JP2013130810A - Depolarizing element, optical measuring device, and projection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a depolarizing element which exhibits a spacial distribution of phase differences without separating an incident light and without depending on a polarization state of the incident light for light of a wide wavelength region and acquires high depolarization for the light of the wide wavelength region.SOLUTION: The depolarizing element comprises a first birefringent medium layer and a second birefringent medium layer. Each of the first birefringent medium layer and the second birefringent medium layer has a uniform thickness and includes at least one region of two types of regions respectively having the same phase difference and a different direction of a phase advancing axis in each of depolarizing element planes. A boundary between the two regions included in the first birefringent medium layer and a boundary between the two regions included in the second birefringent medium layer are aligned with each other. A ratio of a phase difference in the first birefringent medium layer and a phase difference in the second birefringent medium layer is 2±0.1:1. An angle between the phase advancing axes in the two types of regions included in the second birefringent medium layer is 45°±4°.

Description

  The present invention relates to a depolarizing element that eliminates the polarization of incident light, an optical measuring instrument using the same, and a projection display device.

  One of the optical measuring instruments is an optical spectrum analyzer having a Zerni-Turna type optical system. In such an optical measuring instrument called Zerni-Turna type, incident light to be measured is guided to the diffraction grating, the light diffracted by the diffraction grating is stopped by a lens or a concave mirror, and passed through a slit arranged at the focal position, Detect the amount of light. At this time, utilizing the fact that the direction diffracted by the diffraction grating varies depending on the wavelength of the light, by appropriately rotating the diffraction grating so that only light of a specific wavelength passes through the slit, the amount of light for each wavelength of the light to be measured can be reduced. It can be measured.

  In Czerni-Turna type optical measuring instruments, diffraction gratings are generally used at oblique incidence. For this reason, the diffraction efficiencies for the p-polarized light component parallel to the incident surface and the s-polarized light component perpendicular to the incident surface are different, and the amount of light for each wavelength of the measured light cannot be measured correctly depending on the polarization state of the measured light. It was.

  In order to avoid the influence of the polarization dependence of the diffraction efficiency on the diffraction grating, in the Zerni-Turna type optical measuring instrument, the depolarization element (polarization) that cancels the polarization of the measured light before the diffraction grating. A canceling plate, also called a polarization scrambler) is arranged to reduce the degree of polarization of the light to be measured incident on the diffraction grating and convert it to a state close to natural light.

  FIG. 19 is a configuration diagram illustrating an example of a Zerni-Turna type optical measuring device. In the example shown in FIG. 19, light enters from the entrance slit 91, passes through the depolarization element 92, and is converged on the concave mirror 93. Then, the light enters the diffraction grating 94 and is dispersed for each wavelength by the diffraction action of the diffraction grating 94. The light diffracted by the diffraction grating 94 is coupled to the focal position on the exit slit 96 by the concave mirror 95. In this way, the amount of light passing through the exit slit 96 disposed at the focal position is detected.

  An example of a depolarizing element used in such a Zerni-Turna type optical measuring instrument is described in Patent Document 1. FIG. 20 is a configuration diagram illustrating an example of a depolarizing element described in Patent Document 1. The depolarizing element 92 shown in FIG. 20 is configured by bonding two birefringent crystals such as quartz processed into a wedge shape. More specifically, the two wedge-shaped birefringent crystals 921 and 922 are arranged such that the ordinary optical axis that is the crystal axis showing ordinary light refraction and the extraordinary optical axis that is the crystal axis showing extraordinary light refraction overlap each other. It is pasted with the slopes facing each other. In FIG. 20, 923 indicates the ordinary optical axis of the first birefringent crystal 921, and 924 indicates the ordinary optical axis of the second birefringent crystal 922.

  When light having polarization such as linearly polarized light or circularly polarized light is incident on such a depolarizing element 92, the incident light travels along the polarization component that travels along the normal optical axis of the first birefringent crystal 921 and the abnormal axis. The light is divided into polarized light components and travels through the crystal, and is incident on the second birefringent crystal 922. The polarization component that has traveled along the normal optical axis of the first birefringent crystal 921 travels along the extraordinary optical axis of the second birefringent crystal 922. On the other hand, the polarization component that has traveled along the extraordinary optical axis of the first birefringent crystal 921 travels along the ordinary optical axis of the second birefringent crystal 922. At this time, since the distance traveled through the first birefringent crystal 921 and the travel distance traveled through the second birefringent crystal 922 differ depending on the location where the element is transmitted, a spatial distribution occurs in the phase difference. The depolarization element 92 converts the incident light into light having a different polarization state for each location by using the spatial distribution of the phase difference. As a result, the light emitted from the depolarization element 92 can be regarded as having the polarization properties canceled as an average by overlapping various polarization states.

  In the case of using a depolarizing element in which two wedge-shaped birefringent crystals are bonded together, the incident light is refracted by the inclined surface that is the bonding surface, and the traveling direction of the light changes. That is, the angle at which the polarization component refracts traveling along the normal optical axis of the first birefringent crystal 921 and along the extraordinary optical axis of the second birefringent crystal 922, and the first birefringent crystal 921 Since the angle of refracting the polarization component that travels along the extraordinary optical axis and travels along the ordinary optical axis of the second birefringent crystal 922 is different, the light emitted from the element is separated into two according to the polarization component. Furthermore, since the angle of refraction differs depending on the wavelength of light, the angle at which the emitted light is separated differs depending on the wavelength.

  In order to eliminate the polarization dependency of the diffraction grating 94 in the optical measuring instrument, it is necessary to pass both of the lights separated by the depolarization element 92 through the exit slit 96. However, there is a problem that the slit width is limited by the maximum wavelength of the light to be measured because the angle at which the light emitted from the depolarization element 92 is separated differs depending on the wavelength of the light. Note that if linearly polarized light is incident along the normal or extraordinary optical axis of the depolarizer, the light will not be separated, but in this case it will be emitted with the same linearly polarized light, and the original polarization property will be eliminated. Can not.

  On the other hand, it is effective to narrow the slit width in order to improve the wavelength resolution. As a result, there is an undesired restriction that the improvement in wavelength resolution and the maximum wavelength of the light to be measured have a trade-off relationship.

  Therefore, Patent Document 1 describes a method of narrowing the slit width by devising the birefringent axis of the birefringent crystal and the wedge-shaped tilt direction and separating the light in the longitudinal direction of the slit. In the optical measuring instrument described in Patent Document 1, the depolarization element is set so that the normal or extraordinary optical axis of the depolarization element 92 is 45 ° with respect to the p-polarized component and the s-polarized component of the diffraction grating 94. By disposing 92, the light separating direction by the depolarizing element 92 matches the longitudinal direction of the slit width while maintaining the function of eliminating the polarization.

  By the way, as another application of the depolarizing element, it has been proposed to use the depolarizing element in order to improve speckle noise in a projection display device (projector) that displays a projected image on a screen.

  Conventionally, an ultra-high pressure mercury (UHP) lamp has been used as a light source for a projection display device. However, it is proposed to use a laser as a light source from the viewpoint of excellent monochromaticity and long life of the light source. ing. In addition, since the UHP lamp has a broad spectrum in the wavelength band near 645 nm, which is the red wavelength, the laser is used as the red light source, and the UHP lamp is used in the blue and green wavelength bands. It has been proposed to use a combined light source.

  However, in a projection display device using a laser as a light source, the light source is highly coherent, so that light scattered by the unevenness of the screen displaying the image interferes on the retina of the eye and generates granular speckle noise. There was a problem of fear. When speckle noise occurs, the image quality of the projected image is deteriorated, which is not preferable. In such an image projection apparatus, between the light source that emits coherent light and the image light generation unit that modulates the light emitted from the light source to generate image light, or between the image light generation unit and the image light generation Speckle noise can be reduced by disposing a depolarizing element between the projection means for projecting the image light generated by the means and modulating the phase of the incident light.

  For example, Patent Document 2 describes an example in which a depolarizing element having a stripe-like or checkered plane pattern is used for the purpose of reducing speckle noise in an image projection apparatus. 21 and 22 are configuration diagrams showing the depolarizing element described in Patent Document 2. FIG. The depolarizers 81 and 82 shown in FIGS. 21 and 22 each have a birefringent region 801 that functions as a half-wave plate having a phase of 180 ° with respect to light in the green wavelength band, and an isotropic region 802. As a set, and a plurality of the sets are arranged.

Japanese Patent No. 2995985 JP 2006-047421 A

  According to the method described in Patent Literature 1, there is a possibility that the slit width can be narrowed in the optical measurement device without being restricted by the maximum wavelength of the light to be measured by the depolarization element. However, even in this method, since the depolarizing element does not change the light to be measured, the limit for narrowing the slit width is determined by the accuracy of incorporation into the apparatus.

  That is, the conventional depolarizing element has a problem that the light to be measured is separated into a plurality of parts and the direction of separation is changed depending on the wavelength of the incident light. For this reason, when used in a Zerni-Turna type optical measuring instrument, it is necessary to use a slit having a certain width or more, and it is difficult to improve the wavelength resolution.

  Further, the conventional depolarizing element has a problem that high depolarization can be obtained only for light of a specific wavelength. For this reason, in order to obtain high depolarization for all blue, green, and red laser light when used in a projection display device that uses highly coherent light such as laser light as a light source. Three depolarizers optimized for blue, green, and red laser beams had to be prepared, which hindered miniaturization and simplification of the optical system. In addition, when depolarizing elements are applied only to green laser light with high visibility for miniaturization and simplification, speckle noise due to blue laser light and red laser light remains. There was a problem.

  In view of such a problem, the present invention makes it possible to express a spatial distribution in a phase difference without separating incident light with respect to light in a wide wavelength range and without depending on the polarization state of incident light. An object of the present invention is to provide a depolarizing element capable of achieving the above. More specifically, a specific polarization component of the emitted light and a polarization component orthogonal to the incident light can be handled without separating the incident light and without depending on the polarization state of the incident light. An object of the present invention is to provide a depolarizing element capable of converting each of the light quantities of the light into a certain ratio.

  Another object of the present invention is to provide a depolarizing element that can obtain high depolarization properties for light in a wide wavelength range. More specifically, an object of the present invention is to provide a depolarizing element that can cope with a wide wavelength range and can convert linearly polarized light having a specific polarization direction to non-polarized light, that is, light having a polarization degree of zero.

  The depolarizing element according to the present invention includes a first birefringent medium layer and a second birefringent medium layer, wherein the first birefringent medium layer and the second birefringent medium layer are respectively A boundary between each region included in the first birefringent medium layer, including at least one of each of two types of regions having a uniform thickness and a different phase difference and a fast axis direction in the element plane. The phase difference of the first birefringent medium layer and the phase difference of the second birefringent medium layer are coincident with the boundary line of each region included in the second birefringent medium layer. The ratio is 2 ± 0.1: 1, and the angle formed by the fast axes of the two types of regions included in the second birefringent medium layer is 45 ° ± 4 °. The uniform thickness means that the parallelism of the front and back surfaces of the first birefringent medium layer, that is, both interfaces is 0.1 ° or less. The degree of parallelism is 0.1 ° or less.

  The phase difference of the second birefringent medium layer is 300 ° or less with respect to the light with the shortest wavelength among the light incident on the depolarizing element, and 60 with respect to the light with the longest wavelength. It may be more than °.

  The depolarizing element according to the present invention has a wavelength of incident light in a band of 800 nm to 1700 nm, and the second birefringent medium layer has a phase difference with respect to light having the shortest wavelength among incident light. And may be 60 ° or more with respect to light having the longest wavelength.

  The depolarizing element according to the present invention has a wavelength of incident light in a band of 380 nm to 820 nm, and the phase difference of the second birefringent medium layer is smaller than the light having the shortest wavelength among the incident light. And may be 60 ° or more with respect to light having the longest wavelength.

  Further, each of the first birefringent medium layer and the second birefringent medium layer includes two or more of two types of regions having the same phase difference and different fast axis directions in the element plane. In the birefringent medium layer and the second birefringent medium layer, the region having the first fast axis direction and the region having the second fast axis direction are both uniformly distributed in the element plane. It may be arranged.

  The optical measuring instrument according to the present invention guides incident light to be measured to the diffraction grating, stops the light diffracted by the diffraction grating with a lens or a concave mirror, and passes the light through the slit arranged at the focal position to detect the light quantity. An optical measuring instrument having a Zerni-Turner type optical system, comprising one of the depolarizing elements described above in front of the diffraction grating, and the depolarizing element that adjusts the phase difference of the light to be measured incident on the diffraction grating. It is characterized by expressing a spatial distribution.

  The projection display device according to the present invention is a projection display device that uses laser light as a light source, and is provided between the light source and image light generation means that generates image light by modulating light emitted from the light source. Or a depolarizing element including at least two of the two types of depolarizing elements described above between the image light generating means and the projecting means for projecting the image light generated by the image light generating means, It is characterized in that linearly polarized light having a specific polarization direction is incident on the depolarizing element and converted into non-polarized light.

  According to the present invention, polarized light capable of expressing a spatial distribution in a phase difference without separating incident light with respect to light in a wide wavelength range and without depending on the polarization state of incident light. A cancellation element can be provided. Therefore, when used in Zerni-Turna type optical measurement equipment, not only can the influence of polarization dependence of the diffraction grating be avoided, but also the wavelength resolution can be improved without being restricted by the maximum wavelength of the light to be measured. Can do.

  Further, according to the present invention, it is possible to provide a depolarizing element that can obtain high depolarization properties with respect to light in a wide wavelength range. Therefore, when used in a projection display device that uses a laser as a light source, not only can speckle noise be reduced, but only one depolarization element can be used to achieve high polarization for all blue, green, and red laser light. Since the resolvability can be obtained, the projection display device can be reduced in size and simplified.

Sectional drawing which shows the structural example of the depolarizing element of 1st Embodiment. Explanatory drawing which shows an example of the plane pattern of the depolarizing element of 1st Embodiment. Explanatory drawing which shows the other example of the plane pattern of the depolarizer of 1st Embodiment. Explanatory drawing which shows the other example of the plane pattern of the depolarizer of 1st Embodiment. The table | surface which shows an example of the constraint condition given to the parameter applied to a depolarizing element. The relationship between the fast axis direction θ of the first layer first region 131 and the phase difference δ of the second birefringent medium layer 14 with respect to the value of the evaluation function F (δ, θ) in the optical design of the depolarizing element FIG. The table | surface which shows the other example of the restrictions given to the parameter applied to a depolarizer. 6 is a graph showing the relationship between the light wavelength λ and the phase difference δ in the first birefringent medium layer 13. Sectional drawing which shows the other structural example of the depolarizing element of 1st Embodiment. Sectional drawing which shows the other structural example of the depolarizing element of 1st Embodiment. Sectional drawing which shows the other structural example of the depolarizing element of 1st Embodiment. Sectional drawing which shows the structural example of the depolarizing element of 2nd Embodiment. Explanatory drawing which shows an example of the plane pattern of the depolarizing element of 2nd Embodiment. The graph which shows the evaluation result of the depolarizing element of a 1st Example. The graph which shows the evaluation result of the depolarizing element of a 1st Example. The graph which shows the evaluation result of the depolarizing element of a 1st Example. The graph which shows the evaluation result of the depolarizing element of a 1st Example. The graph which shows the evaluation result of the depolarizing element of a 2nd Example. The block diagram of a Zerni-Turna type optical measuring instrument. The perspective view which shows the structural example of the conventional depolarizing element used for a Czerny-Turner type optical measuring device. Explanatory drawing which shows the example of the plane pattern of the conventional depolarizing element used for an image projector. Explanatory drawing which shows the other example of the planar pattern of the conventional depolarizing element used for an image projector.

Embodiment 1. FIG.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. The depolarization element of the present embodiment is assumed to be used in a Zerni-Turna type optical measuring instrument, and depends on the polarization state of incident light with respect to light in a wide wavelength range without separating incident light. In this case, the light is emitted such that the intensity of the polarization component in the X-axis direction of light and the intensity of the polarization component in the Y-axis direction orthogonal thereto are emitted.

  FIG. 1 is a cross-sectional view illustrating an example of a depolarizing element 10 according to the first embodiment. The depolarizing element 10 shown in FIG. 1 includes two birefringent medium layers, that is, a first birefringent layer 13 and a second birefringent medium layer 14 between two transparent substrates 11 and 12. It has been. The two birefringent medium layers 13 and 14 each have one of two types of regions having different fast axis directions (or slow axis directions) in the element plane (in the example shown in FIG. 1, the regions 131 and 132). Or regions 141 and 142). In other words, each of the two birefringent medium layers 13 and 14 is divided into two regions on the plane (on the XY plane in FIG. 1), and the two divided regions have different fast axis directions. ing.

  In the example shown in FIG. 1, in the first birefringent medium layer 13, the region having the first fast axis direction (the left region in FIG. 1) is defined as the first layer first region 131, and the second advance The region having the phase axis direction (the region on the right side in FIG. 1) is shown as the first layer second region 132. Similarly, in the second birefringent medium layer 14, the region having the first fast axis direction (the left region in FIG. 1) is the second layer first region 141, and the second fast axis direction is A region having the right side (the region on the right side in FIG. 1) is shown as a second layer second region 142.

  FIG. 2 is an explanatory diagram showing an example of a planar pattern of the depolarizer 10. 2A schematically shows a planar pattern of the first birefringent medium layer 13 viewed through the transparent substrate 11 of the depolarizer 10 shown in FIG. FIG. 2B shows a planar pattern of the second birefringent medium layer 14 viewed through the transparent substrate 11 and the first birefringent medium layer 13 of the depolarizer 10 shown in FIG. Is schematically shown. A cross-sectional view taken along A-A ′ in FIG. 2 corresponds to FIG. 1.

  The planar pattern of the depolarizing element 10 can be freely determined by the designer. For example, a planar pattern as shown in FIGS. 3 and 4 may be used. That is, when the element is viewed from the upper surface (incident surface), for example, the plane may be formed so as to be divided into two in the lateral direction, or, for example, formed so as to be divided into two in the oblique direction. Also good. 3 and 4 are examples of a plan pattern diagram of the depolarizing element 10 according to the present embodiment, both of which are seen through the transparent substrate 11 of the depolarizing element 10 shown in FIG. 1 schematically shows a planar pattern of one birefringent medium layer 13. A cross-sectional view taken along B-B 'in FIG. 3 and C-C' in FIG. 4 corresponds to FIG.

  The plane pattern of the depolarizing element 10 is optimally designed so that the area ratio of the first layer first region 131 and the first layer second region 132 within the diameter of the incident light is 50:50.

  However, even if the position of the light incident on the depolarizing element is shifted and the area ratio of the first layer first region 131 and the first layer second region 132 within the diameter of the light does not maintain 50:50, the area If the ratio is between 40:60 and 60:40, practically desired characteristics can be obtained. The practically desired characteristics will be described later.

  As shown in FIGS. 2A and 2B, the first birefringent medium layer 13 and the second birefringent medium layer 14 have the same planar pattern, and the first birefringent medium layer 13 and the second birefringent medium layer 13 It is most preferable that the boundary line coincides with the birefringent medium layer 14. For this reason, it is optimal to design the planar pattern of the depolarizer 10 so that the area ratio of the second layer first region 141 and the second layer second region 142 within the diameter of the incident light is also 50:50. It is.

  Although it is most preferable that the first layer boundary line and the second layer boundary line coincide with each other, practically desired characteristics can be obtained as long as the deviation is about 1/100 of the diameter of incident light. Is possible. The practically desired characteristics will be described later.

  The first layer first region 131 and the first layer second region 132 are made of the same birefringent material and have a uniform thickness throughout the first birefringent medium layer 13. Accordingly, the first layer first region 131 and the first layer second region 132 have the same phase difference. The uniform thickness means that the parallelism of the interface is 0.1 ° or less at both interfaces of the first birefringent medium layer.

  Similarly, the second layer first region 141 and the second layer second region 142 are made of the same birefringent material and have a uniform thickness throughout the second birefringent medium layer 14. Accordingly, the second layer first region 141 and the second layer second region 142 have the same phase difference.

  As described above, since the thickness of the two birefringent medium layers 13 and 14 of the depolarizing element 10 is uniform and no slope is formed on the bonding surface of the birefringent medium layer, a wedge-shaped birefringent crystal is formed. The light is not separated by the refracting action due to the inclined surface unlike the conventional depolarizing element in which is bonded.

  Next, a specific configuration of the depolarizer 10 according to this embodiment will be described with reference to FIGS. 1 and 2.

  As long as the transparent substrates 11 and 12 are transparent to incident light, various materials such as a resin plate and a resin film can be used. For example, an optically isotropic material such as glass or quartz glass may be used. In addition, it is preferable to provide an antireflection film made of a multilayer film at the interface between the transparent substrates 11 and 12 and the air because light reflection loss due to Fresnel reflection can be reduced.

Examples of the birefringent material constituting the first birefringent medium layer 13 and the second birefringent medium layer 14 include a polymer liquid crystal obtained by aligning a birefringent liquid crystal monomer and polymerized, and fine irregularities. Birefringence generated due to the shape of a lattice, or a photonic crystal formed by laminating an optical multilayer film on an uneven lattice shape, a birefringent crystal such as crystal or LiNbO ₃ , or an organic film such as polycarbonate A birefringent film obtained by stretching can also be used.

  When a polymer liquid crystal is used, the direction in which the liquid crystal monomer is aligned is the slow axis direction. It is preferable to use a polymer liquid crystal as a material for the birefringent medium layer because the orientation direction can be easily changed. That is, it is preferable that each birefringent medium layer has different fast axis directions (or slow axis directions) for each region.

  In the case of using a photonic crystal, the longitudinal direction of the fine concavo-convex lattice shape and the direction orthogonal to the longitudinal direction become the direction of the birefringence axis (fast axis or slow axis). It is preferable to use a photonic crystal as the material of the birefringent medium layer because it is easy to change the longitudinal direction of the fine uneven shape. That is, as in the case of using a polymer liquid crystal, it is preferable that each birefringent medium layer can have different fast axis directions (or slow axis directions) for each region.

  Further, a birefringent crystal or a birefringent film can also be used as a material for the birefringent medium layer. In this case, a configuration in which the fast axis direction (or the slow axis direction) is different for each region by arranging the materials cut out in the size of each divided region in each birefringent medium layer and bonding them to the transparent substrate, it can.

  Next, an optical design for obtaining the desired characteristics by the depolarizer 10 according to the present embodiment will be described. Here, the desired characteristic is that the light of a wide wavelength range incident on the depolarizing element 10 does not depend on the polarization state, and the intensity of the polarization component in the X-axis direction of the emitted light and the Y that is orthogonal thereto. A characteristic in which the intensity of the polarization component in the axial direction becomes substantially equal.

  In the following description, as the definition of the angle, in the coordinate system of FIG. 2, the X axis is the reference (0 °) and the clockwise direction to the Y axis direction (90 °) is positive.

First, the polarization state of light is expressed using Stokes parameters. The Stokes parameter is composed of four components (S ₀ , S ₁ , S ₂ , S ₃ ), and S ₀ represents the intensity of light. For simplification, it is considered that there are no factors such as absorption, reflection, scattering, and polarizer that change the intensity of incident light in the depolarizing element 10, and S ₀ = 1 and (S ₁ , S ₂ , S ₃ ) Consider the polarization state with the three components.

S ₁ ² + S ₂ ² + S ₃ ² has a value between 0 and 1; when it is 0, it is unpolarized (corresponding to natural light); when it is 1, it is completely polarized; Natural light can be considered as a set or composition of various perfectly polarized light. Hereinafter, the light incident on the depolarizer 10 is designed as completely polarized light. When representative polarization is exemplified using Stokes parameters, linear polarization in the X direction is (1, 0, 0), linear polarization in the Y direction is (-1, 0, 0), and linear polarization in the 45 ° direction is ( (0,1,0), linearly polarized light in the -45 ° direction is (0, -1,0), clockwise circularly polarized light is (0,0,1), and counterclockwise circularly polarized light is (0,0, -1). It is.

The polarization state of the light incident on the depolarization element 10 is (S ₁ in, S ₂ in, S ₃ in), and the polarization state of the light emitted from the depolarization element 10 is (S ₁ out, S ₂ out, S _3). out). In addition, the light transmitted through the first layer first region 131 and the second layer first region 141 of the depolarizer 10 is (S ₁ out ₁ , S ₂ out ₁ , S ₃ out ₁ ), and the depolarizer 10 Let the light transmitted through the first layer second region 132 and the second layer second region 142 be (S ₁ out ₂ , S ₂ out ₂ , S ₃ out ₂ ). Further, the area of the first layer first region 131 within the diameter of the incident light (the same applies to the second layer first region 141) is R1, and the area of the first layer second region 132 (the second layer second region 142 is also equal). When the same is defined as R2, the relationship of the following formula (1) is established.

  Next, when light enters from the transparent substrate 11 side of the depolarizing element 10, passes through the first birefringent medium layer 13 and the second birefringent medium layer 14 in this order, and exits from the transparent substrate 12. The action of the two birefringent medium layers 13 and 14 on the polarization state of incident light will be described.

The phase difference between the phase difference and the first layer a second region 132 of the first layer first region 131 in the thickness of the first birefringent medium layer 13 uniform and equal [delta] _1, advances the first layer first region 131 The phase axis direction is θ ₁₁ , and the fast axis direction of the first layer second region 132 is θ ₁₂ . Similarly, the phase difference between the phase difference and the second layer second region 142 of the second birefringent medium layer 14 has a thickness in a homogeneous second layer first region 141 is equally [delta] _2, the second layer first region The fast axis direction of 141 is θ ₂₁ , and the fast axis direction of the second layer second region 142 is θ ₂₂ . Then, the effect | action which changes the polarization state by the i-th layer j-th area | region can be described using the Mueller matrix Mij of the following formula | equation (2). Here, i is 1 or 2, and j is 1 or 2.

  At this time, the polarization state of the light transmitted through the first layer first region 131 and the second layer first region 141 among the light incident on the depolarizing element 10 is expressed by the following equation (3-1). The Moreover, the polarization state of the light which permeate | transmits the 1st layer 2nd area | region 132 and the 2nd layer 2nd area | region 142 is represented by the following formula | equation (3-2).

  From the above, the polarization state of the light emitted from the depolarizing element 10 is expressed by the following formula (4) using formula (1), formula (3-1), and formula (3-2).

  Next, the desired characteristic of the depolarizer 10, that is, the intensity of the polarization component in the X-axis direction of the emitted light and the intensity of the polarization component in the Y-axis direction orthogonal thereto are independent of the polarization state of the incident light. The relationship between the equal characteristics and the Stokes parameters representing the output polarization state will be described.

The intensity I _X of the polarization component in the X-axis direction and the intensity I _Y of the polarization component in the Y-axis direction of the emitted light can be expressed as the following formula (5) using Stokes parameters.

From equation (5), it can be seen that in order for the intensity I _X and the intensity I _{Y to} be equal, S ₁ out only needs to be zero. That is, S ₁ out becomes zero regardless of the phase difference δ _ij and the fast axis direction θ _ij of the i-th layer and j-th region constituting the depolarizing element 10 without depending on the polarization state of incident light. You just have to decide.

By the way, the value of S ₁ out can be obtained by substituting Equation (2) into Equation (4), but is very complicated. Furthermore, since there are a total of eight parameters δ ₁₁ , δ ₁₂ , δ ₂₁ , δ ₂₂ , θ ₁₁ , θ ₁₂ , θ ₂₁ , and θ ₂₂ that characterize the depolarizing element 10, some parameters are used to simplify the design. It is better to give constraints to these parameters and find the values under those constraints. In addition, it is also possible to obtain each parameter using a computer without giving restrictions.

As an example of the polarization state of incident light, each parameter of the depolarization element 10 is set so that S ₁ out becomes zero when linearly polarized light (1, 0, 0) in the X-axis direction enters the depolarization element 10. The case where a constraint is imposed on is shown below.

  First, in practice, it is effective to consider that the area R1 of the first layer first region 131 and the area R2 of the first layer second region 132 within the diameter of incident light are equal. For example, it is more difficult to intentionally bias the ratio of the area R1 and the area R2 to 6: 4. Here, for convenience of calculation, the area of incident light is set to 1, and area R1 = area R2 = 0.5. Note that the tolerance when the area R1 and the area R2 deviate from the same condition, that is, the tolerance of the area ratio will be described later.

Next, (more specifically, the phase difference with the first layer first region 131 and the first layer second region 132 are both) phase difference first birefringent medium layer 13 has a [delta] _1, second phase difference with the birefringent medium layer 14 (more specifically, the phase difference with the second layer the first region 141 and the second layer second region 142 are both) the ratio of [delta] ₂ is 2: a 1 The phase difference δ ₁ is 2π and the phase difference δ ₂ is π. Since the phase difference is different depending on the wavelength of incident light, it is considered that the wavelength of light having a phase difference of δ ₁ = 2π and δ ₂ = π is incident. Note that the tolerance when the ratio of the phase difference δ ₁ and the phase difference δ ₂ deviates from 2: 1, that is, the tolerance of the phase difference ratio will be described later.

Since the phase difference δ _{1 of} the first birefringent medium layer 13 is 2π, in the first layer first region 131 and the first layer second region 132, the fast axis directions θ ₁₁ , θ of the region Regardless of ₁₂ , the polarization state of the transmitted light is not changed.

At this time, if the fast axis direction θ _{21 of} the second layer first region 141 is 22.5 ° and the fast axis direction θ _{22 of} the second layer second region 142 is −22.5 °, the depolarizer If the X-axis direction linearly polarized light (1, 0, 0) incident on the light is transmitted through the first region side (more specifically, the first layer first region 131 and the second layer first region 141). It is converted into linearly polarized light (0, 1, 0) in the 45 ° direction. Similarly, if the light passes through the second region side (more specifically, the first layer second region 132 and the second layer second region 142), it becomes linearly polarized light (0, -1, 0) in the -45 ° direction. Converted.

By substituting these parameters and the polarization state of the incident light into the above equation (4), the polarization states (S ₁ out, S ₂ out, S ₃ out) of the light emitted from the depolarization element 10 are (0, 0). , 0) is obtained. This means that S ₁ out is zero, and the intensity I _X of the polarization component in the X-axis direction and the intensity I _Y of the polarization component in the Y-axis direction of the emitted light are equal.

So far, a phase difference [delta] ₁ of the first birefringent medium layer 13 is 2 [pi, only the wavelength of a specific light phase difference [delta] ₂ of the second birefringent medium layer 14 becomes [pi, S Several parameters have been determined so that ₁ out becomes zero. Next, with respect to light in a wider wavelength range and without depending on the polarization state of the light incident on the depolarization element 10, each parameter is constrained as a sufficient condition for making S ₁ out zero. Go.

Expanding the wavelength range of light means expanding the width of the phase difference, which is an amount dependent on the wavelength. In the following, 2 as an example, the phase difference [delta] ₁ of the first birefringent medium layer 13 is 2 [pi, the constraint that the phase difference [delta] ₂ is π of the second birefringent medium layer 14, [delta] ₁ is [delta] ₂ Change only to the constraint of being double. That is, δ ₂ = δ and δ ₁ = 2δ ₂ = 2δ.

Further, the fast axis theta ₁₂ of the fast axis direction theta ₁₁ and the first layer a second region 132 of the first layer first region 131 is the remaining _{parameters, θ 11 = θ, θ 12} = -θ 11 = The restriction of −θ is given. Due to this restriction, the action of changing the polarization state of the first layer first region 131 and the first layer second region 132 can be made reciprocal.

FIG. 5 is a table in which the constraints given to each parameter are arranged so far. Substituting the values shown in FIG. 5 into the equations (4) and (2) as the parameters of the depolarizer 10, S ₁ out is given by the following equation (6).

In Expression (6), when S ₁ out is set to zero without depending on the polarization state of incident light, it is understood that the coefficient of S ₁ in on the right side of Expression (6) may be zero.

Here, the coefficient of S ₁ in is an evaluation function F (δ, θ), that is, the following expression (7).

  FIG. 6 is a contour diagram in which the values of the evaluation function F (δ, θ) obtained by calculating the above-described formula (7) and having the horizontal axis as δ and the vertical axis as θ are plotted. As indicated by a dotted line in FIG. 6, θ defined as the fast axis direction of the first layer first region 131 is 79 as a combination of δ and θ where the value of the evaluation function F (δ, θ) is 0. It can be seen that the range of the value of δ defined as the phase difference of the second birefringent medium layer 14 becomes the widest when it is in the vicinity of °.

Here, as a practically desired characteristic of the depolarizer 10, the intensity is given to a state where the intensity I _X of the polarization component in the X-axis direction of the outgoing light is equal to the intensity I _Y of the polarization component in the Y-axis direction. the ratio of I _X may be 0.45 to 0.55. This is synonymous with setting the ratio of the strength I _Y to 0.55 to 0.45. In such a case, the value of the evaluation function F (δ, θ) is −0.1 to 0.1 from the above equations (5) and (6).

  In such a case, the range of θ defined as the fast axis direction of the first layer first region 131 is 79 ± 2 °, and the range of δ defined as the phase difference of the second birefringent medium layer 14 As a result, 83 ° to 276 ° is obtained. As already described, since the phase difference is an amount depending on the wavelength of light, in this example, the second birefringent medium layer is used as the wavelength range in which desired characteristics can be obtained by the depolarizer 10. It can be seen that the phase difference of 14 is in a range from a wavelength indicating 83 ° to a wavelength indicating 276 °.

Further, as a practically desired characteristic of the depolarizer 10, the ratio of the intensity I _X of the polarization component in the X-axis direction of the emitted light may be set to 0.4 to 0.6. This is synonymous with setting the ratio of the intensity I _Y to 0.6 to 0.4. In such a case, the value of the evaluation function F (δ, θ) is −0.2 to 0.2. Then, the range (allowable width) of θ defined as the fast axis direction of the first layer first region 131 is expanded to 78 ° ± 4 °. Note that the range of δ defined as the phase difference of the second birefringent medium layer 14 remains 83 ° to 276 °. Increasing the allowable width of the first layer first region 131 in the fast axis direction θ is preferable because the allowable range of errors in manufacturing the depolarizer 10 can be expanded.

  Alternatively, the range (allowable width) of the fast axis direction θ of the first layer first region 131 is maintained to 77 ° ± 2 °, and the range of the phase difference δ of the second birefringent medium layer 14 is expanded. A combination of 60 ° to 300 ° may be selected. In this case, the wavelength range of light incident on the depolarizing element 10 can be expanded, which is preferable.

  Further, for example, as shown by being surrounded by a one-dot chain line in FIG. 6, when θ is in the vicinity of −56 °, the range of δ is 105 ° to 250 °, and a relatively wide range is obtained as a condition for the phase difference. I understand that In other words, when θ is in the vicinity of −56 °, the second birefringent medium layer 14 has a phase difference of 250 ° from a wavelength at which the second birefringent medium layer 14 has 105 ° as a wavelength range in which desired characteristics can be obtained by the depolarizer 10. It turns out that it becomes the range to the wavelength which shows. Even in such a case, it is understood that the depolarizer 10 can obtain desired characteristics with a wide band of wavelengths.

  Further, for example, as shown by being surrounded by a two-dot chain line in FIG. 6, when δ is 125 ° to 237 °, a wide range of θ of 71 ° ± 11 ° is obtained. That is, when the wavelength range of the light incident on the depolarizing element 10 is between the wavelength of the light having the phase difference δ of the second birefringent medium layer 14 indicating 125 ° and the wavelength of the light indicating 237 °. In addition, the depolarizing element 10 can obtain desired characteristics within a wide tolerance that the fast axis direction θ of the first layer first region 131 is 71 ° ± 11 °.

  The above-described example is merely an example. Specifically, the first layer and the first region are determined depending on characteristics required for the depolarizer 10, a wavelength range of light to be used, and an allowable error in manufacturing the depolarizer 10. The range of the fast axis direction θ of 131 and the range of the phase difference δ of the second birefringent medium layer 14 may be determined as appropriate. If θ and δ are determined, the values of other parameters are also determined from the constraint conditions shown in FIG.

Further, the allowable value when the area ratio of the divided regions is deviated from 1: 1, the phase difference ratio between the first birefringent medium layer 13 and the second birefringent medium layer 14 is deviated from 2: 1. Or when the fast axis direction θ _{21 of} the second layer first region 141 deviates from 22.5 °, or the fast axis direction θ _{22 of} the second layer second region 142 is −22.5 °. The table of FIG. 7 shows an example of allowable values in the case of deviation from the above. Note that the tolerance shown in FIG. 7 does not depend on the polarization state of light in a wide wavelength range incident on the depolarizing element 10, and the intensity of the polarization component in the X-axis direction of the emitted light is 0.4 to 0.4. This is an allowable value when 0.6.

As shown in FIG. 7, the area ratio of the divided regions may be 0.45: 0.55 to 0.55: 0.45 when the area of incident light is 1. The phase difference ratio may be 2 ± 0.1: 1. Further, the fast axis direction theta ₂₁ of the second layer the first region 141 and for the fast axis theta ₂₂ of the second layer second region 142 may be tolerances ± 2 °, respectively.

  By producing the depolarization element 10 using the parameters determined based on the optical design method as described above, the depolarization element 10 having the desired characteristics as described above can be obtained.

  In addition, the characteristics of the depolarizing element 10 are further generalized, and polarization of light in a direction rotated by θout from the X axis of the emitted light is independent of the polarization state with respect to light in a wide wavelength range incident on the depolarizing element 10. A characteristic in which the intensity of the component and the intensity of the polarization component in a direction orthogonal thereto may be set as a desired characteristic. In this case, among the parameters that characterize the depolarizer 10, θout may be added in the fast axis direction of each region.

  In the optical design method described above, the parameters for the depolarization element 10 of the present embodiment to obtain desired characteristics are determined on the assumption that light is incident from the transparent substrate 11 side. Even if the element is rotated by 90 °, 180 °, and 270 °, similar characteristics can be obtained. Furthermore, the same characteristics can be obtained even when the light is incident from the transparent substrate 12 side with the front and back reversed and rotated by 2 × θout.

  Further, the fast axis direction of the first layer first region 131 and the fast axis direction of the first layer second region 132 are interchanged, and at the same time, the fast axis direction of the second layer first region 141 and the second layer second region Similar characteristics can be obtained when the fast axis direction of the region 142 is switched.

  As a supplement, the relationship between the phase difference and the wavelength will be described. FIG. 8 is a graph showing the relationship between the light wavelength λ (horizontal axis) and the phase difference δ (vertical axis) in the first birefringent medium layer 13. δ and λ have the relationship of the following formula (8).

  Here, d represents the thickness of the birefringent medium layer. Δn is the birefringence magnitude of the birefringent material and is a function of the wavelength (λ). Δn can be approximated using the following equations (9) using coefficients A, B, and C. A, B, and C are specific values determined by the birefringent material. The graph of FIG. 8 is a graph.

  That is, the wavelength is the longest when the minimum phase difference that the second birefringent medium layer 14 can have is δmin (λmax), and the wavelength is the shortest when the maximum phase difference is δmax (λmin). Have a relationship.

  Further, the depolarizing element 10 according to the present embodiment can be configured by reducing the number of transparent substrates that are constituent elements, and can be thinned. 9-11 is sectional drawing which shows the other structural example of the depolarizing element 10 which concerns on this embodiment. For example, as shown in FIG. 9, the second birefringent medium layer 14 including the second layer first region 141 and the second layer second region 142 is laminated on the transparent substrate 12, and the second birefringent medium layer 14 is further formed thereon. The first birefringent medium layer 13 including the first layer first region 131 and the first layer second region 132 may be stacked. An antireflection film (not shown) may be applied to the interface between the first birefringent medium layer 13 and the air.

  For example, as shown in FIG. 10, the first birefringent medium layer 13 including the first layer first region 131 and the first layer second region 132 is laminated on the transparent substrate 11, and further on it. The second birefringent medium layer 14 including the second layer first region 141 and the second layer second region 142 may be stacked. An antireflection film (not shown) may be applied to the interface between the second birefringent medium layer 14 and the air.

  For example, as shown in FIG. 11, the first birefringent medium layer 13 including the first layer first region 131 and the first layer second region 132 is laminated on one surface of the transparent substrate 11, and the other The second birefringent medium layer 14 including the second layer first region 141 and the second layer second region 142 may be laminated on the surface. An antireflection film (not shown) may be applied to the interface between the first birefringent medium layer 13 and the air and the interface between the second birefringent medium layer 14 and the air.

  As described above, according to the present embodiment, the intensity of the polarization component in the X-axis direction of the emitted light and the Y-axis direction orthogonal to the intensity of the emitted light do not depend on the polarization state of the incident light in a wide wavelength range. It is possible to obtain the depolarizing element 10 in which the intensity of the polarization component is substantially equal.

  In addition, if the depolarizing element 10 of the present embodiment is used, in an optical measuring instrument having a Zerni-Turner type optical system, incident light is separated without separating incident light with respect to light in a wide wavelength range. The light to be measured can be incident on the diffraction grating without depending on the polarization state. For this reason, the slit width can be reduced without being restricted by the maximum wavelength of the light to be measured by the depolarizer. Therefore, the wavelength resolution can be improved.

  In the case of incorporating into a Zerni-Turna type optical measuring instrument, the depolarizing element 10 may be arranged in front of the diffraction grating as in the example shown in FIG.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to the drawings. The depolarization element of this embodiment assumes the case where it is used for a projection display device using a laser as a light source, and has the characteristic of converting linearly polarized light in the θin direction, which is incident as complete polarized light, into non-polarized light over a wide wavelength range. It has been expressed.

  FIG. 12 is a cross-sectional view showing an example of the depolarizing element 20 according to the second embodiment of the present invention. As in the first embodiment, the depolarizing element 10 shown in FIG. 12 includes two birefringent medium layers, that is, the first birefringent medium layer 23 and the second birefringent medium layer 23 between the two transparent substrates 21 and 22. Two birefringent medium layers 24 are provided. Further, each of the two birefringent medium layers 23 and 24 has two or more of two types of regions having different fast axis directions (or slow axis directions) in the element plane (in the example shown in FIG. 231 group and 232 group or region 241 group and 242 group). In other words, each of the two birefringent medium layers 23 and 24 is divided into four or more regions on a plane (on the XY plane in FIG. 12), and each of the divided regions has two different fast axis directions. One of the fast axis directions. In the present embodiment, the regions having the first fast axis direction and the regions having the second fast axis direction are arranged so as to be uniformly distributed in the element plane in each layer. The area of the region having the first fast axis direction is preferably substantially the same as the area of the region having the second fast axis direction.

  For example, the region having the first fast axis direction and the region having the second fast axis direction are set as one set, and these sets are arranged so that the fast axis directions are different between adjacent regions. Also good. That is, the depolarizing element 20 of the present embodiment has the size of the depolarizing element 10 of the first embodiment sufficiently small with respect to the light diameter, and is connected in the vertical and horizontal directions so that It may be considered that the number of area divisions is increased.

  In the example shown in FIG. 12, in the first birefringent medium layer 23, the region having the first fast axis direction is defined as the first layer first region 231, and the region having the second fast axis direction is defined. Each is shown as a first layer second region 232. Similarly, in the second birefringent medium layer 24, the region having the first fast axis direction is defined as the second layer first region 241, and the region having the second fast axis direction is defined as the second layer. This is shown as a second region 242.

  FIG. 13 is an explanatory diagram illustrating an example of a planar pattern of the depolarizing element 20 according to the present embodiment. FIG. 13A schematically shows a planar pattern of the first birefringent medium layer 23 viewed through the transparent substrate 21 of the depolarizer 20 shown in FIG. FIG. 13B shows a planar pattern of the second birefringent medium layer 24 seen through the transparent substrate 21 and the first birefringent medium layer 23 of the depolarizer 20 shown in FIG. Is schematically shown. A cross-sectional view taken along D-D ′ in FIG. 13 corresponds to FIG. 12.

  As shown in FIGS. 13A and 13B, in this example, the planar patterns of the first birefringent medium layer 23 and the second birefringent medium layer 24 are equal. That is, the first layer boundary line that is the boundary line between the first layer first region 231 and the first layer second region 232, and the boundary line between the second layer first region 141 and the second layer second region 142. It coincides with the two-layer boundary line. Although it is most preferable that the first layer boundary line and the second layer boundary line coincide with each other, practically desired characteristics can be obtained as long as the deviation is about 1/100 of the diameter of incident light. Is possible. The practically desired characteristics will be described later.

  In FIG. 13, the area division number of the depolarizing element 20 is shown as 64 divisions, but the area division number is not limited to this. For example, as the number of area divisions increases, the proportion of the area of both areas within the light diameter, that is, the area having the first fast axis direction and the area having the second fast axis direction is averaged and equalized. Therefore, it is preferable because it becomes tolerant to the deviation between the position where the light is incident and the divided region. Further, it is preferable that the number of regions in the light diameter is larger, because the light becomes unpolarized within the light diameter. However, as the area of each divided region becomes smaller, the requirement for processing accuracy becomes stricter. Therefore, it may be appropriately determined in consideration of the allowable range of errors during manufacturing.

  The depolarizing element 20 can be manufactured with the same optical design as the depolarizing element 10 according to the first embodiment. Hereinafter, in order to explain the function of the depolarizing element 20 according to the present embodiment, the depolarizing element 20 designed with each parameter under the constraint conditions shown in FIG. 5 is used as an example.

When the polarization states (S ₁ out, S ₂ out, S ₃ out) of the light emitted from the depolarizing element 20 are calculated using the above formulas (2) and (4), the following formula (10) is obtained. Given. R1 uses the sum of the areas of the first layer first region 231 group within the diameter of the incident light (the sum of the areas of the second layer first region 231 group is also the same), and R2 is the incident light The total area of the first layer / second area 232 group within the diameter (the total area of the second layer / second area 242 group may be the same) may be used.

Among the formula _(10), wherein indicating the S 1 out is the same as the above equation (6). In addition, when the polarization state (S ₁ in, S ₂ in, S ₃ in) of the light incident on the depolarizer 20 is linearly polarized light (1, 0, 0) in the X-axis direction, S ₂ out and S ₃ out becomes zero. Further, S ₁ out is given by the same equation as the evaluation function F (δ, θ) defined by the above equation (7).

  Here, the degree of polarization P given by the following equation (11) is considered as an index of the degree of polarization of light. When the polarization degree P is 0, it corresponds to non-polarized light, that is, natural light, when it is 1, it is completely polarized light, and when it is in the middle, it is partially polarized light.

Since the polarization state of the outgoing light of the depolarizing element 20 is S ₁ out = F (δ, θ) and S ₂ out = S ₃ out = 0, the polarization degree P of the outgoing polarization is F (δ, θ). There is nothing else. That is, the depolarizing element 20 of the present embodiment assumes that linearly polarized light in a specific direction is incident, and the optical design method shown in the first embodiment has a wide wavelength range of incident light. It can be seen that the evaluation function F (δ, θ) may be made so as to have a parameter such that it is substantially zero. If the linearly polarized light in the direction of 0 ° is incident on the depolarizing element 20 produced using the parameters of the depolarizing element 10 of the first embodiment, the depolarizing element 10 of the first embodiment. Means that the light in the wavelength range allowed is converted to non-polarized light whose polarization degree of the emitted light is substantially zero.

  Here, when converting linearly polarized light in a specific θin direction instead of 0 ° into non-polarized light, among the parameters characterizing the depolarizing element 20, θin may be added in the fast axis direction of each region. Thereby, the characteristic which is the desired characteristic of the depolarization element 20, and converts the linearly polarized light in the θin direction, which is incident as complete polarized light, into non-polarized light with respect to light in a wide wavelength range can be developed.

  Note that the desired characteristic of the depolarizer 20 of the present embodiment is a characteristic that converts linearly polarized light in the θin direction that is incident as complete polarized light into non-polarized light with respect to a wide wavelength range. May not necessarily be 0. For example, if the degree of polarization P of the emitted light is 0.1 or less, it may be considered practically non-polarized light. In addition, for example, if the degree of polarization P of the emitted light is 0.05 or less or 0.01 or less, it is closer to a non-polarized state, and may be regarded as better characteristics. Therefore, it is preferable to set desired characteristics of the depolarizing element 20 according to the application and determine the center value and tolerance of each parameter.

  As described above, when the depolarizing element 20 of the present embodiment is used, in a projection type display device using a highly coherent laser beam or the like as a light source, the degree of polarization of linearly polarized light with respect to light in a wide wavelength range is substantially zero. It is possible to reduce the coherence. Therefore, speckle noise can be stably reduced over the entire projected image. In addition, this makes it possible to reduce the number of depolarizing elements mounted on the projection display device, and to reduce the size and simplify the optical system.

  When incorporated in a projection display device, a light source and an image light generation unit that modulates light emitted from the light source to generate image light, or an image light generation unit and an image light generation unit are provided. What is necessary is just to arrange | position the depolarization element 20 so that the linearly polarized light of a specific polarization direction may inject between the projection means which projects the produced | generated image light. Here, the image light generating means is, for example, a spatial light modulator such as a digital micromirror device (DMD) or a liquid crystal panel. The projection means is, for example, a projection lens system that projects light modulated by a spatial light modulator onto a screen. Whether the light source is configured to use only one laser light source or a plurality of laser light sources that emit light of different wavelengths, a combination of a light source that does not have coherency and a laser light source is combined. The structure to be used may be used. Further, a lens system for collimating or condensing the light beam emitted from the laser light source may be added between the laser light source and the projection lens. Alternatively, the spatial modulator may be a scanning mirror, and the light from the laser light source may be directly projected onto the screen.

  In such a projection display device, for example, light emitted from a light source enters a spatial light modulator via a depolarization element 20 as a phase modulation element. The light beam incident on the spatial light modulator is modulated according to the image signal and projected onto a screen or the like by the projection lens system. At this time, each component may be disposed on the depolarizing element 20 so that the linearly polarized light whose polarization direction is 0 ° or θin in the definition of the angle described above is incident.

  With this configuration, in a projection display device using a laser as a light source, linearly polarized light can be converted into non-polarized light having a polarization degree of substantially zero by the depolarizer 20 with respect to light in a wide wavelength range. Can be reduced.

  Next, an example of the configuration of the present invention will be described in detail using a specific example. The first example is an example of the depolarizing element 10 according to the first embodiment shown in FIGS. 1 and 2. In the present embodiment, the intensity of the polarization component in the X-axis (0 °) direction of the emitted light and the Y-axis (90 perpendicular to the X-axis (90 °) direction of the light with a wavelength of 800 nm to 1700 nm are not dependent on the polarization state. °) A depolarizing element having a characteristic in which the intensity of the polarization component in the direction is substantially equal.

  In this embodiment, quartz glass is used as the transparent substrate 11. First, an antireflection film is formed on the air side surface of the transparent substrate 11. Next, after forming a polyimide film (not shown), rubbing is performed to form an alignment film. At this time, in order to align only the first layer first region 131, the first layer second region 132 is masked with a stainless steel mask and then rubbed in a direction of -11 °. Next, in order to align only the first layer second region 132, the first layer first region 131 is masked with a stainless steel mask and then rubbed in the direction of + 11 °.

Next, a polymer liquid crystal layer having a thickness of 9.3 μm is uniformly formed on the surface of the transparent substrate 11 on which the alignment treatment has been performed, thereby forming the first birefringent medium layer 13. The polymer liquid crystal has physical properties such that the coefficient of the wavelength dispersion formula of the birefringence Δn in the above-described formula (9) is A = 0.095, B = 0.0082, and C = −2.3 × 10 ^−6. Something is used.

At this time, the phase difference of the first birefringent medium layer 13 is 451 ° for light having a wavelength of 800 nm and 193 ° for light having a wavelength of 1700 nm. Further, since the fast axis direction is orthogonal to the rubbing direction, the fast axis direction θ ₁₁ of the first layer first region 131 is 79 °. Further, the fast axis direction theta ₁₂ of the first layer second region 132 is -79 °.

Next, as in the case of the transparent substrate 11, the second layer first region 141 and the second layer second region 142 are provided on the transparent substrate 12 made of quartz glass having an antireflection film on the air side surface. Two birefringent medium layers 14 are formed. Here, the fast axis direction θ _{21 of} the second layer first region 141 is 22.5 °, and the slow axis direction θ _{22 of} the second layer second region 142 is −22.5 °. An orientation process has been performed. The second birefringent medium layer 14 is made of the same polymer liquid crystal as that of the first birefringent medium layer 13 and is uniformly formed to a thickness of 4.65 μm. The phase difference of the second birefringent medium layer 14 is 225.5 ° for light with a wavelength of 800 nm and 96.5 ° for light with a wavelength of 1700 nm.

  Next, the first birefringent medium layer 13 and the second birefringent medium layer 14 are bonded together using a transparent adhesive (not shown) so as to face each other. As the adhesive, an ultraviolet curable adhesive is used.

  The areas of light passing through the first layer first region 131 and the first layer second region 132 of FIG. 2 are equal from the transparent substrate 11 side of the depolarizer 10 thus manufactured. When light is incident, it can be confirmed that the light passes straight without being separated by refraction. This is because the thicknesses of the two birefringent medium layers 13 and 14 of the depolarizing element 10 are uniform, and no slope is formed on the boundary surface.

  Next, evaluation results of characteristics of the depolarizer 10 are shown in FIGS. 14-17 is a graph which shows the evaluation result of the depolarizing element 10 of a present Example. 14-17, the vertical axis | shaft of the graph has shown the intensity | strength of the polarization component of the X-axis direction and the intensity | strength of the polarization component of the Y-axis direction normalized with the emitted light quantity as 1. In FIG. The horizontal axis of the graph is the wavelength of incident light. 14 to 17 show the results of evaluating light having a wavelength of 800 nm to 1700 nm as incident light.

  FIG. 14 is a graph showing a result obtained by entering linearly polarized light having a polarization direction of 0 ° as incident polarized light. FIG. 15 is a graph showing a result obtained by entering linearly polarized light having a polarization direction of 90 ° as incident polarized light. FIG. 16 is a graph showing the results obtained by entering clockwise circularly polarized light as incident polarized light. FIG. 17 is a graph showing the results obtained by making counterclockwise circularly polarized light incident as incident polarized light. In any case, the area of light passing through the first region 131, 141 and the second region 132, 142 in FIG. 2 from the transparent substrate 11 side of the depolarizer 10 is equal. Incident.

  16 to 17, the portion where the dotted line indicating the intensity of the Y direction component disappears indicates that it overlaps with the solid line indicating the intensity of the X direction component. For example, in FIGS. 16 and 17, the X-direction component intensity and the Y-direction component intensity are equal, so that the lines are overlapped.

From equation (6), it can be seen that if the S ₁ out component of the Stokes parameter of the emitted light is zero, the intensity of the X direction component is equal to the intensity of the Y direction component. Further, from the equation (6), it is understood that S ₁ out becomes zero when S ₁ in is zero or the evaluation function F (δ, θ) that is a coefficient thereof is zero. As shown in FIGS. 16 and 17, when light having zero S ₁ in component of the Stokes parameter is incident on the depolarizing element 10 of this embodiment, such as clockwise circularly polarized light or counterclockwise circularly polarized light, The intensity of the X direction component of the emitted light is equal to the intensity of the Y direction component.

  Further, since the polarization state may be considered as a combination of linearly polarized light having a polarization direction of 0 ° and 90 °, or a combination of clockwise circularly polarized light and counterclockwise circularly polarized light, FIG. 14 and FIG. 16 and FIG. 17 show that according to the depolarizing element 10 of the present embodiment, at least the light with a wavelength of 800 nm to 1700 nm is emitted regardless of the incident polarization. It means that the intensity of the X direction component and the intensity of the Y direction component are substantially equal to 0.5.

  Next, a second embodiment will be described. The second example is an example of the depolarizing element 20 according to the second embodiment shown in FIGS. 12 and 13. In this example, a depolarizing element is obtained that obtains the characteristic of converting linearly polarized light in the θin direction incident as complete polarized light into non-polarized light with respect to light in a wavelength band of 380 nm to 820 nm.

The manufacturing method is the same as that of the depolarizing element 10 of the first embodiment. That is, first, a first birefringent medium having a first layer first region 231 group and a first layer second region 232 group on a transparent substrate 21 made of quartz glass having an antireflection film on the air side surface. Layer 23 is formed. Incidentally, alignment treatment is performed so fast axis theta ₁₁ of the first layer first region 231 group respectively become 79 °. The alignment process fast axis theta ₁₂ of the first layer second region 232 groups so that each becomes -79 ° have been made. The polymer liquid crystal as the birefringent material of the first birefringent medium layer 23 has coefficients of formula (9) indicating birefringence Δn of A = 0.0861, B = 0.0037, C = −8. A material having physical properties of 1 × 10 ⁻⁷ is used.

  The thickness of the polymer liquid crystal of the first birefringent medium layer 23 was a uniform thickness of 4.65 μm. At this time, the phase difference of the first birefringent medium layer 23 is 456 ° for light having a wavelength of 400 nm and 224 ° for light having a wavelength of 700 nm.

Next, a second birefringent medium layer having a second layer first region 241 group and a second layer second region 242 group on a transparent substrate 22 made of quartz glass having an antireflection film on the air side surface. 24 is formed. The orientation process is performed so that the fast axis direction θ ₂₁ of the second layer first region 241 group is 22.5 °. Further, the orientation process is performed so that the fast axis direction θ ₂₂ of the second layer second region 242 group is −22.5 °, respectively. The polymer liquid crystal as the birefringent material of the second birefringent medium layer has a coefficient of the wavelength dispersion formula of the birefringence Δn of the above formula (9) as A = 0.0314, B = 0.0013, A material having physical properties of C = −5.5 × 10 ⁻⁶ is used.

  The thickness of the polymer liquid crystal of the second birefringent medium layer 24 was made uniform at 6.38 μm. At this time, the phase difference of the second birefringent medium layer 24 is 227 ° for light having a wavelength of 400 nm and 112 ° for light having a wavelength of 700 nm.

  Next, the first birefringent medium layer 23 and the second birefringent medium layer 24 are bonded together using a transparent adhesive (not shown) so that they face each other. As the adhesive, an ultraviolet curable adhesive is used.

  FIG. 18 shows the evaluation results of the characteristics of the depolarizing element 20 produced in this way. In FIG. 18, the vertical axis of the graph indicates the degree of polarization P of the emitted light. The horizontal axis of the graph is the wavelength of incident light. FIG. 18 shows the result of evaluating linearly polarized light having a wavelength of 350 nm to 850 nm and a polarization direction of 0 ° as incident light. More specifically, the evaluation result of the degree of polarization of the emitted light when such incident light is incident from the transparent substrate 21 side of the depolarizing element 20 is shown.

  As shown in FIG. 18, according to the depolarizing element 20 of this example, the emitted light has a degree of polarization of 0.05 or less and is substantially unpolarized with respect to light having a wavelength of 350 nm to 850 nm. It turns out that it is converted.

(Comparative example)
Next, as a comparative example, a case where light incident on a depolarizing element 92 having a slope as shown in FIG. 20 is separated will be described. In this comparative example, a wedge-shaped quartz crystal having a small apex angle of 10 ° as the depolarizing element 92 faces the inclined surface and exhibits ordinary light refraction and extraordinary light refraction. A description will be given of an example in which the crystal axes (abnormal optical axes) are bonded so that the inclined surfaces face each other so that they overlap each other.

In the ordinary light following equation wavelength dispersion of the refractive index n _o crystal 12, also an approximately given by equation (13) below the wavelength dispersion of the extraordinary refractive index n _e. Ao, Bo, Co, Ae, Be, and Ce are constants, and Ao = 1.5137, Bo = 0.0006, Co = −0.0001, Ae = 1.5405, Be = 0.0006, Ce = −0.0001.

When the wavelength λ of the incident light is 1300 nm, n _o = 1.5343 and n _e = 1.5432. When linearly polarized light having a wavelength of 1300 nm and a polarization direction of 45 ° is perpendicularly incident on the conventional depolarizing element 92, the extraordinary light of the second wedge-shaped crystal passes through the normal optical axis of the first wedge-shaped crystal. The light component that passes through the axis and the light component that passes through the abnormal optical axis of the first wedge-shaped quartz crystal and passes through the ordinary optical axis of the second wedge-shaped quartz crystal are divided into two.

  The component of the light passing through the normal optical axis of the first wedge-shaped quartz is incident on the inclined surface at 10 °, refracted by the difference between the ordinary light refractive index and the extraordinary light refractive index, and proceeds in the direction of 9.942 ° with respect to the inclined surface. . Further, the light enters the air interface of the second wedge-shaped crystal at −0.058 °, is refracted due to the difference between the extraordinary refractive index and the refractive index of air, and in the direction of −0.089 ° to the air interface. Emits into the air. The direction of refraction can be calculated according to Snell's law.

  Similarly, the light component passing through the extraordinary optical axis of the first wedge-shaped quartz is incident on the slope at 10 °, refracted by the difference between the extraordinary refractive index and the ordinary refractive index, and 10.58 ° to the slope. Proceed in the direction of Furthermore, the light enters the air interface of the second wedge-shaped quartz at 0.058 °, is refracted by the difference between the ordinary refractive index and the refractive index of air, and enters the air in the direction of 0.090 ° with respect to the air interface. Exit.

  That is, the light component passing through the abnormal optical axis of the second wedge-shaped crystal through the normal optical axis of the first wedge-shaped crystal and the second component passing through the abnormal optical axis of the first wedge-shaped crystal. The component of the light passing through the ordinary optical axis of the wedge-shaped quartz exits the conventional depolarizing element 92 with a separation angle of 0.179 °. Further, as shown in the equations (12) and (13), it can be seen that since the refractive index of quartz has wavelength dispersion, the separation angle also varies depending on the wavelength.

  The present invention can be widely applied to applications that eliminate the polarization of incident light, but is particularly applicable to applications that improve wavelength resolution in an optical measuring instrument having a Zerni-Turner type optical system. Further, the projection display device using a laser as a light source can be suitably applied to an application for reducing speckle noise while miniaturizing and simplifying an optical system.

10, 20 Depolarization element 11, 12, 21, 22 Transparent substrate 13, 23 First birefringent medium layer 131, 231 First layer first region 132, 232 First layer second region 14, 24 Second Birefringent medium layer 141, 241 Second layer first region 142, 242 Second layer second region

Claims (7)

A first birefringent medium layer;
A second birefringent medium layer,
The first birefringent medium layer and the second birefringent medium layer are each of two types of regions having a uniform thickness and having the same phase difference and different fast axis directions in the element plane. Each including at least one
The boundary line of each region included in the first birefringent medium layer and the boundary line of each region included in the second birefringent medium layer are coincident,
The ratio of the phase difference of the first birefringent medium layer to the phase difference of the second birefringent medium layer is 2 ± 0.1: 1.
The depolarizing element, wherein an angle formed by the fast axes of the two types of regions included in the second birefringent medium layer is 45 ° ± 4 °. The phase difference of the second birefringent medium layer is 300 ° or less with respect to the light with the shortest wavelength among the light incident on the depolarizing element, and 60 ° with respect to the light with the longest wavelength. The depolarizing element according to claim 1. The wavelength of the incident light is in the band of 800 nm to 1700 nm,
The phase difference of the second birefringent medium layer is 300 ° or less with respect to light having the shortest wavelength among incident light and 60 ° or more with respect to light having the longest wavelength. The depolarizing element according to claim 1 or 2. The wavelength of the incident light is in the band of 380 nm to 820 nm,
The phase difference of the second birefringent medium layer is 300 ° or less with respect to light having the shortest wavelength among incident light and 60 ° or more with respect to light having the longest wavelength. The depolarizing element according to claim 1 or 2. The first birefringent medium layer and the second birefringent medium layer each include two or more of two types of regions having the same phase difference and different fast axis directions in the element plane,
In the first birefringent medium layer and the second birefringent medium layer, both the region having the first fast axis direction and the region having the second fast axis direction are uniform in the element plane. The depolarizing element according to any one of claims 1 to 4, wherein the depolarizer is arranged so as to be distributed. Light with a Zerni-Turner type optical system that guides incident measured light to the diffraction grating, stops the light diffracted by the diffraction grating with a lens or a concave mirror, and passes it through a slit arranged at the focal position to detect the amount of light A measuring instrument,
The depolarizing element according to any one of claims 1 to 4 is provided in a front stage of the diffraction grating,
A spatial distribution is expressed in the phase difference of the light to be measured incident on the diffraction grating by the depolarizing element. A projection display device that uses laser light as a light source,
Between the light source and the image light generating means for generating image light by modulating the light emitted from the light source, or the image light generating means, and a projecting means for projecting the image light generated by the image light generating means Between, the depolarizing element according to claim 5 is provided,
A projection-type display device, wherein linearly polarized light having a specific polarization direction is incident on the depolarizing element and converted into non-polarized light.