JP5471467B2 - Optical element, image generation apparatus, and image display apparatus - Google Patents

Description

  The present invention relates to an optical element, an image generation apparatus, and an image display apparatus. More specifically, the present invention relates to an optical element including a plurality of fine metal wires having a line width equal to or smaller than the wavelength of incident light, an image generation apparatus including the optical element, The present invention relates to an image display device including an image generation device.

  In an image display device typified by a liquid crystal projector device, incident light to a spatial modulation element such as a liquid crystal panel, a polarizing plate for extracting a specific polarization component contained in light emitted from the spatial modulation element, In order to improve the light utilization efficiency, a wave plate that can rotate the vibration plane of linearly polarized light by 90 degrees is used.

  Wave plates include half-wave plates and quarter-wave plates, which are made of optical crystals that cause birefringence in incident light and use the difference in refractive index between ordinary rays and extraordinary rays. A phase difference is given to two orthogonal polarization components. A half-wave plate is a half-wave plate in which the optical path difference between the ordinary ray and the extraordinary ray is ½ of a wavelength, and a quarter-wave plate is a quarter. As such an optical crystal, calcite or quartz is used. A wave plate using a plastic material such as polyimide is also widely used.

  For example, Patent Document 1 discloses a polarizer array in which two or more transparent materials are alternately stacked in the z direction on a single substrate parallel to the xy plane in an orthogonal coordinate system x, y, z. Yes. This polarizer array is divided into at least three regions in the xy plane, and each layer has a one-dimensional periodic uneven shape repeated in one direction in the xy plane determined for each region, and is perpendicular to the xy plane or For light incident from an oblique direction, only the polarization component parallel or perpendicular to the uneven shape of each region is transmitted.

  Further, Patent Document 2 has a translucent substrate having a lattice-like pattern formed on the surface with a constant periodic pitch, and has a phase difference between two linearly polarized light beams that are transmitted through the substrate and whose polarization planes are orthogonal to each other. A wave plate that produces the above is disclosed. This wave plate has a high refractive index film made of a film material having a refractive index higher than that of the material of the substrate, and a low refractive index made of a film material having a lower refractive index than the film material of the high refractive index film. A film is sequentially deposited on the surface of the substrate.

  Further, in Patent Document 3, a plurality of fine wires made of metal are embedded and arranged on a flat support so that the pitch (P) of the fine wires is 100 nm or more and 300 nm or less. The ratio (D / P) of the fine wire width (D) to the fine wire pitch (P) is larger than 0.6, and the height of the fine wire in the cross section perpendicular to the length direction of the fine wire is 50 nm or more and 500 nm or less A color filter composed of a metal grating type polarization separation element is disclosed.

  In Patent Document 4, a metal composite structure composed of two or more metal microstructures arranged in a region below the wavelength of incident light and periodically arranged is formed on a support substrate. A polarization control element is disclosed.

  Further, Patent Document 5 has a unit arrangement pattern in which two or more minute metal structures are arranged in a region below the wavelength of incident light, and one or more films that support the metal structures. A polarization control element having a composite array pattern in which a plurality of unit array patterns are arranged in the same two-dimensional plane in the same orientation is disclosed.

  However, the polarizer array disclosed in Patent Document 1 has the disadvantage that the characteristics differ depending on the wavelength and incident angle of incident light. In addition, it is necessary to increase the film thickness in order to obtain a large phase difference.

  Further, the wave plate disclosed in Patent Document 2 has a disadvantage that the characteristics differ depending on the wavelength and incident angle of incident light. In addition, since a structure with a high aspect ratio is required, mass production is difficult, leading to an increase in cost.

  Further, the color filter disclosed in Patent Document 3 uses an organic film, and thus has a disadvantage that light resistance and heat resistance are not sufficient.

  In addition, the polarization control elements disclosed in Patent Document 4 and Patent Document 5 are both in a trade-off relationship between the transmittance and the phase difference, and it is difficult to ensure the transmittance when the phase difference is increased. there were.

  The present invention has been made under such circumstances. The first object of the present invention is excellent in light resistance and heat resistance, and both of two polarization components orthogonal to each other without causing an increase in size and cost. An object of the present invention is to provide an optical element that can transmit light and provide a phase difference therebetween.

  A second object of the present invention is to provide an image generating apparatus that can be reduced in size without increasing the cost.

  A third object of the present invention is to provide an image display device that can be reduced in size without increasing the cost.

According to a first aspect of the present invention, in the optical element having a fine periodic structure including a plurality of fine metal wires each having a line width equal to or less than the wavelength of incident light, the fine periodic structure is transparent and has a refractive index. supported by a support member of n ₁ and covered with a medium having a refractive index of n ₂ , the plurality of fine metal wires are arranged at equal intervals along one direction, and the arrangement pitch p [nm] is Using the wavelength λ of the incident light, it is equal to the value of (λ × n ₁ ) / (2 × n ₂ ), and the incident light has a polarization component parallel to the one direction and perpendicular to the one direction. When the incident light passes through the plurality of thin metal wires, a phase difference having a magnitude of 180 ° is given between the two polarization components, and the plurality of thin metal wires are Using height h [nm] and line width w [nm] , hw / p ³ is 1.128 × 10 ⁻³ It is an optical element characterized by being [nm ⁻¹ ] .
According to a second aspect of the present invention, in the optical element having a fine periodic structure including a plurality of fine metal wires each having a line width equal to or smaller than the wavelength of incident light, the fine periodic structure is transparent and has a refractive index. supported by a support member of n ₁ and covered with a medium having a refractive index of n ₂ , the plurality of fine metal wires are arranged at equal intervals along one direction, and the arrangement pitch p [nm] is Using the wavelength λ of the incident light, it is equal to the value of (λ × n ₁ ) / (2 × n ₂ ), and the incident light has a polarization component parallel to the one direction and perpendicular to the one direction. When the incident light passes through the plurality of fine metal wires, a phase difference of 90 ° is given between the two polarization components, and the plurality of fine metal wires Hw / p ³ is 5.54 × 10 ⁻⁴ [nm using h [nm] and line width w [nm]. ⁻¹ ] is an optical element.

According to the optical element of the present invention, it is excellent in light resistance and heat resistance, transmits both of two polarization components orthogonal to each other without causing an increase in size and cost, and gives a phase difference therebetween. be able to.

According to a third aspect of the present invention, in an image generating apparatus that includes an image forming element and generates an image according to image information, a light beam incident on the image forming element and a light beam emitted from the image forming element An image generating apparatus comprising at least one optical element of the present invention disposed on at least one of the optical paths.

  According to this, it is possible to reduce the size without increasing the cost.

According to a fourth aspect of the present invention, there is provided an image comprising: an image generating device of the present invention that generates an image according to image information; and a projection optical system that projects a light beam from the image generating device onto a projection surface. It is a display device.

  According to this, it is possible to reduce the size without increasing the cost.

It is a block diagram for demonstrating schematic structure of the projector system which concerns on one Embodiment of this invention. It is a figure for demonstrating the structure of the projector apparatus in FIG. It is a figure for demonstrating the image generation apparatus in FIG. It is a figure for demonstrating the function of the polarization conversion element in FIG. It is a figure for demonstrating the function of the quarter wavelength plate in FIG. It is a figure for demonstrating the structure of the wavelength plate used with the image generation apparatus. It is AA sectional drawing of FIG. It is a figure for demonstrating the model of the wavelength plate used for the numerical simulation. It is AA sectional drawing of FIG. It is a figure for demonstrating the calculation result of a numerical simulation. It is a diagram for explaining the relationship between the calculation result array obtained from the pitch p and _{λ × n 1 / (2 ×} n 2). Is a diagram for explaining the relationship between the obtained phase difference φ w · h / p ³ from the operation result. It is a figure for demonstrating the relationship between the transmittance | permeability obtained from the calculation result, and w / p. It is a figure for demonstrating the modification 1 of a wave plate. It is AA sectional drawing of FIG. It is a figure for demonstrating the modification 2 of a wave plate. It is a figure for demonstrating the structure of the wavelength selection filter which has the fine periodic structure body containing the some metal fine wire whose each line width is below the wavelength of incident light. It is AA sectional drawing of FIG. It is BB sectional drawing of FIG. It is a figure for demonstrating the model of the wavelength selection filter used for the numerical simulation. It is AA sectional drawing of FIG. It is a figure for demonstrating the calculation result of a numerical simulation.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a projector system 10 as an image display system according to an embodiment.

  The projector system 10 includes a projector device 1000 as an image display device and a host device 2000.

  The host device 2000 is an image information management device that sends information about an image to the projector device 1000, and a personal computer can be used as an example. The host device 2000 can send information related to the image sent via the network and information related to the image acquired (downloaded) via the network to the projector device 1000.

  The projector device 1000 is a front projection type projector device that displays an enlarged image on a screen 1100 as a projection surface based on information about an image sent from the host device 2000.

  As shown in FIG. 2 as an example, the projector apparatus 1000 includes an image generation apparatus 100, a projection optical system 200, and the like. In this specification, in the XYZ three-dimensional orthogonal coordinate system, the plane on which the projector apparatus 1000 is placed is the XZ plane, and the direction of the light beam emitted from the image generation apparatus 100 toward the projection optical system 200 is the Z-axis direction. Will be described.

  Projection light traveling from the projection optical system 200 toward the screen 1100 is emitted through an opening provided in the housing.

  As shown in FIG. 3 as an example, the image generation apparatus 100 includes a light source 110, a cut filter 111, a pair of fly-eye lens arrays (113A, 113B), a polarization conversion element 141, a condenser lens 115, two dichroic mirrors ( 116A, 116B), reflection mirror 117, three polarization separation elements (118A, 118B, 118C), three reflection type liquid crystal panels (120A, 120B, 120C), three quarter-wave plates (142A, 142B, 142C) , A cross prism 124, a communication interface 131, a main controller 132, and the like.

  The communication interface 131 controls communication between the main control device 132 and the host device 2000.

  The main control device 132 controls the light source 110 and the three reflective liquid crystal panels (120A, 120B, 120C) in accordance with the information regarding the image received via the communication interface 131.

  As the light source 110, a lamp light source such as a xenon lamp, a halogen lamp, a metal halide lamp, or an ultrahigh pressure mercury lamp can be used. A solid light source such as an LED, LD, or semiconductor laser may be used.

  The light source 110 is turned on according to an instruction from the main controller 132. The light beam emitted from the light source 110 is changed to the + Z direction by the reflector.

  The cut filter 111 removes UV components and IR components contained in the light emitted from the light source 110. Thereby, deterioration of each optical element can be suppressed.

  The pair of fly-eye lens arrays (113A, 113B) are arranged on the optical path of the light flux through the cut filter 111, and uniformize the light amount distribution.

  The polarization conversion element 141 is disposed between a pair of fly-eye lens arrays (113A and 113B), and converts the polarization state of the light beam through the fly-eye lens array 113A into a predetermined linearly polarized light (here, S-polarized light). To do. Thereby, the light utilization efficiency can be increased.

  Here, as shown in FIG. 4 as an example, the polarization conversion element 141 includes a polarization separation element 141A having a plurality of polarization separation surfaces that transmit S polarization and reflect P polarization, and the plurality of polarization separation surfaces. And a plurality of half-wave plates 141B for converting the reflected P-polarized light into S-polarized light.

  Returning to FIG. 3, the condenser lens 115 is disposed on the optical path of the light beam via the fly-eye lens array 113B. The condenser lens 115 can adjust the incident angle and illumination area of the illumination light when illuminating each reflective liquid crystal panel.

  The dichroic mirror 116A is disposed on the optical path of the light flux through the condenser lens 115, selectively reflects the blue wavelength component contained in the light flux, and transmits the remaining (green wavelength component + red wavelength component).

  The dichroic mirror 116B is disposed on the optical path of the light beam that has passed through the dichroic mirror 116A, selectively reflects the green wavelength component contained in the light beam, and transmits the rest (red wavelength component).

  The polarization separation element 118A is disposed on the optical path of the light beam that has passed through the dichroic mirror 116B. The polarization separation element 118A has a polarization separation surface that reflects the predetermined linearly polarized light (here, S-polarized light) in the + X direction. Therefore, the light beam transmitted through the dichroic mirror 116B is reflected in the + X direction by the polarization separation element 118A (see FIG. 5).

  The quarter-wave plate 142A is disposed on the + X side of the polarization separation element 118A. The quarter-wave plate 142A converts S-polarized light reflected by the polarization separation surface of the polarization separation element 118A into circularly polarized light.

  The reflective liquid crystal panel 120A is disposed on the + X side of the quarter wave plate 142A. Therefore, the reflective liquid crystal panel 120A is illuminated with a light beam via the quarter-wave plate 142A. This illumination light is modulated by the reflective liquid crystal panel 120A, and image information of a red component is given.

  The light beam modulated and reflected by the reflective liquid crystal panel 120A is incident on the quarter-wave plate 142A again, becomes P-polarized light, and enters the polarization separation element 118A. The light beam passes through the polarization separation element 118A.

  The polarization separation element 118B is disposed on the optical path of the light beam reflected by the dichroic mirror 116B. The polarization separation element 118B has a polarization separation surface that reflects the predetermined linearly polarized light (here, S-polarized light) in the −Z direction. Therefore, the light beam reflected by the dichroic mirror 116B is reflected in the −Z direction by the polarization separation element 118B.

  The quarter wavelength plate 142B is disposed on the −Z side of the polarization separation element 118B. The quarter wavelength plate 142B converts the S-polarized light reflected by the polarization separation surface of the polarization separation element 118B into circularly polarized light.

  The reflective liquid crystal panel 120B is disposed on the −Z side of the quarter wave plate 142B. Therefore, the reflective liquid crystal panel 120B is illuminated with a light beam via the quarter-wave plate 142B. This illumination light is modulated by the reflective liquid crystal panel 120B, and image information of a green component is given.

  The light beam modulated and reflected by the reflective liquid crystal panel 120B is incident on the quarter-wave plate 142B again, becomes P-polarized light, and enters the polarization separation element 118B. The light beam passes through the polarization separation element 118B.

  The reflection mirror 117 is disposed on the optical path of the light beam reflected by the dichroic mirror 116A and reflects the light beam. Here, the reflection mirror 117 reflects the light beam in the + Z direction.

  The polarization separation element 118C is disposed on the optical path of the light beam reflected by the reflection mirror 117. The polarization separation element 118C has a polarization separation surface that reflects the predetermined linearly polarized light (here, S-polarized light) in the −X direction. Therefore, the light beam reflected by the reflection mirror 117 is reflected in the −X direction by the polarization separation element 118C.

  The quarter-wave plate 142C is disposed on the −X side of the polarization separation element 118C. The quarter-wave plate 142C converts S-polarized light reflected by the polarization separation surface of the polarization separation element 118C into circularly polarized light.

  The reflective liquid crystal panel 120C is disposed on the −X side of the quarter wave plate 142C. Therefore, the reflective liquid crystal panel 120C is illuminated with a light beam via the quarter-wave plate 142C. This illumination light is modulated by the reflective liquid crystal panel 120C, and is provided with image information of a blue component.

  The light beam modulated and reflected by the reflective liquid crystal panel 120C is incident on the quarter-wave plate 142C again, becomes P-polarized light, and enters the polarization separation element 118C. The light beam passes through the polarization separation element 118C.

  The cross prism 124 is disposed on the −X side of the polarization separation element 118A, on the + Z side of the polarization separation element 118B, and on the + X side of the polarization separation element 118C. The cross prism 124 has a reflection surface that reflects the light beam that has passed through the polarization separation element 118A in the + Z direction, and a reflection surface that reflects the light beam that has passed through the polarization separation element 118C in the + Z direction.

  Therefore, the luminous flux to which image information of the red component is applied and transmitted through the polarization separation element 118A, the luminous flux to which image information of the green component is transmitted and transmitted through the polarization separation element 118B, and the image information of the blue component are applied and polarized light separation element 118A The transmitted light beam is combined by the cross prism 124. That is, the red component image, the green component image, and the blue component image are combined by the cross prism 124.

  A light beam synthesized by the cross prism 124 is a light beam emitted from the image generation apparatus 100. This light beam is incident on the projection optical system 200.

  The projection optical system 200 displays an enlarged image of the image synthesized by the cross prism 124 on the screen 1100.

  6 and 7 show an optical element 10A that functions as a wave plate. This optical element 10A includes a support member 11, a covering member 12, a plurality of fine metal wires 13, and the like. 7 is a cross-sectional view taken along the line AA in FIG.

  Here, in the xyz three-dimensional orthogonal coordinate system, the height direction of the fine metal wires 13 is described as the z-axis direction.

The support member 11 is preferably a transparent material generally used for an optical element. For example, quartz glass, BK7, borosilicate glass such as Pyrex (registered trademark), optical such as CaF ₂ , ZnSe, Al ₂ O _{3 and the} like. A crystalline material or the like can be used.

  Each thin metal wire 13 is a thin metal wire having a line width equal to or smaller than the wavelength of incident light, and is disposed on the surface of the support member 11 on the + z side. Here, the plurality of fine metal wires 13 are arranged at equal intervals along the x-axis direction. Such a structure is called a fine periodic structure. The plurality of thin metal wires 13 are characterized by the line width w and height h of each thin metal wire 13 and the arrangement pitch p of the plurality of thin metal wires 13.

  As the material of the metal thin wire 13, a material having characteristics close to a perfect conductor in the visible wavelength band is preferable, and Al (aluminum) is suitable. Further, an alloy material mainly composed of Al may be used. Further, materials such as Au (gold), Ag (silver), Pt (platinum), Ni (nickel), Cr (chromium), and Cu (copper) can be used depending on the wavelength band to be used.

  The covering member 12 is disposed on the + z side of the plurality of fine metal wires 13 and covers the plurality of fine metal wires 13. Therefore, the covering member 12 exists between the two adjacent thin metal wires 13 in the x-axis direction.

The covering member 12 is a film-like member, functions as a protective film that improves resistance to external damage and oxidation of the plurality of fine metal wires 13, and operates according to a relative relationship with the support member 11 regarding the refractive index. It plays the role of defining the wavelength. Such membrane-like member, like the support member 11, the light absorption is small, general quartz glass as a coating material for optical elements, BK7, Pyrex (registered trademark), borosilicate glass such as ZnS-SiO ₂ Alternatively, materials such as CaF ₂ , Si, ZnSe, Al ₂ O ₃ , and ZnO can be used.

  As a method of providing the plurality of fine metal wires 13 on the support member 11, a method having a processing accuracy equal to or lower than the diffraction limit of visible light is applied. Specifically, electron beam lithography, DUV (far ultraviolet) lithography, EUV (extreme ultraviolet) lithography, nanoimprint, and the like can be used.

  Next, a method for manufacturing the optical element 10A will be briefly described. Here, as an example, a method using electron beam lithography will be described, but the present invention is not limited to this.

(1) An optical glass on a parallel plate is used as the support member 11, and a metal material such as Al is deposited on the surface of the optical glass by a sputtering method or a vacuum evaporation method to form a metal film. Under the present circumstances, in order to improve the adhesiveness of a metal film at the interface of a metal and optical glass, you may provide base layers, such as Ti and Cr.

(2) A photoresist film is formed on the metal film.

(3) The photoresist film is exposed by electron beam drawing to form an etching mask.

(4) The metal film is etched by RIE (reactive ion etching) through the etching mask. Thereby, unnecessary portions in the metal film are removed.

(5) The etching mask is removed. Thereby, a plurality of fine metal wires having a line width w can be formed on the surface of the optical glass with a pitch p along one direction.

  Note that a lift-off method may be used instead of etching.

(6) As the covering member 12, a transparent film is deposited by sputtering or coating. Thereby, the optical element 10A is obtained.

  Next, a numerical simulation performed for verifying the characteristics of the optical element 10A will be described. Here, as the numerical simulation, a so-called finite difference time domain method (FDTD method) is 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.

  8 and 9 show optical element models used in the numerical simulation. 9 is a cross-sectional view taken along the line AA in FIG.

In this model, an Al metal fine wire is provided on a support substrate (refractive index n ₁ = 1.5) and covered with a dielectric (refractive index n ₂ = 1.38).

  Here, in order to obtain the spectral characteristics of the transmitted light, as shown in FIG. 9, the incident light has a polarization direction of 45 degrees (electric field vibration plane) and has a sufficiently short time width (the spectral width is in the visible light region). A plane wave pulse (spread sufficiently) was incident on a surface at a distance of L11 (in this case, 920 nm) on the + z side from the interface between the support substrate and the fine metal wire.

  Then, the polarization characteristic of the transmitted light was calculated by Fourier transforming the temporal variation of the electric field amplitude subjected to spatial averaging on the observation surface L12 (here, 1000 nm) away from the interface to the −z side.

  Note that the Drude model often used in the calculation of metal materials was applied to the wavelength dispersion characteristics of the dielectric function of Al. Moreover, the code | symbol L13 in FIG. 9 is 80 nm.

  FIG. 10 shows the relationship between the transmittance and wavelength of all polarized components obtained by numerical simulation. Here, w = 88 nm and h = 216 nm are fixed, and the arrangement pitch p is changed in multiple stages. According to this, as the arrangement pitch p increases, the wavelength (peak wavelength or resonance wavelength) at which the transmittance reaches a peak shifts to the longer wavelength side.

FIG. 11 shows the relationship between the value obtained by multiplying the peak wavelength λ by a coefficient of n ₁ / (2 × n ₂ ) and the arrangement pitch p. A broken line in FIG. 11 is a straight line having an inclination of 1. According to this, there is a linear correlation between the arrangement pitch p and λ × n ₁ / (2 × n ₂ ), and the following equation (1) is established. Here, n ₁ = 1.5 and n ₂ = 1.38.

p = λ × n ₁ / (2 × n ₂ ) (1)

  By setting the arrangement pitch p according to the wavelength of the incident light (operating wavelength) so that the above expression (1) is satisfied, a high transmittance can be obtained for the incident light. The above equation (1) is a phenomenologically obtained equation, and even if the arrangement pitch p is deviated by several% to 10% with respect to the value calculated from the above equation (1), an allowable error is obtained. It can be considered within the range.

Figure 12 is the relationship between the line width w and height the product of h values and the phase difference was normalized by p ³ φ (deg) is shown. Value normalized by the product of the line width w and height h p ³ is a value corresponding to the metal filling factor in the fine periodic structure. Here, the phase difference between the polarization component whose electric field direction is the x-axis direction and the polarization component whose electric field direction is the y-axis direction is the phase difference φ.

  The symbol ■ in FIG. 12 indicates a case where the line width w is changed by fixing the height h to 216 mm and the arrangement pitch p to 248 nm, and the symbol ▲ indicates that the line width w is fixed to 88 nm and the arrangement pitch p is fixed to 248 nm. In this case, the height h is changed, and the symbol ◆ indicates the case where the height h is changed while the line width w is fixed to 88 nm and the arrangement pitch p is set to 216 nm. According to this, since the three regression curves obtained by fitting individually ■, ▲, and ◆ are almost coincident, it is possible to determine the phase difference φ depending on the metal filling rate. The curve in FIG. 12 is a regression curve obtained by fitting all of ■, ▲, and ◆, and is represented by the following equation (2).

φ = 1.56807 × 10 ⁵ × (hw / p ³ ) +3.1079 (2)

  FIG. 13 shows the relationship between the transmittance of all polarization components and the duty ratio (w / p) when the wavelength of incident light is 443 nm and the height h is fixed at 216 nm. According to this, when the duty ratio exceeds 0.35, the transmittance is drastically decreased. Therefore, the duty ratio is preferably 0.35 or less.

Based on the result of the above numerical simulation, in order to give the optical element 10A the function of a half-wave plate, the arrangement pitch p of the thin metal wires for the desired operating wavelength is determined using the above equation (1), Within the range where the duty ratio satisfies the condition of 0.35 or less, the height h such that the phase difference φ is π, that is, hw / p ³ = 5.54 × 10 ⁻⁴ using the above equation (2). And the line width w may be determined. Note that a higher transmittance can be obtained as the line width w is thinner.

  The optical element 10A having the function of the half-wave plate is used for the plurality of half-wave plates 141B in the polarization conversion element 141.

In addition, in order to give the optical element 10A the function of a quarter wavelength plate, similarly, the arrangement pitch p of the thin metal wires with respect to a desired operating wavelength is determined using the above equation (1), and the duty ratio is 0. Within the range satisfying the condition of 35 or less, the height h and the line width such that the phase difference φ is π / 2, that is, hw / p ³ = 1.128 × 10 ⁻³ using the above formula (2). What is necessary is just to determine w. Note that a higher transmittance can be obtained as the line width w is thinner.

  The optical element 10A having the function of the quarter wavelength plate is used for the three quarter wavelength plates (142A, 142B, 142C).

  The optical element 10A can have functions other than the half-wave plate and the quarter-wave plate.

  As described above, the optical element 10A has a fine periodic structure in which fine metal wires, which are inorganic materials, are periodically arranged on a plane, and is excellent in light resistance and heat resistance. Moreover, an expensive optical crystal is not used, and the cost of the apparatus can be reduced by using the optical element 10A. In addition, the apparatus can be reduced in size.

  14 and 15 show an optical element 10B as a modification of the optical element 10A. FIG. 15 is a cross-sectional view taken along the line AA in FIG.

  In this optical element 10B, each thin metal wire whose longitudinal direction is the y-axis direction is cut in the middle. Even in this case, the length in the longitudinal direction of the fine metal wires is sufficiently larger than the arrangement pitch p, the above formulas (1) and (2) are satisfied, and the duty ratio in the x-axis direction is 0.35 or less. If the height h and the line width w are set so that, the same characteristics as those of the optical element 10A can be obtained although there is an influence of scattering and diffraction.

  By using the cut fine metal wires, it is possible to avoid the collapse of the high aspect ratio structure at the time of manufacture and the influence of the connection accuracy of electron beam drawing, and to obtain a fine periodic structure with a desired shape with high accuracy.

In addition, when it is not necessary to protect the plurality of fine metal wires 13, the covering member 12 may be omitted as shown in FIG. In this case, air (refractive index n ₂ = 1.00) exists between the two adjacent thin metal wires 13 in the x-axis direction. Even in this case, the same characteristics as those of the optical element 10A can be obtained.

As described above, according to the optical element 10A according to the present embodiment, the fine periodic structure includes the plurality of fine metal wires 13 each having a line width equal to or smaller than the wavelength of the incident light. The support member 11 is transparent and has a refractive index n ₁ and is covered with a covering member 12 having a refractive index n ₂ . The plurality of fine metal wires 13 are arranged at equal intervals along the x-axis direction, and the arrangement pitch p is (λ × n ₁ ) / (2 × n ₂ ) using the wavelength λ of incident light. It is set to be equal to the value.

  Also, the height h and the line width w are set so that a desired phase difference can be obtained within a range where the duty ratio (w / p) satisfies the condition of 0.35 or less.

  In this case, the optical element 10A is excellent in light resistance and heat resistance, transmits both of two polarization components orthogonal to each other without causing an increase in size and cost, and provides a desired phase difference therebetween. Can be granted.

  Further, according to the image generating apparatus 100 according to the present embodiment, the optical element 10A has a plurality of half-wave plates 141B having the function of a half-wave plate, and the optical element 10A has a function of a quarter-wave plate. And quarter-wave plates (142A, 142B, 142C). Therefore, it is possible to reduce the size without increasing the cost.

  Further, according to the projector apparatus 1000 according to the present embodiment, since the image generating apparatus 100 is provided, as a result, it is possible to reduce the size without increasing the cost.

  In the above embodiment, the case where a reflective liquid crystal panel is used as the image forming element has been described. However, the present invention is not limited to this. For example, an image forming element having a light emitting function may be used. In this case, the light source 110 is not necessary. Therefore, further downsizing of the image generating apparatus can be achieved.

<Optical filter>
By the way, an optical filter can be created using the characteristics of the optical element 10A.

  17 to 19 show an optical element 10D that functions as an optical filter. 18 is a cross-sectional view taken along the line AA in FIG. 17, and FIG. 19 is a cross-sectional view taken along the line BB in FIG. Here, the description will focus on differences from the optical element 10A, and the same or equivalent components as those of the optical element 10A described above will be denoted by the same reference numerals, and the description thereof will be simplified or omitted.

  This optical element 10D has two fine periodic structures. Here, the fine periodic structure on the + z side is referred to as a first fine periodic structure, and the fine periodic structure on the −z side is referred to as a second fine periodic structure.

The first fine periodic structure includes a plurality of thin metal wires 13 ₁ having a line width of less than the wavelength of the incident light, the metal thin wires 13 ₁ The plurality of along the y-axis direction, are arranged at equal intervals (See FIG. 18).

The second fine periodic structure includes a plurality of thin metal wires 13 ₂ having a line width of less than the wavelength of the incident light, the metal thin wires 13 ₂ and the plurality of, along the x-axis direction, are arranged at equal intervals (See FIG. 19).

  That is, in each fine periodic structure, the arrangement directions of the plurality of fine metal wires are orthogonal to each other.

A plurality of thin metal wires 13 of the _second fine periodic structure is provided on a surface of the + z side of the support member 11. Then, a plurality of thin metal wires 13 ₂ is covered by the covering member 12. Therefore, the covering member 12 exists between the _two adjacent thin metal wires 132 in the x-axis direction.

A plurality of thin metal wires 13 of the _first fine periodic structure is provided on the covering member 12 covering the plurality of thin metal wires 13 of the _second fine periodic structure. Then, a plurality of thin metal wires 13 ₁ is covered by the covering member 12. That is, a plurality of thin metal wires 13 of the _first fine periodic structure can be assumed to be present in the covering member 12. Therefore, the x-axis direction, between the two thin metal wires 13 ₁ adjacent the coating member 12 exists.

A plurality of thin metal wires 13 ₁ of the first fine periodic structure, the above equation (1) is satisfied, the duty ratio of the y-axis direction within the range satisfying 0.35 or less, using the above equation (2) Thus, the height h and the line width w are set so that the phase difference φ is π. That is, the first fine periodic structure has a function of a half-wave plate.

Further, a plurality of thin metal wires 13 ₂ in the second fine periodic structure, first the same array pitch p and a plurality of thin metal wires 13 ₁ in the fine periodic structure, the height h, is set to be the line width w Yes.

  Next, the operation principle of the optical element 10D will be described. Here, it is assumed that white randomly polarized light enters from the + z side of the optical element 10D. In the first fine periodic structure, the wavelength at which the transmittance reaches a peak (peak wavelength or resonance wavelength) is λ1.

  When the white randomly polarized light is incident on the first fine periodic structure, both TM polarized light and TE polarized light pass through the first fine periodic structure. On the other hand, as for the light whose wavelength is out of λ1, only the TM polarized light is transmitted through the first fine periodic structure.

  When the light transmitted through the first fine periodic structure enters the second fine periodic structure, the light whose wavelength deviates from λ1 is TM-polarized light and cannot pass through the second fine periodic structure. On the other hand, the light having a wavelength in the vicinity of λ1 passes through the second fine periodic structure in both TM polarized light and TE polarized light.

  That is, only light having a wavelength near λ1 can pass through the optical element 10D.

  In the case where the second fine periodic structure is a structure corresponding to a mere polarization selective wire grid polarizing plate, either the TM polarized light or the TE polarized light is the second fine light with a wavelength in the vicinity of λ1. Permeates the periodic structure.

  Next, a numerical simulation performed for verifying the characteristics of the optical element 10D will be described. Again, the finite difference time domain method (FDTD method) was used. However, incident random polarization was expressed by calculating incident polarization independently for TE polarization and TM polarization and taking an average value of transmittance.

  20 and 21 show a model of the optical element used for the numerical simulation. FIG. 21 is a cross-sectional view taken along the line AA in FIG.

  In this model, the first fine periodic structure and the second fine periodic structure are laminated with an interval L23 (here, 64 nm). The first fine periodic structure is embedded in a covering member having a refractive index of 1.38. Moreover, the code | symbol L21 in FIG. 20 is 920 nm, and the code | symbol L22 is 1000 nm.

  Further, for the fine metal wires in each fine periodic structure, (1) the arrangement pitch p is determined with respect to the operating wavelength, (2) the line width w is determined so that the duty ratio w / p is 0.35, 3) The height h was determined so as to obtain a high transmittance.

  FIG. 22 shows the relationship between the wavelength and the transmittance of all polarization components. Since the light on the long wavelength side is located in a wavelength band deviated from the peak wavelength, transmission is blocked. Moreover, it has confirmed that a wavelength selection function could be expressed with respect to arbitrary wavelengths by adjusting the shape and arrangement pitch p of a metal fine wire. The light on the short wavelength side is not sufficiently reduced in transmittance because the shielding property against the linearly polarized light of the metal thin wire is lowered. This can be improved by changing the shape of the fine metal wire of the fine periodic structure on the emission side (here, the second fine periodic structure).

  As described above, the optical element 10D has two fine periodic structures in which fine metal wires, which are inorganic materials, are periodically arranged on a plane, and is excellent in light resistance and heat resistance. In addition, since the optical element has a planar structure, it can be easily stacked and integrated.

It is also possible without first cover member 12 covering the plurality of thin metal wires 13 ₁ of the fine periodic structure. In this case, the y-axis direction, between the two thin metal wires 13 ₁ adjacent, so that the air (refractive index _n 2 = 1.00) is present. Even in this case, the same characteristics as those of the optical element 10D can be obtained.

  As described above, according to the optical element of the present invention, it is excellent in light resistance and heat resistance, transmits two polarized components orthogonal to each other without incurring cost increase, and a desired value therebetween. Suitable for providing a phase difference. The image generation apparatus and the image display apparatus according to the present invention are suitable for downsizing without increasing the cost.

DESCRIPTION OF SYMBOLS 10A ... Optical element, 10B ... Optical element, 10D ... Optical element, 11 ... Supporting member, 12 ... Cover member (medium), 13 ... Metal fine wire, 13 ₁ ... Metal fine wire, 13 ₂ ... Metal fine wire, 100 ... Image generating apparatus , 120A ... reflective liquid crystal panel (image forming element), 120B ... reflective liquid crystal panel (image forming element), 120C ... reflective liquid crystal panel (image forming element), 141B ... 1/2 wavelength plate, 142A ... 1/4 Wave plate, 142B ... 1/4 wavelength plate, 142C ... 1/4 wavelength plate, 200 ... projection optical system, 1000 ... projector device (image display device).

JP 2009-139773 A JP 2005-099099 A JP 2006-154382 A JP 2006-330105 A JP 2007-240618 A

Claims (7)

In an optical element having a fine periodic structure including a plurality of fine metal wires each having a line width equal to or smaller than the wavelength of incident light,
The fine periodic structure is transparent and supported by a support member having a refractive index n ₁ and covered with a medium having a refractive index n ₂ .
The plurality of fine metal wires are arranged at equal intervals along one direction, and the arrangement pitch p [nm] is (λ × n ₁ ) / (2 × n ₂ ) using the wavelength λ of the incident light. ) Value,
The incident light has a polarization component parallel to the one direction and a polarization component perpendicular to the one direction;
When the incident light passes through the plurality of thin metal wires, a phase difference having a magnitude of 180 ° is given between the two polarization components,
The plurality of fine metal wires have a height h [nm] and a line width w [nm] , and hw / p ³ is 1.128 × 10 ⁻³ [nm ⁻¹ ]. . In an optical element having a fine periodic structure including a plurality of fine metal wires each having a line width equal to or smaller than the wavelength of incident light,
The fine periodic structure is transparent and supported by a support member having a refractive index n ₁ and covered with a medium having a refractive index n ₂ .
The plurality of fine metal wires are arranged at equal intervals along one direction, and the arrangement pitch p [nm] is (λ × n ₁ ) / (2 × n ₂ ) using the wavelength λ of the incident light. ) Value,
The incident light has a polarization component parallel to the one direction and a polarization component perpendicular to the one direction;
When the incident light passes through the plurality of fine metal wires, a phase difference of 90 ° is given between the two polarization components,
The plurality of thin metal wires has a height h [nm] and a line width w [nm] , and hw / p ³ is 5.54 × 10 ⁻⁴ [nm ⁻¹ ]. .   3. The optical element according to claim 1, wherein the plurality of thin metal wires have a line width w and w / p is 0.35 or less.   The optical element according to claim 1, wherein the medium is air. Provided on the surface of one of the support member and the medium or inside thereof,
A fine periodic structure including a plurality of fine metal wires each having a line width equal to or smaller than the wavelength of the incident light and arranged at equal intervals along a second direction orthogonal to the first direction; The optical element according to claim 1. In an image generation apparatus that includes an image forming element and generates an image according to image information,
6. The optical element according to claim 1, wherein the optical element is disposed on an optical path of at least one of a light beam incident on the image forming element and a light beam emitted from the image forming element. An image generation apparatus characterized by that. The image generation device according to claim 6 which generates an image according to image information;
A projection optical system that projects a light beam from the image generation device onto a projection surface.

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