Interferometric optical system and spectroscopic device

Abstract

An interferometric optical system (2) for forming interference fringes of incident light (Li) in a predetermined wavelength band is provided with a front group (21) and a rear group (22) respectively disposed on the incident side and emission side of the incident light. The front group is provided with a first optical element (3) that emits, in different directions, first light (L1) and second light (L2) having mutually different polarization states in response to incidence of the incident light. The rear group is provided with a second optical element (4) that brings the emission directions of the first and second light, which are incident from the front group, closer to each other, and focuses the mutually interfering polarization components of the first and second light.

Description

Interference optics and spectroscopic equipment

[0001] The present disclosure relates to interference optical systems and spectroscopic devices.

[0002] Patent Document 1 discloses a multi-channel Fourier transform spectrometer using an image pickup element for the infrared region, etc. The multi-channel Fourier transform spectrometer includes, along the optical path from the light source, a polarizer, a Savart plate as a polarization splitting birefringent element, an analyzer, a converging lens, and an infrared solid-state image pickup element located on the rear focal plane of the lens. Patent Document 1 discloses a measurement target for the absorption spectrum in the near-infrared region (0.8 to 2.7 μm), and a TiO ２ It is also disclosed that calcite is used for the Savart plate for visible and ultraviolet light.

[0003] Patent No. 3095167

[0004] Yadong Deng, et al., "Functional Metasurface Quarter-Wave Plates for Simultaneous Polarization Conversion and Beam Steering", ACS Nano 2021, 15, 11, 18532-18540Noe Ishizuka, et al., "Fabrication of Linear Polarization-Separating Silicon Metalens at Long-Wavelength Infrared", 09 April 2023, Springer, Cham, https: / / doi.org / 10.1007 / 978-3-031-29871-4_15

[0005] The present disclosure provides an interference optical system and a spectroscopic device that can obtain interference fringes from incident light in a predetermined wavelength band.

[0006] The interference optical system disclosed herein forms interference fringes in a predetermined wavelength band, particularly in a predetermined wavelength band including wavelengths longer than near-infrared wavelengths, for incident light. The interference optical system includes a front group and a rear group arranged on the entrance side and exit side of the incident light, respectively. The front group includes a first optical element that outputs first light and second light having different polarization states in different directions in response to the incidence of the incident light. The rear group includes a second optical element that moves the exit directions of the first and second light incident from the front group closer to each other, thereby collecting the polarized components of the first and second light that interfere with each other.

[0007] The spectroscopic device according to the present disclosure includes the above-described interference optical system, a detection unit that detects a light intensity distribution indicating interference fringes formed by the interference optical system, and a control unit that measures the spectral characteristics of incident light based on the detected light intensity distribution.

[0008] According to the interference optical system and spectroscopic device of the present disclosure, interference fringes can be obtained from incident light in a predetermined wavelength band.

[0009] FIG. 1 is a block diagram illustrating the configuration of a spectroscopic device according to a first embodiment of the present disclosure; FIG. 2 is a diagram for explaining the branching of light in an interference optical system of the spectroscopic device according to the first embodiment; FIG. 3 is a waveform diagram illustrating an interferogram in the spectroscopic device; FIG. 4 is a diagram illustrating an example configuration of an interference optical system according to the first embodiment; FIG. 5 is a diagram illustrating an example configuration of a first metamaterial element in an interference optical system; FIG. 6 is a diagram illustrating an example configuration of a second metamaterial element in an interference optical system; Graph illustrating a simulation result of the interference optical system of Example 1. FIG. 2 is a plan view showing an example of the arrangement of cells. FIG. 3 is a plan view showing an example of the arrangement of unit cells in the second metamaterial element of Example 1. FIG. 4 is a graph illustrating a simulation result of the interference optical system of Example 1. FIG. 5 is a perspective view showing an example of the unit cell in the metamaterial structure of Example 2. FIG. 6 is a top view showing an example of the unit cell in the metamaterial structure of Example 2. FIG. 7 is a plan view showing an example of the arrangement of unit cells in the first metamaterial element of Example 2. FIG. 8 is a graph illustrating a simulation result of the first branched light in the interference optical system of Example 2. FIG. 9 is a graph illustrating a simulation result of the second branched light in the interference optical system of Example 2. FIG. 10 is a waveform diagram illustrating an interferogram of opposite phase in the spectroscopic device. FIG. 11 is a diagram illustrating a configuration of the spectroscopic device of Example 3. FIG. 12 is a diagram for explaining the branching of light in the interference optical system of a modified example.

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. However, more detailed explanation than necessary may be omitted. For example, detailed explanation of well-known matters or redundant explanation of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art.

[0011] The present inventors have provided the accompanying drawings and the following description to enable those skilled in the art to fully understand the present disclosure, and do not intend for them to limit the subject matter described in the claims.

[0012] Hereinafter, a first embodiment of the present disclosure will be described with reference to the drawings. In this embodiment, an interference optical system that forms interference fringes of incident light in a predetermined wavelength band and a spectroscopic device using the same will be described.

[0013] 1. Spectroscopic Device The spectroscopic device according to this embodiment will be described with reference to Figures 1 to 3. Figure 1 illustrates the configuration of a spectroscopic device 1 according to this embodiment.

[0014] 1, the spectroscopic device 1 includes an interference optical system 2, a detection unit 11, and a control unit 12. The control unit 12 includes an acquisition unit 13 and a calculation unit 14, for example.

[0015] The spectroscopic device 1 of this embodiment is a device that measures the spectral characteristics of incident light Li incident from a measurement object 10 in an infrared wavelength band including the mid-infrared and far-infrared regions, for example, using Fourier transform infrared spectroscopy (FTIR). The spectroscopic device 1 can be used, for example, to non-invasively realize a blood glucose level sensor by measuring the infrared emission of glucose in human blood. In this case, the measurement object 10 is a part of the human body, such as an earlobe or eardrum.

[0016] In this embodiment, the infrared wavelength band of the incident light Li to be measured by the spectroscopic device 1 includes wavelengths equal to or greater than the near-infrared wavelength, such as 9.25 μm or 9.65 μm. Such an infrared wavelength band is, for example, a wavelength of 5 μm to 20 μm, or may be a wavelength of 8 μm to 12 μm.

[0017] The interference optical system 2 of this embodiment is an optical system that splits incident light Li from, for example, the measurement object 10 into two light beams and causes them to interfere by overlapping with each other. Hereinafter, the two light beams split from the incident light Li by the interference optical system 2 will be referred to as a first branched light L1 and a second branched light L2, respectively. The first branched light L1 and the second branched light L2 are examples of a first light and a second light, respectively, in this embodiment.

[0018] 2 is a diagram for explaining the branching of the incident light Li into first and second branched lights L1 and L2 in the interference optical system 2 of this embodiment. Fig. 2 illustrates the principal rays of the incident light Li and the branched lights L1 and L2 in the interference optical system 2 of this embodiment. Each principal ray is defined as, for example, the central ray of each light beam.

[0019] 2, the interference optical system 2 has an optical axis Az that guides the incident light Li. Hereinafter, the direction parallel to the optical axis Az will be referred to as the Z direction, and the two directions that are perpendicular to the Z direction and orthogonal to each other will be referred to as the X and Y directions. Furthermore, the -Z side of the interference optical system 2 will be referred to as the incident side (or object side), and the +Z side will be referred to as the exit side (or image plane side).

[0020] In the interference optical system 2 of this embodiment, incident light Li incident from the -Z side along the optical axis Az is branched into a first branched light L1 and a second branched light L2 in the YZ plane, as shown in Figure 2, for example. In the example of Figure 2, the first branched light L1 is emitted in a direction tilted by an angle θ from the optical axis Az toward the +Y side. Meanwhile, the second branched light L2 is emitted toward the -Y side, opposite the first branched light L1, in a direction tilted by an angle θ equal to the magnitude of the emission angle of the first branched light L1. The inclination of the emission direction of the first branched light L1 and the inclination of the emission direction of the second branched light L2 with respect to the optical axis Az do not necessarily have to be the same angle θ, and an appropriate tolerance may be included.

[0021] Returning to Figure 1, the interference optical system 2 of this embodiment branches the incident light Li from the object to be measured 10 on the -Z side into first and second branched lights L1, L2, and then emits each branched light L1, L2 to the +Z side so as to form interference fringes between the first and second branched lights L1, L2.

[0022] The interference optical system 2 of this embodiment is configured by combining metamaterials so as to realize the above-described control of the first and second split light beams L1, L2 using polarization. According to the interference optical system 2 of this embodiment, a simple arrangement, such as two groups arranged along the optical axis Az, can make the configuration of the spectroscopic device 1 compact and robust, for example. Details of the interference optical system 2 will be described later.

[0023] The spectroscopic device 1 of this embodiment performs a detection operation to detect an interferogram that shows the interference fringes formed by the interference optical system 2 as a spatial distribution of light intensity, and uses the interferogram to measure spectroscopic characteristics. Fig. 3 shows an example of an interferogram F1 in the spectroscopic device 1 of this embodiment.

[0024] 3, the vertical axis represents light intensity, and the horizontal axis represents position in the Y direction. The center position in the Y direction of the graph in Fig. 3 represents, for example, the position where the optical axis Az passes on the detection surface of the detection unit 11 (Fig. 1).

[0025] In the spectroscopic device 1 of this embodiment, as shown in Fig. 3, for example, an interferogram F1 is formed such that positions of high light intensity and positions of low light intensity are alternately arranged in the Y direction due to interference between the first and second split light beams L1 and L2. The interferogram F1 illustrated in Fig. 3 has the highest light intensity at the center position in the Y direction.

[0026] 1, the detection unit 11 detects the above-described interferogram F1 based on the first and second split light beams L1 and L2 incident from the interference optical system 2. The detection unit 11 has a detection surface that is parallel to the XY plane, for example, and is disposed so that interference fringes between the first and second split light beams L1 and L2 are imaged on the detection surface.

[0027] The detection unit 11 is an imaging element such as a bolometer or a thermopile, and includes a plurality of pixels that are photosensitive in the infrared wavelength band. The detection unit 11 may be a two-dimensional sensor in which pixels are arranged in a two-dimensional array on the detection surface, or a line sensor in which pixels are arranged in a one-dimensional array. The detection unit 11 can be configured with various imaging sensors.

[0028] The detector 11 outputs a detection signal indicating the detection result of the interferogram F1, for example, during the detection operation of the spectroscopic device 1, to the controller 12. The detection signal is expressed as a light intensity distribution of interference fringes of the first and second split light beams L1 and L2 on the detection plane. The detection signal may be in the form of image data including a plurality of pixel values.

[0029] The control unit 12 controls the overall operation of the spectroscopic device 1. The control unit 12 includes, for example, a CPU or an MPU that realizes various functions by executing programs stored in an internal memory. For example, the control unit 12 realizes the functions of the acquisition unit 13 and the calculation unit 14. The internal memory of the control unit 12 includes, for example, a ROM and a RAM.

[0030] The acquisition unit 13 is configured as, for example, an interface circuit in the control unit 12, and acquires the detection signal of the interferogram F1 from the detection unit 11. The acquisition unit 13 includes, for example, an analog-to-digital (A / D) converter, converts the analog detection signal into a digital format, and outputs intensity distribution data in digital format to the calculation unit 14. The acquisition unit 13 may, for example, integrate pixel values ​​in the X direction on the detection surface of the detection unit 11, and output the intensity distribution data of the interferogram F1 as a one-dimensional array in the Y direction.

[0031] The calculation unit 14 calculates the spectral characteristics of the incident light Li by performing a Fourier transform such as FFT on the interferogram F1 based on, for example, the intensity distribution data acquired from the acquisition unit 13. The spectral characteristics of the incident light Li indicate, for example, the intensity distribution, i.e., spectrum, of the incident light Li for each wavelength in the infrared wavelength band or for each wave number corresponding to each wavelength. In the spectroscopic device 1 of this embodiment, the control unit 12 may quantitatively output the intensity of a specific wavelength component in the spectral characteristics calculated as described above as the measurement result of the spectral characteristics, or may output the spectral characteristics in various formats.

[0032] The control unit 12 may include a dedicated hardware circuit designed to realize a desired function. The control unit 12 may include a CPU, an MPU, a GPU, a DSP, an FPGA, an ASIC, or the like. The control unit 12 may have a circuit configuration including one or more processors. The acquisition unit 13 and the calculation unit 14 may have separate circuit configurations.

[0033] According to the spectroscopic device 1 configured as described above, the interference optical system 2 has a simple arrangement, making it easy to measure spectral characteristics in real time with high sensitivity in, for example, a robust or compact device configuration.

[0034] The spectroscopic device of the prior art (Patent Document 1) uses a Savart plate as a polarization-splitting birefringent element in an optical system for obtaining interference fringes. However, the Savart plate transmits wavelengths up to the near-infrared range and cannot be applied to mid-infrared and far-infrared wavelength ranges. Therefore, it has been difficult to realize a spectroscopic device that can measure wavelengths in the mid-infrared and far-infrared ranges using the prior art.

[0035] Therefore, in the interference optical system 2 of this embodiment, a combination of metamaterials is used instead of the Savart plate, and a function similar to that of the Savart plate is realized by combining two metamaterial elements that play different roles in controlling the first and second split light beams L1 and L2. This makes it possible to realize an interferometer that can be applied to a wide wavelength range.

[0036] 2. Interference Optical System The interference optical system 2 in this embodiment will now be described in detail.

[0037] 2.1. Configuration Example An example of the configuration of the interference optical system 2 in this embodiment will be described with reference to FIGS.

[0038] 4, the interference optical system 2 of this embodiment includes a front group 21 and a rear group 22 arranged in order from the −Z side (i.e., the incident side) along the optical axis Az. Incident light Li from the −Z side of the interference optical system 2 is incident on the front group 21 in, for example, an unpolarized polarization state. The front group 21 and the rear group 22 are each composed of one or more optical elements.

[0039] The front group 21 includes, for example, a first metamaterial element 3 and is configured to split the incident light Li into first and second split light beams L1 and L2 using polarization (see FIG. 2 ). The rear group 22 includes, for example, a second metamaterial element 4 and is configured to control the polarization states and emission directions of the first and second split light beams L1 and L2 to cause them to interfere with each other.

[0040] In the configuration example of FIG. 4, the front group 21 includes a polarizer 23, a corrective element 24, and a first metamaterial element 3 arranged in this order from the −Z side.

[0041] The polarizer 23 is composed of, for example, a polarizing plate having an optical axis corresponding to the direction of linearly polarized light to be transmitted. The polarizer 23 transmits the linearly polarized component of incident light in the infrared wavelength band, for example, corresponding to the direction of the optical axis, and blocks other components. The direction of the optical axis of the polarizer 23 can be appropriately selected from various directions along the XY plane, for example.

[0042] The corrective element 24 is configured, for example, by a quarter-wave plate that imparts a phase difference of a quarter wavelength between two orthogonal linearly polarized components, and is positioned so as to convert the polarization state of light incident from the polarizer 23, for example, in the infrared wavelength band, from the linearly polarized light to either right-handed or left-handed circularly polarized light.

[0043] In this configuration example, the incident light Li entering the front group 21 passes sequentially through the polarizer 23 and correction element 24 as described above, and then enters the first metamaterial element 3 in a state where its polarization state is converted to circular polarization.

[0044] The first metamaterial element 3 is an example of a first optical element made of a metamaterial for separating the incident light Li into the first branched light L1 and the second branched light L2 in the front group 21. The first metamaterial element 3 in the interference optical system 2 of this configuration example is illustrated in FIG.

[0045] The first metamaterial element 3 includes a substrate arranged parallel to the XY plane, and a metamaterial structure is provided on the main surface of the substrate, as shown in Fig. 5, for example. The metamaterial structure is formed by arranging a plurality of microstructures (also referred to as meta-atoms), such as convex portions 30 extending in the Z direction, at predetermined intervals in the X and Y directions, as shown in Fig. 5, for example. With this metamaterial structure, the first and second split beams L1 and L2 are separated from the zeroth-order incident beam Li as, for example, ±1st-order diffracted beams. The metamaterial structure of the first metamaterial element 3 is an example of a first array in this embodiment.

[0046] The dimensions and / or spacing of the microstructures in the metamaterial structure, such as the convex portions 30, are, for example, equal to or smaller than the smallest wavelength (e.g., 5 μm to 8 μm) in the infrared wavelength band to be measured by the spectroscopic device 1. The convex portions 30 may have various cross-sectional shapes in the XY plane, such as a pyramidal body having an elliptical cone or polygonal shape, an elliptical cylinder, or a polygonal cylinder. The cross-sectional shape of the convex portions 30 may be cross-shaped (see Non-Patent Document 1). For example, multiple convex portions 30 are arranged in an array in the Y direction at intervals of, for example, approximately 2 to 6 μm, depending on the difference in the propagation direction (and the difference in polarization state) of the first and second split light beams L1 and L2. The shape, size, and arrangement of the convex portions 30 are not limited and may be designed arbitrarily according to specifications. Furthermore, the shape of the microstructure is not limited to a convex shape and may also be a concave shape.

[0047] 5, the metamaterial structure of the first metamaterial element 3 is configured to emit first and second branched beams L1 and L2 having different polarization states in separate emission directions on the +Z side in response to incidence of incident light Li from the -Z side. In this configuration example, the first metamaterial element 3 receives circularly polarized incident light Li and emits the first and second branched beams L1 and L2 as circularly polarized beams that are opposite to each other.

[0048] The first metamaterial element 3 as described above can be constructed by, for example, changing the structure of a metamaterial such as MS4 disclosed in Non-Patent Document 1 from a reflective type to a transmissive type. The change to a transmissive type can be achieved, for example, by using a silicon substrate in the structure disclosed in Non-Patent Document 1 and setting the thickness of the substrate (for example, approximately 0.3 mm to 1 mm) to an extent that light in the mid-infrared / far-infrared range can pass through. The material of the substrate may be composed of a material containing at least one main component selected from the group consisting of silicon, germanium, chalcogenide, chalcohalide, zinc sulfide, zinc selenide, a fluoride compound, thallium halide, sodium chloride, potassium chloride, potassium bromide, cesium iodide, and plastic (such as polyethylene).

[0049] 5, a metamaterial structure made of convex portions 30 is provided on both the +Z side and −Z side principal surfaces of the substrate in the first metamaterial element 3. The metamaterial structures on both principal surfaces may be the same or different. Alternatively, the metamaterial structure may be provided on only one of the +Z side and −Z side principal surfaces of the substrate.

[0050] 4, the rear group 22 of the interference optical system 2 includes, arranged in order from the −Z side, the second metamaterial element 4, an analyzer 25, and a condenser lens 26. In this configuration example, the first and second split light beams L1 and L2 from the front group 21 are circularly polarized in opposite directions and are incident on the second metamaterial element 4 of the rear group 22 in directions that separate them from each other in the Y direction.

[0051] The second metamaterial element 4 is disposed at a predetermined distance on the +Z side from the first metamaterial element 3. The predetermined distance is set, for example, in view of the spatial separation between the incident position of the first branched light L1 and the incident position of the second branched light L2 on the second metamaterial element 4. The second metamaterial element 4 is an example of a second optical element made of a metamaterial for controlling the output direction depending on the polarization state of the incident light. An example of the second metamaterial element 4 in the interference optical system 2 of this configuration example is shown in FIG. 6.

[0052] Similar to the first metamaterial element 3, the second metamaterial element 4 is configured by providing a metamaterial structure on one or both of the main surfaces of a substrate arranged parallel to the XY plane, for example, as shown in Fig. 6. The metamaterial structure of the second metamaterial element 4 is configured by arranging microstructures (i.e., metaatoms) such as convex portions 40 in an array, similar to the first metamaterial element 3. The details of the metamaterial structure of the second metamaterial element 4 can be set separately from the metamaterial structure of the first metamaterial element 3, depending on the required characteristics.

[0053] The second metamaterial element 4, as shown in Fig. 6, for example, collimates the first and second branched beams L1 and L2 that are incident from the -Z side and spaced apart in different polarization states, and outputs them to the +Z side. The second metamaterial element 4 performs collimation by controlling the emission direction of each branched beam L1 and L2 so that the beams are parallel to the optical axis Az within an appropriately set tolerance range, for example. The polarization states of the first and second branched beams L1 and L2 when emitted from the second metamaterial element 4 are, for example, circularly polarized in opposite directions to each other, similar to when they are incident. The polarization states of the first and second branched beams L1 and L2 when emitted may also be circularly polarized in the same direction.

[0054] Such a second metamaterial element 4 can be configured with a metamaterial structure having properties that reproduce the reverse of the first metamaterial element 3 in the example of Fig. 5, for example. Alternatively, the second metamaterial element 4 may be configured with a metamaterial structure that uses the polarization separation metalens disclosed in Non-Patent Document 2 in a reverse manner. The metamaterial structure of the second metamaterial element 4 is an example of the second array in this embodiment.

[0055] 4, the analyzer 25 is configured, for example, by a polarizing plate having an optical axis similar to the polarizer 23. The analyzer 25 transmits, for example, a linearly polarized component of the incident light that corresponds to the direction of the optical axis, and blocks other components.

[0056] In this configuration example, the direction of the optical axis of the analyzer 25 can be set to various directions in the XY plane. In the rear group 22 of the interference optical system 2, the analyzer 25 selectively transmits, for example, a common linearly polarized component from the first and second split beams L1 and L2 after exiting the second metamaterial element 4.

[0057] The condenser lens 26 is configured, for example, by an optical lens having a focal length corresponding to positive refractive power. In the spectroscopic device 1 (FIG. 1), the condenser lens 26 is disposed on the −Z side from the detection surface of the detection unit 11 at a distance equal to the focal length. The optical axis Az of the interference optical system 2 is defined, for example, as the central axis of the condenser lens 26. The distance between the condenser lens 26 and the measurement object 10 may also be set to the focal length. The condenser lens 26 functions as a Fourier transform lens.

[0058] 4 , the condenser lens 26 emits the first and second branched beams L1 and L2, which have been collimated by the second metamaterial element 4, so that the beam directions of the beams converge toward each other, and condenses the beams onto, for example, the detection surface of the detection unit 11. In this way, in the spectroscopic device 1, interference fringes between the first branched beam L1 and the second branched beam L2 of the incident beam Li are formed on the detection surface of the detection unit 11.

[0059] 2.2 Modifications The interference optical system 2 of this embodiment is not limited to the above-described configuration example, and various other configurations can be employed. Modifications of the interference optical system 2 will be described with reference to FIGS.

[0060] Fig. 7 illustrates a modified example of the first metamaterial element 3 in the interference optical system 2 of this embodiment. In the configuration example of Fig. 5, the first metamaterial element 3 controls the polarization states of the first and second split light beams L1 and L2 to circularly polarized light beams in opposite directions to each other, but the interference optical system 2 of this embodiment is not particularly limited to this.

[0061] In this modification, the first metamaterial element 3a may be configured to control the polarization states of the first and second split light beams L1 and L2 separated from the circularly polarized incident light Li to different linear polarizations, as shown in Fig. 7, for example. The first metamaterial element 3a in this modification may be configured by changing the structure of a metamaterial such as MS2 in Non-Patent Document 1 from a reflective type to a transmissive type. The polarization states of the first and second split light beams L1 and L2 are, for example, linearly polarized light that is orthogonal to each other, and such beam branching is not limited to strict linear polarization and may have a tolerance such that the polarization may deviate slightly toward elliptically polarized light.

[0062] In the interference optical system 2 of this modification, the second metamaterial element 4 is configured to collimate the linearly polarized branched beams L1 and L2, instead of collimating the circularly polarized branched beams L1 and L2 in the above-described configuration example. Furthermore, the second metamaterial element 4 is not limited to a configuration that maintains the polarization state of the branched beams L1 and L2 between input and output, but may be configured to convert the polarization state.

[0063] For example, when using the first metamaterial element 3a of Fig. 7, the second metamaterial element 4 may convert the linearly polarized light of each of the branched lights L1 and L2 into circularly polarized light. Furthermore, in the above-described configuration example, the second metamaterial element 4 when using the first metamaterial element 3 of Fig. 5 maintains the circularly polarized light of each of the branched lights L1 and L2. However, a modified configuration is also possible in which the circularly polarized light of each of the branched lights L1 and L2 is converted into linearly polarized light. Such a second metamaterial element 4 may be configured by changing the structure of a metamaterial, such as MS1 of Non-Patent Document 1, from a reflective type to a transmissive type.

[0064] 8 illustrates a first modification of the front group 21 in the interference optical system 2 of this embodiment. In the configuration example of FIG. 4, the front group 21 of the interference optical system 2 includes the corrective element 24, but the corrective element 24 may be omitted.

[0065] 8 has a configuration similar to that of the interference optical system 2 in the configuration example of FIG. 4 , and includes a polarizer 23 and a first metamaterial element 3b forming a front group 21. In the interference optical system 2 of this modification, linearly polarized incident light Li is incident on the first metamaterial element 3b from the polarizer 23 in the front group 21. The first metamaterial element 3b of this modification is configured to separate the linearly polarized incident light Li into first and second split lights L1, L2.

[0066] The first metamaterial element 3b of this modification may be configured to control the polarization states of the first and second branched lights L1, L2 to different linearly polarized lights. In this case, the second metamaterial element 4 is configured to collimate the linearly polarized branched lights L1, L2. The first metamaterial element 3b of this modification may also be configured to control the polarization states of the first and second branched lights L1, L2 to circularly polarized lights in opposite directions. In this case, the second metamaterial element 4 is configured to collimate the circularly polarized branched lights L1, L2. In this modification as well, the second metamaterial element 4 may be configured to maintain the polarization states of the branched lights L1, L2 between input and output, or may be configured to convert the polarization states.

[0067] 9 illustrates a second modification of the front group 21 in the interference optical system 2 of this embodiment. In each of the above configuration examples, the front group 21 of the interference optical system 2 includes the polarizer 23, but the polarizer 23 may also be omitted.

[0068] 9, the front group 21 of the interference optical system 2 is composed only of the first metamaterial element 3c. The first metamaterial element 3c of this modification has the function of separating the first and second split light beams L1 and L2 from the incident light Li as described above, and also has the function of the polarizer 23, for example.

[0069] For example, the first metamaterial element 3c of this modification may have a metamaterial structure on its +Z-side principal surface that separates the incident light Li into the first and second split lights L1 and L2, and a metamaterial structure on its −Z-side principal surface that extracts a specific linearly polarized component from the incident light Li. Alternatively, the first metamaterial element 3c may have a metamaterial structure that performs both of the above functions on only one principal surface. Furthermore, the first metamaterial element 3c of this modification may have the functions of the polarizer 23 and the corrective element 24, and may have a metamaterial structure that extracts a circularly polarized component or a specific polarization state component from the incident light Li.

[0070] Fig. 10 illustrates a first modification of the rear group 22 in the interference optical system 2 of this embodiment. In the configuration example of Fig. 4 , the analyzer 25 of the rear group 22 is disposed between the second metamaterial element 4 and the condenser lens 26. In the interference optical system 2 of this embodiment, the arrangement of the analyzer 25 is not particularly limited to the above, and as shown in Fig. 10 , the analyzer 25 in the rear group 22 may be disposed on the +Z side (i.e., the output side) of the condenser lens 26.

[0071] In the interference optical system 2 of this embodiment, the analyzer 25 is positioned on the +Z side of the second metamaterial element 4 in the rear group 22, thereby making it possible to extract a common polarization component from the first and second branched lights L1, L2 after the emission direction has been controlled according to the polarization state by the second metamaterial element 4.

[0072] 11 illustrates a second modification of the rear group 22 in the interference optical system 2 of this embodiment. In the above configuration example, the rear group 22 of the interference optical system 2 includes the analyzer 25, but the analyzer 25 may be omitted.

[0073] The interference optical system 2 of the modified example shown in FIG. 11 has a configuration similar to that of the interference optical system 2 of the configuration example shown in FIG. 4 , for example, and includes a second metamaterial element 4a and a condenser lens 26 to form a rear group 22. In this modified example, the second metamaterial element 4a has the function of extracting and emitting a specific polarization component, like the analyzer 25, in addition to the function of collimating the first and second split light beams L1 and L2 described above. For example, the second metamaterial element 4a of this modified example may have a metamaterial structure on its −Z-side principal surface that achieves the above-mentioned collimation function, and a metamaterial structure on its +Z-side principal surface that achieves the function of the analyzer 25. Alternatively, the second metamaterial element 4a may have a metamaterial structure that combines the above-mentioned two functions on only one of its principal surfaces.

[0074] 11, the second metamaterial element 4a of this modified example may be configured to collimate the first and second branched beams L1, L2 from the front group 21 and selectively emit a polarization component common to the first and second branched beams L1, L2. This also enables the interference optical system 2 of this embodiment to converge the first and second branched beams L1, L2 from the second metamaterial element 4a to each other using the condenser lens 26 in the rear group 22, thereby forming interference fringes.

[0075] 12 illustrates a second modification of the rear group 22 in the interference optical system 2 of this embodiment. In the above configuration example, the rear group 22 of the interference optical system 2 includes the condenser lens 26, but the condenser lens 26 may be omitted.

[0076] 12, the rear group 22 is composed of an analyzer 25 and a second metamaterial element 4b. In this modification, the second metamaterial element 4b has a function of converging the first and second branched beams L1 and L2 like the converging lens 26, in addition to or instead of the function of collimating the first and second branched beams L1 and L2 described above. The second metamaterial element 4b in this modification may have a metamaterial structure on one or both of the +Z-side and −Z-side principal surfaces, the metamaterial structure being configured by modulating the size of the convex portions 40, etc., so as to have positive optical power in the Y direction.

[0077] 12 , the second metamaterial element 4b of this modification may be configured to converge the first branched light L1 and the second branched light L2 from the front group 21 toward each other. This also enables the interference optical system 2 of this embodiment to form interference fringes of the first and second branched light L1, L2 in the rear group 22 using the second metamaterial element 4b and the analyzer 25.

[0078] 13 illustrates a third modification of the rear group 22 in the interference optical system 2 of this embodiment. In the rear group 22 of the interference optical system 2, both the analyzer 25 and the condenser lens 26 may be omitted.

[0079] In the interference optical system 2 of the modified example shown in Fig. 13, the rear group 22 of the interference optical system 2 is composed of only the second metamaterial element 4c. The second metamaterial element 4c of this modified example has, in addition to or instead of the function of collimating the first and second split light beams L1, L2 described above, a function of focusing the first and second split light beams L1, L2 like the focusing lens 26, and further has a function of extracting and outputting a specific polarization component like the analyzer 25. The second metamaterial element 4c of this modified example has a metamaterial structure configured to combine, for example, the function of the second metamaterial element 4b in the example of Fig. 12 and the function of the second metamaterial element 4a in the example of Fig. 11.

[0080] 13, the second metamaterial element 4c of this modification may be configured to converge the first branched light L1 and the second branched light L2 from the front group 21 toward each other and emit the first and second branched light L1, L2 in a common polarization state. This also allows the interference optical system 2 of this embodiment to form interference fringes of the first and second branched light L1, L2, similar to the above configuration examples.

[0081] 2.3. Detailed Example of Metamaterial An example in which the metamaterial structure is configured in more detail in the interference optical system 2 of this embodiment will be described below.

[0082] 2.3.1. Example 1 Example 1 of the interference optical system 2 will be described below with reference to FIGS.

[0083] 14 illustrates the configuration of the interference optical system 2 of this embodiment. Similar to the various configuration examples described above, the interference optical system 2 of this embodiment includes a front group 21 including a first metamaterial element 31 and a rear group 22 including a second metamaterial element 41, and controls the first and second split beams L1 and L2 of linearly polarized light, for example, similar to the example in FIG. 7 .

[0084] In this embodiment, the first metamaterial element 31 is configured to emit first and second split light beams L1 and L2 having mutually orthogonal polarization directions when randomly polarized incident light Li is incident on the first metamaterial element 31. The interference optical system 2 of this embodiment can be configured, for example, by omitting the polarizer 23 and the correction element 24 (see FIG. 5) from the front group 21, similar to the example of FIG.

[0085] The first metamaterial element 31 of this example has a metamaterial structure in which a plurality of recesses 33, which are an example of a microstructure, are provided on one side (e.g., the +Z side) of a substrate, as shown in Fig. 14. The metamaterial structure of this example is configured by periodically arranging unit shapes, i.e., unit cells 35 (so-called meta-atoms), each including the recesses 33 formed as, for example, square-shaped depressions. The structure of such a unit cell 35 is shown in Fig. 15.

[0086] 15 , the metamaterial structure of this embodiment has a rectangular well-shaped recess 33 dug into each unit cell 35. The recess 33 has opening dimensions such as a width W in the X direction, a length Y in the Y direction, and a depth H in the Z direction. The unit cells 35 have, for example, a square cross section in the XY plane and a side length P, and are arranged at the same period P in the X and Y directions. The unit cells 35 may have different periods in the X and Y directions.

[0087] The unit cell 35 of this example can be constructed by, for example, laminating a zinc sulfide (ZnS) layer 353 having a thickness Hz on silicon (Si) layers 351 and 352 as a substrate, and then digging a rectangular shape to a depth H into the ZnS layer 353 and a Si layer 352 that is a part of the silicon substrate from the ZnS side. Such a unit cell 35 may be constructed by providing an etching stop layer between the Si layers 351 and 352. The ZnS layer 353 may also be omitted, or a different material may be used. Furthermore, protrusions may be used instead of the recesses 33.

[0088] For example, in this embodiment, the length of one side of the unit cell 35, i.e., the period P, is 3.4 μm, and the thickness Hz of the ZnS layer 353 is 1.3 μm. The width W and length L of the recess 33 are each varied within a range of 0.8 to 2.9 μm depending on the location on the substrate (see FIG. 16). The above dimensions are shorter than the reference wavelength. This allows, for example, the function of a metamaterial to be realized through the interference of light. Furthermore, the depth H of the recess 33 is, for example, 35 μm, which is longer than the reference wavelength. This allows the efficiency of the interference of light incident on the metamaterial structure to be improved. An example of such an arrangement is shown in FIG. 16.

[0089] In this embodiment, the width W and length L of the recess 33 in the first metamaterial element 31 are modulated in the Y direction and are uniform in the X direction, as illustrated in Fig. 16. Such a metamaterial structure of the first metamaterial element 31 can achieve the function of separating the first and second split light beams L1 and L2 using linearly polarized light.

[0090] 14 , in the interference optical system 2 of this embodiment, the second metamaterial element 41 is configured with a metamaterial structure including a plurality of recesses 43 in each unit cell 45, similar to, for example, the first metamaterial element 31. The various dimensions of the unit cell 45 of the second metamaterial element 41 can be set in the same manner as, for example, the unit cell 35 of the first metamaterial element 31 ( FIG. 15 ).

[0091] 17 shows an example of the arrangement of unit cells 45 in the second metamaterial element 41 of this embodiment. In this embodiment, the width W and length L of the recess 43 in the second metamaterial element 41 are modulated in the Y direction and are uniform in the X direction, as shown in Fig. 17. This metamaterial structure of the second metamaterial element 41 allows the first and second split light beams L1, L2 from the first metamaterial element 31 to be output in a parallel manner.

[0092] A numerical simulation that confirmed the effects of the first and second metamaterial elements 31 and 41 in the interference optical system 2 of this embodiment will be described with reference to FIG.

[0093] 18 illustrates a simulation result of the interference optical system 2 of this example. In this simulation, various polarization components of the incident light Li were incident on the first metamaterial element 31, and it was confirmed how the first and second split lights L1 and L2 propagated through a medium such as air and were emitted from the second metamaterial element 41. Rsoft Meta Optics Designer was used as the simulation software.

[0094] 18A illustrates a simulation result of the first branched light L1 in the interference optical system 2 of this embodiment. FIG. 18B illustrates a simulation result of the second branched light L2 in the interference optical system 2 of this embodiment. In each graph of FIG. 18A and FIG. 18B, the horizontal axis indicates the position in the Y direction, the vertical axis indicates the position in the Z direction, and the shading in each graph indicates the intensity |Ey| of the electric fields Ey and Ex. ２ , |Ex| ２ In addition, the positions where the first and second metamaterial elements 31 and 41 are arranged are shown in each graph.

[0095] 18(A) shows the results of a simulation of the propagation of a light component of incident light Li having a polarization plane parallel to the Y direction. Fig. 18(A) shows that the first branched light L1 obtained when the incident light Li is perpendicularly incident on the first metamaterial element 31 is shifted by approximately 1000 μm to the +Y side when it exits the second metamaterial element 41. Furthermore, it can be seen that the ray direction of the first branched light L1 exiting the second metamaterial element 41 is approximately parallel to the ray direction of the incident light Li entering the first metamaterial element 31.

[0096] 18(B) shows the results of a simulation of the propagation of a light component of incident light Li having a polarization plane parallel to the X direction, i.e., a light component having a polarization direction orthogonal to that of FIG. 18(A). FIG. 18(B) shows that the second branched light L2 obtained when incident light Li is perpendicularly incident on the first metamaterial element 31 is shifted by approximately 1000 μm to the −Y side when it exits the second metamaterial element 41. It can also be seen that the direction of the second branched light L2 exiting the second metamaterial element 41 is substantially parallel to the direction of the incident light Li that is perpendicularly incident on the first metamaterial element 31.

[0097] In this embodiment, the shift amount of the light beam is approximately 1000 μm, but a design that changes the shift amount may be adopted. For example, the shift amount may be changed appropriately by adjusting the distance between the first metamaterial element 31 and the second metamaterial element 41, and can be changed, for example, from approximately 100 μm to 5000 μm. The shift amount may be changed by adjusting the periodicity of the metamaterial structure.

[0098] As described above, according to the interference optical system 2 of this embodiment, by appropriately setting the shapes of the microstructures constituting the two types of metamaterials, the incident light Li can be separated into two parallel beams of light with orthogonal polarization directions. The interference optical system 2 of this embodiment can be realized by using the first and second metamaterial elements 31 and 41 having this function.

[0099] 2.3.2. Example 2 Example 2 of the interference optical system 2 will be described below with reference to FIGS.

[0100] 19 illustrates the configuration of the interference optical system 2 of this embodiment. The interference optical system 2 of this embodiment includes, for example, a first metamaterial element 32 in the front group 21 and a second metamaterial element 42 in the rear group 22, similar to Example 1, and controls the first and second split light beams L1 and L2 with circularly polarized light instead of linearly polarized light.

[0101] In this embodiment, the first metamaterial element 32 is configured to emit a first branched light L1 having a left-handed polarization and a second branched light L2 having a right-handed polarization when, for example, randomly polarized incident light Li is incident thereon. The first metamaterial element 32 of this embodiment has a metamaterial structure in which a plurality of convex portions 34, which are an example of a microstructure, are provided on one side (e.g., the +Z side) of a substrate, as shown in Fig. 19 for example. The metamaterial structure of this embodiment is configured by periodically arranging unit cells 36, each including a convex portion 34 formed by, for example, a columnar protrusion.

[0102] 20 is a perspective view showing an example of a unit cell 36 of a first metamaterial element 32 in this example. In this example, the material of the protrusions 34 and the substrate that constitute the unit cell 36 is, for example, silicon. The unit cell 36 in this example has a period P (for example, 2.8 μm) similar to Example 1, for example. The protrusions 34 in this example are formed in the shape of, for example, a rectangular pillar, and have a width W (for example, 1.8 μm), a length L (for example, 1.3 μm), and a height H (for example, 20 μm).

[0103] 21 is a top view of an example of a unit cell 36 in this example, viewed from the +Z side. The metamaterial structure of this example has, for example, a rotation angle φ of the protrusions 34 set for each unit cell 36. The rotation angle φ of the protrusions 34 is defined, for example, within the range of 0 to 180 degrees, with the Z direction perpendicular to the substrate as the rotation axis, and is modulated differently depending on the position on the substrate (see FIG. 22).

[0104] 22 shows an example of the arrangement of unit cells 36 in the first metamaterial element 32 of this embodiment. In this embodiment, the rotation angle φ of the convex portions 34 in the first metamaterial element 32 is modulated so that the convex portions 34 gradually rotate along the Y direction. The rotation angle φ is uniform in the X direction. This metamaterial structure of the first metamaterial element 32 can achieve the function of separating the first and second split light beams L1 and L2 using circularly polarized light.

[0105] 23 shows an example arrangement of unit cells 46 in a second metamaterial element 42 of this example. In this example, the second metamaterial element 42 is configured in the same manner as, for example, the first metamaterial element 32, and includes a convex portion 44 for each unit cell 46 in the metamaterial structure. In this example, the rotation angle φ of the convex portion 44 of the second metamaterial element 42 is modulated so as to rotate gradually in the Y direction and is uniform in the X direction, similar to, for example, the first metamaterial element 41.

[0106] The metamaterial structure of the second metamaterial element 42 allows the first and second split light beams L1, L2 from the first metamaterial element 32 to be output in parallel with each other (see FIG. 19 ). For example, in the same way that the first metamaterial element 32 controls the ray angle when outputting the first split light beam L1 from the incident light Li, the second metamaterial element 42 controls the ray angle between the input and output of the second split light beam L2. Due to this ray control, the direction of circular polarization can be reversed between the input and output of the second metamaterial element 42.

[0107] Fig. 24 illustrates a simulation result of the first branched light L1 in the interference optical system 2 of this embodiment. Fig. 25 illustrates a simulation result of the second branched light L2 in the interference optical system 2 of this embodiment. In Figs. 24 and 25, graphs of the respective simulation results are shown in the same manner as Fig. 18.

[0108] FIG. 24A shows the electric field intensity |Ey| in the Y direction in a propagation simulation of the left-handed circularly polarized component of the incident light Li. ２ FIG. 24B shows the electric field intensity |Ex| in the X direction in a propagation simulation similar to that in FIG. ２25A and 25B show the electric field intensity |Ey| in a propagation simulation of the right-handed circularly polarized component of the incident light Li. ２ , |Ex| ２ are shown respectively.

[0109] 24(A) and 24(B) show that the first branched light L1 obtained when the incident light Li is incident on the first metamaterial element 32 is shifted by approximately 1000 μm toward the +Y direction when it exits the second metamaterial element 42. Also, FIGS. 25(A) and 25(B) show that the second branched light L2 obtained when the incident light Li is incident on the first metamaterial element 32 is shifted by approximately 1000 μm toward the −Y direction when it exits the second metamaterial element 42. Furthermore, FIGS. 24(A) to 25(B) show that the ray direction of the incident light Li to the first metamaterial element 32 and the ray directions of the first and second branched lights L1 and L2 exiting the second metamaterial element 42 are substantially parallel. In this example, the amount of shift of the light rays was approximately 1000 μm; however, a design that changes the amount of shift may be adopted, as in Example 1 described above.

[0110] As described above, according to the interference optical system 2 of this embodiment, by appropriately setting the shapes of the microstructures constituting the two types of metamaterials, it is possible to separate the incident light Li into two parallel beams of circularly polarized light in opposite directions. The interference optical system 2 of this embodiment can also be realized by the first and second metamaterial elements 32, 42 having this function.

[0111] 3. Summary As described above, in this embodiment, the interference optical system 2 forms interference fringes of the incident light Li in an infrared wavelength band, which is an example of a predetermined wavelength band and includes wavelengths longer than near-infrared wavelengths. The interference optical system 2 includes a front group 21 and a rear group 22, which are arranged on the entrance side and exit side of the incident light Li, respectively. The front group 21 includes a first metamaterial element 3, which is an example of a first optical element. The first metamaterial element 3 emits first and second branched lights L1, L2, which are examples of first and second lights having different polarization states, in different directions in response to the incidence of the incident light Li. The rear group 22 includes a second metamaterial element 4, which is an example of a second optical element, which brings the exit directions of the first and second branched lights L1, L2 incident from the front group 21 closer to each other, thereby focusing the polarized components of the first and second branched lights L1, L2 that interfere with each other.

[0112] According to the above-described interference optical system 2, with a simple configuration including a front group 21 equipped with a first metamaterial element 3 and a rear group 22 equipped with a second metamaterial element 4, interference fringes can be obtained from incident light Li in a predetermined wavelength band, such as the infrared wavelength band including wavelengths longer than near-infrared wavelengths.

[0113] In the interference optical system 2 of this embodiment, the first metamaterial element 3, which is an example of a first optical element, diffracts the incident light Li so as to emit the first and second branched lights L1, L2 in different directions in response to the incidence of the incident light Li. The second metamaterial element 4, which is an example of a second optical element, diffracts the first and second branched lights L1, L2 incident from the front group 21 so as to bring the emission directions of the first and second branched lights L1, L2 closer to each other. The interference optical system 2 of this embodiment can easily obtain interference fringes from the incident light Li in a predetermined wavelength band due to electromagnetic interactions such as diffraction in the metamaterial elements 3, 4.

[0114] In the interference optical system 2 of this embodiment, the first metamaterial element 3 has an example of a metamaterial structure as a first array in which convex portions 30 as an example of a microstructure having wavelengths smaller than a reference wavelength included in a predetermined infrared wavelength band are arranged in an array so as to emit the first branched light L1 and the second branched light L2 in response to the incidence of the incident light Li (see FIG. 5 ). The second metamaterial element 4 has an example of a metamaterial structure as a first array in which convex portions 40 as an example of a second array configured separately from the first array are arranged in an array so as to bring the emission directions of the first branched light L1 and the second branched light L2 closer to each other (see FIG. 5 ). The interference optical system 2 of this embodiment allows for easy generation of interference fringes from the incident light Li in an infrared wavelength band including the reference wavelength. The reference wavelength is, for example, the minimum wavelength in the infrared wavelength band. The reference wavelength may be selected from the infrared wavelength band as appropriate, taking into account the measurement target or various specifications of the spectroscopic device 1, and may have an appropriate tolerance. For example, for a reference wavelength of 8 to 12 μm, the microstructures may have a size or arrangement interval of 1 to 6 μm, which is smaller than the reference wavelength.

[0115] In the interference optical system 2 of this embodiment, the second metamaterial element 4 is arranged at a distance on the output side from the first metamaterial element 3 so as to leave a gap between the position where the first branched light L1 is incident and the position where the second branched light L2 is incident from the first metamaterial element 3. This makes it possible to easily obtain interference fringes from the incident light Li by using the first metamaterial element 3 and the second metamaterial element 4 at a distance from each other.

[0116] In the interference optical system 2 of this embodiment, the front group 21 may further include a polarizer 23 and a corrective element 24 (see FIG. 4 ). The polarizer 23 is disposed on the incident side of the incident light Li relative to the first metamaterial element 3 and selectively transmits a predetermined linearly polarized component of the incident light Li. The corrective element 24 is disposed between the first metamaterial element 3 and the polarizer 23 and converts the linearly polarized component of the incident light Li that has passed through the polarizer 23 into a circularly polarized component. The first metamaterial element 3 separates the circularly polarized component of the incident light Li into a first branched light L1 and a second branched light L2. With this interference optical system 2, interference fringes can be easily obtained from the incident light Li by utilizing circularly polarized light.

[0117] In the interference optical system 2 of this embodiment, the front group 21 may further include a polarizer 23 in addition to the first metamaterial element 3b ( FIG. 8 ). The polarizer 23 is disposed closer to the incident side of the incident light Li than the first metamaterial element 3b and selectively transmits a predetermined linearly polarized component of the incident light Li. The first metamaterial element 3b separates the linearly polarized component of the incident light Li into a first branched light L1 and a second branched light L2. With this interference optical system 2, interference fringes can be easily obtained from the incident light Li using linearly polarized light.

[0118] In the interference optical system 2 of this embodiment, the first metamaterial element 3c may extract a predetermined polarization component from the incident light Li and separate the extracted polarization component into the first branched light L1 and the second branched light L2 ( FIG. 9 ). With this interference optical system 2, interference fringes can be easily obtained from the incident light Li in a simple configuration, for example, with the front group 21 composed only of the first metamaterial element 3c.

[0119] In the interference optical system 2 of this embodiment, the first metamaterial element 3 may output the first branched light L1 and the second branched light L2 as circularly polarized light in opposite directions to each other (see FIG. 5 ). With this interference optical system 2, the first and second branched lights L1 and L2 can be easily obtained from the incident light Li by utilizing circular polarization.

[0120] In the interference optical system 2 of this embodiment, the first metamaterial element 3 a may output the first branched light L1 and the second branched light L2 as linearly polarized light that is orthogonal to each other (see FIG. 7 ). With this interference optical system 2, the first and second branched lights L1 and L2 can be easily obtained from the incident light Li by utilizing linearly polarized light.

[0121] In the interference optical system 2 of this embodiment, the second metamaterial element 4 may collimate the first branched light L1 and the second branched light L2 from the front group 21 to each other (see FIG. 6 ). The rear group 22 is arranged on the output side of the incident light Li relative to the second metamaterial element 4 and further includes a condenser lens 26 that converges the collimated first branched light L1 and the second branched light L2 to each other (see FIG. 4 ). With this interference optical system 2, interference fringes between the first and second branched light L1 and L2 can be obtained with a simple configuration in which the different polarization states of the first and second branched light L1 and L2 from the front group 21 are utilized to collimate the light using the second metamaterial element 4 and then condense the light.

[0122] In the interference optical system 2 of this embodiment, the rear group 22 may further include an analyzer 25 that is arranged closer to the output side of the incident light Li (i.e., on the +Z side) than the second metamaterial element 4 and that selectively transmits components of the first branched light L1 and the second branched light L2 that have a common polarization state. The analyzer 25 may be arranged between the second metamaterial element 4 and the collecting lens 26 (see FIG. 4 ), or may be arranged on the +Z side of the collecting lens 26 (see FIG. 10 ).

[0123] In the interference optical system 2 of this embodiment, the second metamaterial element 4a may collimate the first branched light L1 and the second branched light L2 from the front group 21 and emit the first branched light L1 and the second branched light L2 in a common polarization state (see FIG. 11 ). In this case, the rear group 22 further includes a condenser lens 26. Alternatively, the second metamaterial element 4b may converge the first branched light L1 and the second branched light L2 from the front group 21 toward each other (see FIG. 12 ). In this case, the rear group 22 further includes an analyzer 25. Alternatively, the second metamaterial element 4c may converge the first branched light L1 and the second branched light L2 from the front group 21 toward each other (see FIG. 13 ).

[0124] In the interference optical system 2 of this embodiment, the second metamaterial element 4 may output the first branched light L1 and the second branched light L2 as circularly polarized light in opposite directions, based on the polarization states of the first branched light L1 and the second branched light L2 from the front group 21. Alternatively, the second metamaterial element 4 may output the first branched light L1 and the second branched light L2 as linearly polarized light that is orthogonal to each other, based on the polarization states of the first branched light L1 and the second branched light L2 from the front group 21.

[0125] In this embodiment, the spectroscopic device 1 includes an interference optical system 2, a detection unit 11, and a control unit 12. The detection unit 11 detects an interferogram F1, which is an example of a light intensity distribution indicating interference fringes formed by the interference optical system 2. The control unit 12 measures the spectral characteristics of the incident light Li based on the detected interferogram F1. According to the spectroscopic device 1 of this embodiment, the interference optical system 2 can obtain interference fringes of the incident light Li in, for example, the infrared wavelength band.

[0126] 26 and 27, a second embodiment will be described. In the second embodiment, a spectroscopic device 1A will be described that improves the measurement accuracy of the spectral characteristics of the measurement object 10 by performing multiple detection operations with the orientation of the analyzer 25 changed.

[0127] Hereinafter, the description of the configuration and operation similar to those of the spectroscopic device 1 and interference optical system 2 according to the first embodiment will be omitted as appropriate, and the spectroscopic device 1A and interference optical system 2 according to this embodiment will be described.

[0128] 26 illustrates the configuration of a spectroscope 1A according to embodiment 2. In addition to the same configuration as that of the spectroscope 1 ( FIG. 1 ) according to embodiment 1, the spectroscope 1A according to this embodiment further includes a drive unit 15 that rotationally drives the analyzer 25. In this embodiment, the polarization states of the first and second split light beams L1 and L2 incident on the analyzer 25 from the second metamaterial element 4 are set to, for example, circularly polarized light in opposite directions to each other.

[0129] In the spectroscopic device 1A of this embodiment, the drive unit 15 includes, for example, a drive mechanism capable of rotating the analyzer 25 in the XY plane, such as around the optical axis Az, and a drive circuit that rotationally drives the drive mechanism. For example, the drive unit 15 includes various motors or actuators. For example, the control unit 12 of this embodiment controls the rotational drive of the analyzer 25 by the drive unit 15. By controlling the rotation of the analyzer 25 by the drive unit 15, the orientation of the optical axis of the analyzer 25 is controlled to rotate in at least two directions that are orthogonal to each other on the XY plane.

[0130] The spectroscopic device 1A of this embodiment, for example, first performs an operation of detecting interference fringes between the first and second split light beams L1 and L2, similar to the first embodiment. After this first detection operation, for example, the control unit 12 rotates the optical axis of the analyzer 25 by a rotation angle of 90° in the XY plane using the drive unit 15, thereby performing a second detection operation. During the first detection operation, for example, an interferogram F1 ( FIG. 3 ) similar to that of the first embodiment is detected by the detection unit 11 of the spectroscopic device 1A. An example of an interferogram F2 detected by the detection unit 11 during the second detection operation is shown in FIG. 27. The rotational drive by the drive unit 15 is not necessarily limited to a rotation angle of 90°, but may be an orthogonal rotation with an appropriate tolerance.

[0131] According to the spectroscopic device 1A of this embodiment, the directions of the optical axes of the analyzer 25 before and after rotation are orthogonal to each other. As a result, the phase of the interference component in the second interferogram F2, whose light intensity increases or decreases due to interference between the first and second split light beams L1 and L2, is inverted from the phase of the first interferogram F1, as shown in Fig. 27, for example. Hereinafter, the phase of the interferogram F1 in the example of Fig. 3 will be referred to as the forward phase, and the phase of the interferogram F2 in the example of Fig. 27 will be referred to as the reverse phase.

[0132] In the spectroscopic device 1A of the present embodiment, the control unit 12 performs the first and second detection operations described above, and causes the acquisition unit 13 to sequentially acquire data of an in-phase interferogram F1 and an anti-phase interferogram F2 based on detection signals from the detection unit 11. In the present embodiment, for example, the calculation unit 14 of the control unit 12 calculates the difference between the in-phase interferogram F1 and the anti-phase interferogram F2. The calculation unit 14 performs a Fourier transform on the thus calculated difference interferogram in the same manner as in the first embodiment, thereby calculating the spectral characteristics of the incident light Li.

[0133] According to the spectroscopic device 1A of this embodiment, by calculating the difference between the in-phase and out-of-phase interferograms F1 and F2, it is possible to cancel out noise of non-interfering components such as offset and increase the amplitude of interfering components. In this way, the spectroscopic device 1A of this embodiment can improve the signal-to-noise ratio and increase the measurement accuracy of the spectroscopic characteristics.

[0134] As described above, the spectroscopic device 1A of this embodiment further includes a driver 15 that rotates the orientation of the analyzer 25. The controller 12 acquires in-phase and out-phase interferograms F1 and F2 as examples of the first and second intensity distributions detected by the detector 11 in two states in which the driver 15 rotates the analyzer 25 so that the orientation is orthogonal to each other, and measures the spectral characteristics from the difference between the first intensity distribution and the second intensity distribution. This spectroscopic device 1A can improve the signal-to-noise ratio and the measurement accuracy of the spectral characteristics. The orthogonal rotation of the driver 15 may be performed by an appropriate rotation angle of 90° with a tolerance, for example, a rotation angle of 85° to 95°.

[0135] (Embodiment 3) Hereinafter, embodiment 3 will be described with reference to Fig. 28. In embodiment 2, a spectroscopic device 1A was described that sequentially acquires two types of interferograms F1 and F2 by controlling the rotation of the analyzer 25. In embodiment 3, a spectroscopic device 1B will be described that is configured to simultaneously acquire two types of interferograms F1 and F2 instead of controlling the rotation of the analyzer 25.

[0136] Hereinafter, the description of the configuration and operation similar to those of the spectroscopic devices 1, 1A and interference optical system 2 according to the first and second embodiments will be omitted as appropriate, and the spectroscopic device 1B and interference optical system 2 according to this embodiment will be described.

[0137] Fig. 28 illustrates the configuration of a spectroscopic device 1B according to embodiment 3. The spectroscopic device 1B of this embodiment has a configuration similar to that of the spectroscopic device 1 (Fig. 1) according to embodiment 1, but includes an analyzer 25B having a structure for simultaneously forming two types of interferograms F1 and F2, as shown in Fig. 28, instead of the analyzer 25. In this embodiment, the polarization states of the first and second split light beams L1 and L2 incident on the analyzer 25B from the second metamaterial element 4 are set to, for example, circularly polarized light in opposite directions to each other.

[0138] 28 , the analyzer 25B of this embodiment has a structure divided into two in the X direction, which intersects with the Y direction in which the first and second split light beams L1 and L2 are aligned, and includes a polarizing plate 61 on the +X side and a polarizing plate 62 on the −X side. The polarizing plates 61 and 62 have optical axes that are perpendicular to each other. The orthogonal arrangement of the polarizing plates 61 and 62 does not necessarily require the angle between the two optical axes to be 90°, but may also be an orthogonal arrangement with an appropriate tolerance.

[0139] In the interference optical system 2 of this embodiment, the +X side light beam of the first branched light L1 and the +X side light beam of the second branched light L2 pass through the +X side polarizing plate 61 of the analyzer 25B and form interference fringes on a part of the detection unit 11. On the other hand, the −X side light beam of the first branched light L1 and the −X side light beam of the second branched light L2 pass through the −X side polarizing plate 62 of the analyzer 25B and form interference fringes on a part of the detection unit 11 that is different from the part described above.

[0140] In the spectroscopic device 1B of this embodiment, the detection unit 11 can simultaneously detect in-phase and out-of-phase interferograms F1 and F2 from the interference fringes between the first and second branched lights L1 and L2 on the +X side and the interference fringes between the first and second branched lights L1 and L2 on the -X side.

[0141] In the spectroscopic device 1B of this embodiment, the acquisition unit 13 generates, for example, intensity distribution data indicating an in-phase interferogram F1 and intensity distribution data indicating an anti-phase interferogram F2 based on the detection result of the detection unit 11, and outputs them to the calculation unit 14. The acquisition unit 13 may, for example, integrate pixel values ​​in the X direction separately in two regions on the detection surface of the detection unit 11 corresponding to the interference fringes on the +X side and the interference fringes on the −X side, respectively.

[0142] In the spectroscopic device 1B of this embodiment, the calculation unit 14 calculates the spectroscopic characteristics by performing a Fourier transform on the difference between the in-phase and out-phase interferograms F1 and F2, similar to embodiment 2. As described above, the spectroscopic device 1B of this embodiment can achieve the same improved accuracy of the spectroscopic characteristics as embodiment 2 with a single detection operation.

[0143] As described above, in the interference optical system 2 of the spectroscopic device 1B of this embodiment, the analyzer 25B includes the polarizing plate 61, which is an example of a first polarizing plate, and the polarizing plate 62, which is an example of a second polarizing plate. The polarizing plate 61 is arranged so that a portion of the light beams in the first branched light L1 and a portion of the light beams in the second branched light L2 are incident thereon, and selectively transmits a predetermined linearly polarized component. The polarizing plate 62 is arranged so that a light beam different from the portion of the light beams in the first branched light L1 and a light beam different from the portion of the light beams in the second branched light L2 are incident thereon, and selectively transmits a linearly polarized component that is orthogonal to the predetermined linearly polarized component. With this interference optical system 2, it is possible to simultaneously obtain in-phase and out-of-phase interferograms F1 and F2.

[0144] In the spectroscopic device 1B of this embodiment, the detection unit 11 detects an interferogram F1 of an example of a first intensity distribution in phase based on light incident from the polarizing plate 61, and detects an interferogram F2 of an example of a second intensity distribution in antiphase based on the light beam incident from the polarizing plate 62. The control unit 12 measures the spectroscopic characteristics from the difference between the first intensity distribution and the second intensity distribution. According to the spectroscopic device 1B of this embodiment, each of the interferograms F1 and F2 can be obtained in a single detection operation, thereby achieving both improved measurement accuracy of the spectroscopic characteristics and improved processing efficiency.

[0145] (Other Embodiments) As described above, embodiments 1 to 3 have been described as examples of the technology disclosed in this application. However, the technology in this disclosure is not limited to these, and can be applied to embodiments in which modifications, substitutions, additions, omissions, etc. are made as appropriate. Furthermore, it is also possible to combine the components described in each of the above embodiments to create new embodiments. Therefore, other embodiments will be described below as examples.

[0146] In the above-described first to third embodiments, the first and second branched beams L1 and L2 are branched on the same plane in the interference optical system 2 (see FIG. 2), but the branching of the first and second branched beams L1 and L2 does not have to be on the same plane. Such a modification will be described with reference to FIG.

[0147] 29 is a diagram illustrating the branching of first and second branched light beams L1 and L2 in a modified interference optical system 2. In this embodiment, the interference optical system 2 may branch incident light beam Li incident along the optical axis Az from the −Z side into a first branched light beam L1 in the YZ plane and a second branched light beam L2 in the XZ plane, as shown in FIG. 29 . In the example of FIG. 29 , the first branched light beam L1 is emitted in a direction tilted from the optical axis Az toward the +Y side by an angle θ. Meanwhile, the second branched light beam L2 is emitted in a direction tilted from the optical axis Az toward the −X side by an angle θ equal to the magnitude of the emission angle of the first branched light beam L1.

[0148] The interference optical system 2 of this embodiment can be realized, for example, by employing a metamaterial structure configured to achieve the above-described branching of the first and second branched beams L1 and L2 in the first metamaterial element 3 of the front group 21. Even with this interference optical system 2, it is possible to easily obtain interference fringes of incident light Li in the infrared wavelength band, for example, as in the above-described embodiments.

[0149] In each of the above embodiments, an interference optical system including the first and second metamaterial elements 3 and 4, respectively, has been described as an example of the first and second optical elements. In this embodiment, one or both of the first and second optical elements do not necessarily have to be the first / second metamaterial elements 3 and 4, and may be various optical elements that achieve equivalent functions. For example, the first / second optical elements may be diffractive elements other than metamaterial elements.

[0150] In the above-described embodiments, examples have been described in which the spectroscopic device 1 is applied to a blood glucose sensor, but the use of the spectroscopic device 1 of the present embodiment is not particularly limited thereto. The spectroscopic device 1 of the present embodiment can be applied to various uses, for example, measuring spectral characteristics in the mid-infrared region / far-infrared region. For example, the spectroscopic device 1 of the present embodiment may be applied to an application in which, using plastic as the measurement object 10, the spontaneous emission of plastic in the infrared wavelength band is detected.

[0151] Furthermore, in this embodiment, the spectroscopic device 1 is not particularly limited to a passive type that uses the spontaneous emission of light from the measurement object 10 as the incident light Li, but may also be an active type that is used in combination with a light source such as an infrared light source. For example, the spectroscopic device 1 of this embodiment may measure the absorption spectrum of the measurement object 10 as its spectroscopic characteristic by detecting an interferogram F1 of interference fringes of the incident light Li from the measurement object 10 while irradiating the measurement object 10 with excitation light from the light source.

[0152] Furthermore, in this embodiment, the infrared wavelength band to be measured by the spectroscopic device 1 may include the near-infrared range, or may be the near-infrared range. Furthermore, the predetermined wavelength band to be measured by the spectroscopic device 1 is not necessarily limited to the infrared wavelength band, and may include wavelengths shorter than infrared wavelengths or longer than infrared wavelengths. Furthermore, the predetermined wavelength band does not have to include the infrared range, and may be, for example, the visible light range. In the spectroscopic device 1 of this embodiment, the metamaterial structure of each of the metamaterial elements 3 and 4 is set, for example, according to the wavelength band to be measured.

[0153] As described above, the embodiments have been described as examples of the technology in the present disclosure, and for that purpose, the accompanying drawings and detailed description have been provided.

[0154] Therefore, the components shown in the accompanying drawings and detailed description may include not only essential components for solving the problem, but also components that are not essential for solving the problem in order to illustrate the above technology. Therefore, the fact that these non-essential components are shown in the accompanying drawings or detailed description should not be interpreted as immediately indicating that these non-essential components are essential.

[0155] Furthermore, since the above-described embodiments are intended to illustrate the technology of the present disclosure, various modifications, substitutions, additions, omissions, etc. may be made within the scope of the claims or their equivalents.

[0156] (Examples of Aspects) Various aspects of the present disclosure will be exemplified below.

[0157] A first aspect of the present disclosure is an interference optical system that forms interference fringes of incident light in a predetermined wavelength band, and includes a front group and a rear group arranged on the incident side and the exit side of the incident light, respectively. The front group includes a first optical element that emits first light and second light having different polarization states in different directions depending on the incidence of the incident light. The rear group includes a second optical element that brings the emission directions of the first and second light incident from the front group closer to each other, and collects polarized components of the first and second light that interfere with each other.

[0158] In a second aspect, in the interference optical system according to the first aspect, the first optical element diffracts the incident light so as to emit the first light and the second light in different directions in response to the incidence of the incident light, and the second optical element diffracts the first and second light so as to bring the emission directions of the first and second light incident from the front group closer to each other.

[0159] In a third aspect, in the interference optical system described in the first or second aspect, the first optical element includes a first array in which microstructures smaller than wavelengths in a predetermined wavelength band are arranged in an array so as to emit first light and second light in response to the incidence of incident light, and the second optical element includes a second array configured separately from the first array so as to bring the emission directions of the first and second light closer to each other.

[0160] In a fourth aspect, in the interference optical system according to any one of the first to third aspects, the predetermined wavelength band includes a reference wavelength longer than a near-infrared wavelength.

[0161] In a fifth aspect, in the interference optical system described in any of the first to fourth aspects, the first optical element comprises a first array in which microstructures at 1 to 6 μm, which are smaller than a reference wavelength of 8 to 12 μm, are arranged in an array so as to emit first light and second light in response to the incidence of incident light, and the second optical element comprises a second array configured separately from the first array so as to bring the emission directions of the first and second light closer to each other.

[0162] In a sixth aspect, in the interference optical system described in any of the first to fifth aspects, the second optical element is positioned at a distance from the first optical element on the exit side so as to leave a gap between the position where the first light is incident from the first optical element and the position where the second light is incident.

[0163] In a seventh aspect, in the interference optical system described in any of the first to sixth aspects, the front group further comprises a polarizer that is arranged on the incident side of the incident light from the first optical element and that selectively transmits a predetermined linearly polarized component of the incident light, and a correction element that is arranged between the first optical element and the polarizer and that converts the linearly polarized component of the incident light that has passed through the polarizer into a circularly polarized component, and the first optical element is a first metamaterial element that separates a first light and a second light from the circularly polarized component of the incident light.

[0164] In an eighth aspect, in the interference optical system described in any of the first to sixth aspects, the front group is arranged on the incident side of the incident light relative to the first optical element, and further includes a polarizer that selectively transmits a predetermined linearly polarized component of the incident light, and the first optical element is a first metamaterial element that separates a first light and a second light from the linearly polarized component of the incident light.

[0165] In a ninth aspect, in the interference optical system described in any of the first to sixth aspects, the first optical element is a first metamaterial element that extracts a predetermined polarization component from the incident light and separates the first light and the second light from the extracted polarization component.

[0166] In a tenth aspect, in an interference optical system described in any of the first to ninth aspects, the first metamaterial element outputs the first and second lights with the polarization states of the first and second lights being circularly polarized in opposite directions to each other.

[0167] In an eleventh aspect, in an interference optical system described in any of the first to ninth aspects, the first metamaterial element emits the first and second lights with their polarization states as linearly polarized lights that are orthogonal to each other.

[0168] In a twelfth aspect, in the interference optical system described in any of the first to eleventh aspects, the second optical element is a second metamaterial element that collimates the first and second light from the front group, and the rear group further includes a focusing lens that is arranged on the output side of the incident light from the second metamaterial element and converges the collimated first and second light.

[0169] In a thirteenth aspect, in the interference optical system described in the twelfth aspect, the rear group is arranged on the output side of the incident light from the second metamaterial element, and further includes an analyzer that selectively transmits components of the first and second light that have a common polarization state.

[0170] In a fourteenth aspect, in the interference optical system described in the thirteenth aspect, the analyzer comprises a first polarizing plate arranged so that a portion of the light beam in the first light and a portion of the light beam in the second light are incident thereon, and which selectively transmits a predetermined linearly polarized component, and a second polarizing plate arranged so that a light beam different from the portion of the light beam in the first light and a light beam different from the portion of the light beam in the second light are incident thereon, and which selectively transmits a linearly polarized component that is orthogonal to the predetermined linearly polarized light.

[0171] A fifteenth aspect is a spectroscopic device comprising an interference optical system according to any one of the first to fourteenth aspects, a detection unit that detects a light intensity distribution that indicates interference fringes formed by the interference optical system, and a control unit that measures the spectral characteristics of incident light based on the detected light intensity distribution.

[0172] In a sixteenth aspect, in the spectroscopic device described in the fifteenth aspect, the rear group is arranged on the exit side of the incident light from the second optical element, and further includes an analyzer that selectively transmits components of the first and second light that have a common polarization state, and the spectroscopic device further includes a drive unit that rotates the orientation of the analyzer, and the control unit acquires the first and second intensity distributions detected by the detection unit in two states in which the orientation of the analyzer is rotated by the drive unit so that they are orthogonal to each other, and measures the spectroscopic characteristics from the difference between the first intensity distribution and the second intensity distribution.

[0173] In a seventeenth aspect, in the spectroscopic device according to the fifteenth or sixteenth aspect, the rear group is arranged closer to the output side of the incident light than the second optical element, and further includes an analyzer that selectively transmits components of the first and second lights that have a common polarization state, the analyzer is arranged so that a portion of the light beam in the first light and a portion of the light beam in the second light are incident on the analyzer, and the analyzer includes a first polarizing plate that selectively transmits a predetermined linearly polarized component, and a second polarizing plate that is arranged so that a portion of the light beam in the first light and a portion of the light beam in the second light are incident on the analyzer, and selectively transmits a linearly polarized component that is orthogonal to the predetermined linearly polarized component, the detection unit detects a first intensity distribution based on the light beam incident from the first polarizing plate and detects a second intensity distribution based on the light beam incident from the second polarizing plate, and the control unit measures the spectral characteristics from the difference between the first intensity distribution and the second intensity distribution.

[0174] The present disclosure is applicable to applications for obtaining interference fringes of incident light in a predetermined wavelength band, and is applicable to various applications for measuring spectral characteristics in the mid-infrared / far-infrared range, for example.

Claims

1. An interference optical system that forms interference fringes of incident light in a predetermined wavelength band, comprising a front group and a rear group respectively arranged on the incident side and the exit side of the incident light, the front group including a first optical element that emits first light and second light having different polarization states in different directions in response to the incidence of the incident light, and the rear group including a second optical element that brings the emission directions of the first and second lights incident from the front group closer to each other and condenses the polarization components that interfere with each other among the first and second lights.

2. The interference optical system according to claim 1, wherein the first optical element diffracts the incident light so as to emit the first light and the second light in the different directions in response to the incidence of the incident light, and the second optical element diffracts the first and second lights so as to bring the emission directions of the first and second lights incident from the front group closer to each other.

3. The interference optical system according to claim 1, wherein the first optical element includes a first array in which fine structures smaller than the wavelength of the predetermined wavelength band are arranged in an array so as to emit the first light and the second light in response to the incidence of the incident light, and the second optical element includes a second array configured separately from the first array so as to bring the emission directions of the first and second lights closer to each other.

4. The interference optical system according to claim 1, wherein the predetermined wavelength band includes a reference wavelength longer than the near-infrared wavelength.

5. The interference optical system according to claim 4, wherein the first optical element includes a first array in which fine structures in the range of 1 to 6 μm, which are smaller than the reference wavelength of 8 to 12 μm, are arranged in an array so as to emit the first light and the second light in response to the incidence of the incident light, and the second optical element includes a second array configured separately from the first array so as to bring the emission directions of the first and second lights closer to each other.

6. The interference optical system according to claim 1, wherein the second optical element is arranged at a distance from the emission side of the first optical element so as to create a gap between the position where the first light is incident from the first optical element and the position where the second light is incident.

7. The front group is disposed on the incident side of the incident light with respect to the first optical element, and includes a polarizer that selectively transmits a component of a predetermined linearly polarized light among the incident light, and a correction element that is disposed between the first optical element and the polarizer and converts the linearly polarized light component that has passed through the polarizer in the incident light into a circularly polarized light component. The first optical element is the first metamaterial element that separates the first light and the second light from the circularly polarized light component in the incident light. The interference optical system according to claim 1.

8. The front group is disposed on the incident side of the incident light with respect to the first optical element, and further includes a polarizer that selectively transmits a component of a predetermined linearly polarized light among the incident light. The first optical element is the first metamaterial element that separates the first light and the second light from the linearly polarized light component in the incident light. The interference optical system according to claim 1.

9. The first optical element is the first metamaterial element that extracts a predetermined polarization component from the incident light and separates the first light and the second light from the extracted polarization component. The interference optical system according to claim 1.

10. The first metamaterial element emits the first and second lights with the polarization states of the first and second lights being circularly polarized lights opposite to each other. The interference optical system according to any one of claims 7 to 9.

11. The first metamaterial element emits the first and second lights with the polarization states of the first and second lights being linearly polarized lights orthogonal to each other. The interference optical system according to any one of claims 7 to 9.

12. The second optical element is the second metamaterial element that parallelizes the first and second lights from the front group. The rear group is disposed on the emission side of the incident light with respect to the second metamaterial element, and further includes a condenser lens that converges the parallelized first and second lights. The interference optical system according to claim 1.

13. The rear group is disposed on the emission side of the incident light with respect to the second metamaterial element, and further includes an analyzer that selectively transmits components having a common polarization state from the first and second lights. The interference optical system according to claim 12.

14. The analyzer is arranged such that a partial light beam in the first light and a partial light beam in the second light are incident thereon, and includes a first polarizing plate that selectively transmits a component of a predetermined linearly polarized light; and a second polarizing plate that is arranged such that a light beam different from the partial light beam in the first light and a light beam different from the partial light beam in the second light are incident thereon, and that selectively transmits a component of a linearly polarized light orthogonal to the predetermined linearly polarized light. The interference optical system according to claim 13.

15. A spectroscopic apparatus comprising: the interference optical system according to claim 1; a detection unit that detects a light intensity distribution indicating interference fringes formed by the interference optical system; and a control unit that measures spectroscopic characteristics of the incident light based on the detected light intensity distribution.

16. The rear group is arranged on the emission side of the incident light with respect to the second optical element, and further includes an analyzer that selectively transmits components of a polarization state common to each other from the first and second lights. The spectroscopic apparatus further includes a drive unit that rotates the orientation of the analyzer. The control unit acquires first and second intensity distributions respectively detected by the detection unit in two states where the orientation of the analyzer is rotated by the drive unit so as to be orthogonal to each other, and measures the spectroscopic characteristics from a difference between the first intensity distribution and the second intensity distribution. The spectroscopic apparatus according to claim 15.

17. The rear group is arranged on the emission side of the incident light with respect to the second optical element, and further includes an analyzer that selectively transmits components of a polarization state common to each other from the first and second lights. The analyzer is arranged such that a partial light beam in the first light and a partial light beam in the second light are incident thereon, and includes a first polarizing plate that selectively transmits a component of a predetermined linearly polarized light; and a second polarizing plate that is arranged such that a light beam different from the partial light beam in the first light and a light beam different from the partial light beam in the second light are incident thereon, and that selectively transmits a component of a linearly polarized light orthogonal to the predetermined linearly polarized light. The detection unit detects a first intensity distribution based on the light incident from the first polarizing plate, and detects a second intensity distribution based on the light beam incident from the second polarizing plate. The control unit measures the spectroscopic characteristics from a difference between the first intensity distribution and the second intensity distribution. The spectroscopic apparatus according to claim 15.

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