Interference light generating element and hologram recording device

Abstract

To provide a compact hologram recording device which acquires a multiple hologram for reproducing a clear three-dimensional image including information about optical characteristics such as a wavelength.SOLUTION: A hologram recording device 10 comprises: an imaging element 5; and an interference light generation element 1 which is attached to an imaging surface of the imaging element 5. The interference light generation element 1 generates two light waves L1, L2 having mutually-different phases from object light LOBJ that is incident, and the imaging element 5 records an interference fringe formed with the two light waves L1, L2 as a hologram. The interference light generation element 1 comprises, in an order from the side on which light is incident, a first birefringence member 11, a phase element array 20 which changes the phase difference in two or more ways by spatially dividing a polarization component in the direction in parallel with or orthogonal to the optical axis of the first birefringence member 11, and a polarizing plate 32 which tilts the direction of the transmission axis with respect to the optical axis of the first birefringence member 11.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an interference light generating element and a hologram recording device including the same. [Background technology]

[0002] Information on optical properties such as light wavelength and polarization is being utilized in a wide variety of ways, including identifying molecular composition in optical microscopes including fluorescence microscopes, obtaining various cellular information such as the orientation and localization of biopolymers without staining, as vital signs such as the health status of living organisms, estimating the deterioration state of manufactured products and materials, the types and properties of substances and materials, and as useful features for object recognition and identification using the naked eye and robot vision. Unlike conventional methods that use multiple cameras to acquire optical information about the three-dimensional space of a specimen (subject), digital holography technology has been disclosed that records multiple holograms on a single imaging element and reconstructs a three-dimensional image from the acquired multiple holograms through signal processing. Furthermore, by generating two light waves to form the interference fringes that form the hologram using incoherent light, it is possible to use natural light as a light source or record light emitted by the specimen itself (Patent Documents 1-3, Non-Patent Documents 1-5). In particular, a single-path method that generates two light waves with different radii of curvature on a single optical path (Patent Document 3, Non-Patent Documents 1-5) allows for a more compact hologram recording device.

[0003] In Non-Patent Documents 1 and 2, a polarization-sensitive bifocal lens such as a birefringent lens is used to generate light waves with different radii of curvature from orthogonal linearly polarized light, a polarization-sensitive phase modulator is used to shift the phase of one of the light waves, and then a polarizer with a diagonal transmission axis aligns the polarization components of the two light waves to form interference fringes, and the phase modulator is electrically driven to change the amount of phase shift to obtain a temporally dispersed multiple hologram.Non-Patent Document 1 also describes using a multi-bandpass filter to narrow the R, G, and B light beams, so that even temporally incoherent light such as natural light becomes partially temporally coherent light, allowing images to be reproduced for each wavelength band from a multiple hologram recorded with a monochrome imaging element.

[0004] In Patent Document 3 and Non-Patent Documents 3 and 4, a phase shifter array, which is an array of polarization-sensitive phase shifters such as liquid crystal spatial light modulators, generates light waves with different radii of curvature using orthogonal linear polarization, while shifting the phase of one of the light waves. The light waves then pass sequentially through a quarter-wave plate and a polarizer array to simultaneously generate four sets of light waves with phase shifts of 0, π / 2, π, and 3π / 2, and are captured in a single exposure. In Non-Patent Document 4, wavelength (color) information can also be obtained by capturing the image using a color image sensor equipped with R, G, and B color filter arrays. In Non-Patent Document 5, a polarization-sensitive bifocal lens, such as a birefringent lens, generates two light waves with different radii of curvature from orthogonal linear polarization, and a polarization-sensitive phase shifter array shifts the phase of one light wave by a cell (phase shifter) that varies depending on the wavelength. The polarization components of the two light waves are then aligned using a polarizer with a diagonal transmission axis to form interference fringes, and the interference fringes of the R, G, and B light are multiplexed and recorded using a monochrome image sensor. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6308594 [Patent Document 2] Japanese Patent Application Publication No. 2017-076038 [Patent Document 3] Patent No. 6245551 [Non-patent literature]

[0006] [Non-Patent Document 1] T. Tahara, et al., “Multiwavelength three-dimensional microscopy with spatially incoherent light, based on computational coherent superposition”, Optics Letters Volume 45, Issue 9, pp. 2482-2485, 2020 [Non-patent document 2] T. Tahara, et al., “Two-step phase-shifting interferometry for self-interference digital holography”, Optics Letters Volume 46, Issue 3, pp. 669-672, 2021 [Non-patent document 3] T. Tahara, et al., “Single-shot phase-shifting incoherent digital holography”, Journal of Optics (IOP Publishing) Volume 19, Number 6, 065705, 2017 [Non-patent document 4] T. Tahara, et al., “Single-shot incoherent color digital holographic microscopy system with static polarization-sensitive optical elements”, Journal of Optics (IOP Publishing) Volume 22, Number 10, 105702, 2020 [Non-Patent Document 5] T. Tahara, et al., “Single-shot wavelength-multiplexed digital holography for 3D fluorescent microscopy and other imaging modalities”, Applied Physics Letters Volume 117, Issue 3, 031102, 2020 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 3 and Non-Patent Documents 1 to 5, it is necessary to provide a distance between an optical element, such as a bifocal lens made of a birefringent material that generates light waves to form interference fringes, and the imaging surface of the imaging element, and further compactification is required. Furthermore, Fresnel reflection at the interfaces between the optical elements and the air between the optical elements and the imaging element can cause light loss, reducing the light utilization efficiency, and the image reproduced from the acquired multiplexed hologram can become dark relative to the object light. Therefore, there is room for improvement in these technologies.

[0008] The present invention aims to provide a compact hologram recording device that acquires multiple holograms for reconstructing bright three-dimensional images containing information on optical properties such as wavelength, and an interference light generating element that generates light waves that form each interference fringe of the multiple hologram. [Means for solving the problem]

[0009] The interference light generating element according to the present invention comprises: The light exit surface is attached to the light entrance surface of the image sensor, A first birefringent member, a phase modulation element that divides the polarized light components in a direction parallel to or orthogonal to the optical axis of the first birefringent member into at least one of time and space and changes the phase difference in two or more ways, and a polarizer whose transmission axis is tilted with respect to the optical axis of the first birefringent member, are arranged along the traveling direction of light. Delivery the polarizer is disposed on the light output side of the first birefringent member and the phase modulation element. The laminated layers are laminated without gaps along the direction of light travel from the light incident surface to the light exit surface, and an anti-reflection film is provided between at least one of the laminated layers. This is the configuration.

[0010] Another interference light generating element according to the present invention has a light exit surface attached to a light incident surface of an imaging element, and includes, in order from the light incident side, a first birefringent member, a polarizer array formed by two-dimensionally arranging a plurality of polarizers having different transmission axis directions, and Distributing Place it in preparation The laminated layers are laminated without any gaps from the light incident surface to the light exit surface, and an anti-reflection film is provided between at least one of the laminated layers. This is the configuration.

[0011] The hologram recording device of the present invention is configured to include an imaging element and any of the above-mentioned interference light generating elements attached to the light incident surface of the imaging element, wherein the interference light generating element generates two light waves with different phases from the incident light wave, and the imaging element records the interference fringes formed by the two light waves as a hologram. [Effects of the Invention]

[0012] The interference light generating element and hologram recording device according to the present invention are compact devices that can reproduce bright images from holograms obtained from a self-luminous subject without increasing the brightness of the illumination light directed at the subject. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a cross-sectional view illustrating a schematic configuration of a hologram recording device including an interference light generating element according to a first embodiment of the present invention. [Figure 2] FIG. 1 is an exploded view illustrating a schematic configuration of an interference light generating element according to a first embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram illustrating the configuration of a modified example of a hologram recording device including an interference light generating element according to the first embodiment of the present invention. [Figure 4] FIG. 1 is a cross-sectional view for schematically explaining the configuration of a hologram recording device including an interference light generating element according to a first modified example of the first embodiment of the present invention. [Figure 5] FIG. 10 is a cross-sectional view for schematically explaining the configuration of a hologram recording device including an interference light generating element according to a second modification of the first embodiment of the present invention. [Figure 6] FIG. 10 is a cross-sectional view illustrating the configuration of a hologram recording device including an interference light generating element according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a cross-sectional view illustrating the configuration of a hologram recording device including an interference light generating element according to a third embodiment of the present invention. [Figure 8]FIG. 11 is a cross-sectional view illustrating a schematic configuration of a hologram recording device including an interference light generating element according to a modified example of the third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] Embodiments of an interference light generating element and a hologram recording device according to the present invention will be described with reference to the drawings. The interference light generating element according to the present invention is an optical component that is attached to the imaging surface of an imaging element (image sensor) to form a hologram recording device. The hologram recording device according to the present invention can be applied to digital holographic microscopes, three-dimensional image analysis devices, digital holography devices, and the like. For clarity of explanation, the size and positional relationships of the devices and their elements shown in the drawings may be exaggerated and the shapes may be simplified. In addition, some elements in cross-sectional views do not have patterns. In the following description, identical or similar elements are designated by the same reference numerals, and their description will be omitted as appropriate.

[0015] [First embodiment] As shown in FIG. 1, a hologram recording device 10 according to a first embodiment of the present invention includes an image sensor 5 and an interference light generating element 1 attached to the light incident surface (imaging surface) of the image sensor 5, and also includes a light source (not shown) as needed. Hologram recording device 10 further includes a computer 6 that drives and controls image sensor 5, and a cover 19 made of a glass plate or the like that covers the light incident surface of interference light generating element 1. An object OBJ, which is the subject of hologram recording device 10, is placed on cover 19. Depending on the object OBJ, hologram recording device 10 may also include a glass cell that houses the object OBJ, and may further include a rotation mechanism that rotates the glass cell in two- or three-axis directions. Hologram recording device 10 constitutes a self-interferometer with an in-line optical system, and transmits light (light waves) L from object OBJ. OBJThe interference light generating element 1 receives this light and generates two light waves with different phases, and the interference fringes formed by these two light waves are recorded as a hologram by the image capturing element 5. If the two light waves that form the interference fringes are referred to as one set, then as will be described later, the interference light generating element 1 simultaneously generates two or more sets of light waves, and the image capturing element 5 can record a multiplexed hologram with a single exposure.

[0016] In the hologram recording device 10, the interference light generating element 1 is attached to the imaging surface (light incident surface) of the imaging element 5. The interference light generating element 1 according to the first embodiment of the present invention includes, in order from the light incident side, a first birefringent member 11, a phase shifter array (phase modulation element) 20 that spatially divides polarization components parallel to or orthogonal to the optical axis of the first birefringent member 11 to change the phase difference in two or more ways, and a polarizing plate (polarizer) 32 whose transmission axis is tilted with respect to the optical axis of the first birefringent member 11. The interference light generating element 1 preferably further includes a second birefringent member 12 whose optical axis is orthogonal to the optical axis of the first birefringent member 11, connected to the light exit surface of the first birefringent member 11, i.e., between the first birefringent member 11 and the phase shifter array 20. Furthermore, it is preferable that the interference light generating element 1 further comprises a polarizing plate 31, on the light incident side of the first birefringent member 11, whose transmission axis direction is inclined with respect to the optical axis of the first birefringent member 11. The interference light generating element 1 comprises these components (optical elements) stacked without any gaps. Furthermore, the interference light generating element 1 may comprise an anti-reflection film (AR coating) made of a dielectric multilayer film on the top or bottom surface of any of these components, and it is particularly preferable to provide an anti-reflection coating (AR coating) between components with a large difference in refractive index. (between layers) The anti-reflection coating suppresses Fresnel reflection at the interface between the components, further reducing light loss. Each component is preferably a flat plate with a predetermined uniform thickness, and is formed to a size equal to or larger than the imaging surface of the imaging element 5 when viewed from the plane (light incident surface). The smaller the overall thickness of the interference light generating element 1, i.e., the light path length (geometric distance) in the normal direction of the light incident surface, is relative to the length of one side of the imaging surface of the imaging element 5, the smaller the object light L OBJ The maximum divergence angle can be increased.

[0017] The hologram recording device 10 is configured so that there is no gap (air) between the upper surface of the cover 19, on which the object OBJ is placed, and the imaging surface of the imaging element 5. Therefore, it is preferable that the light incident surface of the interference light generating element 1 is horizontal. Furthermore, as described above, the components constituting the interference light generating element 1 are flat, so the imaging element 5 is placed with its imaging surface facing upward and horizontal. Since light enters the interference light generating element 1 from the top surface and travels downward within the interference light generating element 1, in this embodiment, the light incident side is referred to as "up." Note that the interference light generating element 1 of the hologram recording device 10 does not include a lens, which is a magnifying optical system, and therefore the subject is an object OBJ whose dimensions are such that it can be contained within the imaging element 5 when viewed from a plane (light incident surface).

[0018] (light source) Light from object OBJ (object light) L OBJ is visible light, natural light (unpolarized) with random polarization direction, and does not need to be coherent light. OBJThe light source that irradiates the object OBJ with light to generate a hologram can be a common lighting device such as a white LED (light-emitting diode), fluorescent lamp, halogen lamp, or mercury lamp, or sunlight. Furthermore, by combining monochromatic light sources such as red (R), green (G), and blue (B) LEDs, a multiplexed hologram that can reproduce images with high color reproducibility can be obtained. Alternatively, the light source can be a phosphor, including autofluorescence, spontaneously emitted Raman scattered light, or a self-luminous material, including bioluminescence, which emits light without a light source. These can also be used as the object OBJ. Therefore, the hologram recording device 10 can be applied to a digital holographic microscope for observing phosphors or self-luminous materials. When the object OBJ is a phosphor, a light source is provided that irradiates light (excitation light) that simultaneously excites multiple phosphors with different emission colors contained in the object OBJ (see the modified example shown in FIG. 4 ). Thus, the hologram recording device 10 can include the above-described light source as needed. The arrangement of the light source in the hologram recording device 10 is not particularly limited, but it can be arranged in the same manner as the light source that irradiates the subject (object OBJ) in a general optical microscope. Here, as an example, the hologram recording device 10 is light The hologram recording device 10 is configured to use a body as an object OBJ and not use a light source. For this reason, the hologram recording device 10 is provided with a housing (not shown) that blocks external light.

[0019] (image sensor) The image sensor 5 converts the incident light into an electric signal for each of the two-dimensionally arranged pixels and outputs the electric signal. In the hologram recording device 10 according to this embodiment, the image sensor 5 receives the L OBJIn order to capture light in each of the R, G, and B wavelength bands included in the image sensor 5 without distinguishing between them, a monochromatic (monochrome) image sensor that is sensitive to all of these wavelength bands is used. Such an image sensor mounted on a typical digital microscope can be used as the image sensor 5. Specific examples include a complementary metal-oxide semiconductor (CMOS) image sensor or a charge-coupled device (CCD) image sensor, each pixel of which is equipped with a photodiode made of Si with wide spectral sensitivity including the visible region. Alternatively, an array of commercially available photodetectors such as an electron multiplier tube can be used as the image sensor 5.

[0020] (calculator) The computer 6 incorporates a control device that drives and controls the image sensor 5 and a storage device that stores holograms acquired by the image sensor 5. To this end, the computer 6 is equipped with a central processing unit (CPU) and memories such as read-only memory (ROM), random access memory (RAM), or flash memory. A commercially available personal computer (PC) or the like can be used as the computer 6. Alternatively, the computer 6 may be configured as a camera module integrated with the image sensor 5 and the interference light generating element 1. The computer 6 may be configured as a circuit board having a planar shape similar to that of the image sensor 5 and disposed below the image sensor 5 (see FIG. 3), or may be formed on the same silicon substrate as the CMOS image sensor that constitutes the image sensor 5.

[0021] (First birefringent member, second birefringent member) The first birefringent member 11 and the second birefringent member 12 are each made of a birefringent material, and together they form the object light L OBJThe first birefringent member 11 is an optical element for generating two light waves L1 and L2 from the object light L. Examples of birefringent materials include crystals such as quartz, β-barium borate (BaB2O4, BBO) crystal, α-BBO crystal, calcite (CaCO3), rutile (TiO2) crystal, and yttrium vanadate (YVO4) crystal, metamaterial materials, and photonic crystals, which have structural birefringence. Alternatively, a gradient index (GRIN) lens using liquid crystal and having birefringence may be applied to the birefringent members 11 and 12. The first birefringent member 11 is arranged with its optical axis in one direction on the light incident surface, and in this embodiment, the direction of the optical axis of the first birefringent member 11 is defined as the 90° direction (the direction perpendicular to the paper surface in FIG. 1). The first birefringent member 11 birefringes the object light L OBJ Of these, light that is incident at an angle relative to the incident surface is split into an ordinary ray, which is linearly polarized at 0° (left and right in FIG. 1), and an extraordinary ray, which is linearly polarized at 90°, by being refracted at angles according to their respective refractive indices, generating light waves L1 and L2. Here, the optical axis of the first birefringent member 11 is the slow axis, and therefore the light wave L1, which is an ordinary ray, has a larger refraction angle than the light wave L2. On the other hand, the second birefringent member 12 is arranged with its optical axis (slow axis) in the 0° direction. Therefore, the second birefringent member 12 causes the light wave L2, which is linearly polarized at 90°, to travel as an ordinary ray at a larger refraction angle than the light wave L1.

[0022] The first birefringent member 11 and the second birefringent member 12 divide the object light L OBJ From the birefringent member 11, 12, two light waves L1, L2 are generated, which are spherical waves with different radii of curvature. The interference light generating element 1 includes two birefringent members 11, 12 whose optical axes are orthogonal to each other, so that two light waves L1, L2 that favorably form interference fringes can be easily generated. The first birefringent member 11 and the second birefringent member 12 are configured so that the total optical path length (optical distance) across these two layers and the polarization-sensitive phase shifter array 20 has an appropriate difference between the light waves L1 and L2. This will be described in detail later in the explanation of the phase shifter array 20. Note that the thickness of the birefringent members 11, 12 can be made smaller as the difference in refractive index between the ordinary ray and the extraordinary ray increases (the birefringence is stronger).

[0023] (phaser array) The phase shifter array 20 is a phase modulation element that spatially divides linearly polarized light at either 0° or 90° to change the phase difference in N ways (N≧2). To achieve this, the phase shifter array 20 is formed by randomly arranging N types of phase shifters, each of which shifts the phase of the linearly polarized light by different amounts, in a two-dimensional array. The phase shifter array 20 allows the interference light generating element 1 to form N interference fringe patterns. The number of interference fringe patterns is set according to the number of holograms required based on the optical information to be acquired from the object OBJ and the image reproduction method, and the phase shifter array 20 is designed based on this number. For simplicity, N=2 is used here. The phase shifter array 20 includes phase shifters 2a and 2b and shifts the phase of linearly polarized light at 0°. That is, the phase shifter array 20 converts the light wave L1 into light waves L1a and L1b with different phases for each cell (phase shifter). It is preferable that the cells 2a and 2b of the phase shifter array 20 each provide a phase distribution of a spherical wave without aliasing. By providing a phase distribution of spherical waves without aliasing, the phase shifter array 20 functions as a lens, and unnecessary orders of light waves are not generated, resulting in higher light utilization efficiency than when a diffractive lens is used. Furthermore, the phase shifter array 20 is preferably arranged so that the phase shifters 2a and 2b are equal in number or nearly so. This results in the light waves L1a and L1b having equal intensities (intensity ratio of 1) or nearly so. Furthermore, the number of cells in the phase shifter array 20 is preferably equal to or less than the number of pixels in the image sensor 5, and more preferably the same number (same arrangement).

[0024] Furthermore, in this embodiment, the retarders 2a and 2b each shift the phase by an amount corresponding to the wavelength. Specifically, the phase is shifted by an amount corresponding to each wavelength band of R, G, and B. A retarder array 20 in which such retarders 2a and 2b having polarization sensitivity and wavelength dependence are arranged can be implemented using a photonic crystal in which microwave plates are arranged, or an optical element in which a structural birefringent medium having a subwavelength periodic structure is arranged. Alternatively, a transmissive liquid crystal spatial light modulator mounted on a liquid crystal display (LCD) or the like can be implemented as the retarder array 20. By applying a voltage of different magnitude to each cell, retarders with phase shift amounts corresponding to the magnitude of the voltage can be arbitrarily arranged.

[0025] Here, the thickness of the first birefringent member 11 is d1, the refractive index for ordinary rays is n10, and the refractive index for extraordinary rays is n1 e , the thickness of the second birefringent member 12 is d2, the refractive index for ordinary rays is n20, and the refractive index for extraordinary rays is n2 e The thickness of the phase shifter array 20 (or the liquid crystal layer when the phase shifter array 20 is a liquid crystal spatial light modulator) is expressed as d PS , the refractive index for ordinary rays is n PS0 , the refractive index for extraordinary rays is n PSe The optical path length in the normal direction of the incident surface of the light can be calculated approximately as follows: e d2+n PSe d PS ), the light wave L2 is (n1 e d1+n20d2+n PS0 d PS) The material and thickness of the birefringent members 11 and 12 are designed so that the optical path length difference falls within an appropriate range, so that the light waves L1 and L2 are spaced apart enough to form interference fringes on the imaging surface of the imaging element 5. Specifically, for example, the optical path length difference between the light waves L1 and L2 is adjusted so that an interference fringe is formed in at least one pixel of the imaging element 5. A formula for calculating the coherence length can be used to set the optical path length difference, and clear interference fringes can be formed by adjusting the optical path length difference so that it falls within the calculated value. In this embodiment, the optical path length of the light wave L1 is configured to be longer than that of the light wave L2.

[0026] (polarizing plate) The polarizing plate 32 converts the 0° linearly polarized light and the 90° linearly polarized light separated by the first birefringent member 11 into linearly polarized light with the same polarization component. To achieve this, the polarizing plate 32 is arranged so that its transmission axis is inclined with respect to the optical axes of the first birefringent member 11 and the second birefringent member 12, i.e., in a direction other than 0° or 90°. This polarizing plate 32 allows the light wave L1 (L1a, L1b) and the light wave L2 to interfere with each other. The polarizing plate 32 is preferably arranged so that the 0° polarization component and the 90° polarization component of the light transmitted through the polarizing plate 32 have the same intensity or nearly so. Therefore, when the light waves L1 and L2 before entering the polarizing plate 32 have the same intensity, the transmission axis is preferably oriented in the 45° or 135° direction. In this embodiment, the transmission axis of the polarizing plate 32 is oriented in the 45° direction. When the intensity ratio of the two light waves forming the interference fringes is 1 or closer to 1, a clear interference fringe is formed, and the calculation for reconstructing an image from the acquired hologram becomes simple. OBJ The polarizer 31 is provided as necessary to control the intensity ratio between the 0° linearly polarized light and the 90° linearly polarized light separated by the first birefringent member 11. For this purpose, the polarizer 31 is arranged so that its transmission axis is oriented in a direction other than 0° or 90°, and is preferably oriented in the 45° or 135° direction to make the intensity ratio 1, and in this embodiment, the 45° direction, the same as the polarizer 32, is more preferably used.

[0027] (Hologram recording method) A hologram recording method using the hologram recording device 10 will be described with reference to Fig. 1 and Fig. 2. In Fig. 1 and Fig. 2, light L from an object OBJ spreads out in all directions from the center of the incident surface and enters the interference light generating element 1. OBJ In the drawings, light rays are represented by thick arrows, and linearly polarized light is indicated by a double-headed arrow indicating the polarization direction. In FIG. 1 and cross-sectional views of modified examples described later, 45° linearly polarized light is indicated by a double-headed arrow that is shorter than that of 0° linearly polarized light, and 90° linearly polarized light (perpendicular to the paper surface) is indicated by a double-headed arrow with a white circle (○) and a dot (·) at its center. In FIG. 2, birefringent members 11 and 12 are each indicated by a double-headed arrow indicating the optical axis direction.

[0028] Object light L generated from object OBJ OBJ is incoherent and unpolarized light, but passes through the polarizing plate 31 and becomes linearly polarized at an angle of 45°. OBJ When light enters the first birefringent member 11, it is separated into a light wave L1 that is linearly polarized at 0° and a light wave L2 that is linearly polarized at 90°, which is an ordinary ray, with an intensity ratio of 1, except for light that is incident perpendicularly to the plane of incidence, and the light waves travel at different refraction angles. When the light leaves the first birefringent member 11 and enters the second birefringent member 12, the light waves L1 and L2 travel with their refraction angles swapped. Note that here, differences between the refractive index of the first birefringent member 11 for the ordinary ray (light wave L1), the refractive index of the second birefringent member 12 for the ordinary ray (light wave L2), and the refractive index of the other members among the connected members are ignored.

[0029] Of the light waves L1 and L2 that pass through the phase shifter array 20, the light wave L1, which is linearly polarized at 0°, undergoes a phase shift that varies depending on the cells (phase shifters) 2a and 2b of the phase shifter array 20, transforming into light waves L1a and L1b with different phases. The light waves L1a and L1b then form spherical waves. Furthermore, the light waves L1a and L1b also have different phase differences with respect to the light wave L2, whose phase remains unchanged. The phase difference between the light waves L1 and L2 is also due to the difference in the total optical path length of the birefringent members 11 and 12 and the phase shifter array 20. Furthermore, because the phase shifters 2a and 2b are wavelength-dependent, two light waves with phases shifted by two shift amounts are formed for each wavelength band of the R, G, and B colors. As a result, the phase shifter array 20 transforms the light wave L1 into a total of six light waves, two for each wavelength band. Light waves L1a, L1b, and L2 emitted from the phase shifter array 20 are all linearly polarized at 45° by the polarizer 32. Then, light waves L1a and L2, and light waves L1b and L2, which are in the same wavelength band, form interference fringes on the imaging surface of the image sensor 5, and two patterns for each of the R, G, and B colors are superimposed, resulting in a total of six interference fringe patterns. The image sensor 5 captures these six interference fringe patterns together and records them as a multiplexed hologram.

[0030] (Digital holography device) A multi-color three-dimensional image of the object OBJ can be reconstructed by signal processing from the multiplexed hologram recorded by the imaging element 5 (Non-Patent Documents 1 to 5). By incorporating an image reconstruction device that performs such signal processing into the computer 6, a digital holography device can be configured.

[0031] (Variation) The interference light generating element 1 may include only the first birefringent member 11 or the second birefringent member 12, as long as it can generate two appropriate light waves L1, L2 that form interference fringes. With such a configuration, the interference light generating element 1 can reduce the number of parts, further reduce optical loss, and can also be made smaller. The interference light generating element 1 may also be made thinner (smaller) by using one of the birefringent members 11, 12 as a positive crystal and the other as a negative crystal. By making the interference light generating element 1 thinner, the object light L OBJ This can increase the maximum divergence angle of the interference light generating element 1. Furthermore, the retarder array 20 of the interference light generating element 1 can also be disposed above the first birefringent member 11 (between the polarizing plate 31) or between the first birefringent member 11 and the second birefringent member 12. However, it is preferable that the retarder array 20 be closer to the imaging element 5. Furthermore, the retarders 2a and 2b of the retarder array 20 may be wavelength-independent, for example, broadband wave plates. This configuration can be used when wavelength information is not required, such as when the image to be reproduced is monochrome, or when the imaging element 5 is a color image sensor equipped with a color filter array 40 (see FIG. 6) on the imaging surface. The same applies when reproducing images in only the near-infrared wavelength range. In this case, the hologram recording device 10 is equipped with a near-infrared light source, and the optical elements of the interference light generating element 1 and the imaging element 5 are selected to correspond to the near-infrared wavelength range.

[0032] (Modification of Hologram Recording Device) The hologram recording device may be arranged so that the object OBJ is not placed on the light incident surface of the interference light generating element 1, but is arranged so that the incident surface of the interference light generating element 1 faces the object OBJ from above or to the side at a distance. As shown in FIG. 3 , a hologram recording device 10A according to a modified example places the interference light generating element 1 above the object OBJ with its light incident surface facing downward. The hologram recording device 10A includes an image sensor 5 and the interference light generating element 1, as well as a light source 7 that irradiates the object OBJ with light L, a light shielding plate 18 with an opening formed therein that covers the light incident surface of the interference light generating element 1, a filter 41 that removes light in an unnecessary wavelength band, and a computer 6. The hologram recording device 10A may further include an objective lens on the light incident side of the interference light generating element 1. The hologram recording device 10A is configured to receive light L from an external source and convert it into object light L. OBJ The object OBJ that generates the hologram is the subject. Hologram recording device 10A is, for example, a camera mounted on a smartphone, and is provided inside housing H of the smartphone.

[0033] (light source) As described in the above embodiment, the light source 7 is, for example, a white LED. In addition to illumination light from the light source 7, sunlight can be used as the light L, and a combination of these may also be used. In the hologram recording device 10A, the light source 7 is disposed close to the interference light generating element 1 with its light emission surface facing downward, similar to the light incidence surface of the interference light generating element 1. The light source 7 may also be turned on by the computer 6 in synchronization with the imaging of interference fringes by the imaging element 5.

[0034] (filter) In the hologram recording device 10A, the light L may include not only illumination light from the light source 7 but also sunlight and the like, and the object light L OBJThe light enters the interference light generating element 1 together with the sunlight. If the imaging element 5 is also sensitive to light outside the visible range, such as infrared light, it is preferable to provide a filter 41 that removes light outside the visible range so that such light contained in sunlight does not enter the imaging element 5. The filter 41 may be, for example, an infrared cut filter (IRCF) used in digital cameras, a multi-bandpass filter for improving coherence, or a filter that blocks light of wavelengths other than those to be measured in order to measure light in a specific wavelength range, whether visible light or near-infrared light. The filter 41 is located on the light incident side of the imaging element 5, and in FIG. 3 is located between the interference light generating element 1 (polarizing plate 32) and the imaging element 5.

[0035] (Light shielding plate) In the hologram recording device 10A, there is a certain distance between the object OBJ and the light incident surface of the interference light generating element 1, and the object light L OBJ Since the object light L tends to spread widely, it is preferable to provide a light-shielding plate 18 having an opening formed as a diaphragm on the incident surface (on the polarizing plate 31). The opening of the light-shielding plate 18 is formed in the center of the light incident surface and has a circular or polygonal shape in a plan view. The diaphragm prevents the object light L in the interference light generating element 1 from spreading widely. OBJ and object beam L OBJ This reduces the spread angle of the light waves L1 and L2 generated from the incident light, making it possible to block light with an unmeasurable incident angle and to prevent the light waves L1 and L2 from reaching outside the imaging surface of the imaging element 5.

[0036] As shown in Figure 3, a hologram recording device 10A in which the light incident surface of the interference light generating element 1 faces the object OBJ from above may be equipped with a light-transmitting stage such as a glass plate on which the object OBJ is placed, and a light source 7 may be arranged below the stage.

[0037] (First Modification) The hologram recording device according to the first embodiment is configured to acquire a multiplexed hologram by including an interference light generating element having a phase shifter array that spatially divides specific linearly polarized light and changes the phase difference in two or more ways, but it is also possible to acquire multiple holograms by dividing the light in time and changing the phase difference in two or more ways. Below, a hologram recording device according to a first modification of the first embodiment of the present invention will be described with reference to FIG.

[0038] A hologram recording device 10B according to a modification of the first embodiment includes an image sensor 5 and an interference light generating element 1B attached to the light incident surface (imaging surface) of the image sensor 5. The hologram recording device 10B further includes a light source 7A that irradiates the object OBJ with light L, a filter 42 that removes light in unnecessary wavelength bands, a computer 6A that drives and controls the image sensor 5 and the phase modulator 21 of the interference light generating element 1B, and a cover 19 that covers the light incident surface of the interference light generating element 1B. The hologram recording device 10B receives light (light waves) L from the object (subject) OBJ. OBJ When the light beam is incident on the interference light generating element 1B, it generates two light waves with different phases, and the interference fringes formed by these two light waves are recorded as a hologram by the image capturing element 5. As will be described later, the interference light generating element 1B generates the two light waves by switching the phase difference between them over time, and each time this happens, the image capturing element 5 is exposed to light, allowing multiple holograms to be recorded sequentially.

[0039] As an example, hologram recording device 10B is a fluorescence microscope in which a phosphor is used as object OBJ. To this end, hologram recording device 10B includes light source 7A that emits light (excitation light) L that simultaneously excites multiple phosphors with different emission colors contained in object OBJ. Here, object light (fluorescence) L OBJ are red (R), green (G), and blue (B) lights, and the excitation light L is ultraviolet (UV) light.

[0040] In the hologram recording device 10B, the interference light generating element 1B is attached to the imaging surface (light incidence surface) of the imaging element 5. The interference light generating element 1B according to the modification of the first embodiment includes, in order from the light incidence side, a first birefringent member 11, a phase modulator (phase modulation element) 21 that temporally divides the polarization component parallel to or orthogonal to the optical axis of the first birefringent member 11 to change the phase difference in two or more ways, and a polarizing plate (polarizer) 32 whose transmission axis direction is tilted with respect to the optical axis of the first birefringent member 11. As with the interference light generating element 1 according to the above embodiment, the interference light generating element 1B preferably further includes a second birefringent member 12 whose optical axis is orthogonal to the optical axis of the first birefringent member 11, and a polarizing plate 31. That is, the interference light generating element 1B has a configuration in which the phase shifter array 20 of the interference light generating element 1 (see FIG. 1) is replaced with a phase modulator 21.

[0041] (filter) In the hologram recording device 10B, the excitation light L is irradiated not only onto the object OBJ but also onto the light incident surface of the interference light generating element 1B. If the image capturing element 5 is also sensitive to the wavelength region of the excitation light L, a filter 42 is provided to remove the excitation light L so that the excitation light L does not enter the image capturing element 5. The filter 42 absorbs or reflects light in the wavelength region (UV) of the excitation light L and also reflects light in the wavelength region (UV) of the object light L. OBJ It is a bandpass filter that transmits light in the wavelength ranges (R, G, B) of the interference light (fluorescence), and a dichroic mirror or the like used in a fluorescence microscope can be applied. The filter 42 is arranged on the light incident side of the imaging element 5, and is preferably arranged on the light incident surface (on the polarizing plate 31) of the interference light generating element 1B.

[0042] (phase modulator) The phase modulator 21 is a phase modulation element that temporally divides linearly polarized light at either 0° or 90° to change the phase difference in N ways (N≧2). Here, the phase modulator 21 shifts the phase of linearly polarized light at 0° and further switches the shift amount between N ways at high speed using electrical means. The phase modulator 21 allows the interference light generating element 1B to switch the interference fringes it forms into N patterns. As with the previous embodiment, the number of interference fringe patterns is set based on the optical information to be acquired from the object OBJ, the image reproduction method, and the like. In this modified example, the phase modulator 21 also shifts the phase by an amount corresponding to the wavelength. A liquid crystal element having liquid crystal sandwiched between two transparent electrode films can be used as the phase modulator 21, which has polarization sensitivity and wavelength dependency. The liquid crystal element can change the amount of phase shift of the transmitted light by changing the magnitude of the voltage applied to the liquid crystal. Furthermore, a liquid crystal element with a high response speed is preferably used for the phase modulator 21 in order to switch the phase shift amount at high speed. Alternatively, a wave plate in which the amount of phase modulation is controlled by voltage, an electro-optical (EO) element utilizing the electro-optical effect, or an optical element that modulates the phase of light utilizing the magneto-optical effect may be used as the phase modulator 21. The magnitude of the voltage applied to these phase modulators 21 is switched by a signal from the computer 6A.

[0043] Computer 6A exposes image sensor 5 in synchronization with the switching of the voltage applied to phase modulator 21. For this reason, in hologram recording device 10B according to this modified example, image sensor 5 preferably has a high response speed similar to phase modulator 21.

[0044] (Hologram recording method) A hologram recording method using the hologram recording device 10B will be described with reference to Fig. 4. Excitation light L and object light (fluorescent light) L are incident on the light incident surface of the interference light generating element 1B. OBJ is irradiated, but the filter 42 filters out the object light L OBJ Only the object light L is incident on the interference light generating element 1B. As in the embodiment shown in FIGS. OBJis transmitted through the polarizing plate 31 to become linearly polarized light at an angle of 45°, and is then transmitted through the first birefringent member 11 and the second birefringent member 12 in that order, where it is split into a light wave L1 linearly polarized at 0° and a light wave L2 linearly polarized at 90°.

[0045] Of the light waves L1 and L2 transmitted through the second birefringent member 12, the light wave L1, which is linearly polarized at 0°, has its phase shifted by a predetermined amount by the phase modulator 21. Furthermore, because the phase modulator 21 is wavelength-dependent, light waves with phases shifted by different amounts for the wavelength bands of R, G, and B are generated. As a result, the phase modulator 21 converts the light wave L1 into a total of three light waves, one for each wavelength band. The light waves L1 and L2 emitted from the phase modulator 21 are both linearly polarized at 45° by the polarizing plate 32. Then, on the imaging surface of the image sensor 5, the light waves L1 and L2, which are in the same wavelength band, form interference fringes, i.e., a total of three patterns of interference fringes for the R, G, and B colors, overlap. The image sensor 5 captures these three patterns of interference fringes together and records them as a multiplexed hologram. Furthermore, the phase modulator 21 changes the amount of phase shift of the light wave L1 by switching the magnitude of the applied voltage using the computer 6A, resulting in a change in the interference fringe pattern. Accordingly, the image sensor 5 again captures the interference fringes of each color together and records them as a multiplexed hologram. In this way, the image sensor 5 sequentially captures the formed interference fringes while switching the applied voltage to the phase modulator 21, thereby obtaining the number of holograms required to reconstruct the image.

[0046] Like the hologram recording device 10 according to the above embodiment, the hologram recording device 10B may be compatible with light other than visible light, such as near-infrared light, and may also include the light-shielding plate 18 (see FIG. 3) of the above-described modified example. The interference light generating element 1B may also include only the first birefringent member 11 or the second birefringent member 12. The interference light generating element 1B may also have the phase modulator 21 disposed on the first birefringent member 11 (between the polarizing plate 31) or between the first birefringent member 11 and the second birefringent member 12.

[0047] In the hologram recording device 10B of this modification, the imaging time for one image becomes longer as the number of required holograms increases, resulting in a decrease in temporal resolution. On the other hand, in the hologram recording device 10 of the previous embodiment, the pixels of each multiplexed hologram become discrete, resulting in a decrease in spatial resolution of the reproduced image. Therefore, the interference light generating element 1 of the hologram recording device 10 employs a transmissive liquid crystal spatial light modulator as the phase shifter array 20. By driving this phase shifter array 20 with a signal from the computer 6A, as in the previous modification, it is possible to obtain multiple multiplexed holograms divided spatially and temporally. Specifically, the phase shift amount for each cell (phase shifter) of the liquid crystal spatial light modulator or the phase shifter arrangement pattern is changed, and the image sensor 5 captures the image each time. It is preferable to use a liquid crystal spatial light modulator with a high response speed.

[0048] (Second Modification) The liquid crystal spatial light modulator applied to the phase shifter array can also be a reflective type. Reflective liquid crystal spatial light modulators generally facilitate cell miniaturization and have superior high-speed response compared to transmissive types. A hologram recording device according to a second modified example of the first embodiment of the present invention will now be described with reference to FIG. 5.

[0049] A hologram recording device 10C according to a modification of the first embodiment includes an image sensor 5 and an interference light generating element 1C attached to the light incident surface (imaging surface) of the image sensor 5. The hologram recording device 10C further includes a computer 6B that drives and controls the image sensor 5 and the spatial light phase modulator 20A of the interference light generating element 1C, a light shielding plate 18 having an opening formed therein that covers the light incident surface of the interference light generating element 1C, a cover 19 that covers the entire incident surface, and, if necessary, a light source 7 and a filter 41 (see FIG. 3) or a light source 7A and a filter 42 (see FIG. 4). The hologram recording device 10C receives light (light waves) L from an object (subject) OBJ. OBJWhen the light beam is incident on the interference light generating element 1C, it generates two light waves with different phases, and the interference fringes formed by these two light waves are recorded as a hologram by the image capturing element 5. As will be described later, the interference light generating element 1C simultaneously generates two or more sets of light waves and switches the phase difference between each set of light waves, and each time this occurs, the image capturing element 5 performs exposure to sequentially record a plurality of multiplexed holograms.

[0050] In a hologram recording device 10C, an interference light generating element 1C is attached to the imaging surface (light incident surface) of an imaging element 5. The interference light generating element 1C according to a modification of the first embodiment includes, along the light traveling direction, a first birefringent member 11A, a spatial light phase modulator (phase modulation element) 20A that reflects and outputs incident light and spatially and temporally divides polarization components parallel to or orthogonal to the optical axis of the first birefringent member 11A to change the phase difference in a total of four or more ways, and a polarizing plate (polarizer) 32 whose transmission axis direction is inclined with respect to the optical axis of the first birefringent member 11A. The first birefringent member 11A has an inclined surface inclined with respect to the light incident surface, and the light incident and exit surfaces of the spatial light phase modulator 20A are connected to this inclined surface. The interference light generating element 1C preferably further includes a second birefringent member 12A whose optical axis is perpendicular to the optical axis of the first birefringent member 11A, and a polarizing plate 31, similar to the interference light generating element 1 according to the above embodiment.

[0051] Like the interference light generating element 1, the interference light generating element 1C has a horizontal light incident surface, but its exit surface is non-parallel to the incident surface and is assumed to be vertical in this example. Therefore, the imaging element 5 is positioned with its imaging surface oriented vertically. The interference light generating element 1C differs from the interference light generating element 1 (see FIG. 1 ) in that the light-transmitting retarder array 20 is replaced with a reflective spatial light phase modulator 20A, and the spatial light phase modulator 20A is positioned with its light incident and exit surfaces facing obliquely upward. Accordingly, the first birefringent member 11A has an inclined surface formed in accordance with the orientation of the spatial light phase modulator 20A, and the light incident and exit surfaces of the spatial light phase modulator 20A are connected to this inclined surface. A second birefringent member 12A and a polarizing plate 32 are positioned in accordance with the traveling direction of the light reflected by the spatial light phase modulator 20A. In the interference light generating element 1C, the spatial light phase modulator 20A, which is a phase modulation element, is connected to the first birefringent member 11A, and therefore the polarizing plate 32 is connected to the light exit surface of the second birefringent member 12A.

[0052] (Spatial light phase modulator) The spatial light phase modulator 20A is a reflective liquid crystal spatial light modulator mounted in a liquid crystal projector or the like. Specifically, an LCOS (Liquid Crystal on Silicon)-SLM (SLM) is preferred, and a high response speed is preferred. The spatial light phase modulator 20A can arbitrarily arrange retarders with phase shift amounts corresponding to the magnitude of the voltage by applying different voltages to each cell. The retarders and their arrangement pattern of the spatial light phase modulator 20A are similar to those of the retarder array 20 of the interference light generating element 1. N types of retarders that shift the phase of linearly polarized light by different amounts (N≧2) are randomly arranged two-dimensionally. Each retarder shifts the phase by an amount corresponding to the wavelength. Here, as in the previous embodiment, N=2, and the spatial light phase modulator 20A includes retarders 2a and 2b, and shifts the phase of linearly polarized light at 0°. The spatial light phase modulator 20A further changes the magnitude of the voltage applied to each cell to change the amount of phase shift for each cell (phase shifter) or the arrangement pattern of the phase shifters. This driving of the spatial light phase modulator 20A is controlled by a signal from the computer 6B, similar to the phase modulator 21 of the interference light generating element 1B according to the modified example.

[0053] The spatial light phase modulator 20A is disposed with its light incident and exit surfaces tilted relative to the light incident surface of the interference light generating element 1C in order to reflect the light (light waves L1, L2) incident from above to the side (right in FIG. 5). More specifically, the reflected light from the spatial light phase modulator 20A reaches the outside of the light incident surface of the interference light generating element 1C. The closer the tilt angle of the spatial light phase modulator 20A is to 45°, the closer the object light L OBJ On the other hand, if the tilt angle is large, the incident angle of the light waves L1 and L2 that spread to the side light emission side to the spatial light phase modulator 20A becomes large and approaches 90° (in the incident / exit plane direction). Here, the spatial light phase modulator 20A is C The light source is positioned at an angle of 45° to the incident surface of the light source.

[0054] (First birefringent member) The first birefringent member 11A, like the first birefringent member 11 of the above embodiment, OBJ 5A and 5B. In the interference light generating element 1C, the first birefringent member 11A is connected to the light input / output surface of the tilted spatial light phase modulator 20A, and therefore has a surface tilted with respect to the horizontal light input surface. Here, the surface is tilted at 45° to match the spatial light phase modulator 20A. In the first birefringent member 11A, the light waves L1 and L2 traveling from above are reflected by the spatial light phase modulator 20A connected to the tilted lower surface and travel laterally. In this way, the light waves L1 and L2 change traveling direction in the first birefringent member 11A, so it is preferable that the first birefringent member 11A be arranged so that the direction of its optical axis (here, the slow axis) is at a 90° angle (perpendicular to the plane of the paper in FIG. 5A). Here, the first birefringent member 11A is formed so that the lateral light exit surface forms an angle with respect to the incident surface that is twice the inclination angle of the spatial light phase modulator 20A so that light beams expanding and traveling in different directions at the same angle have the same optical path length. Therefore, here, the light exit surface is set to 90°, which is twice 45°, i.e., a vertical side surface. Furthermore, the path length of light incident in the normal direction to the incident surface of the first birefringent member 11A is the sum of the length from the center of the incident surface to the inclined surface in the normal direction and the length of the perpendicular line from the point on the inclined surface to the exit surface, which is long. Therefore, it is preferable to select a material with low birefringence so as not to excessively increase the optical path length difference between the light waves L1 and L2 in the interference light generating element 1C.

[0055] (Second birefringent member) The second birefringent member 12A, like the second birefringent member 12 in the above embodiment, acts together with the first birefringent member 11A to form the object light L OBJThe interference light generating element 1C is a flat optical element made of a birefringent material and having a uniform thickness, for generating two light waves L1 and L2 from the first birefringent member 11A, and is disposed with its optical axis direction perpendicular to that of the first birefringent member 11A. In the interference light generating element 1C, the second birefringent member 12A is connected to the light exit surface of the first birefringent member 11A, and is therefore disposed with its connecting surface, i.e., its entrance surface, perpendicular. Therefore, the second birefringent member 12A is disposed with its optical axis (slow axis) direction at 0° (the vertical direction in FIG. 5). Also, similar to the above embodiment, the total optical path length of the birefringent members 11A and 12A and the spatial light phase modulator 20A is configured so that there is an appropriate difference between the light waves L1 and L2, such as being within the coherence length. In this case, the material of the first birefringent member 11A and the material and thickness of the second birefringent member 12A are designed based on the path length of the light incident in the normal direction to the light incident surface, instead of the thickness of the first birefringent member 11A. In order to reduce the size of the interference light generating element 1C, it is preferable to reduce the thickness by selecting a material whose birefringence is at least stronger than that of the first birefringent member 11A.

[0056] (Light shielding plate) Since the optical path length of the light waves L1 and L2 in the first birefringent member 11A is long in the interference light generating element 1C, it is preferable to provide a light blocking plate 18 with an opening formed on the light incident surface (on the polarizing plate 31) of the interference light generating element 1C. The opening of the light blocking plate 18 is formed in the center of the light incident surface in the shape of a circle or a polygon close to a circle, large enough to contain the object OBJ in a plan view. The aperture prevents the object light L1 from passing through the interference light generating element 1C. OBJ and object beam L OBJ The spread angle of the light waves L1 and L2 generated from the light source 5 is reduced, and the light waves L1 and L2 can be prevented from reaching the outside of the imaging surface of the imaging element 5.

[0057] (Hologram recording method) A hologram recording method using the hologram recording device 10C will be described with reference to Fig. 5. As in the embodiment shown in Figs. OBJThe light L1 is transmitted through the polarizing plate 31 and becomes linearly polarized at 45°. It then enters the first birefringent member 11A and is split into a 0° linearly polarized light wave L1 and a 90° linearly polarized light wave L2. A misalignment occurs at the entrance / exit surface of the spatial light phase modulator 20A, which is connected to the inclined surface of the first birefringent member 11A. The light waves L1 and L2 that reach the spatial light phase modulator 20A are reflected and travel laterally through the first birefringent member 11A. Furthermore, of the light waves L1 and L2 reflected by the spatial light phase modulator 20A, the light wave L1, which is linearly polarized at 0°, undergoes a phase shift that varies depending on the cells (phase shifters) 2a and 2b of the spatial light phase modulator 20A, resulting in light waves L1a and L1b with different phases. Furthermore, because the phase shifters 2a and 2b are wavelength-dependent, two light waves with phases shifted by two amounts are generated for each wavelength band of the R, G, and B colors. The light waves L1a, L1b and L2 exit from the side surface of the first birefringent member 11A and enter the second birefringent member 12A.

[0058] Light waves L1a, L1b, and L2 are linearly polarized at 45° by polarizer 32. Then, light waves L1a and L2, and light waves L1b and L2, each of which has the same wavelength band, form interference fringes on the imaging surface of image sensor 5. This results in six overlapping interference fringe patterns—two for each of the R, G, and B colors. Image sensor 5 captures these six interference fringe patterns together and records them as a multiplexed hologram. Furthermore, spatial light phase modulator 20A changes the magnitude of the applied voltage using computer 6B, thereby changing the amount of phase shift of light wave L1, resulting in a change in the interference fringe pattern. Accordingly, image sensor 5 again captures the six interference fringe patterns together and records them as a multiplexed hologram. In this way, image sensor 5 sequentially captures the formed interference fringes while switching the applied voltage to spatial light phase modulator 20A, thereby acquiring the number of holograms required to reconstruct the image.

[0059] Similar to the hologram recording device 10 according to the previous embodiment, the hologram recording device 10C according to this modification may be compatible with light other than visible light, such as near-infrared light. Furthermore, the interference light generating element 1C may have the second birefringent member 12A connected to the incident surface of the first birefringent member 11A, or may have only the first birefringent member 11A without the second birefringent member 12A.

[0060] Second Embodiment The hologram recording devices according to the first embodiment and its modifications are configured to acquire a multiplexed hologram by using an interference light generating element that includes a phase modulator or a phase shifter array that splits specific linearly polarized light at least in time and / or space to change the phase difference in two or more ways, but it is also possible to acquire multiple holograms by transmitting circularly polarized light through a polarizer array in which polarizers with different transmission axis directions are arranged two-dimensionally and splitting the light spatially to change the phase difference in two or more ways. A hologram recording device according to a second embodiment of the present invention will now be described.

[0061] As shown in FIG. 6, a hologram recording device 10D according to the second embodiment includes an image sensor 5 and an interference light generating element 1D mounted on the light incident surface (imaging surface) of the image sensor 5. The hologram recording device 10D further includes a color filter array 40 connected to the imaging surface of the image sensor 5, a computer 6 that drives and controls the image sensor 5, a cover 19 that covers the incident surface, and, if necessary, a light source 7 or light source 7A, filters 41 and 42, and a light shielding plate 18 (see FIG. 5). The hologram recording device 10D receives light (light waves) L from an object (subject) OBJ. OBJ The interference light generating element 1D receives this light and generates two light waves with different phases, and the interference fringes formed by these two light waves are recorded as a hologram by the image capturing element 5. If the two light waves that form the interference fringes are referred to as one set, then as will be described later, the interference light generating element 1D simultaneously generates two or more sets of light waves, and the image capturing element 5 can record a multiplexed hologram with a single exposure.

[0062] An interference light generating element 1D according to a second embodiment of the present invention comprises, in order from the light incident side, a first birefringent member 11, a quarter-wave plate 22 whose slow axis is inclined at 45° or 135° with respect to the optical axis of the first birefringent member 11, and a polarizer array 30 formed by two-dimensionally arranging a plurality of polarizers whose transmission axes are different in direction. The interference light generating element 1D preferably further comprises a second birefringent member 12 whose optical axis is perpendicular to the optical axis of the first birefringent member 11, connected to the light exit surface of the first birefringent member 11, i.e., between the first birefringent member 11 and the quarter-wave plate 22. The interference light generating element 1D preferably further comprises a polarizing plate 31 whose transmission axis is inclined with respect to the optical axis of the first birefringent member 11, on the light incident side of the first birefringent member 11. D The optical element has these components (optical elements) stacked without any gaps.

[0063] (1 / 4 wavelength plate) The quarter-wave plate 22 converts the 0° linearly polarized light and the 45° linearly polarized light separated by the first birefringent member 11 and then the second birefringent member 12 into circularly polarized light with opposite rotations, i.e., right-handed circularly polarized light and left-handed circularly polarized light. To achieve this, the quarter-wave plate 22 is disposed with its slow axis tilted at 45° or 135° with respect to the optical axis of the first birefringent member 11. The quarter-wave plate 22 is preferably a broadband wave plate that is not wavelength-dependent. The quarter-wave plate 22 may also be a three-quarter-wave plate.

[0064] (polarizer array) The polarizer array 30 is formed by two-dimensionally arranging polarizers with different transmission axes. The polarizers are arranged so that the transmission axes of adjacent polarizers are not perpendicular to each other, and the difference in the transmission axis directions is preferably 30° to 60°. Therefore, when the transmission axis directions of the polarizers are two-directional, they are preferably set in 45° increments, such as 0° and 45°. When the transmission axis directions of the polarizers are four-directional, they are preferably set at 0°, 45°, 90°, and 135°. In FIG. 6 , the polarizer array 30 includes polarizers 3a and 3b whose transmission axes are oriented at 90° and 45°, respectively. Similarly to the phase shifter array 20 of the interference light generating element 1 according to the first embodiment, the polarizer array 30 preferably includes polarizers 3a and 3b each providing a phase distribution of a spherical wave without aliasing. The polarizer array 30 preferably includes the same number of polarizers 3a and 3b as the number of polarizers 3a and 3b. Furthermore, the number of cells (polarizers) in the polarizer array 30 is preferably equal to or less than the number of pixels in the imaging element 5, and more preferably the same number (same arrangement).

[0065] (Color filter array) The color filter array 40 is disposed on the imaging surface of the image sensor 5, which is a monochrome image sensor, to form a single-plate color image sensor. The color filter array 40 is made up of three color filters arranged in a mosaic pattern, each of which transmits light in one of the wavelength bands of R, G, or B and absorbs light other than those. For example, the color filter array 40 may be arranged in a Bayer pattern, which is common in color image sensors. The color filter array 40 preferably has cells (color filters) arranged in the same manner as the pixels of the image sensor 5, or in an integer multiple of the number of pixels, for example, one cell for every 2×2 pixels.

[0066] (Hologram recording method) A hologram recording method using the hologram recorder 10D will be described with reference to Fig. 6. As in the first embodiment shown in Figs. OBJ is transmitted through the polarizing plate 31 to become linearly polarized light at an angle of 45°, and is then transmitted through the first birefringent member 11 and the second birefringent member 12 in that order, where it is split into a light wave L1 linearly polarized at an angle of 0° and a light wave L2 linearly polarized at an angle of 90° with an intensity ratio of 1.

[0067] The quarter-wave plate 22 converts light wave L1 into right-handed circularly polarized light and light wave L2 into left-handed circularly polarized light. When these counter-circularly polarized light waves L1 and L2 pass through the polarizer array 30, they become light waves L1a and L1b and light waves L2a and L2b, which are linearly polarized in the transmission axis direction of each cell (polarizer) 3a and 3b through which they pass. Furthermore, the amount of phase shift between the 0° polarization component and the 90° polarization component, i.e., the light waves L1 and L2, differs depending on the transmission axis direction of the polarizers 3a and 3b. As a result, the phase difference between light waves L1a and L2a and the phase difference between light waves L1b and L2b differs. Specifically, the phase difference between light waves L1a and L2a and the phase difference between light waves L1b and L2b that pass through polarizers 3a and 3b whose transmission axis directions differ by 45° differs by π / 2. As a result, light waves L1a and L2a, and light waves L1b and L2b, have the same polarization direction and therefore form interference fringes, respectively. Furthermore, two patterns of interference fringes are formed on the imaging surface of the imaging element 5, with different phase differences between light waves L1a and L2a and between light waves L1b and L2b.

[0068] Light waves L1a, L2 and light waves L1b, L2b pass through color filter array 40, and only light in the wavelength bands of R, G, and B for each color filter passes through and reaches image sensor 5. Image sensor 5 captures two patterns of interference fringes together for each pixel corresponding to the color filter of each color in color filter array 40, and records them as a multiplexed hologram.

[0069] (Variation) In the hologram recording device 10D, the color filter array 40 and the polarizer array 30 may be interchanged. Furthermore, when capturing light of two colors, for example, R and G, the hologram recording device 10D may include color filters of two colors, R and G, in the color filter array 40. Conversely, the hologram recording device 10D may include color filters of four or more colors in the color filter array 40 to capture light of these four or more colors. Furthermore, when the image to be reproduced is monochrome, the hologram recording device 10D does not require the color filter array 40. Furthermore, the hologram recording device 10D may not include the color filter array 40, and the imaging element 5 may be a stacked color image sensor. This configuration improves spatial resolution. Furthermore, like the hologram recording device 10 according to the first embodiment, the hologram recording device 10D may be compatible with light other than visible light, such as near-infrared light. Furthermore, the interference light generating element 1D may include only the first birefringent member 11 or the second birefringent member 12. In addition, the interference light generating element 1D may be equipped with a geometric phase lens, such as a polarized direct flat lens, that splits unpolarized light into circularly polarized light with opposite rotations, instead of the birefringent members 11, 12 and the quarter-wave plate 22 (see non-patent document 4).

[0070] Third Embodiment In the hologram recording devices according to the first and second embodiments, the interference light generating element generates two light waves that form interference fringes from the object light, but it is also possible to obtain a hologram by forming interference fringes from the object light and the reference light. Below, we will explain a hologram recording device according to a third embodiment of the present invention.

[0071] As shown in FIG. 7, a hologram recording device 10E according to the third embodiment includes an image sensor 5 and an interference light generating element 1E mounted on the light incident surface (imaging surface) of the image sensor 5. The hologram recording device 10E further includes a light source (not shown) that irradiates the interference light generating element 1E and the object (subject) OBJ with light L, a computer 6 that drives and controls the image sensor 5, and a cover 19 that covers the incident surface. In the hologram recording device 10E, the object OBJ is placed on the interference light generating element 1E (on the cover 19) in an area that is included in the imaging surface of the image sensor 5 in a planar (light incident surface) view. In the hologram recording device 10E, the interference light generating element 1E generates light (light waves) L from the object OBJ irradiated with light L. OBJ The incident light is the object light L OBJ The light L incident outside the incident area is used as the reference light, and the light L, L OBJ The hologram recording device 10E generates light waves with different phases from each other, and the interference fringes formed by these two light waves are recorded as a hologram by the image capture device 5. If the two light waves that form the interference fringes are referred to as one pair, then as will be described later, the interference light generating element 1E simultaneously generates two or more pairs of light waves, and the image capture device 5 can record a multiplexed hologram with a single exposure. The hologram recording device 10E can acquire three-dimensional information about a light-transmitting object OBJ as a subject, and can be applied to, for example, a quantitative phase microscope.

[0072] An interference light generating element 1E according to a third embodiment of the present invention includes, in order from the light incident side, a phase shifter array (phase modulation element) 20B, a birefringent member (first birefringent member) 13, and a polarizing plate (polarizer) 32 whose transmission axis direction is tilted with respect to the optical axis of the birefringent member 13 in a planar view. The phase shifter array 20B spatially divides at least the polarization component parallel to the optical axis of the birefringent member 13 to change the phase difference in two or more ways. In addition, in the interference light generating element 1E, in a hologram recording device 10E, the phase shifter array 20B is arranged side by side in the optical axis direction of the birefringent member 13 (the left-right direction in FIG. 7 ) without overlapping with the image sensor 5 in a planar view. In addition, the polarizing plate 32 is arranged in at least the same region as the image sensor 5 in a planar view. In the interference light generating element 1E, the light exit surface of the polarizing plate 32 is connected to the imaging surface of the image sensor 5. The interference light generating element 1E preferably further includes a polarizing plate 33 whose transmission axis is perpendicular to the optical axis of the birefringent member 13 on the light incident side of the birefringent member 13 in the same region as the image sensor 5 in plan view, and the phase shifter array 20B and the polarizing plate 33 are arranged adjacent to the light incident surface of the birefringent member 13. In the interference light generating element 1E, the region directly above the image sensor 5 is called the object light incident region, and the region adjacent to this region in the optical axis direction of the birefringent member 13 in plan view is called the reference light incident region A. Ref That is, the interference light generating element 1E is configured to separate the phase shifter array 20B from the reference light incident region A Ref In the interference light generating element 1E, a polarizing plate 33 is provided in the object light incident region, and a polarizing plate 32 is provided in at least the object light incident region. Ref It is preferable that the shape and dimensions of the imaging surface, ie, the object light incidence area, of the imaging element 5. Therefore, the interference light generating element 1E has a shape in which two imaging elements 5 are arranged adjacent to each other in a plan view.

[0073] (light source) The light L emitted by the light source of the hologram recording device 10E is unpolarized and does not have to be coherent light, as in the first and second embodiments, but is parallel light perpendicular to the light incident surface of the interference light generating element 1E (with an incident angle of 0°). For this purpose, the light source is equipped with an illumination device including an LED or the like and optical elements such as a collimator, and emits parallel light of a luminous flux that encompasses the entire light incident surface of the interference light generating element 1E. A part of the light L is incident on the object OBJ, and object light L is emitted from the object OBJ. OBJ is incident on the interference light generating element 1E. Ref The light L incident on the Ref a,L Ref b is generated.

[0074] (birefringent material) The birefringent member 13 is a flat optical element made of a birefringent material and having a uniform thickness, and is provided over the entire light incident surface of the interference light generating element 1E. The birefringent member 13 divides the object light L OBJ and reference beam L Ref a,L Ref a and b are converted into two light waves that can interfere on the imaging surface of the image sensor 5, the traveling directions of these lights are controlled. The birefringent material can be selected from the same materials as the birefringent members 11 and 12 in the first embodiment. The birefringent member 13 is arranged with its optical axis (direction indicated by the open double arrow in FIG. 7) in one direction, and in this embodiment, the direction of the optical axis of the birefringent member 13 on the light incident surface is defined as the 0° direction (the left-right direction in FIG. 7). The birefringent member 13 converts linearly polarized light at 90° (the direction perpendicular to the paper surface in FIG. 7) into an ordinary ray, so that the object light L OBJ is linearly polarized at an angle of 90° and travels toward the image sensor 5. Then, the extraordinary ray is linearly polarized at an angle of 0° and the reference light L Ref a,L Ref b. Furthermore, the birefringent member 13 tilts its optical axis in the thickness direction (incidence direction of light L) in order to refract the extraordinary ray of the perpendicularly incident light L toward the object light incidence region side. Here, it is assumed that the birefringent member 13 is a positive crystal, and the optical axis is tilted in the direction of the thickness direction (incidence direction of light L) in the reference light incidence region A. Ref The tilt angle is from the side toward the object light incident region side.

[0075] The birefringent member 13 is a reference light incident region A Ref The extraordinary ray (reference ray L Ref a,L Ref The material and thickness of the birefringent member 13 are designed so that the object light Lb) is incident on the imaging surface of the imaging element 5. Specifically, when the refraction angle of the extraordinary ray is expressed as φ (0°<φ<90°), the thickness of the birefringent member 13 is (1 / tanφ) times the length of the imaging element 5 in the 0° direction. Therefore, the larger the refraction angle φ of the extraordinary ray, the thinner the birefringent member 13 is designed to be. If the thickness of the birefringent member 13 is small, the interference light generating element 1E can be made smaller (thinner), and the object light L OBJ Therefore, it is preferable that the birefringent member 13 is made of a material with strong birefringence and is disposed in the optical axis direction where the refraction angle φ is maximized.

[0076] (phaser array) The phase shifter array 20B has the same configuration as the phase shifter array 20 of the interference light generating element 1 according to the first embodiment, and is formed by randomly arranging N types of phase shifters (N≧2) in two dimensions, each of which shifts the phase of 0° linearly polarized light, which is the extraordinary ray in the birefringent member 13, by different amounts. Each phase shifter shifts the phase by an amount corresponding to the wavelength. Here, as in the previous embodiment, N=2, and the phase shifter array 20B includes phase shifters 2a and 2b. Alternatively, the phase shifter array 20B can use a polarization-independent holographic optical element or diffractive optical element as the phase shifter.

[0077] (polarizing plate) The polarizing plate 32 has the same configuration as the polarizing plate 32 of the interference light generating element 1 according to the first embodiment, and is configured to polarize the object light L OBJ and the reference beam L, which is linearly polarized at 0°. Ref a,L Ref The polarizing plate 33 converts the object light L and b into linearly polarized light with the same polarization component so that they can interfere with each other. OBJ is linearly polarized light at an angle of 90°, which is an ordinary ray in the birefringent member 13, the direction of the transmission axis is set to 90°, and the light is provided on the light incident side of the birefringent member 13 as needed.

[0078] (Hologram recording method) A hologram recording method using the hologram recording device 10E will be described with reference to Fig. 7. When parallel light L is irradiated perpendicularly onto the interference light generating element 1E, part of the light is irradiated onto the object OBJ, and the object light L is emitted from the object OBJ. OBJ is incident on the interference light generating element 1E. OBJ The object light L is incoherent and unpolarized light like the light L, but is transmitted through the polarizing plate 33 and becomes linearly polarized at 90°. OBJ When the reference light incident region A enters the birefringent member 13, it is an ordinary ray and therefore travels without being affected by the optical axis direction of the birefringent member 13, and reaches the polarizing plate 32. Ref The light L incident on the phase shifter array 20B is then incident on the phase shifter array 20B, and the 0° polarization component is phase-shifted by a different amount for each cell (phase shifter) 2a, 2b, resulting in a light wave (reference light) L with a different phase. Ref a,L Ref b. Then, the reference light L Ref a,L Ref Each of the phase shifters 2a and 2b forms a spherical wave. Furthermore, since the phase shifters 2a and 2b have wavelength dependency, two light waves with phases changed by two shift amounts are formed for each wavelength band of the R, G, and B colors. The phase shifter array 20B converts the 0° polarization component into the reference light L Ref a,L Ref When the light L changed to b is incident on the birefringent member 13, the 90° polarization component travels straight as an ordinary ray and is transmitted, and the 0° polarization component, i.e., the reference light L Ref a,L Ref Ray b is refracted as an extraordinary ray so as to approach the optical axis direction and reaches the polarizing plate 32 .

[0079] Object light L OBJ and reference light L Ref a,L Ref b are linearly polarized at an angle of 45° by the polarizing plate 32. Then, on the imaging surface of the imaging element 5, the object light L OBJ and reference beam L Ref a, object light L OBJ and reference beam L RefInterference fringes are formed at points b and b, and six patterns of interference fringes are superimposed on each other, two for each of the R, G, and B colors. The image sensor 5 captures an image of these six patterns of interference fringes together and records them as a multiplexed hologram.

[0080] (Variation) The hologram recording device 10E may include a light shielding plate 18 (see FIG. 5) of a modification of the first embodiment in an object light incident region (on the polarizing plate 33) of the light incident surface of the interference light generating element 1E. OBJ and reference beam L Ref a,L Ref In order to adjust the optical path length difference between the object light L and the object light Lb, the birefringent member 13 may be provided by laminating two or more birefringent materials. The birefringent materials have different refractive indices for at least one of the ordinary ray and the extraordinary ray, or different tilt angles of the optical axes in the thickness direction. The interference light generating element 1E may not be provided with a polarizing plate 33. In this case, the object light L OBJ The birefringent member 13 is configured to refract the light so that the 0° polarization component does not enter the imaging element 5. The interference light generating element 1E may include a phase modulator 21 instead of the phase shifter array 20B, as in the interference light generating element 1B (see FIG. 4) according to a modification of the first embodiment, to change the phase difference in two or more ways by dividing the phase difference in time. Furthermore, as in the modification of the first embodiment, the interference light generating element 1E may use a transmissive liquid crystal spatial light modulator as the phase shifter array 20B and drive it by electrical means, thereby obtaining a multiplexed hologram divided spatially and temporally into many parts. The phase shifter array or phase modulator, such as a liquid crystal spatial light modulator, may also be a reflective type, as in the modification of the first embodiment. A hologram recording device according to a modification of the third embodiment of the present invention will now be described with reference to FIG. 8.

[0081] A hologram recording device 10F according to a modification of the third embodiment includes an image sensor 5 and an interference light generating element 1F mounted on the light incident surface (imaging surface) of the image sensor 5. The hologram recording device 10F further includes a light source (not shown) that irradiates light L onto the interference light generating element 1F and the object (subject) OBJ, a computer 6B that drives and controls the image sensor 5 and the spatial light phase modulator 20A of the interference light generating element 1F, and a cover 19 that covers the incident surface. The light source has the same configuration as in the previous embodiment. Similar to the hologram recording device 10E according to the previous embodiment, the hologram recording device 10F has an object OBJ placed on the interference light generating element 1F (on the cover 19) in an area that is included in the imaging surface of the image sensor 5 in a planar (light incident surface) view. In the hologram recording device 10F, the interference light generating element 1F generates light (light waves) L from the object OBJ irradiated with light L. OBJ The incident light is the object light L OBJ The light L incident outside the incident area is used as the reference light, and the light L, L OBJ The interference light generating element 1F generates light waves with different phases from each other, and the interference fringes formed by these two light waves are recorded as a hologram by the image sensor 5. As will be described later, the interference light generating element 1F simultaneously generates two or more sets of light waves and switches the phase difference between each set of light waves, and each time this occurs, the image sensor 5 performs exposure to sequentially record multiple multiplexed holograms.

[0082] The interference light generating element 1F according to the modification of the third embodiment includes, along the light traveling direction, a birefringent member (first birefringent member) 13A, a spatial light phase modulator (phase modulation element) 20A that reflects and outputs incident light and spatially and temporally divides at least the polarization component parallel to the optical axis of the birefringent member 13A to change the phase difference in four or more ways in total, and a polarizing plate (polarizer) 32 whose transmission axis direction is tilted with respect to the optical axis of the birefringent member 13A in a planar view. Also, like the interference light generating element 1E according to the above embodiment, the interference light generating element 1F includes a region (object light incident region) directly above the imaging element 5 in the hologram recording device 10F, and a reference light incident region A adjacent to this region in the optical axis direction of the birefringent member 13A in a planar view. RefThe spatial light phase modulator 20A has a light incident and exit surface that is located in the reference light incident area A of the birefringent member 13A. Ref The interference light generating element 1F is also provided with a polarizing plate 32 at least in the object light incident region. The interference light generating element 1F further includes a polarizing plate 33, whose transmission axis is oriented perpendicular to the optical axis of the birefringent member 13A, in the object light incident region, on the light incident surface of the birefringent member 13A, and a polarizing plate 34, whose transmission axis is oriented in the same direction as the optical axis of the birefringent member 13A, in the reference light incident region A. Ref In the interference light generating element 1F, it is preferable to provide the reference light incident region A Ref In plan view, it is preferable that the length of the reference light incident region A in the direction perpendicular to the optical axis of the birefringent member 13A is the same as that of the object light incident region (the same as that of the image sensor 5). Ref On the other hand, the length of the birefringent member 13A in the optical axis direction is designed according to the arrangement of the spatial light phase modulator 20A, as will be described later.

[0083] (birefringent material) The birefringent member 13A is a flat optical element made of a birefringent material and having a uniform thickness, and is provided over the entire light incident surface of the interference light generating element 1F. Similar to the birefringent member 13 of the interference light generating element 1E according to the above embodiment, the birefringent member 13A is configured to divide the object light L incident from different regions of the light incident surface of the interference light generating element 1F. OBJ and Light L Ref (Reference light L Ref a,L Ref b) into two light waves that can interfere on the imaging surface of the imaging element 5, the traveling directions of these lights are controlled. The birefringent member 13A is arranged with its optical axis (direction indicated by a hollow double arrow in FIG. 8) in one direction, and in this modification, the direction of the optical axis of the birefringent member 13A on the light incident surface is defined as the 0° direction (the left-right direction in FIG. 8). The birefringent member 13A turns linearly polarized light at 90° (the direction perpendicular to the paper surface in FIG. 8) into an ordinary ray, so that the object light L OBJ is linearly polarized at an angle of 90° and travels toward the image sensor 5. Then, the extraordinary ray is linearly polarized at an angle of 0° and the reference light L Ref a,L Ref Let's call it b.

[0084] In this modification, the birefringent member 13A further includes a reference beam incident region A Ref The extraordinary ray of light L incident on Ref ) is incident on the spatial light phase modulator 20A, and the reflected reference light L Ref a,L Ref b is inclined toward the object light incident region and travels obliquely downward so as to be incident on the image sensor 5. For this purpose, the birefringent member 13A is Ref The side of the birefringent member 13A that is the connection surface with the spatial light phase modulator 20A is a surface that is not parallel to the light incident surface (horizontal surface), that is, a vertical surface or an inclined surface, and the light L Ref and reference light L Ref a,L Ref Specifically, if the refraction angle of the extraordinary ray of the birefringent member 13A is φ (0°<φ<90°) and the transmission angle (incidence angle to the polarizing plate 32) of the extraordinary ray reflected by the spatial light phase modulator 20A is α (0°<α<90°), the inclination angle of the connection surface with the spatial light phase modulator 20A with respect to the light incident surface is (90°+φ / 2-α / 2). In FIG. 8, α>φ, and in this case, the reference light incident area A of the birefringent member 13A Ref The side surface on the side of the birefringent member 13A is an inclined surface with the outer surface facing diagonally downward. The birefringent member 13A tilts the optical axis in the thickness direction (incidence direction of the light L) in order to refract the extraordinary ray of the perpendicularly incident light L toward the spatial light phase modulator 20A. Furthermore, the birefringent member 13A tilts the optical axis in the thickness direction (incidence direction of the light L) in order to refract the extraordinary ray of the perpendicularly incident light L toward the spatial light phase modulator 20A. Ref (L Ref a,L Ref In order to make the optical path length of b) uniform, the direction of the optical axis is set so that the angle of incidence and the angle of reflection of the extraordinary ray on the spatial light phase modulator 20A are equal (specular reflection). Here, it is assumed that the birefringent member 13A is a positive crystal, and the optical axis is set so that the angle of incidence is equal to the angle of reflection of the extraordinary ray on the spatial light phase modulator 20A from the object light incident region side to the reference light incident region A. Ref Tilt it to the side.

[0085] Furthermore, the birefringent member 13A distributes the reference light L Ref a,L Ref b is incident on the reference beam incident area ARef The length in the 0° direction is designed. It is preferable to set α>φ. In this case, the reference beam incident area A Ref The length in the 0° direction of the birefringent member 13A may be shorter than the object light incident area, and can be made shorter as the transmission angle α is set larger. Furthermore, the thickness of the birefringent member 13A can be made smaller as the transmission angle α is set larger.

[0086] (Spatial light phase modulator) The spatial light phase modulator 20A can have the configuration described in the modified example of the first embodiment, and in this modified example, the phase of the 0° linearly polarized light, which is the extraordinary ray in the birefringent member 13A, is shifted. Also, in this modified example, as described above, the spatial light phase modulator 20A has a light incident / exit surface that is located in the reference light incident area A of the birefringent member 13A. Ref 8, the spatial light phase modulator 20A is connected to the side surface of the reference light incident region A of the birefringent member 13A, and is disposed vertically or at an angle. Ref The reference light incident area A does not have to be provided on the entire side surface of the imaging element 5. Ref It is preferable that the spatial light phase modulator 20A is designed based on the inclination angle of the light incident / exit surface, the exit angle of the extraordinary ray of the birefringent member 13A, and the length of the imaging element 5 in the 0° direction so that all light incident from the side exits the spatial light phase modulator 20A.

[0087] (polarizing plate) The polarizing plate 32 and the polarizing plate 33 have the same configuration as the polarizing plate 32 and the polarizing plate 33 of the interference light generating element 1E according to the embodiment. Ref Of the light L incident on Ref a,L Ref In order to prevent light other than b, i.e., 90° linearly polarized light, which is the ordinary ray in the birefringent member 13A, from entering the imaging element 5, the direction of the transmission axis is set to 0°, and the birefringent member 13A is provided on the light incident side as needed.

[0088] (Hologram recording method) A hologram recording method using the hologram recorder 10F will be described with reference to Fig. 8. When parallel light L is irradiated perpendicularly onto the interference light generating element 1F, part of the light is irradiated onto the object OBJ, and the object light L is emitted from the object OBJ, as in the embodiment shown in Fig. 7. OBJ is incident on the interference light generating element 1F, passes through the polarizing plate 33, and becomes linearly polarized at 90°. OBJ When the reference light incident region A enters the birefringent member 13A, it is an ordinary ray, and therefore travels without being affected by the optical axis direction of the birefringent member 13A, and reaches the polarizing plate 32. Ref The light L incident on the polarizer 34 passes through the polarizer 34 and becomes linearly polarized light L Ref Light L Ref When the light L is incident on the birefringent member 13A, it is an extraordinary ray, so it is refracted so as to approach the optical axis direction, and is then incident on the spatial light phase modulator 20A and reflected. Ref The phase changes with a different shift amount for each cell (phase shifter) 2a, 2b, and the light wave (reference light) L Ref a,L Ref b. Then, the reference light L Ref a,L Ref Each of the phase shifters 2a and 2b forms a spherical wave. Furthermore, since the phase shifters 2a and 2b have wavelength dependency, two light waves with phases changed by two shift amounts are formed for each wavelength band of each color of R, G, and B. The reference light L emitted from the spatial light phase modulator 20A Ref a,L Ref Light b travels downward through the birefringent member 13A at an angle to the object light incident region and reaches the polarizing plate 32.

[0089] Object light L OBJ and reference light L Ref a,L Ref b are both linearly polarized at an angle of 45° by the polarizing plate 32. Then, as in the above embodiment, the object light L OBJ and reference beam L Ref a, object light L OBJ and reference beam L Refb form interference fringes, and two patterns for each of the R, G, and B colors are overlapped, resulting in a total of six interference fringe patterns. The image sensor 5 captures an image of these six interference fringe patterns collectively and records them as a multiplexed hologram. Furthermore, the spatial light phase modulator 20A controls the reference light L by switching the magnitude of the applied voltage using a computer 6B. Ref a,L Ref The amount of phase shift of b is changed, and as a result, the interference fringe pattern changes. In accordance with this, the image sensor 5 again captures six patterns of interference fringes together and records them as a multiplexed hologram.

[0090] The hologram recording device 10F may be provided with a light shielding plate 18 (see FIG. 5) of a modified example of the first embodiment in the object light incident region (on the polarizing plate 33) of the light incident surface of the interference light generating element 1F, similar to the hologram recording device 10E according to the previous embodiment. Also, the interference light generating element 1F may be provided with a birefringent member 13A formed by stacking two or more birefringent materials, similar to the birefringent member 13 of the previous embodiment. However, the spatial light phase modulator 20A is connected to the side of one of the birefringent materials. Also, the interference light generating element 1F may not be provided with the polarizing plate 33. Furthermore, the interference light generating element 1F may be configured without the polarizing plate 34. In this case, the reference light incident region A Ref The birefringent member 13A is configured so that 90° linearly polarized light of all the light L incident on the birefringent member 13A is emitted outside the imaging plane of the imaging element 5. The interference light generating element 1F may also include a phase modulator 21 instead of the spatial light phase modulator 20A, and in this case, the phase modulator 21 is of a reflective type, with one of the electrode films of the liquid crystal element being a metal electrode.

[0091] The above describes various embodiments for implementing the interference light generating element and hologram recording device according to the present invention, but the present invention is not limited to these embodiments, and various modifications are possible within the scope of the claims. [Explanation of symbols]

[0092] 10, 10A, 10B, 10C, 10D, 10E, 10F Hologram recording device 1, 1B, 1C, 1D, 1E, 1F Interference light generating element 11, 11A First birefringent member 12, 12A Second birefringent member 13, 13A birefringent member (first birefringent member) 18 Shade 20,20B Phase shifter array (phase modulation element) 20A Spatial Light Phase Modulator (Phase Modulation Element) 21 Phase modulator (phase modulation element) 22 1 / 4 wave plate 2a,2b phaser 30 Polarizer Array 31 Polarizing plate 32 Polarizing plate (polarizer) 33 Polarizing plate 34 Polarizing plate 3a,3b Polarizer 40 Color Filter Array 41,42 Filter 5. Image sensor 6,6A,6B calculator 7,7A light source

Claims

1. a first birefringent member; a phase modulation element that divides the polarization component in a direction parallel to or orthogonal to the optical axis of the first birefringent member into at least one of time and space and changes the phase difference in two or more ways; a polarizer whose transmission axis is tilted with respect to the optical axis of the first birefringent member, and the polarizer is disposed along the traveling direction of the light; the polarizer is disposed on a light exit side of the first birefringent member and the phase modulation element, The light exit surface is attached to the light entrance surface of the image sensor, An interference light generating element characterized in that it is stacked without gaps along the direction of light travel from the light incident surface to the light exit surface, and has an anti-reflection film on one or more of the stacked layers.

2. 2. The interference light generating element according to claim 1, wherein the phase modulation element has wavelength dependency.

3. In order from the light incident side, a first birefringent member; a polarizer array in which a plurality of polarizers having different transmission axis directions are two-dimensionally arranged, The light exit surface is attached to the light entrance surface of the image sensor, An interference light generating element, characterized in that it is laminated without any gaps from a light incident surface to a light exit surface, and an anti-reflection film is provided on one or more of the laminated layers.

4. The phase modulation element reflects and emits incident light, The interference light generating element described in claim 1 or claim 2, characterized in that the first birefringent member has a surface that is non-parallel to the light incident and exit surfaces, and the light incident and exit surfaces of the phase modulation element are connected to this surface without any gaps.

5. a second birefringent member having an optical axis perpendicular to the optical axis of the first birefringent member; 5. The interference light generating element according to claim 1, wherein the second birefringent element is connected to the light exit surface of the first birefringent element or is arranged on the light incident side of the first birefringent element.

6. an imaging element; and the interference light generating element according to any one of claims 1 to 5 attached to a light incident surface of the imaging element, A hologram recording device in which the interference light generating element generates two light waves with different phases from an incident light wave, and the imaging element records the interference fringes formed by the two light waves as a hologram.

Images