JP5614339B2 - Spectroscopic sensor and angle limiting filter - Google Patents

Description

  The present invention relates to a spectroscopic sensor and an angle limiting filter.

  In fields such as medicine, agriculture, and the environment, a spectroscopic sensor is used for diagnosing and inspecting an object. For example, in the medical field, a pulse oximeter that measures blood oxygen saturation using light absorption of hemoglobin is used. In the field of agriculture, a sugar content meter that measures the sugar content of fruits using light absorption of sugar is used.

  Patent Document 1 listed below discloses a spectral imaging sensor that limits a transmission wavelength band to a photoelectric conversion element by limiting an incident angle with an optical fiber that optically connects an interference filter and the photoelectric conversion element. ing.

JP-A-6-129908

  However, the conventional spectral sensor has a problem that it is difficult to reduce the size. For this reason, it becomes difficult to install a large number of sensors at desired locations or to install them at all times.

  The present invention has been made in view of the above technical problems. Some aspects of the invention relate to miniaturizing spectroscopic sensors and angle limiting filters.

In some embodiments of the present invention, the angle limiting filter includes a first light shielding layer having a first opening and a second opening having a second opening and located above the first light shielding layer. The first opening and the second opening so that the first opening and the second opening are partially overlapped and shifted from each other when viewed from above the second light shielding layer. A light shielding layer is disposed.
According to this aspect, the configuration in which the light path is formed by the light shielding layer enables the formation of a fine pattern and the manufacture of a small angle limiting filter. In addition, by arranging the first opening and the second opening so as to partially overlap and have a shifted position, it is possible to manufacture an angle limiting filter including an optical path having an arbitrary inclination angle. Become.

In the above-described aspect, there is further included a third light-shielding layer that has a third opening and is located above the second light-shielding layer, and a positional shift amount between the first opening and the second opening. It is desirable that the amount of positional deviation between the second opening and the third opening is substantially the same.
According to this, it is possible to reduce the curvature of the optical path and improve the selection characteristic of the incident angle by the angle limiting filter.

In the above-described aspect, it is desirable that the first and second openings have substantially the same size.
According to this, it is possible to reduce the curvature of the optical path and improve the selection characteristic of the incident angle by the angle limiting filter.

In the above-described aspect, it is desirable that the first and second light shielding layers are made of a material having a reflectance lower than that of aluminum.
According to this, by configuring the light shielding layer with a substance having low light reflectance, light that hits the wall surface of the optical path and passes through the optical path can be reduced. It is possible to make it difficult for light having an incident angle exceeding the light path to pass.

In the aspect described above, the first and second light shielding layers are formed above the semiconductor substrate, and the first metal layer and the second light shielding layer are formed in a region surrounding the first and second light shielding layers above the semiconductor substrate. It is desirable that the two metal layers are laminated via an insulating layer.
According to this, the plurality of metal layers constituting the wiring layer on the semiconductor circuit are formed in the region surrounding the first and second light shielding layers, so that the reflected light from the metal layer enters the optical path. Therefore, it is possible to make it difficult for light having an incident angle exceeding the limit angle range to pass through the optical path.

In the above-described aspect, it is desirable that the first and second light shielding layers are formed of a conductor and are electrically connected to the first and second metal layers, respectively.
According to this, the first and second light shielding layers are used as part of the electric circuit by electrically connecting the first and second light shielding layers and the first and second metal layers. Can do.

In another aspect of the present invention, the spectroscopic sensor detects the above-described angle limiting filter, a wavelength limiting filter that limits the wavelength of light that can pass through the angle limiting filter, and light that has passed through the angle limiting filter and the wavelength limiting filter. A light receiving element.
According to this aspect, since the above-mentioned angle limiting filter is used, a small spectroscopic sensor can be manufactured. Further, the wavelength of transmitted light can be selected by inclining the optical path of the angle limiting filter without forming an inclined structure for inclining the wavelength limiting filter.
Note that “upward” means a direction opposite to the direction toward the back surface with respect to the front surface of the substrate.

The figure which shows the angle limiting filter and spectral sensor which concern on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The figure which shows the formation process of the angle limiting filter which concerns on 1st Embodiment. The schematic diagram which shows the angle limiting filter which concerns on 2nd Embodiment. The schematic diagram which shows the angle limiting filter which concerns on 3rd Embodiment. The schematic diagram which shows the angle limiting filter which concerns on 4th Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail. In addition, this embodiment demonstrated below does not unduly limit the content of this invention described in the claim. Further, not all of the configurations described in the present embodiment are essential as a solution means of the present invention. The same constituent elements are denoted by the same reference numerals, and description thereof is omitted.

<1. First Embodiment>
FIG. 1 is a schematic diagram showing an angle limiting filter and a spectroscopic sensor according to the first embodiment of the present invention. 1A is a plan view of the spectroscopic sensor, and FIG. 1B is a cross-sectional view taken along the line BB of FIG. 1A.
The spectroscopic sensor 1 includes an angle limiting filter 10, a wavelength limiting filter 20, and a light receiving element 30 (see FIG. 1B). In FIG. 1A, the wavelength limiting filter 20 is omitted.

  A P-type silicon substrate 3 as a semiconductor substrate on which the spectroscopic sensor 1 is formed applies a predetermined reverse bias voltage to the light receiving element 30 or detects a current based on the photovoltaic power generated in the light receiving element 30, An electronic circuit 40 that amplifies an analog signal corresponding to the magnitude of the current and converts it into a digital signal is formed (see FIG. 1A). By connecting a plurality of aluminum (Al) alloy layers for wiring (not shown) to the semiconductor elements constituting the electronic circuit 40, electrical connection between the semiconductor elements of the electronic circuit 40 and the outside of the electronic circuit 40 are performed. Electrical connection is made.

  A conductive plug (not shown) is connected between the plurality of aluminum alloy layers. This conductive plug electrically connects the upper and lower aluminum alloy layers at the place where the conductive plug is disposed.

<1-1. Angle limit filter>
As shown in FIG. 1B, the angle limiting filter 10 is formed on a P-type silicon substrate 3 on which the light receiving element 30 is formed. In the angle limiting filter 10 of this embodiment, a wall portion that defines an optical path is formed by a plurality of light shielding layers 13 a to 13 d made of a light shielding body formed by the same process as the conductive plug on the electronic circuit 40. Each of the light shielding layers 13 a to 13 d has at least one opening 15. The light shielding layers 13a to 13d are made of tungsten (W). However, the light shielding layers 13a to 13d are not limited to tungsten, and are not limited to tungsten. Titanium, titanium tungsten, titanium, tantalum, tantalum nitride, chromium, and molybdenum may be used.

On the P-type silicon substrate 3, aluminum alloy layers 11 a to 11 e as a plurality of metal layers formed by the same multi-layer wiring process as the aluminum alloy layer on the electronic circuit 40 are translucent (by the light receiving element 30). The layers are laminated through silicon oxide (SiO ₂ ) layers 12a to 12f as insulating layers having light transmissivity with respect to light having a wavelength to be received. In addition, as a metal layer, it is not restricted to the aluminum alloy layers 11a-11e, A copper (Cu) alloy layer may be formed.

  The light shielding layers 13a to 13d are made of a material that does not substantially transmit light having a wavelength to be received by the light receiving element 30, and are continuously formed on a P-type silicon substrate 3 in a lattice-like predetermined pattern over a plurality of layers. It is formed. Thereby, at least one part of the opening part 15 formed in each of the light shielding layers 13a-13d overlaps each other. An optical path along the stacking direction of the light shielding layers 13a to 13d is formed by the opening 15 formed in each of the light shielding layers 13a to 13d.

  The wall portion formed by the light shielding layers 13a to 13d limits the incident angle of light passing through the optical path. That is, when the light incident on the optical path is inclined with respect to the direction of the optical path, the light hits any one of the light shielding layers 13a to 13d, and a part of the light is directed to any one of the light shielding layers 13a to 13d. Absorbed and the rest is reflected. Since the reflected light becomes weak due to repeated reflections before passing through the optical path, the light that can pass through the angle limiting filter 10 is substantially limited to light having an inclination with respect to the optical path within a predetermined limiting angle range. The

  The regions corresponding to the openings 15 of the light shielding layers 13a to 13d are filled with the above-described silicon oxide layers 12b to 12e having translucency.

  In the above-described aspect, since the wall portion is formed by forming the plurality of light shielding layers 13a to 13d in a lattice-like predetermined pattern on the P-type silicon substrate 3, it is possible to form a fine pattern. A small angle limiting filter 10 can be manufactured. Moreover, compared with the case where a spectroscopic sensor is comprised by bonding a member with an adhesive material, a manufacturing process can be simplified and the reduction | decrease of the transmitted light by an adhesive material can also be suppressed.

  In a preferred embodiment, the light shielding layers 13a to 13d are made of the same material (tungsten or the like) as the above-described conductive plug. As a result, the angle limiting filter 10 can be formed by a semiconductor process at the same time as forming an aluminum alloy layer or a conductive plug for wiring for the electronic circuit 40 formed on the same P-type silicon substrate 3. it can.

  Moreover, in a preferable aspect, the aluminum alloy layers 11a to 11e are formed in a region surrounding the wall portion formed by the light shielding layers 13a to 13d. In a preferred embodiment, the wall surface of the optical path is formed only by the light shielding layers 13a to 13d, not the aluminum alloy layers 11a to 11e having high light reflectance. As a result, it is possible to suppress the light incident on the optical path from being reflected by the wall surface of the optical path and passing through the optical path, so that it is possible to make it difficult for light having an incident angle exceeding the limit angle range to pass through the optical path. .

  Further, in a preferred embodiment, the light shielding layers 13a to 13d have positions where the opening 15 of the lower light shielding layer and the opening 15 of the upper light shielding layer partially overlap and are shifted from each other. ing. Specifically, the light shielding layers from the lowermost light shielding layer 13a to the uppermost light shielding layer 13d are formed at positions that are sequentially shifted in a certain direction at a certain pitch. As a result, an optical path is formed at a constant inclination angle with respect to the surface of the P-type silicon substrate 3. An optical path having an arbitrary inclination angle can be formed by appropriately setting the shift amount X of the position of the opening 15.

  Moreover, in a preferable aspect, the light shielding layers 13a to 13d are electrically connected to the aluminum alloy layers 11a to 11d through the end surfaces of the aluminum alloy layers 11a to 11d, respectively. Then, for example, the light receiving element 30 formed on the P-type silicon substrate 3 and the lowermost light shielding layer 13a are electrically connected, whereby the light receiving element 30 and the aluminum alloy layers 11a to 11e are electrically connected. It is possible.

<1-2. Wavelength limiting filter>
The wavelength limiting filter 20 is obtained by laminating a number of low refractive index thin films 21 such as silicon oxide (SiO ₂ ) and high refractive index thin films 22 such as titanium oxide (TiO ₂ ) on the angle limiting filter 10. is there.
The low-refractive index thin film 21 and the high-refractive index thin film 22 each have a predetermined thickness of, for example, a submicron order, and are laminated over a total of, for example, about 60 layers, for example, to have a total thickness of, for example, about 6 μm.

With the above configuration, the wavelength limiting filter 20 limits the wavelength of light (light that can pass through the angle limiting filter 10) that enters the angle limiting filter 10 within a predetermined limiting angle range.
That is, the incident light incident on the wavelength limiting filter 20 is partially reflected light and partially transmitted light at the boundary surface between the low refractive index thin film 21 and the high refractive index thin film 22. A part of the reflected light is reflected again at the interface between the other thin film 21 having a low refractive index and the thin film 22 having a high refractive index, and is combined with the above-described transmitted light. At this time, the light of the wavelength that matches the optical path length of the reflected light strengthens the reflected light and the transmitted light in phase, and the light of the wavelength that does not match the optical path length of the reflected light intensifies the phase of the reflected light and transmitted light. Weaken (interfer) without matching.

  Here, the optical path length of the reflected light is determined by the inclination angles of the low refractive index thin film 21 and the high refractive index thin film 22 with respect to the direction of the incident light. Therefore, when the above-described interference action is repeated in, for example, the low-refractive index thin film 21 and the high-refractive index thin film 22 covering a total of 60 layers, only light of a specific wavelength is wavelength-limited according to the incident angle of incident light. The light passes through the filter 20 and is emitted from the wavelength limiting filter 20 at a predetermined emission angle (for example, the same angle as the incident angle to the wavelength limiting filter 20).

  The angle limiting filter 10 allows only light incident on the angle limiting filter 10 to pass within a predetermined limit angle range. Therefore, the wavelength of light passing through the wavelength limiting filter 20 and the angle limiting filter 10 is determined by the film thickness (optical path length) of each of the low refractive index thin film 21 and the high refractive index thin film 22 and the angle limiting filter 10. The wavelength is limited to a predetermined range determined by the limited angle range of incident light to be generated.

  The wavelength limiting filter 20 may be inclined with respect to the P-type silicon substrate 3. In order to form the tilted wavelength limiting filter 20, an inclined structure having translucency is formed on the angle limiting filter 10, and a low refractive index thin film and a high refractive index thin film are formed thereon. By appropriately setting the tilt angle of the tilt structure, the wavelength limiting filter 20 can be tilted to an arbitrary tilt angle with respect to the P-type silicon substrate 3 and incident light. However, it is often easier to finely adjust the inclination angle of the optical path of the angle limiting filter 10 than to finely adjust the inclination angle of the inclined structure by setting the shift amount X of the opening 15. According to this embodiment, since the inclination angle of the optical path of the angle limiting filter 10 can be finely adjusted, the sensitivity of the spectral filter can be improved.

  In the present embodiment, the wavelength limiting filter 20 is formed on a flat surface on the angle limiting filter 10 in parallel with the surface of the P-type silicon substrate 3. Thus, without forming an inclined structure for inclining the wavelength limiting filter, the angle limiting filter 10 having a different inclination angle for each optical path as shown in FIG. 1 is formed on one substrate. The light having a plurality of wavelengths can be detected by one spectroscopic sensor 1.

  Further, in the present embodiment, not only can the detection wavelength by the spectroscopic sensor 1 be finely adjusted by the inclination angle of the optical path of the angle limiting filter 10, but the spectroscopic sensor 1 can be selected according to the incident angle distribution of the incident light to the spectroscopic sensor 1. Sensitivity can be optimized. For example, in a pulse oximeter used to measure blood oxygen saturation in the medical field, light is irradiated to a measurement target such as human skin from a light source such as an LED, and the reflected light is detected by the spectroscopic sensor 1. In this case, the reflected light is not necessarily incident perpendicular to the surface of the P-type silicon substrate 3. When the incident light has an intensity peak at an incident angle other than normal, the sensitivity of the spectroscopic sensor 1 can be increased by matching the intensity peak with the limit angle of incident light incident on the angle limiting filter 10.

<1-3. Light receiving element>
The light receiving element 30 is an element that receives light that has passed through the wavelength limiting filter 20 and the angle limiting filter 10 and converts it into photovoltaic power.

  The light receiving element 30 includes various semiconductor regions formed in the P-type silicon substrate 3 by ion implantation or the like. As a semiconductor region formed in the P-type silicon substrate 3, for example, a first semiconductor region (well) 31 of the first conductivity type and the first semiconductor region 31 are surrounded by the first semiconductor region 31. And a second semiconductor region 32 of the second conductivity type formed in this way. The first conductivity type is, for example, N type, and the second conductivity type is, for example, P type.

  The first semiconductor region 31 can be connected to a first external electrode (not shown). The second semiconductor region 32 is connected to the lower end of the angle limiting filter 10, and the angle limiting filter 10 can be further connected to a second external electrode (not shown). A reverse bias voltage can be applied to the PN junction formed between the first semiconductor region 31 and the second semiconductor region 32 via the first external electrode and the second external electrode. Yes.

  When the light passing through the angle limiting filter 10 is received by the light receiving element 30, a photovoltaic force is generated at the PN junction formed between the first semiconductor region 31 and the second semiconductor region 32. Current is generated. By detecting this current by the electronic circuit 40 connected to the second external electrode, the light received by the light receiving element 30 can be detected.

1 shows a first light receiving element 30 for receiving light having a wavelength (λ) transmitted through the optical path of the angle limiting filter 10 perpendicular to the P-type silicon substrate 3, and an optical path having an inclination angle θ _1. In order to receive light having a wavelength (λ ₂ = λ cos θ ₂ ) transmitted through a _second light receiving element 30 for receiving light having a wavelength (λ ₁ = λ cos θ ₁ ) transmitted through the optical path and an optical path having an inclination angle θ ₂ The third light receiving element 30 is shown. The light reception signals generated from these light receiving elements 30 are output to the electronic circuit 40 via the second external electrodes provided separately. Thereby, light of a plurality of wavelengths can be detected separately.

<1-4. Manufacturing Method of First Embodiment>
Here, a method for manufacturing the spectroscopic sensor 1 according to the first embodiment will be described. In the spectroscopic sensor 1, the light receiving element 30 is first formed on the P-type silicon substrate 3, then the angle limiting filter 10 is formed on the light receiving element 30, and then the wavelength limiting filter is formed on the angle limiting filter 10. 20 is produced.

  First, the light receiving element 30 is formed on the P-type silicon substrate 3. For example, first, an N-type first semiconductor region 31 is formed by performing ion implantation or the like on the P-type silicon substrate 3. Then, further ion implantation or the like is performed on the first semiconductor region 31 to form a P-type second semiconductor region 32. This step can be performed simultaneously with the formation of the electronic circuit 40 formed on the same P-type silicon substrate 3.

Next, the angle limiting filter 10 is formed on the light receiving element 30.
2 to 10 are a plan view and a cross-sectional view showing a forming process of the angle limiting filter according to the first embodiment. 2 to 10, the illustration of the P-type silicon substrate 3 is omitted.

  (1) First, a silicon oxide layer 12a is formed by silicon oxide or the like on the P-type silicon substrate 3 on which the light receiving element 30 is formed. Next, the aluminum alloy layer 11a is formed simultaneously with the formation of the aluminum alloy layer for wiring for the electronic circuit 40. A titanium film and a titanium nitride film are preferably formed on the lower surface and the upper surface of the aluminum alloy layer 11a, respectively. Next, a silicon oxide layer 12b is formed on the silicon oxide layer 12a and the aluminum alloy layer 11a (FIG. 2).

(2) Next, a part of the silicon oxide layer 12b is etched to form a groove in the silicon oxide layer 12b. Next, a light shielding layer 13a made of tungsten is embedded in the groove formed in the silicon oxide layer 12b (FIG. 3). The light shielding layer 13a is formed simultaneously with the formation of the conductive plug for connecting the aluminum alloy layer for wiring for the electronic circuit 40.
In the step (2), it is desirable that the end surface of the aluminum alloy layer 11a is located at the center of the outermost groove among the grooves for embedding the light shielding layer 13a. As a result, both the light shielding layer 13a and the aluminum alloy layer 11a are electrically connected and the end face of the aluminum alloy layer 11a is not exposed in the optical path can be realized more reliably. it can.

The angle limiting filter 10 is formed by repeating the above steps (1) and (2) a predetermined number of times. The second aluminum alloy layer 11b and the light shielding layer 13b are formed at positions shifted by a predetermined pitch in the plane direction with respect to the first aluminum alloy layer 11a and the light shielding layer 13a (FIGS. 4 and 4). 5). The same applies to the third and subsequent layers (FIGS. 6 to 10).
The width and thickness of the light shielding layer are preferably constant from the first light shielding layer 13a to the uppermost light shielding layer 13d. Further, it is desirable to maintain the same pitch in the third and subsequent layers as to the displacement of the upper light-shielding layer relative to the lower light-shielding layer. Thereby, the curvature of an optical path can be reduced and the selection characteristic of the incident angle by the angle limiting filter 10 can be improved.

Next, the wavelength limiting filter 20 is formed on the angle limiting filter 10. For example, first, the silicon oxide layer 12 f is formed on the angle limiting filter 10. Next, as shown in FIG. 1, a large number of low refractive index thin films 21 and high refractive index thin films 22 are alternately stacked.
The spectroscopic sensor 1 is manufactured through the above steps.

<2. Second Embodiment>
FIG. 11 is a schematic diagram showing an angle limiting filter according to the second embodiment of the present invention. 11A is a plan view of the angle limiting filter, and FIG. 11B is a cross-sectional view taken along the line BB of FIG. 11A.

In the second embodiment, the end surfaces of the aluminum alloy layers 11a to 11e are not covered with the light shielding layers 13a to 13d, and the end surfaces of the aluminum alloy layers 11a to 11e are exposed in the optical path. That is, the light shielding layers 13a to 13d are formed on the aluminum alloy layers 11a to 11d, respectively. In this configuration, the reflectivity of the wall surface of the optical path is higher than in the first embodiment, which may be disadvantageous in limiting the incident angle, but the tilt angle of the optical path can be greatly tilted. The degree of freedom is improved.
The other points are the same as in the first embodiment.

<3. Third Embodiment>
FIG. 12 is a schematic diagram showing an angle limiting filter according to the third embodiment of the present invention. 12A is a plan view of the angle limiting filter, and FIG. 12B is a cross-sectional view taken along the line BB of FIG. 12A.

In the third embodiment, only one end surfaces of the aluminum alloy layers 11a to 11d are covered with the light shielding layers 13a to 13d, and the other end surfaces of the aluminum alloy layers 11a to 11d are exposed in the optical path. In this configuration, since the reflectance of the wall surface of the optical path is higher than that of the first embodiment, it may be disadvantageous in limiting the incident angle, but the wall surface of the optical path is less than that of the second embodiment. Since the reflectance is low, it is advantageous in limiting the incident angle.
Other points are the same as those in the first embodiment and the second embodiment.

<4. Fourth Embodiment>
FIG. 13 is a schematic diagram showing an angle limiting filter according to the fourth embodiment of the present invention. 13A is a plan view of the angle limiting filter, and FIG. 13B is a cross-sectional view taken along the line BB of FIG. 13A.

  In the fourth embodiment, the distance between the first opening 15a and the second opening 15b of the light shielding layer 13 is wide, and the space between the first opening 15a and the second opening 15b is large. Furthermore, not only the light shielding layers 13a to 13d but also the aluminum alloy layers 11a to 11d are formed. According to this structure, even when the space | interval of the 1st opening part 15a of the light shielding layers 13a-13d and the 2nd opening part 15b is wide, the material of the light shielding layers 13a-13d is reduced, ensuring light-shielding property. be able to.

The other points are the same as in the first embodiment.
The angle limiting filters according to the second to fourth embodiments described above can also be applied to the spectroscopic sensor according to the first embodiment.

  DESCRIPTION OF SYMBOLS 1 ... Spectroscopic sensor, 3 ... P-type silicon substrate (semiconductor substrate), 10 ... Angle limiting filter, 11a-11e ... Aluminum alloy layer (metal layer), 12a-12f ... Silicon oxide layer (insulating layer), 13a-13d ... Light shielding layer, 15, 15a, 15b ... opening, 20 ... wavelength limiting filter, 21 ... thin film with low refractive index, 22 ... thin film with high refractive index, 30 ... light receiving element, 31 ... first semiconductor region, 32 ... first 2 semiconductor regions, 40... Electronic circuit.

Claims (5)

A first light shielding layer having a first opening;
A first metal layer located in a region surrounding the first light shielding layer;
A second light-shielding layer having a second opening and positioned above the first light-shielding layer;
A second metal layer located in a region surrounding the second light shielding layer;
Including
The first and second light shielding layers have a position where the first opening and the second opening are partially overlapped and shifted from each other when viewed from above the second light shielding layer. Arranged ,
The angle limiting filter , wherein the first light shielding layer is in contact with an end face of the first metal layer, and the second light shielding layer is in contact with an end face of the second metal layer . In claim 1,
A third light-blocking layer having a third opening and positioned above the second light-blocking layer;
An angle limiting filter in which a displacement amount between the first opening and the second opening portion and a displacement amount between the second opening portion and the third opening portion are substantially the same. In claim 1 or claim 2,
An angle limiting filter in which the first and second openings have substantially the same size. In any one of Claims 1 thru | or 3,
The first and second light shielding layers are angle limiting filters made of a material having a lower reflectance than aluminum. An angle limiting filter according to any one of claims 1 to 4 ,
A wavelength limiting filter that limits the wavelength of light that can pass through the angle limiting filter;
A light receiving element for detecting light that has passed through the angle limiting filter and the wavelength limiting filter;
A spectroscopic sensor comprising:

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