JP2012255821A - Polarization conversion element, polarization conversion unit and projection type video device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarization conversion element having a compact structure, achieving heat resistance and a long service life and having good conversion efficiency.SOLUTION: A polarization separation element 21 includes a polarization separation part 21B on a surface in an incident side of a light-transmitting substrate 21A, the polarization separation part separating the incident light into P-polarized light P and S-polarized light S, transmitting the P-polarized light P and reflecting the S-polarized light S. A reflection element 22 reflects the S-polarized light S reflected by the polarization separation part 21B, into a direction approximately parallel to an optical path of the P-polarized light P transmitted through the polarization separation part 21B. The reflection element 22 includes: a reflection element substrate 23 comprising a crystal material having birefringence and optical rotation; and a mirror 24 disposed on the reflection element substrate 23. The reflection element substrate 23 includes a quarter-wave plate 23A in which the S-polarized light S is incident thereto is converted into a beam of right-handed circularly polarized light, and the beam is reflected by the mirror 24 into a beam of left-handed circularly polarized light to exit as P-polarized light P.

Description

  The present invention relates to a polarization conversion element, a polarization conversion unit including the polarization conversion element, and a projection video apparatus.

  A projection type video apparatus such as a liquid crystal projector 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 liquid crystal projector, in order to improve the light utilization efficiency, random polarized light emitted from the light source device (light that is mixed with P-polarized light whose polarization planes are orthogonal to each other and S-polarized light and linearly polarized light with various polarization plane directions) A polarization conversion element is used to divide light (hereinafter referred to as random light) into a plurality of intermediate light beams, convert the divided intermediate light beams into one type of linearly polarized light, and emit the light uniformly. Yes.

The polarization conversion element has a structure in which a polarization beam splitter array is formed by alternately arranging polarization separation films and reflection films inside a transparent member, and a phase difference plate is provided on the surface of the polarization beam splitter array. A plurality of retardation plates are arranged at predetermined intervals on the light exit surface side of the transparent member at predetermined intervals (Patent Document 1).
Conventionally, an organic material, for example, a half-wave plate made of a polycarbonate film, may be used as the retardation plate, and the half-wave plate and the polarizing beam splitter array are bonded with an organic adhesive. Yes.
As a method for manufacturing this polarization conversion element, a multilayer body is formed by laminating a plurality of transparent substrates such as colorless and transparent glass each having a polarization separation film and a reflection film formed on both main surfaces. For example, a half-wave plate is attached to the exit surface of the lens array obtained by cutting the surface at an angle of, for example, 45 degrees with an adhesive.
The polarization conversion element manufactured as described above is mounted in an optical engine of a liquid crystal projector in a state of being incorporated in a plane rectangular frame (Patent Document 2).
Instead of providing a retardation plate on the light exit surface side of the transparent member, a quarter-wave plate manufactured using a plastic film obtained by biaxially stretching a polycarbonate film or a polyacrylate film is used as a reflective film with an adhesive. There is a polarization conversion element having a bonded structure (Patent Document 3).

In recent years, with the demand for longer life as an optical component, the problem of adhesive deterioration has arisen. In the conventional examples shown in Patent Documents 1 to 3, since the translucent substrate on which the reflective film is formed and another translucent substrate are bonded and fixed with an adhesive, there is a problem of deterioration of the adhesive.
In order to solve this problem, as a means for joining two light-transmitting substrates such as glass and quartz, a Si skeleton containing a siloxane (Si—O) bond on the surface and having a crystallinity of 45% or less The desorption existing in the vicinity of the surface of the bonding film is formed by a plasma polymerization method and a bonding film including a leaving group composed of an organic group bonded to the Si skeleton, and applying energy to the bonding film There has been proposed a bonding method in which the two light-transmitting substrates are bonded to each other by the adhesiveness developed in the region on the surface of the bonding film by detaching the group from the Si skeleton (Patent Document 4).
By adopting this bonding method, the bonding means is mineralized, the problem of deterioration of the bonding film is solved, and it is possible to extend the life of optical components bonded using the bonding method.
Then, using the bonding technique proposed in Patent Document 4, the first bonding layer is arranged as the uppermost layer using SiO ₂ as an intermediate layer of the polarization separation film made of a multilayer film as a part of the bonding layer. A first light-transmitting substrate on which a first multilayer film is formed, and a second light-transmitting substrate on which a second multilayer film in which a second bonding layer is disposed as an uppermost layer is formed 1. A polarization beam splitter has been proposed in which the first and second bonding layers are integrated by molecular bonding and the first and second multilayer films are stacked to form the polarization separation film. (Patent Document 5).

However, in Patent Document 5, the molecular bonding film formed by the plasma polymerization film is composed of a very thin film of several tens of nm, and this bonding film is formed on the surface of the translucent substrate using the plasma polymerization method. If deposits such as dust and dirt adhere to the surface of the translucent substrate during the process, the deposits are much higher than the thickness of the bonding film. The problem is that translucent substrates cannot be bonded to each other in a predetermined area centered on a certain area, and bubbles or the like are mixed in the area, which has a great adverse effect on optical characteristics, bonding reliability, and product life. There is.
Therefore, the inventors of the present application paid attention to the structure of the polarization conversion element proposed in Patent Document 6. In Patent Document 6, an optical block (polarization conversion element) is configured by mounting optical components such as a PBS (polarization separation element), a mirror, and a half-wave plate in a groove formed on a substrate. Has been. PBS is formed by surface-depositing, for example, a dielectric multilayer film formed by alternately and repeatedly laminating TiO ₂ (high refractive index material) and SiO ₂ (low refractive index material) on a glass plate. It is press-fitted to the substrate at a predetermined angle with respect to the direction. The mirror can reflect incident light by depositing, for example, aluminum or a dielectric multilayer film on a rectangular glass plate. Then, the S wave (S polarized light) separated and reflected by the PBS is mounted on the substrate at an angle at which the S wave is reflected to the emission side. The ½ wavelength plate is formed by attaching a ½ retardation film obtained by uniaxially stretching a polycarbonate, polyvinyl alcohol, or polyethylene terephthalate film to a rectangular glass plate, for example. And it mounts | wears with the position which the S wave (S polarized light) reflected by the mirror injects, converts into P wave (P polarized light), and radiate | emits. In this way, by configuring an optical block with a PBS, a mirror, a half-wave plate, etc., random polarized light including incident P wave (P-polarized light) and S wave (S-polarized light) is converted into P wave (P (Polarized light) can be unified and emitted, and the incident side area and the emission side area of the optical block can be made substantially the same.

By the way, it is well known that quartz has not only birefringence but also optical rotation, and this optical rotation can affect the performance of the quartz wave plate.
To solve this problem, two wave plates made of an optical crystal material having optical rotation ability are laminated so that their crystal optical axes intersect each other at a predetermined angle, and a polarization trajectory is generated using a Poincare sphere. Analyze and configure the birefringence phase difference of both wave plates, the optical axis azimuth angle, the optical rotation power, and the relationship between the angle formed by the rotation axis and the neutral axis to satisfy a predetermined relational expression obtained by an approximate expression. Thus, a quarter-wave plate has been proposed which attempts to reduce the influence of optical rotation and improve characteristics in a wide band (Patent Document 7).
Furthermore, with respect to a single wave plate made of an inorganic material such as quartz, quartz that has birefringence and optical rotation and exhibits sufficient light resistance and reliability against a blue-violet laser with a short wavelength and high output, etc. A quarter-wave plate with excellent optical properties, which is formed of a crystal plate made of an inorganic material and can have an ellipticity optimally, that is, close to a high value of 0.9 or higher or substantially close to 1, has been proposed. (Patent Document 8).
In addition, a half-wave plate made of a quartz substrate is disposed at an angle of 45 °, a wire grid polarizer is disposed on the incident surface side to function as a polarizing beam splitter, and a reflection mirror is disposed on the half-wave plate and the main surface. A polarization conversion element constructed by alternately arranging glass substrates on which a glass substrate is formed (Patent Document 9)

JP 2000-298212 A Japanese Patent No. 3610774 Japanese Patent No. 4191125 Japanese Patent No. 4337935 JP 2010-60770 A Republished WO98 / 23993 JP-A-2005-158121 JP 2010-134414 A JP 2004-029168 A

However, in the conventional polarization conversion element proposed in Patent Document 6, PBS is formed by alternately and repeatedly laminating TiO ₂ (light refractive index material) and SiO ₂ (low refractive index material) on the surface of a glass plate. Since the polarization separation film is formed by vapor-depositing a dielectric multilayer film, etc., not only there is a risk of peeling at the interface between the glass substrate and the polarization separation film due to thermal distortion caused by the difference in thermal expansion coefficient. Also, heat dissipation on the glass plate is limited, and it is not possible to sufficiently satisfy the demand for high heat resistance and long life.
Here, in consideration of the heat dissipation effect, it is conceivable to use a quartz plate instead of the glass plate for PBS. However, since quartz has not only birefringence but also optical rotation, it is simply a glass plate. If is replaced with a quartz plate, the optical rotation problem cannot be solved.
Patent Document 7 solves the problem of optical rotation in a quarter-wave plate, but it does not relate to a reflective element that constitutes a polarization conversion element. Have difficulty.
By simply applying the technical ideas described in Patent Document 7 and Patent Document 8 to Patent Document 9 as they are, it is difficult to solve the following problems raised by the present inventors. There was found.

Therefore, the inventors of the present application applied the technical idea related to optical rotation compensation that has been attempted in the conventional examples as shown in Patent Document 7 and Patent Document 8 focusing on the effect of optical rotation on the phase difference. An attempt was made to try to realize a polarization conversion element capable of causing an optical action to rotate the incident polarization plane of P-polarized light by 90 deg to convert it to S-polarized light and to emit it.
That is, first, the technique proposed in Patent Document 7 and Patent Document 8 for the optical design of the quartz half-wave plate disposed at an inclination of 45 deg so as to be sandwiched between the stacked interfaces of the prism array (polarizing beam splitter array). Applying the idea will be considered based on FIG.
In this case, the translucent substrate holding the quartz half-wave plate is a general glass material, and the refractive index n1 = 1.53 of the glass material and the refractive index n2 = 1.54 of the crystal Therefore, the optical path (optical axis) of the light transmitted through the prism array is the interface between the glass and the quartz half-wave plate when the light enters the quartz half-wave plate, and the light is Refraction hardly occurs at the interface between the quartz half-wave plate and the glass when emitted from the quartz half-wave plate, that is, the optical path (optical axis) hardly changes, and the light is polarized. Will be transmitted.
In FIG. 53, the optical axis direction viewed from the normal line PL of the main surface (incoming and outgoing surfaces) of the quartz half-wave plate WP is θ _0, and the light ray R1 traveling in the quartz half-wave plate WP If the optical axis orientation with respect to is θ ₁ and the angle between the normal line PL of the principal surface of the quartz half-wave plate WP and the light ray R 1 is θ ₂ , these angles have the following relationship.
θ ₀ = atan (tan θ ₁ × cos θ ₂ ) (A1)
At this time, since θ ₁ = 45 deg and θ ₂ = 45 deg, θ ₀ is
θ ₀ = atan (tan (45 deg) × cos (45 deg))
= Atan (1/2 ^1/2 )
= 35.3deg
And calculated.
However, a quartz half-wave plate as proposed in Patent Document 9 is disposed with an inclination of 45 deg, and a polarization separation unit composed of a wire grid polarizer, a dielectric multilayer film, or the like is disposed on the incident surface side. In a polarization conversion element configured by functioning as a polarization beam splitter and inclining a reflection part at 45 deg so as to be parallel to the half-wave plate and alternately arranging these in order, There is no glass that sandwiches the half-wave plate, and what is in contact with the quartz half-wave plate is air. That is, from the relationship between the refractive index n0 = 1.00 of air and the refractive index n2 = 1.54 of quartz, the optical path (optical axis) of the light transmitted through the polarization conversion element is 1/2 wavelength made of quartz. Refraction occurs at the interface between the air and the quartz half-wave plate when entering the plate, and at the interface between the quartz half-wave plate and the air when light exits from the quartz half-wave plate. Therefore, the optical path (optical axis) changes.
θ ₀ = atan (tan θ ₁ × cos θ ₂ ) (A1)
At this time, since θ ₁ = 45 deg and θ ₂ = 27.2 deg, θ ₀ is
θ ₀ = atan (tan (45 deg) × cos (27.2 deg))
= Atan (1 x 0.88941)
= 41.65deg
Therefore, when the quartz half-wave plate is inclined to 45 deg and is in contact with air, the quartz crystal 1 is refracted on the optical axis of the incident light at the interface with the incident / exit surface of the quartz half-wave plate. As a result of studying the optical design of the / 2 wavelength plate, the following specifications were obtained.
Design wavelength 520 nm
Design phase difference 460.11 deg
Optical axis direction 41.65 deg
Cutting angle 90 deg
The cutting angle is defined as the angle formed between the normal line of the principal surface of the quartz half-wave plate and the crystal optical axis. The design phase difference is defined as a design phase difference when light having a design wavelength λ is incident from a direction parallel to the normal line of the main surface of the quartz half-wave plate. The optical axis azimuth (θ ₀ ) is the polarization plane (polarization plane) of the linearly polarized light and the crystal optical axis when viewed from the normal line of the main surface (input / output surface) of the quartz half-wave plate It is defined by the angle between
The relationship between the wavelength of the quartz half-wave plate and the polarization conversion efficiency in this case is shown as a design value in the graph of FIG.
When the distance of the optical path inside the quartz half-wave plate is t1, the phase difference Γ of the light transmitted through the quartz half-wave plate through the optical path is calculated by the following relational expression. The
Γ1 = 2π / λ × (ne-no) × t1
In this equation, the length t1 of the optical path is obtained so that Γ1 = 180 deg, the thickness to in the normal direction of the principal surface of the quartz half-wave plate is obtained, and the position at the design wavelength λ in the normal direction is obtained. A phase difference Γo is calculated.
Γo = 2π / λ × (ne-no) × to
cos (θ2) = to / t1
to = t1 × cos (θ2)
Γo = 2π / λ × (ne−no) × t1 × cos (θ2)
This Γo is defined as a design phase difference, and here, Γo = 160.11 (deg).
By the way, a quartz half-wave plate is obtained by cutting a quartz lambert obtained by shaping (Lambert processing) a quartz crystal using a wire saw or the like at a predetermined cutting angle as a design value. Manufactured separately in pieces.
However, in this manufacturing process, if the wafer is cut from the crystal lambert at an incorrect cutting angle or is cut at a cutting angle exceeding the allowable range, if the wafer is processed with the thickness of the above-described design plate thickness to, As shown in Table 1, there is a problem that the design phase difference Γo is shifted, that is, Γo ≠ 160.11 deg, and all the quartz half-wave plates are defective.

If the cutting angle is shifted from the design value of 90 deg to 80 deg and the cutting is performed with the design plate thickness to without considering the angle deviation, the design phase difference Γo is 160.11 deg. The phase difference greatly deviates from 175.50 deg.
This is because the extraordinary refractive index ne and the ordinary refractive index no depend on the cutting angle in the formula Γo = 2π / λ × (ne−no) × to, and these values change according to the cutting angle. Because it does.
Therefore, the phase difference Γ of the light transmitted through the distance t1 of the optical path inside the quartz half-wave plate disposed at an inclination of 45 deg is greatly deviated from 180 deg.
As a result, the polarization conversion efficiency changes greatly as shown in FIG. 54, and there is a problem that the polarization conversion efficiency is greatly lowered and deteriorated in a wavelength band of 550 nm or less.

  Therefore, an object of the present invention is to adjust the plate thickness in accordance with the angle deviation even in the case where the crystal material having birefringence and optical rotation such as quartz is cut out of the design value. The polarization conversion element having a quarter-wave plate that can be adjusted to an optimal design plate thickness to review the design phase difference and ensure that the polarization conversion efficiency in a predetermined wavelength band is equal to or greater than a specified value. It is to realize a polarization conversion unit and a projection type video apparatus.

[Application Example 1]
The polarization conversion element according to this application example includes a translucent substrate disposed so as to form a predetermined angle with respect to the incident light, and a first surface orthogonal to the incident light on the incident-side surface of the translucent substrate. A polarization separation unit that separates linearly polarized light into second linearly polarized light, transmits the first linearly polarized light, and reflects the second linearly polarized light; and an air layer that is substantially parallel to and between the translucent substrate. A reflective element that is disposed through the second linearly polarized light reflected by the polarization separating unit and reflects in a direction substantially parallel to the optical path of the first linearly polarized light that has passed through the polarized light separating unit. The reflective element includes a reflective element substrate made of a crystal material having birefringence and optical rotation, and a mirror provided on the reflective element substrate, and the reflective element substrate is incident The second linearly polarized light is converted into first circularly polarized light, and the first circularly polarized light is converted into the mirror. In reflected as a second circular polarization of the reverse rotation, characterized in that it is a wavelength plate for emitting converts the second circular polarization to a first linearly polarized light.
In this application example having this configuration, the lens array is composed of a polarization separation element having a polarization separation portion provided on a light-transmitting substrate and a reflection element having a mirror provided on a reflection element substrate. A transparent member such as glass provided between them is unnecessary, and the structure becomes compact.
Moreover, as the reflective element substrate of the reflective element, a crystalline material having a higher thermal conductivity than glass is used, and an air layer is formed between the reflective element and the translucent substrate. Heat dissipation effect is high, and heat resistance and long life can be achieved.
And since the crystal material has birefringence and optical rotation, the vibration surface of linearly polarized light propagating in the direction of the optical axis is twisted as light advances, and the polarization state changes and polarization conversion efficiency decreases. However, in this application example, since the wave plate that converts linearly polarized light into circularly polarized light is used for the reflective element substrate, the incident second linearly polarized light is converted into circularly polarized light that rotates to the left or right. The circularly polarized light is reflected by the mirror as circularly polarized light that rotates to the left or right, and then exits as the first linearly polarized light. Can be eliminated.

[Application Example 2]
In the polarization conversion element according to this application example, the reflective element substrate is formed of a single phase difference plate, the optical axis direction viewed from the normal line of the reflective element substrate is θ ₀ , and the reflective element substrate The optical axis orientation with respect to the light beam traveling in the direction is θ ₁ , the angle formed by the optical path of the light beam and the normal line of the crystal optical axis is θ ₂ , the refractive index of the reflective element substrate is n _c , When the refractive index of the layer adjacent to the substrate and n _a, the optical axis azimuth theta ₀ is
θ ₀ = atan (tan θ ₁ × cos θ ₂ ) (A1)
n _a sin α = n _c sin θ ₂ (A2)
It is obtained from the formula of
In this application example having this configuration, when the reflective element substrate is composed of one sheet, a polarization conversion element with good conversion efficiency can be easily provided.

[Application Example 3]
In the polarization conversion element according to this application example, the reflection element substrate includes two retardation plates, a first phase difference plate and a second phase difference plate, and the first element viewed from the normal line of the reflection element substrate. The optical axis direction of one phase difference plate is θ ₀₁ , the optical axis direction with respect to a light beam traveling in the first phase difference plate is θ ₁₁ , and the angle formed by the normal line of the light beam and the crystal optical axis is θ _21. and the refractive index of the first retardation plate n _c1, the refractive index of the layer adjacent to the first phase difference plate and n _a,
The optical axis direction θ ₀₁ of the first retardation plate is
θ ₀₁ = atan (tan θ ₁₁ × cos θ ₂₁ ) (A11)
n _a sin α = n _c1 sin θ ₂₁ (A21)
From the formula of
The optical axis direction of the second retardation plate viewed from the normal line of the reflecting element substrate is θ _02, and the optical axis direction with respect to the light beam traveling through the second retardation plate is θ _12. The angle between the normal of the optical axis is θ ₂₂ , the refractive index of the second retardation plate is n _c2 , and the refractive index of the first retardation plate adjacent to the second retardation plate is n _c1. ,
The optical axis direction θ ₀₂ of the second retardation plate is
θ ₀₂ = atan (tan θ ₁₂ × cos θ ₂₂ ) (A12)
n _C1 sinα = n _c2 sinθ ₂₂ (A22)
It is obtained from the formula of
In this application example having this configuration, it is possible to easily provide a polarization conversion element with good conversion efficiency when the reflection element substrate is formed of two retardation plates.

[Application Example 4]
In the polarization conversion element according to this application example, the translucent substrate is made of a crystal material having birefringence and optical rotation, and passes through the polarization separation unit and is incident on the translucent substrate. The polarized light is emitted from the emission side surface of the translucent substrate while maintaining the polarization plane of the first linearly polarized light.
In this application example having this configuration, the translucent substrate is also made of a crystalline material having a higher thermal conductivity than that of glass. Therefore, the heat dissipation effect is higher than in the conventional case, and heat resistance and longer life can be achieved.

[Application Example 5]
The polarization conversion element according to this application example is characterized in that the predetermined angle is approximately 45 (deg) or 135 (deg).
In this application example having this configuration, the polarization separation unit can reflect the second linearly polarized light toward the reflecting element at a substantially right angle with respect to the incident light. Therefore, the light beam reflected by the reflecting element is reflected on the first straight line. It can be reflected in a direction substantially parallel to the optical path of polarized light.

[Application Example 6]
The polarization conversion element according to this application example is characterized in that the crystal material is quartz.
In this application example having this configuration, a polarization conversion element can be provided at a low cost by using a crystal that can be obtained at a lower cost than a crystal material such as sapphire.

[Application Example 7]
The polarization conversion unit according to this application example includes the polarization conversion element having the above-described configuration and a holding member that holds the polarization conversion element, and the holding member includes both end portions of the reflective element substrate and the light transmitting member. It has a pair of holding | maintenance board which hold | maintains the both ends of a property board | substrate, respectively, and a pair of connection board which each connects the both ends of the said pair of holding | maintenance board.
In this application example having this configuration, since the polarization separation element and the reflection element configured to include the translucent substrate and the polarization separation unit can be compactly accommodated in the holding member, handling becomes convenient.

[Application Example 8]
In the polarization conversion unit according to this application example, the pair of holding plates and the pair of connecting plates are integrally formed, and the translucent substrate and the reflective element are formed on portions of the pair of holding plates facing each other. Guide grooves are provided for guiding the substrates, respectively, and the guide grooves are respectively opened on one side of the pair of holding plates.
In this application example having this configuration, the polarization conversion unit can be assembled simply by inserting the polarization separation element and the reflection element along the guide grooves, respectively, so that assembly work is facilitated.

[Application Example 9]
The polarization conversion unit according to this application example is formed separately from the pair of holding plates and the pair of connecting plates, and the pair of connecting plates engages the pair of holding plates in a direction facing each other. It has a piece.
In this application example having this configuration, the pair of connecting members urge the pair of holding members in directions close to each other to securely hold the polarization separation element and the reflection element. Can be prevented from falling off from the polarization separation unit.

[Application Example 10]
The projection type video apparatus according to this application example attempts to project a light source, a polarization conversion element that converts the light from the light source into the second linearly polarized light and emits the light, and the light emitted from the polarization conversion element. A light modulation unit that modulates light according to image information to be projected, and a projection optical system that projects light modulated by the light modulation unit, and the polarization conversion element is a polarization conversion element having the above-described configuration. Features.
In this application example having this configuration, since the polarization conversion efficiency of the polarization conversion element is high, it is possible to provide a projection type video apparatus with high projection accuracy.

[Application Example 11]
The projection type video apparatus according to this application example is characterized in that the light modulation means is a liquid crystal panel.
In this application example having this configuration, it is possible to provide a liquid crystal projector capable of achieving the above-described effects.

1 is a schematic diagram of a polarization conversion element according to a first embodiment of the present invention. Schematic of the quarter wave plate which comprises a reflective element. Schematic which shows the Poincare sphere for demonstrating the principle of FIG. The figure for demonstrating the optical axis direction of a quarter wavelength plate. (A) is a graph showing the relationship between the cutting angle Z and the design wavelength λ, and (B) is a graph showing the relationship between the cutting angle Z and the plate thickness to. The graph which shows the polarization conversion efficiency of the quarter wavelength plate of 1st Embodiment. FIG. 4A is an end view of a crystal plate constituting a polarization separation element, and FIG. 4B is a front view showing a part of the crystal plate. The relationship of the optical axis direction in a quartz wavelength plate, plate | board thickness, and a cutting angle is shown, (A) is an end elevation, (B) is a perspective view. Schematic which shows the Poincare sphere for demonstrating the principle of FIG. Schematic for demonstrating refraction angle (phi). The schematic diagram of a translucent board | substrate in case the cutting angle q is 0 deg. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 0 deg. The schematic diagram of a translucent board | substrate in case the cutting angle q is 15deg. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 15 degrees. The schematic diagram of a translucent board | substrate in case the cutting angle q is 30 degrees. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 30 degrees. The schematic diagram of a translucent board | substrate in case the cutting angle q is 45 degrees. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 45 deg. The schematic diagram of a translucent board | substrate in case the cutting angle q is 60deg. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 60 degrees. The schematic diagram of a translucent board | substrate in case the cutting angle q is 75deg. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 75 degrees. The schematic diagram of a translucent board | substrate in case the cutting angle q is 90deg. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 90 deg. The schematic diagram of a translucent board | substrate in case the cutting angle q is 105 degrees. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 105 degrees. The schematic diagram of a translucent board | substrate in case the cutting angle q is 120 degrees. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 120 deg. The schematic diagram of a translucent board | substrate in case the cutting angle q is 135 degrees. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 135 deg. The schematic diagram of a translucent board | substrate in case the cutting angle q is 150 degrees. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 150 deg. The schematic diagram of a translucent board | substrate in case the cutting angle q is 165deg. The graph which shows 0 degree direction intensity | strength (transmission characteristic) in case the cutting angle q is 165deg. The graph which shows the relationship between the crossing angle x and the maximum value y of plate | board thickness yo permitted. (A) is a schematic diagram showing a state where the crossing angle x is −90 deg, (B) is a schematic diagram showing a state where the crossing angle x is −45 deg, and (C) is a schematic diagram showing a state where the crossing angle x is 0 deg. Schematic of the polarization conversion element concerning 2nd Embodiment of this invention. The figure for demonstrating the optical axis direction of a quarter wavelength plate. The figure for demonstrating the optical axis direction of the quarter wavelength plate of the example different from the quarter wavelength plate of FIG. 38A is a graph showing the relationship between the cutting angle Z and the design wavelength λ, and FIG. 38B is a graph showing the relationship between the cutting angle Z and the plate thickness to. . 39A is a graph showing the relationship between the cutting angle Z and the design wavelength λ, and FIG. 39B is a graph showing the relationship between the cutting angle Z and the plate thickness to. . The graph which shows the polarization conversion efficiency of the quarter wavelength plate shown by FIG. The graph which shows the polarization conversion efficiency of the quarter wavelength plate shown by FIG. Schematic of the polarization conversion element concerning 3rd Embodiment of this invention. The schematic block diagram of the liquid-crystal projector in which 4th Embodiment of this invention was integrated. The perspective view which shows the polarization conversion unit concerning 4th Embodiment. (A) is a top view of a holding member, (B) is sectional drawing of a holding member. The disassembled perspective view which shows a part of holding member. The perspective view which shows the polarization conversion unit concerning 5th Embodiment of this invention. The disassembled perspective view which shows a part of holding member. The perspective view of the polarization splitting element concerning 6th Embodiment of this invention. Schematic of the polarization conversion element concerning the modification of this invention. The figure for demonstrating the optical axis azimuth | direction of the crystal | crystallization half wavelength plate which is a premise of this invention. The graph which shows the polarization conversion efficiency of the translucent board | substrate of a prior art example.

Embodiments of the present invention will be described with reference to the drawings. Here, in each embodiment, the same component is denoted by the same reference numeral, and description thereof is omitted or simplified.
1 to 36 show a first embodiment.
FIG. 1 shows an outline of the first embodiment.
In FIG. 1, the polarization conversion unit 1 of the first embodiment includes a polarization conversion element 2 and a holding member 3 that holds the polarization conversion element 2. The holding member 3 is a flat rectangular plate made of, for example, synthetic resin.
The polarization conversion element 2 includes polarization separation elements 21 and reflection elements 22 arranged alternately. One end of each of the polarization separation elements 21 and the reflection elements 22 is fitted into a recess (not shown) of the holding member 3. Are combined.
In FIG. 1, a plurality of, for example, two polarization separation elements 21 and two reflection elements 22 are arranged on the left and right sides of the center of the holding member 3, and among these, the polarization separation elements are arranged on the left side with respect to the center. 21 and the reflection element 22 and the polarization separation element 21 and the reflection element 22 arranged on the right side are arranged symmetrically with respect to the center.

The polarization separation element 21 includes a translucent substrate 21A arranged such that the incident-side main surface and the emission-side main surface form a predetermined angle with respect to the incident light IL, in this embodiment, 45 deg. The incident light IL is separated from the incident-side surface of the substrate 21A into P-polarized light P that is first linearly polarized light and S-polarized light S that is second linearly polarized light, and P-polarized light P is transmitted. The surface of the polarization separation unit 21B that reflects the S-polarized light S and the main surface opposite to the main surface on the side on which the incident light IL of the translucent substrate 21A on which the polarization separation unit 21B is disposed (on the emission side) The main surface) has antireflection portions 21C provided respectively.
The translucent substrate 21A is formed in a planar rectangular plate shape from quartz having birefringence and optical rotation.
The polarization separation unit 21B includes, for example, a low refractive index layer made of silicon oxide (SiO ₂ ) and a high refractive index layer made of alumina oxide (Al ₂ O ₃ ), for example, in a predetermined order and an optical film thickness. It is composed of a dielectric multilayer film which is optically in-plane uniform.
The antireflection portion 21C is formed, for example, by depositing a material such as a dielectric multilayer film in which silicon dioxide and titanium oxide are alternately laminated in sequence.

The reflection element 22 includes a reflection element substrate 23 made of a crystal material having birefringence and optical rotation, and a plate-like mirror 24 provided on the reflection element substrate 23 at a predetermined interval. The reflective element substrate 23 and the mirror 24 are arranged in parallel with each other and in parallel with the polarization separation element 21. The mirror 24 includes a crystal plate 24A and a reflective film 24B provided on a surface of the crystal plate 24A facing the reflective element substrate 23. The reflective film 24B is formed of a multilayer film formed by evaporating a material such as silicon dioxide or titanium oxide.
The reflective element substrate 23 includes a quarter-wave plate 23A having a thickness of m and antireflection portions 23B provided on both surfaces of the quarter-wave plate 23A. The antireflection portion 23B has the same structure as the antireflection portion 22B of the polarization separation element 21.
The principle of the quarter wavelength plate 23A will be described with reference to FIGS.
FIG. 2 shows an outline of the quarter-wave plate 23A, and FIG. 3 shows a Poincare sphere for explaining the principle of FIG. FIG. 2 shows an outline for explaining the optical path of the quarter-wave plate 23A and an outline viewed from the normal line of the quarter-wave plate 23A.

In FIG. 2, S-polarized light S incident at an incident angle α of 45 deg from one main surface 23a of the quarter-wave plate 23A is converted into circularly-polarized light that rotates to the right with a phase difference = 90 deg and is ¼ wavelength. The light is emitted from the other main surface 23b of the plate 23A. The emitted clockwise circularly polarized light is reflected by the reflection mirror 24B, becomes circularly polarized light whose rotation direction is reversed, and is incident on the other main surface 23b of the quarter-wave plate 23A again. The circularly polarized light whose rotation direction is counterclockwise is converted into P-polarized light P with a phase difference = 90 deg, and is emitted from one main surface 23a of the quarter-wave plate 23A. In FIG. 2, the optical axis azimuth with respect to the forward path of the ray T1 traveling through the 1/4-wave plate 23A is shown as theta _1, the optical axis azimuth with respect to the return path of the ray T1 traveling through the 1/4-wave plate 23A is It is shown as theta _'1. The angle formed by the normal line PL orthogonal to the main surface of the quarter-wave plate 23A and the crystal optical axis PO is the cutting angle q. In this embodiment, the cutting angle q is 90 degrees.

The principle of the above optical action will be described using the Poincare sphere shown in FIG. FIG. 3 shows a case where a light beam is incident along a normal to the main surface of the quarter wave plate.
3, first, forward of the rotating shaft by turning the equator the S1 axis only 2 [Theta] ₁ becomes R1 axis. In the quarter wave plate 23A according to the present embodiment, the optical axis direction θ ₁ is 45 deg (θ ₁ = 45 deg), and the position of the optical axis R1 (outward path) on the Poincare sphere is 2θ from the S1 axis on the equator. ₁ = 90 deg. S-polarized light S incident on the quarter-wave plate 23A becomes clockwise circularly polarized light with a phase difference = 90 deg. That is, as shown in FIG. 3, first, in the forward path, the linearly polarized light (S-polarized light S) incident from the point P1 of the S1 axis is rotated from the point P1 by a phase difference = 90 deg. Move to the point P2, which is the North Pole. When the circularly polarized light beam R1 is reflected by the mirror 24, the rotational direction of the circularly polarized light is reversed. Accordingly, since the light is circularly polarized light whose rotation is reversed on the return path, the point P2 is converted to the point P3 which is the south pole of the Poincare sphere, and the optical axis direction θ1 ′ is
θ1 ′ = 180 deg−θ1 = 180−45 = 135 deg
Because
2θ ₁ ^′ = 2 × 135 = 270 deg
It becomes.
The optical axis R2 on the return path has an optical axis direction θ ′ ₁ of 135 deg (θ ′ ₁ = 135 deg), and the position of the optical axis on the Poincare sphere is located at 2θ ₁ = 270 deg from the S1 axis on the equator. , R2.
As shown in FIG. 3, when the phase difference is rotated by 90 deg about the R2 axis as a rotation axis, the light emitted from the quarter wavelength plate 23A follows the trajectory from the point P3 which is the south pole to the point P4. P.

Here, in the present embodiment, since the normal line PL of the quarter-wave plate 23A and the direction of the light beam traveling inside do not match, the actual optical axis direction θ ₀ is not 45 deg.
FIG. 4 is a diagram for explaining the optical axis orientation of the quarter-wave plate.
In FIG. 4, the optical axis orientation viewed from the normal line of the quarter-wave plate 23A is θ ₀ , the optical axis orientation with respect to the light beam Q1 traveling through the quarter-wave plate 23A is θ ₁ , and the crystal optical axis PO is When the angle between the normal line PL and light Q1 and theta _2, the following relationship holds true for these angles.
θ ₀ = atan (tan θ ₁ × cos θ ₂ ) (A1)
Furthermore, the layer adjacent the refractive index of 1/4-wave plate 23A and _n c, 1/4-wavelength plate 23A and the air layer, when the refractive index of air and _{n a,} refraction at 1/4-wave plate 23A Since the angle is θ ₂ , the following relationship is established by Snell's method.
n _a sin α = n _c sin θ ₂ (A2)
In this embodiment, 1/4 is the refractive index nc of the crystal which is a material of the wave plate 23A is 1.54, the refractive index _{n c} of the air is 1.00, the incident angle α is 45 deg, wherein From (A2), θ ₂ is 27.2 deg.
Furthermore, since θ ₂ is 27.2 deg and θ ₁ is 45 deg, θ ₀ is 41.7 deg from equation (A1). Further, in the present embodiment, the quarter wavelength plate 23A is designed to have a plate thickness m of 0.014 mm, a wavelength of 520 nm, and a phase difference of 80 deg.

In the present embodiment, the ¼ wavelength plate 23A is a single plate A type, and the incident angle to the ¼ wavelength plate 23A is centered at 45 (deg) and ± 10 (deg) from the center. When tilting at an angle in the range of degrees, the polarization conversion efficiency when the incident angle is changed in 5 (deg) steps is analyzed by simulation, and the polarization conversion efficiency in a predetermined wavelength band is averaged in the wavelength band The average transmission loss at the average polarization conversion efficiency was evaluated. That is, the transmission characteristics when the polarization conversion element according to this embodiment is mounted on a projection type video apparatus,
M: Transmission loss within 10% in the 500-600nm band,
N: In the 400 to 700 nm band, the transmission loss is set to a standard of 20% or less, and the design conditions are set to satisfy these two M and N standards.
In the A type, the following condition (A) is satisfied.
Condition (A): When the design wavelength is λ, the thickness of the quarter-wave plate 23A is to, and the cutting angle of the inorganic crystal material constituting the quarter-wave plate 23A is Z, the design wavelength λ and the cutting angle Z The relation of the plate thickness to satisfies the expressions (1), (2), (3), and (4).
λ ≤-0.1186 × Z ² + 20.288 × Z- 226.56 (1)
^{λ ≧ 0.1089 × Z 2 - 18.802} × Z + 1265.4 ··· (2)
^{to ≦ 3E-06 × Z 2} - 0.0003 × Z + 0.0209 ··· (3)
^{to ≧ 9E-06 × Z 2} - 0.0013 × Z + 0.0626 ··· (4)
Expressions (1) and (2) show the relationship between the design wavelength λ and the cutting angle Z. Of these, Expression (1) is an upper limit relational expression, and Expression (2) is a lower limit relational expression. . Equations (3) and (4) show the relationship between the cutting angle Z and the plate thickness to, and of these, Equation (3) is the upper relationship, and Equation (4) is the lower relationship. It is.
Table 2 shows the result of analyzing the polarization conversion efficiency by simulation, and shows the relationship between the cutting angle Z and the design wavelength λ and the relationship between the cutting angle Z and the plate thickness to. The relationship between the cutting angle Z and the design wavelength λ is also shown in FIG. 5A, and the relationship between the cutting angle Z and the plate thickness to is also shown in FIG.

From Table 2 and FIGS. 5A and 5B, the range of the design wavelength λ and the cutting angle Z for satisfying the transmission characteristics is
455 ≦ λ ≦ 640 (nm)
65 ≦ Z ≦ 110 (deg)
It is.
If the design wavelength λ and the cutting angle Z are designed so that the relation (3) which is the upper limit relational expression and the expression (4) which is the lower limit relational expression are satisfied, for example, FIG. As described above, the standards M and N of the transmission characteristics (transmission loss) can be satisfied.

FIG. 6 shows the polarization conversion efficiency of the designed quarter wavelength plate 23A as described above. In FIG. 6, the horizontal axis indicates the wavelength, the vertical axis indicates the polarization conversion efficiency, and the incident angle α is set to 35 deg, 40 deg, 45 deg, 50 deg, and 55 deg. The polarization conversion efficiency of the P-polarized light P emitted from the quarter-wave plate 23A is shown. At these incident angles α, there is no significant difference in polarization conversion efficiency, and in FIG. 6, data at incident angles α from 35 deg to 55 deg are included in the thick curve L.
As shown in FIG. 6, the polarization conversion efficiency shows a value of 0.7 or more from a wavelength of 400 nm to 700 nm, and particularly shows a high value of 0.9 or more from a wavelength of 450 nm to 650 nm.

A schematic configuration of the translucent substrate 21A is shown in FIG. FIG. 7A is a schematic view of the translucent substrate 21A viewed from the end surface, and FIG. 7B is a front view showing a part of the translucent substrate 21A.
In FIG. 7A, the translucent substrate 21A has a plate thickness yo, and incident light IL is incident and transmitted as outgoing light OL. Incident light IL is incident within a divergence angle + α to −α. Corresponding to the incident light IL, the outgoing light OL is also emitted in the range of the divergence angle + α to −α.
The angle formed between the normal line PL orthogonal to the main surface of the translucent substrate 21A and the crystal optical axis PO is the cutting angle q.
The angle formed by the crystal optical axis PO of the translucent substrate 21A and the optical axis of the incident light IL is the intersection angle x.

Since the translucent substrate 21A of the polarization separation element 21 is a quartz plate having birefringence and optical rotation, it is necessary to design the polarization conversion efficiency of the outgoing light OL with respect to the incident light IL.
The process leading to the design will be described with reference to FIGS. 8A and 8B show the relationship between the optical axis orientation, the plate thickness, and the cutting angle in the quartz wavelength plate. FIG. 8A is an end view, and FIG. 8B is a perspective view.
In general, parameters for designing a wave plate made of quartz include an optical axis azimuth θ, an optical rotation set by a cutting angle q, and a phase difference Γ set by a plate thickness yo. Here, as shown in FIG. 7 defined by the Poincare sphere, the present inventors set the crystal optical axis PO, and studied the configuration of the crystal plate in which no phase difference Γ due to linear birefringence occurs, Furthermore, the application of an optical element, in which the phase difference 2ρ due to circular birefringence, that is, so-called rotation of polarized light due to optical rotation, is suppressed, to the polarization conversion element was studied.
When the angle between the projection optical axis obtained by projecting the crystal optical axis PO of the crystal plate on the plane perpendicular to the optical axis of the incident light IL and the plane of polarization of the P-polarized light P is defined as the azimuth angle θ, θ = 0 (deg) When the crystal plate is arranged so that the linear birefringence phase difference Γ is zero.
The azimuth angle θ was fixed at 0 (deg), and the degree of influence on the phase difference Γ ′ (corresponding to the plate thickness yo) by 2q corresponding to the optical rotation power was repeatedly evaluated and verified by simulation and experiment.
FIG. 9 shows a schematic configuration of a Poincare sphere for explaining a polarization state.
In FIG. 9, first, the position of the polarization of the linearly polarized light P1 is set on the S1 axis and on the equator. The S1 axis is rotated on the equator by 2θ to become the R1 axis, this R1 axis is raised by the cutting angle 2q to be the R2 axis, and this R2 axis is rotated by an angle corresponding to the phase difference Γ, and P1 becomes P2. The optical axis azimuth θ, the cutting angle q, and the phase difference Γ are adjusted so that this P2 has a desired polarization state.

In the present embodiment, the cutting angle q is defined as an angle formed between the normal line PL and the crystal optical axis PO with respect to the main surface of the translucent substrate 21A.
For each translucent substrate (quartz plate) cut out at each cutting angle, the value of Γ ′ acting on the incident light IL (P-polarized light) was evaluated.

When the incident light IL enters the translucent substrate 21A, the incident light IL is refracted and travels through the translucent substrate 21A. And when it radiate | emits from 21 A of translucent board | substrates, it will radiate | emit as emitted light refracted in the direction parallel to the optical axis of incident light IL. Here, as shown in FIG. 10, the incident light IL is refracted at a refraction angle φ when it enters the translucent substrate 21 </ b> A.
The inventors of the present application make the refraction angle φ refracted when incident light enters the translucent substrate 21A, the optical axis of the light traveling in the actual translucent substrate 21A and the crystal optical axis PO. The angle β was determined, and experiments and evaluations were performed focusing on the fact that the optical rotation 2q changes according to β.

The relationship between the cutting angle q and the transmission characteristics of the translucent substrate 21A will be described.
FIG. 11 is a schematic diagram of the light-transmitting substrate when the cutting angle q is 0 deg. FIG. 12 is a graph showing the 0-degree direction strength as the transmission characteristic in that case. In FIG. 12, the incident angle of the incident light IL is 0 deg. Since the main surface of the translucent substrate 21A is disposed with an inclination of 45 deg with respect to the incident angle, the normal line orthogonal to the main surface of the translucent substrate 21A is 135 deg. On the other hand, the crystal optical axis PO is set to 135 deg as apparent from FIG. Therefore, in FIG. 11, the cutting angle q is 0 deg.
In FIG. 12, when the divergence angle α is −10 deg, −10, when the divergence angle α is −5 deg, α-5, when the divergence angle α is 0 deg, α0, when the divergence angle α is +5 deg, α + 5, and divergence. The case where the angle α is +10 deg is displayed as α + 10. The same applies to other figures corresponding to FIG.
12, α0, α + 5, and α + 10 have a high 0 degree direction intensity (transmission characteristics) of 0.9 or higher, but α-10 and α-5 have a 0 degree direction intensity of less than 0.8 depending on the wavelength. In some cases.

FIG. 13 is a schematic diagram of a translucent substrate when the cutting angle q is −10 deg. FIG. 14 is a graph showing the 0-degree direction strength in that case.
In FIG. 14, α-5, α0, α + 5, and α-10 have a high 0 degree direction intensity (transmission characteristics) of 0.9 or higher, but at α + 10, the 0 degree direction intensity is less than 0.8 depending on the wavelength. In some cases.
FIG. 15 is a schematic diagram of a translucent substrate when the cutting angle q is 30 deg. FIG. 16 is a graph showing the 0-degree direction strength in that case.
In FIG. 16, at 0 + 10, the 0 degree direction intensity (transmission characteristic) is as high as 0.9 or more, but at 0-5, α0, α + 5, and α-10, the 0 degree direction intensity is less than 0.8 depending on the wavelength. In some cases.

FIG. 17 is a schematic diagram of a translucent substrate when the cutting angle q is 45 degrees, and FIG. 18 is a graph showing the 0-degree direction strength in that case.
In FIG. 18, α-10, α-5, α0, α + 5, and α + 10 all had a high 0 degree direction strength of 0.9 or more.
FIG. 19 is a schematic diagram of a translucent substrate when the cutting angle q is 60 degrees, and FIG. 20 is a graph showing the 0-degree direction strength in that case.
In FIG. 20, the 0 degree direction intensity may be less than 0.8 in all of α-10, α-5, α0, α + 5, and α + 10.
FIG. 21 is a schematic diagram of a translucent substrate when the cutting angle q is 75 deg. FIG. 22 is a graph showing the 0-degree direction strength in that case.
In FIG. 22, the 0 degree direction intensity is less than 0.8 in all of α-10, α-5, α0, α + 5, and α + 10.

FIG. 23 is a schematic diagram of a translucent substrate when the cutting angle q is 90 deg. FIG. 24 is a graph showing the 0-degree direction strength in that case.
In FIG. 24, there are cases where the 0 degree direction intensity is less than 0.8 in all of α-10, α-5, α0, α + 5, and α + 10.
FIG. 25 is a schematic diagram of the light-transmitting substrate when the cutting angle q is −75 deg. FIG. 26 is a graph showing the 0-degree direction strength in that case.
In FIG. 26, there are cases where the 0 degree direction intensity is less than 0.8 in all of α-10, α-5, α0, α + 5, and α + 10.
FIG. 27 is a schematic diagram of a translucent substrate when the cutting angle q is −60 deg. FIG. 28 is a graph showing the 0-degree direction strength in that case.
In FIG. 28, there are cases where the 0 degree direction strength is less than 0.8 in all of α-10, α-5, α0, α + 5, and α + 10.

FIG. 29 is a schematic diagram of a translucent substrate when the cutting angle q is −45 deg. FIG. 30 is a graph showing the 0-degree direction strength in that case.
In FIG. 30, the 0 degree direction intensity may be less than 0.8 in all of α-10, α-5, α0, α + 5, and α + 10.
FIG. 31 is a schematic diagram of a translucent substrate when the cutting angle q is −30 deg. FIG. 32 is a graph showing the 0-degree direction strength in that case.
In FIG. 32, there were cases where the 0 degree direction intensity was less than 0.8 in all of α-10, α-5, α0, α + 5, and α + 10.
FIG. 33 is a schematic diagram of a light-transmitting substrate when the cutting angle q is −15 deg. FIG. 34 is a graph showing the 0-degree direction strength in that case.
In FIG. 34, α-10, α-5, α + 5, α + 10 and 0 degree direction intensity may be less than 0.8.

From the above relationship, the relationship between the intersection angle x and the maximum value y of the allowable plate thickness yo is obtained. The relationship between the intersection angle x and the maximum value y of the allowable plate thickness yo is shown in FIG. Here, the allowable maximum value y of the plate thickness yo is a plate thickness at which the polarization conversion efficiency (0 degree direction intensity) is 0.8 or more in the range of all divergent light (α is ± 10 deg).
Then, an axis set in a direction perpendicular to a plane including the crystal optical axis PO and the optical axis of the incident light IL is centered on the intersection of the crystal optical axis PO of the translucent substrate 21A and the optical axis of the incident light IL. Assuming that the axis is an axis and the counterclockwise direction of the central axis is positive (plus) when viewed from the direction perpendicular to the plane including the crystal optical axis PO and the optical axis of the incident light IL, the crossing angle x is −90 ( deg) ≦ x ≦ + 90 (deg).
In FIG. 35, when the intersection angle x is −90 deg <x ≦ −80 deg (area Q1),
The maximum value y of the thickness yo of the translucent substrate 21A is
y = −0.0058x ² −0.9672x−38.858 (mm) (1)
Is required.
Here, when the intersection angle x is -90 deg, y is 0.8653 mm, and when the intersection angle x is -80 deg, y is 1.1257 mm.
0.8653 mm <y ≦ 1.1257 mm.
FIG. 36A shows a state where the crossing angle x is -90 deg.

When the intersection angle x is −80 deg <x ≦ −55 deg (area Q2),
The maximum value y of the thickness yo of the translucent substrate 21A is
y = 2 × 10 ⁻⁶ x ⁵ + 0.0008x ⁴ + 0.1145x ³
+ 7.9738x ² + 276.92x + 3842.1 (mm) (2)
Is required.
Here, when the intersection angle x is −80 deg, y is 1.1257 mm, and when the intersection angle x is −55 deg, y is 3.8506 mm.
1.1257 mm <y ≦ 3.8506 mm.
When the intersection angle x is −55 deg <x ≦ −35 deg (area Q3),
The maximum value y of the thickness yo of the translucent substrate 21A is
3.7 (mm) ≦ y. That is, if the maximum allowable value y of the plate thickness yo is 3.7 mm or more, it is free.
FIG. 36B shows a state where the crossing angle x is −45 deg.

When the intersection angle x is −35 deg <x ≦ −15 deg (area Q4),
The maximum value y of the thickness yo of the translucent substrate 21A is
y = -4 × 10 ⁻⁵ x ⁴ −0.0045x ³ −0.1828x ²
-3.1831x-18.449 (3)
Is required.
Here, when the intersection angle x is −35 deg, y is 3.7030 mm, and when the intersection angle x is −15 deg, y is 1.2999 mm. Therefore, in the area Q4,
3.7030 mm <y ≦ 1.2999 mm.
When the intersection angle x is −15 deg <x ≦ + 5 deg (area Q5), the maximum value y of the plate thickness yo of the translucent substrate 21A is
y = 9 × 10−06x ⁴ + 0.0002x ³ + 0.0071x ²
+ 0.1786x + 2.4607 (4)
Is required.
Here, when the intersection angle x is −15 deg, y is 1.2999 mm, and when the intersection angle x is +5 deg, y is 3.5554 mm. Therefore, in the range of the area Q6, 1.2999 mm <y ≦ 3.5554 mm. It is.
Note that FIG. 36C shows a state where the crossing angle x is 0 deg.
When the intersection angle x is +5 deg <x ≦ + 10 deg (area Q6),
The thickness y of the translucent substrate 21A is y = −0.5597x + 6.33541 (5)
Is required.
Here, when the intersection angle x is +5 deg, y is 3.5554 mm, and when the intersection angle x is +10 deg, y is 0.7566 mm. Therefore, in the area Q6, 0.7566 mm ≦ y <3.5554 mm. is there.

When the intersection angle x is +10 deg <x ≦ + 30 deg (area Q7),
The thickness y of the translucent substrate 21A is y = 1 × 10 ⁻⁵ x ⁴ −0.0008x ³ −0.0224x ² −0.2833x.
+2.0276 (6)
Is required.
Here, when the crossing angle x is +10 deg, y is 0.7566 mm, and when the crossing angle x is +30 eg, y is 0.7016 mm. Therefore, in the area Q7, 0.7016 mm ≦ y <0.755 6 mm. is there.
When the intersection angle x is +30 deg <x ≦ + 35 deg (area Q8),
The thickness y of the light transmitting substrate 21A is y = 0.3878x-10.931 (7)
Is required.
Here, when the intersection angle x is +30 deg, y is 0.7016 mm, and when the intersection angle x is +35 deg, y is 2.6404 mm. Therefore, in the area Q8, 0.7016 mm ≦ y <2.6404 mm. is there.

When the intersection angle x is +35 deg <x ≦ + 75 deg (area Q9),
The plate thickness y of the translucent substrate 21A is y = 5 × 10 ⁻⁹ x ⁶ −2 × 10 ⁻⁶ x ⁵ + 0.0002x ⁴ −0.0176x ³
+ 0.7441x ² -16.972x + 165.72 (8)
Is required.
Here, at +35 deg, y is 2.6404 mm, when crossing angle x is +70 deg, y is 0.6906 mm, and at +75 deg, y is 0.9520 mm. Therefore, in the range of area Q9, 0.6906 mm ≦ It is y <= 2.6404mm.
When the intersection angle x is +75 deg <x <+90 deg (area Q10),
The thickness y of the translucent substrate 21A is y = 9 × 10 ⁻⁵ x ³ −0.0215x ² + 1.6761x−42.176 (9)
Is required.
Here, when the crossing angle x is +75 deg, y is 0.9520 mm, when the crossing angle x is +85 deg, y is 0.8284 mm, and when the crossing angle x is +90 deg, y is 0.8653 mm. In the range of Q10, 0.8284 mm ≦ y ≦ 0.9520 mm.

In the first embodiment having the above configuration, the following operational effects can be achieved.
(1) The polarization conversion element 2 includes a polarization separation element 21 and a reflection element 22, and the polarization separation element 21 includes a translucent substrate 21A disposed so as to form a predetermined angle with respect to the incident light IL, and the transmission substrate 21A. On the incident side surface of the optical substrate 21A, a polarization separation unit 21B that separates incident light into P-polarized light P and S-polarized light S, transmits P-polarized light P, and reflects S-polarized light S is provided. Is arranged substantially parallel to the translucent substrate 21A with an air layer interposed therebetween, and the S-polarized light S reflected by the polarization separation unit 21B is substantially parallel to the optical path of the P-polarization P transmitted through the polarization separation unit 21B. It reflects in the direction. The reflection element 22 includes a reflection element substrate 23 made of a crystal material having birefringence and optical rotation, and a mirror 24 provided on the reflection element substrate 23. The reflection element substrate 23 is incident on the reflection element substrate 23. The s-polarized light S is converted into a circularly polarized light beam R1 that rotates to the right, and this light beam R1 is reflected as a circularly polarized light beam R2 that rotates to the left by the mirror 24 and is emitted as P-polarized light P. Have. Accordingly, the polarization conversion element 2 is composed of the polarization separation element 21 configured by providing the polarization separation unit 21B on the translucent substrate 21A and the reflection element 22 having the mirror 24 provided on the reflection element substrate 23. Therefore, a transparent member such as glass provided between them is not required, and the weight and the structure become compact. In addition, a crystal material having a higher thermal conductivity than that of glass is used as the reflecting element substrate 23, and an air layer is formed between the reflecting element 22 and the polarization separating element 21, so that heat is radiated as compared with the conventional case. It is highly effective and can achieve heat resistance and long life. Since the quarter-wave plate 23A is used as the reflecting element substrate 23, the incident S-polarized light S is converted to circularly polarized light that rotates to the right, and this circularly polarized light is converted to circularly polarized light that rotates to the left by the mirror 24. Since it is emitted as P-polarized light P after being reflected, it is aligned with the P-polarized light P that is transmitted by the polarization separation unit 21B, and the change in the polarization state can be eliminated.

(2) One quarter-wave plate 23A is provided for one reflecting element 22, the optical axis direction viewed from the normal line PL of the quarter-wave plate 23A is θ _0, and the quarter-wave plate 23A the optical axis azimuth with respect to ray R1 traveling middle and theta _1, the angle between the normal line PL of the light R1 and the crystal optical axis PO and θ _2, 1/4 the refractive index _n c of the wavelength plate 23A, 1 / 4 and the refractive index of the wavelength plate 23A and the adjacent air layer and _{n a,} an optical axis azimuth theta _{0, "θ 0 = atan (tanθ 1 ×} cosθ 2) (A1) " _{"n a sinα} = _{n c sinθ 2} Since it is obtained from the equation (A2), the polarization conversion element 2 with good conversion efficiency can be easily provided in the case where the quarter wavelength plate 23 </ b> A is composed of one reflection element 22.

(3) Since the plate material constituting a part of the mirror 24 of the reflection element 22 is not the glass but the crystal plate 24A, the heat dissipation effect is enhanced from this point as well, and the heat resistance and the life can be further increased. .
(4) Since a crystalline material is used as the light-transmitting substrate 21A, this crystalline material has a higher heat dissipation effect than glass, so that heat resistance and longer life can be achieved.
(5) Since a crystal material having birefringence and optical rotation is used as the translucent substrate 21A, there is a possibility that the polarization state changes and the polarization conversion efficiency is lowered, but the light is transmitted through the polarization separation unit 21B. Since the P-polarized light P incident on the translucent substrate 21A is emitted from the exit-side surface of the translucent substrate 21A while maintaining the plane of polarization, the change in the polarization state can be eliminated and the optical characteristics can be reduced. Can be good.

(6) Since the translucent substrate 21A is arranged as approximately 45 (deg) or 135 (deg) with respect to the incident light IL, the polarization separation unit 21B of the polarization separation element 21 converts the S-polarized light S to the incident light. Since the light can be reflected toward the reflecting element 22 at a substantially right angle, the light S-polarized light S reflected by the reflecting element 22 can be made substantially parallel to the P-polarized light P. Therefore, since the reflected light of the reflective element 22 and the transmitted light of the polarization separation element 21 can be easily aligned, the polarization conversion element 2 can be easily assembled.

(7) Since the translucent substrate 21A is formed of quartz, the quartz can be obtained at a lower cost than other crystal materials such as sapphire, so that the polarization conversion element 2 can be provided at a lower cost.
(8) When the angle formed between the projection optical axis obtained by projecting the crystal optical axis PO of the translucent substrate 21A on the plane perpendicular to the optical axis of the incident light IL and the plane of polarization of the P-polarized light P is defined as θ Since = 0 (deg), the translucent substrate 21A having high polarization conversion efficiency can be easily set under the condition that the phase difference Γ due to birefringence does not occur (Γ = 0).

(9) The angle formed by the crystal optical axis PO of the translucent substrate 21A and the optical axis of the incident light IL is defined as an intersection angle x, and the intersection of the crystal optical axis PO of the translucent substrate 21A and the optical axis of the incident light IL. And a direction perpendicular to the plane including the crystal optical axis PO and the optical axis of the incident light IL, and the axis perpendicular to the plane including the crystal optical axis PO and the optical axis of the incident light IL as a central axis. From the above, when the counterclockwise direction of the central axis is positive, the crossing angle x is set so as to satisfy −90 (deg) ≦ x ≦ + 90 (deg). Therefore, the P-polarized light P that has been transmitted through the polarization separation unit 21B and entered the light-transmitting substrate 21A can be reliably emitted from the light-emitting side surface of the light-transmitting substrate 21A while maintaining its polarization plane.

(10) The intersection angle x and the maximum value y of the plate thickness yo of the translucent substrate 21A were obtained from the approximate expression for each of a plurality of areas. In other words, when “−90 (deg) ≦ x ≦ −80 (deg)”, “y = −0.0058x ² −0.9672x−38.858 (mm)” is satisfied, and “−80 When (deg) <x ≦ −55 (deg) ”,“ y = 2 × 10 ⁻⁶ x ⁵ + 0.0008x ⁴ + 0.1145x ³ + 7.99738x ² + 276.92x + 3842.1 (mm) ”is satisfied. Thus, when “−35 (deg) <x ≦ −15 (deg)”, “y = −4 × 10 ⁻⁵ x ⁴ −0.0045x ³ −0.1828x ² −3.1831x−18. 449 (mm) ”and when“ −15 (deg) <x ≦ + 5 (deg) ”,“ y = 9 × 10 ⁻⁶ x ⁴ + 0.0002x ³ + 0.0071x ² + 0.1786x + 2 .4607 (mm) And satisfy “y = −0.5597x + 6.3354 (mm)” when “+5 (deg) <x ≦ + 10 (deg)”, and satisfy “+10 (deg) <x ≦ + 30 (deg) ”,“ y = 1 × 10 ⁻⁵ x ⁴ −0.00008x ³ −0.0224x ² −0.2833x + 2.0276 (mm) ”is satisfied, and“ +30 (deg) ) <X ≦ + 35 (deg) ”so that“ y = 0.3878x-10.931 (mm) ”is satisfied, and when“ +35 (deg) <x ≦ + 75 (deg) ”, “Y = 5 × 10 ⁻⁹ x ⁶ −2 × 10 ⁻⁶ x ⁵ + 0.0002x ⁴ −0.0176x ³ + 0.7441x ² −16.972x + 165.72 (mm)” is satisfied, and “+75 ( deg) <x When the +90 (deg) ", and to satisfy the" ^{y = 9 × 10 -5 x 3} -0.0215x 2 + 1.6761x-42.176 (mm) ". Therefore, since the maximum value y of the appropriate plate thickness yo can be obtained for each area, the optical characteristics can be improved by obtaining high polarization conversion efficiency.

(11) By setting the crossing angle x so as to satisfy −55 (deg) <x ≦ −35 (deg), particularly close to −45 (deg), the maximum value y of the plate thickness yo Regardless, good polarization conversion efficiency can be obtained.
(12) Since the polarization separation unit 21B is composed of a dielectric multilayer film, the polarization separation element 21 can be easily manufactured.

(13) As the quarter-wave plate 23A made of a single plate, since an inorganic crystal material having birefringence and optical rotation is used, there is a risk that the polarization conversion state changes and the polarization conversion efficiency decreases. The relationship between the design wavelength λ, the cutting angle Z, and the plate thickness to is λ ≦ −0.1186 × Z ² + 20.288 × Z− 226.56 (1), λ ≧ 0.1089 × Z ² -18.802 × Z + 1265.4 ・ ・ ・(2), to ≦ 3E- 06 × Z 2 - 0.0003 × Z + 0.0209 ··· (3), to ≧ 9E-06 × Z 2 - 0.0013 satisfying × Z + .0626 relationship (4) Thus, the change in the polarization state can be eliminated, and the optical characteristics can be improved.

Next, a second embodiment of the present invention will be described with reference to FIGS.
The second embodiment is characterized in that the number of quarter-wave plates 23A per reflection element 22 is two, and the other configuration is the same as that of the first embodiment.
FIG. 37 shows an outline of a polarization conversion element according to the second embodiment of the present invention.
In FIG. 37, in one reflective element 22, the reflective element substrate 23 includes a laminated quarter wavelength plate 23A and a reflective film provided on the side of the quarter laminated wavelength plate 23A facing the polarization separation portion 21B. (Not shown). The laminated quarter-wave plate 23 </ b> A is composed of two retardation plates, a first retardation plate 231 and a second retardation plate 232 each made of quartz, and the first retardation plate 231 has a reflection film (not shown). Is provided. In the present embodiment, the mirror 24 is a reflective film 24 </ b> B formed directly on the second retardation plate 232.

As the quarter laminated wave plate 23A, a so-called D type shown in FIG. 38, that is, a laminated retardation plate in which a first inorganic crystal material 231 and a second inorganic crystal material 232 each made of quartz are bonded together. 39, there is a common name, WB1 type, a wide-band retardation plate in which a first inorganic crystal material 231 and a second inorganic crystal material 232 are bonded together.
The D type shown in FIG. 38 is bonded so that the crystal optical axes PO ₁ and PO _{2 of} the first phase difference plate 231 and the second phase difference plate 232 cross each other, and the phase difference of the first phase difference plate 231 is obtained. Γ ₁ = 360 ° + γ + n × 360 ° (where −90 ° ≦ γ ≦ + 90 °, n: non-negative integer), and the phase difference of the second retardation plate 232 is Γ ₂ = Γ ₁ -90 ° or 270 ° In addition, the azimuth angle of the crystal optical axis PO ₁ of the first retardation plate 231 is θ ₀₁ = 45 ° + k ₁ , and the azimuth angle of the crystal optical axis PO ₂ of the second retardation plate 232 is θ ₀₂ = 135 ° + k _2. As described above, the phase difference tolerance γ of the first retardation plate 231 and the optical axis orientations of the first retardation plate 231 and the second retardation plate 232 so that the polarization state of the emitted light satisfies a desired ellipticity. For determining the allowable deviations k ₁ and k ₂ (for example, JP 2010-107912 A) Publication).

In the example of the so-called D type shown in FIG. 38, the refractive indexes n _{c1 and} n _c2 of the crystal that is the material of the first retardation plate 231 and the second retardation plate 232 are 1.54, and the refractive index n of air _{Since a} is 1.00 and the incident angle α is 45 deg, θ ₀₁ is 41.7 deg and θ ₀₂ is 138.3 deg from the equation (A12) and equation (A21). Furthermore, in Example 1, the thickness _{m 1} of the first phase plate 231 and 0.055 mm, the wavelength is 520 nm, to design the phase difference as 310Deg, the thickness _{m 2} of the second phase difference plate 232 0. The design was 041 mm, the wavelength was 520 nm, and the phase difference was 230 deg.
An example of the commonly-known WB1 type shown in FIG. 39 is such that the first phase difference plate 231 and the second phase difference plate 232 are superposed such that the crystal optical axes PO ₁ and PO ₂ cross each other, and the first phase difference plate 231 and Each phase difference, optical axis orientation, and optical rotation ability of the second phase difference plate 232 satisfy a predetermined mathematical formula (for example, Japanese Patent No. 4553056).
Commonly known in the WB1 type example, the first phase plate 231 is a material the refractive index of the crystal _{n c1, n c2} is the second phase difference plate 232 is 1.54, the refractive index _{n a} of the air 1.00 Since the incident angle α is 45 deg, θ ₀₁ is 20.2 deg and θ ₀₂ is 90 deg from equation (A12) and equation (A21). Furthermore, in Example 2, the thickness _{m 1} of the first phase plate 231 and 0.031 mm, the wavelength is 520 nm, to design the phase difference as 160Deg, the thickness _{m 2} of the second phase difference plate 232 0. The design was 013 mm, the wavelength was 520 nm, and the phase difference was 80 deg.

In the examples shown in FIGS. 38 and 39, the optical axis azimuth θ ₀₁ of the first phase difference plate 231 and the optical axis azimuth θ ₀₂ of the second phase difference plate 232 are obtained from the following equations.
That is, the optical axis direction with respect to the light beam traveling through the first retardation plate 231 is θ ₁₁ , the angle between the light beam and the normal line of the crystal optical axis PO ₁ is θ _21, and the refractive index of the first retardation plate 231. _Is n _c1 and the refractive index of the air layer is n _a ,
The optical axis direction θ ₀₁ of the first retardation film 231 is
θ ₀₁ = atan (tan θ ₁₁ × cos θ ₂₁ ) (A11)
n _a sin α = n _c1 sin θ ₂₁ (A21)
It can be obtained from the following formula.
Similarly, the optical axis direction with respect to the light beam traveling in the second phase difference plate 232 is θ ₁₂ , the angle between the light beam and the normal line of the crystal optical axis PO ₂ is θ _22, and the second phase difference plate 231 is refracted. the rate _{n c2,} and the refractive index of the first retardation plate 231 adjacent to the second phase plate 231 and _{n c1,}
The optical axis direction θ ₀₂ of the second retardation plate 232 is
θ ₀₂ = atan (tan θ ₁₂ × cos θ ₂₂ ) (A12)
n _C1 sinα = n _c2 sinθ ₂₂ (A22)
It can be obtained from the following formula.

In the example of the so-called D type shown in FIG. 38, the incident angle to the quarter-wave plate 23A is centered on 45 (deg) and tilted at an angle in the range of ± 10 (deg) degrees from the center. The polarization conversion efficiency when the incident angle is changed in (deg) step is analyzed by simulation, and when the polarization conversion efficiency in a predetermined wavelength band is averaged in the wavelength band, the transmission loss in the averaged polarization conversion efficiency is calculated. Evaluated on average. That is, the transmission characteristics when the polarization conversion element according to this embodiment is mounted on a projection type video apparatus,
M: Transmission loss within 10% in the 500-600nm band,
N: In the 400 to 700 nm band, the transmission loss is set to a standard of 20% or less, and the design conditions are set to satisfy these two M and N standards.
In the D type, the following condition (B) is satisfied.
Condition (B): When the design wavelength is λ, the thickness of the quarter-wave plate 23A is to, and the cutting angle of the inorganic crystal material constituting the quarter-wave plate 23A is Z, the design wavelength λ and the cutting angle Z The relation of the plate thickness to satisfies the expressions (5), (6), (7), and (8).
λ ≤-10.899 × Z ² + 1959.9 × Z- 87469 (5)
^{λ ≧ 6.4048 × Z 2 - 1154.5} × Z + 52476 ··· (6)
to ≤ -0.0142 × Z ² + 2.5613 × Z- 114.36 (7)
^{to ≧ 0.0088 × Z 2 - 1.594} × Z + 72.352 ··· (8)
Here, the plate thickness to is defined as the plate thickness of a retardation plate formed by bonding the first inorganic crystal material 231 and the second inorganic crystal material 232 together. That is, the total thickness of the plate thickness m1 of the first inorganic crystal material 231 and the plate thickness m2 of the second inorganic crystal material 232 is obtained.
Expressions (5) and (6) show the relationship between the design wavelength λ and the cutting angle Z. Of these, Expression (5) is an upper limit relational expression, and Expression (6) is a lower limit relational expression. . Expressions (7) and (8) show the relationship between the cutting angle Z and the plate thickness to, among which Expression (7) is the upper limit relational expression and Expression (8) is the lower limit relational expression. It is.
Table 3 shows the result of analyzing the polarization conversion efficiency by simulation, and shows the relationship between the cutting angle Z and the design wavelength λ and the relationship between the cutting angle Z and the plate thickness to. The relationship between the cutting angle Z and the design wavelength λ is also shown in FIG. 40A, and the relationship between the cutting angle Z and the plate thickness to is also shown in FIG.

From Table 3 and FIGS. 40A and 40B, the range of the design wavelength λ and the cutting angle Z for satisfying the transmission characteristics is
455 ≦ λ ≦ 640 (nm)
87 ≦ Z ≦ 93 (deg)
It is.
If the design wavelength λ and the cutting angle Z are designed so that the upper limit relational expression (7) and the lower limit relational expression (8) are satisfied, the above transmission characteristics (transmission loss) ) Standards M and N can be satisfied.

In the example of the so-called WB1 type shown in FIG. 39, when the incident angle to the quarter-wave plate 23A is centered on 45 (deg) and tilted at an angle in the range of ± 10 (deg) degrees from the center, 5 The polarization conversion efficiency when the incident angle is changed in (deg) step is analyzed by simulation, and when the polarization conversion efficiency in a predetermined wavelength band is averaged in the wavelength band, the transmission loss in the averaged polarization conversion efficiency is calculated. Evaluated on average. That is, the transmission characteristics when the polarization conversion element according to this embodiment is mounted on a projection type video apparatus,
M: Transmission loss within 10% in the 500-600nm band,
N: In the 400 to 700 nm band, the transmission loss is set to a standard of 20% or less, and the design conditions are set to satisfy these two M and N standards.
In the WB1 type, the following condition (C) is satisfied.
Condition (C): When the design wavelength is λ, the thickness of the quarter-wave plate 23A is to, and the cutting angle of the inorganic crystal material constituting the quarter-wave plate 23A is Z, the design wavelength λ and the cutting angle Z The relation of the plate thickness to satisfies the expressions (9), (10), (11) and (12).
λ ≦ -0.0488 × Z ² + 5.8238 × Z + 552.71 (9)
λ ≧ 0.0149 × Z ² -0.281 × Z + 290.79 ・ ・ (10)
^{to ≦ 2E-05 × Z 2} - 0.0024 × Z + 0.1453 ·· (11)
^{to ≧ 1E-05 × Z 2} - 0.0018 × Z + 0.0824 ··· (12)
Here, the plate thickness to is defined as the plate thickness of a retardation plate formed by bonding the first inorganic crystal material 231 and the second inorganic crystal material 232 together. That is, the total thickness of the plate thickness m1 of the first inorganic crystal material 231 and the plate thickness m2 of the second inorganic crystal material 232 is obtained.
Expressions (9) and (10) show the relationship between the design wavelength λ and the cutting angle Z. Of these, Expression (9) is an upper limit relational expression, and Expression (10) is a lower limit relational expression. . Expressions (11) and (12) show the relationship between the cutting angle Z and the plate thickness to, among which the expression (11) is the upper limit relational expression and the expression (12) is the lower limit relational expression. It is.
Table 4 shows the result of analyzing the polarization conversion efficiency by simulation, and shows the relationship between the cutting angle Z and the design wavelength λ and the relationship between the cutting angle Z and the plate thickness to. The relationship between the cutting angle Z and the design wavelength λ is also shown in FIG. 41A, and the relationship between the cutting angle Z and the plate thickness to is also shown in FIG.

From Table 4 and FIGS. 41A and 41B, the range of the design wavelength λ and the cutting angle Z for satisfying the transmission characteristics is as follows.
315 ≦ λ ≦ 725 (nm)
50 ≦ Z ≦ 110 (deg)
It is.
If the design wavelength λ and the cutting angle Z are designed so as to satisfy the upper limit relational expression (11) and the lower limit relational expression (12), the above transmission characteristics (transmission loss) ) Standards M and N can be satisfied.

  As described above, FIG. 42 shows the polarization conversion efficiency of the laminated quarter-wave plate 23A of an example of the so-called D type. In FIG. 42, the horizontal axis indicates the wavelength, the vertical axis indicates the polarization conversion efficiency, and the S-polarized light S is laminated on the quarter-wave plate 23A with the incident angle α being 35, 40, 45, 50, and 55 degrees. The polarization conversion efficiency of the P-polarized light P that is incident and emitted from the laminated quarter-wave plate 23A is shown. At these incident angles α, there is no significant difference in the polarization conversion efficiency, and in FIG. 42, data with an incident angle α from 35 deg to 55 deg is included in the thick curve L. As shown in FIG. 42, the polarization conversion efficiency shows a value of 0.7 or more from a wavelength of 400 nm to 700 nm, and particularly shows a high value of 0.9 or more from a wavelength of 450 nm to 650 nm.

As described above, FIG. 43 shows the polarization conversion efficiency of the laminated quarter-wave plate 23A of an example of the so-called WB1 type. In FIG. 43, the horizontal axis indicates the wavelength, the vertical axis indicates the polarization conversion efficiency, and the incident angle α is set to 35 deg, 40 deg, 45 deg, 50 deg, and 55 deg. The polarization conversion efficiency of the P-polarized light P emitted from the quarter-wave plate 23A is shown. In FIG. 43, symbol L35 is when the incident angle α is 35 deg, L40 is when the incident angle α is 40 deg, L45 is when the incident angle α is 45 deg, and L50 is when the incident angle α is 50 deg. L55 is the case where the incident angle α is 55 deg.
As shown in FIG. 43, the polarization conversion efficiency shows a value of 0.7 or more from a wavelength of 400 nm to 700 nm, and particularly shows a high value of 0.9 or more from a wavelength of 450 nm to 700 nm.

Therefore, in 2nd Embodiment, there can exist the following effect other than the same effect as (1) (4)-(12) of 1st Embodiment.
(14) The reflection element substrate 23 is a set of two plates of a first phase difference plate 231 and a second phase difference plate 232, and the optical axis direction of the first phase difference plate 231 viewed from the normal line PL is θ ₀₁ , The optical axis orientation with respect to the light ray R1 traveling through the first phase difference plate 231 is θ ₁₁ , and the angle between the light ray R _{1 and} the normal line of the crystal optical axis PO ₁ is θ _21. rate of _{n c1,} and the refractive index of the air layer and _{n a,} an optical axis azimuth theta ₀₁ of the first phase plate _{231, θ 01 = atan (tanθ} 11 × cosθ 21) (A11), n a sinα = n Calculated from the equation _c1 sinθ ₂₁ (A21). The optical axis direction of the second retardation plate 232 viewed from the normal line PL is θ ₀₂ , the optical axis direction with respect to the light ray R 1 traveling through the second retardation plate 232 is θ _12, and this light ray R 2 and crystal optics If the angle formed by the normal line PL of the axis PO ₂ is θ ₂₂ , the refractive index of the second retardation plate 232 is n _c2 , and the refractive index of the first retardation plate 231 is n _c1 , the second retardation plate 232. obtaining the optical axis azimuth _{θ 02, θ 02 = atan (} tanθ 12 × cosθ 22) (A12), from the equation of _{n C1 sinα = n c2 sinθ 22} (A22). Therefore, when the reflection element substrate 23 is composed of the two retardation plates 231 and 232, a polarization conversion element with good conversion efficiency can be easily provided.
(15) Since the reflection element 22 includes the reflection film 24B provided directly on the second retardation plate 232, the crystal plate 24A is unnecessary, and the polarization conversion unit can be reduced in weight as compared with the first embodiment. Can do.

(16) Since an inorganic crystal material having birefringence and optical rotation is used as the so-called D-type quarter-wave plate 23A, there is a risk that the polarization conversion state changes and the polarization conversion efficiency decreases. However, the relationship between the design wavelength λ, the cutting angle Z, and the plate thickness to is λ ≦ −10.899 × Z ² + 1959.9 × Z−87469 (5), λ ≧ 6.4048 × Z ² −1154.5 × Z + 52476 ··· (6), to ≦ -0.0142 × Z 2 + 2.5613 × Z- 114.36 ··· (7), to ≧ 0.0088 × Z 2 - satisfies 1.594 × Z + 72.352 ··· (8) relationship Thus, the change in the polarization state can be eliminated, and the optical characteristics can be improved.
(17) Since an inorganic crystal material having birefringence and optical rotation is used as the WB1 type broadband quarter-wave plate 23A of the so-called WB1 type, there is a fear that the polarization state changes and the polarization conversion efficiency decreases. However, the relationship between the design wavelength λ, the cutting angle Z, and the plate thickness to is λ ≦ −0.0488 × Z ² + 5.8238 × Z + 552.71 (9), λ ≧ 0.0149 × Z ² −0.281 × Z + 290.79・ (10), to ≦ 2E-05 × Z ² − 0.0024 × Z + 0.1453 ・ ・ (11), to ≧ 1E-05 × Z ² − 0.0018 × Z + 0.0824 (12) is satisfied. Thus, the change in the polarization state can be eliminated, and the optical characteristics can be improved.

Next, a third embodiment of the present invention will be described with reference to FIG.
The third embodiment differs from the first embodiment in the structure of the reflective element, and the other configurations are the same as those in the first embodiment.
FIG. 44 shows an outline of the polarization conversion element according to the third embodiment.
In FIG. 44, in 3rd Embodiment, it replaces with the reflection preventing part 23B provided in the surface on the opposite side to the surface into which incident light enters among the reflection preventing parts 23B provided in both surfaces of the quarter wave plate 23A. The reflective film 24B is provided. That is, in the third embodiment, the reflection element 22 is configured by the reflection film 24B provided directly on the quarter-wave plate 23A.
Therefore, in 3rd Embodiment, there can exist the effect of (1)-(13) of 1st Embodiment, and the effect of (14)-(17) of 2nd Embodiment.

Next, a fourth embodiment of the present invention will be described with reference to FIGS.
The fourth embodiment is an example in which the polarization conversion unit 4 is provided in a liquid crystal projector 100 that is a projection type video apparatus, and the structure of the holding member 5 is different from the polarization conversion unit 1 of the third embodiment.
FIG. 45 shows a schematic configuration of a liquid crystal projector.
45, the liquid crystal projector 100 includes an integrator illumination optical system 110, a color separation optical system 120, a relay optical system 130, a light modulation device 140 that modulates light emitted from a light source according to image information, a light A projection optical device 150 that enlarges and projects the light modulated by the modulation device 140.
The integrator illumination optical system 110 is an optical system for illuminating image forming areas of three transmissive liquid crystal panels 141R, 141G, and 141B described later, and includes a light source device 111, a first lens array 112, A polarization conversion device 200 and a superimposing lens 113 are provided.

The light source device 111 reflects the radial light beam emitted from the light source lamp 114 by the reflector 115 into a substantially parallel light beam, and emits the substantially parallel light beam to the outside.
The polarization conversion device 200 includes a second lens array 210, a light shielding plate 220, and a polarization conversion unit 4.
The color separation optical system 120 includes two dichroic mirrors 121 and 122 and a reflection mirror 123. The dichroic mirrors 121 and 122 divide a plurality of lights emitted from the integrator illumination optical system 110 into red, green, and blue 3 Separate into colored light. The blue light separated by the dichroic mirror 121 is reflected by the reflection mirror 123, passes through the field lens 142, and reaches the blue transmission liquid crystal panel 141B.
Of the red light and green light transmitted through the dichroic mirror 121, the green light is reflected by the dichroic mirror 122, passes through the field lens 142, and reaches the green transmissive liquid crystal panel 141G.
The relay optical system 130 includes an incident side lens 131, a relay lens 133, and reflection mirrors 132 and 134. The red light separated by the color separation optical system 120 passes through the dichroic mirror 122, passes through the relay optical system 130, passes through the field lens 142, and reaches the transmissive liquid crystal panel 141R for red light.
The light modulation device 140 includes transmissive liquid crystal panels 141R, 141G, and 141B, and a cross dichroic prism 143. The cross dichroic prism 143 combines the optical images modulated for each color light to form a color optical image.

The polarization conversion unit 4 includes a polarization conversion element 2 and a holding member 5 that holds the polarization conversion element 2.
The specific structure of the holding member 5 is shown in FIGS.
46 is a perspective view of the holding member 5, FIG. 47A is a plan view of the holding member 5, and FIG. 47B is a cross-sectional view of the holding member 5.
In these drawings, the holding member 5 connects a pair of holding plates 51 that hold both ends of the polarization separation element 21 and both ends of the reflecting element 22, and both ends of the pair of holding plates 51, respectively. And a pair of connecting plates 52. The holding plate 51 and the connecting plate 52 are integrally formed in a planar rectangular frame shape from synthetic resin.
A plurality of pairs of guide grooves 51 </ b> A for guiding the polarization separating element 21 and the reflecting element 22 are formed in portions of the pair of holding plates 51 facing each other. These guide grooves 51A are formed so that the longitudinal direction thereof is 45 deg or 135 deg with respect to incident light.

  46 and 47, four pairs of guide grooves 51A are illustrated for accommodating the polarization separating element 21, and two pairs are illustrated for accommodating the reflecting element 22. This is because the configuration of the groove 51A is enlarged for easy understanding, and in fact, two pairs are provided to accommodate the two polarization separation elements 21 in accordance with the polarization conversion element 2 shown in FIG. In this structure, two pairs are provided to accommodate two reflecting elements 22. However, the number of guide grooves 51A is not limited to that described above, and corresponds to the number of polarization separation elements 21 and reflection elements 22 that are actually provided.

  FIG. 48 is an exploded perspective view of a part of the holding member 5. In FIG. 48, the guide groove 51 </ b> A has a step formed so that one end is opened on one side surface of the holding plate 51 and the other end is in contact with the end of the polarization separation element 21 or the reflection element 22. The width of the guide groove 51A is the same as or slightly larger than the width of the polarization separation element 21 or the reflection element 22, and the length of the guide groove 51A is the same as or slightly larger than the length of the polarization separation element 21 or the reflection element 22. Is formed.

Therefore, in the fourth embodiment, in addition to the same effects as the effects (1) to (17) of the third embodiment, the following effects can be achieved.
(18) A polarization conversion unit 4 having a polarization conversion element 2 that converts the light from the light source device 111 into P-polarized light P and emits it, and a light modulation device that modulates the light emitted from the polarization conversion element 2 according to image information 140 and the projection optical device 150 that projects the light modulated by the light modulation device 140 constitute the liquid crystal projector 100, so that the polarization conversion efficiency of the polarization conversion element 2 increases and the liquid crystal projector 100 Projection accuracy can be increased.

(19) Since the light modulation device 140 includes the transmissive liquid crystal panels 141R, 141G, and 141B, the liquid crystal projector 100 with high projection accuracy can be provided also from this point.
(20) The polarization conversion unit 4 includes a holding member 5 that holds the polarization conversion element 2, and the holding member 5 holds a pair of holdings that hold both ends of the polarization separation element 21 and both ends of the reflection element 22. Since the plate 51 and the pair of connecting plates 52 for connecting both ends of the pair of holding plates 51 are respectively connected, the polarization separating element 21 and the reflecting element 22 can be compactly accommodated in the holding member. , Handling becomes convenient.

(21) Since the pair of holding plates 51 and the pair of connecting plates 52 are integrally formed, the holding member 5 can be easily manufactured by appropriate means such as injection molding.
(22) Guide grooves 51 </ b> A for guiding the polarization separation element 21 and the reflection element 22 are formed in the opposing portions of the pair of holding plates 51, and these guide grooves are formed on one side surface of the pair of holding plates 51. Since the openings are opened, the polarization conversion unit 4 can be assembled simply by inserting the polarization separating element 21 and the reflecting element 22 along the guide grooves 51A, respectively, and the assembling work is facilitated.

Next, a fifth embodiment of the present invention will be described with reference to FIGS.
In the fifth embodiment, the structure of the holding member is different from that of the fourth embodiment, and other configurations are the same as those of the fourth embodiment.
FIG. 49 is a perspective view showing a polarization conversion unit according to the fifth embodiment, and FIG. 50 is an exploded perspective view showing a part of the holding member.
In these drawings, the polarization conversion unit 6 includes a polarization conversion element 2 having the same structure as that of the third embodiment, and a holding member 7 that holds the polarization conversion element 2.
The holding member 7 includes a pair of holding plates 71 and a pair of connecting plates 72 provided at ends of the pair of holding plates 71, and the pair of holding plates 71 and the pair of connecting plates 72 are formed separately. Has been.

The pair of holding plates 71 has a plate shape formed of a synthetic resin, and a plurality of pairs of guide grooves 71A for guiding the end portions of the polarization separation element 21 and the reflection element 22 are formed in portions facing each other. Yes. These guide grooves 71A are formed such that the longitudinal direction thereof is 45 deg or 135 deg with respect to incident light. The guide groove 71A is a recess having a rectangular plane.
In FIG. 49, a total of six pairs of guide grooves 71A are shown, but actually, four pairs are provided to accommodate the four polarization separation elements 21 in accordance with the polarization conversion element 2. In this structure, four pairs are provided to accommodate four reflecting elements 22.

The pair of connecting plates 72 includes a long plate member 721 and an engagement piece 722 that is connected to the plate member 721 and biases the pair of holding plates 71 in a direction facing each other.
The plate member 721 and the engagement piece 722 are integrally formed from an elastic material, for example, a metal, a synthetic resin, or the like. The engaging piece 722 is formed by being bent with respect to the plate material 721, and a convex holding portion 722 </ b> A that engages with the concave portion 71 </ b> B formed on the holding plate 71 is formed at the center portion thereof. The convex holding portion 722 </ b> A and the concave portion 71 </ b> B are formed to extend in a direction orthogonal to the longitudinal direction of the holding plate 71.

Therefore, in the fifth embodiment, the same operational effects as the operational effects of the third embodiment and the operational effects similar to the operational effects of the fourth embodiment can be achieved, and the following operational effects are exhibited. Can do.
(23) The holding member 7 includes a pair of holding plates 71 and a pair of connecting plates 72 provided at end portions of the pair of holding plates 71, and the pair of connecting plates 72 includes a long plate material 721. And an engagement piece 722 that is connected to the plate member 721 and biases the pair of holding plates 71 in a direction facing each other. Therefore, since the pair of holding plates 71 are urged by the pair of connecting plates 72 in the direction approaching each other, the polarization separation element 21 and the reflection element 22 can be reliably held by the holding member 7. The element 21 and the reflective element 22 are not accidentally dropped from the holding member 7.

(24) Since the engagement piece 722 has the holding portion 722A that engages with the recess 71B formed in the holding plate 71, the connecting plate 72 is not displaced in the longitudinal direction of the holding plate 71. Therefore, it is possible to prevent the connecting plate 72 from being accidentally detached from the holding plate 71.
(25) Since the guide groove 71A formed on the holding plate 71 and holding the end portions of the polarization separation element 21 and the reflection element 22 is a concave portion having a rectangular plane, polarization in the plane of the holding plate 71 is achieved. The movement of the separation element 21 and the reflection element 22 is restricted. Therefore, also from this point, the polarization separation element 21 and the reflection element 22 are not accidentally dropped from the holding member 7.

Next, a sixth embodiment of the present invention will be described with reference to FIG.
The sixth embodiment is different from the first embodiment in the configuration of the polarization separation element, and the other configurations are the same as those in the first embodiment.
FIG. 51 is a perspective view of the polarization separation unit 210B of the polarization separation element 21 according to the fifth embodiment. In FIG. 51, the polarization separation unit 210B of the polarization separation element 21 is formed of a conductive electrode 21E made of a number of parallel metal wires supported by a dielectric substrate 21D. The conductive electrode 21E has a pitch or period of P, an individual conductor width of W, and a thickness of t. Incident light IL is incident on the polarization separation element 21 at an angle R from the perpendicular. Incident light IL is reflected as S-polarized light S and is not diffracted but transmitted as P-polarized light P. Here, the period P, the width W, and the thickness t are set according to the frequency region of light to be used and other conditions.

Therefore, according to the sixth embodiment, the same operational effects as those of the first embodiment can be achieved, and the following operational effects can be achieved.
(26) Since the polarization separation unit 210B of the polarization separation element 21 is configured with a metal wire grid, the polarization conversion element can be easily manufactured.

Note that the present invention is not limited to the above-described embodiments, and it goes without saying that modifications and improvements within the scope of achieving the objects and effects of the present invention are included in the contents of the present invention. Absent.
For example, in the embodiment, the antireflection portions 21C and 22B are provided on both surfaces of the polarization separation element 21 and the reflection element 22, but in the present invention, it is not always necessary to provide the antireflection portions 21C and 22B. However, if the antireflection portions 21C and 22B are provided as in the above embodiments, the amount of light transmitted through the polarization separation element 21 and the reflection element 22 increases.
Further, in the second embodiment, the first retardation plate 231 and the second retardation plate 232 are stacked. However, in the present invention, as shown in FIG. 52, the first retardation plate 231 and the second retardation plate 232 are stacked. The anti-reflection part 23B may be formed on both surfaces of the first retardation plate 231 and one surface of the second retardation plate 232 with the retardation plate 232 spaced apart.

Further, although the polarization conversion element is used in the liquid crystal projector, in the present invention, it can be used in a projection apparatus other than the liquid crystal projector.
Furthermore, the reflective element 22 does not necessarily need to use quartz, and glass may be used instead of quartz. In the polarization separation element 21, it is not always necessary to use quartz for the translucent substrate 21A. Instead of quartz, a crystal material having birefringence and optical rotation such as sapphire may be used.
Furthermore, in the above-described embodiment, the polarization separation element 21 is set to approximately 45 (deg) or 135 (deg) with respect to the incident light IL. However, the present invention is not limited to this. For example, 60 (deg) ) Or 120 (deg).

  The present invention can be used in a liquid crystal projector and other projection type video apparatuses.

  DESCRIPTION OF SYMBOLS 1, 4, 6 ... Polarization conversion unit, 2 ... Polarization conversion element, 3, 5, 7 ... Holding member, 21 ... Polarization separation element, 21A ... Translucent substrate, 21B ... Polarization separation part, 22 ... Reflection element, 23 ... reflective element substrate, 23A ... 1/4 wavelength plate, 23B ... antireflection part, 231 ... first retardation plate, 232 ... second retardation plate, 24 ... mirror, 24A ... quartz plate, 24B ... reflection film, 51, 71 ... holding plate, 51A, 71A ... guide groove, 52, 72 ... connecting plate, 100 ... liquid crystal projector (projection type image device), 111 ... light source device, 140 ... light modulation device (light modulation means), 141R, 141G, 141B ... Transmission type liquid crystal panel, 150 ... Projection optical device (projection optical system), 210B ... Polarization separation unit, 722 ... Engagement piece, 722A ... Suppression unit, IL ... Incident light, OL ... Emission light, PO ... Crystal Optical axis, P ... P polarized light (first Linearly polarized light), S ... S-polarized light (second linear polarized light), x ... cross axis, q ... cutting angle

Claims (11)

A translucent substrate disposed at a predetermined angle with respect to incident light;
On the incident side surface of the translucent substrate, the incident light is separated into first linearly polarized light and second linearly polarized light orthogonal to each other, the first linearly polarized light is transmitted, and the second linearly polarized light is transmitted. A polarized light separating part that reflects;
An optical path of the first linearly polarized light that is disposed substantially in parallel with the translucent substrate with an air layer interposed between the second linearly polarized light reflected by the polarized light separating unit and transmitted through the polarized light separating unit. A reflective element that reflects in a direction substantially parallel to
Have
The reflective element is
A reflective element substrate made of a crystal material having birefringence and optical rotation;
A mirror provided on the reflective element substrate;
Have
The reflective element substrate is:
Converting the incident second linearly polarized light into first circularly polarized light;
Reflecting the first circularly polarized light as the second circularly polarized light that is reversely rotated by the mirror;
A polarization conversion element characterized by being a wavelength plate that converts the second circularly polarized light into first linearly polarized light and emits the same. The polarization conversion element according to claim 1,
The reflective element substrate is composed of one retardation plate,
The optical axis direction viewed from the normal line of the reflective element substrate is θ ₀ ,
The optical axis direction with respect to the light beam traveling in the reflecting element substrate is θ ₁ ,
The angle formed by the optical path of the light beam and the normal of the crystal optical axis is θ ₂ ,
The refractive index n _c of the substrate for the reflective element _and the refractive index of the layer adjacent to the substrate for the reflective element and n _a, the optical axis azimuth theta ₀ is
θ ₀ = atan (tan θ ₁ × cos θ ₂ ) (A1)
n _a sin α = n _c sin θ ₂ (A2)
A polarization conversion element obtained from the formula: The polarization conversion element according to claim 1,
The reflective element substrate is made of two retardation plates, a first retardation plate and a second retardation plate,
The optical axis direction of the first retardation plate viewed from the normal line of the reflecting element substrate is θ _01, and the optical axis direction with respect to the light beam traveling through the first retardation plate is θ _11. the angle between the normal line of the optical axis and theta _21, and the refractive index of the first retardation plate n _c1, the refractive index of the layer adjacent to the first phase difference plate and n _a, the first of The optical axis direction θ ₀₁ of the phase difference plate is
θ ₀₁ = atan (tan θ ₁₁ × cos θ ₂₁ ) (A11)
n _a sin α = n _c1 sin θ ₂₁ (A21)
From the formula of
The optical axis direction of the second retardation plate viewed from the normal line of the reflecting element substrate is θ _02, and the optical axis direction with respect to the light beam traveling through the second retardation plate is θ _12. The angle between the normal of the optical axis is θ ₂₂ , the refractive index of the second retardation plate is n _c2 , and the refractive index of the first retardation plate adjacent to the second retardation plate is n _c1. The optical axis direction θ ₀₂ of the second retardation plate is
θ ₀₂ = atan (tan θ ₁₂ × cos θ ₂₂ ) (A12)
n _C1 sinα = n _c2 sinθ ₂₂ (A22)
A polarization conversion element obtained from the formula: In the polarization conversion element according to any one of claims 1 to 3,
The translucent substrate is made of a crystal material having birefringence and optical rotation,
The first linearly polarized light that has been transmitted through the polarization separation unit and incident on the translucent substrate is emitted from the exit-side surface of the translucent substrate while maintaining the polarization plane of the first linearly polarized light. A characteristic polarization conversion element. In the polarization conversion element according to any one of claims 1 to 4,
The predetermined angle is approximately 45 (deg) or 135 (deg). In the polarization conversion element according to any one of claims 1 to 5,
The polarization conversion element, wherein the crystal material is quartz. A polarization conversion element according to any one of claims 1 to 6, and a holding member that holds the polarization conversion element,
The holding member includes a pair of holding plates for holding both ends of the reflective element substrate and both ends of the translucent substrate, respectively.
A polarization conversion unit comprising: a pair of connecting plates that respectively connect both ends of the pair of holding plates. In the polarization conversion unit according to claim 7,
The pair of holding plates and the pair of connecting plates are integrally formed,
Guide grooves for guiding the translucent substrate and the reflective element substrate are provided in portions of the pair of holding plates facing each other,
The polarization conversion unit, wherein the guide groove is opened on one side surface of the pair of holding plates. The polarization conversion unit according to claim 8, wherein
The pair of holding plates and the pair of connecting plates are formed separately.
The polarization conversion unit according to claim 1, wherein the pair of connecting plates have engagement pieces that urge the pair of holding plates in a direction facing each other. A light source;
A polarization conversion element that converts the light from the light source into the second linearly polarized light and emits it;
Light modulation means for modulating the light emitted from the polarization conversion element according to image information to be projected;
A projection optical system that projects the light modulated by the light modulation means;
Have
The projection type image apparatus, wherein the polarization conversion element is the polarization conversion element according to any one of claims 1 to 6. In the projection type video device according to claim 10,
A projection-type image apparatus, wherein the light modulation means is a liquid crystal panel.

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