorganic material, and a dielectric inorganic material are laminated.

  However, in the configuration described in the cited document 1, the above-mentioned problem that “the element configuration is complicated and it is difficult to reduce the price and the allowable incident angle is limited” has not been solved.

  The present invention has been made in view of such a current situation, and while having a simple structure, it has excellent heat resistance and light resistance, can maintain transmittance and extinction ratio characteristics, and has a reflectance. The main object of the present invention is to provide a polarizing element that is low and can increase the allowable incident angle.

  To achieve the above object, the present invention provides a transparent support, a metal structure layer provided on the support and two-dimensionally arranged with an island-like metal structure extending in one direction, A metal thin wire structure layer provided on a support at intervals from the metal structure layer in the light traveling direction and periodically arranged with a thin metal wire structure, and each island-shaped metal The structure has a wide portion and a narrow portion, and the wide portion and the narrow portion have a shape that is continuous in the one direction.

  According to the present invention, it is possible to realize a polarizing element that can obtain a high transmittance and extinction ratio, have a low reflectance, contribute to a reduction in cost with a simple structure, and can have a large allowable incident angle.

It is a longitudinal cross-sectional view of the polarizing element which concerns on the 1st Embodiment of this invention. 2A and 2B are horizontal sectional views of the polarizing element, in which FIG. 1A is a sectional view taken along line A-A ′ of FIG. 1, and FIG. 2B is a sectional view taken along line B-B ′ of FIG. It is a horizontal sectional view which shows the shape of the metal structure which comprises a metal structure layer. It is a figure which shows the model used for the numerical simulation, (a) is a longitudinal cross-sectional view, (b), (c) is a horizontal sectional view. It is a figure which shows the result of a numerical simulation. It is a horizontal sectional view showing a model in the numerical simulation of the dependence on the width of the narrow part. It is a figure which shows the result (spectral shape) of the same numerical simulation. It is a figure which shows the result (change of the reflectance with respect to width) of the same numerical simulation. It is a figure which shows the result of the numerical simulation of the dependence with respect to the length of a narrow part. It is a horizontal sectional view showing a model in a numerical simulation of the dependence on the position of the narrow part. It is a figure which shows the result of the same numerical simulation. It is a longitudinal cross-sectional view of the polarizing element which concerns on 2nd Embodiment. FIG. 13A is a horizontal sectional view of the polarizing element, FIG. 13A is a sectional view taken along line A-A ′ in FIG. 12, and FIG. 13B is a sectional view taken along line B-B ′ in FIG. 12. It is a longitudinal cross-sectional view of the polarizing element which concerns on 3rd Embodiment. It is a horizontal sectional view which shows the shape and arrangement | positioning form of the metal structure of the polarizing element which concern on 4th Embodiment. It is a schematic block diagram of the image display apparatus which concerns on 5th Embodiment.

Embodiments of the present invention will be described below with reference to the drawings.
The first embodiment will be described with reference to FIGS. As shown in the figure, the polarizing element 2 includes at least two layers of a microstructure made of a metal material in the support and / or the support. One of the two layers has a structure in which metal thin wire structures are periodically arranged, and the other has a structure in which a plurality of divided island-like metal structures are periodically arranged in a two-dimensional plane. ing.
More specifically, the metal structure layer 6 is supported on one side (upper surface in the figure) of the first support (substrate) 4 formed of a transparent material, and the metal structure layer 6 is a transparent material. It is covered with. The transparent material that covers the metal structure layer 6 serves as the second support 8, and the thin metal wire structure layer 10 is provided on the upper surface of the second support 8 in the figure.

2A is a cross-sectional view taken along the line AA ′ in FIG. 1A, that is, a top view showing the metal structure layer 10, and FIG. 2B is a cross-sectional view taken along the line BB ′. The top view showing the figure, ie, the metal structure layer 6, is shown.
In other words, FIG. 2B is a top view of a periodic array of a plurality of island-shaped metal structures 12 arranged in a transparent coating material. Here, the “island shape” means an independent solid shape.
The fine metal wire structure layer 10 is composed of a plurality of fine metal wire structures 11 extending in the longitudinal direction (stretching direction) of the metal structure 12.
In the polarizing element 2, light is incident from the lower side of FIG. 1, that is, from the side of the layer including the island-shaped metal structure 12, and the metal structure layer 6 formed of the island-shaped metal structure and the metal thin wire having the metal thin wire structure Outgoing light is obtained through the structural layer 10.
The light reflected by the polarizing element 2 is transmitted once through the metal structure layer 6 and the component reflected by the metal structure layer 6, and then again through the metal structure layer 6 after being reflected by the metal thin wire structure layer 10. And the components due to multiple reflection are superimposed and emitted outside the polarizing element.

  Here, if the metal thin line structure layer 10 has a reflection type polarization selection function and the metal structure layer 6 has an absorption type polarization selection function with a small amount of reflected light, the reflected light from the metal thin line structure layer 10 is reflected. The metal structure layer 6 can absorb efficiently and the reflected light can be reduced.

A specific material and manufacturing method of the polarizing element 2 will be described.
The first support 4 is a substrate that supports the island-shaped metal structure 12 and is preferably a transparent material that is generally used for optical elements, such as quartz glass, BK7, and Pyrex (registered trademark). An optical crystal material such as silicate glass, CaF ₂ , ZnSe, Al ₂ O ₃ is used.
Al is suitable for the island-shaped metal structure 12 and the metal fine wire structure which is an upper layer in the light traveling direction. Moreover, materials such as Au, Ag, and Cru can be used depending on the alloy / mixed material containing Al as a main component and the operating wavelength band. In order to produce a laminated structure made of a metal material, a structure in which the metal structure 12 is embedded and used as the second support is necessary.

For the second support 8, a glass material having a refractive index in the vicinity of 1.5 is suitable, and is generally used as a coating material for optical elements with little absorption.
Specifically, materials such as quartz glass, Pyrex (registered trademark), borosilicate glass such as ZnS—SiO ₂ , CaF ₂ , Si, ZnSe, Al ₂ O ₃ , and ZnO can be used. In addition, a spin-on-glass material mainly composed of a glass material can be used.
As a method for patterning a metal material, a method having a processing accuracy equal to or lower than the diffraction limit of visible light is applied. Specific methods that can be used include a method using electron beam lithography, DUV / EUV lithography, nanoimprinting, and etching utilizing alteration of material properties.

Hereinafter, as a general method, a method by electron beam lithography will be described, but the manufacturing method is not necessarily limited. Optical glass on a parallel plate is used as a support, a metal material such as Al is deposited by sputtering or vacuum evaporation, and a photoresist film is formed on the metal film.
Here, in order to improve the adhesion of the film at the interface between the metal and the support substrate, an underlayer such as Ti or Cr may be provided. Subsequently, the negative pattern is exposed so as to leave a rectangular metal pattern by electron beam drawing. After that, unnecessary metal portions are etched by RIE or the like, and then the remaining photoresist pattern is removed, whereby a metal microstructure can be formed at the support substrate interface.
Instead of forming the metal structure pattern by etching, it is also effective to form a metal pattern by using a lift-off method in which a metal material is deposited on the photoresist pattern and then the photoresist is removed. In order to produce a laminated structure, a spin-on-glass material is spin-coated to form a smooth surface on which a second metal fine wire structure is formed, and then the above-described electron beam lithography method is repeated.

Based on FIG. 3, the shape of the island-shaped metal structure 12 in the polarizing element 2 will be described.
In the polarizing element 2 according to the present embodiment, as shown in FIG. 1 and FIG. 2, an island-shaped metal structure that is characterized in that a reflection type and an absorption type polarization selection structure are stacked and has absorption characteristics. However, it is characterized in that it exhibits absorption characteristics depending on its shape and size.
FIG. 3 is a diagram showing the shape of a single island-like metal structure 12, and the metal structure layer 6 is a structure in which this structure is periodically arranged in a two-dimensional plane. As shown in FIG. 3 (a), the island-shaped metal structure 12 has a shape extending in one direction (vertical direction in FIG. 3), a wide portion 12a having a wide width inside the structure, and a width. Narrow narrow portion 12b.
In such a structure, the length L in the stretching direction and the operating wavelength (resonance due to the structure) have a strong correlation. Further, when the width W2 in the direction orthogonal to the extending direction of the narrow width portion 12b is 30 nm or less, absorption characteristics appear, and 20 nm or less is preferable.

If the island-shaped metal structure as shown in FIG. 3 is provided with a wide portion and a narrow portion, a low reflection polarizing element can be realized due to the absorption reduction of the reflected light component, but the wide portion and the narrow portion can be realized. The wavelength dependence of absorption varies greatly depending on the positional relationship and / or asymmetry of the parts.
Below, the example of a shape which can be utilized as an island-shaped metal structure is demonstrated. FIG. 3A shows a centrally symmetric shape (180-degree rotational symmetry). 3B and 3C show a shape having asymmetry in the stretching direction, and FIG. 3D shows a shape having asymmetry in the direction perpendicular to the stretching direction. That is, the wide part has a shape composed of two types of lengths in the extending direction.
FIG. 3E shows a shape having asymmetry simultaneously in the directions parallel and perpendicular to the stretching direction. For each structure, the wavelength dependence of the absorption characteristics varies greatly.

FIG. 4 is a diagram for explaining a model of a numerical simulation performed for verifying the operation of the polarizing element 2.
In order to verify that the reflected light can be reduced by the configuration of the polarizing element, a numerical simulation was performed. As the numerical simulation method, a finite difference time domain method (FDTD method) was used in which the Maxwell equation describing the time-space response of an electromagnetic field is differentiated into a time domain and a spatial domain.
A structure in which an Al microstructure was disposed on a support substrate (refractive index 1.51) 4 and the upper portion of the support substrate 4 was covered with a dielectric material (refractive index 1.38) 8 was used. By imposing a periodic boundary condition at the calculation region boundary, the periodic structure element 6 that is infinite in a plane direction parallel to the support substrate 4 is expressed.
In this numerical simulation, in order to obtain the polarization characteristics of the transmitted light spectrum, linearly polarized light perpendicular to the longitudinal direction of the metal structure 12 and parallel linearly polarized light shown in the plan view (XY plane) of FIG. A plane wave pulse with a sufficiently short time width (spectrum width sufficiently spread in the visible light region) is incident from the support substrate interface, and the time variation of the electric field amplitude subjected to spatial averaging is Fourier-transformed on the observation surface separated by more than the wavelength. The polarization characteristics of transmitted light and reflected light were calculated by conversion.
The wavelength dispersion characteristic of the dielectric function of Al was given by the Drude model often used in the calculation of metal materials. The dimensions of the island-shaped metal structure 12 and the thin metal wire structure 11 are as described in FIG.

FIG. 5 shows the result of the numerical simulation.
5A shows the transmittance obtained by the numerical simulation using the parameters shown in FIG. 4, FIG. 5B shows the reflectance, and FIG. 5C shows the absorptance.
Since the absorptivity cannot be obtained directly from the numerical simulation, it is a value calculated using the transmittance and the reflectance obtained by the numerical simulation. The “TM component” shown in the legend of FIG. 5 is a polarization component orthogonal to the extending direction of the metal (Al) fine wire structure or the island-shaped metal (Al) structure, and the “TE component” is the TM component. It is an orthogonal polarization component.
As shown in FIG. 5A, the transmittance of the TE component has a small value and cannot be recognized on the graph by overlapping with the axis of transmittance 0. It was confirmed that in the wavelength band from 475 nm to 630 nm, a high transmittance was obtained for the TM component, and the reflected light of the TE component to be blocked was reduced to 10% or less.

  As shown in FIG. 5C, the absorptance is 90% in the same wavelength band, and most of the light energy on the blocked side is converted to heat by absorption of the island-shaped metal structure or metal thin wire structure. Was confirmed. A metal material has high heat resistance, does not cause deterioration of the polarizing element due to heat generation, has a low reflectance, and can realize a polarizing element having high heat resistance and light resistance.

FIG. 6 is a diagram showing a numerical simulation model for confirming the dependence on the width of the narrow portion in the polarizing element of the present invention, and FIG. 7 is a diagram for explaining the result.
In order to confirm the effect of the narrow portion in the island-shaped metal (Al) structure, the change in transmittance and reflectance when the width of the narrow portion (W2 in FIG. 3) is changed is shown in FIG. A simulation was performed using the parameters used in FIG.
However, as shown in FIG. 6, the dimension of the narrow width portion was changed at 40 nm (matched with the wide width portion), 24 nm, and 12 nm.
As shown in FIG. 7A, almost no change in transmittance was observed in the three structures. On the other hand, as shown in FIG. 7B, it was found that the reflectance in the vicinity of the wavelength of 500 nm rapidly decreases as the line width of the narrow portion decreases. As a result, it was confirmed that a polarizing element having a low reflectance over a wide wavelength band could be realized.

FIG. 8 is a diagram for explaining the dependence on the size of the narrow portion in the polarizing element of the present invention.
In order to confirm the specific dimensions of the narrow width portion of the present polarizing element, a numerical simulation using the same parameters as in FIG. 6 was carried out when the line width of the narrow width portion was varied.
The fluctuation amount is 12 nm to 40 nm (narrow portion = wide portion). FIG. 8 is a graph plotting changes in reflectivity at a wavelength of 496 nm. It was confirmed that the reflectivity changes sharply when the line width of the narrow portion is 30 nm or less. From this result, it was found that good low reflection characteristics can be obtained by setting the line width of the narrow portion to 30 nm or less, preferably 20 nm or less.

FIG. 9 is a diagram for explaining the result of a numerical simulation for confirming the dependence on the length of the narrow portion in the polarizing element of the present invention.
Under the same conditions as the parameters used in FIGS. 5 to 7, the transmittance of the TM component and the reflectance of the TE component with respect to the length of the narrow portion (W1 in FIG. 3) in the island-shaped metal structure Was calculated.
When the length of the narrow portion was 16 nm, smooth reflection characteristics were obtained although the wavelength band showing low reflection narrowed. Further, it has been found that when the length of the narrow width portion is increased, the wavelength band showing low reflection becomes wide, while the reflectance varies. When the length of the narrow portion was 64 nm, the reflectance was about 25% or less, and it was confirmed that the length of the narrow portion should be about 65 nm or less. The length of the narrow portion takes an optimum value depending on the desired low reflection wavelength band.

10 and 11 are diagrams for explaining a model and a result of a numerical simulation for confirming the dependency on the position of the narrow portion in the polarizing element of the present invention.
A numerical simulation was performed on the island-shaped metal (Al) structure shown in FIG. 10 under the same conditions as the parameters used in FIGS.
With respect to the metal structure described with reference to FIG. 4, the position of the narrow portion is axisymmetric about the axis in the extending direction.
As shown in FIG. 11 (a), the transmittance is almost the same as the numerical simulation of FIG. 5, but as shown in FIG. 11 (b), the reflectance has a spectral shape having a dip near wavelengths of 450 nm and 610 nm. The wavelength region exhibiting low reflection characteristics is broadened.
However, the central reflectance increases to about 25%. From this result, it was confirmed that the position of the narrow portion in the direction perpendicular to the extending direction of the island-shaped metal structure acts on the width of the low reflection wavelength band of the polarizing element. On the other hand, the effect of the position change in the direction parallel to the extending direction of the island-shaped metal structure broadens the low reflection wavelength band as it approaches the center, but the effect was very small.

  As described above, the polarizing element of the present invention is a layer in which a layer composed of a metal thin wire structure having reflective polarization selectivity and an island-shaped metal structure having absorption polarization selectivity are two-dimensionally arranged. As a shape of the metal structure, light is incident from the side of the absorption-type polarization selective structure by providing the island-shaped metal structure with a wide portion and a narrow portion for exhibiting absorption characteristics. Then, since the reflection type polarization selection structure is in the next stage in the light traveling direction, the reflected light travels back and forth through the absorption type polarization selection structure, so that more of the blocking polarization component is absorbed and the reflected light can be reduced. .

A second embodiment will be described based on FIGS. The same parts as those in the above embodiment are denoted by the same reference numerals, and unless otherwise specified, the description of the configuration and functions already described is omitted, and only the main parts will be described (the same applies to other embodiments below).
The polarizing element 16 according to this embodiment includes at least two fine structures made of a metal material, as shown in FIGS.
More specifically, the thin metal wire structure layer 10 is provided on one side (upper surface) of the first support 4, and the metal structure layer 6 is provided on the opposite side (lower surface). The metal structure layer 6 is coated with a transparent second support 8.
The reason for this is to realize a low reflectance in the visible wavelength region when an Al material is used as the metal material. Further, the metal structure 12 is protected by the second support 8, so that the resistance to mechanical damage is improved.

In this polarizing element, light enters from the lower side of FIG. 12, that is, the side of the layer including the island-shaped metal structure, and the metal structure layer 6 made of the island-shaped metal structure and the metal thin-wire structure including the metal thin-wire structure. Outgoing light is obtained through the layer 10.
The light reflected by the polarizing element is transmitted once through the metal structure layer 6 and the component reflected by the metal structure layer 6, and then again through the metal structure layer 6 after being reflected by the metal thin wire structure layer 10. And the components due to multiple reflection are superimposed and emitted outside the polarizing element.
Here, the metal fine line structure layer 10 has a reflection type polarization selection function, and the metal structure layer 6 has an absorption type polarization selection function with a small amount of reflected light. The metal structure layer 6 can absorb efficiently and the reflected light can be reduced.
The material configuration and manufacturing method of this polarizing element are exactly the same as those shown in FIGS. The shape of the island-like metal structure is exactly the same as that described with reference to FIG.

FIG. 14 shows a third embodiment.
In the second embodiment, the metal structure layer 6 is coated with the transparent second support 8, but a configuration without a coating portion may be used.
In particular, when it is desired to realize low reflection characteristics on the short wavelength side, the configuration in which the island-shaped metal structure is exposed exhibits good transmission and low reflection characteristics.
In each of the above-described embodiments, the support body is configured by the first support body and the second support pair. However, in the polarizing element 18 of the present embodiment, the support body is configured by only the first support body 4. Yes.

FIG. 15 shows a fourth embodiment.
The present embodiment is characterized in that the metal structure layer 6 has a configuration in which a plurality of island-shaped metal structures having different narrow-width portions are arranged two-dimensionally.
That is, the island-shaped metal structure has a configuration in which a plurality of metal structures having narrow portions at different positions are periodically arranged in a two-dimensional plane.
Here, an example is shown in which three structures (Structure 1, Structure 2, Structure 3) are arranged while shifting their positions.
As described with reference to FIGS. 5 and 11, when the position of the narrow portion is changed, the spectral characteristics of the reflectance change. However, as shown in FIG. 11, the reflectance spectrum has a dip shape and is not uniform. become. Therefore, by arranging a plurality of metal structures 12 in which the positions of the narrow portions are shifted, the reflection spectrum is smoothed and good reflection characteristics can be obtained.

FIG. 16 shows an image display device (fifth embodiment) using the polarizing element.
A liquid crystal projector 30 as an image display device includes three color image forming units 31R, 31G, and 31B of R, G, and B, a light combining prism 32, a projection lens 33, and a screen 34.
Each of the image forming units 31R, 31G, and 31B is formed by laminating a light source 35, a polarizing element 2, a liquid crystal panel 36, and a polarizing plate 37.
When the liquid crystal projector 30 projects an image on the screen 34, the light emitted from the light source 35 of each of the image forming units 31R, 31G, and 31B is transmitted from the polarizing element 2 through the liquid crystal panel 36 and the polarizing plate 37. The light is combined by the light combining prism 32 and the combined light is projected onto the screen 33 by the projection lens 32 to display an image.
When displaying an image, a full-color image can be continuously projected onto the screen 33, and a high-quality image can be stably displayed. Further, the liquid crystal projector 30 can be manufactured with a simple configuration, and the liquid crystal projector 30 can be provided at a low price.

  In the present embodiment, the liquid crystal projector has been described as the image display device. However, when the polarizing element 2 is disposed on the front surface of the LED array and used as the backlight of the liquid crystal display, a diffusion plate, a color filter, and a polarizing plate become unnecessary. The configuration of the liquid crystal display can be simplified.

2 Polarizing element 4, 8 Support body 6 Metal structure layer 10 Metal fine wire structure layer 11 Metal fine wire structure 12 Island-like metal structure 12a Wide portion 12b Narrow portion

Special table 2010-530995 gazette

Claims (9)

A transparent support,
A metal structure layer provided on the support and two-dimensionally arranging island-like metal structures extending in one direction;
A thin metal wire structure layer provided on the support at a distance from the metal structure layer in the direction of travel of light and having a continuous thin metal wire structure disposed periodically;
Each of the island-shaped metal structures has a wide portion and a narrow portion, and the wide portion and the narrow portion have a shape that is continuous in the one direction. Polarizing element. The polarizing element according to claim 1,
The support comprises a first support provided with the metal structure layer and a second support covering the metal structure layer, and the metal fine wire structure layer is formed on the second support. A polarizing element provided. The polarizing element according to claim 1,
The metal structure layer is provided on one side of the support, and the metal thin wire structure layer is provided on the opposite side to the one side in the light traveling direction of the support. Polarizing element. The polarizing element according to claim 3,
A polarizing element, wherein the metal structure layer is covered with a transparent support. In the polarizing element as described in any one of Claims 1-4,
Each of the island-shaped metal structures has the narrow portion so as to have a 180-degree rotationally symmetric shape. In the polarizing element as described in any one of Claims 1-4,
Each of the island-shaped metal structures has the narrow portion so as to have an asymmetric shape with respect to the stretching direction and / or the direction orthogonal to the stretching direction. The polarizing element according to claim 6,
The polarizing element, wherein the metal structure layer has a configuration in which a plurality of island-shaped metal structures having different positions of the narrow portions are two-dimensionally arranged. In the polarizing element as described in any one of Claims 1-7,
The narrow width portion has a minimum width in a direction perpendicular to the stretching direction of 30 nm or less and a minimum length in a direction parallel to the stretching direction of 65 nm or less.   The image display apparatus using the polarizing element as described in any one of Claims 1-8.

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