JP2013003368A - Polarization conversion element, polarization conversion unit and projection device - Google Patents

Abstract

The present invention realizes a polarization conversion element having a wavelength plate that reliably functions as a half-wave plate for a wide wavelength band by using an ultraviolet curable resin adhesive having excellent heat resistance and light resistance as an adhesive. .
An optical element having a plurality of light-transmitting substrates and a polarization separation film and a reflection film alternately provided between the light-transmitting substrates, and disposed on the light output surface thereof, the polarization surface of the emitted light being In the polarization conversion element including the laminated wave plate rotated by θ, the thickness of the adhesive layer for adhering the translucent substrate is 5 μm or more and 10 μm or less, and the wave plate has a phase difference Γ1 with respect to the light of the design wavelength λ. The first wave plate 30 and the second wave plate 40 having the phase difference Γ2 are stacked so that the optical axes intersect with each other, and Γ1 = 360 (deg), Γ2 = 180 (deg), The azimuth angle θ1 = −16 (deg), the azimuth angle θ2 of the wave plate 40 = 45 (deg), and the plate thicknesses Z1 = 27 (deg) and Z2 = 18 (deg) were satisfied.
[Selection] Figure 16

Description

  The present invention relates to a polarization conversion element, a polarization conversion unit, and a projection device for converting a randomly polarized light beam from a light source into one type of polarized light beam.

A projection type video device (projection device) such as a liquid crystal projector is a device that modulates light emitted from a light source device according to image information and enlarges and projects the modulated optical image on a screen.
In this projection device, random polarized light emitted from the light source device (P-polarized light and S-polarized light whose polarization planes are orthogonal to each other, and linearly polarized light having various polarization plane directions are mixed to improve the light utilization efficiency. Light (polarized light such as light, circularly polarized light, elliptically polarized light, etc.) (hereinafter referred to as random light) is divided into a plurality of intermediate light beams, and the divided intermediate light beams are converted into one type of linearly polarized light to be unified. Thus, a polarization conversion element is used to emit light.
In general, such a polarization conversion element has a structure as disclosed in Patent Document 1.

Such a polarization conversion element generally has PBS functions on both main surfaces (an optical functional film having a function of transmitting either linearly polarized light of P-polarized light and S-polarized light orthogonal to each other and reflecting the other linearly polarized light). A so-called polarization separation film) and a reflecting mirror film are formed on the incident surface (lamination surface) by creating a multilayered structure in which transparent substrates such as colorless and transparent glass are alternately laminated. An organic material is formed on the surface of the output side of a polarizing beam splitter (PBS) array (prism array) obtained by cutting at a predetermined angle, for example, 45 (deg) (or 135 (deg)). For example, a half-wave plate made of polycarbonate film is bonded with an organic adhesive, and random light emitted from the light source is selectively PB by a light-shielding plate disposed on the optical path. Separated into a S polarized beam and a P polarized incident on film, for example, P-polarized light beam is transmitted through the PBS film, S polarized beam reflects the PBS film.
When the P-polarized light beam transmitted through the PBS film is incident on the half-wave plate, the phase is shifted by 180 (deg), so that it is converted into S-polarized light and incident from the half-wave plate. The S-polarized light beam that has been reflected is further reflected by the reflecting mirror film, and is emitted from the exit surface of the area where the half-wave plate of the PBS array is not disposed.
As a result, light emitted from the polarization conversion element is unified into S-polarized light.
However, contrary to the above, the S-polarized light beam is transmitted through the PBS film to reflect the P-polarized light beam, and the S-polarized light beam transmitted through the PBS film is converted into a P-polarized light beam by a half-wave plate. The P-polarized light beam reflected by the PBS film is reflected by a reflecting mirror film and is emitted from the exit surface of the area where the half-wave plate of the PBS array is not disposed, thereby exiting from the polarization conversion element. It is also possible to unify the light to be p-polarized light.

FIG. 30 is a diagram illustrating a configuration of a general polarization conversion element.
The light-transmitting substrate 98 on which the polarization separation film 91 and the reflection (mirror) film 92 are formed and the light-transmitting substrate 98 on which these films are not formed are alternately bonded by the adhesive layer 93, and this bonding is performed. The laminated body is cut out at a predetermined angle, for example, 45 (deg) (or 135 (deg)), the cut surface is polished, and the bonding layer is formed on the element body 95 on which the light incident surface 951 and the light emitting surface 952 are formed. A phase difference plate 97 is joined via 96.
By the way, white light source lamps as light sources used in liquid crystal projectors and the like that employ a polarization conversion element having the above-described configuration have recently been increasing in output and shortening arc length. And the heat load on the half-wave plate is increasing.
Therefore, when the polarization conversion element as shown in FIG. 30 is manufactured, the adhesive (adhesive layer 93) conventionally used for laminating and bonding the translucent substrate 98 is compatible with high-intensity lamp light. There is a problem that the light transmittance decreases due to deterioration.
The reason is that the conventionally used adhesive is composed of a component having a high short wavelength light absorptivity, and because the viscosity is high, the coating amount increases and the adhesive layer 93 becomes thick. It is conceivable that the amount of absorption increases and that the composition is composed of components having a low decomposition temperature.

Further, in the conventional polarization conversion element shown in FIG. 30, the adhesive layer 93 is thick as described above. When the laminate is cut out in such a state that the adhesive layer 93 is thick, the adhesive layer 93 is formed at the end of the adhesive layer 93. Distortion will occur. When the cut surface is polished in a state where this distortion occurs, the corner portion 981 of the translucent substrate 98 in the vicinity of the adhesive layer 93 is shaved as shown in FIG. As a result, a gap is generated in the bonding layer 96 for bonding the phase difference plate 97 to the element body 95, the phase difference plate 97 is easily peeled off, and bubbles 961 are formed, resulting in a decrease in light transmittance. There is also a problem.
In addition, there is a problem in that a region where light is effectively transmitted is reduced by cutting off the corner portion 981 of the translucent substrate 98 in the vicinity of the adhesive layer 93.

JP 2000-298212 A Patent No. 2519198 JP 2010-128329 A International Publication No. 2007/046241

In order to solve these problems, Patent Documents 2 and 3 disclose a spatial plate without laminating these first and second wave plates in an example of a wave plate composed of a first wave plate and a second wave plate. A configuration is disclosed in which the light-transmitting substrates constituting the polarization conversion element are spaced apart from each other without using an adhesive. Thus, it is possible to avoid the influence of deterioration of the adhesive and the deterioration of the optical properties of the polarization conversion element due to the corners of the light-transmitting substrate being shaved during polishing. Problems such as control of the crossing angle of the optical axes and the necessity of forming and providing an antireflection film on the front and back surfaces of each wave plate, high manufacturing complexity, high costs, and an increase in the size of the optical element occur. Therefore, it is not preferable.
Furthermore, as a half-wave plate (retardation plate) used for the polarization conversion element as described above, it can be applied to a liquid crystal projector using three wavelength bands of R, G, and B which are the three primary colors of light. The phase difference is 180 (deg) at a predetermined wavelength, the polarization conversion efficiency is 1 over a wide band, and P-polarized light can be reliably converted into S-polarized light, or S-polarized light can be converted into P-polarized light. A half-wave plate is required, and a half-wave plate having such a specification is also proposed in Patent Document 4 and the like.
The present invention has been made in order to solve the above-described problems. As an adhesive, an ultraviolet-curing resin adhesive having excellent heat resistance and light resistance is used, and further, a broadband with respect to incident light. An object of the present invention is to realize a structure of a polarization conversion element provided with a wave plate that reliably functions as a half-wave plate.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A polarization conversion element of this application example has a light incident surface and a light output surface that are substantially parallel to each other, and is formed by a joint surface having a predetermined inclination angle with respect to the light incident surface or the light output surface. A plurality of light-transmitting substrates bonded via an adhesive layer and a plurality of light-transmitting substrates are alternately provided at boundaries between the light-transmitting substrates, and the polarization directions of light incident on the light incident surface are different from each other. A polarization separation unit that separates two types of linearly polarized light and transmits one linearly polarized light and reflects the other linearly polarized light; and a reflecting unit that reflects the reflected linearly polarized light beam of the other and changes the direction of the optical path; , And an optical element that is arranged on the light exit surface, and rotates the polarization plane of one of the two types of linearly polarized light to convert it into linearly polarized light parallel to the polarization plane of the other linearly polarized light And a phase difference plate that emits, and the adhesive layer includes: It is an external-curing type adhesive and has a thickness of 5 μm or more and 10 μm or less, and the retardation plate is disposed on the light output surface in the region above the polarization separation unit or the region above the reflection unit. The first wave plate having the phase difference Γ1 with respect to the light having the wavelength λ and the second wave plate having the phase difference Γ2 with respect to the light having the wavelength λ are arranged so that their optical axes intersect with each other. A phase difference plate that converts the polarization plane of incident linearly polarized light into linearly polarized light rotated by a rotation angle θ = 90 (deg) and outputs the linearly polarized light, and satisfies the following expressions (1) and (2): ,
Γ1 = 360 (deg) (1)
Γ2 = 180 (deg) (2)
The polarization conversion element is characterized in that the optical axis azimuth angle θ1 of the first wave plate and the optical axis azimuth angle θ2 of the second wave plate satisfy any one of the following conditions 1 to 4.
Condition 1: θ1 = −16 (deg), θ2 = 45 (deg)
Condition 2: θ1 = 16 (deg), θ2 = 135 (deg)
Condition 3: θ1 = 74 (deg), θ2 = 135 (deg)
Condition 4: θ1 = 106 (deg), θ2 = 45 (deg)

According to this application example, by using an ultraviolet curable resin adhesive excellent in heat resistance and light resistance performance as an adhesive when creating an optical element, it has high heat resistance and light resistance, and further, the optical axis azimuth is By setting as described above, it is possible to realize a structure of a polarization conversion element including a retardation plate that functions as a half-wave plate with certainty for broadband light.
Further, since the thickness of the adhesive layer is 10 μm or less and is sufficiently thin, the corner portion of the translucent substrate is not scraped when the light incident surface or the like is polished. Therefore, there is no problem that the light transmission region becomes narrow.

  Application Example 2 The polarization conversion element of this application example is the polarization conversion element described in Application Example 1, wherein the first and second wave plates are made of inorganic optical crystals, and The angle formed between the normal line on the main surface and the crystal optical axis of the inorganic optical crystal is the cutting angle Z1 of the first wave plate, and the normal line on the main surface of the second wave plate and the crystal of the inorganic optical crystal When the angle formed with the optical axis is the cutting angle Z2 of the second wave plate, the cutting angle Z1 and the cutting angle Z2 are different.

  According to this application example, by making the cutting angles of the wave plates different from each other, it is possible to obtain a substantially equivalent thickness that is convenient for handling while satisfying the design phase difference based on the respective optical axis azimuth angles. .

  Application Example 3 The polarization conversion element of this application example is the polarization conversion element according to Application Example 1 or 2, wherein the cutting angle Z1 and the cutting angle Z2 are Z1 = 27 (deg) and Z2 = 18 (deg). ) Is satisfied.

  According to this application example, each wave plate can have a thickness of about 0.3 mm that is most convenient for handling.

  Application Example 4 The polarization conversion element according to this application example is the polarization conversion element according to any one of Application Examples 1 to 3, wherein the retardation film is formed on the edge of the optical element with the polarization separation film. A plurality of base portions joined along the direction in which the reflective films are alternately arranged; and a plurality of base portions that are continuously formed on the base portions and disposed on the light exit surface side of the polarization separation film or the reflective film. And a phase difference portion main body.

  According to this application example, since the retardation portion main body constituting the retardation plate is not directly joined to the optical element, it is not necessary to use an adhesive for joining the two, and optical characteristics are deteriorated due to deterioration of the adhesive. It can be prevented.

  Application Example 5 The polarization conversion element according to this application example is the polarization conversion element according to any one of Application Examples 1 to 4, wherein the adhesive layer contains a modified acrylate or a modified methacrylate as a main component. .

  According to this application example, by using an ultraviolet curable resin adhesive excellent in heat resistance and light resistance performance for adhesion of the transparent substrate, the polarization conversion element can have high heat resistance and high light resistance and can have a long life.

  Application Example 6 The polarization conversion element of this application example is the polarization conversion element according to any one of application examples 1 to 5, wherein the retardation plate and the light exit surface are bonded by a bonding layer. The layer includes an Si skeleton having an atomic structure including a siloxane bond (Si—O) and a leaving group bonded to the Si skeleton, and the Si skeleton from which the leaving group is eliminated among the Si skeletons. The unbonded hand is an active hand and is bonded to the phase difference plate and the light emitting surface.

  According to this application example, the translucent substrate and the phase difference plate are bonded by an inorganic method, so that the adhesive does not thermally deteriorate, and the polarization conversion element has a long life with high heat resistance and high light resistance. I can do it.

  [Application Example 7] The polarization conversion element of this application example is the polarization conversion element according to any one of Application Examples 1 to 5, wherein the translucent substrate and the phase difference plate are bonded by a bonding layer, The bonding layer contacts the microcrystalline continuous thin film provided on the translucent substrate and the microcrystalline continuous thin film provided on the retardation plate, and contacts the microcrystalline continuous thin film on the translucent substrate. The phase difference plate is formed by an atomic diffusion bonding method that causes atomic diffusion at the contact interface and crystal grain boundary with the microcrystalline continuous thin film, or provided on either the light-transmitting substrate or the phase difference plate. Atomic diffusion that causes atomic diffusion at a contact interface and a grain boundary between the microcrystalline continuous thin film and the microcrystalline structure by bringing the microcrystalline continuous thin film into contact with the microcrystalline structure provided on either side It is formed by a bonding method.

  According to this application example, the translucent substrate and the phase difference plate are bonded by an inorganic method, so that the adhesive does not thermally deteriorate, and the polarization conversion element has a long life with high heat resistance and high light resistance. I can do it.

  Application Example 8 A polarization conversion unit according to this application example includes the polarization conversion element according to any one of Application Examples 1 to 7, and a fixed frame that fixes the polarization conversion element.

  According to this application example, by providing the polarization conversion element of the present invention, a polarization conversion unit having a long lifetime and excellent optical characteristics can be obtained.

  Application Example 9 A polarization conversion unit of this application example includes a light source device that emits light, a polarization conversion unit of Application Example 8 that converts light from the light source device into one type of polarized light, and the polarization conversion unit. A light modulation device that modulates polarized light from the unit according to image information, and a projection optical device that enlarges and projects the optical image formed by the light modulation device.

  According to this application example, by using the polarization conversion element of the present invention, a light projecting device having a long life and excellent optical characteristics can be obtained.

The figure which shows an example of the polarization conversion element which concerns on the 1st Embodiment of this invention. Schematic explaining the composition of a plasma polymerization film. The disassembled perspective view which shows the polarization conversion element which concerns on other embodiment. Sectional drawing which expanded and showed a part of polarization conversion element of FIG. The figure explaining the manufacturing process of the polarization conversion element concerning this embodiment. The figure explaining the manufacturing process of the polarization conversion element concerning this embodiment. The figure which shows the measurement result of the tensile strength in a hardening test. The figure which shows the measurement result of the shear strength in a hardening test. The figure explaining the manufacturing process of the polarization conversion element concerning this embodiment. The figure explaining the manufacturing process of the polarization conversion element concerning this embodiment. The figure explaining the manufacturing process of the polarization conversion element concerning this embodiment. The figure which shows the heat resistance test of the Example concerning this embodiment, and a prior art example. The figure which shows the result of the flatness test of the Example concerning this embodiment. The figure which shows the result of the flatness test of the Example which concerns on this embodiment. The figure which shows the result of the flatness test of a comparative example. The figure which shows the structure of a lamination | stacking 1/2 wavelength plate. The disassembled perspective view which shows the structure of the lamination | stacking 1/2 wavelength plate as an example of the phase difference plate which concerns on other embodiment of this invention. The disassembled perspective view which shows the structure of the lamination | stacking 1/2 wavelength plate as an example of the phase difference plate which concerns on other embodiment of this invention. The disassembled perspective view which shows the structure of the lamination | stacking 1/2 wavelength plate as an example of the phase difference plate which concerns on other embodiment of this invention. The figure which shows the Poincare sphere which shows the locus | trajectory of the polarization state in the lamination | stacking 1/2 wavelength plate shown in FIG. The figure which shows the Poincare sphere which shows the locus | trajectory of the polarization state in the lamination | stacking 1/2 wavelength plate shown in FIG. The figure which shows the Poincare sphere which shows the locus | trajectory of the polarization state in the lamination | stacking 1/2 wavelength plate shown in FIG. The figure for demonstrating transition of the track | orbit on the Poincare sphere of a linearly polarized light in the lamination | stacking 1/2 wavelength plate of the structure shown in FIG. The figure which shows the conversion efficiency of the laminated half wavelength plate with respect to 400 nm to 700 nm. The figure which shows the conversion efficiency of the laminated half wavelength plate with respect to 400 nm to 700 nm. The figure which shows the conversion efficiency of the laminated half wavelength plate with respect to 400 nm to 700 nm. The figure which shows the external appearance of the polarization conversion unit incorporating the polarization conversion element which concerns on embodiment of this invention. FIG. 28 is an exploded perspective view of the polarization conversion unit of FIG. 27. The figure which shows the liquid crystal projector as an example of the light projection apparatus to which the polarization conversion element which concerns on embodiment of this invention is applied. The figure explaining the structure of a general polarization conversion element. The figure explaining the structure of a general polarization conversion element.

Embodiments of the present invention will be described below in detail with reference to the drawings.
FIG. 1 is a diagram showing an example of a polarization conversion element according to the first embodiment of the present invention.
As shown in FIG. 1, a polarization conversion element 1 according to the present invention includes an element main body (optical element) 10 that is the above-described PBS array, and an inorganic optical crystal such as quartz that is selectively bonded to the element main body 10. A phase difference plate (laminated half-wave plate) 20.
Since inorganic optical crystals such as quartz are excellent in thermal conductivity, they are superior in heat resistance and have no fear of deterioration of optical properties due to high heat, compared to a phase plate made of an organic material described in the background art.
In addition to quartz, lithium tantalate, sapphire, etc. can be applied as the material of the retardation film.
As shown in FIG. 27 described later, in the polarization conversion element 1, two element bodies 10 are connected and incorporated, but only a part is shown in FIG.
As shown in FIG. 1, the element body 10 includes a plurality of light transmissive substrates 11, polarization separation films (polarization separation portions) 12 and reflection films (reflection) that are alternately provided between the plurality of light transmissive substrates 11. Part) 13 and an adhesive layer 14 provided between the plurality of translucent substrates 11 and bonding the translucent substrate 11.

The element body 10 includes a light incident surface 16 and a light emitting surface 17 that are substantially parallel to each other.
Further, the element body 10 has a plurality of light-transmitting substrates 11 formed of a polarization separation film (polarization separation unit) 12 and a reflection film (reflection film) by a joint surface 11 a having a predetermined inclination angle with respect to the light incident surface 16 or the light emitting surface 17. Bonded by the adhesive layer 14 with the reflective portions 13 alternately interposed therebetween.
The polarization separation film 12 selectively transmits P-polarized light and reflects S-polarized light among input light (S-polarized light and P-polarized light) from the outside.
The reflection film 13 reflects the S-polarized light reflected by the polarization separation film 12 toward the light exit surface 17.
Here, the adhesive layer 14 has a thickness of 5 μm or more and 10 μm or less.
Since the adhesive layer 14 is formed of an ultraviolet curable adhesive mainly composed of modified acrylate or modified methacrylate, the thickness can be set as described above.
Conventional ultraviolet curable adhesives do not have modified acrylate or modified methacrylate as a main component, and thus have a high viscosity and have an adhesive layer thickness of 10 μm to 20 μm.

As described above, when the thickness of the adhesive layer exceeds 10 μm, distortion occurs in the end portion of the adhesive layer in the manufacturing process of the polarization conversion element described later with reference to FIGS. 5 to 11. Therefore, when the light incident surface 16 and the light emitting surface 17 are polished (FIG. 11), the corners of the translucent substrate 11 near the strain are scraped. As a result, when the phase difference plate 20 is bonded to the light emitting surface 17 of the light transmissive substrate 11, a gap is generated between the light transmissive substrate 11 and the phase difference plate 20, and bubbles are generated. .
Thereby, the translucent board | substrate 11 and the phase difference plate 20 are not fully joined, but the phase difference plate 20 becomes easy to peel.
Further, the light transmittance is reduced by the bubbles generated between the translucent substrate 11 and the phase difference plate 20.

On the other hand, when the thickness of the adhesive layer is less than 5 μm, when dust or the like is mixed into the adhesive layer, the adhesive strength of the adhesive layer is reduced by the dust or the like.
However, if the thickness of the adhesive layer is 5 μm or more and 10 μm or less, the corners of the translucent substrate 11 are difficult to be scraped, so that bubbles are not generated, and the retardation plate 20 is easily peeled off from the translucent substrate 11, It is possible to solve the problem that the light transmittance is lowered.
Examples of the adhesive used in the present embodiment include UT20, HR54 (trade name, manufactured by Adel Co., Ltd.), and the like.

In FIG. 1, the phase difference plate 20 is bonded to the upper region of the polarization separation film 12 on the light emitting surface 17 of the translucent substrate 11 by the bonding layer 21.
The retardation plate 20 is a half-wave plate made of quartz as described above, and converts the P-polarized light transmitted through the polarization separation film 12 into S-polarized light.
However, in the polarization conversion element 1, the phase difference plate 20 is provided on the upper part of the reflection film 13 in the case where the P conversion light is emitted in a unified manner.
The bonding layer 21 is a plasma polymerized film for molecular bonding, and its main material is polyorganosiloxane. The plasma polymerized film includes a Si skeleton formed by a plasma polymerization method and including a siloxane bond and a crystallinity of 45% or less, and a desorber made of an organic group bonded to the Si skeleton. Then, by applying energy, the leaving group existing in the vicinity of the surface is released from the Si skeleton, thereby exhibiting adhesiveness.

2A and 2B are schematic diagrams for explaining the composition of the plasma polymerized film. FIG. 2A shows the composition before applying energy, and FIG. 2B shows the composition after applying energy.
As described above, as shown in FIG. 2A, the plasma polymerized film includes a siloxane bond (Si—O) 21A including the Si skeleton 21B and a leaving group 21C bonded to the Si skeleton 21B. .
When energy is applied to the bonding layer 21 made of a plasma polymerized film as shown in FIG. 2A, as shown in FIG. 2B, the leaving group 21C shown in FIG. Desorbed from the Si skeleton 21B. Thereby, active hands 21D are generated on the surface and inside of the bonding layer 21 and are activated.
As a result, adhesiveness is developed on the surface of the bonding layer 21. When such adhesiveness is expressed, the bonding layer 21 can be strongly bonded. The crystallinity of the Si skeleton 21B of the bonding layer 21 is preferably 45% or less, and more preferably 40% or less. Thereby, the Si skeleton 21B includes a sufficiently random atomic structure, and the characteristics of the Si skeleton 21B become apparent.
Here, “activate” means that the bonding groups 21C on the surface and inside of the bonding layer 21 are desorbed and bonds that are not terminated in the Si skeleton 21B (hereinafter referred to as “unbonded hands” or “dangling hands”). It is also referred to as a “ring bond”), a state in which this dangling bond is terminated by a hydroxyl group (OH group), or a state in which these states are mixed.
Therefore, the active hand 21D means an unbonded hand (dangling bond), or a bond in which the unbonded hand is terminated by a hydroxyl group. According to such an active hand 21D, the bonding layer 21 can be firmly bonded. Is possible.

As described above, when energy is applied to the plasma polymerized film, active hands are generated on the surface and inside thereof, so that strong adhesiveness is exhibited in the plasma polymerized film.
Moreover, since it is an inorganic joining method that does not use an adhesive, the optical characteristics are not affected by the deterioration of the adhesive.
Further, since the thickness of the adhesive layer 14 is not less than 5 μm and not more than 10 μm, the corners of the translucent substrate 11 are hard to be scraped, so that the bonding layer 21 is formed without a gap by the plasma polymerization method. And the phase difference plate 20 can be strongly bonded.
In addition, the joining method of the phase difference plate 20 and the light emission surface 17 is not restricted to this plasma polymerization method, You may join by the adhesive agent which has the above-mentioned modified methacrylate or modified acrylate as a main component.

Further, the bonding layer 21 may be formed not only by a plasma polymerization method but also by an atomic diffusion bonding method.
In the atomic diffusion bonding method, first, a microcrystalline continuous thin film is formed on each of the light-transmitting substrate 11 and the phase difference plate 20 constituting the element body 10 by vacuum film formation such as sputtering or ion plating in a vacuum vessel. Film. Then, the microcrystalline continuous thin films are overlapped during film formation or after film formation to cause atomic diffusion at the bonding interface and the crystal grain boundary, so that the light-transmitting substrate 11 and the phase difference plate 20 are strongly bonded. It is a method of joining.
In addition to superimposing the microcrystalline continuous thin films, a microcrystalline continuous thin film is formed on one of the translucent substrate 11 and the phase difference plate 20, and a microcrystalline structure is formed on the other. Atomic diffusion bonding can also be performed by superimposing a continuous crystal thin film and a microcrystalline structure.
Also in this case, since it is an inorganic joining method that does not use an adhesive, the optical characteristics are not affected by the deterioration of the adhesive.

FIG. 3 is an exploded perspective view showing a polarization conversion element according to another embodiment.
4 is an enlarged cross-sectional view of a part of the polarization conversion element of FIG.
In addition, about the structure similar to FIG. 1, the same code | symbol is attached | subjected and detailed description is abbreviate | omitted.
The polarization conversion element shown in FIGS. 3 and 4 is bonded to the element body 10 as a PBS array and functions as a half-wave plate, and rotates the polarization plane of incident linearly polarized light by 90 (deg). A quartz phase difference plate 20 that emits the light.
The element main body 10 has a substantially rectangular parallelepiped shape, and the end portions in the longitudinal direction where the two element main bodies 10A and 10B face each other are bonded to each other, and are in a symmetrical relationship with respect to the bonding surface 10C.
The element body 10 has a light incident surface 10D and a light emitting surface 10E that are substantially parallel to each other.
In addition, the element body 10 includes the polarization separation films 12 and the reflection films 13 that are alternately arranged along the longitudinal direction between the plurality of translucent substrates 11.
The plurality of translucent substrates 11 are bonded to each other by a bonding surface 11a having a predetermined inclination angle with respect to the light incident surface 10D or the light emitting surface 10E.

The polarization separation film 12 and the reflection film 13 are alternately provided at the boundary portion 11 </ b> B between the plurality of translucent substrates 11.
The polarization separation film 12 separates the light incident on the light incident surface 10D into two different types of linearly polarized light whose polarization directions are orthogonal to each other, transmits one linearly polarized light, and reflects the other linearly polarized light.
In the present embodiment, the polarization separation film 12 selectively transmits P-polarized light among the randomly polarized light incident on the light incident surface 10D and reflects S-polarized light.
The reflective film 13 reflects the other linearly polarized light reflected by the polarization separation film 12 and changes the direction of the optical path. That is, the reflective film 13 reflects the S-polarized light reflected by the polarization separation film 12 toward the light exit surface 10E.
As shown in FIG. 4, the element body 10 includes an adhesive layer 14 that joins a plurality of translucent substrates 11 to each other.

Here, the adhesive layer 14 can use an optical adhesive such as an ultraviolet curing type. When an ultraviolet curable adhesive is used, the viscosity is high, and the thickness of the adhesive layer 14 is about 10 μm to 20 μm.
Further, when an ultraviolet curable adhesive mainly composed of modified acrylate or modified methacrylate is used, the thickness of the adhesive layer 14 can be reduced to 5 μm or more and 10 μm. Examples of the ultraviolet curable adhesive mainly composed of modified acrylate or modified methacrylate include UT20 and HR154 (trade name, manufactured by Adel Co., Ltd.).
The adhesive layer 14 has a predetermined thickness W1.

The phase difference plates 20 (20A, 20B) are respectively disposed on the light emitting surfaces 10E of the two element bodies 10A, 10B.
The phase difference plate 20 generates a phase difference of 180 (deg) in the P-polarized light transmitted through the polarization separation film 12 and rotates the polarization plane of the P-polarized light by 90 (deg), so that it is reflected by the reflection film 13. It is converted into linearly polarized light parallel to the polarization plane of the S-polarized light, that is, converted into S-polarized light and emitted.
Moreover, as shown in FIG. 3, the phase difference plate 20 has a comb shape (border shape).
The phase difference plate 20 (20A, 20B) is bonded to the element body 10 and does not transmit light, and a base portion 20C (20C1, 20C2), and a phase difference portion 20D (20D1, 20D1, 20D1) that extends from the base portion 20C and transmits light. 20D2).
That is, the base portion 20 </ b> C is disposed outside the effective area (E) that is the optical region of the element body 10. The base 20C is joined along the longitudinal direction, that is, along the direction in which the polarization separation film 12 and the reflection film 13 are alternately arranged.

Then, the base portion 20C1 of one retardation plate 20A is joined to one edge portion 10F among the edge portions parallel to the longitudinal direction of the element body 10, and the base portion 20C2 of the other retardation plate 20B The phase difference plate 20A is close to the tip portion 20E1 of the phase difference portion 20D1.
That is, the base portion 20C1 of one phase difference plate 20A is close to the tip portion 20E2 of the phase difference portion 20D2 in the other phase difference plate 20B, and the base portion 20C2 of the other phase difference plate 20B is one phase difference plate. 20A is approaching the tip portion 20E1 of the phase difference portion 20D1.
Note that the base 20C has a long rectangular main plane and a width of, for example, about 3 mm to 4 mm.

The base 20C is bonded to the element body 10 by a bonding film (not shown).
Similar to the adhesive layer 14, this bonding film is provided by an optical adhesive such as an ultraviolet curing type or a plasma polymerization film. Since the bonding film is desirably disposed outside the effective area E, which is an optical region, not disposed on the optical path, the bonding film is disposed between the base portion 20C and the edge portions 10F and 10G parallel to the longitudinal direction of the element body 10. It is desirable that only be formed.
The phase difference plate 20 (phase difference portion 20D) has a so-called strip shape, and the thickness thereof is the same as that of the base portion 20C. The phase difference portion 20 </ b> D extends from the base portion 20 </ b> C and is disposed in an upper region of the polarization separation film 12 on the light exit surface 10 </ b> E of the element body 10. A plurality of adjacent phase difference portions 20D are arranged with a gap W2 having a predetermined width, and the S-polarized light reflected by the reflective film 13 passes through the gap W2.
As shown in FIG. 4, the phase difference portion 20 </ b> D has a light incident surface 20 </ b> F that faces the light emitting surface 10 </ b> E of the element body 10.

A slight gap W3 is provided between the light incident surface 20F of the phase difference portion 20D and the light emitting surface 10E of the element body 10. Therefore, it is desirable that antireflection films (not shown) are formed on the light incident surface 20F of the phase difference portion 20D and the light emitting surface 10E of the optical element 310, respectively.
3 and 4, the phase difference portion 20D of the phase difference plate 20 is not bonded to the element body 10 with an adhesive, so that deterioration of optical characteristics due to deterioration of the adhesive can be avoided.
Further, since the plurality of phase difference portions 20D are integrated with the base portion 20C, the phase difference plate 20 can be easily assembled to the element body 10.

Next, the manufacturing process of the element body 10 will be described in more detail.
The manufacturing process is roughly divided into a film forming process, an adhesion process, a cutting process, and a polishing process.
5 to 11 are views for explaining a manufacturing process of the polarization conversion element according to the present embodiment, particularly the element body.
[Film formation process]
In the first film formation step, as shown in FIG. 5, first, a plurality of translucent substrates (colorless and transparent substrates such as glass) 11A are prepared. These translucent substrates 11A have a first surface 11A1 and a second surface 11A2 that are substantially parallel to each other.
Among the plurality of translucent substrates 11A, the polarization separation film 12 is formed on the first surface 11A1 of some translucent substrates 11A, and the reflection film 13 is formed on the second surface 11A2.
Any of these films is formed on the first surface 11A1 and the second surface 11A2 of the other translucent substrate 11A, or any film is not formed.

[Adhesion process]
In the bonding step shown in FIG. 6, the translucent substrate 11A on which the polarization separation film 12 and the reflective film 13 are formed and the translucent substrate 11A on which these films are not formed are alternately attached by the adhesive 14A. Combined. At this time, the polarization separation films 12 and the reflection films 13 are alternately stacked with the light-transmitting substrate 11A interposed therebetween.
Here, an adhesive mainly composed of a modified acrylate or a modified methacrylate is used as the adhesive 14A, and the coating amount is adjusted so that the thickness after curing is 5 to 10 μm.

Next, as shown in FIG. 7, ultraviolet rays are irradiated from a direction substantially perpendicular to the first surface 11A1 of the translucent substrate 11A. Since the ultraviolet rays pass through the polarization separation film 12 and the reflection film 13, all the adhesives 14A in FIG. 7 are cured simultaneously.
Thereby, the adhesive layers 14 are formed between the polarization separation film 12 and the translucent substrate 11A and between the reflective film 13 and the second translucent substrate, respectively. And the laminated body 400 with which the some translucent board | substrate 11A was joined is formed.
In addition, you may irradiate an ultraviolet-ray from the direction substantially parallel to 1st surface 11A1 of 11 A of translucent board | substrates.

Here, the relationship between the curing conditions of the adhesive 14A and the adhesive strength of the adhesive layer 14 obtained by each curing condition will be described.
As shown in Table 1 below, curing test 1 to curing test 7 were carried out by changing the amount of ultraviolet (UV) irradiation. As a result, the tensile strength was as shown in Table 1 and FIGS. 8 (A) and (B), and the shear strength was as shown in Table 1 and FIGS. 9 (A) and (B).
That is, FIG. 8 (A), (B) as shown in, the amount of ultraviolet irradiation is 15,000 / cm ² or more 45,000mJ / cm ² or less, particularly 20,000mJ / cm ² or more 35,000mJ / cm ² or less In this case, the tensile strength of the adhesive layer 14 is increased, which is preferable. Further, as shown in FIGS. 9A and 9B, the ultraviolet irradiation amount is 15,000 mJ / cm ² or more and 60,000 mJ / cm ² or less, particularly 25,000 mJ / cm ² or more and 50,000 mJ / cm ² or less. Is preferable because the shear strength of the adhesive layer 14 is increased. In Table 1, each curing test is performed twice.

The tensile strength test and the shear strength test were carried out by the following test methods. That is, a test product prepared by adhering two white glass plates having a size of 10 mm × 10 mm with an adhesive 14A is subjected to a tensile load in a direction perpendicular or parallel to the bonding surface with a tensile tester. The load when the white glass plate was separated was measured.














[Table 1]

Next, as shown in FIG. 10, as a cutting process, the stacked body 400 is cut substantially parallel to the cut surface that forms a predetermined angle θ (about 45 degrees) with the first surface 11 </ b> A <b> 1, and the stacked block 410 is cut out. .
In the subsequent polishing step shown in FIG. 11, the element body 10 of the polarization conversion element 1 is obtained by polishing the cut surface 410 </ b> A of the cut-out laminated block 410 with the polishing apparatus 500.

[Heat resistance test]
According to Example 1 and Comparative Example 1, the heat resistance of the adhesive (adhesive layer) used in the present invention was evaluated.
FIG. 12 is a diagram showing a heat resistance test of Example 1 and Conventional Example 1. FIG.
In Example 1, two glass plates were bonded together with an adhesive (UT20, manufactured by Adel Co., Ltd.) and irradiated with a predetermined amount of ultraviolet rays. Thereby, the test piece 600 of Example 1 was produced.
On the other hand, in Comparative Example 1, two glass plates were bonded together with a conventional adhesive (PHOTO Bond 300 Sunrise MSI Co., Ltd.) and irradiated with a predetermined amount of ultraviolet rays. Thereby, the test piece 601 of the comparative example 1 was produced.
When these test pieces 600 and 601 are fixed in the fixed frame 610, the test pieces 600 and 601 are assembled in a place where the polarization conversion element of the projector is to be installed, and the light from the light source lamp is irradiated on the test pieces 600 and 601. The projector cooling mechanism was adjusted so that the temperature of the test piece was 120 ° C. FIG. 12 shows the test results when left in this environment for 3800 hours.

As shown in FIG. 12, yellowing 620 was partially observed in the adhesive layer of the test piece 601, while yellowing was not observed in the adhesive layer of the test piece 600.
Furthermore, as a result of continuing the test pieces 600 and 601 in this environment, severe yellowing was observed in the adhesive layer of the test 601 after 4800 hours. On the other hand, in the adhesive layer of the test piece 600, a slight yellowing was observed so as not to affect the optical characteristics.
Therefore, it can be seen that the adhesive layer formed by the adhesive of the present invention is excellent in heat resistance.

[Flatness test]
(Example 2 to Example 11 and Comparative Example 2)
From Example 2 to Example 11 and Comparative Example 2, the flatness of the light incident surface and the light exit surface of the polarization conversion element of the present invention was evaluated.
FIG. 13 is a diagram showing the results of flatness tests from Example 2 to Example 6 according to the present invention, and FIG. 14 is the results of flatness tests from Examples 7 to 11 according to the present invention. FIG. 16 is a diagram showing the results of the flatness test of Comparative Example 2.
(Example 2 to Example 6)
In Example 2, an element body 10 as shown in FIG. 26 described later was produced using the same adhesive as in Example 1. And the left element main body 10 was used among two right and left element main bodies 10 shown by FIG. And the sectional view in the approximate center of the light incident surface 16 of the element body 10 was obtained by the following measuring method. Here, the cross-sectional view is a cross-sectional view in the left-right direction of FIG.
In the obtained cross-sectional view, a convex portion that swelled relatively upward was selected, and the vertices of the concave portions near the left and right of the convex portion were connected by lines. The distance from this line to the top of the convex portion was converted on the scale of the vertical axis to calculate the “height difference”.

In Example 3 to Example 6, the element body 10 was produced in the same manner as in Example 2, and the light incident surface 16 was measured to obtain a cross-sectional view. From the cross-sectional view, two “height differences” were calculated in the same manner as in Example 2. FIG. 13 shows the results.
(Examples 7 to 11 and Comparative Example 2)
In Example 7 to Example 11, sectional views were obtained in the same manner as in Example 2 for the light emitting surface 17 of the element body 10 produced in Examples 2 to 6, respectively. From the obtained cross-sectional view, two “level differences” were calculated in the same manner as in Example 2.
In Comparative Example 2, an element body was prepared in the same manner as in Example 2 except that the same adhesive as in Comparative Example 1 was used as the adhesive, and a cross-sectional view of the light emission surface was obtained. Two points of “height difference” were calculated from the obtained cross-sectional view in the same manner as in Example 2.

The results of Example 7 to Example 11 and Comparative Example 2 are shown in FIGS.
As a method for measuring the cross-sectional view, a laser interferometer G102S (Fujinon Co., Ltd. (currently manufactured by Fuji Film Co., Ltd.)) is used to irradiate the light incident surface or light output surface of the device body, and the reflected light from the device body is originally Interference fringes are obtained by interfering with the parallel light. The wavelength of light set by the laser interferometer is 685 nm.
By analyzing the obtained interference fringes with interference fringe analysis software (Fujinon Co., Ltd. (currently Fuji Film Co., Ltd.)), a cross-sectional view of the light incident surface or the light emitting surface is obtained.
As shown in FIGS. 13 and 14, in Examples 2 to 11 using the adhesive of the present invention, the flatness is excellent because the difference in height between the light incident surface and the light emitting surface is small. all right.
On the other hand, as shown in FIG. 15, in the comparative example using the conventional adhesive agent, it was found that the flatness was poor because the height difference on the light incident surface was large.

[Wave plate structure]
Below, the structure of the phase difference plate which concerns on embodiment of this invention is demonstrated.
16A and 16B are diagrams showing a configuration of a laminated half-wave plate as an example of a retardation plate according to an embodiment of the present invention, where FIG. 16A is a perspective view, FIG. 16B is an exploded perspective view, and FIG. ) Is a side view.
As shown in FIG. 16 (a), the laminated half-wave plate 20 according to the present invention includes a first wave plate 30 and a second wave plate 40 each using an inorganic optical crystal such as quartz. The optical axes 31 and 41 are bonded so that they intersect, and as a whole, the phase of the linearly polarized light A incident from the light source side is shifted by 180 (deg) and the polarization plane is rotated by 90 (deg). It is configured to function as a half-wave plate that converts to polarized light B and emits it.
As shown in FIG. 16B, the optical axis azimuth angle of the first wave plate 30 is θ1, and the optical axis azimuth angle of the second wave plate 40 is θ2.
The optical axis azimuth is an angle formed between the crystal optical axis and the polarization plane of linearly polarized light incident on the laminated wave plate.
Further, as shown in FIG. 16C, the cutting angle of the first wave plate 30 (referring to the intersecting angle between the normal direction on the main surface of the crystal plate and the crystal optical axis (Z axis)) Z1 is 27 (Deg) (also referred to as 27 (deg) Z), and the cutting angle Z2 of the second wave plate 40 is defined as 18 (deg) (also referred to as 18 (deg) Z).
The value of this cutting angle takes into account the ease of handling in the assembly process. In wave plates having the same phase difference, the birefringence difference (difference between the extraordinary refractive index ne and the ordinary refractive index no) decreases as the cutting angle is reduced from 90 degrees, while the thickness of the wave plate is On the contrary, it gets thicker.
In particular, in a single-mode wave plate with a thin plate thickness, in order to prevent cracking and breakage of the wave plate from the viewpoint of handling during the processing process or the assembly process, the cutting angle is made smaller than 90 (Deg) Z, It is advantageous to increase the thickness of the wave plate. However, if the cutting angle is large, this time, the wave plate is easily affected by the incident diverging light.
Therefore, in this embodiment, the angle of cut is set so that each of the wave plates 30 and 40 satisfies the design phase difference based on the respective optical axis azimuth and has a thickness of about 0.3 mm that is most convenient for handling. By making them different from each other, the design is performed so that the plate thickness t1 of the first wave plate 30 and the plate thickness t2 of the second wave plate 40 are substantially equal (about 0.3 mm).

In the present invention, when the laminated half-wave plate 20 is used as a polarization conversion element incorporated in a liquid crystal projector, the phase difference of the first wave plate 30 with respect to light (green) having a predetermined design wavelength λ, for example, 520 nm, is Γ1, The phase difference of the second wave plate 40 is set to Γ2, and the second wave plate 40 has a wavelength relative to the light of the wavelength λ1 with respect to light having a plurality of wavelength bands λ1 and λ2 (λ1 <λ2) having different wavelength bands. When the phase difference is Γ21 and the phase difference for light of wavelength λ2 is Γ22,
Γ1 = 360 (deg) (1)
Γ2 = 180 (deg) (2)
ΔΓ2 = (Γ22−Γ21) / 2 (3)
cos2θ1 = 1− (1-cosΔΓ2) / {2 {1-cos (mΔΓ2)}} (4)
However, m = 2
The thicknesses of the first and second wave plates 30 and 40 are set so as to satisfy the above.

The relationship between the phase difference Γ with respect to light of wavelength λ and the plate thickness t of the wave plate is Γ = 2π / λ × (ne−no) × t (ne is the refractive index of extraordinary light, and ne is the refractive index of ordinary light. ).
Considering the above-mentioned manufacturing convenience that the plate thickness t1 of the first wave plate 30 and the plate thickness t2 of the second wave plate 40 are about 0.3 mm, when Z1 = 27 (deg), When t1 = 0.2753 mm and Z2 = 18 (deg), t2 = 0.2965 mm, which satisfies the above plate thickness condition.
It is assumed that the value of (ne-no) in the above equation changes as the wavelength plate cutting angle changes.
By the way, the laminated half-wave plate 20 has a polarization conversion efficiency of 1 in each wavelength band (R (red: 400 nm band), G (green: 500 nm band), B (blue: 675 nm)) necessary for the liquid crystal projector. Therefore, the phase difference is required to be 180 (deg).

In order to set the phase difference to 180 (deg) in a wide wavelength band desired when the half-wave plate 20 is configured as a whole using the first and second wave plates 30 and 40, the stacking layer 1/2 Regarding the first and second wave plates 30 and 40 constituting the wave plate 20, respective phase differences Γ1 and Γ2 at respective predetermined wavelengths (for example, 520 nm), respective optical axis azimuth angles θ1 and θ2, and a cutting angle Z1. , Z2 and other parameters are varied to obtain the optimum phase difference, conversion efficiency and the like.
As a result, the phase difference Γ1, the optical axis azimuth angle θ1 and the cutting angle Z1 of the first wave plate 30 and the phase difference Γ2, the optical axis azimuth angle θ2 and the cutting angle Z2 of the second wave plate 40 are:
Γ1 = 360 (deg), θ1 = −16 (deg), Z1 = 27 (deg) (5)
Γ2 = 180 (deg), θ2 = 45 (deg), Z2 = 18 (deg) (6)
When satisfying the above, it has been found that the phase difference is 180 (deg) with respect to the light in the three RGB wavelength bands, and the polarization conversion efficiency is almost 1.
When θ1 = −16 (deg), the thickness of the first wave plate 30 with the cutting angle Z1 = 27 (deg) is 0.2753 mm, and when θ2 = 45 (deg), the cutting angle Z2 = The thickness of the second wave plate 40 that is 18 (deg) is 0.2965 mm.
Here, the range of values that the design wavelength λ can take is 510 ≦ λ ≦ 530 (nm).
In FIG. 16, the optical axis azimuth and cutting angle of the first wave plate 30 and the second wave plate 40 may be interchanged. In other words, the stacking order of the first wave plate 30 and the second wave plate 40 may be switched with respect to the light incident direction.
Specifically, the design phase difference Γ1 of the first wave plate 30 is Γ1 = 180 (deg), the design phase difference Γ2 of the second wave plate 40 is Γ2 = 360 (deg), and the first wave plate The optical axis azimuth angle θ1 and cutting angle Z1 of 30 and the optical axis azimuth angle θ2 and cutting angle Z2 of the second wave plate 40 are θ1 = 45 (deg), Z1 = 18 (deg) (5) ′.
θ2 = −16 (deg), Z2 = 27 (deg) (6) ′
It can be.
In this case, the plate thickness t1 of the first wave plate 30 is 0.2965 mm, and the plate thickness t2 of the second wave plate 40 is 0.2753 mm.

FIG. 17 is an exploded perspective view showing a configuration of a laminated half-wave plate as an example of a phase difference plate according to another embodiment of the present invention.
In FIG. 17, the optical axis azimuth angle θ1 of the first wave plate 30 and the optical axis azimuth angle θ2 of the second wave plate 40 in FIG.
Note that the cutting angle of each wave plate is not 90 (deg) Z, but has the same relationship as that shown in FIG.
In the case shown in FIG. 17, the phase difference Γ1, optical axis azimuth angle θ1 and cutting angle Z1 of the first wave plate 30 and phase difference Γ2, optical axis azimuth angle θ2 and cutting angle Z2 of the two wave plates are
Γ1 = 360 (deg), θ1 = 16 (deg), Z1 = 27 (deg) (7)
Γ2 = 180 (deg), θ2 = 135 (deg), Z2 = 18 (deg) (8)
By satisfying the above, the phase difference becomes 180 (deg) with respect to the light in the three wavelength bands, and the polarization conversion efficiency becomes almost 1.
Also in this case, even if the phase difference, the optical axis azimuth angle, and the cutting angle of the first wave plate 30 and the second wave plate 40 are switched as in the following formulas (7) ′ and (8) ′, the polarization The conversion efficiency can be almost 1.
Γ1 = 180 (deg), θ1 = 135 (deg), Z1 = 18 (deg) (7) ′
Γ2 = 360 (deg), θ1 = 16 (deg), Z2 = 27 (deg) (8) ′
FIG. 18 is an exploded perspective view showing a configuration of a laminated half-wave plate (hereinafter, laminated half-wave plate) as an example of a retardation plate according to still another embodiment of the present invention.
This is obtained by rotating the optical axis azimuth angle of each wave plate in the configuration of FIG. 16 by 90 °.
In this case, the phase difference Γ1, optical axis azimuth angle θ1 and cutting angle Z1 of the first wave plate 30, phase difference Γ2, optical axis azimuth angle θ2 and cutting angle Z2 of the second wave plate are:
Γ1 = 360 (deg), θ1 = 74 (deg), Z1 = 27 (deg) (9)
Γ2 = 180 (deg), θ2 = 135 (deg), Z2 = 18 (deg) (10)
By satisfying the above, the phase difference becomes 180 (deg) with respect to the light in the three wavelength bands, and the polarization conversion efficiency becomes almost 1.
Also in the case of FIG. 18, the phase difference, the optical axis azimuth angle, and the cutting angle between the first wave plate 30 and the second wave plate 40 may be interchanged as in the following formulas (9) ′ and (10) ′. The polarization conversion efficiency can be almost 1.
Γ1 = 180 (deg), θ1 = 135 (deg), Z1 = 18 (deg) (9) ′
Γ2 = 360 (deg), θ1 = 16 (deg), Z2 = 27 (deg) (10) ′
FIG. 19 is an exploded perspective view showing a configuration of a laminated half-wave plate (hereinafter referred to as a laminated half-wave plate) as an example of a phase difference plate according to another embodiment of the present invention.
In FIG. 19, the optical axis azimuth θ1 of the first wave plate 30 and the optical axis azimuth θ2 of the second wave plate 40 in FIG.
In this case, the phase difference Γ1, the optical axis azimuth angle θ1 and the cutting angle Z1 of the first wave plate 30 and the phase difference Γ2 of the second wave plate, the cutting angle Z2 of the optical axis azimuth angle θ2,
Γ1 = 360 (deg), θ1 = 106 (deg), Z1 = 27 (deg) (11)
Γ2 = 180 (deg), θ2 = 45 (deg), Z2 = 18 (deg) (12)
By satisfying the above, the phase difference becomes 180 (deg) with respect to the light in the three wavelength bands, and the polarization conversion efficiency becomes almost 1.
Also in the case of FIG. 19, even if the optical axis azimuth angle and the cutting angle of the first wave plate 30 and the second wave plate 40 are switched as in the following formulas (11) ′ and (12) ′, the polarization conversion is performed. The efficiency can be almost 1.
Γ1 = 180 (deg), θ1 = 45 (deg), Z1 = 18 (deg) (11) ′
Γ2 = 360 (deg), θ1 = 106 (deg), Z2 = 27 (deg) (12) ′

・・・（１４）

・・・（１５）
第１及び第２の波長板３０、４夫々の位相差Γ１、Γ２、光学軸方位角度θ１、θ２を設定して、式（１４）、（１５）よりミューラ行列Ｒ１、Ｒ２を求める。 Next, explanation will be given on whether the above-mentioned optical axis azimuth angles θ1 and θ2 were found as follows.
First, a calculation method for finding an example of the laminated half-wave plate according to the present invention will be briefly described. The polarization state after the linearly polarized light passes through the two wave plates can be expressed using a Mueller matrix or a Johns matrix.
E = R2 / R1 / I (13)
Here, I is a vector representing the polarization state of incident light, and E is a vector representing the polarization state of outgoing light. R1 is the Mueller matrix of the first wave plate 30 in the laminated half-wave plate 20, and R2 is the Mueller matrix of the second wave plate 40, which are represented by the following equations.

(14)

... (15)
The phase differences Γ1, Γ2 and optical axis azimuth angles θ1, θ2 of the first and second wave plates 30, 4 are set, and the Mueller matrices R1, R2 are obtained from the equations (14), (15).

・・・（１６）
Ｅの行列要素Ｓ_０１、Ｓ_１１、Ｓ_２１、Ｓ_３１はストークスパラメータと呼ばれ、偏光状態を表している。このストークスパラメータを用いて、波長板の位相差Γは次式のように表される。

・・・（１７）
Γ＝（２ｍ−１）×π 但し、ｍは正の整数
このように、式（１７）を用いて位相差を算出することができる。
さらに、出射光の偏光状態を表す行列Ｅと、偏光子の行列Ｐとの積を計算し、得られた光量を評価値とすれば、偏光状態を正確に判定する。これを変換効率と定義する。
具体的には、偏光子の行列Ｐの透過軸を９０（ｄｅｇ）に設定し、行列Ｐと出射光偏光状態を表す行列Ｅとの積から得られる行列Ｔのストークスパラメータより、９０（ｄｅｇ）方向の偏光面成分の光量を算出することができる。出射光偏光状態を表す行列Ｅと、偏光子の行列Ｐとの、積は次式のようになる。 When the polarization state I of the incident light is set, the polarization state E of the emitted light can be calculated from the equation (13).
The case where a Mueller matrix is used as the matrix will be described. The polarization state E of the emitted light is expressed by the following equation.

... (16)
The matrix elements S ₀₁ , S ₁₁ , S ₂₁ and S ₃₁ of E are called Stokes parameters and represent the polarization state. Using this Stokes parameter, the phase difference Γ of the wave plate is expressed as follows.

... (17)
Γ = (2m−1) × π where m is a positive integer. Thus, the phase difference can be calculated using Expression (17).
Further, if the product of the matrix E representing the polarization state of the outgoing light and the matrix P of the polarizer is calculated and the obtained light quantity is used as the evaluation value, the polarization state is accurately determined. This is defined as conversion efficiency.
Specifically, the transmission axis of the matrix P of the polarizer is set to 90 (deg), and from the Stokes parameter of the matrix T obtained from the product of the matrix P and the matrix E representing the outgoing light polarization state, 90 (deg) The amount of the polarization plane component in the direction can be calculated. The product of the matrix E representing the outgoing light polarization state and the polarizer matrix P is given by the following equation.

・・・（１９）
ここで、ベクトルＴのストークスパラメータのＳ_０２が光量を表している。入射光量を１に設定すればＳ_０２が変換効率となる。
位相差、変換効率とも積層１／２波長板を透過した後の偏光状態を表す行列Ｅから求めることができる。 T = P · E (18)
Here, the matrix T represents the conversion efficiency, and is represented by the following equation (19) in terms of the Stokes parameters of the elements.

... (19)
Here, S ₀₂ of the Stokes parameters of the vector T represents the amount of light. If the amount of incident light is set to 1, S ₀₂ becomes the conversion efficiency.
Both the phase difference and the conversion efficiency can be obtained from the matrix E representing the polarization state after passing through the laminated half-wave plate.

Using the above conversion efficiency as an evaluation criterion, the phase differences Γ1 and Γ2 at predetermined wavelengths (for example, a wavelength of 520 nm) for the first and second waveplates 30 and 40, which are various parameters of the laminated half-wave plate, are used. Each of the optical axis azimuth angles θ1 and θ2 and the cutting angles Z1 and Z2 were variously changed and simulated using a computer.
The simulation was repeated to select the above parameters when the conversion efficiency was good in a desired wide wavelength band. The cutting angles were selected so that the thicknesses t1 and t2 of the respective wave plates were about 0.3 mm so as to satisfy the above-described manufacturing conditions.

The results will be described below.
In the first and second wave plates 30 and 40 of the laminated half-wave plate 20 shown in FIG. 16, the cutting angle of the first wave plate 30 is 27 (deg) Z, and the cutting angle of the second wave plate 40 Is 18 (deg) Z and the design wavelength λ is 520 nm, the phase difference Γ1 and the optical axis azimuth angle θ1 of the first wave plate 30 are 360 (deg), −16 (deg), and the second wavelength, respectively. When the plate phase difference Γ2 and the optical axis azimuth angle θ2 were set to 180 (deg) and 35 (deg) ≦ θ2 ≦ 55 (deg), respectively, the conversion efficiency of the laminated half-wave plate 20 was obtained by simulation. As a result, good wavelength-conversion efficiency (polarization conversion efficiency) was obtained (described later).
The range of the optical axis azimuth angles θ1 and θ2 is effective within a range of ± 5 (deg) from the set angle in accordance with required specifications or as an allowable error.

Here, the optical action of the first wave plate 30 and the second wave plate 40 constituting the laminated half-wave plate 20 shown in FIG. 16 will be described with reference to FIG.
FIG. 20A is a diagram for explaining the transition of the trajectory of the linearly polarized light A incident on the laminated half-wave plate 20 on the Poincare sphere. FIG. 20B is a diagram showing the locus of the polarization state of light incident on the laminated half-wave plate 20 in the Poincare sphere shown in FIG. 20A viewed from the S2 axis direction (projected on the S1S3 plane). Figure).
Further, FIG. 20C is a view of the locus of the polarization state seen from the S1 axis direction in order to explain the function of the first wave plate 30 of the laminated half-wave plate 20 according to the present invention (S2S3). The figure projected on the plane).
20B and 20C, when the light beam of linearly polarized light A is incident on a predetermined position P0 on the equator of the Poincare sphere, the first wavelength plate 30 causes 360 (about the optical axis R1 (2θ1) to be centered. deg) rotate to reach P1 (P0 = P1), and further rotate 180 (deg) around the optical axis R2 (2θ2) by the second wave plate 40 to reach P2 (equator). It can be seen that the light beam emitted from the / 2 wavelength plate 1 becomes the linearly polarized light B rotated by θ = 90 (deg) with respect to the linearly polarized light A (incident light) and is emitted from the laminated half wavelength plate 20.

Here, when the phase difference Γ2 of the second wave plate 40 causes a phase change of ΔΓ2 due to the change of the wavelength of the incident light, the phase change ΔΓ2 is offset by the phase change ΔΓ1 due to the wavelength of the first wave plate 30. For example, the wavelength dependence of the laminated half-wave plate 20 can be suppressed, and it can function as a half-wave plate in a wide band.
Further, the phase change ΔΓ2 due to the wavelength of the second wave plate 40 has a constant value determined by the wavelength dispersion of the substrate material, and the phase change ΔΓ1 due to the wavelength of the first wave plate 30 is equal to the first wavelength. The size of the plate 30 can be varied by adjusting the in-plane azimuth angle θ1.
Therefore, a relational expression between the first wave plate 30 and the second wave plate 40 is derived below.
When the wavelength of the incident light changes between the reference wavelength (design wavelength) λ and the wavelengths λ1 to λ2 (λ1 <λ2), the first wavelength plate 30 and the second wavelength plate 40 have a wavelength dependency due to the wavelength dependency of the wavelength plate. The phase difference changes from Γ1 and Γ2, respectively.
In addition, in the phase difference of the second wave plate,
When defined as Γ21: phase difference at wavelength λ1 Γ22: phase difference at wavelength λ2, the phase change ΔΓ2 due to the wavelength of the second wave plate 40 satisfies the following expression.
ΔΓ2 = (Γ22−Γ21) / 2 (20)

In FIG. 20B, it is assumed that the coordinate P0 (P1) on the Poincare sphere has changed to P1 ″ due to the phase change ΔΓ2 generated in the second wave plate 40, and the distance of P0 → P1 ″ is approximately When represented by a straight line x2, ΔΓ2 and x2 satisfy the relationship of the following expression.
(X2) ² = 2k ² -2k ² cos ΔΓ2 (21)
However, k shows the radius of a Poincare sphere.
Similarly, in FIG. 20C, it is assumed that the coordinate P0 (P1) on the Poincare sphere is changed to P1 ′ by the phase change ΔΓ1 generated in the first wave plate 30, and this P0 → P1 ′ When the distance is approximately represented by a straight line x1, ΔΓ1 and x1 satisfy the relationship of the following expression (22).
(X1) ² = 2r ² -2r ² cos ΔΓ1 (22)
However, r is a radius when rotating Γ11 with R1 as the rotation axis.
Also, r can be expressed by the following equation (23) using the in-plane azimuth angle θ1 of the first wave plate 30.
r ² = 2k ² -2k ² cos 2θ1 (23)

Further, when Expression (23) is substituted into Expression (22), Expression (24) is obtained.
(X1) ² = 4k ² (1-cos 2θ1) (1-cos ΔΓ1) (24)
Therefore, in order for the phase changes of the first wave plate 30 and the second wave plate 40 to cancel each other,
x1 ≒ x2
And (x1) ² = (x2) ² from Equation (21) and Equation (24)
The relationship 2k ² −2k ² cos ΔΓ ² = 4k ² (1−cos 2θ1) (1−cos ΔΓ1) is established.
Therefore, when k is normalized and put together, Expression (25) is obtained.
cos2θ1 = 1− (1-cosΔΓ2) / {2 (1-cosΔΓ1)} (25)
Next, the first wave plate 30 and the second wave plate 40 are made of the same dispersion substrate material,
Γ11 / Γ22 = m
Then, equation (26) is obtained.
ΔΓ1 = mΔΓ2 (26)
Therefore, when equation (26) is substituted into equation (25), equation (27) is obtained.
cos2θ1 = 1− (1-cosΔΓ2) / {2 (1-cosmΔΓ2)} (27)
Expression (27) indicates that the in-plane azimuth angle θ1 of the first wave plate 30 is determined by the phase change ΔΓ2 caused by the second wave plate 40.

Next, specific parameters of the first wave plate 30 and the second wave plate 40 constituting the laminated half-wave plate 20 are calculated using the above-described calculation formula.
As a specific example, parameters are calculated for a laminated half-wave plate that functions as a half-wave plate in a wide wavelength band in the wavelength range of 350 nm to 850 nm.
For example, when the phase difference Γ1 = 360 (deg) of the first wave plate 20 and the phase difference Γ2 = 180 (deg) of the second wave plate 3,
m = Γ1 / Γ2 = 2
It becomes.
Next, for θ2, the value of θ2 is set to 45 (deg) in order to emit the linearly polarized light incident on the second wave plate 40 as linearly polarized light rotated by 90 (deg). In order to optimize the solution obtained by the above, the variable range is set to ± 10 (deg),
θ2 = 45 (deg) ± 10 (deg) (35 (deg) ≦ θ2 ≦ 55 (deg)) (28)
It was.

FIG. 21 is a diagram for explaining the transition of the trajectory on the Poincare sphere of linearly polarized light in the laminated half-wave plate having the configuration shown in FIG.
When light enters as linearly polarized light A having a polarization direction parallel to the equator from a predetermined position P0 on the equator, it is rotated by 360 (deg) about the optical axis R1 by the first wave plate 30. Then, it is shifted to P1 (on the equator), and further rotated by 180 (deg) around the optical axis R2 by the second wave plate 40 to reach P2 (on the equator). It turns out that it becomes the linearly polarized light B rotated by = 90 (deg), and is emitted from the half-wave plate 20 to be a half-layer wave plate similar to the case of FIG.
Moreover, said Formula (20)-(27) is materialized similarly to the case of FIG. 16 (FIG. 20).

FIG. 22 is a diagram for explaining the transition of the trajectory on the Poincare sphere of linearly polarized light in the laminated half-wave plate having the configuration shown in FIG.
When light enters as linearly polarized light A having a polarization direction parallel to the equator from a predetermined position P0 on the equator, it is rotated by 360 (deg) about the optical axis R1 by the first wave plate 30. Then, it is shifted to P1 (on the equator), and further rotated by 180 (deg) around the optical axis R2 by the second wave plate 40 to reach P2 (on the equator). It turns out that it becomes the linearly polarized light B rotated by = 90 (deg), and is emitted from the half-wave plate 20 to be a half-layer wave plate similar to the case of FIG.
Moreover, said Formula (20)-(27) is materialized similarly to the case of FIG.

FIG. 23 is a diagram for explaining the transition of the trajectory on the Poincare sphere of linearly polarized light in the laminated half-wave plate having the configuration shown in FIG.
When light enters as linearly polarized light A having a polarization direction parallel to the equator from a predetermined position P0 on the equator, it is rotated by 360 (deg) about the optical axis R1 by the first wave plate 30. Then, it is shifted to P1 (on the equator), and further rotated by 180 (deg) around the optical axis R2 by the second wave plate 40 to reach P2 (on the equator). It turns out that it becomes the linearly polarized light B rotated by = 90 (deg), and is emitted from the half-wave plate 20 to be a half-layer wave plate similar to the case of FIG.
Moreover, said Formula (20)-(27) is materialized similarly to the case of FIG.

FIG. 24 is a diagram showing the conversion efficiency of the laminated half-wave plate 20 of the present invention for wavelengths from 400 nm to 700 nm. The design wavelength λ of each wave plate is 510 nm, and the incident angle is from −10 (deg) to +10 (deg). It is a graph which shows the change of the polarization conversion efficiency for every wavelength at the time of changing to.
The laminated half-wave plate 20 of the present invention has an incident angle dependency. When the incident angle is +10 (deg), the polarization conversion efficiency deteriorates as the wavelength increases. Moreover, when the incident angle is -5 (deg) and the incident angles are -5 (deg) and -10 (deg), the polarization conversion efficiency at low wavelengths is poor, and the polarization conversion efficiency improves as the wavelength increases. ing.
However, as a whole, the polarization conversion efficiency is 0.5 or more at each incident angle at the design wavelength of 510 nm. In particular, when the incident angle is from −10 deg to 5 deg, high polarization conversion efficiency is obtained at the entire design wavelength range from 400 nm to 700 nm. Show.
Further, at an incident angle of 0 deg, the polarization conversion efficiency was very good, almost 1 in the range of 450 nm to 650 nm.
Since the wavelengths of blue, green, and red used in the liquid crystal projector are 400 nm band, 500 nm band, and 675 nm band, respectively, the laminated half-wave plate 20 having the above parameters can be satisfactorily applied to a liquid crystal projector or the like.

FIG. 25 is a diagram showing the conversion efficiency of the laminated half-wave plate 20 of the present invention for wavelengths from 400 nm to 700 nm. The design wavelength λ of each wave plate is 520 nm, and the incident angle is from −10 (deg) to +10 (deg). It is a graph which shows the change of the polarization conversion efficiency for every wavelength at the time of changing to.
The laminated half-wave plate 20 of the present invention has an incident angle dependency. When the incident angle is +10 (deg), the polarization conversion efficiency deteriorates as the wavelength increases. Moreover, when the incident angle is -5 (deg) and the incident angles are -5 (deg) and -10 (deg), the polarization conversion efficiency at low wavelengths is poor, and the polarization conversion efficiency improves as the wavelength increases. ing.
However, as a whole, the polarization conversion efficiency is 0.5 or more at each incident angle at the design wavelength of 510 nm. In particular, when the incident angle is from −10 deg to 5 deg, high polarization conversion efficiency is obtained at the entire design wavelength range from 400 nm to 700 nm. Show.
Further, at an incident angle of 0 deg, the polarization conversion efficiency was very good, almost 1 in the range of 450 nm to 650 nm.
Since the wavelengths of blue, green, and red used in the liquid crystal projector are 400 nm band, 500 nm band, and 675 nm band, respectively, the laminated half-wave plate 20 having the above parameters can be satisfactorily applied to a liquid crystal projector or the like.

FIG. 26 is a diagram showing the conversion efficiency of the laminated half-wave plate 20 of the present invention for wavelengths from 400 nm to 700 nm. The design wavelength λ of each wave plate is 530 nm, and the incident angle is from −10 (deg) to +10 (deg). It is a graph which shows the change of the polarization conversion efficiency for every wavelength at the time of changing to.
The laminated half-wave plate 20 of the present invention has an incident angle dependency. When the incident angle is +10 (deg), the polarization conversion efficiency deteriorates as the wavelength increases. Moreover, when the incident angle is -5 (deg) and the incident angles are -5 (deg) and -10 (deg), the polarization conversion efficiency at low wavelengths is poor, and the polarization conversion efficiency improves as the wavelength increases. ing.
However, as a whole, at a design wavelength of 530 nm, the polarization conversion efficiency is 0.5 or more at each incident angle, and particularly at an incident angle of −10 deg to 5 deg, a high polarization conversion efficiency is obtained at the entire design wavelength range of 400 nm to 700 nm. Show.
Further, at an incident angle of 0 deg, the polarization conversion efficiency was very good, almost 1 in the range of 450 nm to 650 nm.
Since the wavelengths of blue, green, and red used in the liquid crystal projector are 400 nm band, 500 nm band, and 675 nm band, respectively, the laminated half-wave plate 20 having the above parameters can be satisfactorily applied to a liquid crystal projector or the like.
It should be noted that the wavelength band that the laminated half-wave plate should support may be applicable not only to RGB but also to four wavelengths and five wavelengths added with colors of other wavelengths.

FIG. 27 is a diagram illustrating an appearance of a polarization conversion unit incorporating the polarization conversion element according to the embodiment of the present invention.
FIG. 28 is an exploded perspective view of the polarization conversion unit of FIG.
The polarization conversion unit 120 shown in FIGS. 27 and 28 includes a unit frame 200, the polarization conversion element 1 of the present invention, a light shielding plate 210, a lens array 220, and a clip 230. A polarization conversion element 1 having two polarization conversion element bodies to be described later is inserted from one opening surface (lower surface in FIG. 28) side of the unit frame 200, and from the other opening surface (upper surface in FIG. 28) side. The light shielding plate 210 and the lens array 220 are inserted in this order. These optical elements 210 and 220 are sandwiched from four directions by four clips 230 in a state of being accommodated in the unit frame 200. Since the clip 230 is formed of an elastic body, it can be easily attached and detached, and each component of the polarization conversion unit 120 can be easily attached to and detached from the unit frame.
The unit frame 200 allows the polarization conversion element 1 to be placed on the liquid crystal projector in such a posture that the angle at which the light beam from the light source is incident on the polarization conversion element 1 (especially a PBS film described later) is always constant and PS conversion can be performed accurately. Can be incorporated.

FIG. 29 is a diagram showing a liquid crystal projector as an example of a light projecting device to which the polarization conversion element according to the embodiment of the present invention is applied.
A projection display device (liquid crystal projector) 100 shown in FIG. 29 includes a light source 110, a first lens array 111, a polarization conversion unit 120 incorporating the polarization conversion element according to the present invention, and a superimposing lens 121. The illumination optical system is provided. Further, a color light separation optical system 130 including dichroic mirrors 131 and 132 and a reflection mirror 133 is provided. Furthermore, a light guiding optical system including an incident side lens 140, a relay lens 141, and reflection mirrors 142 and 143 is provided. In addition, three field lenses 144, 145, and 146, three liquid crystal light valves 150R, 150G, and 150B, a cross dichroic prism 160, and a projection lens 170 are provided.
The reflection mirror 146 has a function of reflecting the light emitted from the superimposing lens 121 in the direction of the color light separation optical system 130. The color light separation optical system 130 has a function of separating light emitted from the superimposing lens 121 into three color lights of red, green, and blue by two dichroic mirrors 131 and 132. The first dichroic mirror 131 transmits the red light component of the light emitted from the superimposing lens 121 and reflects the blue light component and the green light component. The red light transmitted through the first dichroic mirror 131 is reflected by the reflection mirror 133, passes through the field lens 144, and reaches the liquid crystal light valve 150R for red light. The field lens 144 converts each partial light beam emitted from the superimposing lens 121 into a light beam parallel to the central axis (principal light beam). The same applies to the field lenses 145 and 146 provided in front of the other liquid crystal light valves.

Of the blue light and green light reflected by the first dichroic mirror 131, the green light is reflected by the second dichroic mirror 132, passes through the field lens 145, and reaches the liquid crystal light valve 150G for green light. On the other hand, the blue light passes through the second dichroic mirror 132, passes through the light guide optical system, that is, the incident side lens 140, the reflection mirror 142, the relay lens 141, and the reflection mirror 143, and further passes through the field lens 146. The liquid crystal light valve 150B for blue light is reached.
The light guide optical system is used for blue light because the optical path length of the blue light is longer than the optical path lengths of the other color lights, thus preventing a reduction in light utilization efficiency due to light diffusion or the like. It is to do. That is, this is to transmit the light beam incident on the incident side lens 140 to the field lens 146 as it is.

The three liquid crystal light valves 150R, 150G, and 150B have a function as light modulation means for modulating incident light according to given image information (image signal). As a result, the color lights incident on the three liquid crystal light valves 150R, 150G, and 150B are modulated in accordance with given image information to form images of the respective color lights.
The three colors of modulated light emitted from the three liquid crystal light valves 150R, 150G, and 150B are incident on the cross dichroic prism 160.
The cross dichroic prism 160 has a function as a color light combining unit that combines three colors of modulated light to form a color image. In the cross dichroic prism 160, a dielectric multilayer film that reflects red light and a dielectric multilayer film that reflects blue light are formed in a substantially X shape at the interface of four right-angle prisms. These dielectric multilayer films combine three colors of modulated light to form combined light for projecting a color image. The combined light generated by the cross dichroic prism 160 is emitted in the direction of the projection lens 170. The projection lens 170 has a function of projecting the combined light on the projection screen, and displays a color image on the projection screen.

In addition, by incorporating a polarization conversion unit equipped with the polarization conversion element of the present invention having excellent heat resistance and light resistance as described later, a clear image can be projected for a long time using a light source with high brightness and high heat generation. It can be a liquid crystal projector.
Further, as in the present invention, the polarization conversion element of the present invention includes a retardation plate (laminated half-wave plate) that reliably functions as a half-wave plate in a wide wavelength band. A liquid crystal projector capable of projecting bright and clear images can be realized.

DESCRIPTION OF SYMBOLS 1 Polarization conversion element, 10 PBS array (element main body), 10A element main body, 10C joint surface, 10D light incident surface, 10E light emission surface, 10F edge part, 11 translucent board | substrate, 11A translucent board | plate material, 12 polarized light Separation film, 13 Reflection film, 14 Adhesive layer, 14A Adhesive, 16 Light incident surface, 17 Light exit surface, 20 Wavelength plate, 20A Phase difference plate, 20B Phase difference plate, 20C base, 20C1 base, 20C2 base, 20D position Phase difference portion, 20D1 phase difference portion, 20D2 phase difference portion, 20E tip portion, 20E1 tip portion, 20E2 tip portion, 20F light incident surface, 21 bonding layer, 30 wavelength plate, 31 optical axis, 31A bonding surface, 31A1 boundary portion, 40 Wavelength plate, 91 Polarization separating film, 92 Reflecting film, 93 Adhesive layer, 95 Element body, 96 Bonding layer, 97 Phase difference plate, 98 Translucent substrate, 1 DESCRIPTION OF SYMBOLS 10 Light source, 111 Lens array, 120 Polarization conversion unit, 121 Superimposing lens, 130 color light separation optical system, 131 Dichroic mirror, 132 Dichroic mirror, 133 Reflecting mirror, 140 Incident side lens, 141 Relay lens, 142 Reflecting mirror, 143 Reflecting mirror 144 field lens, 145 field lens, 146 field lens, 146 reflection mirror, 150B liquid crystal light valve, 150G liquid crystal light valve, 150R liquid crystal light valve, 160 cross dichroic prism, 170 projection lens, 200 unit frame, 210 optical element, 210 Shading plate, 220 lens array, 230 clip, 310 optical element, 400 laminate, 410 laminate block, 410A cut surface, 500 polishing Device 600 specimens, 601 test, 601 test pieces, 610 fixed frame, 620 yellowing, 951 light incident surface, 952 light emitting surface, 961 bubbles, 981 corners

Claims (9)

Having a light entrance surface and a light exit surface substantially parallel to each other;
A plurality of translucent substrates bonded via an adhesive layer by a bonding surface having a predetermined inclination angle with respect to the light incident surface or the light emitting surface;
Provided alternately at the boundary between the plurality of translucent substrates, the light incident on the light incident surface is separated into two different types of linearly polarized light whose polarization directions are orthogonal to each other, and one linearly polarized light is transmitted. An optical element having a polarization separation unit that reflects the other linearly polarized light, and a reflection unit that reflects the reflected light beam of the other linearly polarized light and changes the direction of the optical path;
A phase difference plate that is arranged on the light exit surface, rotates one of the two types of linearly polarized light, converts it into a linearly polarized light parallel to the other linearly polarized light, and emits it. And comprising
The adhesive layer is an ultraviolet curable adhesive having a thickness of 5 μm or more and 10 μm or less,
The phase difference plate is the light exit surface, and is disposed in an upper region of the polarization separation unit or an upper region of the reflection unit,
A first wave plate having a phase difference Γ1 with respect to light having a wavelength λ and a second wave plate having a phase difference Γ2 with respect to light having the wavelength λ are arranged so that their optical axes intersect each other. Become
A phase difference plate that converts a polarization plane of incident linearly polarized light into linearly polarized light that is rotated by a rotation angle θ = 90 (deg), and outputs the linearly polarized light.
The following formulas (1) and (2) are satisfied,
Γ1 = 360 (deg) (1)
Γ2 = 180 (deg) (2)
An optical axis azimuth θ1 of the first wave plate and an optical axis azimuth θ2 of the second wave plate satisfy any one of the following conditions 1 to 4. .
Condition 1: θ1 = −16 (deg), θ2 = 45 (deg)
Condition 2: θ1 = 16 (deg), θ2 = 135 (deg)
Condition 3: θ1 = 74 (deg), θ2 = 135 (deg)
Condition 4: θ1 = 106 (deg), θ2 = 45 (deg) The material of the first and second wave plates is an inorganic optical crystal,
The angle formed between the normal line on the main surface of the first wave plate and the crystal optical axis of the inorganic optical crystal is the cutting angle Z1 of the first wave plate,
When the angle formed between the normal line on the main surface of the second wave plate and the crystal optical axis of the inorganic optical crystal is the cutting angle Z2 of the second wave plate,
The polarization conversion element according to claim 1, wherein the cutting angle Z1 is different from the cutting angle Z2. The cutting angle Z1 and the cutting angle Z2 are
Z1 = 27 (deg), Z2 = 18 (deg)
The polarization conversion element according to claim 1, wherein: The retardation plate is
A base part joined to an edge of the optical element along a direction in which the polarization separation part and the reflection part are alternately arranged;
A plurality of retardation portions main bodies formed continuously from the base portion and disposed on the light exit surface side of the polarization separation portion or the reflection portion. The polarization conversion element according to any one of the above. In the polarization conversion element according to any one of claims 1 to 4,
The polarization conversion element, wherein the adhesive layer contains a modified acrylate or a modified methacrylate as a main component. In the polarization conversion element according to any one of claims 1 to 5,
The retardation plate and the light exit surface are joined by a joining layer,
The bonding layer includes a Si skeleton having an atomic structure including a siloxane bond (Si—O), and a leaving group bonded to the Si skeleton,
Of the Si skeleton, a dangling bond of the Si skeleton from which the leaving group is eliminated becomes an active hand and is bonded to the retardation plate and the light exit surface. In the polarization conversion element according to any one of claims 1 to 5,
The translucent substrate and the retardation plate are bonded by a bonding layer,
The bonding layer is formed by bringing the microcrystalline continuous thin film provided on the light transmitting substrate into contact with the microcrystalline continuous thin film provided on the retardation plate, Formed by an atomic diffusion bonding method that causes atomic diffusion at the contact interface and crystal grain boundary of the retardation plate with the microcrystalline continuous thin film, or on either one of the translucent substrate and the retardation plate An atom that causes atomic diffusion at a contact interface and a crystal grain boundary between the microcrystalline continuous thin film and the microcrystalline structure by bringing the microcrystalline continuous thin film provided into contact with the microcrystalline structure provided on either side A polarization conversion element formed by a diffusion bonding method. The polarization conversion element according to any one of claims 1 to 7,
A fixed frame for fixing the polarization conversion element;
A polarization conversion unit comprising: A light source device that emits light;
The polarization conversion unit according to claim 8,
A light modulation device that modulates polarized light from the polarization conversion unit according to image information;
A projection optical device that projects light modulated by the light modulation device;
A projection apparatus comprising:

Images