Spectrometer and measurement method

Abstract

The present invention provides a spectrometer comprising: a mirror device with a movable part; a diffraction grating that outputs diffracted light when measurement light is incident on a diffractive surface; and a first photodetector that detects the diffracted light. The angle of incidence of the measurement light onto the diffractive surface changes according to the rotation angle of the movable part, and the wavelength of the diffracted light detected by the first photodetector changes according to the angle of incidence of the measurement light onto the diffractive surface. The spectrometer includes first and second operating modes. In the first operating mode, a detection result is acquired from the first photodetector with the mirror device driven such that the measurement light from the mirror device is incident on the diffractive surface. In the second operating mode, a detection result is acquired from the first photodetector with the mirror device driven such that the measurement light from the mirror device travels outside the diffractive surface.

Description

Spectrometer and measurement method

[0001] One aspect of the present disclosure relates to a spectrometer and a measurement method using the spectrometer.

[0002] For example, Patent Document 1 describes a spectrophotometer including a light source, a spectroscope that extracts monochromatic light from the light source and is capable of scanning the wavelength of the monochromatic light, and a detector that detects light from a sample relative to the monochromatic light. In the spectrophotometer described in Patent Document 1, a shutter that can be moved forward and backward relative to the optical path by driving a motor is provided downstream of the diffraction grating that constitutes the spectroscope. When the optical path is blocked by the shutter, no light is incident on the detector. At this time, the detection signal from the detector becomes a dark signal, and dark signal data is collected.

[0003] JP 2010-107402 A

[0004] The above-described spectrometer is required to be compact. Furthermore, it is also required to acquire dark output values ​​at high speed. Therefore, an object of one aspect of the present disclosure is to provide a spectrometer and a measurement method that can achieve a compact device and high-speed acquisition of dark output values.

[0005] A spectrometer according to one aspect of the present disclosure includes: [1] "a mirror device having a support part, a movable part, a coupling part coupling the movable part to the support part so that the movable part can swing around a predetermined axis, and a first reflecting surface provided on the movable part, wherein the mirror device reflects measurement light by the first reflecting surface at an angle corresponding to a rotation angle of the movable part around the axis; a diffraction grating having a diffracting surface, wherein the diffraction grating outputs diffracted light dispersed according to wavelength when the measurement light from the mirror device is incident on the diffracting surface; and a first photodetector detecting the diffracted light output from the diffraction grating, wherein the movable part is coupled to the first reflecting surface and a first photodetector configured to detect the diffracted light, and the angle of incidence of the measurement light on the diffraction surface changes according to the rotation angle of a movable part, the wavelength of the diffracted light detected by the first photodetector changes according to the angle of incidence of the measurement light on the diffraction surface, and the spectrometer includes, as operation modes, a first mode in which the mirror device is driven so that the measurement light from the mirror device is incident on the diffraction surface, and a detection result of the first photodetector is acquired, and a second mode in which the mirror device is driven so that the measurement light from the mirror device travels outside the diffraction surface, and a detection result of the first photodetector is acquired.

[0006] In this spectrometer, the angle of incidence of the measurement light on the diffraction surface is changed by a mirror device having a movable part that can swing around a predetermined axis. This allows for a more compact device compared to, for example, a case in which a diffraction grating is rotated by a motor. The spectrometer also includes a first operating mode in which the mirror device is driven so that the measurement light from the mirror device is incident on the diffraction surface, and a second operating mode in which the mirror device is driven so that the measurement light from the mirror device travels outside the diffraction surface (not incident on the diffraction surface). A dark output value can be obtained from the detection result of the first photodetector in the second mode. By driving the mirror device to switch between a state in which the measurement light is incident on the diffraction surface and a state in which the measurement light travels outside the diffraction surface, the spectrometer can be more compact compared to, for example, a case in which a shutter is used, as in Patent Document 1. Furthermore, the dark output value can be obtained more quickly compared to, for example, a case in which a motor-driven shutter is used to obtain the dark output value, as in Patent Document 1. Therefore, this spectrometer allows for a more compact device and faster acquisition of the dark output value.

[0007] A spectrometer according to one aspect of the present disclosure may be [2] "the spectrometer according to [1], in which, in the second mode, the measurement light that travels along a predetermined optical axis and is incident on the first reflecting surface is reflected by the first reflecting surface so as to return along the optical axis." In this case, it is possible to prevent the measurement light that travels outside the diffractive surface in the second mode from becoming stray light due to reflection within the spectrometer, for example, and to prevent the generation of stray light when acquiring a dark output value.

[0008] A spectrometer according to one aspect of the present disclosure may be [3] "the spectrometer according to [1] or [2], further including a fixing member to which the mirror device is fixed, the mirror device further including a drive element for generating a drive force that oscillates the movable part, the fixing member being formed of a metal material." When the mirror device includes a drive element, heat generated in the drive element may affect the detection accuracy of the first photodetector. In this regard, in the spectrometer according to [3], the fixing member is formed of a metal material, so that heat generated in the mirror device can be efficiently dissipated via the fixing member, and a decrease in the detection accuracy of the first photodetector can be suppressed.

[0009] A spectrometer according to one aspect of the present disclosure may be [4] "the spectrometer according to any one of [1] to [3], further comprising: a fixed member to which the mirror device is fixed; a monitor light source that outputs monitor light; and a second photodetector that detects the monitor light; wherein the mirror device further has a second reflecting surface provided on the movable part on a back side opposite to a front side on which the first reflecting surface is provided; a through-hole formed in the fixed member; and the mirror device is fixed to the fixed member so that the second reflecting surface faces the through-hole; and the monitor light output from the monitor light source is incident on the second reflecting surface through the through-hole, reflected by the second reflecting surface, and detected by the second photodetector through the through-hole." In this case, the rotation angle of the movable part can be monitored with high accuracy based on the detection result of the second photodetector. Furthermore, the through-hole formed in the fixed member functions as an aperture for the monitor light, thereby preventing the monitor light from the monitor light source from entering the first photodetector as stray light.

[0010] A spectrometer according to one aspect of the present disclosure may be [5] "the spectrometer according to [4], wherein the through hole is tapered so that its width narrows toward the mirror device." In this case, the monitor light from the monitor light source is less likely to leak toward the surface of the movable part, and the monitor light can be prevented from entering the first photodetector as stray light. Furthermore, the monitor light can be incident on the second reflecting surface at an angle, and vignetting of the detection result of the second photodetector is less likely to occur.

[0011] A spectrometer according to one aspect of the present disclosure may be [6] "the spectrometer according to [4] or [5], wherein the opening width of the through-hole on the mirror device side is narrower than the width of the movable part of the mirror device." In this case, the monitor light from the monitor light source is less likely to leak to the surface side of the movable part, and the monitor light can be prevented from entering the first photodetector as stray light.

[0012] A spectrometer according to one aspect of the present disclosure may be [7] "the spectrometer according to any one of [1] to [6], wherein the first photodetector includes a plurality of detection elements having different wavelength sensitivity ranges." In this case, the measurable wavelength range can be widened.

[0013] A spectrometer according to one aspect of the present disclosure may be [8] "the spectrometer according to [7], wherein the plurality of detection elements are aligned along the wavelength dispersion direction of the diffracted light at the incident position on the first photodetector." In this case, a larger light receiving area can be ensured and light utilization efficiency can be improved, compared to, for example, a case where the plurality of detection elements are aligned along a direction perpendicular to the wavelength dispersion direction.

[0014] A spectrometer according to one aspect of the present disclosure may be [9] "the spectrometer according to [8], wherein the distance between the plurality of detecting elements is 1 mm or less." In this case, the difference in wavelength resolution between the plurality of detecting elements can be reduced. Furthermore, the difference in wavelength of diffracted light incident on the plurality of detecting elements can be reduced, which facilitates calculations based on the detection results of the plurality of detecting elements.

[0015] A spectrometer according to one aspect of the present disclosure may be

[10] "the spectrometer according to [7], wherein the plurality of detecting elements are arranged in a direction perpendicular to the wavelength dispersion direction of the diffracted light at the incident position on the first photodetector." In this case, for example, the difference in wavelength resolution between the plurality of detecting elements can be reduced compared to when the plurality of detecting elements are arranged in the wavelength dispersion direction. Furthermore, the difference in wavelength of the diffracted light incident on the plurality of detecting elements can be reduced, which facilitates calculations based on the detection results of the plurality of detecting elements.

[0016] A spectrometer according to one aspect of the present disclosure may be

[11] "the spectrometer according to any one of [1] to

[10] , further including a calculation unit that receives a detection result of the first photodetector, wherein the calculation unit subtracts a value corresponding to the detection result of the first photodetector acquired in the second mode from a value corresponding to the detection result of the first photodetector acquired in the first mode." In this case, by subtracting a dark output value acquired in the second mode from an output value acquired in the first mode, it is possible to perform measurement taking the dark output value into consideration.

[0017] A spectrometer according to one aspect of the present disclosure is

[12] "further comprising a calculation unit that receives a detection result of the first photodetector, the first photodetector including a first detection element and a second detection element, (1) the first detection element has sensitivity to wavelength ranges corresponding to the n-th (n is an integer of 1 or more) and (n+1)th diffracted light, the second detection element has sensitivity to a wavelength range corresponding to the (n+1)th diffracted light, and the calculation unit subtracts a value corresponding to the detection result of the second detection element from a value corresponding to the detection result of the first detection element." Alternatively, the spectrometer may be the one described in any one of [1] to

[11] , wherein (2) the first detection element has sensitivity to a wavelength range corresponding to the m-th (m is an integer equal to or less than −1) and (m−1)-th order diffracted light, and the second detection element has sensitivity to a wavelength range corresponding to the (m−1)-th order diffracted light, and the calculation unit calculates the output value of the m-th order diffracted light by subtracting a value corresponding to the detection result of the second detection element from a value corresponding to the detection result of the first detection element. In this case, the output value of the n-th order or m-th order diffracted light can be calculated with high accuracy.

[0018] A spectrometer according to one aspect of the present disclosure may be

[13] "the spectrometer according to any one of [1] to

[12] , further including a calculation unit that receives the detection result of the first photodetector, wherein the mirror device further includes a drive element for generating a drive force that oscillates the movable part, and the calculation unit corrects the detection result of the first photodetector in the second mode based on an input signal to the drive element or an output value from the drive element." In the second mode, the rotation angle of the movable part is larger than in the first mode, so that power consumption in the drive element increases and heat is more likely to be generated. In this regard, the spectrometer of

[13] can correct the detection result of the first photodetector in the second mode based on the input signal to the drive element or the output value from the drive element so as to reduce the influence of heat generation in the drive element.

[0019] A spectrometer according to one aspect of the present disclosure may be

[14] "the spectrometer according to any one of [1] to

[13] , which acquires the detection result of the first photodetector in the second mode each time the rotation angle of the movable part is changed and the detection result of the first photodetector is acquired in the first mode." In this case, because a dark output value is acquired each time the rotation angle of the movable part is changed, it is possible to perform measurements with high accuracy even if, for example, the dark output value is prone to change.

[0020] A spectrometer according to one aspect of the present disclosure may be

[15] "the spectrometer according to any one of [1] to

[13] , in which the detection result of the first photodetector is acquired in the second mode before or after acquiring the detection result of the first photodetector multiple times in the first mode while changing the rotation angle of the movable part." In this case, since a dark output value is acquired once for multiple measurements, the measurement time can be shortened.

[0021] A measurement method according to one aspect of the present disclosure is

[16] "a measurement method using a spectroscope, the spectroscope including: a mirror device having a support portion, a movable portion, a connecting portion connecting the movable portion to the support portion so that the movable portion can swing around a predetermined axis; a first reflecting surface provided on the movable portion; the mirror device reflecting measurement light by the first reflecting surface at an angle corresponding to a rotation angle of the movable portion around the axis; a diffraction grating having a diffracting surface, the diffraction grating outputting diffracted light dispersed according to wavelength when the measurement light from the mirror device is incident on the diffracting surface; and a first light detection device detecting the diffracted light output from the diffraction grating. and a detector, wherein an incident angle of the measurement light onto the diffraction surface changes according to a rotation angle of the movable part, and a wavelength of the diffracted light detected by the first photodetector changes according to the incident angle of the measurement light onto the diffraction surface, and the measurement method may include: a first step of acquiring a detection result of the first photodetector while driving the mirror device so that the measurement light from the mirror device is incident onto the diffraction surface; and a second step of acquiring a detection result of the first photodetector while driving the mirror device so that the measurement light from the mirror device travels outside the diffraction surface.

[0022] The spectrometer used in this measurement method changes the angle of incidence of the measurement light on the diffraction surface using a mirror device with a movable part that can swing around a predetermined axis. This allows for a more compact device compared to, for example, rotating a diffraction grating using a motor. This measurement method also includes a first step of driving the mirror device so that the measurement light from the mirror device is incident on the diffraction surface, and a second step of driving the mirror device so that the measurement light from the mirror device travels outside the diffraction surface (not incident on the diffraction surface). A dark output value can be obtained from the detection result of the first photodetector in the second step. By driving the mirror device to switch between a state in which the measurement light is incident on the diffraction surface and a state in which the measurement light travels outside the diffraction surface, this allows for a more compact device compared to, for example, using a shutter as in Patent Document 1. Furthermore, this measurement method allows for faster acquisition of dark output values ​​compared to, for example, using a motor-driven shutter as in Patent Document 1. Therefore, this measurement method allows for a more compact device and faster acquisition of dark output values.

[0023] The measurement method according to one aspect of the present disclosure may be

[17] "the measurement method according to

[16] , further including a third step of subtracting a value corresponding to the detection result of the first photodetector acquired in the second step from a value corresponding to the detection result of the first photodetector acquired in the first step." In this case, by subtracting the dark output value acquired in the second step from the output value acquired in the first step, it is possible to perform measurement taking the dark output value into consideration.

[0024] The measurement method according to one aspect of the present disclosure may be the measurement method described in

[16] or

[17] , wherein: [1] the first photodetector includes a first detection element and a second detection element; (1) the first detection element is sensitive to a wavelength range corresponding to the n-th order (n is an integer equal to or greater than 1) and (n+1)-th order diffracted light, and the second detection element is sensitive to a wavelength range corresponding to the (n+1)-th order diffracted light, and in the measurement method, an output value of the n-th order diffracted light is calculated by subtracting a value corresponding to the detection result of the second detection element from a value corresponding to the detection result of the first detection element; or (2) the first detection element is sensitive to a wavelength range corresponding to the m-th order (m is an integer equal to or less than -1) and (m-1)-th order diffracted light, and the second detection element is sensitive to a wavelength range corresponding to the (m-1)-th order diffracted light, and in the measurement method, an output value of the m-th order diffracted light is calculated by subtracting a value corresponding to the detection result of the second detection element from a value corresponding to the detection result of the first detection element. In this case, the output value of the nth or mth order diffracted light can be calculated with high precision.

[0025] According to one aspect of the present disclosure, it is possible to provide a spectrometer and a measurement method that can reduce the size of the device and increase the speed at which dark output values ​​can be acquired.

[0026] 4 is a configuration diagram of a spectrometer of an embodiment. FIG. 5 is a perspective view of a mirror unit. FIG. 6 is a plan view of the mirror unit. FIG. 7 is a plan view of the mirror unit taken along line IV-IV in FIG. 3. FIG. 8 is a bottom view of the mirror unit. FIG. 9 is a plan view of a mirror device. (a) and (b) are diagrams for explaining the arrangement of detection elements in a first photodetector. (a) is a graph showing the relationship between primary light, secondary light, and tertiary light, and (b) is a graph showing an example of the sensitivity characteristics of a first detection element, a second detection element, and a third detection element. FIG. 10 is a graph for explaining an example of measurement results. FIG. 11 is a graph for explaining an example of measurement results. FIG. 12 is a diagram for explaining a second mode.

[0027] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted.

[0028] 1, the spectrometer 1 includes an optical fiber 2, a slit member 3, a collimator 4, mirrors 5 and 6, a mirror unit 7, a diffraction grating 8, a collecting mirror 9, a first photodetector 10, a substrate unit 11, a light source 12, a collecting lens 13, an ND filter 14, a cylindrical lens 15, and a second photodetector 16. Each component except for the optical fiber 2 and the substrate unit 11 is fixed on, for example, a plate-shaped base member (not shown). The mirror unit 7 includes a mirror device 17 and a fixing member 18 to which the mirror device 17 is fixed.

[0029] In general, in the spectrometer 1, the measurement light L1 introduced from the optical fiber 2 is reflected by the mirror device 17 and incident on the diffraction surface 8a of the diffraction grating 8. When the measurement light L1 is incident on the diffraction surface 8a, the diffraction grating 8 outputs diffracted light L2 dispersed according to wavelength. The diffracted light L2 is then detected by the first photodetector 10. The angle of incidence of the measurement light L1 on the diffraction surface 8a changes depending on the rotation angle of the movable part 22 of the mirror device 17 (described later), and the wavelength of the diffracted light L2 detected by the first photodetector 10 changes depending on the angle of incidence of the measurement light L1 on the diffraction surface 8a. Therefore, by performing measurements while controlling the rotation angle of the movable part 22, the intensity of light of a specific wavelength contained in the measurement light L1 can be measured. In this way, the spectrometer 1 separates and detects light of a specific wavelength from the measurement light L1.

[0030] The optical fiber 2, the slit member 3, the collimator 4, the mirrors 5 and 6, the mirror unit 7, the diffraction grating 8, the collecting mirror 9, and the first photodetector 10 constitute a spectroscopic optical system for spectroscopically separating the measurement light L1. The optical fiber 2, the slit member 3, the collimator 4, the mirrors 5 and 6, the mirror unit 7, the diffraction grating 8, the collecting mirror 9, and the first photodetector 10 are arranged on the optical path in this order. In the spectroscopic optical system of this embodiment, when viewed from a direction perpendicular to the plane of the paper in FIG. 1 , the diffraction grating 8 is arranged between the collimator 4 and the collecting mirror 9. When viewed from this direction, the measurement light L1 traveling from the mirror 6 toward the mirror unit 7 (mirror device 17) intersects with the diffracted light L2 output from the diffraction surface 8 a of the diffraction grating 8.

[0031] The optical fiber 2 is fixed to a fiber fixing portion 2a fixed on, for example, a base member. The optical fiber 2 guides measurement light L1 of the measurement object to a slit member 3. The slit member 3 has a slit 3a facing the output end of the optical fiber 2. The measurement light L1 output from the optical fiber 2 passes through the slit 3a and proceeds to the collimator 4. The shape of the measurement light L1 proceeding to the collimator 4 is determined according to the shape of the slit 3a. The collimator 4 collimates the measurement light L1. Mirrors 5 and 6 reflect the measurement light L1 from the collimator 4 so that it proceeds to a mirror unit 7 (mirror device 17).

[0032] The mirror unit 7 will be described with reference to FIGS. 2 to 6. The mirror unit 7 includes a mirror device 17 and a fixing member 18 to which the mirror device 17 is fixed. As shown in FIG. 6, the mirror device 17 includes a support portion 21, a movable portion 22, a pair of connecting portions 23, and a first reflecting surface 24. The support portion 21, the movable portion 22, and the pair of connecting portions 23 are integrally formed, for example, by an SOI (Silicon on Insulator) substrate. In other words, the mirror device 17 is a MEMS (Micro Electro Mechanical Systems) device manufactured by processing a semiconductor substrate using MEMS technology (patterning, etching, etc.). The mirror device 17 is fixed to the fixing member 18 on the back side of the support portion 21 (the side facing the fixing member 18) by, for example, a resin adhesive (not shown).

[0033] The support portion 21 is formed, for example, in the shape of a rectangular frame. The support portion 21 includes a pair of electrode pads 21a for applying a drive current to the coil 26 (described later) and a pair of wirings 21b extending from the electrode pads 21a over one of the connecting portions 23 to the coil 26 and electrically connected to the coil 26 ( FIGS. 3 and 6 ). While FIG. 6 shows a simplified view of the connection between the coil 26 and the wirings 21b, in reality, one wiring 21b is connected to one end of the coil 26, and the other wiring 21b is connected to the other end of the coil 26. The electrode pads 21a are electrically connected to wiring WR (described later) made of a flexible substrate via metal wires 21c ( FIG. 3 ). The metal wires 21c are made of, for example, gold, silver, copper, aluminum, or alloys thereof. The thickness of the support portion 21 in the Z direction is 1 mm or less, for example, approximately 500 μm. The width of the support portion 21 (mirror device 17) in the X direction is, for example, about 5 mm, and the width of the support portion 21 in the Y direction is, for example, about 8 mm. The width of the support portion 21 in the Y direction is larger than the width of the support portion 21 in the X direction. This allows the magnet 19 to be brought closer to the mirror device 17 in the X direction to increase the magnetic force acting on the coil 26 from the magnet 19 (described later), while also allowing the wiring WR to be drawn out from the mirror device 17 in the Y direction.

[0034] The movable section 22 has a first section 31 and a second section 32. The first section 31 is formed, for example, in a circular shape in a plan view (when viewed from the Z direction). The Z direction is a direction perpendicular to the first reflecting surface 24. The second section 32 is formed, for example, in a substantially rectangular ring shape in a plan view. The second section 32 surrounds the first section 31 in a plan view. The second section 32 is connected to the first section 31 via a pair of connecting sections 33. The pair of connecting sections 33 are located, for example, at the centers of two sides of the rectangular inner edge of the second section 32 that are parallel to the Y direction. In this example, each connecting section 33 is composed of a pair of sections extending along the X direction.

[0035] The second part 32 has a rectangular annular inner part 321, a rectangular annular outer part 322 that surrounds the inner part 321 in a plan view, and a pair of connecting parts 323 that extend along the Y direction and connect the inner part 321 to the outer part 322 on one side and the other side in the Y direction. In this example, each connecting part 323 is composed of a pair of parts that extend along the Y direction. A coil 26 (driving element) is disposed in the outer part 322 to generate a driving force that causes the movable part 22 to swing. The coil 26 is wound, for example, in a spiral shape (whorl shape) multiple times. A magnetic field generated by the magnet 19 acts on the coil 26.

[0036] The pair of connecting portions 23 connect the movable portion 22 to the support portion 21 so that the movable portion 22 can swing around the axis A. The axis A is parallel to the Y direction. Each connecting portion 23 extends along the Y direction. Each connecting portion 23 functions as a torsion bar that is torsionally deformed when the movable portion 22 swings around the axis A.

[0037] The thickness of the movable part 22 and the connecting part 23 in the Z direction is, for example, about 100 μm. The thickness of the movable part 22 is smaller than the thickness of the support part 21. This makes it possible to prevent the movable part 22 from coming into contact with the fixed member 18 during swinging, even in the case where the opening width W1 (for example, about 2 mm) of the through-hole 41 a is smaller than the width W2 (for example, about 3 mm) of the movable part 22, as in this example.

[0038] The first reflecting surface 24 is provided on the first portion 31 of the movable portion 22. More specifically, the first reflecting surface 24 is provided on the front surface (one side in the Z direction) of the first portion 31. A second reflecting surface 25 ( FIG. 4 ) is provided on the back surface (the other side in the Z direction) of the first portion 31. The first reflecting surface 24 and the second reflecting surface 25 are formed by the surface of a layer formed in a circular, elliptical, or rectangular shape and made of a metal material such as aluminum, an aluminum-based alloy, gold, or silver. The first reflecting surface 24 and the second reflecting surface 25 are formed flat, for example, perpendicular to the Z direction.

[0039] An example of a method for driving the mirror device 17 will be described. As an example, a high-frequency driving current is applied to the coil 26. At this time, a magnetic field generated by the magnet 19 acts on the coil 26, generating a Lorentz force in the coil 26. As a result, the movable part 22 is oscillated around the axis A at, for example, a resonant frequency level (resonant driving). By driving the mirror device 17 in this manner, the measurement light L1 can be reflected by the first reflecting surface 24 for scanning. As another example, a driving current of a constant magnitude may be applied to the coil 26. In this case, the movable part 22 rotates around the axis A according to the magnitude of the driving current and stops at a predetermined rotation angle. In this way, the movable part 22 may be driven statically (linear driving). Note that, even in linear driving, the movable part 22 can be continuously oscillated, similar to resonant driving, by applying a driving current such as a triangular wave to the coil 26.

[0040] 2 to 5, the fixing member 18 is formed, for example, in a substantially rectangular shape with long sides parallel to the X direction in a plan view. The fixing member 18 is formed of a metal material such as an aluminum alloy or non-magnetic stainless steel. For example, the width of the fixing member 18 in the X direction is approximately 40 mm, and the width of the fixing member 18 in the Y direction is approximately 14 mm. The aspect ratio of the fixing member 18 (width in the X direction / width in the Y direction) is greater than 1, preferably 2 or greater. By reducing the size of the fixing member 18 in the Y direction, which is perpendicular to the direction in which the pair of magnets 19 face each other, the overall size (thinning) of the spectrometer 1 in the Y direction can be reduced.

[0041] The fixing member 18 has a fixing portion 41 in the center to which the mirror device 17 is fixed. A pair of arrangement grooves 42 for arranging the magnets 19 are formed on both sides of the fixing portion 41 in the X direction. The magnets 19 are formed, for example, in a rectangular parallelepiped shape. The pair of magnets 19 face each other in the X direction, and the mirror device 17 is arranged in the center between the pair of magnets 19. This allows a uniform magnetic field to be applied to the coil 26 of the mirror device 17. The depth D of the arrangement groove 42 is equal to or greater than one-third of the thickness T of the magnet 19. This allows the pair of magnets 19, which have an attractive force acting between them, to be reliably held by the arrangement groove 42. This also facilitates the arrangement (assembly) of the magnets 19 in the arrangement groove 42.

[0042] For example, the depth D of the placement groove 42 is about 2 mm, and the thickness T of the magnet 19 is about 4 mm. In this example, the magnet 19 protrudes in the Z direction relative to the placement surface of the fixed portion 41 on which the mirror device 17 is placed. This makes it easier to place the magnet 19 in the placement groove 42. For example, the width of the magnet 19 in the X direction is about 7 mm, and the width of the magnet 19 in the Y direction is about 10 mm. The width of the magnet 19 in the X direction is larger than the width of the mirror device 17 in the X direction, and the width of the magnet 19 in the Y direction is larger than the width of the mirror device 17 in the Y direction. This allows the magnet 19 to be made larger, and the magnetic force acting on the coil 26 to be increased. The maximum thickness Ta of the fixed member 18 is, for example, about 4 mm.

[0043] The magnet 19 is in surface contact with the surface of the fixing portion 41 at the end of the arrangement groove 42 on the mirror device 17 side, with the surface of the magnet 19 facing the surface of the fixing portion 41. This makes it possible to easily position the magnet 19 relative to the arrangement groove 42 while bringing the magnet 19 close to the mirror device 17 within the arrangement groove 42. By bringing the magnet 19 and the mirror device 17 closer to each other, the magnetic force acting on the coil 26 provided on the mirror device 17 is increased, allowing the mirror device 17 to be driven efficiently. For example, the distance between the pair of magnets 19 in the X direction is about 7 mm, and the distance between the magnet 19 and the mirror device 17 in the X direction is about 1 mm.

[0044] A resin adhesive (not shown) may be used to secure the magnet 19 to the fixing member 18. For example, the width of the placement groove 42 in the X direction is approximately 10 mm, which is larger than the width of the magnet 19 in the X direction. The width (maximum width) of the placement groove 42 in the Y direction is approximately 12 mm, which is larger than the width of the magnet 19 in the Y direction. This facilitates placement of the magnet 19 in the placement groove 42. Furthermore, space can be secured within the placement groove 42 for the adhesive to escape, thereby preventing problems caused by adhesive adhering to the mirror device 17. A gap of approximately 1 mm is provided between the placement groove 42 and the mirror device 17 in the X direction. This prevents adhesive from coming into contact with the mirror device 17 even if it spills out from the placement groove 42 toward the mirror device 17. Note that in this example, the magnet 19 does not contact the side surface of the placement groove 42 in the Y direction; however, the magnet 19 may be in surface contact with either side surface of the placement groove 42 in the Y direction.

[0045] In a plan view, recesses 42a are formed at each of the four corners of the arrangement groove 42. The recesses 42a are formed in a rounded shape. In this example, the recesses 42a are curved in an arc shape. By forming the recesses 42a, for example, when the magnet 19 is brought into surface contact with the side surface of the fixing portion 41, adhesive remains at the corners (recesses 42a), preventing the adhesive from reaching the mirror device 17. Furthermore, for example, when the magnet 19 is pressed against the corners of the arrangement groove 42 to fix it, stress concentration on the magnet 19 can be reduced compared to when the corners of the arrangement groove 42 are formed at right angles without the recesses 42a. Note that the recesses 42a do not necessarily have to be formed. If the recesses 42a are not formed, the fixing member 18 and the mirror unit 7 can be made smaller in the Y direction.

[0046] The fixing member 18 is fixed to the base member with four screws (not shown) and two positioning pins (not shown). Specifically, base fixing portions 18a for fixing the fixing member 18 to the base member are provided at both ends of the fixing member 18 in the X direction. The thickness of the base fixing portions 18a in the Z direction is, for example, approximately 2 mm, and the base fixing portions 18a are formed to have the same thickness as the portion of the fixing member 18 where the arrangement groove 42 is formed. Threaded holes 18b into which the screws are threaded are formed at both ends of each base fixing portion 18a in the Y direction. A positioning hole 18c into which the positioning pin is inserted is formed in the center of each base fixing portion 18a in the Y direction. The positioning hole 18c on one side in the X direction (left side in FIG. 3) is formed as a circular hole, and the positioning hole 18c on the other side in the X direction (right side in FIG. 3) is formed as a long hole extending along the X direction. The position in the XY directions is restricted by the positioning hole 18c (round hole) on one side in the X direction, and the rotation in the XY plane is restricted by the positioning hole 18c (oval hole) on the other side in the X direction.

[0047] In this embodiment, the width of the magnet 19 in the X direction (approximately 7 mm) is larger than the width of the arrangement groove 42 in the X direction (approximately 10 mm). This leaves a gap of approximately 3 mm between the end of the magnet 19 in the X direction (the end on the fixing hole side) and the side surface of the arrangement groove 42. This allows for a large distance in the X direction between the magnet 19 and the fixing holes (screw holes 18 b and positioning holes 18 c). As a result, the workability when fixing the fixing member 18 to the base member can be improved, the fixing strength of the fixing member 18 can be ensured, and the positioning accuracy can be improved. The distance between the end of the magnet 19 in the X direction (the end on the fixing hole side) and the side surface of the arrangement groove 42 can be larger than the distance between the magnet 19 and the mirror device 17 in the X direction, or can be smaller than the width of the magnet 19 and the width of the mirror device 17 in the X direction. This allows for space to escape for the adhesive used to fix the magnet 19, ensuring the workability when fixing the fixing member 18 to the base member while miniaturizing the mirror unit 7 in the X direction.

[0048] The fixed portion 41 has a through-hole 41a formed therethrough along the Z direction. Monitor light L3, described later, is incident on the through-hole 41a. The through-hole 41a is tapered so that its width narrows as it approaches the mirror device 17. In this example, the through-hole 41a is tapered in both cross sections parallel to the Z direction. The through-hole 41a has circular opening edges on both the mirror device 17 side and the opposite side ( FIG. 5 ). The mirror device 17 is fixed to the fixed portion 41 so that the second reflecting surface 25 (rear surface) faces the through-hole 41a. In other words, the mirror device 17 is fixed to the fixed portion 41 so that the first reflecting surface 24 (front surface) faces away from the fixed member 18. The opening width W1 of the through-hole 41a on the mirror device 17 side is narrower than the width W2 of the movable portion 22. That is, when viewed from the mirror device 17 side, the through-hole 41a is covered by the movable portion 22. The opening width W1 may be narrower than the width of the second reflecting surface 25 (first reflecting surface 24).

[0049] For example, the opening width W1 is about 2 mm, and the width W2 of the movable part is about 3 mm. The opening width of the through-hole 41 a on the light source 12 side (the side opposite the mirror device 17) is, for example, about 9 mm. The opening width of the through-hole 41 a on the light source 12 side may be larger than the width of the mirror device 17 in the X direction and the width of the magnet 19 in the X direction. Also, in the cross section of FIG. 4 , the opening edge of the through-hole 41 a on the light source 12 side may be located outside the end of the magnet 19 on the mirror device 17 side (the side opposite the mirror device 17). This allows the monitor light L3 emitted from the light source 12 to be reliably guided to the second reflecting surface 25.

[0050] A wiring WR made of, for example, a flexible printed circuit (FPC) is connected to the mirror device 17. The wiring WR is drawn out from the mirror device 17 along the Y direction, which is perpendicular to the X direction in which the pair of magnets 19 face each other. This allows the wiring WR to be drawn out more appropriately than, for example, when the wiring WR is drawn out from the mirror device 17 along the direction in which the pair of magnets 19 face each other. In addition, in this example, the fixing member 18 has an elongated shape in the X direction in which the pair of magnets 19 face each other (a shape in which the length in the X direction is longer than the length in the Y direction). This allows the size of the mirror unit 7 to be reduced in the Y direction, which is perpendicular to the X direction in which the pair of magnets 19 face each other, thereby enabling the spectrometer 1 to be miniaturized. The wiring WR is electrically connected to, for example, an electrode pad 21a formed on a support portion 21 of the mirror device 17 via a metal wire 21c (FIGS. 3 and 6).

[0051] Referring again to FIG. 1 , the diffraction grating 8 has a diffracting surface 8a. The measurement light L1 reflected by the first reflecting surface 24 of the mirror device 17 is incident on the diffracting surface 8a. In this example, the diffraction grating 8 is configured as a reflective type, reflecting the measurement light L1 at the diffracting surface 8a and outputting diffracted light L2 dispersed according to wavelength. The diffracting surface 8a has numerous grooves 8b arranged along a predetermined direction. These grooves 8b form a blazed grating. While the grooves 8b are depicted enlarged in FIG. 1 for the sake of explanation, the actual grooves 8b are so small that they are invisible to the naked eye, with a groove period of, for example, approximately several μm. When the measurement light L1 is incident on the diffracting surface 8a, diffracted light L2 dispersed according to wavelength along the predetermined direction (the direction in which the grooves 8b are arranged) is output. In this example, the diffracting surface 8a is formed in the central portion of the surface of the diffraction grating 8 facing the mirror device 17. A non-diffracting region 8c, where the diffracting surface 8a is not formed, exists in the outer portion of the surface of the diffraction grating 8 facing the mirror device 17. When the measurement light L1 is incident on the non-diffraction region 8c, the diffraction grating 8 does not output the diffracted light L2. The diffraction grating 8 may be configured as a transmissive type. In this case, the measurement light L1 is diffracted by the diffraction surface 8a when passing through the diffraction grating 8. The diffraction grating 8 may not have the non-diffraction region 8c, and the diffraction surface 8a may be formed on the entire surface of the diffraction grating 8 facing the mirror device 17.

[0052] The collecting mirror 9 collects the diffracted light L2 output from the diffraction grating 8 onto the first photodetector 10. The first photodetector 10 detects the diffracted light L2 collected by the collecting mirror 9. In the spectrometer 1, the angle of incidence of the measurement light L1 on the diffraction surface 8a changes depending on the rotation angle of the movable portion 22 of the mirror device 17, and the wavelength of the diffracted light L2 detected by the first photodetector 10 changes depending on the angle of incidence of the measurement light L1 on the diffraction surface 8a. In this embodiment, the diffracted light L2 is collected by the collecting mirror 9, which is separate from the diffraction grating 8. However, the collecting mirror 9 may be omitted by, for example, forming the diffraction surface 8a of the diffraction grating 8 as a concave surface. In this case, the optical system can be further miniaturized.

[0053] As shown in FIG. 7A , the first photodetector 10 includes a first detection element 51, a second detection element 52, and a third detection element 53. The first detection element 51, the second detection element 52, and the third detection element 53 have sensitivity wavelengths in the near-infrared and / or mid-infrared regions, and have different sensitivity wavelength ranges. For example, the first detection element 51 has sensitivity wavelengths in the near-infrared and mid-infrared regions, while the second detection element 52 and the third detection element 53 have sensitivity wavelengths in the near-infrared region. As an example, as shown in FIG. 8B , the first detection element 51 is a detection element using InAsSb for the semiconductor layer and is sensitive to a wavelength range (wavelength region) up to approximately 5 μm. The second detection element 52 is a detection element using InGaAs for the semiconductor layer and is sensitive to a wavelength range up to approximately 2.6 μm. The third detection element 53 is a detection element using InGaAs for the semiconductor layer and is sensitive to a wavelength range up to approximately 1.7 μm. The detecting elements 51 to 53 may have a wavelength sensitivity in the visible light range.

[0054] As shown in FIGS. 8A and 8B , the wavelength range of sensitivity of the first detection element 51 corresponds to first-, second-, and third-order diffracted light L2. Hereinafter, the first-order diffracted light L2 will also be referred to as first-order light, the second-order diffracted light L2 as second-order light, and the third-order diffracted light L2 as third-order light. As shown in FIG. 8A , when the mirror angle (the rotation angle of the movable part 22) is the same, the wavelength of the detected second-order light is half that of the first-order light, and the wavelength of the detected third-order light is half that of the second-order light. That is, when the mirror angle is the same, the diffracted light L2 incident on the first photodetector 10 includes not only the first-order light, which is the measurement wavelength, but also higher-order light such as second-order light having half the wavelength of the first-order light and third-order light having half the wavelength of the second-order light. The wavelength range of sensitivity of the first detection element 51 includes the wavelength ranges of the first-order light, second-order light, and third-order light. The second detection element 52 has a wavelength sensitivity range corresponding to the second and third order light, and includes the wavelength ranges of the second and third order light. The third detection element 53 has a wavelength sensitivity range corresponding to the third order light, and includes the wavelength range of the third order light.

[0055] In the spectrometer 1, the output values ​​of the primary, secondary, and tertiary light are calculated by the following calculation. The following calculation is performed by the calculation unit 64, which will be described later. Specifically, the calculation unit 64 first calculates the output value of the tertiary light (the tertiary light component) from the detection result (detection intensity) of the third detection element 53. Next, the calculation unit 64 calculates the output value of the secondary light (the value corresponding to the detection result of the third detection element 53) by subtracting the output value of the tertiary light (the value corresponding to the detection result of the third detection element 53) from the detection result (detection intensity) of the second detection element 52. Next, the calculation unit 64 calculates the output value of the primary light (the primary light component) by subtracting the output value of the secondary light (the value corresponding to the detection result of the second detection element 52) ​​and the output value of the tertiary light (the value corresponding to the detection result of the third detection element 53) from the detection result (detection intensity) of the first detection element 51. By using the primary, secondary, and tertiary light in this way, the measurable wavelength range can be widened. In actual calculations, the value obtained by multiplying the detection result (detection intensity) of each detection element by the sensitivity at that wavelength (value corresponding to the detection result) is used. In other words, calculations are performed taking into account the sensitivity ratio of each detection element at that wavelength.

[0056] FIG. 9 is a graph showing an example of measurement results. In this example, the results were compared when the measurement light L1 was transmitted through a polystyrene film and when it was not. The measurement light L1 was light from a tungsten lamp, and a high-pass filter was used to cut off wavelengths below 1.45 μm. The two upper graphs G1 and G2 in FIG. 9 show the results (reference data) when the measurement light L1 was not transmitted through the polystyrene film. The two lower graphs G3 and G4 in FIG. 9 show the results (sample data) when the measurement light L1 was transmitted through the polystyrene film. The graphs G1 and G3 show the acquired data, and the graphs G2 and G4 show the spectral data calculated based on the acquired data. A comparison of the graphs G2 and G4 reveals that when the measurement light L1 was transmitted through the polystyrene film, the intensity decreased in the wavelength range of approximately 3300 to 3500 nm, indicating that the measurement light L1 was absorbed by the polystyrene film in this wavelength range.

[0057] Fig. 10 is a graph showing the measurement results of Fig. 9 together with the measurement results by FTIR (Fourier Transform Infrared Spectroscopy). Fig. 10 shows that spectrometer 1 can perform spectroscopic measurement with high accuracy over a wavelength range as wide as that of FTIR.

[0058] Referring again to FIG. 7 , the arrangement of the first detection element 51, the second detection element 52, and the third detection element 53 in the first photodetector 10 will be described. In FIG. 7 , the outer edge of the base of the CAN package 55 ( FIG. 1 ) on which the detection elements 51 to 53 are mounted is indicated by the symbol B. In the example of FIG. 7( a), the first detection element 51, the second detection element 52, and the third detection element 53 are aligned along the wavelength dispersion direction DR of the diffracted light L2 at the incident position on the first photodetector 10. In the example of FIG. 7( b), the first detection element 51, the second detection element 52, and the third detection element 53 are aligned along a direction perpendicular to the wavelength dispersion direction DR. The wavelength dispersion direction DR is the direction in which the diffracted light L2 is dispersed, and the diffracted light L2 dispersed along the wavelength dispersion direction DR is incident on the first photodetector 10. As shown in FIG. 7 , the diffracted light L2 is observed as a rainbow strip on the first photodetector 10. This rainbow band moves along the wavelength dispersion direction DR in response to the rotation of the movable portion 22 of the mirror device 17. As a result, the wavelength of the diffracted light L2 incident on each of the detecting elements 51 to 53 changes.

[0059] In the example of FIG. 7( a), the light receiving area (length in the direction perpendicular to the wavelength dispersion direction DR) of each detection element 51-53 can be increased, thereby improving light utilization efficiency. However, because the incident wavelength varies depending on the position of the detection elements 51-53, calculation-based correction is required during measurement. Furthermore, the wavelength resolution varies depending on the position of the detection elements 51-53. That is, because the detector is optically designed to focus at the center of the base of the CAN package 55, the further away from the center, the more likely defocusing occurs, leading to a decrease in wavelength resolution. In this regard, in the example of FIG. 7( a), the distance between the detection elements 51-53 in the wavelength dispersion direction DR is set to 1 mm or less. This reduces the difference in wavelength of the diffracted light L2 incident on the detection elements 51-53, facilitating calculations based on the detection results of the detection elements 51-53. Furthermore, the difference in wavelength resolution between the detection elements 51-53 can be reduced.

[0060] In the example of FIG. 7( b), the detecting elements 51-53 are aligned in a direction perpendicular to the wavelength dispersion direction DR. This reduces (eliminates) the difference in wavelength of the diffracted light L2 incident on the detecting elements 51-53, facilitating calculations based on the detection results of the detecting elements 51-53. This also reduces (eliminates) the difference in wavelength resolution between the detecting elements 51-53. The width of the diffracted light L2 incident on the first photodetector 10 (the width in the direction perpendicular to the wavelength dispersion direction DR) is determined by the shape of the slit 3a in the slit member 3. While increasing the size of the slit 3a increases the width of the diffracted light L2 on the first photodetector 10, this also requires increasing the sizes of the first reflecting surface 24 of the mirror device 17, the focusing mirror 9, the detecting elements 51-53, and the like. Therefore, the size of the slit 3a must be appropriately set, taking into account the required S / N ratio.

[0061] Referring again to FIG. 1 , the substrate unit 11 includes a wiring board 61 and a plurality of electronic components 62 mounted on the wiring board 61. The first photodetector 10 is mounted on the wiring board 61. The plurality of electronic components 62 include, for example, a control unit 63 that controls the operation of each element of the spectrometer 1, including the mirror device 17, and a calculation unit 64 that performs predetermined calculations based on the detection results of the first photodetector 10 and the second photodetector 16. The control unit 63 and the calculation unit 64 are configured by, for example, a computer including a processor such as a CPU and a storage medium such as a RAM and a ROM. The control unit 63 and the calculation unit 64 may be configured as separate elements or as a common element. At least one of the control unit 63 and the calculation unit 64 may be provided separately from the substrate unit 11. For example, at least one of the control unit 63 and the calculation unit 64 may be configured by a computer arranged outside the spectrometer 1 and connected to the spectrometer 1 so as to be able to communicate with it. The control unit 63 and the calculation unit 64 are interchangeable, and the processing described as being performed by the control unit 63 may be performed by the calculation unit 64, and the processing described as being performed by the calculation unit 64 may be performed by the control unit 63.

[0062] The light source 12, the condenser lens 13, the ND filter 14, the cylindrical lens 15, the mirror unit 7, and the second photodetector 16 constitute a monitor optical system for monitoring the rotation angle (deflection angle) of the movable part 22 of the mirror device 17. The condenser lens 13, the ND filter 14, the cylindrical lens 15, the mirror unit 7, and the second photodetector 16 are arranged in this order on the optical path of the monitor light L3 output from the light source 12.

[0063] The light source 12 is a monitor light source that outputs monitor light L3. The light source 12 is configured, for example, by an LD (Laser Diode) or an LED (Light Emitting Diode). The center wavelength of the monitor light L3 output from the light source 12 does not overlap with the wavelength sensitivity range of the detection elements 51 to 53 of the first photodetector 10. This makes it possible to prevent the monitor light from being detected as stray light by the first photodetector 10. The monitor light L3 is, for example, light in the visible range.

[0064] The condenser lens 13 condenses the monitor light L3. The ND filter 14 reduces the amount of light of the monitor light L3. In this example, the ND filter 14 is disposed at an angle with respect to the optical axis of the monitor light L3. This suppresses the generation of stray light due to reflection on the surface of the ND filter 14. The cylindrical lens 15 diffuses the monitor light L3 into a line shape. The monitor light L3 from the cylindrical lens 15 is reflected by the second reflecting surface 25 of the movable portion 22 of the mirror device 17. Specifically, the monitor light L3 enters the through-hole 41a ( FIG. 4 ) of the fixed member 18 described above and enters the second reflecting surface 25 through the through-hole 41a. The monitor light L3 reflected by the second reflecting surface 25 travels through the through-hole 41a, exits from the through-hole 41a, and is detected by the second photodetector 16.

[0065] The second photodetector 16 is, for example, an image sensor (line sensor) made of silicon. The calculation unit 64 monitors (measures) the rotation angle of the movable part 22 based on the detection result of the second photodetector 16. In this example, the monitor light L3 diffused in a line is incident on the second reflecting surface 25 and detected by the second photodetector 16, which is an image sensor. This allows the rotation angle of the movable part 22 to be measured in real time (the rotation angle can be measured at any angle). More specifically, for example, by pre-storing angle information corresponding to each pixel number of the image sensor, the rotation angle of the movable part 22 can be determined from the pixel number at which the monitor light L3 is incident. When the monitor light L3 is incident on multiple pixels and outputs from the multiple pixels are acquired, the angle corresponding to the pixel with the maximum output may be determined as the rotation angle, or the rotation angle may be determined by calculating the average value of the outputs. When performing fixed-point measurement in which the rotation angle is measured only at one or more specific angles, the second photodetector 16 may be configured by providing one or more detection elements each having a single channel. However, from the viewpoint of monitoring the rotation angle with high accuracy and simplifying the calculation of the rotation angle, it is preferable to use an image sensor. In the above example, the calculation unit 64 monitors the rotation angle of the movable part 22 based on the detection result of the second photodetector 16. However, it is also possible to store in advance the correspondence between the pixel information (pixel number, etc.) of the image sensor constituting the second photodetector 16 and the wavelength measured by the first photodetector 10, and monitor the measured wavelength in real time based on the pixel information (without using information on the rotation angle). This makes it easier to obtain wavelength information.

[0066] The operation of the spectrometer 1 (a measurement method using the spectrometer 1) will be described. The spectrometer 1 includes a first mode (first step) and a second mode (second step) as operation modes. The processing of the first mode and the second mode is executed by the control unit 63 or the calculation unit 64. In the first mode, the mirror device 17 is driven so that the measurement light L1 from the mirror device 17 is incident on the diffraction surface 8 a of the diffraction grating 8, and a detection result of the first photodetector 10 is acquired. In the second mode, the mirror device 17 is driven so that the measurement light L1 from the mirror device 17 travels outside the diffraction surface 8 a (does not enter the diffraction surface 8 a), and a detection result of the first photodetector 10 is acquired. The first mode corresponds to normal spectroscopic measurement, and the second mode is a mode for acquiring a dark output value in a dark state in which the light to be detected is not incident on the first photodetector 10. The calculation unit 64 calculates the measurement result by subtracting the detection result of the first photodetector 10 acquired in the second mode from the detection result of the first photodetector 10 acquired in the first mode (third step). For this calculation, a value corresponding to the detection result of the first photodetector 10 (for example, a value taking into account the sensitivity at each wavelength) may be used instead of the detection result of the first photodetector 10 itself. Monitoring of the rotation angle of the movable part 22 using the monitor optical system is performed in both the first mode and the second mode.

[0067] In the first mode, as shown in FIG. 1, the measurement light L1 from the mirror device 17 is incident on the diffractive surface 8a of the diffraction grating 8. In other words, the control unit 63 controls the mirror device 17 so that the measurement light L1 is incident on the diffractive surface 8a. In the second mode, as shown in FIG. 11, the measurement light L1 from the mirror device 17 travels outside the diffractive surface 8a. In other words, the control unit 63 controls the mirror device 17 so that the measurement light L1 does not enter the diffractive surface 8a. In the second mode, the rotation angle of the movable unit 22 is larger than in the first mode. In this example, as shown in FIG. 11, the measurement light L1 travels along a predetermined optical axis P and enters the first reflecting surface 24, and is reflected by the first reflecting surface 24 so as to return along the optical axis. The measurement light L1 reflected by the first reflecting surface 24 returns along the optical path in the spectroscopic optical system and enters the slit 3a of the slit member 3. This prevents the measurement light L1 from being reflected within the spectrometer 1 and becoming stray light.

[0068] In the second mode, for example, the movable part 22 may be driven in a stepwise manner (i.e., the movable part 22 may be stopped at each rotation angle corresponding to the wavelength to be measured) to obtain a dark output value at each rotation angle. Alternatively, a driving current such as a triangular wave may be applied to the coil 26 of the mirror device 17 to continuously rotate the movable part 22, and an average output value over a predetermined time width may be obtained as the dark output value. In the former case, the dark output value at each rotation angle can be obtained with a high S / N ratio and wavelength resolution. In the latter case, dark output values ​​corresponding to multiple wavelengths can be obtained at high speed.

[0069] The order in which the first mode and the second mode are performed is not limited, and the second mode may be performed after the first mode, or vice versa. Furthermore, when measurements at multiple wavelengths are continuously performed, the detection result of the first photodetector 10 may be obtained in the second mode each time the rotation angle of the movable part 22 is changed and a detection result of the first photodetector 10 is obtained in the first mode. That is, the dark output value may be obtained in the second mode each time a measurement is performed in the first mode. Alternatively, the detection result of the first photodetector 10 may be obtained in the second mode before or after multiple detection results of the first photodetector 10 are obtained in the first mode while changing the rotation angle of the movable part 22. That is, one dark output value may be obtained in the second mode for multiple measurements in the first mode.

[0070] In the second mode, the calculation unit 64 may correct the detection result of the first photodetector 10 in the second mode based on the input signal to or the output value from the coil 26 so as to reduce the influence of heat generation in the coil 26. When the mirror device 17 is driven, heat is generated by the passage of current through the coil 26. This heat may affect the detection accuracy of the first photodetector 10. The influence of heat on the detection accuracy of the first photodetector 10 is likely to be significant when the first photodetector 10 is sensitive to the mid-infrared range. Furthermore, in the second mode, the rotation angle of the movable part 22 is larger than in the first mode, which increases the power consumption of the coil 26 and makes it more likely to generate heat. In this regard, the influence of heat generation in the coil 26 can be reduced by correcting the detection result of the first photodetector 10 in the second mode based on the input signal to or the output value from the coil 26. The input signal to the coil 26 is, for example, a current or voltage applied to the coil 26. The output value from the coil 26 is, for example, a resistance value, a voltage value, or a current value in the coil 26. These values ​​correspond to the amount of heat generated in the coil 26. In addition to or instead of the correction in the second mode, in the first mode, the calculation unit 64 may correct the detection result of the first photodetector 10 in the first mode based on the input signal to the coil 26 or the output value from the coil 26 so as to reduce the influence of heat generation in the coil 26.

[0071] In the spectrometer 1, the angle of incidence of the measurement light L1 on the diffraction surface 8a is changed by a mirror device 17 having a movable part 22 that can swing around an axis A. This allows for a more compact device compared to, for example, rotating the diffraction grating 8 using a motor. The spectrometer 1 also includes two operating modes: a first mode in which the mirror device 17 is driven so that the measurement light L1 from the mirror device 17 is incident on the diffraction surface 8a, and a second mode in which the mirror device 17 is driven so that the measurement light L1 from the mirror device 17 travels outside the diffraction surface 8a (does not enter the diffraction surface 8a). A dark output value can be obtained from the detection result of the first photodetector 10 in the second mode. For example, depending on the type of photodetector that constitutes the first photodetector 10, the dark output may be prone to fluctuations due to electrical or thermal factors. Therefore, obtaining the dark output is extremely important for achieving accurate spectroscopic measurements. By driving the mirror device 17 to switch between a state in which the measurement light L1 is incident on the diffraction surface 8a and a state in which it travels outside the diffraction surface 8a, the device can be made more compact than when a shutter is used as in Patent Document 1, for example. Furthermore, the dark output values ​​can be acquired more quickly than when a motor-driven shutter is used to acquire the dark output values ​​as in Patent Document 1, for example. Furthermore, the dark output values ​​can be acquired more quickly than when the diffraction grating 8 is rotated by a motor to acquire the dark output values. Therefore, the spectrometer 1 can be made more compact and acquire dark output values ​​more quickly.

[0072] In the second mode, the measurement light L1 that travels along the optical axis P and is incident on the first reflecting surface 24 is reflected by the first reflecting surface 24 so as to return along the optical axis P ( FIG. 11 ). This prevents the measurement light L1 that travels outside the diffractive surface 8 a in the second mode from becoming stray light due to reflection, for example, within the spectrometer 1, and thus prevents the generation of stray light when acquiring dark output values.

[0073] The mirror device 17 is fixed to a fixing member 18, the mirror device 17 has a coil 26 for generating a driving force that oscillates the movable part 22, and the fixing member 18 is made of a metal material. When the mirror device 17 has the coil 26, heat generated in the coil 26 may affect the detection accuracy of the first photodetector 10. In this regard, in the spectrometer 1, the fixing member 18 is made of a metal material, so that the heat generated in the mirror device 17 can be efficiently dissipated to the outside of the spectrometer via the fixing member 18 and the base member to which the fixing member 18 is fixed, and a decrease in the detection accuracy of the first photodetector 10 can be suppressed.

[0074] The spectrometer 1 includes a light source 12 (monitoring light source) that outputs monitor light L3 and a second photodetector 16 that detects the monitor light L3. A mirror device 17 has a second reflecting surface 25 provided on the movable part 22 on the back side opposite to the front side on which the first reflecting surface 24 is provided. A through hole 41a is formed in a fixed member 18, and the mirror device 17 is fixed to the fixed member 18 so that the second reflecting surface 25 faces the through hole 41a. The monitor light L3 output from the light source 12 is incident on the second reflecting surface 25 through the through hole 41a, reflected by the second reflecting surface 25, and detected by the second photodetector 16 through the through hole 41a. This allows the rotation angle of the movable part 22 to be monitored with high accuracy based on the detection result of the second photodetector 16. Furthermore, the through hole 41a formed in the fixing member 18 functions as an aperture for the monitor light L3, thereby preventing the monitor light L3 from the light source 12 from entering the first photodetector 10 as stray light.

[0075] The through-hole 41a is tapered so that its width narrows as it approaches the mirror device 17. This makes it difficult for the monitor light L3 from the light source 12 to leak toward the surface side of the movable part 22, and prevents the monitor light L3 from entering the first photodetector 10 as stray light. Furthermore, the monitor light L3 can be incident on the second reflecting surface 25 at an angle, and vignetting of the detection result of the second photodetector 16 is less likely to occur. In other words, it is possible to prevent the monitor light L3 that enters the second reflecting surface 25 through the through-hole 41a and the monitor light L3 that is reflected by the second reflecting surface 25 and travels toward the second photodetector 16 through the through-hole 41a from being blocked by the fixing member 18.

[0076] The opening width W1 of the through-hole 41a on the mirror device 17 side is narrower than the width W2 of the movable part 22 of the mirror device 17. This makes it difficult for the monitor light L3 from the light source 12 to leak onto the surface side of the movable part 22, and makes it possible to prevent the monitor light L3 from entering the first photodetector 10 as stray light.

[0077] The first photodetector 10 includes a first detection element 51, a second detection element 52, and a third detection element 53, which have different wavelength sensitivity ranges, thereby widening the measurable wavelength range.

[0078] 7A, the detection elements 51 to 53 are aligned along the wavelength dispersion direction DR of the diffracted light L2 at the incident position on the first photodetector 10. In this case, a larger light receiving area can be ensured and the light utilization efficiency can be increased compared to, for example, a case in which the detection elements 51 to 53 are aligned along a direction perpendicular to the wavelength dispersion direction DR.

[0079] In the example of FIG. 7( a), the distance between the detecting elements 51 to 53 may be 1 mm or less. In this case, the difference in wavelength resolution between the detecting elements 51 to 53 can be reduced. Furthermore, the difference in wavelength of the diffracted light L2 incident on the detecting elements 51 to 53 can be reduced, making it possible to facilitate calculations based on the detection results of the detecting elements 51 to 53. In the example of FIG. 7( b), the distance between the detecting elements 51 to 53 may be 1 mm or less. In this case, the dead space between the detecting elements 51 and 52 and between the detecting elements 52 and 53 can be reduced, thereby increasing the light utilization efficiency.

[0080] 7B, the detecting elements 51 to 53 are aligned in a direction perpendicular to the wavelength dispersion direction DR of the diffracted light L2 at the incident position on the first photodetector 10. In this case, the difference in wavelength resolution between the detecting elements 51 to 53 can be made smaller than when the detecting elements 51 to 53 are aligned along the wavelength dispersion direction DR. Furthermore, the difference in wavelength of the diffracted light L2 incident on the detecting elements 51 to 53 can be made smaller, which makes it easier to perform calculations based on the detection results of the detecting elements 51 to 53.

[0081] The calculation unit 64 subtracts the value corresponding to the detection result of the first photodetector 10 acquired in the second mode from the value corresponding to the detection result of the first photodetector 10 acquired in the first mode. In this way, by subtracting the dark output value acquired in the second mode from the output value acquired in the first mode, it is possible to perform measurement taking the dark output value into consideration.

[0082] The first photodetector 10 includes a first detection element 51 having sensitivity in a wavelength range corresponding to the first-, second-, and third-order diffracted light L2, a second detection element having sensitivity in a wavelength range corresponding to the second- and third-order diffracted light L2, and a third detection element having sensitivity in a wavelength range corresponding to the third-order diffracted light L2. The calculation unit 64 calculates the output value of the first-order diffracted light L2 by subtracting a value corresponding to the detection result of the second detection element 52 and a value corresponding to the detection result of the third detection element 53 from a value corresponding to the detection result of the first detection element 51. This allows the output value of the first-order diffracted light L2 to be calculated with high accuracy. The calculation unit 64 also calculates the output value of the second-order diffracted light L2 by subtracting a value corresponding to the detection result of the third detection element 53 from a value corresponding to the detection result of the second detection element 52. This allows the output value of the second-order diffracted light L2 to be calculated with high accuracy.

[0083] The calculation unit 64 corrects the detection result of the first photodetector 10 in the second mode based on the input signal to the coil 26 or the output value from the coil 26. In the second mode, the rotation angle of the movable part 22 is larger than in the first mode, so that the power consumption in the coil 26 increases and heat is more likely to be generated. In this regard, the spectrometer 1 can correct the detection result of the first photodetector 10 in the second mode based on the input signal to the coil 26 or the output value from the coil 26 so as to reduce the influence of heat generation in the coil 26.

[0084] The detection result of the first photodetector 10 may be acquired in the second mode each time the rotation angle of the movable part 22 is changed and a detection result of the first photodetector 10 is acquired in the first mode. In this case, since the dark output value is acquired each time the rotation angle of the movable part 22 is changed, accurate measurement can be performed even if the dark output value is prone to change, for example.

[0085] Alternatively, the detection result of the first photodetector 10 may be obtained in the second mode before or after the detection result of the first photodetector 10 is obtained multiple times in the first mode while changing the rotation angle of the movable part 22. In this case, the dark output value is obtained once for multiple measurements, thereby shortening the measurement time.

[0086] The present disclosure is not limited to the above-described embodiments. For example, the materials and shapes of the components are not limited to those described above, and various materials and shapes can be adopted.

[0087] In the second mode of the above embodiment, the measurement light L1 is reflected by the first reflecting surface 24 so as to return along the optical axis P. However, the propagation direction of the measurement light L1 from the mirror device 17 is not limited as long as the measurement light L1 travels outside the diffraction surface 8a. For example, the measurement light L1 from the mirror device 17 may be incident on the non-diffraction region 8c of the diffraction grating 8. However, in this case, the measurement light L1 reflected by the non-diffraction region 8c may be incident on the first photodetector 10 as stray light, so it is preferable that the measurement light L1 travel outside the diffraction grating 8.

[0088] In the above embodiment, the driving element for generating a driving force that causes the movable portion 22 to swing is the coil 26. However, this is not limited to this, and may be, for example, a piezoelectric element. In this case, the piezoelectric element may be provided, for example, in the connecting portion 23. In the above embodiment, the through hole 41a formed in the fixed member 18 is tapered. However, the width of the through hole 41a may be uniform along the Z direction. In the above embodiment, the through hole 41a is tapered in all cross sections parallel to the Z direction. However, it is sufficient that the through hole 41a is tapered in a cross section passing through the center of the through hole 41a and parallel to the X direction (a direction parallel to the axis A), and the through hole 41a does not have to be tapered in a cross section passing through the center of the through hole 41a and parallel to the Y direction. The opening width W1 of the through hole 41a may be equal to or greater than the width W2 of the movable portion 22. In the above embodiment, two magnets 19 are disposed. However, four magnets 19 may be disposed. In this case, the additional two magnets 19 may be disposed so as to sandwich the mirror device 17 in the Y direction. The distance between the detecting elements 51 to 53 in the wavelength dispersion direction DR may be greater than 1 mm.

[0089] In the above embodiment, the output value of the first-order diffracted light L2 is calculated by subtracting the value corresponding to the detection result of the second detection element 52 and the value corresponding to the detection result of the third detection element 53 from the value corresponding to the detection result of the first detection element 51. However, the output value of the first-order diffracted light L2 may be calculated by subtracting only the value corresponding to the detection result of the second detection element 52 from the value corresponding to the detection result of the first detection element 51. The first photodetector 10 may not have the third detection element 53. That is, although the first-order light, the second-order light, and the third-order light are used in the above embodiment, only the first-order light and the second-order light may be used. Alternatively, the second detection element 52 and the third detection element 53 may be omitted, and only the first-order light may be used. The process of correcting the detection result of the first photodetector 10 in the second mode based on the input signal to the coil 26 or the output value from the coil 26 may not be performed.

[0090] The primary light, secondary light, and tertiary light in the above embodiment may be replaced with -primary light, -secondary light, and -tertiary light. That is, in the above embodiment, the first detection element 51 is sensitive to the primary light, secondary light, and tertiary light, the second detection element 52 is sensitive to the secondary light and tertiary light, and the third detection element 53 is sensitive to the tertiary light, and the calculation unit 64 calculates the output value of the secondary light by subtracting the detection result of the third detection element 53 from the detection result of the second detection element 52, and calculates the output value of the primary light by subtracting the detection results of the second detection element 52 and the third detection element 53 from the detection result of the first detection element 51. However, the first detection element 51 may be sensitive to −1st order light, −2nd order light, and −3rd order light, the second detection element 52 may be sensitive to −2nd order light and −3rd order light, and the third detection element 53 may be sensitive to −3rd order light. The calculation unit 64 may calculate the output value of −2nd order light by subtracting the detection result of the third detection element 53 from the detection result of the second detection element 52, and calculate the output value of −1st order light by subtracting the detection results of the second detection element 52 and the third detection element 53 from the detection result of the first detection element 51. The first detection element 51 may be sensitive to a wavelength range corresponding to the nth order (n is an integer greater than or equal to 1) and (n+1)th order diffracted light L2, and the second detection element 52 may be sensitive to a wavelength range corresponding to the (n+1)th order diffracted light. In the above embodiment, n is 1. n may be 2 or greater. For example, when n is 2, second order light and third order light are used. The first detection element 51 may be sensitive to a wavelength range corresponding to the m-th order (m is an integer equal to or less than -1) and (m-1)-th order diffracted light L2, and the second detection element 52 may be sensitive to a wavelength range corresponding to the (m-1)-th order diffracted light. In the above modification, m is -1. m may also be -2 or less. For example, when m is -2, -2nd order light and -3rd order light are used.

[0091] The first photodetector 10 may have only one detection element. In this case, the spectrometer 1 is configured as a monochromator-type spectrometer that separates and detects only light of a specific wavelength from the measurement light L1. Even when the multiple detection elements 51-53 of the first photodetector 10 are aligned along a direction perpendicular to the wavelength dispersion direction DR, as shown in FIG. 7( b), the spectrometer 1 is also a monochromator-type spectrometer. On the other hand, when the multiple detection elements 51-53 of the first photodetector 10 are aligned along the wavelength dispersion direction DR, as shown in FIG. 7( a), the incident wavelengths of the detection elements 51-53 vary slightly depending on the positions of the detection elements 51-53. In this case, the spectrometer 1 can be considered either a monochromator-type spectrometer or a polychromator-type spectrometer that separates and detects light of multiple wavelengths from the measurement light L1.

[0092] 1...spectroscope, 8...diffraction grating, 8a...diffraction surface, 10...first photodetector, 12...light source (monitoring light source), 16...second photodetector, 17...mirror device, 18...fixed member, 21...support portion, 22...movable portion, 23...connecting portion, 24...first reflecting surface, 25...second reflecting surface, 26...coil (driving element), 41a...through hole (Figure 4), 51...first detecting element, 52...second detecting element, 64...calculating portion, A...axis, DR...wavelength dispersion direction, L1...measurement light, L2...diffracted light, L3...monitor light, W1...aperture width, W2...width.

Claims

1. A spectroscope comprising: a support portion; a movable portion; a connecting portion that connects the movable portion to the support portion such that the movable portion can swing around a predetermined axis; a first reflecting surface provided on the movable portion; a mirror device that reflects measurement light by the first reflecting surface at an angle corresponding to a rotation angle of the movable portion around the axis; a diffraction grating having a diffraction surface that outputs diffracted light dispersed according to a wavelength when the measurement light from the mirror device is incident on the diffraction surface; and a first photodetector that detects the diffracted light output from the diffraction grating, wherein an incident angle of the measurement light on the diffraction surface changes according to a rotation angle of the movable portion, and a wavelength of the diffracted light detected by the first photodetector changes according to the incident angle of the measurement light on the diffraction surface, and as an operation mode, a first mode of acquiring a detection result of the first photodetector in a state where the mirror device is driven so that the measurement light from the mirror device is incident on the diffraction surface, and a second mode of acquiring a detection result of the first photodetector in a state where the mirror device is driven so that the measurement light from the mirror device travels outside the diffraction surface.

2. The spectroscope according to claim 1, wherein in the second mode, the measurement light that travels along a predetermined optical axis and is incident on the first reflecting surface is reflected by the first reflecting surface so as to return along the optical axis.

3. The spectroscope according to claim 1 or 2, further comprising a fixing member to which the mirror device is fixed, wherein the mirror device further has a driving element for generating a driving force for swinging the movable portion, and the fixing member is formed of a metal material.

4. The spectroscopic device further comprises a fixing member to which the mirror device is fixed, a monitor light source that outputs monitor light, and a second photodetector that detects the monitor light. The mirror device further has a second reflection surface provided on the movable portion on the back side opposite to the front side where the first reflection surface is provided. A through hole is formed in the fixing member. The mirror device is fixed to the fixing member such that the second reflection surface faces the through hole. The monitor light output from the monitor light source is incident on the second reflection surface through the through hole, reflected by the second reflection surface, and detected by the second photodetector through the through hole. The spectroscopic device according to any one of claims 1 to 3.

5. The spectroscopic device according to claim 4, wherein the through hole is formed in a tapered shape such that the width becomes narrower as it approaches the mirror device.

6. The spectroscopic device according to claim 4 or 5, wherein the opening width of the through hole on the side of the mirror device is narrower than the width of the movable portion of the mirror device.

7. The spectroscopic device according to any one of claims 1 to 6, wherein the first photodetector includes a plurality of detection elements having mutually different sensitivity wavelength ranges.

8. The spectroscopic device according to claim 7, wherein the plurality of detection elements are arranged along the wavelength dispersion direction of the diffracted light at the incident position on the first photodetector.

9. The spectroscopic device according to claim 8, wherein the distance between the plurality of detection elements is 1 mm or less.

10. The spectroscopic device according to claim 7, wherein the plurality of detection elements are arranged along a direction perpendicular to the wavelength dispersion direction of the diffracted light at the incident position on the first photodetector.

11. The spectroscopic device further comprises an arithmetic unit that receives the detection result of the first photodetector. The arithmetic unit subtracts the value corresponding to the detection result of the first photodetector obtained in the second mode from the value corresponding to the detection result of the first photodetector obtained in the first mode. The spectroscopic device according to any one of claims 1 to 10.

12. The spectroscopic apparatus according to any one of claims 1 to 11, further comprising an arithmetic unit that receives the detection result of the first photodetector, wherein the first photodetector includes a first detection element and a second detection element, and (1) the first detection element has sensitivity in a wavelength range corresponding to the n-th order (n is an integer of 1 or more) and (n + 1)-th order diffracted light, the second detection element has sensitivity in a wavelength range corresponding to the (n + 1)-th order diffracted light, and the arithmetic unit calculates the output value of the n-th order diffracted light by subtracting the value corresponding to the detection result of the second detection element from the value corresponding to the detection result of the first detection element, or (2) the first detection element has sensitivity in a wavelength range corresponding to the m-th order (m is an integer of -1 or less) and (m - 1)-th order diffracted light, the second detection element has sensitivity in a wavelength range corresponding to the (m - 1)-th order diffracted light, and the arithmetic unit calculates the output value of the m-th order diffracted light by subtracting the value corresponding to the detection result of the second detection element from the value corresponding to the detection result of the first detection element.

13. The spectroscopic apparatus according to any one of claims 1 to 12, further comprising an arithmetic unit that receives the detection result of the first photodetector, wherein the mirror device further includes a driving element for generating a driving force for swinging the movable part, and the arithmetic unit corrects the detection result of the first photodetector in the second mode based on an input signal to the driving element or an output value from the driving element.

14. The spectroscopic apparatus according to any one of claims 1 to 13, wherein the detection result of the first photodetector in the second mode is obtained each time the rotation angle of the movable part is changed to obtain the detection result of the first photodetector in the first mode.

15. The spectroscopic apparatus according to any one of claims 1 to 13, wherein the detection result of the first photodetector in the second mode is obtained before or after the detection result of the first photodetector in the first mode is obtained a plurality of times while changing the rotation angle of the movable part.

16. A measurement method using a spectroscope, wherein the spectroscope includes a support portion, a movable portion, a connecting portion that connects the movable portion to the support portion so that the movable portion can swing around a predetermined axis, a first reflecting surface provided on the movable portion, a mirror device that reflects measurement light by the first reflecting surface at an angle corresponding to the rotation angle of the movable portion around the axis, a diffraction grating that has a diffraction surface and outputs diffracted light dispersed according to a wavelength when the measurement light from the mirror device is incident on the diffraction surface, and a first photodetector that detects the diffracted light output from the diffraction grating, the incident angle of the measurement light on the diffraction surface changes according to the rotation angle of the movable portion, and the wavelength of the diffracted light detected by the first photodetector changes according to the incident angle of the measurement light on the diffraction surface, and the measurement method includes a first step of obtaining a detection result of the first photodetector in a state where the mirror device is driven so that the measurement light from the mirror device is incident on the diffraction surface, and a second step of obtaining a detection result of the first photodetector in a state where the mirror device is driven so that the measurement light from the mirror device travels outside the diffraction surface.

17. The measurement method according to claim 16, further comprising a third step of subtracting a value corresponding to the detection result of the first photodetector obtained in the second step from a value corresponding to the detection result of the first photodetector obtained in the first step.

18. The first photodetector includes a first detection element and a second detection element. (1) The first detection element has sensitivity in a wavelength range corresponding to the n-th (n is an integer of 1 or more) and (n + 1)-th diffracted lights, and the second detection element has sensitivity in a wavelength range corresponding to the (n + 1)-th diffracted light. In the measurement method, the output value of the n-th diffracted light is calculated by subtracting the value corresponding to the detection result of the second detection element from the value corresponding to the detection result of the first detection element, or (2) the first detection element has sensitivity in a wavelength range corresponding to the m-th (m is an integer of -1 or less) and (m - 1)-th diffracted lights, and the second detection element has sensitivity in a wavelength range corresponding to the (m - 1)-th diffracted light. In the measurement method, the output value of the m-th diffracted light is calculated by subtracting the value corresponding to the detection result of the second detection element from the value corresponding to the detection result of the first detection element. The measurement method according to claim 16 or 17.

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