Photodetector and spectroscopic measuring device

Abstract

This optical detector detects a primary light ray among light rays to be measured that are spectrally separated in an X-axis direction. The optical detector comprises a package with an opening, a window portion that covers the opening and allows the primary light ray to pass therethrough, and an optical detection element positioned inside the package, having a light-receiving region opposing the window portion, and detecting the primary light ray. The light-receiving region includes a plurality of optical detection channels arranged in the X-axis direction. The window portion includes an optical transmission member having a light incident surface and a light exit surface, and a linear variable filter coating that is formed on one of the light incident surface and the light exit surface, and has a transmission wavelength changing along the X-axis direction.

Description

Technical Field

[0001] The present disclosure relates to a photodetector and a spectroscopic measurement device.

Background Art

[0002] There is known a spectroscopic measurement device including a light incident portion for incident the light to be measured, a diffraction grating for dispersing the light to be measured incident from the light incident portion, and a photodetector for detecting the light to be measured dispersed by the diffraction grating. In such a spectroscopic measurement device, even when trying to detect light of a predetermined order (for example, first-order light) among the dispersed light to be measured, light other than the predetermined order (for example, higher-order light such as second-order light or higher) may be superimposed on the light of the predetermined order. Therefore, a filter member for removing light other than the predetermined order may be disposed in front of the photodetector (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when a filter member is disposed in front of the photodetector, there is a risk of an increase in stray light. For example, stray light may increase when the light to be measured is multiply reflected inside the filter member or when multiply reflected between the filter member and the window portion of the photodetector. Suppressing the influence of such stray light is extremely important for generating accurate spectral data.

[0005] An object of the present disclosure is to provide a photodetector and a spectroscopic measurement device capable of detecting light of a predetermined order among the dispersed light to be measured.

Means for Solving the Problems

[0006] One aspect of the present disclosure is a photodetector that detects light of a predetermined order from light to be measured spectrally separated in a predetermined direction, comprising: a package having an aperture; a window portion that closes the aperture and transmits light of the predetermined order; and a photodetector disposed within the package and having a light-receiving region facing the window portion, which detects light of the predetermined order, wherein the light-receiving region includes a plurality of photodetector channels arranged in the predetermined direction, and the window portion comprises a light-transmitting member having a light-incident surface and a light-emitting surface, and a linear variable filter coating formed on one of the light-incident surface and the light-emitting surface, wherein the transmitted wavelength changes along the predetermined direction, the photodetector.

[0007] In the photodetector described in [1] above, the window portion that closes the opening of the package includes a light-transmitting member and a linear variable filter coat in which the transmitted wavelength changes along a predetermined direction in which the light to be measured is spectrally separated. This makes it possible to suppress the incidence of light of an order other than a predetermined order for each of the multiple wavelength components contained in the light to be measured to the photodetector element. Furthermore, in the photodetector described in [1] above, the linear variable filter coat is formed on either the light incident surface or the light output surface of the light-transmitting member. For example, if a filter coat of a single transmitted wavelength is formed on both the light incident surface and the light output surface of the light-transmitting member, the light to be measured may be reflected multiple times between the filter coat formed on the light incident surface and the filter coat formed on the light output surface. However, in the photodetector described in [1] above, the generation of stray light due to multiple reflections can be suppressed. As a result, the photodetector described in [1] above can detect light of a predetermined order among the spectrally separated light to be measured.

[0008] One aspect of the present disclosure is a photodetector [2] "the photodetector according to [1] above, wherein the linear variable filter coat is formed on the light incident surface." The photodetector according to [2] allows for easier and more reliable bonding of the package and the window compared to the case where the linear variable filter coat is located on the light output surface.

[0009] One aspect of the present disclosure is a photodetector [3] "the photodetector according to [1] or [2] above, wherein the light of a predetermined order is primary light." Primary light has a higher light intensity than secondary or higher-order light. According to the photodetector described in [3], by making the linear variable filter coat function as a higher-order light cut filter for transmitting primary light among the light to be measured, spectral data with excellent signal-to-noise ratio can be generated.

[0010] One aspect of the present disclosure is a photodetector according to any one of the above [1] to [3], wherein the linear variable filter coat is a linear variable long-pass filter coat in which the cut-on wavelength changes along the predetermined direction, or a linear variable band-pass filter coat in which the transmission wavelength band changes along the predetermined direction. According to the photodetector described in [4], the transmission of higher-order light is suppressed with respect to light of a predetermined order, thereby suppressing the appearance of unnatural peaks in spectral data caused by such higher-order light.

[0011] One aspect of the present disclosure is a photodetector according to any one of [1] to [4] above, wherein the window portion further includes a reflection reduction layer formed on the other of the light incident surface and the light emission surface. According to the photodetector described in [5], stray light generated by multiple reflections of the light to be measured between the light emission surface and the light receiving region can be reduced.

[0012] One aspect of the spectroscopic measuring apparatus of this disclosure is [6] "a spectroscopic measuring apparatus comprising: a light incident unit for injecting light to be measured; a diffraction grating for spectrally analyzing the light to be measured that has been incident from the light incident unit; an analysis unit for generating spectral data of the light to be measured; and a photodetector as described in any one of [1] to [5] above."

[0013] According to the spectroscopic measuring apparatus described in [6] above, the photodetector can detect light of a predetermined order from the spectrally separated light to be measured. [Effects of the Invention]

[0014] According to the present disclosure, it is possible to provide a photodetector and a spectroscopic measurement device that can detect light of a predetermined order among the spectroscopically measured light to be measured.

Brief Description of the Drawings

[0015] [Figure 1] FIG. 1 is a diagram showing the configuration of a spectroscopic measurement device according to an embodiment. [Figure 2] FIG. 2 is a plan view of the photodetector shown in FIG. 1. [Figure 3] FIG. 3 is a cross-sectional view of the photodetector along line III-III shown in FIG. 2. [Figure 4] FIG. 4 is a diagram showing the transmission wavelength characteristics of the linear variable filter coat shown in FIG. 2. [Figure 5] FIG. 5 is a diagram showing how primary light passes through the window portion shown in FIG. 2. [Figure 6] FIG. 6 is a diagram showing how stray light is generated in the window portion shown in FIG. 2. [Figure 7] FIG. 7 is a diagram showing the transmission wavelength characteristics of the filter coat included in the window portion of the first comparative example. [Figure 8] FIG. 8 is a diagram showing how primary light passes through the window portion shown in FIG. 7 and how stray light is generated in the window portion shown in FIG. 7. [Figure 9] FIG. 9 is a diagram showing how stray light is generated in the window portion of the second comparative example. [Figure 10] FIG. 10 is a diagram showing how the light to be measured passes through the window portion of the modified example.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In each figure, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted. [Configuration of Spectroscopic Measurement Device]

[0017] As shown in FIG. 1, the spectroscopic measurement device 1 includes a light incident unit 2, a diffraction grating 3, a photodetector 10, a lens 5, and an analysis unit 6. The spectroscopic measurement device 1 is a device that generates spectral data of a plurality of wavelength components L2 included in the measurement light L1 by spectroscopically measuring the measurement light L1.

[0018] The light incident unit 2, the diffraction grating 3, and the lens 5 guide the measurement light L1 to the light receiving region 13a of the light detection element 13 included in the photodetector 10, and form a spectroscopic image of a plurality of wavelength components L2 of the measurement light L1 on the light receiving region 13a of the photodetector 10 along the wavelength axis (a so-called Czerny-Turner optical system). In the present embodiment, the diffraction grating 3 is a reflection type diffraction grating. The measurement light L1 is spectroscopically separated by the diffraction grating 3 in a direction perpendicular to the direction in which the measurement light L1 is incident. Here, the direction in which the measurement light L1 is spectroscopically separated (that is, the direction parallel to the wavelength axis) is referred to as the X-axis direction, the direction perpendicular to the X-axis direction is referred to as the Y-axis direction, and the direction perpendicular to the X-axis direction and the Y-axis direction is referred to as the Z-axis direction. Further, the photodetector 10 blocks the secondary light and detects the primary light among the measurement light L1. The secondary light may appear as an unnatural peak in the spectral data. Therefore, it is necessary to block the secondary light in order to extract light of a predetermined order (primary light). Details will be described later.

[0019] The light incidence unit 2 is positioned to direct the light to be measured L1 into the spectroscopic measuring device 1. The light incidence unit 2 adjusts the amount of incident light L1. The light incidence unit 2 is, for example, a slit member. The slit formed in the slit member opens in a rectangular shape, with the X-axis direction being the shorter side and the Z-axis direction being the longer side, when viewed from the Y-axis direction. Increasing the width of the shorter side increases the amount of incident light L1, so the analysis unit 6 obtains spectral data with less noise but lower wavelength resolution. On the other hand, narrowing the width of the shorter side decreases the amount of incident light L1, so the analysis unit 6 obtains spectral data with improved wavelength resolution but higher noise. The light incidence unit 2 may be composed of, for example, a slit member and an optical fiber that transmits the light to be measured L1 to the slit member. Alternatively, the light incidence unit 2 may be composed of, for example, a slit member and a lens that focuses the light to be measured L1 from the outside of the slit member.

[0020] The diffraction grating 3 is positioned opposite the light incident section 2 in the Y-axis direction. Since the diffraction grating 3 is of the reflective type, it spectrally separates the light L1 to be measured in the direction opposite to the direction in which the light L1 is incident. The diffraction grating 3 is composed of multiple grating grooves (not shown). The multiple grating grooves are aligned along the X-axis direction, which is perpendicular to the direction in which the light L1 is incident, and extend along the Z-axis direction, which is perpendicular to this alignment. The light L1 incident on the diffraction grating 3 is spectrally separated according to multiple wavelength components L2 along the X-axis direction, which is the direction in which the multiple grating grooves are aligned.

[0021] The photodetector 10 is positioned opposite the diffraction grating 3 in the Y-axis direction. The photodetector 10 has a photodetector element 13. The photodetector element 13 includes a light-receiving region 13a that receives multiple wavelength components L2. In the photodetector 10, a spectral image with the wavelength axis in the X-axis direction is formed on the light-receiving region 13a. The light-receiving region 13a is elongated with the X-axis direction as its longitudinal direction and has multiple photodetector channels arranged along the X-axis direction (a predetermined direction). In other words, the direction in which the multiple photodetector channels are arranged coincides with the direction in which the light under test L1 is spectrally dispersed. Therefore, each wavelength component L2 is incident on different positions (different photodetector channels) at regular intervals along the longitudinal direction of the light-receiving region 13a. Each photodetector channel is composed of multiple pixels along the Z-axis direction. The photodetector 10 receives the spectral image over a predetermined exposure time in the light-receiving region 13a and outputs spectral data S of each wavelength component L2. The photodetector 13 is, for example, a CCD image sensor or CMOS image sensor formed on a semiconductor substrate. The CCD image sensor may be an interline type, a frame transfer type, or a full frame transfer type.

[0022] In this embodiment, the photodetector 10 is positioned at the same location as the light incident section 2 in the Y-axis direction. The photodetector 10 is positioned at a certain distance from the light incident section 2 in the Z-axis direction, on the side where multiple wavelength components L2 are incident. In other words, the photodetector 10 is offset from the light incident section 2 along the direction perpendicular to the wavelength axis (Z-axis direction), on the side where multiple wavelength components L2 are incident.

[0023] Lens 5 is positioned in the Y-axis direction between the light incident section 2 and the photodetector 10 and the diffraction grating 3. Lens 5 guides the light to be measured L1 incident from the light incident section 2 to the diffraction grating 3 and forms a spectral image of multiple wavelength components L2 on the light-receiving area 13a of the photodetector 10. Lens 5 is a convex lens having a surface 5a and a convex surface 5b opposite to surface 5a. Surface 5a faces the light incident section 2 and the photodetector 10. Surface 5a is a flat surface, a concave surface, or a convex surface. The convex surface 5b faces the diffraction grating 3 and is a surface that is curved convexly on the opposite side from surface 5a.

[0024] The analysis unit 6 generates spectral data S of the light L1 under measurement based on data acquired from the photodetector 10. The details of the analysis performed by the analysis unit 6 will be described later. The analysis unit 6 includes a storage unit that stores data acquired from the photodetector 10 and analysis results. The analysis unit 6 may also control the photodetector 4. The analysis unit 6 may be a computer or tablet terminal equipped with a processor such as a CPU (Central Processing Unit) and a storage medium such as RAM (Random Access Memory) or ROM (Read Only Memory). The analysis unit 6 may also be composed of a microcontroller or an FPGA (Field Programmable Gate Array).

[0025] In the spectroscopic measuring device 1 configured as described above, the light to be measured L1, incident from the light incident section 2, is incident on the surface 5a at a constant angle of incidence. The light to be measured L1 incident on the surface 5a is refracted at the surface 5a according to the difference between the refractive index of air and the refractive index of lens 5, travels through lens 5, and exits from the convex surface 5b. The light to be measured L1 exiting from the convex surface 5b is refracted at the convex surface 5b according to the difference between the refractive index of lens 5 and the refractive index of air, and is guided to the diffraction grating 3 in the subsequent stage.

[0026] Multiple wavelength components L2, spectrally separated by the diffraction grating 3, are incident on the lens 5. The lens 5 receives the multiple wavelength components L2 with a constant angle of incidence relative to the convex surface 5b. The multiple wavelength components L2 incident on the convex surface 5b are refracted by the convex surface 5b according to the difference between the refractive index of air and the refractive index of lens 5, travel through the lens 5, and exit from surface 5a. The multiple wavelength components L2 exiting from surface 5a are refracted by surface 5a according to the difference between the refractive index of lens 5 and the refractive index of air, and are imaged by the subsequent photodetector 4, forming a spectral image in the light-receiving region 13a. [Photodetector configuration]

[0027] As shown in Figures 2 and 3, the photodetector 10 further comprises a package 11 and a window portion 12. The package 11 is composed of a bottom wall 111, side walls 112, and a top wall 113. The bottom wall 111 is flat. The side walls 112 are frame-shaped with rectangular openings. The top wall 113 is cap-shaped with rectangular openings. The side walls 112 are positioned on the bottom wall 111 and joined to the bottom wall 111. The top wall 113 are positioned on the side walls 112 and joined to the side walls 112. As a result, a space SP is formed inside the package 11. As an example, the bottom wall 111, side walls 112, and top wall 113 are each made of metal.

[0028] A photodetector element 13 is positioned on the bottom wall 111. The photodetector element 13 is positioned in the space SP within the package 11. An aperture 11a is formed in the package 11. Specifically, the aperture 11a is formed in the top wall 113 so as to face the photodetector element 13. When viewed from the Y-axis direction, the inner edge of the top wall 113 forming the aperture 11a is smaller than the inner edges of the side wall 112 and the top wall 113 forming the space SP. In other words, the top wall 113 has a stepped shape when viewed from the Z-axis direction, such that the area of ​​the inner edge decreases from the inner edge forming the space SP to the inner edge forming the aperture 11a. The aperture 11a allows multiple wavelength components L2 to be incident into the package 11.

[0029] The window portion 12 is positioned on the top wall 113 so as to close the opening 11a. The window portion 12 faces the light-receiving area 13a of the photodetector element 13 located inside the package 11 in the Y-axis direction. The window portion 12 includes a light-transmitting member 121 and a linear variable filter coat 122. The light-transmitting member 121 includes a light-incident surface 121a and a light-emitting surface 121b that face each other in the Y-axis direction. In this embodiment, the airtightness of the space SP is ensured by joining the light-emitting surface 121b of the window portion 12 with the surrounding portion of the opening 11a in the top wall 113. When viewed from the Y-axis direction, the light-transmitting member 121 has a rectangular shape with the X-axis direction as the longer side and the Z-axis direction as the shorter side. The light-transmitting member 121 is made of, for example, glass, quartz, silicon, germanium, plastic, etc.

[0030] The linear variable filter coat 122 is formed on the light incident surface 121a. Similar to the light transmitting member 121, the linear variable filter coat 122 has a rectangular shape when viewed from the Y-axis direction, with the X-axis direction as the longer side and the Z-axis direction as the shorter side. The outer edge of the linear variable filter coat 122 does not perfectly coincide with the outer edge of the light transmitting member 121, and there is a portion 123 where the linear variable filter coat 122 and the light incident surface 121a do not overlap. Specifically, the length of the shorter side of the linear variable filter coat 122 is the same as the length of the shorter side of the light transmitting member 121, and the length of the longer side of the linear variable filter coat 122 is shorter than the length of the longer side of the light transmitting member 121. Therefore, in the examples of Figures 2 and 3, one short side of the linear variable filter coat 122 coincides with one short side of the light-transmitting member 121, but the other short side of the linear variable filter coat 122 is located inward from the other short side of the light-transmitting member 121. The linear variable filter coat 122 is formed by coating the light incident surface 121a with an insulating multilayer film by vapor deposition or the like, and is formed continuously without gaps. For example, the thickness of the linear variable filter coat 122 gradually increases in a slope shape along the X-axis from one short side.

[0031] When viewed from the Y-axis direction, the inner edge of the top wall 113 forming the opening 11a is larger than the outer edge of the photodetector element 13. Furthermore, the outer edge of the light-transmitting member 121 is larger than the inner edge of the top wall 113 forming the opening 11a. In addition, a portion of the outer edge of the photodetector element 13 overlaps with the portion 123 where the linear variable filter coat 122 and the light incident surface 121a do not overlap. Specifically, the other short side of the photodetector element 13 is located outside the other short side of the linear variable filter coat 122.

[0032] The transmission wavelength of the linear variable filter coating 122 changes along the X-axis direction (a predetermined direction). Specifically, as you move away from the portion 123 where the linear variable filter coating 122 and the light incident surface 121a do not overlap, the transmission wavelength gradually changes to a higher wavelength band. In other words, the blocked wavelength band gradually increases. Figure 4 illustrates an example of the transmission wavelength characteristics of the linear variable filter coating 122. The transmission wavelength characteristic T1 of the portion closest to the portion 123 where the linear variable filter coating 122 and the light incident surface 121a do not overlap shows that the transmittance begins to increase from approximately 430 nm, and at approximately 460 nm the transmittance becomes approximately 0.9, with the cut-on wavelength (the wavelength at which the transmittance reaches 50%) being approximately 450 nm. On the other hand, the transmission wavelength characteristic T2 of the portion furthest from the portion 123 where the linear variable filter coat 122 and the light incident surface 121a do not overlap shows that the transmittance begins to increase from approximately 780 nm, and at approximately 830 nm the transmittance becomes approximately 0.9, with a cut-on wavelength of approximately 810 nm. The transmission wavelength of the linear variable filter coat 122 gradually changes to a higher wavelength band between T1 and T2. In this embodiment, multiple wavelength components L2 are incident along the direction in which the transmission wavelength of the linear variable filter coat 122 is changing. Therefore, in each wavelength component L2, primary light is transmitted while secondary light is suppressed from being incident on the photodetector element 13.

[0033] Referring to Figure 5, the relationship between each wavelength component L2 and the transmitted wavelength will be explained in more detail. As shown in Figure 5, the multiple wavelength components L2 include wavelength components having center wavelengths of λ11 to λ15. The order of λ11 to λ15 is all primary. Here, for example, λ11: 300 nm, λ12: 450 nm, λ13: 600 nm, λ14: 750 nm, and λ15: 900 nm. The diffraction angles of λ11 to λ15 increase in the order listed above, and they are incident on the linear variable filter coat 122 along the direction in which the transmitted wavelength changes in the order listed above. Here, the secondary light of λ11 is denoted as λ21, and the secondary light of λ12 is denoted as λ22. The center wavelength value of λ21 is the same as that of λ11, 300 nm, but the diffraction angle of λ21 is different from that of λ11. The diffraction angle of λ21 is the same as that of λ13, which has twice the center wavelength of λ11. In other words, λ21 is incident at the same position as λ13. Similarly, the secondary light λ22 (center wavelength 450 nm) of λ12 is incident at the same position as λ15, which has twice the center wavelength of λ12. The linear variable filter coat 122 functions as a filter to transmit primary light (λ11~λ15) of multiple wavelength components L2 and block secondary light (λ21, λ22). Therefore, the window portion 12 allows primary light from each wavelength component L2 to pass through, and the photodetector 10 detects the primary light. Since the linear variable filter coat 122 transmits wavelength components above the center wavelength of the primary light, it functions as a long-pass filter. In other words, the linear variable filter coat 122 is a linear variable long-pass filter coat in which the cut-on wavelength changes along the X-axis direction (a predetermined direction). Note that λ11 is incident in the portion 123 where the linear variable filter coat 122 and the light incident surface 121a do not overlap. This is because the center wavelength of λ11 is 300 nm, and therefore it is blocked by the linear variable filter coating 122.

[0034] Here, λ11 to λ15 are incident on the linear variable filter coat 122 so that they correspond to the transmission wavelengths. For example, the transmission wavelength characteristics corresponding to the incident position of λ13 transmit the primary light λ13 (center wavelength 600 nm) while blocking the secondary light λ21 (center wavelength 300 nm). Similarly, the transmission wavelength characteristics corresponding to the incident position of λ15 transmit the primary light λ15 (center wavelength 900 nm) while blocking the secondary light λ22 (center wavelength 450 nm). [Mechanism of Action and Effects]

[0035] In the photodetector 10, the window portion 12 that closes the opening 11a of the package 11 includes a light-transmitting member 121 and a linear variable filter coat 122 in which the transmission wavelength changes along the X-axis direction, which is the direction in which the light to be measured L1 is spectrally separated. This makes it possible to suppress the incidence of secondary light (λ21, λ22) on the photodetector element 13 for each of the multiple wavelength components L2 contained in the light to be measured L1. In addition, in the photodetector 10, the linear variable filter coat 122 is formed on the light incident surface 121a of the light-transmitting member 121. For example, if a filter coat with a single transmission wavelength is formed on both the light incident surface 121a and the light output surface 121b of the light-transmitting member 121, the light to be measured L1 may undergo multiple reflections between the filter coat formed on the light incident surface 121a and the filter coat formed on the light output surface 121b. However, the photodetector 10 can suppress the generation of stray light due to multiple reflections. As described above, the photodetector 10 can detect the primary light (λ11~λ15) of the spectrally separated light L1 being measured.

[0036] In the photodetector 10, the linear variable filter coat 122 is formed on the light incident surface 121a. This allows for easier and more reliable bonding between the package 11 and the window portion 12 compared to when the linear variable filter coat 122 is located on the light emission surface 121b. Furthermore, compared to when the linear variable filter coat 122 is located on the light emission surface 121b, the light emission surface 121b of the window portion 12 is more easily bonded to the surrounding portion of the opening 11a in the top wall 113, thereby making it easier to ensure the airtightness of the space SP.

[0037] In the photodetector 10, light of a predetermined order is primary light (λ11~λ15). Primary light (λ11~λ15) has a higher light intensity than secondary light (λ21,λ22). Therefore, the photodetector 10 can generate spectral data S with excellent signal-to-noise ratio by using the linear variable filter coating 122 as a secondary light cut filter to transmit primary light (λ11~λ15) of the light L1 being measured.

[0038] In the photodetector 10, the linear variable filter coat 122 is a linear variable long-pass filter coat in which the cut-on wavelength changes along the X-axis. As a result, the transmission of secondary light (λ21, λ22) is suppressed with respect to primary light (λ11~λ15), thereby suppressing the appearance of unnatural peaks in the spectral data S caused by the secondary light (λ21, λ22).

[0039] According to the spectroscopic measurement device 1, the photodetector 10 can detect the primary light (λ11~λ15) of the spectrally separated light L1 being measured. [Comparative Example]

[0040] As shown in Figure 6, some of the light L1 to be measured that enters the window portion 12 may be reflected by the light-emitting surface 121b of the light-transmitting member 121, and then reflected by the surface of the linear variable filter coating 122, resulting in stray light L3. Stray light L3 may appear as an unnatural peak in the spectral data and should therefore be suppressed. However, compared to the comparative example described later, the linear variable filter coating 122 can reduce the causes of stray light L3 generation.

[0041] Referring to Figures 7 and 8, the window portion 12a of the first comparative example will be described. As shown in Figure 7(a), in the window portion 12a, a filter coat 122a is formed on the light incident surface 121a of the light transmitting member 121, and a filter coat 122b is formed on the light output surface 121b of the light transmitting member 121. When viewed from the Y-axis direction, the filter coats 122a and 122b have a rectangular shape with the X-axis direction as the longer side and the Z-axis direction as the shorter side. One of the shorter sides of the filter coat 122a coincides with one of the shorter sides of the light transmitting member 121 and one of the shorter sides of the filter coat 122b. The other shorter side of the filter coat 122a is located inside the other shorter side of the light transmitting member 121 and outside the other shorter side of the filter coat 122b. As shown in Figure 7(b), the filter coats 122a and 122b each have the characteristics of a single different transmission wavelength. An example of the transmission wavelength characteristics is as follows: The transmission wavelength characteristic T3 of filter coat 122a shows that the transmittance begins to increase from approximately 420 nm, and at approximately 450 nm, the transmittance is approximately 0.9. The cut-on wavelength is approximately 440 nm. On the other hand, the transmission wavelength characteristic T4 of filter coat 122b shows that the transmittance begins to increase from approximately 520 nm, and at approximately 570 nm, the transmittance is approximately 0.9. The cut-on wavelength is approximately 550 nm.

[0042] Referring to Figure 8, the relationship between each wavelength component L2 and the transmitted wavelength will be explained in more detail. The values ​​of the center wavelengths of λ11 to λ15 are the same as in the embodiment. Filter coats 122a and 122b function as filters that transmit primary light (λ11 to λ15) of multiple wavelength components L2 and block secondary light (λ21, λ22), similar to the linear variable filter coat 122. For example, λ13 passes through filter coats 122a and 122b, but λ21 is blocked by filter coat 122a. Here, when filter coats 122a and 122b are used, stray light is generated due to various factors. For example, since the other short side of filter coat 122b is located inward from the other short side of filter coat 122a, the other short side of filter coat 122b becomes the end face when viewed from the Z-axis direction. One of the multiple wavelength components L2 may be scattered at the end face of the filter coat 122b, causing stray light L3. Furthermore, one of the multiple wavelength components L2 may undergo multiple reflections between the filter coat 122a and the filter coat 122b, also causing stray light L3. In either case, stray light L3 cannot occur when the linear variable filter coat 122 of the embodiment is used as part of the window portion 12. Therefore, in the photodetector 10 of the embodiment, it is possible to suppress the incidence of stray light L3 due to scattering and multiple reflections on the photodetector element 13.

[0043] Next, with reference to Figure 9, the window portion 12b of the second comparative example will be described. In the window portion 12b, instead of forming a filter coat on the light-transmitting member 121, a filter member 122c, which is thicker than the filter coat, is placed on the light incident surface 121a. The filter member 122c and the light-transmitting member 121 are combined to form the window portion 12b. In this case, stray light L3 is generated by various factors. For example, stray light L3 is generated by multiple reflections inside the filter member 122c or by multiple reflections between the filter member 122c and the light incident surface 121a or the light emission surface 121b. In other words, the number of places where stray light can be generated is significantly increased compared to the linear variable filter coat 122 of the embodiment. [Differentiation]

[0044] This disclosure is not limited to the embodiments described above. The linear variable filter coat 122 may be a linear variable bandpass filter coat in which the transmission wavelength band changes along the X-axis. In this case, the linear variable filter coat 122 functions as a filter that transmits only wavelength components within a certain range that include the central wavelength of the primary light for each wavelength component L2. As a result, the transmission of secondary light is suppressed with respect to the primary light, and the appearance of unnatural peaks caused by the secondary light in the spectral data S can be suppressed. Furthermore, the spectroscopic measurement device 1 in the embodiment is a Dyson optical system equipped with a light incident unit 2, a diffraction grating 3, a photodetector 10, a lens 5, and an analysis unit 6, but a different optical system may be used. For example, a Czernitus-Turner optical system may be used. Moreover, if an optical system different from the Dyson optical system is used, the diffraction grating 3 may be a transmission-type diffraction grating. In addition, the linear variable filter coat 122 may be formed on the light emission surface 121b. Furthermore, the light blocked by the linear variable filter coat 122 is not limited to secondary light. For example, higher-order light (such as third-order or fourth-order light) may be blocked, diffracted light of negative order may be blocked, or reflected light (zero-order light) may be blocked. On the other hand, the linear variable filter coating 122 may transmit light of an order other than primary light (for example, light of the orders mentioned above) as a predetermined order, and block primary light.

[0045] As shown in Figure 10, the window portion 12 may further include a reflection reduction layer 124. The window portion 12 shown in Figure 10 includes a light-transmitting member 121, a linear variable filter coat 122, and a reflection reduction layer 124. In the window portion 12 shown in Figure 10, the linear variable filter coat 122 is formed on the light incident surface 121a of the light-transmitting member 121, and the reflection reduction layer 124 is formed on the light emission surface 121b of the light-transmitting member 121. The reflection reduction layer 124 is formed as a single layer of, for example, magnesium fluoride (MgF2), silicon dioxide (SiO2), titanium oxide (TiO2), zirconia (ZrO2), or tantalum pentoxide (Ta2O5), or by lamination of multiple such materials.

[0046] In the window portion 12 shown in Figure 10, the reflection reduction layer 124 is formed over the entire surface of the light-emitting surface 121b. That is, when viewed from the Y-axis direction, the outer edge of the reflection reduction layer 124 coincides with the outer edge of the light-transmitting member 121. However, the reflection reduction layer 124 may be formed on only a part of the light-emitting surface 121b. For example, the reflection reduction layer 124 may be formed so as to overlap at least with the linear variable filter coat 122 when viewed from the Y-axis direction. In that case, the outer edge of the reflection reduction layer 124 may coincide with the outer edge of the linear variable filter coat 122 when viewed from the Y-axis direction.

[0047] The anti-reflection layer 124 is, for example, an AR coating (Anti-Reflection coating). In this case, when the reflected light L4 of the light to be measured L1 reflected from the light-receiving region 13a enters the anti-reflection layer 124, the reflected light L4 is canceled out by light interference in the anti-reflection layer 124. For example, in the anti-reflection layer 124, the reflected light L4 is canceled out by interference between the light reflected from the surface of the anti-reflection layer 124 on the light-transmitting member 121 side and the light reflected from the surface of the anti-reflection layer 124 on the light-receiving region 13a side. If the anti-reflection layer 124 is not formed, the reflected light L4 is reflected from the light-emitting surface 121b of the light-transmitting member 121 and can become stray light due to multiple reflections between the light-emitting surface 121b and the light-receiving region 13a. In the window portion 12 shown in Figure 10, the formation of the anti-reflection layer 124 on the light-emitting surface 121b reduces stray light caused by the reflected light L4.

[0048] The reflection reduction layer 124 is not limited to an AR coating. The reflection reduction layer 124 may be, for example, a multilayer film. In that case, the refractive index of the reflection reduction layer 124 will vary from layer to layer. For example, the refractive index of the reflection reduction layer 124 may change stepwise from the refractive index of the air gap between the reflection reduction layer 124 and the light-receiving region 13a (the refractive index of air) to the refractive index of the light-transmitting member 121. In that case, the reflected light L4 will not be reflected at the light-emitting surface 121b of the light-transmitting member 121, but will be emitted to the outside via the light-transmitting member 121 and the linear variable filter coating 122.

[0049] The linear variable filter coating 122 is formed on the light-emitting surface 121b of the light-transmitting member 121, and the reflection reduction layer 124 may be formed on the light-incident surface 121a of the light-transmitting member 121. In this case, for example, in the reflection reduction layer 124, the reflected light L4 is canceled out by interference between the light reflected on the surface of the reflection reduction layer 124 on the light-transmitting member 121 side and the light reflected on the surface of the reflection reduction layer 124 on the opposite side of the light-transmitting member 121. [Explanation of Symbols]

[0050] 1...Spectroscopic measuring device, 2...Light incident section, 3...Diffraction grating, 10...Photodetector, 6...Analysis section, 11...Package, 11a...Aperture, 12...Window section, 13...Photodetector element, 13a...Light receiving area, 121...Light transmitting member, 121a...Light incident surface, 121b...Light output surface, 122...Linear variable filter coating, 124...Reflection reduction layer, L1...Light under measurement, S...Spectral data.

Claims

1. A photodetector that detects light of a predetermined order from light to be measured that has been spectrally separated in a predetermined direction, A package having an opening, The aforementioned opening is closed, and a window portion that transmits light of the predetermined order is provided, The package comprises a photodetector having a light-receiving region facing the window portion and detecting light of a predetermined order, The light-receiving region includes a plurality of light detection channels arranged in the predetermined direction, The aforementioned window section is A light-transmitting member having a light-incident surface and a light-emitting surface, The filter includes a linear variable filter coating formed on the light incident surface, the transmission wavelength of which changes along the predetermined direction, The outer edge of the light-transmitting member is larger than the inner edge of the opening of the package. A photodetector in which the light-emitting surface of the light-transmitting member is joined to the surrounding portion of the opening of the package.

2. The photodetector according to claim 1, wherein the light of the predetermined order is primary light.

3. The photodetector according to claim 1, wherein the linear variable filter coating is a linear variable long-pass filter coating in which the cut-on wavelength changes along the predetermined direction, or a linear variable band-pass filter coating in which the transmission wavelength band changes along the predetermined direction.

4. The photodetector according to claim 1, wherein the window portion further includes a reflection reduction layer formed on the other of the light incident surface and the light output surface.

5. A light incident section into which the light to be measured is incident, A diffraction grating for spectrally analyzing the light to be measured that enters from the light incident section, An analysis unit that generates spectral data of the light being measured, A spectroscopic measuring device comprising a photodetector according to any one of claims 1 to 4.

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