JP4258958B2 - Method and apparatus for manufacturing polarization phase modulation element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a polarization phase modulation element.Manufacturing method and manufacturing apparatusAndFor example,Integrator optics used in projector lighting systemsInPolarization phase modulation element capable of improving the light utilization efficiency by adding a polarization conversion functionofProduction methodAnd manufacturing equipmentIt is about.
[0002]
[Prior art]
In a spatial light modulation element that displays an image by light modulation of specific polarization, such as a liquid crystal panel, illumination light other than the specific polarization is absorbed by the polarizer, and therefore generally about half of the illumination light is lost. In order to solve this problem and improve the light utilization efficiency, various illumination systems that perform polarization conversion by separating the polarization and rotating the polarization plane (that is, the vibration plane of the electric vector) have been proposed. An example is shown in FIG.
[0003]
FIG. 21 shows a liquid crystal projector that projects a display image of the liquid crystal panel (28) onto a screen surface (not shown) by a projection lens (29). In order to illuminate the liquid crystal panel (28), the liquid crystal projector has a lamp (20), a first lens array (22A), a second lens array (22B), a PBS (polarizing beam splitter) array (24), 1/2. An illumination system including a wave plate (25), an overlapping lens (26), and a condenser lens (27) is provided. The lamp (20) is composed of a light source (20a) that emits illumination light and a parabolic mirror (20b) that makes the illumination light from the light source (20a) substantially parallel light, and is emitted from the lamp (20). The illuminated light is incident on a lens array type integrator optical system composed of the first and second lens arrays (22A, 22B).
[0004]
FIG. 22 shows the lens cell pattern (P1) of the first lens array (22A). The first lens array (22A) is formed by arranging rectangular lens cells substantially similar to the liquid crystal panel (28) in a two-dimensional array, and divides incident light by a plurality of lens cells. Then, a plurality of light source images (ellipses in FIG. 23) are formed in the vicinity of the second lens array (22B) having the same array structure as the first lens array (22A). Since each lens cell of the first lens array (22A) and the liquid crystal panel (28) are in a conjugate relationship via each lens cell of the second lens array (22B), the spatial energy distribution of the illumination light is The liquid crystal panel (28) is uniformly illuminated without being wasted.
[0005]
The illumination light emitted from the second lens array (22B) enters the PBS array (24) located in the vicinity thereof and is separated into two linearly polarized lights (that is, TM polarized light and TE polarized light) whose polarization planes are orthogonal to each other. The In FIG. 21, the solid line is TM-polarized light (the vibration direction of the electric vector is parallel to the paper surface), and the broken line is TE-polarized light (the vibration direction of the electric vector is perpendicular to the paper surface). A strip-shaped half-wave plate (25) is affixed to the exit side of the PBS array (24). Of the two polarized lights separated by the PBS array (24), only the TE polarized light is 1/2. The light enters the wave plate (25).
[0006]
FIG. 23 shows the arrangement of the lens cell pattern (P2) of the second lens array (22B), the light source image formed by the first lens array (22A), and the pasting of the half-wave plate (25, hatched portion). The relationship with the attachment pattern is shown. In FIG. 23, the ellipse overlapping the half-wave plate (25) is a light source image composed of TE polarized light, and the ellipse (cross hatch portion) located on the same lens cell as that of each light source image is TM polarized light. (The direction of polarization: the direction of the arrow in the ellipse). The half-wave plate (25) converts TE polarized light into TM polarized light by rotating the polarization plane of TE polarized light by 90 °. Therefore, all illumination light becomes TM polarized light. The illumination light aligned with the TM polarized light passes through the overlapping lens (26) and the condenser lens (27), and then illuminates the liquid crystal panel (28).
[0007]
As can be seen from FIGS. 21 to 23, in the above-described lens array type integrator optical system, the second lens array (22B) is composed of lens cells having the same shape and size as the first lens array (22A). For this reason, it is difficult to make the integrator optical system compact while maintaining high light utilization efficiency. In addition, since the F number is restricted, it is difficult to make the projection lens (29) compact. In FIG. 21, the lens cell size of the first lens array (22A) is d1, the optical distance from the first lens array (22A) to the second lens array (22B) is F1, and the size of the liquid crystal panel (28) is Assuming that the optical distance from the superposed lens (26) to the condenser lens (27) is F2, the relationship d1: F1 = d2: F2 is substantially established, and the illumination F number is substantially determined by F1 / D.
[0008]
In order to solve the above problem, an integrator optical system in which the second lens array is configured by a plurality of types of lens cells having different aperture shapes and aperture sizes is proposed in Japanese Patent Laid-Open No. 10-197827. According to this configuration, since the interval between the light source images is narrowed and the F number is increased, the light utilization efficiency can be improved and the size can be reduced.
[0009]
[Problems to be solved by the invention]
In the integrator optical system described in Japanese Patent Application Laid-Open No. 10-197827, the illumination light is separated into two linearly polarized light whose polarization planes are orthogonal to each other by a polarization separating element and pasted to each lens cell of the second lens array. By rotating the plane of polarization of one linearly polarized light by 90 ° with the wave plate, the planes of polarization of the two linearly polarized lights are made the same. This polarization conversion allows only linearly polarized light with the same plane of polarization to be incident on the polarizer, so there is almost no light loss due to the polarizer, making it possible to achieve illumination with high light utilization efficiency for the spatial light modulator. Become. However, since the second lens array is composed of a plurality of types of lens cells having different aperture shapes and aperture sizes, it is difficult to attach a half-wave plate to each lens cell. In addition, since the lens cell becomes finer as the distance from the center of the second lens array increases, it is actually impossible to cut and paste fine half-wave plates of various shapes.
[0010]
  The present invention has been made in view of such a situation, and is an easy-to-manufacture and compact polarization phase modulation element.Manufacturing method and manufacturing apparatusThe purpose is to provide.
[0011]
[Means for Solving the Problems]
  In order to achieve the above object, the polarization phase modulation element of the first inventionManufacturing methodIsThe photosensitive material capable of recording the exposure amount as a refractive index modulation is made up of the two light beams by making two coherent light beams having the same wavelength symmetrically or substantially symmetrical with respect to the normal of the surface of the photosensitive material. A method of manufacturing a polarization phase modulation element comprising a refractive index modulation type hologram, wherein the photosensitive material is exposed with interference fringes, wherein the pitch of the interference fringes is smaller than a working wavelength, and the surface of the photosensitive material is The exposure is performed through a mask so that a region to be exposed forms a predetermined pattern, and the diffracted light generated by the mask is removed by a diffracted light cut optical system. I doIt is characterized by that.
[0012]
  Polarization phase modulation element of the second inventionManufacturing methodIn the configuration of the first invention,Repeat the exposure multiple times and switch the pattern and the interference fringes to different ones for each exposureIt is characterized by that.
[0013]
  Polarization phase modulation element of the third inventionManufacturing methodIs the aboveFirstIn the configuration of the invention of 2,The pattern is switched by exchanging the mask.It is characterized by that.
[0014]
  Polarization phase modulation element of 4th inventionManufacturing methodIs the above1st, 2nd orIn the configuration of the third invention,Further, a blazed diffraction grating surface is formed on the surface of the photosensitive material by oblique etching, and a resin plane is formed by filling the blazed concave portion with a resin having optical isotropic property or substantially isotropic property.It is characterized by that.
[0015]
  Polarization phase modulation element of 5th inventionManufacturing methodIsIn the first, second, third, or fourth aspect of the invention, the region of the photosensitive material surface that is exposed is exposed. 0.001 ~ 0.1mm The exposure is performed through a mask so as to form a pitch periodic structure.It is characterized by that.
[0016]
  Polarization phase modulation element of 6th inventionManufacturing methodThe above1, 2nd, 3rd or 4thIn the configuration of the invention of0.001 ~ 0.1mm Exposure with pitch interference fringes is performed overlapping the exposure.It is characterized by that.
[0017]
  The manufacturing method of the polarization phase modulation element of the seventh invention is:In the configuration of the first, second, third, fourth, fifth, or sixth invention, a light guide prism is attached to the surface of the photosensitive material in a close contact state or a liquid immersion state.Then, the exposure is performed.
[0018]
  Manufacture of polarization phase modulation element of eighth inventionapparatusIsThe photosensitive material capable of recording the exposure amount as a refractive index modulation is made up of the two light beams by making two coherent light beams having the same wavelength symmetrically or substantially symmetrical with respect to the normal of the surface of the photosensitive material. A polarization phase modulation device comprising a refractive index modulation type hologram that exposes the photosensitive material with an interference fringe, wherein the pitch of the two light fluxes is smaller than the wavelength used. An angle difference is set to be large, and a mask having an opening made of a predetermined pattern is formed so that a region to be exposed on the surface of the photosensitive material forms a predetermined pattern. It has a diffracted light cut optical system that removes the diffracted light generated by the mask so that only the next light is used.It is characterized by that.
[0019]
  Manufacture of polarization phase modulation element of ninth inventionapparatusIn the configuration of the eighth invention,The diffracted light cut optical system is composed of two lenses and a slit plate disposed between them, and the slit plate is formed with a slit that allows only zero-order light to pass through.It is characterized by that.
[0029]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, the polarization phase modulation element embodying the present inventionManufacturing method and manufacturing equipment, etc.Will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the part which is the same in the said prior art example and each embodiment, and an equivalent part, and duplication description is abbreviate | omitted suitably.
[0030]
《Structural birefringence and holograms》
When the fine structure is oriented, optical anisotropy called structural birefringence occurs. For example, as shown in FIG. 8, let us consider a case where light travels in parallel with a layer in a one-dimensional periodic multilayer structure composed of two types of isotropic dielectrics. If the pitch Λ of this periodic structure is sufficiently small compared to the wavelength of light, this fine structure acts like a negative uniaxial crystal with respect to the light {optical axis (ax) is perpendicular to the layer. }. Therefore, the TE wave (electric vector vibration direction is parallel to the layer) and the TM wave (electric vector vibration direction perpendicular to the layer) have different refractive indices for the light used.
[0031]
If an interference fringe having a pitch smaller than the wavelength of light is recorded on the hologram, it is possible to constitute the fine structure having a periodic refractive index distribution. For example, with respect to a photosensitive material capable of recording the exposure amount as a refractive index modulation (that is, a difference in refractive index occurs depending on the exposure amount), the same wavelength is symmetrically or substantially symmetrical with respect to the normal of the photosensitive material surface. Two coherent beams are incident. Then, the photosensitive material is exposed with interference fringes (that is, energy distribution) composed of two light beams, and a refractive index modulation type hologram is obtained.
[0032]
FIG. 7 shows the angle difference (°) between the two light beams (ie, the object beam and the reference beam), and the interference fringe spacing (μm) when creating a hologram on a photosensitive material with a production wavelength of 500 (nm) and a refractive index of 1.5. , Shows the relationship. As can be seen from the graph of FIG. 7, by increasing the angle difference between the two light beams, the pitch of the interference fringes can be made smaller than the wavelength used (that is, the fringe pitch can be made finer). For example, if the manufacturing wavelength is 532 (nm), the fringe pitch (Λ, the interference fringe spacing) is 200 (nm), and the respective dielectric constants of the isotropic dielectric (FIG. 8) are 1.41 and 1.35, the fine The structure can function as a half-wave plate with a thickness of 200 (μm).
[0033]
<Hologram type polarization phase modulation element>
In creating a hologram, the fringe pitch can be miniaturized as described above, so that a polarization phase modulation element having various functions can be easily manufactured by patterning a region where structural birefringence occurs. . As examples of the polarization phase modulation element, a hologram phase element having a function of a phase plate, a polarization separation element having a polarization separation function, and a manufacturing method thereof will be described below.
[0034]
FIG. 1 is a system configuration diagram schematically showing a hologram phase element manufacturing apparatus. This manufacturing apparatus includes a laser light source (10), an expander (11), a mask (M), a mask holder (12), a diffracted light cut optical system (13), a half mirror (14), a mirror (15A, 15B), a light guide. An optical prism (16), a rotary stage (19) and the like are provided. The laser light emitted from the laser light source (10) is expanded in beam diameter by the expander (11), and light flux is restricted by the mask (M) attached to the mask holder (12). The laser beam that has passed through the mask (M) passes through the diffracted light cut optical system (13), and is then split into two light beams (object beam and reference beam) by the half mirror (14), and by the mirrors (15A, 15B). After the reflection, the light is incident on the light guide prism (16) to expose the photosensitive material (17). This photosensitive material (17) is a hologram sensitive material made of a photopolymer capable of recording an exposure amount as a refractive index modulation.
[0035]
The mask holder (12) is for facilitating replacement and positioning when a plurality of masks (M) are used, and FIG. 2 shows an example thereof. The mask holder (12) shown in FIG. 2 can fix three types of masks (M1 to M3), and the mask (M1 to M3) on which the laser beam enters is a rotation (X1: rotation) of the mask holder (12). Switched by axis). 4 and 5 show specific examples of the mask (M). In the mask (M0 to M3), openings made of predetermined patterns (Q0 to Q3) are formed. Therefore, it is possible to make only the laser beam incident on each aperture enter the diffracted light cut optical system (13).
[0036]
The position of the mask (M) is not limited to between the expander (11) and the half mirror (14). For example, exposure can be performed by disposing a mask (M) on the surface of the photosensitive material (17). However, when the opening width of the mask (M) is reduced, the generation of ghost due to diffraction cannot be ignored. For this reason, as shown in FIG. 1, it is desirable to regulate the light beam with the mask (M) before separating the laser light into two light beams with the half mirror (14), and between the mask (M) and the half mirror (14). It is further desirable to dispose the diffracted light cut optical system (13).
[0037]
FIG. 3 shows a specific example of the diffracted light cut optical system (13). In FIG. 3, the short broken line indicates the 0th-order light, and the long broken line indicates the ± first-order light. The diffracted light cut optical system (13) is composed of two lenses (L1, L2) and a slit plate (PL) disposed between them. The slit plate (PL) is formed with a slit (SL) that allows only the 0th-order light to pass through, and ± 1st-order light is shielded by the slit plate (PL). Therefore, even if diffracted light is generated in the mask (M), the generated diffracted light is removed by the diffracted light cut optical system (13).
[0038]
The photosensitive material (17) is set on the rotary stage (19) as shown in FIG. 1 in a state of being attached (or applied) to the surface of the glass substrate (18). Since the rotation axis (X2) of the rotary stage (19) is parallel to the normal of the surface of the photosensitive material (17), the light flux with respect to the surface of the photosensitive material (17) even if the rotary stage (19) rotates. The incident angle does not change. In order to prevent adverse effects due to unnecessary light transmitted through the photosensitive material (17), a black absorbing plate (not shown) that absorbs unnecessary light is attached to the back surface of the glass substrate (18) in a close contact state or a liquid immersion state. ing.
[0039]
A light guide prism (16) is attached to the surface of the photosensitive material (17) in a close contact state or a liquid immersion state. For example, the light guide prism (16) is disposed in close contact with the photosensitive material (17) via a liquid (paraffin or the like) having the same refractive index as that of the photosensitive material (17). When the light guide prism (16) is used in this way, there is no air layer between the light guide prism (16) and the photosensitive material (17), so the fringe pitch is reduced while preventing the occurrence of ghosts due to interface reflection. Can be small.
[0040]
The operation of the light guide prism (16) will be described in more detail. FIG. 6 (A) shows an optical path when laser light is incident on the photosensitive material (17) through the light guide prism (16), and FIG. 6 (B) is directly incident on the photosensitive material (17). The optical path of the case is shown. Laser light is incident on the photosensitive material (17) at an angle θ and travels through the photosensitive material (17) at an angle θ ′. To reduce the fringe pitch, the angle θ in the photosensitive material (17) is used. It is necessary to increase '(Fig. 7). As shown in FIG. 6B, when the light guide prism (16) is not provided, if an attempt is made to increase the angle θ ′, loss due to surface reflection increases and ghosts are likely to occur. The critical angle of the angle θ ′ is limited. As shown in FIG. 6 (A), if a light guide member such as a light guide prism (16) is provided, each laser beam is incident substantially perpendicularly to the two surfaces of the light guide prism (16), and criticality is achieved. It is possible to realize θ ′ that is greater than or equal to the corner without the loss or the like.
[0041]
As shown in FIG. 1, by making two coherent light beams of the same wavelength incident symmetrically (or substantially symmetrical) with respect to the normal (X2) of the surface of the photosensitive material (17), interference fringes composed of the two light beams are incident. Thus, the photosensitive material (17) can be exposed. At this time, it is possible to make the pitch of the interference fringes smaller than the operating wavelength by increasing the angle difference between the two light beams (FIG. 7). Accordingly, interference fringes having a pitch smaller than the used wavelength can be recorded as a refractive index distribution.
[0042]
Since exposure to the photosensitive material (17) is performed through the mask (M) described above, the area of the photosensitive material (17) subjected to exposure has the same pattern as the opening formed in the mask (M). become. Therefore, a fine structural birefringence region in which interference fringes having a pitch smaller than the used wavelength are recorded as a refractive index distribution can be configured with a predetermined pattern. For example, if the mask (M0) of FIG. 4 is used, a hologram phase element having a structural birefringence region functioning as a half-wave plate with a pattern (Q0, hatched portion) shown in FIG. 10 can be obtained. Further, if a mask having a strip-shaped opening is used, the structural birefringence region functioning as a half-wave plate is formed in the same strip-shaped pattern as in the conventional example {attachment of the half-wave plate (25) in FIG. A hologram phase element having an attached pattern (shaded portion)} can be obtained.
[0043]
With the hologram exposure using the mask (M) as described above, the structural birefringence region can be easily configured with a fine pattern, and at the same time, it is optically shielded by the mask (M) (non-exposure). A non-structurally birefringent region having isotropic (or substantially isotropic) can be formed with a fine pattern. Then, if the use light is arranged so as to be incident on the surface of the photosensitive material (17) perpendicularly or substantially perpendicularly (normal direction or substantially normal direction), the patterned structural birefringence region is formed into a phase plate ( It is possible to function as a half-wave plate or the like. The production wavelength and the use wavelength may be different. For example, the production wavelength may be an ultraviolet wavelength and the use wavelength may be a visible wavelength.
[0044]
If the exposure to the photosensitive material (17) is repeated a plurality of times and the pattern and the interference fringes are switched to different ones for each exposure, the structural birefringence region has two or more patterns and each pattern Hologram phase elements having different interference fringes recorded in the structural birefringence region can be manufactured. For example, when the mask holder (12) is rotated and the masks (M1 to M3; FIGS. 2 and 5) are exchanged, the patterns (Q1 to Q3) can be switched. In addition, the direction of the interference fringes {that is, the direction of the optical axis (ax)} can be switched by rotating the rotary stage (19) to switch the incident direction of the two light beams. By sequentially switching the pattern and the interference fringes, a hologram phase element having a structural birefringence region of three types of patterns (Q1 to Q3) shown in FIG. 12 is obtained. It is also possible to switch the fringe pitch by changing the wavelength of the two light beams and the light beam incident angle. In this case, a plurality of structural birefringent regions (1/2 wavelength plates, It is also possible to mix a quarter wavelength plate or the like in a plurality of patterns.
[0045]
If an opening having a pattern having a certain periodicity is formed in the mask (M), as shown in FIG. 13, a fine structure in which interference fringes having a pitch (Λ 2) smaller than the wavelength used is recorded as a refractive index distribution. The birefringent region (α) can be configured with a pattern having the same periodicity (pitch: Λ 1) as the opening formed in the mask (M). Β in FIG. 13 corresponds to a constant refractive index region that has not been exposed by light shielding with the mask (M), that is, a non-structurally birefringent region. Therefore, the distribution of the refractive index (n) at the position (X) in the optical axis (ax) direction is as shown in FIG. For example, if the above-described exposure (FIG. 1) is performed through the mask (M) so that the exposed area (α) on the surface of the photosensitive material (17) forms a periodic structure with a pitch of 0.001 to 0.1 mm, the structural compound can be obtained. A constant periodic structure (type 1 diffraction grating structure) in which refraction regions (α) and nonstructural birefringence regions (β) are alternately arranged is obtained, and the pitch (Λ1) of the periodic structure is 0.001 at which diffraction occurs. ~ 0.1mm.
[0046]
If exposure with an interference fringe having a pitch larger than the use wavelength is overlapped with exposure with an interference fringe having a pitch smaller than the use wavelength, as shown in FIG. 15, a pitch (Λ2) smaller than the use wavelength is obtained. A fine structural birefringence region (α) in which the interference fringes are recorded as a refractive index distribution is composed of a periodic pattern (pitch: Λ1) including a region (γ) in which the refractive index is saturated by superposition Can do. A saturated region (γ) in FIG. 15 corresponds to a nonstructural birefringence region (constant refractive index). Accordingly, the distribution of the refractive index (n) at the position (X) in the optical axis (ax) direction is as shown in FIG. For example, if exposure with 0.001 to 0.1 mm pitch interference fringes is performed overlapping the above-described exposure (FIG. 1), the structural birefringence region (α) and the non-structural birefringence region (γ) are alternately arranged. A constant periodic structure (type 2 diffraction grating structure) is obtained without a mask (M), and the pitch (Λ1) of the periodic structure is 0.001 to 0.1 mm at which diffraction occurs.
[0047]
As described above, in the binary type diffraction grating structure (FIGS. 13 and 15) in which the part (α) having the fine periodic structure showing structural birefringence and the part (β, γ) not having the periodic structure are periodically arranged, If the phase difference between the light passing through the birefringent region (α) and the light passing through the non-structural birefringent region (β, γ) is an integral multiple of 2π, all light is transmitted without being diffracted (L0: transmitted light). If the phase difference is π, there is no transmitted light traveling straight and all diffracted waves (L1: diffracted light). That is, the TE wave is the case where the electric field direction of the incident light is parallel to the interference fringes, the TM wave is the case where the magnetic field direction is parallel, and the refractive index of the structural birefringence region (α) for the TE wave and TM wave is nTE, nTM. If the refractive indices of the non-structurally birefringent regions (β, γ) with respect to the TE wave and the TM wave are n0TE and n0TM, n0TE = n0TM and nTE ≠ nTM, for example, ΔnTE = nTE−n0TE = 2mπ, ΔnTM When n = nTM−n0TM = (2m + 1) π (m: integer), the TE wave goes straight as 0th order light (L0), and the TM wave is diffracted as ± first order light (L1). Therefore, the binary diffraction grating structure (FIGS. 13 and 15) has a function (polarization separation function) as a polarization separation element (that is, PBS: polarizing beam splitter).
[0048]
Next, a blazed diffraction grating structure (FIG. 17) having a polarization separation function similar to the binary diffraction grating structure (FIGS. 13 and 15) will be described. This diffraction grating structure is configured in a polarization phase modulation element having a refractive index modulation type hologram (17H) as shown in FIG. In the hologram (17H), interference fringes with a pitch smaller than the wavelength used are recorded as a refractive index distribution, and on the hologram (17H) surface, a blazed diffraction grating surface comprising grooves parallel to the interference fringes ( 17d) is formed. Further, the blazed concave portion of the diffraction grating surface (17d) is filled with a resin (17I) having optical isotropy (or substantially isotropic properties).
[0049]
The blazed shape of the diffraction grating surface (17d) may be one type, but the diffraction grating surface (17d) may be composed of two or more regions having different blazed shapes (diffraction grating pitch, groove direction, etc.). . 9 and 11 show examples of blaze patterns (R1 to R6) in each region constituting the diffraction grating surface (17d). 9 shows three types of blaze patterns (R1 to R3) having different diffraction grating pitches, and FIG. 11 shows six types of blaze patterns (R1 to R6) having different diffraction grating pitches and groove directions. By matching the groove direction of the diffraction grating surface (17d) in each region with the direction of structural birefringence due to the refractive index distribution in the hologram (17H), the polarization separation direction can be changed for each region. It is. Further, the polarization separation angle can be changed for each region in accordance with the size of the diffraction grating pitch.
[0050]
In constructing the diffraction grating structure shown in FIG. 17D, the photosensitive material is first exposed with interference fringes having a pitch smaller than the wavelength used, thereby creating a hologram 17H shown in FIG. Exposure may be performed through the mask (M) by the manufacturing apparatus (FIG. 1) so that the region to be exposed on the surface of the photosensitive material forms a predetermined pattern. If there is no need for patterning, there is no mask (M). You may expose to. Next, as shown in FIG. 17B, a blazed diffraction grating surface (17d) is formed on the surface of the photosensitive material {that is, the surface of the hologram (17H)} by oblique etching. Then, as shown in FIG. 17C, the resin flat surface (17f) is formed by filling the blazed concave portion with a resin (17I) having optical isotropy (or substantially isotropic properties). (Element flattening).
[0051]
Although the diffraction grating structure (FIG. 17) can be manufactured with a small number of steps, the same birefringence action as that when a birefringent material such as liquid crystal is used is realized by the structural birefringence of the hologram (17H). Enables polarization separation. Therefore, the polarization separation function will be described in detail below by giving an example of a polarization separation element using the birefringence of liquid crystal.
[0052]
FIG. 18 mainly shows a surface relief type (film thickness modulation type) diffraction grating (2), a liquid crystal (3) made of nematic liquid crystal or smectic liquid crystal, an opposing flat plate (4), and a sealant (5). This is a polarization separation element (1) provided as a major component. The diffraction grating (2) is made of a resin transparent sheet having optically isotropic properties, and has a blazed diffraction grating surface (2a). The liquid crystal (3) adjacent to the diffraction grating surface (2a) forms a uniaxial optical anisotropic layer having optical anisotropy, and the hologram (17H) is a liquid crystal (3) It corresponds to. Further, the opposing flat plate (4) adjacent to the liquid crystal (3) with the liquid crystal (3) sandwiched between the diffraction grating (2) is a transparent substrate made of resin or glass. An alignment film (4a) is provided on the liquid crystal (3) side surface of the opposing flat plate (4), and the alignment film (4a) has the liquid crystal (3) along the groove direction of the diffraction grating surface (2a). The rubbing process is performed so that it may be homogeneously oriented. The direction of the interference fringes recorded on the hologram (17H) corresponds to the orientation direction of the liquid crystal (3).
[0053]
Since the liquid crystal (3) is a birefringent material having optical anisotropy, the refractive index for ordinary light and the refractive index for extraordinary light are different. Therefore, the diffraction effect exerted by the diffraction grating surface (2a) located at the boundary with the optically isotropic diffraction grating (2) is also different between ordinary light and extraordinary light. In this polarization separation element (1), each material is selected such that the refractive index for either one of ordinary light or extraordinary light is the same as the refractive index of the diffraction grating (2). For example, if the refractive index of the liquid crystal (3) with respect to ordinary light and the refractive index of the diffraction grating (2) are the same, the ordinary light is not diffracted and passes through the diffraction grating surface (2a), and the extraordinary light is reflected by the diffraction grating. The light is deflected by receiving the diffraction effect on the surface (2a). Conversely, when the refractive index of the liquid crystal (3) and the refractive index of the diffraction grating (2) for the extraordinary light are the same, the extraordinary light is not diffracted and passes through the diffraction grating surface (2a), and the ordinary light is transmitted. The light is deflected by receiving the diffraction action on the diffraction grating surface (2a). Since the hologram (17H) acts in the same manner as the liquid crystal (3), either the ordinary light or the extraordinary light {diffracted light (L0) in FIG. 17} has a diffraction effect on the diffraction grating surface (17d). It will be received and deflected.
[0054]
As described above, the liquid crystal (3) or the hologram (17H) is adjacent to the diffraction grating surface (2a or 17d), so that the incident illumination light is converted into two linearly polarized beams whose polarization planes are orthogonal to each other {for example, in FIG. It can be separated into transmitted light (L0) and diffracted light (L1)}. Moreover, since the diffraction grating surface (2a or 17d) has a blazed shape, high diffraction efficiency can be obtained. If the diffraction efficiency on the diffraction grating surface (2a or 17d) is high, the polarization conversion efficiency is also high, so that the light utilization efficiency can be improved.
[0055]
<Integrator optics>
Next, a lens array type integrator optical system having a polarization conversion function using the above-described hologram phase element and polarization separation element will be described. Each of the liquid crystal projectors shown in FIGS. 19 and 20 includes an integrator optical system of a type different from the conventional example (FIG. 21). The integrator optical system shown in FIG. 19 includes a polarization separating element (21), an integrated lens array (22) in which the first and second lens arrays (22a, 22b) are integrated as one optical element, and a hologram phase. The integrator optical system shown in FIG. 20 includes a polarization separation element (21), first and second lens arrays (22A, 22B), and a second lens array (22B). And a hologram phase element (23A) integrated with each other.
[0056]
The first lens array (22a, 22A) is formed by arranging rectangular lens cells substantially similar to the liquid crystal panel (28) in a two-dimensional array, and divides incident light by a plurality of lens cells. Then, each lens cell of the array structure {first and second lens arrays (22a, 22A; 22b, 22B) comprising the same number of lens cells as the first lens array (22a, 22A) forms a pair. }, A plurality of light source images (the ellipses in FIGS. 10 and 12) are formed in the vicinity of the second lens array (22b, 22B) having. Since each lens cell of the first lens array (22a, 22A) and the liquid crystal panel (28) are in a conjugate relationship via each lens cell of the second lens array (22b, 22B), the spatial of the illumination light The energy distribution is made uniform, and the liquid crystal panel (28) is illuminated uniformly without waste.
[0057]
In the integrator optical system shown in FIGS. 19 and 20, polarization separation is performed by the polarization separation element (21) disposed in the vicinity of the first lens array (22a, 22A) (or in the vicinity of its conjugate position). The polarization plane is rotated by the hologram phase element (23, 23A) disposed in the vicinity of the second lens array (22b, 22B) (or in the vicinity of the conjugate position thereof). As the polarization separation element (21), a polarization phase modulation element (FIG. 17) having a blazed diffraction grating structure using the structural birefringence of the hologram (17H), or the birefringence of the liquid crystal (3) is used. A polarization separation element (1, FIG. 18) having a blazed diffraction grating structure is used. Further, as the hologram phase element (23, 23A), a polarization phase modulation element obtained by the manufacturing apparatus (FIG. 1), that is, interference fringes having a pitch smaller than the used wavelength is recorded as a refractive index distribution (1/2 A hologram phase element having a structural birefringence region (which functions as a wave plate) in a predetermined pattern is used.
[0058]
By the way, in the configuration in which the polarization separation is performed by the PBS array (24) and the polarization plane is rotated by the half-wave plate (25) as in the conventional example (FIG. 21), the shape and processing accuracy of the PBS array (24) are obtained. , Physical restrictions are imposed on the accuracy of attaching the half-wave plate (25). For this reason, even if it is attempted to reduce the pitch of the PBS array (24) and the width of the half-wave plate (25), about 2 mm is the limit. If the manufacturing apparatus (FIG. 1) is used, a structural birefringence region having a width of 2 mm or less that functions as a half-wave plate can be finely and complicatedly patterned. A hologram phase element (23, 23) configured with a structural birefringence region corresponding to the opening of the mask (M) and a non-structural birefringence region corresponding to the light shielding region of the mask (M), each having a width of 2 mm or less. By using 23A), it becomes possible to control polarization more finely and more complex than before. Considering the polarization separation matching with respect to the rotation of the polarization plane in this fine and complex pattern, it is desirable to perform polarization separation with the blazed diffraction grating structure (FIGS. 17 and 18). By combining the polarization separating element (21) having a blazed diffraction grating structure with the hologram phase element (23, 23A), it is possible to achieve miniaturization of the integrator optical system as shown in FIG.
[0059]
If the lens cell size (d1) is reduced while maintaining the ratio (d1: F1) between the lens cell size (d1) and the optical distance (F1), the optical distance (F1) is shortened and the integrator optical system becomes smaller. Accordingly, as shown in FIG. 19, the first and second lens arrays (22a, 22b) can be integrally molded, and downsizing and cost reduction can be achieved. Although the PBS array (24) cannot be miniaturized, the structure of the polarization separation element (21) having a blazed diffraction grating structure itself does not depend on the lens cell size (d1). Further, as described above, it is easy to miniaturize the pattern of the structural birefringence region in the hologram phase element (23, 23A). Therefore, it is possible to reduce the lens cell size (d1). In FIG. 19, the lens cell size (d1) is shown as 1/3 the size of the conventional example (FIG. 21), but in actuality, it can be configured with a finer pitch.
[0060]
As can be seen from the positional relationship (FIG. 23) between the lens cell pattern (P2) and the light source image (ellipse) in the conventional example (FIG. 21), the relative area occupied by the light source image is smaller in the lens cells located in the periphery. . Therefore, the size of the entire second lens array (22B) can be reduced if the aperture of the lens cell is made smaller toward the periphery to make the light source image dense. If the overall size of the second lens array (22B) is reduced, the F number of the illumination system (FIG. 21) is increased, so that the F number required for the projection lens (29) can also be increased. Accordingly, it is possible to achieve a reduction in size and cost of the projection lens (29) while maintaining high light utilization efficiency.
[0061]
In the second lens array (22b, 22B) used in the integrator optical system shown in FIG. 19 and FIG. 20, the lens cells located at the periphery have smaller apertures (so-called deformed), and the first lens array (22a, 22A). If the light source images are made dense in units of lens cells by appropriately decentering each lens cell of), the overall size of the second lens array (22b, 22B) can be reduced as described above. FIG. 10 shows the lens cell pattern (P2) of the second lens array (22b, 22B) in which the opening of the lens cell is deformed in one vertical direction, and FIG. Fig. 6 shows a lens cell pattern (P2) of the second lens array (22b, 22B) which has been deformed. As can be seen by comparing the outer circumference circles (dashed lines) of the lens cell patterns (P2) shown in FIG. 23, FIG. 10, and FIG. 12, the lens cells can be more closely packed as the deforming direction of the aperture is increased. The entire size (diameter of the outer circumference circle) of the two-lens array (22b, 22B) can be reduced.
[0062]
As shown by the lens cell pattern (P2) in FIGS. 10 and 12, when the second lens array (22b, 22B) is composed of two or more types of lens cells having different aperture shapes and aperture sizes, polarized light In order to make the pair of separated light source images (that is, the TM polarized image and the TE polarized image on each lens cell) close and dense, the angle and direction of polarization separation by the polarization separation element (21) are also in lens cell units. It is necessary to adjust with. In other words, it can be said that it is desirable to reduce the polarization separation angle and to make the polarization separation direction substantially perpendicular to the deforming direction as the periphery of the lens cell pattern (P2).
[0063]
When the second lens array (22b, 22B) of the lens cell pattern (P2) shown in FIG. 10 is used, as shown in FIG. The polarization separation element (21) of three types of blaze patterns (R1 to R3) having different diffraction grating pitches is used so as to be different for each lens cell of 22a and 22A). The pitch of the diffraction grating of the blaze patterns (R1 to R3) is rougher toward the periphery along one upper and lower direction. Further, when the second lens array (22b, 22B) of the lens cell pattern (P2) shown in FIG. 12 is used, the separation angle and the separation direction of the two linearly polarized lights are as shown in FIG. The polarization separation elements (21) of six types of blaze patterns (R1 to R6) having different diffraction grating pitches and groove directions are used so as to be different for each lens cell of 22a and 22A). The diffraction grating pitch of the blaze patterns (R1 to R6) is coarser toward the periphery along the four diagonal directions, and the groove direction is substantially radial corresponding to the deforming direction.
[0064]
The polarization separation element (21) separates the illumination light into two linearly polarized lights (TM polarized light and TE polarized light) whose polarization planes are orthogonal to each other by the above-described birefringence action and diffraction action. 19 and 20, the solid line is TM polarized light, and the broken line is TE polarized light. 10 and 12, the ellipse displayed in cross hatch is a light source image composed of TM polarized light, and the ellipse located on the same lens cell as each light source image is a light source image composed of TE polarized light. The arrow direction is the polarization direction. 10 and 12, the structural birefringence region pattern (Q0 to Q3) indicated by oblique lines is a half-wave plate in the hologram phase element (23, 23A) {the oblique lines indicate the direction of the optical axis (ax). (± 22.5 °, 45 °). } Is a structural birefringence region that functions as As described above, the structural birefringence region pattern (Q0) of FIG. 10 is manufactured using the mask (M0) of FIG. 4, and the structural birefringence region pattern (Q1 to Q3) of FIG. ) To (C) masks (M1 to M3).
[0065]
At least one of the two polarized lights separated by the polarization separating element (21) (only TE polarized light in FIG. 10) enters the structural birefringence region of the hologram phase element (23, 23A). In the structural birefringence region forming the patterns (Q0 to Q3), the polarization direction of the incident light is aligned in one vertical direction by rotating the polarization plane of the incident light by a predetermined angle (90 ° in FIG. 10). Conversion into polarized light (TM polarized light in FIG. 10). The illumination light whose polarization direction is aligned passes through the overlapping lens (26) and the condenser lens (27), and then illuminates the liquid crystal panel (28).
[0066]
If the lens cell openings are deformed in a plurality of directions like the lens cell pattern (P2) of the second lens array (22b, 22B) shown in FIG. 12, the F number can be increased, but the polarization separation direction is changed to the first direction. One lens array (22a, 22A) must be changed in units of lens cells. Since there are four types of polarization separation directions by the blaze pattern (P1) shown in FIG. 11, there are four types of polarization directions (arrows) of the light source image, but structural birefringence that functions as a half-wave plate. The area is composed of three types of patterns (Q1 to Q3) with different optical axis (ax) directions in the lens cell unit of the second lens array (22b, 22B). It is possible to align.
[0067]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a polarization phase modulation element that is easy to manufacture and compact. Further, by using the polarization separation element, an integrator optical system with high light utilization efficiency can be realized.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram schematically showing a hologram phase element manufacturing apparatus.
FIG. 2 is a plan view showing an example of a mask holder used in the manufacturing apparatus of FIG.
3 is an optical configuration diagram showing an example of a diffracted light cut optical system used in the manufacturing apparatus of FIG. 1. FIG.
FIG. 4 is a plan view showing a specific example of a mask for forming one type of structural birefringence region.
FIG. 5 is a plan view showing a specific example of a mask for forming three types of structural birefringence regions.
FIG. 6 is an optical path diagram for explaining the action of the light guide prism with respect to an incident light beam when exposing a photosensitive material.
FIG. 7 is a graph showing the dependence of the interference fringe interval on the angle formed by two light beams.
FIG. 8 is a schematic diagram showing a one-dimensional periodic multilayer structure that generates structural birefringence.
FIG. 9 is a plan view showing a relationship between a lens cell pattern of a first lens array and a blaze pattern of a polarization separation element that performs polarization separation in one direction.
FIG. 10 shows a lens cell pattern of the second lens array, an arrangement of light source images formed by the first lens array, a structural birefringence region pattern of a hologram phase element having one type of structural birefringence region, The top view which shows the relationship.
FIG. 11 is a plan view showing a relationship between a lens cell pattern of the first lens array and a blaze pattern of a polarization separation element that performs polarization separation in four directions.
FIG. 12 shows a lens cell pattern of the second lens array, an arrangement of light source images formed by the first lens array, a structural birefringence region pattern of a hologram phase element having three types of structural birefringence regions, The top view which shows the relationship.
FIG. 13 is a schematic diagram showing a binary diffraction grating structure (type 1) in which a structural birefringent region and an unstructured birefringent region are periodically arranged.
14 is a graph showing a refractive index distribution in the diffraction grating structure (type 1) of FIG.
FIG. 15 is a schematic diagram showing a binary diffraction grating structure (type 2) in which a structural birefringent region and an unstructured birefringent region are periodically arranged.
16 is a graph showing a refractive index distribution in the diffraction grating structure (type 2) of FIG.
FIG. 17 is a process diagram showing a method for manufacturing a blazed diffraction grating structure composed of holograms showing structural birefringence.
FIG. 18 is a cross-sectional view showing a blazed polarization separation element including a liquid crystal and a blazed diffraction grating.
FIG. 19 is an optical configuration diagram showing a liquid crystal projector provided with an illumination system including an integrator optical system in which the first and second lens arrays are integrated.
FIG. 20 is an optical configuration diagram showing a liquid crystal projector provided in an illumination system with an integrator optical system in which a second lens array and a hologram phase element are integrated.
FIG. 21 is an optical configuration diagram showing a liquid crystal projector including a conventional integrator optical system having a polarization conversion function in an illumination system.
22 is a plan view showing a lens cell pattern of the first lens array in FIG. 21. FIG.
FIG. 23 shows the relationship between the lens cell pattern of the second lens array, the arrangement of the light source image formed by the first lens array, and the affixing pattern of the half-wave plate in the integrator optical system in FIG. FIG.
[Explanation of symbols]
1 ... Polarization separation element
2 ... Diffraction grating
2a Diffraction grating surface
3 ... LCD
12… Mask holder
M, M0 to M3 ... Mask
17… Sensitive material
17H… Hologram
17d ... Diffraction grating surface
17I… resin
17f… Plastic plane
21… Polarization separation element
22 ... Integrated lens array
22A, 22a ... 1st lens array
22B, 22b ... 2nd lens array
23,23A… Hologram phase element
28… LCD panel
P1 ... Lens cell pattern of the first lens array
P2 ... Lens cell pattern of the second lens array
Q0 to Q3 ... Structural birefringence region pattern (mask opening pattern)
R1 ~ R6 ... blaze pattern
α ... Structural birefringence region
β, γ ... unstructured birefringence region
L0 ... transmitted light
L1 ... Diffracted light

Claims (9)

The photosensitive material capable of recording the exposure amount as a refractive index modulation is made up of the two light beams by making two coherent light beams having the same wavelength symmetrically or substantially symmetrical with respect to the normal of the surface of the photosensitive material. A method for producing a polarization phase modulation element comprising a refractive index modulation hologram, wherein the photosensitive material is exposed with interference fringes.
As well as smaller than the wavelength using the pitch of the interference fringes, the area to be exposed on the photosensitive material surface have rows said exposed through a mask so as to form a predetermined pattern, the diffraction diffracted light generated by the mask A method of manufacturing a polarization phase modulation element , wherein the two light beams are interfered with only zero-order light by being removed by a light cut optical system . With repeated a plurality of times the exposure, the pattern and method for producing a polarizing phase modulator of claim 1, wherein the switching the interference fringes to differ for each exposure. 3. The method of manufacturing a polarization phase modulation element according to claim 2, wherein the pattern is switched by exchanging the mask. Further, a blazed diffraction grating surface is formed on the surface of the photosensitive material by oblique etching, and a resin plane is formed by filling the blazed concave portion with a resin having optical isotropic property or substantially isotropic property. The method for manufacturing a polarization phase modulation element according to claim 1 , 2 or 3 . Claim 1, 2, 3 or 4 polarization phase modulating element according to area to be exposed of the photosensitive material surface and performing the exposure through a mask to form a periodic structure of 0.001~0.1mm pitch Manufacturing method. Claim 1 of the exposure of the interference fringes 0.001~0.1mm pitch and performing overlapping with the exposure, 2, 3 or 4 method for producing a polarizing phase modulation device according. 7. The method of manufacturing a polarization phase modulation element according to claim 1, wherein a light guide prism is attached to the surface of the photosensitive material in a close contact state or a liquid immersion state to perform the exposure. The photosensitive material capable of recording the exposure amount as a refractive index modulation is made up of the two light beams by making two coherent light beams having the same wavelength symmetrically or substantially symmetrical with respect to the normal of the surface of the photosensitive material. An apparatus for manufacturing a polarization phase modulation element comprising a refractive index modulation type hologram, wherein the photosensitive material is exposed with interference fringes.
  The angle difference between the two light beams is set to be large so that the pitch of the interference fringes is smaller than the wavelength used.
  A mask having an opening made of the predetermined pattern is formed so that a region to be exposed on the surface of the photosensitive material forms a predetermined pattern. An apparatus for manufacturing a polarization phase modulation element, comprising a diffracted light cut optical system for removing diffracted light generated by the mask. The diffracted light cut optical system is composed of two lenses and a slit plate disposed between them, and the slit plate is formed with a slit that allows only zero-order light to pass through. The apparatus for manufacturing a polarization phase modulation element according to claim 8.

Images