JP2009223074A - Polarization converting element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarization converting element having a polarization converting function converting only one polarization component of two orthogonal polarization components of incident light into the other and to provide the polarization converting element capable of reducing the number of optical elements. <P>SOLUTION: In the polarization converting element wherein a plurality of units in each of which at least a structural body (1) by a conductive material and a structural body (2) by a conductive material are disposed at an interval (v) shorter than a wavelength of light in a direction parallel to a propagation direction of incident light are disposed on the same plane on a supporting body or in the internal part of the supporting body, the structural body (1) has a shape having point symmetry and no line symmetry in the plane perpendicular to the propagation direction of incident light and the structural body (2) has a shape having different lengths to two axes orthogonal to the propagation direction of incident light. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a polarization conversion element that achieves high light utilization efficiency and a reduction in the number of optical elements, and the polarization conversion element according to the present invention can be used for an image projection apparatus such as a liquid crystal projector and a display apparatus.

  In a display device that controls on / off of pixels using polarized light such as a liquid crystal projector, it is necessary to introduce linearly polarized light inclined in a specific direction into a spatial modulation device (liquid crystal panel). Conventionally, since only one direction of linearly polarized light component is extracted from random polarized light obtained from a light source via a polarizing plate (polarization selecting element), 50% or more of light is not used. On the other hand, in recent years, high light utilization efficiency has been realized by using a polarization conversion element, rotating the polarization plane of the remaining polarization component that has been an unnecessary component by 90 °, and introducing it again into the spatial modulation device. . Thereby, a high brightness liquid crystal projector or the like is realized.

  The above-described polarization conversion element normally uses a polarization separation function that utilizes a polarization separation element that branches the optical paths of two orthogonal polarization components and a half-wave plate (phase shift) that rotates one polarization plane by 90 °. Is realized. Widely used as a general polarization separation element is a polarizing beam splitter in which dielectric multilayer films having different refractive indexes are alternately laminated on a glass prism or a flat substrate surface. By setting the film structure and the incident angle so that the Brewster angle is at the interface, the P-polarized light (polarized light parallel to the incident surface) goes straight and the S-polarized light (deviation perpendicular to the incident surface) Wave) is reflected in the right-angle direction, and the polarized light can be separated. However, compared with a prism type polarizer using the birefringence of the crystal, there is a defect that the separation performance is low (ten and several dB). In addition, phase shifters that use the anisotropy of the refractive index use optical crystal materials that exhibit birefringence. Usually, expensive anisotropic crystals such as rutile and calcite are precisely shaped into a wedge or prism type. It is realized by performing proper polishing. Such an element is extremely expensive, has difficulty in miniaturization, and has a problem that a usable wavelength region is limited. In addition, the film thickness, that is, the optical path difference is adjusted by bonding the optical crystal material film, and the polarization state is controlled. Therefore, there is a problem that the dependence on the optical crystal material is strong and the degree of freedom of polarization controllability is low. there were. Furthermore, in the polarization conversion element combined with the above-described polarization control element, it is difficult to reduce the number of optical elements, and there is a problem in cost reduction and size reduction.

  In response to the above problems, a single-plate polarization conversion element has been realized by a composite structure of a phase shifter and a polarization separation element, and the polarization conversion element has been reduced in size, simplified in production process and alignment, and mechanically stable. Many configurations have been proposed as described below (Patent Documents 1 to 4).

  The problem in Patent Document 1 (Japanese Patent Laid-Open No. 07-294906) is to realize video display with high light source efficiency, that is, high luminance or low power consumption. FIG. 15 shows the configuration of the polarization separation element. The light source light 1 is non-polarized light in which various kinds of polarized light are mixed, and this light is converged on the working surface of the splitter 4 through each lens element of the lens plate 2 over the entire surface. Then, the splitter 4 passes the P wave component as it is through the working surface. On the other hand, the S-wave component is separated by the working surface of the splitter 4 and reflected by the prism 5, and is converted into polarized light at the exit surface, for example, a 90 ° conversion device by a combination of a mirror or a right-angle prism, or a half wavelength. By passing the phase plate (in this embodiment, the half-wave plate 6), the S wave becomes a P wave and is emitted in parallel with the transmitted light of the splitter 4. As described above, all the light incident on the lens element of the lens plate 2 is emitted as polarized light of the P wave by the polarization conversion plate 3 and supplied to the liquid crystal display plate 10.

The problem in Patent Document 2 (Japanese Patent Application Laid-Open No. 2007-279893) is to provide a polarization conversion element in which the polarization separation film does not peel off or generate cracks at the interface with the glass flat plate, As shown in FIG. 16A, the first light transmissive member 2 including the polarization separation film 10 and the reflective film 4 and the second light transmissive member that is alternately bonded to the first light transmissive member 2. And a half-wave plate 5 that converts the polarized light into either the optical path of the polarized light transmitted through the polarization separation film 10 or the optical path of the polarized light reflected by the reflective film 4. As shown in FIG. 16B, the polarization separation film 10 has a first polarization separation film layer film 10a in which SiO ₂ films 12 and lanthanum titanate films 11 having compressive stress are alternately laminated, and a tensile stress. MgF ₂ having film 13 and the lanthanum titanate film 1 It was formed by the second polarization separation layer 10b laminated alternately and.

  The problem in Patent Document 3 (Japanese Patent Application Laid-Open No. 2006-317965) is that light can be produced without increasing the number of polarization separation elements or polarization separation films that can reduce the number of layers of polarization separation films and shorten the time required for production. It is to provide a polarization conversion element and a projection display device including a polarization separation element that can improve the use efficiency, and separates incident light into two types of polarized light as shown in FIG. The polarization separation element 330, and a selective phase difference plate 381 that converts one of the two types of polarized light from the polarization separation element into the other polarization light, the polarization separation element 330 each having a parallelogram shape in cross section. A first transparent substrate and a second transparent substrate that are alternately bonded to each other, and polarized light is provided between the first transparent substrate and the second transparent substrate. Separation film 20 and reflection film 30 alternate It is placed.

  The problem in Patent Document 4 (Japanese Patent Application Laid-Open No. 2007-155835) is that the work man-hours that arise from the necessity to affix all the half-wave plates at predetermined positions with high accuracy in the conventional polarization conversion element are avoided and complicated. As shown in FIG. 18, the first prism having the entrance surface, the first exit surface, the polarization separation surface, and the reflection surface, the second exit surface, the first plane, and the second plane. A polarization conversion element comprising a plurality of optical units composed of a quartz half-wave plate and the half-wave plate comprising a first exit surface and a second exit surface. The first quartz plate covering the entire surface, the outer size is the same as the first quartz plate, and the main surface is externally exposed on either the first emission surface or the second emission surface. To the second quartz plate where the convex thick part is formed Ri is formed.

  The problem in Patent Document 5 (Japanese Patent Application Laid-Open No. 2005-077755) is a polarization conversion optical system that includes a polarization separation element, a microlens array, and a polarization conversion element, and the macrolens array and the polarization conversion element are positioned with a predetermined accuracy. In this system, the positioning of the macro lens array and the polarization conversion element is facilitated, and the size and thickness are reduced. As shown in FIG. 19, the micro lens array 5 is formed in advance, and the micro lens array By making substantially parallel light incident at a predetermined incident angle and forming a polarization conversion element using the focused light from the microlens array, the microlens array and the polarization conversion element are automatically positioned with high accuracy. By forming it, it becomes possible to reduce the size and thickness.

Similarly to the above, the following configuration is known as a polarization conversion element using a phase shifter and a polarization separation element, which has an additional function, and realizes easy alignment (patent) Reference 6).
The problem in Patent Document 6 (Japanese Patent Application Laid-Open No. 2007-163597) is that it has a polarization conversion function obtained by a conventional polarization conversion element and a wavelength-selective phase difference plate, and has a reduced number of optical components and a structure in an image projection apparatus. As shown in FIG. 20, the wavelength selective polarization conversion element 5 includes light P in the first polarization direction and light in the second polarization direction. The polarization separation film 32 having a characteristic in which the transmittance for S varies between a transmittance higher than 50% and a transmittance lower than 50% according to the wavelength range, and light transmitted or reflected by the polarization separation film A retardation plate 33 for converting the polarization direction of the first and second polarization directions between the first polarization direction and the second polarization direction. The polarization conversion element emits light in two wavelength regions as polarized light having one of the first and second polarization directions, and emits light in the other wavelength regions in the first and second polarization directions. Are emitted as polarized light having the other polarization direction.

Further, the following is known as a configuration of a polarization conversion function that simplifies the structure by using a birefringent material or a fine structure as a polarization separation element (Patent Documents 7 and 8).
The problem in Patent Document 7 (Japanese Patent Application Laid-Open No. 2007-093964) is to provide a polarization conversion element with a low manufacturing cost. As shown in FIG. 21, the polarization conversion element 5 includes a birefringent plate 6. A half-wave plate 7 is provided at a predetermined position of the birefringent plate 6. When random polarized light L1 is incident on the polarization conversion element 5, in the birefringent plate 6, the component of linearly polarized light in the direction orthogonal to the optical axis of the birefringent plate 6 becomes an ordinary ray and passes through the optical path of the incident light L1 as it is. It goes straight and becomes linearly polarized light L2 and is emitted from the second path. On the other hand, the linearly polarized light component in the direction parallel to the optical axis of the birefringent plate 6 becomes an extraordinary ray and is refracted by the birefringent plate 6 to be separated into the linearly polarized light L3. On the other hand, a half-wave plate 7 is provided on the exit surface of the linearly polarized light L3 that becomes an extraordinary ray, and the polarization plane of the linearly polarized light is rotated by 90 deg. The light is converted into linearly polarized light L3 ′ in the polarization direction and emitted from the first path.

  The problem in Patent Document 8 (Japanese Patent Laid-Open No. 2007-225744) is to provide a polarization conversion element with excellent productivity that can efficiently convert non-polarized light into linearly polarized light, and a liquid crystal projector or liquid crystal display using the same. As shown in FIG. 22, the polarization separation layer 12 separates light having no incident angle of 0 degrees into linearly polarized light T1 that emits light in a substantially normal direction and linearly polarized light T2 that emits in an oblique direction with respect to the normal. And a polarization control layer 11 that passes through without converting the polarization state of the linearly polarized light T1 almost completely into the polarization state of the linearly polarized light T2, and without converting the polarization state of the linearly polarized light T2 by 50% or more. A polarization conversion element is obtained.

Similar to Patent Documents 1 to 8 above, there is a patent document related to our proposed technology as a polarization conversion element using a phase shifter and a polarization separation element.
The problem in Patent Document 9 (Japanese Patent Application Laid-Open No. 2007-79542) is that polarization conversion with excellent manufacturability is achieved by efficiently switching an unpolarized light beam to a light beam in one polarization direction and simultaneously reducing the number of polarization separation surfaces. The polarization separation element includes a plurality of polarization separation units 10 and a plurality of phase modulation units 20 as shown in FIG. The light flux enters each polarization separation section and is separated into transmitted light (P-polarized light) and reflected light (S-polarized light). The light beam reflected by the polarization separation unit is reflected again at a position different from the incident light position of the adjacent polarization separation unit, and is emitted in the same direction as the transmitted light. The phase modulation unit is provided in one of the optical paths of the transmitted light and the reflected light, and aligns the emitted light with P-polarized light or S-polarized light. Shifting the incident light position and the emission position of the reflected light from the adjacent polarization separation section at the polarization separation section is achieved by shifting the angle of the polarization separation section from 45 °.

In addition, as optical elements having a configuration related to the polarization conversion element of the present invention, the following techniques that the inventors have proposed so far are known (Patent Documents 10 to 13).
The problem in Patent Document 10 (Japanese Patent Laid-Open No. 2006-330105) is to provide a polarization control element having excellent heat resistance and light resistance, high light transmittance or high reflectance, and a high degree of design freedom. As shown in FIG. 24 (a), a metal composite structure composed of two or more metal microstructures arranged in a region below the wavelength of incident light and periodically arranged The body 6 is formed on a support substrate and has a structure in which interaction by near-field light works, so that the light transmittance is high and a sufficient phase difference can be given. A polarization control element having excellent light resistance is obtained.

  The problem in Patent Document 11 (Japanese Patent Application Laid-Open No. 2006-330106) is a polarization control that has high light transmittance, can provide a sufficient phase difference, has a high degree of design freedom, and has excellent heat resistance and light resistance. As shown in FIG. 24 (b), the light incident on the flat surface of the transparent glass substrate 1 with a metal structure (metal particles 2) smaller than the wavelength of the incident light is provided. A two-dimensional arrangement with a distance smaller than the wavelength of the light, the light transmittance is high, a sufficient phase difference can be given, the design freedom is high, and the polarization control element is excellent in heat resistance and light resistance. 10 is assumed. In addition to a flat substrate, there is a configuration in which a metal structure is provided on a lens or a microlens.

  The problem in Patent Document 12 (Japanese Patent Application Laid-Open No. 2006-330107) is to provide a wavelength control plate that generates a phase difference and to provide a polarization control element with excellent heat resistance, as shown in FIG. As described above, a pattern of metal particles (first metal particles 2 and second metal particles 3) made of two or more kinds of metals or alloys is continuously formed on a transparent dielectric substrate 1 such as a glass substrate. Thus, a polarization plate 10 that realizes a wave plate that generates a phase difference in the polarization component of transmitted light or reflected light, has excellent heat resistance, and has a high degree of freedom in designing a polarization state is provided.

  The problem in Patent Document 13 (Japanese Patent Application Laid-Open No. 2006-330108) is that the support substrate on which the metal microstructures are arranged has a sub-wavelength structure, and generates strong evanescent light on the surface layer of the substrate. By combining light, light emission and light absorption are generated more strongly, and the control performance of optical characteristics is improved. As shown in FIG. 24 (d), the light is arranged in a region below the wavelength of incident light. The polarization control element 10 is formed on the glass substrate 1 by the metal composite structure composed of the metal microstructures 6 that are arranged periodically and has a height on the surface of the glass substrate 1. It has a periodic structure that is periodically modulated, and the periodic structure has a period smaller than the wavelength of the incident light.

  Although the polarization conversion elements shown in Patent Documents 1 to 8 and the technique proposed by us (Patent Document 9) realize a single-plate polarization conversion element, a polarizing beam splitter and a reflective film are stacked and cut out in an oblique direction. Further, since the polarization conversion function is realized by the configuration in which the half-wave plate is provided in the region where one polarization component is transmitted, there is a problem that the manufacturing process becomes extremely complicated. In addition, the half-wave plate, which is a film of anisotropic material, needs a certain thickness to obtain a sufficient polarization conversion function, and there is a limit to realizing a thin and small polarization conversion element. . Furthermore, in order to spatially divide the two polarization components, intensity unevenness occurs, and in order to avoid this, it is necessary to provide a microlens array, and there are problems in miniaturization and reduction in the number of optical elements. It was.

  In view of these problems, another technique proposed by us (Patent Documents 10 to 13) proposes a configuration that realizes a polarization control function using the fine structure of a conductive material. The purpose of the present invention is to provide a polarization control element having a property, and no polarization conversion function is provided.

  The problems of Patent Documents 1 to 8 and the technique proposed by us (Patent Document 9) are that the conventional polarization conversion element independently varies the amplitude or phase of two orthogonal polarization components, and the difference in film thickness and absorption rate. This is due to the fact that it does not have a mechanism for converting only one component into the other.

JP 7-294906 A JP 2007-279893 A JP 2006-317965 A JP 2007-155835 A Japanese Patent Laid-Open No. 2005-77545 JP 2007-163597 A JP 2007-93964 A JP 2007-225744 A JP 2007-79542 A JP 2006-330105 A JP 2006-330106 A JP 2006-330107 A JP 2006-330108 A

The present invention has been made in view of the above, and provides a configuration having different polarization control functions for two orthogonal polarization components.
An object of the present invention is to provide a polarization conversion element having a polarization conversion function for converting only one polarization component of two orthogonal polarization components of incident light into the other. Another object of the present invention is to provide a polarization conversion element that can reduce the number of optical elements.
Another object of the present invention is to provide a specific structure of a structure made of a conductive material used in the polarization conversion element according to claim 1.
A third object of the present invention is to provide an additional configuration for improving the polarization conversion efficiency of the polarization conversion element according to the first and second aspects.
Another object of the present invention is to provide a polarization conversion element having a polarization conversion function of converting only one polarization component of two orthogonal polarization components of incident light into the other. Another object of the present invention is to provide a polarization conversion element that can reduce the number of optical elements.
Another object of the present invention is to provide a specific structure of a structure made of a conductive material used in the polarization conversion element according to claim 4.
A sixth object of the present invention is to provide a configuration for controlling the operating wavelength band of the polarization conversion element according to any one of the first to fifth aspects. Another object of the present invention is to provide a configuration of a polarization conversion element that is resistant to external impact.

The above problems are solved by the present invention described below.
(1) “At least the structure (1) made of a conductive material and the structure (2) made of a conductive material on the support or inside the support in a direction parallel to the propagation direction of incident light The structure (1) has a configuration in which a plurality of units arranged at intervals (v) are arranged in the same plane, and the structure (1) is point-symmetric and line-symmetric in a plane perpendicular to the propagation direction of incident light. A polarization conversion element characterized in that the structure (2) has a shape different in length with respect to two axes perpendicular to the propagation direction of incident light ",
(2) “The structure 1 is composed of a plurality of microstructures made of a conductive material, and two or more of the microstructures are arranged close to each other at an interval equal to or smaller than the size of the microstructure. The polarization conversion element according to item (1), wherein:
(3) “Conductivity having a shape oriented in the same axial direction as the structure (2) above the surface forming the structure (1) or below the surface forming the structure (2) The polarization conversion element according to item (1) or (2), wherein the structure (3) is made of a material.
(4) “having at least a structure (1) made of a conductive material and a structure (2) made of a conductive material in a direction parallel to the propagation direction of incident light on or inside the support, The body (1) has a shape that is point-symmetric in the plane perpendicular to the propagation direction of incident light and has no line symmetry, and is spaced from the structure (2) by an interval (v) that is less than or equal to the wavelength of the light. The structure (2) has a configuration in which a plurality of elements are arranged in the same plane in close proximity, and the structure (2) has a stripe structure continuous in one axial direction with respect to two axes orthogonal to the propagation direction of incident light. A polarization conversion element characterized by having, "
(5) “The structure 1 is constituted by a plurality of microstructures made of a conductive material, and two or more of the microstructures are arranged close to each other at an interval equal to or smaller than the size of the microstructure. The polarization conversion element according to item (4), wherein:
(6) "Any of the above-mentioned items (1) to (5), wherein a dielectric film that contacts or covers the structure (1) or the structure (2) is disposed. Description of polarization conversion element ".

The polarization conversion element according to claim 1 of the present invention has a structure (1) made of a conductive material exhibiting optical rotation by a structure having point symmetry and a structure having different lengths with respect to two orthogonal axes. By arranging the units in which the structures (2) made of the conductive material exhibiting polarization selectivity are arranged in the same plane, the polarization conversion function can be realized without using a plurality of optical elements. In addition, there are effects that the number of optical elements can be reduced and the optical device can be reduced in size and price.
In addition, the polarization conversion element according to claim 2 of the present invention has a structure (1) made of a conductive material exhibiting optical rotation by a structure having point symmetry, and has different lengths with respect to two orthogonal axes. By arranging a unit in which the structures (2) made of a conductive material exhibiting polarization selectivity according to the structure are stacked in the same plane and using a plurality of microstructures as the structure (1), a plurality of structures are obtained. The polarization conversion function can be realized without using the optical element, and a polarization conversion element with a high degree of design freedom can be provided.
A polarization conversion element according to claim 3 of the present invention is the same as the polarization conversion element according to claim 1 or 2, but is a conductive material having polarization selectivity by a structure having different lengths with respect to two orthogonal axes. By arranging the structures (3) made of the active material in a stacked manner, the polarization conversion efficiency can be improved.
In addition, the polarization conversion element according to claim 4 of the present invention includes a structure (1) exhibiting optical rotatory power by a structure having point symmetry and a stripe made of a conductive material continuous in one direction of two orthogonal axes. By arranging the structure (2) having a structure, there is an effect that a polarization conversion function can be realized without using a plurality of optical elements. In addition, there are effects that the number of optical elements can be reduced and the optical device can be reduced in size and price.
Further, the polarization conversion element according to claim 5 of the present invention includes a structure (1) exhibiting optical rotation by a structure having point symmetry, and a stripe made of a conductive material continuous in one direction of two orthogonal axes. By arranging the structure (2) having a structure and using a plurality of microstructures as the structure (1), a polarization conversion function can be realized without using a plurality of optical elements, and design flexibility can be improved. There is an effect that a high polarization conversion element can be provided.
The polarization conversion element according to claim 6 of the present invention can control the operating wavelength band of the polarization conversion element by coating the polarization conversion element according to claims 1 to 5 with a dielectric film. The polarization converting element that is resistant to external impact can be provided.

  Exemplary embodiments of a polarization conversion element according to the present invention will be explained below in detail with reference to the accompanying drawings.

(First embodiment)
The polarization conversion element according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an explanatory diagram showing the function of the polarization conversion element according to the first embodiment of the present invention. This polarization conversion element converts only the polarization component in the y-axis direction of incident light into the polarization component in the x-axis direction for incident random polarization by the interaction of the structure made of the conductive material contained in the element and the light. In addition, linearly polarized light is acquired with high efficiency by transmitting the polarization component of the incident light in the x-axis direction as it is.

  The configuration of the polarization conversion element of the present invention will be described with reference to FIG. FIG. 2 is a diagram illustrating the configuration of the polarization control element and the shape of the structures (1) and (2) made of a conductive material contained in the polarization control element. The left figure in FIG. 2 (cross section AA) is a sectional view in the direction parallel to the propagation direction of the incident light of this polarization conversion element, and the right figure in FIG. 2 (cross section BB, cross section CC) is perpendicular to the propagation direction of the incident light. It is sectional drawing cut out by two surfaces so that the structures (1) and (2) by an electroconductive member may be cut | disconnected in an arbitrary direction. This polarization conversion element includes a structure (1) made of a conductive material having a shape that is point-symmetric and has no line symmetry in a plane perpendicular to the propagation direction of incident light, and is orthogonal to the propagation direction of incident light. A structure in which a plurality of units in which a structure (2) made of a conductive material having different shapes with respect to two axes is stacked on a support or inside the support is arranged in the same plane. Have. Since the structure (1) and the structure (2) interact with each other through near-field light that exists in the vicinity of the substance, the distance between the structure (1) and the structure (2) in the optical path direction (V) is arranged close to the wavelength of incident light or less.

Section BB in FIG. 2 is a plan view showing a plane for cutting the structure 1, and each of the structures (1) has a point symmetry that matches the original shape by a rotation operation with the center of gravity as a fulcrum. have. Further, it is characterized in that there is no line symmetry such that the folded shape matches a specific axis. A structure having such a shape causes a strong interaction between light and a conductive material that resonates with electronic vibration (plasmon) inside a conductive substance in a specific wavelength range. Therefore, when linearly polarized light is incident, It exhibits optical rotation that rotates the polarization plane of linearly polarized light.
A cross section CC in FIG. 2 is a plan view showing a surface for cutting the structure (2). In the case of the example in FIG. 2, the cross section CC has a rectangular shape extending long in the vertical direction of the paper. In a structure having such a shape, since the plasmon resonance conditions are different between the longitudinal direction of the rectangle and the direction orthogonal thereto, polarization anisotropy or polarization selectivity occurs in transmitted light or reflected light. The polarization conversion function of the present polarization control element can be obtained by the above-described competitive effect of optical rotation and polarization selectivity.

  In FIG. 2, a structure having a shape in which two cubes are in contact with each other is illustrated as the structure (1). However, it is a structure made of a conductive material having point symmetry and emits optical rotation. Any shape may be used. Here, since a linear structure such as a simple rectangular parallelepiped or a cylinder, that is, a structure having line symmetry, does not exhibit optical rotation, such a structure is used for this polarization conversion element. Can not. Hereinafter, a structure having point symmetry and no line symmetry used in the present polarization conversion element is simply expressed as point symmetry. Further, the point symmetry is a requirement for designing the polarization conversion element, and does not limit the symmetry shift caused by a manufacturing error or the like.

  FIG. 3 is a plan view showing an example of a structure showing optical rotation. FIGS. 3 (a) and 3 (b) are structures in which the structures having a square and rectangular cross section are in contact with each other or are overlapped with each other and have a shift with respect to a vertical or horizontal axis. Moreover, as shown in FIG.3 (c), the structure where the edge part of the rectangular structure bent antisymmetrically may be sufficient. FIG. 3 (d) shows an antisymmetric curved arc structure, FIG. 3 (e) shows an overlapping structure of rectangular and circular structures, and FIG. 3 (f) shows an elliptical overlapping structure. . In addition to these, any structure having any shape may be used as long as it has a point symmetry and has a strong optical rotation. Further, the height of the structure and the shape in the height direction are factors that affect the strength of optical interaction with the stacked structure (2), and the structure (1) and the structure (2) It is necessary to select an optimal height and shape together with the interval (v), and it is not always necessary to have a shape having a rectangular cross section.

  Further, in FIG. 2 cross-section CC, as an example of the structure (2), a rectangular structure having a longitudinal direction in the vertical direction of the figure is shown, but it absorbs a polarization component in a direction perpendicular to the longitudinal direction. Any shape may be used as long as it has anisotropy in scattering characteristics. For example, in addition to thin-film circular patterns and rectangular patterns, cylinders, elliptical cylinders, spheroids, rectangular parallelepiped shapes, and the like can be used.

  There are various arrangements of the units constituted by the structure (1) and the structure (2), but in order to obtain high polarization conversion efficiency, as shown in the plan view on the right side of FIG. It is more preferable to arrange in the order. Further, the interval between adjacent units is preferably equal to or less than the wavelength of incident light so that the influence of diffraction or unevenness of light intensity does not appear in the emitted light. Alternatively, a polarization conversion element having angle dependency may be configured by actively using the diffraction effect by setting the interval to the wavelength of incident light. The structures (1) and (2) need to be arranged at or below the wavelength as described above, so the size of the structures (1) and (2) is the wavelength of the incident light. The following sizes are preferred. However, since the shape of the structure is different in length and width, it is not necessary to strictly limit the size to a wavelength or less.

  The material used for the structure (1) and the structure (2) made of a conductive material is a conductive material as a material in which the structure (1) and the structure (2) interact strongly through near-field light. A material that can strongly excite plasmons, which are the collective motion of electrons inside, is suitable. As a conductive material that can strongly excite plasmons in the visible light region, general metal materials such as Al, Au, Cu, Ag, a combination thereof, or an alloy material / mixed material containing these as a main component can be used.

Next, the support of the present polarization conversion element will be described with reference to FIGS.
In the left diagram of FIG. 2, the structure (1) is arranged at the support interface and the structure (2) is embedded in the support for ease of manufacturing, but as shown in FIG. 4. In addition, the structure (1) and the structure (2) may be embedded in the support. In this case, the number of steps in production increases, but an optical element that is resistant to external impact can be provided. In the left diagram of FIG. 2, the structure (2) is arranged on the light transmission surface side. However, the structure (1) and the structure (2) may be stacked in the reverse order. Absent. The material used as the support is preferably a transparent material having low absorption at a wavelength in the visible light region in order to obtain high efficiency. Quartz glass or borosilicate glass such as BK7 or Pyrex (registered trademark) is used as CaF ₂ , ZnSe. An optical crystal material such as Al ₂ O ₃ is used.

Next, a method for manufacturing the present polarization conversion element will be described with reference to FIGS. This polarization conversion element is produced by the process shown in FIG. First, a resist is applied on a substrate, the resist is exposed by electron beam lithography, and a concavo-convex pattern is formed on the glass surface by reactive dry etching (step 1). Subsequently, a conductive material such as Au is formed by sputtering or vapor deposition (step 2), and then a structure made of a lower conductive material is produced by lift-off along with the removal of the resist (step 3). Subsequently, SiO _{2 is formed} into a film by sputtering or the like, a resist is applied, and the resist is exposed and rinsed by electron beam lithography to produce an uneven shape (step 4). Subsequently, a conductive material is deposited by sputtering or vapor deposition (step 5), and the structure is left by lift-off along with the removal of the resist, thereby producing a structure made of the upper conductive material (step 6). The above is an example of a manufacturing process. Instead of drawing by electron beam lithography, a method of performing batch exposure using DUV (far ultraviolet) / EUV (deep ultraviolet) lithography technology or a mold called a mold is used to apply heat. There is also a method of manufacturing using a nanoimprint processing technology that is pressed over.

  Next, a numerical simulation performed for verifying the operation of the polarization conversion element will be described with reference to FIGS. As a numerical simulation method, a finite difference time domain method (FDTD method) was used in which Maxwell's equations describing the time-space response of an electromagnetic field are differentiated into a time domain and a spatial domain.

  FIG. 6 is a cross-sectional view for explaining a model of the present polarization control element used in the numerical simulation, and the calculation was performed with a configuration in which light is incident from the structure 2 side. In order to obtain the spectral characteristics of the transmitted light, a pulse light having a sufficiently short time width (the spectral width is sufficiently spread in the visible light region) is incident as incident light from a surface away from the lower end of the structure 2 by 840 nm. The polarization characteristics of the transmitted light were evaluated on a transmission surface separated by 1000 nm. In addition, assuming that the conductive material constituting the structures (1) and (2) is Au, a dielectric function obtained by superimposing the Drude model and the Lorentz model to describe the response of electrons in Au to the photoelectric field. Was used to introduce the chromatic dispersion characteristics of the material. For the purpose of verifying the operating principle, the calculation was performed assuming that the surrounding medium of the Au structure was vacuum (refractive index n = 1).

  FIG. 7 is an example of a numerical simulation result for the following Au structure, and the transmittances of the x component and the y component when the linearly polarized light oscillating in the x axis direction is incident are respectively oscillated in the Txx, Txy, and y axis directions. The transmittances of the x component and y component when linearly polarized light is incident are plotted as Tyx and Tyy, respectively. The structure (1) uses a shape in which the ends of rectangular dots are in contact, and is set to w = h = 80 nm and Lx = 128 nm, and the structure (2) has w = h = 80 nm and Ly = 328 nm. Set to a rectangular parallelepiped. Further, the interval (v) between the structures (1) and (2) was set to v = 16 nm. Here, the minimum cell size in the numerical simulation was 4 nm. Further, by setting the calculation space to Px = 200 nm and Py = 400 nm and applying a periodic boundary to the calculation region boundary, the structure (1) having a pitch of substantially 200 nm in the x-axis direction and 400 nm in the y-axis direction is obtained. Calculation equivalent to the periodic structure of the unit composed of the structure (2) was performed.

  In the result of FIG. 7, when attention is paid to the Txy component and the Tyx component, the Txy component is almost zero in the region near the wavelength of 730 nm, whereas the Txy component has a value of about 0.35, and only the x component of the incident light. Has been confirmed to selectively convert to the y component. In this simulation result, the Txx component, which is a direct transmission component of incident polarized light, is observed among the two orthogonally polarized components, and the Tyy component is also cut (reflected). Although it is not an element that can be taken out well, the shape and arrangement of the structure, the selection of a transparent material as a background medium (support), or an additional polarization selection structure (for example, the structure shown in claim 3) should be provided Thus, a highly efficient polarization conversion element can be provided.

  As shown in the numerical simulation results in FIG. 7, the present polarization control element utilizes a strong resonance interaction between a structure and a light made of a conductive material disposed on or inside the support. As such, it has a unique operating wavelength band depending on the materials used and the shape of the structure. For example, in FIG. 7, the operation is performed in a wavelength band of about 700 to 800 nm with the half-value width as an operating wavelength band. In order to use it for a projection device such as a liquid crystal projector, a polarization conversion element that operates at a wavelength corresponding to RGB is required. However, depending on a desired operating wavelength band, the above-described conductive material and support material By selecting, the center wavelength of the operating wavelength band can be greatly varied, and a polarization conversion element that operates in a desired wavelength band can be realized. For example, when Ag, which is a metal material, is used as the conductive material, since the plasmon resonance wavelength is on the short wavelength side, the operating wavelength band of the polarization conversion element is also shifted to the short wavelength side.

  As described above, this polarization conversion element is formed by forming a laminated structure of a structure made of a conductive material having two types of symmetry on a support or inside a support, and thereby, among two orthogonal polarization components, Because it has a mechanism to convert one component to the other, random polarization can be efficiently converted to linear polarization without combining multiple optical elements, reducing the number of optical elements and optical It becomes possible to realize downsizing and cost reduction of the apparatus.

(Second Embodiment)
A polarization conversion element according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a diagram illustrating the configuration of the polarization control element and the shape of a structure made of a conductive material included in the polarization conversion element. As in the description of claim 1, the polarization conversion element includes a structure (1) made of a conductive material having a shape that is point-symmetric and has no line symmetry in a plane perpendicular to the propagation direction of incident light. , A unit in which a structure (2) made of a conductive material having different shapes with respect to two axes perpendicular to the propagation direction of incident light is laminated on or inside the support is the same. It has a configuration in which a plurality are arranged in the plane.

  The difference from the first embodiment is that two or more isolated microstructures are used as the structure (1) as shown in the cross section BB in FIG. By controlling the symmetry of the position to form the structure, it is possible to control the polarization conversion characteristics and to obtain ease of manufacture. Since the structure (1) and the structure (2) need to interact with each other through near-field light, the distance (v) between the structure (1) and the structure (2) should be close to the wavelength of incident light or less. Deploy. In addition to exhibiting optical rotation because the structure (1) is a point-symmetric structure, as shown in the cross-section CC of FIG. 8, the structure (2) has a structure extending in one direction, so that polarization selection is possible. Thus, the polarization conversion function can be obtained in the present polarization control element due to these competitive effects.

  In FIG. 8 cross section BB, a structure in which two cubes are close to each other is illustrated as a structure (1) made of a conductive material. However, a strong optical rotation via a plasmon generated in a conductive material is a structure having point symmetry. Any shape may be used as long as it exhibits the property.

  FIG. 9 is a plan view showing an example of a shape showing optical rotation. FIGS. 9A and 9D show a composite structure having a structure with a rectangular cross section close to each other, and FIG. 9B shows a composite structure with a triangular prism shape. It is known that the strong electric field enhancement effect by plasmons is concentrated on the sharp part of the microstructure made of the conductive material, and the structure shown in FIG. 9B produces a strong optical rotation effect. In addition, a structure in which a diagonal portion of a rectangular structure is cut away (FIG. 9C), two elliptic cylinders or spheroids are arranged so that the major axis or minor axis does not coincide with each other (FIG. 9 ( e)) also has point symmetry, that is, it exhibits optical rotation. Further, the structure (1) made of a conductive material may be a set of a plurality of three or more microstructures. FIGS. 9F to 9H are examples in which the structure (1) is formed using three, four, and five microstructures, respectively. In addition to these, any structure may be used as long as it is a point-symmetric structure using an isolated microstructure and has a strong optical rotation. In addition, since the shape of the structure in the height direction affects the strength of optical interaction with the structure (2) arranged in a stacked manner, the distance between the structure (1) and the structure (2) ( In combination with v), it is necessary to select an optimum height and shape, and it is not necessarily a shape having a rectangular cross section. The point symmetry described above is a design requirement, and does not limit the symmetry shift caused by a manufacturing error or the like.

  The structure 2 made of a conductive material may be exactly the same as that described in the first embodiment, and may be a cylinder or an ellipse as long as the structure has polarization anisotropy with respect to two orthogonal linearly polarized lights. Any shape such as a column, a spheroid, or a rectangular parallelepiped shape may be used.

  The materials used for the structure (1) and the structure (2) made of a conductive material may be the same as those in the first embodiment, and Al, Au, which are general metal materials that can strongly excite plasmons in the visible light region. Cu, Ag, a combination thereof, or an alloy material / mixed material containing these as a main component can be used.

  The arrangement of the units constituted by the structures 1 and 2 is the same as that described in the first embodiment, but it is preferable to arrange them periodically as shown in the right diagram of FIG. It is preferable that the interval between adjacent units is equal to or less than the wavelength of incident light. Alternatively, a polarization conversion element having angle dependency may be configured by actively using the diffraction effect by setting the interval to the wavelength of incident light. In order to make the arrangement of units the same as or less than the wavelength, the size of the structure (1) and the structure (2) is preferably a size equal to or smaller than the wavelength of the incident light. In addition, the isolated microstructure constituting the structure (1) similarly has a size equal to or smaller than the wavelength. The shape of the microstructure is not necessarily isotropic and cannot be uniquely determined as described with reference to FIG. Therefore, the size of the structure is defined as shown in FIG.

  FIG. 10 is a plan view of the structure 1 cut along a plane perpendicular to the propagation direction of incident light. The two-dimensional shape has a diameter d of a circle having the same area as that of the microstructure, or spatial In the case of a microstructure having an asymmetric shape, the major axis d1 and the minor axis d2 of an ellipse having the same area as the microstructure are defined as the size of the microstructure. Therefore, the size of the microstructure is set so that the diameter d of the circle or the major and minor diameters d1 and d2 of the ellipse is smaller than the wavelength of the incident light.

The structure (1) and the structure (2) of the present polarization conversion element are shown in the left diagram of FIG. 8 in which the structure (1) is arranged at the support interface and the structure (2) is embedded inside the support. Although the structure is shown, as described with reference to FIG. 4 in the first embodiment, the structure (1) and the structure (2) are both embedded in the support body, and are resistant to external impacts. It is good also as a structure. Further, the order of stacking the structure (1) and the structure (2) is not particularly limited, and may be any order with respect to the light incident direction. The material used as a support for holding these structures is preferably a transparent material having low absorption at a wavelength in the visible light region, such as quartz glass, borosilicate glass such as BK7 and Pyrex (registered trademark), CaF ₂ , An optical crystal material such as ZnSe or Al ₂ O ₃ is used.

  The manufacturing method of this polarization conversion element is as described with reference to FIG. 5 in the first embodiment, and is manufactured using a lift-off method using electron beam lithography and reactive dry etching. Alternatively, instead of using electron beam lithography, there are a method of performing batch exposure using DUV (far ultraviolet) / EUV (deep ultraviolet) lithography technology, and a method of manufacturing using nanoimprint processing technology.

  In the present polarization conversion element having the above-described configuration, a stacked structure of a structure made of a conductive material having two types of symmetry is formed on or inside the support, and of the two orthogonal polarization components Because it has the function of converting one component into the other component, it can efficiently convert random polarized light into linearly polarized light without combining multiple optical elements, reducing the number of optical elements, It becomes possible to achieve downsizing and cost reduction of the optical device. Further, since the structure 1 is composed of a plurality of isolated microstructures, a polarization control element with a high degree of design freedom can be realized.

(Third embodiment)
A polarization conversion element according to a third embodiment of the present invention will be described with reference to FIGS. 3 to 5, 9, 11, and 12. FIG. 11 is a diagram illustrating the configuration of the polarization control element and the shape of a structure made of a conductive material included in the polarization conversion element, and includes two orthogonal cross sections parallel to the propagation direction of incident light ( ZX plane, YZ plane). This polarization conversion element is a structure (as described in the first and second embodiments) made of a conductive material having a shape that is point-symmetric and has no line symmetry in a plane perpendicular to the propagation direction of incident light. 1) and the structure (2) made of a conductive material having different shapes with respect to two axes orthogonal to the propagation direction of incident light, and the same shape and orientation as the structure (2) The units formed by stacking the structures (3) having the structure are arranged in the same plane. Here, in FIG. 11, the longitudinal axis of the structure (2) is set as the Y axis, and the propagation direction of the incident light is set as the Z axis. By arranging the structure (2) and the structure (3) in a stacked manner in the propagation direction of incident light, and setting the interval (v) in the vicinity of an integral multiple of ½ wavelength of light inside the support. The scattered light can have directivity, and the ratio of transmitted light or reflected light can be adjusted. Similarly to the first and second embodiments, since the structure (1) has a point-symmetric structure, the structure (2) and the structure (3) have one optical rotation. Since the polarization selectivity is exhibited due to the structure extending in the direction, the polarization conversion function can be obtained by these competitive effects. Therefore, the polarization conversion element has the first and second characteristics by having the directivity. It becomes possible to improve the polarization conversion characteristics of the polarization conversion element described in the embodiment.

  The structure (1) made of a conductive material is the same as that described in the first and second embodiments, and has a structure with point symmetry and strong optical rotatory power through plasmons generated in the conductive material. The structure (1) as shown in FIG. 3 is a single structure having point symmetry, or a plurality of the structures (1) as shown in FIG. The isolated microstructures may be in any form of point symmetry or a plurality of isolated microstructures that are not isotropic in shape.

  The structure (2) and the structure (3) made of a conductive material are the same as those described for the structure (2) in the first and second embodiments, and are polarized with respect to two orthogonal linearly polarized lights. As long as the structure has anisotropy, it may have any shape such as a cylinder, an elliptical column, a spheroid, and a rectangular parallelepiped.

  Materials used for the structure (1), the structure (2), and the structure (3) made of a conductive material are Al, Au, Cu, Ag, which are general metal materials that can strongly excite plasmons in the visible light region. A combination thereof, or an alloy material / mixed material containing these as a main component can be used.

In FIG. 11, the structure (1), the structure (2), and the structure (3) of the present polarization conversion element are arranged on the support interface in FIG. 11, and the structure (2) and the structure ( 3) shows the configuration embedded in the support, but as described in the first embodiment with reference to FIG. 4, the structure (1), the structure (2), and the structure are provided inside the support. (3) may be a structure in which all are embedded, and may be configured to withstand external impacts. Further, the order of stacking the structure (1), the structure (2), and the structure (3) is not particularly limited. For example, as shown in FIG. 12, the structure (1) may be arranged between the structure (2) and the structure (3). The material used as a support for holding these structures is preferably a transparent material having low absorption at a wavelength in the visible light region, such as quartz glass, borosilicate glass such as BK7 and Pyrex (registered trademark), CaF ₂ , An optical crystal material such as ZnSe or Al ₂ O ₃ is used.

  The arrangement of the units constituted by the structure (1), the structure (2) and the structure (3) is the same as described in the first embodiment, but it is preferable to arrange them periodically. It is preferable that the interval between adjacent units is equal to or less than the wavelength of the incident light. Alternatively, a polarization conversion element having angle dependency may be configured by actively using the diffraction effect by setting the interval to the wavelength of incident light.

  The manufacturing method of this polarization conversion element is as described with reference to FIG. 5 in the first embodiment, and is manufactured using a lift-off method using electron beam lithography and reactive dry etching. Alternatively, instead of using electron beam lithography, there are a method of performing batch exposure using DUV (far ultraviolet) / EUV (deep ultraviolet) lithography technology, and a method of manufacturing using nanoimprint processing technology.

  In the present polarization conversion element having the above-described configuration, a stacked structure of a structure made of a conductive material having two types of symmetry is formed on or inside the support, and of the two orthogonal polarization components Because of the third structure (3) that has the function of converting one component into the other component and that also gives the directivity to the scattered light in the structure, polarized light with high polarization conversion efficiency. A conversion element can be realized.

(Fourth embodiment)
A polarization conversion element according to a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 13 is a diagram illustrating the configuration of the polarization control element and the shape of a structure made of a conductive material included in the polarization conversion element. This polarization conversion element has a configuration in which a structure (1) made of a conductive material having a shape that is point-symmetric and has no line symmetry in a plane perpendicular to the propagation direction of incident light is arranged in the same plane. And a structure (2) made of a conductive material having a stripe structure continuous in one axial direction with respect to two axes perpendicular to the propagation direction of incident light. The structure (1) and the structure (2) ) Are laminated on the support or inside the support at intervals equal to or less than the wavelength of the incident light. FIGS. 13A and 13B show two examples of plan views of the polarization control element cut along a cross section passing through the structure (2). FIG. 13 (a) shows the structure (2). It is an element in which the structure (1) is arranged so as to overlap with the conductive material portion constituting the structure, and (b) shows the structure (1) so as to overlap the gap portion without the conductive material constituting the structure (2). The arranged elements are shown. As shown in FIGS. 13A and 13B, the polarization conversion characteristics vary depending on the positional relationship between the structures (1) and (2), but there is no difference in the principle that the polarization conversion function appears. Like the structure (2), the stripe structure made of a conductive material is widely used as a wire grid polarizer and exhibits strong polarization selectivity. In addition, since the structure (1) has a point-symmetric structure and exhibits optical rotation, the structure (1) and the structure (2) interact with the incident light. A polarization conversion function can be obtained.

  The structure (1) made of a conductive material is the same as that described in the first and second embodiments, and has a structure with point symmetry and strong optical rotatory power through plasmons generated in the conductive material. The structure (1) as shown in FIG. 3 is a single structure having point symmetry, or a plurality of the structures (1) as shown in FIG. The isolated microstructures may be in any form of point symmetry or a plurality of isolated microstructures that are not isotropic in shape. The arrangement of the structures (1) is the same as described in the first embodiment, but it is preferable to arrange them periodically, and the interval (v) between adjacent units is equal to or less than the wavelength of the incident light. Is preferable. Alternatively, a polarization conversion element having angle dependency may be configured by actively using the diffraction effect by setting the interval to the wavelength of incident light.

  The structure (2) made of a conductive material has a polarization selectivity and a structure in which a stripe structure of a conductive material is formed at intervals equal to or smaller than the wavelength of the incident light so as not to cause diffraction of the incident light due to the stripe structure. And

  The materials used for the structure (1) and the structure (2) made of a conductive material may be the same as those in the first embodiment, and Al, Au, which are general metal materials that can strongly excite plasmons in the visible light region. Cu, Ag, a combination thereof, or an alloy material / mixed material containing these as a main component can be used.

The structure (1) and the structure (2) of the present polarization conversion element have a structure in which the structure (1) or the structure (2) is arranged at the support interface, as in the first and second embodiments. Alternatively, the structure (1) and the structure (2) may be both embedded in the support. The element in which the structure (1) and the structure (2) are embedded in the support has an advantage of being strong against external impacts. Further, the order of stacking the structure (1) and the structure (2) is not particularly limited, and may be any order with respect to the light incident direction. The material used as a support for holding these structures is preferably a transparent material having low absorption at a wavelength in the visible light region, such as quartz glass, borosilicate glass such as BK7 and Pyrex (registered trademark), CaF ₂ , An optical crystal material such as ZnSe or Al ₂ O ₃ is used.

  The manufacturing method of this polarization conversion element is as described with reference to FIG. 5 in the first embodiment, and is manufactured using a lift-off method using electron beam lithography and reactive dry etching. Alternatively, instead of using electron beam lithography, there are a method of performing batch exposure using DUV (far ultraviolet) / EUV (deep ultraviolet) lithography technology, and a method of manufacturing using nanoimprint processing technology.

  In this polarization conversion element having the above configuration, a structure in which a structure made of a conductive material having point symmetry is laminated adjacent to a stripe structure made of a conductive material is formed on or inside the support. Because it has the function of converting one of the two orthogonal polarization components to the other, it can efficiently convert random polarized light into linearly polarized light without combining multiple optical elements. Thus, the number of optical elements can be reduced, and the optical device can be reduced in size and price.

(Fifth embodiment)
A polarization conversion element according to a fifth embodiment of the present invention will be described with reference to FIGS. 2, 3, 5, 8, 9, 11, 13, and 14. FIG. 14 is a cross-sectional view illustrating the configuration of the polarization conversion element, which is cut along a plane parallel to the propagation direction of incident light. Similar to the polarization conversion elements described in the first to fourth embodiments, this polarization conversion element is a conductive material having a shape that is point-symmetric and has no line symmetry in a plane perpendicular to the propagation direction of incident light. The structure (2) having a configuration in which the structure (1) made of the conductive material is arranged in the same plane and has different shapes with respect to two axes orthogonal to the propagation direction of the incident light ) At least. Alternatively, as described in the fourth embodiment, the structure (2) may be an element using a stripe structure made of a conductive material. Furthermore, this polarization conversion element has a configuration in which a dielectric film having a refractive index different from that of the support is provided so as to be in contact with or cover the structure (1) and the structure (2). .

When the dielectric film is in contact with a structure made of a conductive material, the resonance wavelength of plasmons generated in the conductive material is shifted according to the refractive index of the dielectric film material. For example, when a dielectric material having a higher refractive index than that of the support is used as the dielectric film, the plasmon resonance wavelength shifts to the longer wavelength side. Therefore, the operating wavelength band of the present polarization conversion element can be selected by selecting the dielectric film material. In addition, by covering the structure with a dielectric film, it is possible to provide a polarization conversion element that is resistant to external impact. The dielectric film material is preferably a material having low absorptivity and low anisotropy with respect to polarized light in the same manner as the support, and is generally used as a coating material for optical elements, such as quartz glass, BK7, Pyrex (registered trademark), Borosilicate glass such as ZnS—SiO ₂ , CaF ₂ , Si, ZnSe, Al ₂ O ₃ , ZnO and the like are suitable. A multilayer film may be used as the dielectric film, and in this case, the reflectance and transmittance can be controlled.

  The polarization conversion function of this polarization conversion element is the same as described in the first to fourth embodiments. The optical rotation of the structure (1) made of a conductive material and the structure (2) or structure (2 ) And the structure (3) are caused by the competitive effect of polarization selectivity. Therefore, the structure (1) made of a conductive material may be any structure as long as it has a point symmetry and emits strong optical rotation through plasmons generated in the conductive material. The shape of (1) is a single structure having point symmetry, or a plurality of isolated microstructures constituting the structure (1) as shown in FIG. 9 are arranged in point symmetry These may be any form of a plurality of isolated microstructures that are not isotropic in shape. Further, the structure (2) made of a conductive material is a continuous structure as shown in FIG. 13 even if it has an isolated polarization selectivity as shown in the cross section CC of FIG. 2 or FIG. A stripe structure may be used. Moreover, as shown in FIG. 11, the directivity of scattered light may be improved and the polarization conversion efficiency may be improved by arranging the third structure (3). The arrangement of the units by the structure (1) or the structure (1) and the structure (2) (and the structure (3)) is periodically arranged as described in the first embodiment. It is more preferable that the interval between adjacent units is less than or equal to the wavelength of the incident light. Alternatively, a polarization conversion element having an angle dependency may be configured by actively using the diffraction effect by setting the interval (v) to the wavelength of incident light. Specific materials used for the structure (1) and the structure (2) of the conductive material used for the main conversion element are Al, Au, and Cu, which are general metal materials that can strongly excite plasmons in the visible light region. , Ag, a combination thereof, or an alloy material / mixed material containing these as a main component can be used.

The structure (1) and the structure (2) of the present polarization conversion element have a configuration in which the structure (1) or the structure (2) (or the structure (3)) is disposed at the support interface. Further, the order of stacking the structure (1) and the structure (2) (and the structure (3)) is not particularly limited, and may be any order with respect to the incident direction of light. The material used as a support for holding these structures is preferably a transparent material having low absorption at a wavelength in the visible light region, such as quartz glass, borosilicate glass such as BK7 and Pyrex (registered trademark), CaF ₂ , An optical crystal material such as ZnSe or Al ₂ O ₃ is used.

  The manufacturing method of this polarization conversion element is as described with reference to FIG. 5 in the first embodiment, and is manufactured using a lift-off method using electron beam lithography and reactive dry etching. Alternatively, instead of using electron beam lithography, there are a method of performing batch exposure using DUV (far ultraviolet) / EUV (deep ultraviolet) lithography technology, and a method of manufacturing using nanoimprint processing technology.

  In this polarization conversion element having the above configuration, a structure in which a structure made of a conductive material having point symmetry is laminated adjacent to a structure made of a conductive material having polarization selectivity is provided on the support or the support. By forming it inside and further forming a dielectric film, it has the function of converting one of the two orthogonal polarization components into the other, and can control the operating wavelength band. Furthermore, it is possible to provide an element that is resistant to external impacts.

It is a figure explaining the function of the polarization conversion element of the present invention. It is sectional drawing explaining the structure of the polarization conversion element of the 1st Embodiment of this invention. It is a figure explaining the shape of the structure 1 by an electroconductive material. It is sectional drawing explaining the different structure of the polarization conversion element of the 1st Embodiment of this invention. It is a figure explaining the manufacturing process of the polarization conversion element of this invention. It is a figure explaining the model of numerical simulation. It is a figure explaining the result of numerical simulation. It is sectional drawing explaining the structure of the polarization conversion element of the 2nd Embodiment of this invention. It is a figure explaining the shape of the structure 1 by an electroconductive material. It is a figure explaining the definition of the size of a microstructure. It is sectional drawing explaining the structure of the polarization conversion element of the 3rd Embodiment of this invention. It is sectional drawing explaining the different structure of the polarization conversion element of the 3rd Embodiment of this invention. It is sectional drawing explaining the structure of the polarization conversion element of the 4th Embodiment of this invention. It is sectional drawing explaining the structure of the polarization conversion element of the 5th Embodiment of this invention. It is a figure explaining patent document 1. It is a figure explaining patent document 2. FIG. It is a figure explaining patent document 3. FIG. It is a figure explaining patent document 4. It is a figure explaining patent document 5. It is a figure explaining patent document 6. FIG. It is a figure explaining patent document 7. It is a figure explaining patent document 8. It is a figure explaining patent document 9. FIG. It is a figure explaining patent documents 10-13.

Explanation of symbols

(About Figure 15)
DESCRIPTION OF SYMBOLS 1 Non-polarized light source light 2 Lens plate 3 Polarization conversion plate 4 Polarizing beam splitter 5 Prism 6 1/2 wavelength plate 10 Liquid crystal display plate (about FIG. 16)
DESCRIPTION OF SYMBOLS 1 Polarization conversion element 2 1st light-transmissive member 2a Light incident surface 2b Light output surface 2c First film formation surface 2d Second film formation surface 3 Second light-transmissive member 3a Light incident surface 3b Light exit surface 4 Reflector 5 Half-wave plate 10 Polarization separation film 10a First polarization separation film layer 10b Second polarization separation film layer 11 High refractive index film (lanthanum titanate film)
12 First low refractive index film (SiO ₂ film)
13 Second low refractive index film (MgF ₂ film)
14 Glass flat plate (About Fig. 17)
20 Polarization separation film 30 Reflection film 320 Polarization conversion element 321 Substrate 322 Substrate 330 Polarization separation element 381 λ / 2 phase difference plate (about FIG. 18)
DESCRIPTION OF SYMBOLS 10 Polarization conversion element 11 1st prism 11a Incident surface 11d 1st output surface 12 2nd prism 12a 2nd output surface 13 Polarization separation film 14 Reflective film 15 1/2 wavelength plate 15a 1st crystal plate 15b 1st 2 crystal plate 16 thick part 18 lens array (FIG. 19)
DESCRIPTION OF SYMBOLS 1 Wedge prism 2 Polarization separation material 3 Lens base 4 Micro lens array 5 Resin layer 7 1/2 wavelength element (about FIG. 20)
5 Wavelength Selective Polarization Conversion Element 31 Reflective Film 32 Wavelength Selective Polarization Separating Film 33 Phase Difference Plate 34 Light-shielding Plate (About FIG. 21)
5 Polarization Conversion Element 6 Birefringent Plate 7 1/2 Wave Plate (About FIG. 22)
3 Anisotropic film 4 Beam light 11 Layer made of isotropic material 12 Layer made of anisotropic (uniaxial) material (about FIG. 23)
DESCRIPTION OF SYMBOLS 10 Polarization separation part 20 Phase modulation part 100 Light beam (About FIG. 24a)
DESCRIPTION OF SYMBOLS 1 Support substrate 2 Metal microstructure 4 Incident light 5a Transmitted light 5b Reflected light 6 Metal composite structure (about FIG. 24b)
DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Metal particle 4 Straight knitting light 5 Elliptical knitting light 10 Knitting light control element (about FIG. 24c)
DESCRIPTION OF SYMBOLS 1 Dielectric layer 2 1st metal particle 3 2nd metal particle 10 Braided light control element (about FIG. 24d)
DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Metal microstructure 4 Linear knitting light 5 Elliptical knitting light 6 Metal microstructure 10 Knitting light control element

Claims (6)

On the support or inside the support, at least the structure (1) made of the conductive material and the structure (2) made of the conductive material in the direction parallel to the propagation direction of the incident light are separated by a distance less than the wavelength of the light (v) The structure (1) has a configuration with point symmetry and no line symmetry in a plane perpendicular to the propagation direction of incident light. And the structure (2) has a shape having different lengths with respect to two axes orthogonal to a propagation direction of incident light. The structure 1 is composed of a microstructure made of a plurality of conductive materials, and two or more of the microstructures are arranged close to each other at an interval equal to or smaller than the size of the microstructure. The polarization conversion element according to claim 1. A structure made of a conductive material having a shape oriented in the same axial direction as that of the structure (2) on the surface forming the structure (1) or below the surface forming the structure (2) The polarization conversion element according to claim 1, wherein (3) is arranged. At least a structure (1) made of a conductive material and a structure (2) made of a conductive material in a direction parallel to the propagation direction of incident light on or inside the support, the structure (1) Has a shape that is point-symmetric in the plane perpendicular to the propagation direction of incident light and has no line symmetry, and is close to the structure (2) at an interval (v) equal to or less than the wavelength of the light, The structure (2) has a configuration in which a plurality of elements are arranged in the same plane, and the structure (2) has a stripe structure continuous in one axial direction with respect to two axes orthogonal to the propagation direction of incident light. A polarization conversion element. The structure 1 is composed of a microstructure made of a plurality of conductive materials, and two or more of the microstructures are arranged close to each other at an interval equal to or smaller than the size of the microstructure. The polarization conversion element according to claim 4. The polarization conversion element according to any one of claims 1 to 5, further comprising a dielectric film in contact with or covering the structure (1) or the structure (2).

Images