JP6656914B2 - Detector, interrogator, and strain detection system - Google Patents

Description

  The present invention relates to a detection device and an interrogator for a fiber Bragg grating (FBG) sensor, and a strain detection system including the FBG sensor.

  An FBG sensor is known as one of optical fiber sensors that detect changes in temperature and strain using light. The FBG sensor has a cylindrical core and a fiber Bragg grating formed on a part of the core. In a fiber Bragg grating, the refractive index of the core changes periodically in the axial direction of the core.

  Of the light that has entered the core of the FBG sensor from one side in the axial direction, light having a predetermined wavelength (center wavelength) is reflected by the fiber Bragg grating to be return light, and light having other wavelength components is reflected by the fiber Bragg grating. pass. When strain or temperature change occurs in the FBG sensor, the period of the fiber Bragg grating changes, and the wavelength of the return light reflected by the fiber Bragg grating shifts from the center wavelength. Therefore, a change in temperature or strain generated in the FBG sensor can be detected by inputting broadband light to the FBG sensor and measuring a shift amount of the wavelength of the return light from the center wavelength.

  In addition, a plurality of FBG sensors having different center wavelengths are incorporated in series in one optical fiber, and changes in temperature and strain at a plurality of positions are detected through one optical fiber. . Specifically, the FBG sensor is, for example, an intrusion detection system that detects overbreaks or illegal intrusions of airports, ports, plants, etc., a water level monitoring system that monitors the water level of dams, rivers, sewers, etc. in real time, It is used for pressure measurement systems for space.

  Patent Document 1 discloses that a reflected light from an FBG sensor is separated into a transmitted light and a reflected light by a fiber-shaped optical filter for strain measurement, and a return light is divided based on a sum and a difference between the transmitted light intensity and the reflected light intensity. An FBG sensing device for obtaining a wavelength is disclosed. Patent Literature 2 shows an example of multi-point measurement using a plurality of FBG sensors connected in series.

JP 2005-326326 A JP-A-2002-267537

  It is desirable that the detection device for analyzing the return light from the FBG sensor be compact. In particular, since a detection device for analyzing return light from a plurality of FBG sensors has a complicated configuration and tends to be large, it is desired that the detection device has a compact configuration.

  An object of the present invention is to provide a compact detection device for detecting the wavelength of the return light from the FBG sensor, and an interrogator and a strain detection system including the detection device.

According to a first aspect of the present invention,
A detection device for respectively detecting the wavelengths of a plurality of return lights from a plurality of FBG sensors arranged in series in an optical fiber,
A beam splitter that divides the plurality of return lights into a plurality of light beams,
A plurality of light separation surfaces each of which separates each of the plurality of light beams into transmitted light and reflected light, and a plurality of reflection surfaces each of which reflects the transmitted light or the reflected light and makes the transmitted light and the reflected light substantially parallel to each other; And the prism of
A plurality of transmitted light receiving units that respectively receive the transmitted light from the plurality of prisms,
A plurality of reflected light receiving units that respectively receive the reflected light from the plurality of prisms,
A detection device is provided in which the transmittance of the light separating surface of the plurality of prisms changes in regions having different wavelength widths.

  In the detection device according to the first aspect, a pair of transmissions that receive a pair of the transmitted light and the reflected light from each of the plurality of prisms among the plurality of transmitted light receiving units and the plurality of reflected light receiving units. The light receiving unit and the reflected light receiving unit may be respectively arranged on the same plane.

  In the detection device according to the first aspect, the pair of transmitted light receiving units and reflected light receiving units may be defined on a single light receiving surface of a single photodetector.

  In the detection device according to the first aspect, a dielectric multilayer film may be provided on each of the light separating surfaces of the plurality of prisms, and a change in transmittance of each of the light separating surfaces may be linear. Good.

  In the detection device according to the first aspect, the plurality of prisms may be integrally joined.

  In the detection device according to the first aspect, the beam splitter may include a wavelength division surface, and the plurality of return lights may be wavelength-divided into a plurality of light beams.

  The detection device according to the first aspect may further include a polarization separation surface that separates the plurality of return lights into P-polarized light and S-polarized light, and that enters the P-polarized light into the beam splitter.

  In the detection device according to the first aspect, the polarization separation surface may be formed in a prism, the beam splitter may be formed as a prism, and the beam splitter and the polarization separation surface are formed. The prism, the plurality of prisms, the plurality of transmitted light receiving units, and the plurality of reflected light receiving units may be integrally joined.

According to a second aspect of the present invention,
A light source for irradiating the FBG sensor with broadband light;
A detection device according to the first aspect,
An interrogator is provided, comprising: a plurality of transmitted light receiving units; and a calculating unit that calculates respective wavelengths of the plurality of return lights based on detection signals from the plurality of reflected light receiving units.

According to a third aspect of the present invention,
A detection device for detecting the wavelength of the return light from the FBG sensor,
A light separating surface for separating the return light into transmitted light and reflected light,
A reflecting surface that reflects one of the transmitted light or the reflected light to make the transmitted light and the reflected light substantially parallel,
A transmitted light receiving unit that receives the transmitted light from the light separation surface,
A reflected light receiving unit that receives the reflected light from the light separation surface,
A detection device is provided in which the transmittance of the light separation surface changes in a region of a predetermined wavelength width.

  In the detection device according to a third aspect, the transmitted light receiving unit and the reflected light receiving unit may be arranged on the same plane.

  In the detection device according to the third aspect, the transmitted light receiving unit and the reflected light receiving unit may be defined on a single light receiving surface of a single photodetector.

  In the detection device according to the third aspect, the light separation surface and the reflection surface may be defined in the same prism.

According to a fourth aspect of the present invention,
A light source for irradiating the FBG sensor with broadband light;
A detection device according to a third aspect,
There is provided an interrogator including: the transmitted light receiving unit; and a calculating unit that calculates a wavelength of the return light based on a detection signal from the reflected light receiving unit.

  In the interrogator according to the second aspect or the fourth aspect, the calculation unit may obtain a strain amount of the FGB sensor based on the calculation result.

According to a fifth aspect of the present invention,
An FBG sensor,
A strain detection system comprising the interrogator of the second aspect or the fourth aspect is provided.

  According to the present invention, there is provided a compact detection device for detecting the wavelength of return light from the FBG sensor, and an interrogator and a strain detection system including the detection device.

FIG. 1 is a block diagram showing a configuration of an interrogator according to the embodiment of the present invention. FIG. 2 is a schematic perspective view illustrating a configuration of a detection device for an FBG sensor according to the embodiment of the present invention. FIG. 3 is a side view of the detection device of FIG. FIG. 4 is a plan view of the detection device of FIG. FIG. 5 is an explanatory diagram for explaining the operation of the FBG sensor. FIG. 6 is a graph showing how the return light from the FBG sensor shifts from the center wavelength. FIGS. 7A to 7C are graphs showing changes in the transmittance of the optical filter for P-polarized broadband light. FIG. 8 is a graph showing a change in transmittance of the optical filter for unpolarized broadband light. FIG. 9 is a schematic perspective view showing a configuration of a detection device for an FBG sensor according to a modification of the present invention.

<Embodiment>
An interrogator according to an embodiment of the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the interrogator 100 of the present embodiment mainly includes a light source 10, a coupler 20, a detection unit (detection device) 30, and a calculation unit 40.

  The light source 10 is a swept laser or a broadband light source that covers the wavelength range of the swept laser, and is not limited, but irradiates light having a wavelength of about 1520 nm to about 1580 nm in the present embodiment.

  The coupler 20 is a 1 × 2 coupler in which two optical fibers are fused, and has a first end connected to the light source 10 via the optical fiber OF1, and a third end connected to the detection unit via the optical fiber OF3. 30. Further, a plurality of FBG sensors 201, 202, and 203 are incorporated in series in the optical fiber OF2 extending from the second end.

  The coupler 20 sends light from the light source 10 to the FBG sensors 201, 202, and 203, and sends return light from each of the FBG sensors 201, 202, and 203 superimposed in the optical fiber OF2 to the detection unit 30. As the coupler 20, a commercially available optical fiber coupler can be used.

  As shown in FIGS. 2, 3, and 4, the detection unit 30 is incident on the detection unit 30 via the ferrule 31 connecting the optical fiber OF3 and the optical fiber 31a of the detection unit 30, and the ferrule 31 and the optical fiber 31a. A polarizing prism 32 for separating the polarized light into P-polarized light and S-polarized light; a beam splitter 33 for separating (dividing) the P-polarized light from the polarizing prism 32 into three lights belonging to different wavelength bands; It mainly includes a filter prism 34 that separates each of the three light beams into transmitted light and reflected light and emits them in parallel. The detection unit 30 further includes a first photodetector PD1, a second photodetector PD2, and a third photodetector PD3 that receive each of the three pairs of parallel lights emitted from the filter prism. In this embodiment, photodiodes are used for the first photodetector PD1, the second photodetector PD2, and the third photodetector PD3.

  Hereinafter, the traveling direction of the light emitted from the optical fiber 31a is referred to as “the optical axis direction of the detection unit” or simply “the optical axis direction”.

  The polarizing prism 32 is a polarizing beam splitter that separates outgoing light from the optical fiber 31a into P-polarized light and S-polarized light. In the present embodiment, two right angle prisms are combined with a polarizing film 32f functioning as a polarizing filter interposed therebetween. It is a cube-shaped prism. The joining surface of the two right-angle prisms with the polarizing film 32f interposed therebetween is a polarization splitting surface.

  The polarizing film 32f of the polarizing prism 32 is provided along the vertical direction so as to be located at an angle of 45 ° with respect to the optical axis direction of the detection unit 30. As a result, light emitted from the optical fiber 31a is incident on the polarizing film 32f at an incident angle of 45 °, passes through the polarizing film 32f and travels in the optical axis direction, and is reflected by the polarizing film 32f. It is separated into S-polarized light traveling in the horizontal direction orthogonal to the optical axis direction (see FIGS. 2 and 4).

The beam splitter 33 separates the P-polarized light emitted from the polarizing prism 32 into light having a wavelength of less than about 1540 nm, light having a wavelength of about 1540 nm or more, less than about 1560 nm, and light having a wavelength of about 1560 nm or more. In the present embodiment, the beam splitter 33 is a compound prism composed of one right-angle prism and two parallelogram prisms, and a right-angle prism P _{REC is provided on} one of a pair of side surfaces of the first parallelogram prism P _PAL 1. Is joined to the other side surface of the second parallelogram prism _PPAL2 . The right-angle prism _{P REC} and bonding surface of the first parallelogram prism _{P PAL} 1 (wavelength division surface), a first film 33f1 that functions as a low-pass filter that transmits light having a wavelength less than about 1540nm is interposed . A second film functioning as a high-pass filter that transmits light having a wavelength of about 1560 nm or more is provided on a bonding surface (wavelength dividing surface) between the first parallelogram prism P _PAL 1 and the second parallelogram prism P _PAL 2. 33f2 is interposed. Bonding surface which faces the second parallelogram prism _{P PAL} 2 is a reflective surface 33r.

  The first film 33f1 of the beam splitter 33 is provided along the horizontal direction so as to be located at an angle of 45 ° with respect to the optical axis direction of the detection unit 30. Further, the second film 33f2 and the reflection surface 33r are provided in parallel with the first film 33f1.

  The P-polarized light emitted from the polarizing prism 32 enters the first film 33f1 at an incident angle of 45 °, passes through the first film 33f1, travels in the optical axis direction, and is reflected by the first film 33f1. The light is then separated into reflected light that travels in the vertical direction perpendicular to the optical axis direction. Since the first film 33f1 transmits light having a wavelength of less than about 1540 nm, the wavelength band of transmitted light is less than about 1540 nm, and the wavelength band of reflected light is about 1540 nm or more.

  The reflected light reflected by the first film 33f1 is incident on the second film 33f2 at an incident angle of 45 °, is reflected by the second film 33f2 and travels in the optical axis direction, and is reflected by the second film 33f2. It is separated into transmitted light that passes through and travels in the vertical direction. Since the second film 33f2 transmits light having a wavelength of about 1560 nm or more and reflects light having a wavelength of about 1560 nm or less, the wavelength band of the reflected light is about 1540 nm or more and less than about 1560 nm, and the wavelength band of the transmitted light is about 1560 nm. That is all.

  The transmitted light that has passed through the second film 33f2 is totally reflected by the reflection surface 33r and travels in the optical axis direction.

  The filter prism 34 includes three parallel P-polarized lights emitted from the beam splitter 33 in the optical axis direction, that is, P-polarized light having a wavelength of less than about 1540 nm, P-polarized light having a wavelength of about 1540 nm or more, and a wavelength of about 1560 nm and a wavelength of about 1560 nm. Each of the above P-polarized light is separated into transmitted light and reflected light.

  As will be described later in detail, in this embodiment, the return light from the FBG sensor 201 is P-polarized light having a wavelength of less than about 1540 nm, and the return light from the FBG sensor 202 is P-polarized light having a wavelength of about 1540 nm or more and less than about 1560 nm. The return light from 203 belongs to P-polarized light having a wavelength of about 1560 nm or more.

  The filter prism 34 is a composite prism in which three prism pairs PP1, PP2, and PP3 each including one right-angle prism and one parallelogram prism are joined. The prism pair PP1 has a structure in which an inclined surface of a right-angle prism and one of a pair of side surfaces of a parallelogram prism are joined, and a dielectric multilayer film 34f1 is interposed on the joining surface. The other of the pair of side surfaces of the parallelogram prism is a reflection surface 34r1.

  Similarly, the prism pair PP2, PP3 has a structure in which the inclined surface of the right-angle prism and one of the pair of side surfaces of the parallelogram prism are joined, and the joining surfaces are interposed with the dielectric multilayer films 34f2, 34f3. The other of the pair of side surfaces of the parallelogram prism is a reflection surface 34r2, 34r3. The prism pairs PP1, PP2, and PP3 are joined in a row so that the dielectric multilayer films 34f1, 34f2, and 34f3 form a continuous surface, and the reflecting surfaces 34r1, 34r2, and 34r3 form a continuous surface.

The dielectric multilayer films 34f1, 34f2, 34f3 are each formed of a film material such as SiO ₂ (n = 1.46), TiO ₂ (n = 2.40), MgF ₂ (n = 1.38). These materials are formed by laminating these materials on the slope of the right-angle prism using vapor deposition, sputtering, or the like. Each of the dielectric multilayer films 34f1, 34f2, and 34f3 functions as a light separation filter. The light separation characteristics (filter characteristics) of the dielectric multilayer films 34f1, 34f2, 34f3 will be described later in detail.

  The dielectric multilayer film 34f1 of the prism pair PP1 is provided along the vertical direction so as to be located at an angle of 45 ° with respect to the optical axis direction of the detection unit 30. The P-polarized light having a wavelength of less than about 1540 nm emitted from the beam splitter 33 enters the dielectric multilayer film 34f1 at an incident angle of 45 °, transmits through the dielectric multilayer film 34f1, and travels in the optical axis direction. Is reflected by the dielectric multilayer film 34f1 and is separated into reflected light traveling in the horizontal direction orthogonal to the optical axis direction. The reflected light is totally reflected by the reflection surface 34r1 parallel to the dielectric multilayer film 34f1 and travels in the optical axis direction. That is, the transmitted light and the reflected light are emitted from the prism pair PP1 as a pair of light parallel to each other.

  The dielectric multilayer film 34f2 of the prism pair PP2 is provided along the vertical direction so as to be located at an angle of 45 ° with respect to the optical axis direction of the detection unit 30. The P-polarized light having a wavelength of about 1540 nm or more and less than about 1560 nm emitted from the beam splitter 33 is incident on the dielectric multilayer film 34f2 at an incident angle of 45 °, passes through the dielectric multilayer film 34f2, and travels in the optical axis direction. The transmitted light is separated into reflected light that travels in the horizontal direction orthogonal to the optical axis direction after being reflected by the dielectric multilayer film 34f2. The reflected light is totally reflected by the reflecting surface 34r2 parallel to the dielectric multilayer film 34f2 and travels in the optical axis direction. That is, the transmitted light and the reflected light are emitted from the prism pair PP2 as a pair of light parallel to each other.

  The dielectric multilayer film 34f3 of the prism pair PP3 is provided along the vertical direction so as to be located at an angle of 45 ° with respect to the optical axis direction of the detection unit 30. The P-polarized light having a wavelength of about 1560 nm or more emitted from the beam splitter 33 enters the dielectric multilayer film 34f3 at an incident angle of 45 °, transmits through the dielectric multilayer film 34f3, and travels in the optical axis direction. Is reflected by the dielectric multilayer film 34f3 and is separated into reflected light traveling in the horizontal direction orthogonal to the optical axis direction. The reflected light is totally reflected by the reflecting surface 34r3 parallel to the dielectric multilayer film 34f3 and travels in the optical axis direction. That is, the transmitted light and the reflected light are emitted from the prism pair PP3 as a pair of light parallel to each other.

  The first photodetector PD1 is disposed such that the light receiving surface DS1 (FIGS. 3 and 4) is orthogonal to the optical axis direction, and of the light emitted from the prism pair PP1 of the filter prism 34, a dielectric multilayer. The transmitted light transmitted through the film 34f1 is transmitted to the first region DS11 (transmitted light receiving portion) of the light receiving surface DS1, and the reflected light reflected by the dielectric multilayer film 34f1 and the reflecting surface 34r1 is transmitted to the second region DS12 (reflected). Light receiving portion). The pair of light beams from the prism pair PP1 are respectively condensed by a condenser lens (not shown) and enter the light receiving surface DS1.

  The second photodetector PD2 is disposed so that the light receiving surface DS2 is orthogonal to the optical axis direction, and of the light emitted from the prism pair PP2 of the filter prism 34, the transmitted light transmitted through the dielectric multilayer film 34f2. Denotes the first region DS21 (transmitted light receiving portion) of the light receiving surface DS2, and the reflected light reflected by the dielectric multilayer film 34f2 and the reflecting surface 34r2 enters the second region DS22 (reflected light receiving portion) of the light receiving surface DS2. . The pair of light beams from the prism pair PP2 are respectively condensed by a condenser lens (not shown) and enter the light receiving surface DS2.

  The third photodetector PD3 is disposed such that the light receiving surface DS3 is orthogonal to the optical axis direction, and of the light emitted from the prism pair PP3 of the filter prism 34, the transmitted light transmitted through the dielectric multilayer film 34f3. Denotes the first region DS31 (transmitted light receiving portion) of the light receiving surface DS3, and the light reflected by the dielectric multilayer film 34f3 and the reflecting surface 34r3 enters the second region DS32 (reflected light receiving portion) of the light receiving surface DS3. . The pair of light beams from the prism pair PP3 are respectively condensed by a not-shown condensing lens and enter the light receiving surface DS3.

  The first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 are arranged so that the light receiving surfaces DS1, DS2, and DS3 spread on the same plane. Further, the first regions DS11, DS21, DS31 and the second regions DS12, DS22, DS32 are on the same plane because they are defined on the same light receiving surface.

  The first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 each include a photoelectric conversion unit (not shown) for converting light energy into a current, and an IV amplifier (not shown) for converting a current into a voltage. ) Is connected to the calculation unit 40.

  The calculating unit 40 calculates the intensity of the voltage signal input from the first area DS11 of the light receiving surface DS1 of the first photodetector PD1 via the photoelectric conversion unit and the IV amplifier, and calculates the intensity of the voltage signal from the second area DS12 from the photoelectric conversion unit and the IV amplifier. The wavelength of the return light from the FBG sensor 201 is calculated by comparing with the intensity of the voltage signal input via the FBG. Similarly, the calculation unit 40 compares the intensity of the voltage signal from the first area DS21 of the light receiving surface DS2 of the second photodetector PD2 with the intensity of the voltage signal from the second area DS22, and returns from the FBG sensor 202. The wavelength of the light is calculated, the intensity of the voltage signal from the first region DS31 of the light receiving surface DS3 of the third photodetector PD3 is compared with the intensity of the voltage signal from the second region DS32, and the return from the FBG sensor 203 is performed. Calculate the wavelength of light. The calculation of the wavelength of the return light from the FBG sensors 201, 202, and 203 will be described later in detail.

  Next, a description will be given of a method of performing multi-point measurement of the distortion of the measured object using the interrogator 100 and the FBG sensors 201, 202, and 203.

  When measuring the strain generated in the measured object at a plurality of points (three points in this embodiment), first, a plurality of FBG sensors are attached to the measured object. In the present embodiment, it is assumed that three FBG sensors 201, 202, and 203 are attached. Next, the light source 10 emits broadband light having a wavelength band of about 1520 nm to about 1580 nm, and is incident on the FBG sensors 201, 202, and 203 via the optical fiber OF1, the coupler 20, and the optical fiber OF2.

  As shown in FIG. 5, each of the FBG sensors 201, 202, and 203 has an optical fiber core C having a refractive index of n, and a fiber Bragg grating portion fbg is formed in a part of the optical fiber core C. In the fiber Bragg grating portion fbg, the refractive index of the optical fiber core C periodically changes with a period length に in the axial direction of the optical fiber core C.

  As for the incident light that enters the optical fiber core C in one of the axial directions of the optical fiber core C, for example, from the left side in FIG. The light of other wavelengths returned as return light passes through the fiber Bragg grating section fbg and is sent to the right side in FIG.

  In the present embodiment, when no distortion occurs in the FBG sensor 201, the wavelength of the return light from the FBG sensor 201 is λb = 1530 nm. Further, when no distortion occurs in the FBG sensor 202, the wavelength of the return light from the FBG sensor 202 is λb = 1550 nm, and when no distortion occurs in the FBG sensor 203, the return from the FBG sensor 203 occurs. The wavelength of the light is λb = 1570 nm. Such a wavelength of the return light in a state where no distortion occurs in the FBG sensor is referred to as a center wavelength of the FBG sensor.

  In the broadband light incident on the FBG sensor 201 via the optical fiber OF2, only light having a center wavelength of 1530 nm is reflected by the fiber Bragg grating unit fbg in a state where no distortion occurs in the FBG sensor 201, and the optical fiber OF2 is returned as light. Is returned to. Light of other wavelengths passes through the fiber Bragg grating portion fbg of the FBG sensor 201. Strictly speaking, the wavelength of the return light is not only 1530 nm, but as shown by a solid line in FIG. 6, the return light is distributed with a predetermined spread on the long wavelength side and the short wavelength side with the center wavelength at 1530 nm as a peak.

  Light that has passed through the FBG sensor 201 enters the FBG sensor 202 via the optical fiber OF2. With respect to the broadband light that has entered the FBG sensor 202, only light having a center wavelength of 1550 nm is reflected by the fiber Bragg grating unit fbg of the FBG sensor 202 when no distortion occurs in the FBG sensor 202, and is returned to the optical fiber OF2 as return light. It is. Light of other wavelengths passes through the fiber Bragg grating portion fbg of the FBG sensor 202. The wavelength of the return light is not strictly limited to 1550 nm. It is distributed with a predetermined spread on the long wavelength side and the short wavelength side with a center wavelength of 1550 nm as a peak.

  Light that has passed through the FBG sensor 202 enters the FBG sensor 203 via the optical fiber OF2. With respect to the broadband light that has entered the FBG sensor 203, only light having a center wavelength of 1570 nm is reflected by the fiber Bragg grating portion fbg of the FBG sensor 203 when no distortion occurs in the FBG sensor 203, and is returned to the optical fiber OF2 as return light. It is. Light of other wavelengths passes through the fiber Bragg grating portion fbg of the FBG sensor 203. Note that the wavelength of the return light is not strictly limited to 1570 nm. It is distributed with a predetermined spread on the long wavelength side and the short wavelength side with the center wavelength of 1570 nm as a peak.

  Return light returned from each of the FBG sensors 201, 202, and 203 to the optical fiber OF2 is sent to the detection unit 30 via the coupler 20 and the optical fiber OF3 as superimposed light superimposed in the optical fiber OF2, and detected. The light is emitted from the optical fiber 31a of the section 30 toward the polarizing prism 32 on the optical axis. Next, the P-polarized light and the S-polarized light separated by the polarizing film 32f of the polarizing prism 32 and transmitted through the polarizing film 32f enter the first film 33f1 functioning as a low-pass filter of the beam splitter 33. The S-polarized light reflected by the polarizing film 32f is not used in the interrogator 100 and the detection unit 30 of the present embodiment.

  The P-polarized light that has passed through the polarizing film 32f enters the first film 33f1, and is separated into transmitted light and reflected light. Here, the first film 33f1 transmits light having a wavelength of less than about 1540 nm and reflects other light. Therefore, of the return light from the FBG sensors 201, 202, and 203, only the return light from the FBG sensor 201, which is light near the center wavelength of 1530 nm, passes through the first film 33f1 and travels in the optical axis direction. , 203 are reflected by the first film 33f1 and travel in a vertical direction orthogonal to the optical axis direction.

  The return light from the FBG sensors 202 and 203 reflected by the first film 33f1 then enters the second film 33f2 parallel to the first film 33f1 at an incident angle of 45 °, and is transmitted and reflected light. Separated. Here, the second film 33f2 transmits light having a wavelength of about 1560 nm or more and reflects other light. Therefore, of the return light from the FBG sensors 202 and 203, the return light from the FBG sensor 202, which is light near the center wavelength of 1550 nm, is reflected by the second film 33f2, travels in the optical axis direction, and is light near the center wavelength of 1570 nm. The return light from the FBG sensor 203, which passes through the second film 33f2, travels in the vertical direction perpendicular to the optical axis direction.

  The return light from the FBG sensor 203 that has passed through the second film 33f2 is then reflected by the reflection surface 33r parallel to the second film 33f2 and travels in the optical axis direction.

  The return light from the FBG sensor 201 that has passed through the first film 33f1 of the beam splitter 33 enters the dielectric multilayer film 34f1 of the prism pair PP1 of the filter prism 34, and is converted into transmitted light and reflected light by the dielectric multilayer film 34f1. Separated. Here, as shown in FIG. 7A, the filter characteristic of the dielectric multilayer film 34f1 is such that the transmittance for light having a wavelength of 1525 nm or less is about 10% and the transmittance for light having a wavelength of 1535 nm or more is about 90%. In the section from the wavelength of 1525 nm to the wavelength of 1535 nm, the transmittance increases as the wavelength of the light increases, and the transmittance for the light having the wavelength of 1530 nm is approximately 50%. The dielectric multilayer film 34f1 desirably has a filter characteristic in which transmittance changes linearly in a region having a predetermined wavelength width, for example, a region having a wavelength width of at least 5 nm, at least 8 nm, or at least 10 nm.

  Since the return light from the FBG sensor 201 has a wavelength distribution with a peak at the center wavelength of 1530 nm, the wavelength of the P-polarized light incident on the dielectric multilayer film 34f1 also has a peak near the center wavelength of 1530 nm, and It is symmetrically distributed on the long side and the long wavelength side (FIG. 6). Therefore, about 50% of the P-polarized light incident on the dielectric multilayer film 34f1 is transmitted through the dielectric multilayer film 34f1, and the remaining 50% is reflected by the dielectric multilayer film 34f1. The reflected light reflected by the dielectric multilayer film 34f1 is then reflected by the reflection surface 34r1, and becomes parallel to the transmitted light transmitted through the dielectric multilayer film 34f1.

  The transmitted light transmitted through the dielectric multilayer film 34f1 and the reflected light reflected by the dielectric multilayer film 34f1 and the reflection surface 34r1 are respectively the first region DS11 and the second region DS1 of the light receiving surface DS1 of the first photodetector PD1. The signal is detected by the DS 12 and converted into a voltage signal corresponding to the amount of light received via the photoelectric conversion unit and the IV amplifier. Here, since the light amounts of the transmitted light and the reflected light are substantially the same, the voltage signal corresponding to the light amount of the transmitted light of the dielectric multilayer film 34f1 is substantially equal to the voltage signal corresponding to the light amount of the reflected light.

  The calculation unit 40 obtains the wavelength of the return light from the FBG sensor 201 based on the ratio between the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light. Here, based on the result that the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light are substantially the same, the calculation unit 40 sets the wavelength of the return light from the FBG sensor 201 to the center wavelength. It is determined to be 1530 nm.

  The return light from the FBG sensor 202 reflected by the second film 33f2 of the beam splitter 33 is incident on the dielectric multilayer film 34f2 of the prism pair PP2 of the filter prism 34, and is transmitted and reflected by the dielectric multilayer film 34f2. Is separated into Here, as shown in FIG. 7B, the filter characteristic of the dielectric multilayer film 34f2 is such that the transmittance for light having a wavelength of 1545 nm or less is about 10% and the transmittance for light having a wavelength of 1555 nm or more is about 90%. In the section from the wavelength of 1545 nm to the wavelength of 1555 nm, the transmittance increases as the wavelength of the light increases, and the transmittance for the light having the wavelength of 1550 nm is almost 50%. The dielectric multilayer film 34f2 desirably has a filter characteristic in which transmittance changes linearly in a region having a predetermined wavelength width, for example, a region having a wavelength width of at least 5 nm, at least 8 nm, or at least 10 nm.

  Since the return light from the FBG sensor 202 has a wavelength distribution with a peak at the center wavelength of 1550 nm, the wavelength of P-polarized light incident on the dielectric multilayer film 34f2 also has a peak near the center wavelength of 1550 nm, and And symmetrically distributed on the long wavelength side and the long wavelength side. Therefore, about 50% of the P-polarized light incident on the dielectric multilayer film 34f2 is transmitted through the dielectric multilayer film 34f2, and the remaining 50% is reflected by the dielectric multilayer film 34f2. The reflected light reflected by the dielectric multilayer film 34f2 is then reflected by the reflection surface 34r2, and becomes parallel to the transmitted light transmitted through the dielectric multilayer film 34f2.

  The calculation unit 40 obtains the wavelength of the return light from the FBG sensor 202 based on the ratio between the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light. Here, the calculation unit 40 determines the wavelength of the return light from the FBG sensor 202 as the center wavelength based on the result that the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light are substantially the same. It is determined to be 1550 nm.

  The return light from the FBG sensor 203 transmitted through the second film 33f2 of the beam splitter 33 and reflected by the reflection surface 33r is incident on the dielectric multilayer film 34f3 of the prism pair PP3 of the filter prism 34, and the dielectric multilayer film 34f3 The light is separated into transmitted light and reflected light. Here, as shown in FIG. 7C, the filter characteristic of the dielectric multilayer film 34f3 is such that the transmittance for light having a wavelength of 1565 nm or less is about 10% and the transmittance for light having a wavelength of 1575 nm or more is about 90%. In the section from the wavelength of 1565 nm to the wavelength of 1575 nm, the transmittance increases as the wavelength of the light increases, and the transmittance for the light having the wavelength of 1570 nm is approximately 50%. The dielectric multilayer film 34f3 desirably has a filter characteristic in which transmittance changes linearly in a region having a predetermined wavelength width, for example, a region having a wavelength width of at least 5 nm, at least 8 nm, or at least 10 nm.

  Since the return light from the FBG sensor 203 has a wavelength distribution having a peak at the center wavelength of 1570 nm, the wavelength of the P-polarized light incident on the dielectric multilayer film 34f3 similarly has a peak near the center wavelength of 1570 nm, and And symmetrically distributed on the long wavelength side and the long wavelength side. Therefore, about 50% of the P-polarized light incident on the dielectric multilayer film 34f3 is transmitted through the dielectric multilayer film 34f3, and the remaining 50% is reflected by the dielectric multilayer film 34f3. The reflected light reflected by the dielectric multilayer film 34f3 is then reflected by the reflection surface 34r3, and becomes parallel to the transmitted light transmitted through the dielectric multilayer film 34f3.

  The calculation unit 40 obtains the wavelength of the return light from the FBG sensor 203 based on the ratio between the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light. Here, based on the result that the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light are substantially the same, the calculation unit 40 sets the wavelength of the return light from the FBG sensor 203 to the center wavelength. It is determined to be 1570 nm.

  When distortion occurs in the object to be measured, distortion also occurs in the FBG sensors 201, 202, and 203 attached to the object to be measured, and the period length の of the fiber Bragg grating portion fbg of each of the FBG sensors 201, 202, and 203 becomes larger. Change. For example, when the object to be measured is distorted and the FBG sensor 201 is extended in the longitudinal direction, the period length Λ of the fiber Bragg grating portion fbg of the FBG sensor 201 also increases, so that the interference condition in the fiber Bragg grating portion fbg Due to λb = 2nΛ, the wavelength λb of the generated return light shifts to a longer wavelength side than the center wavelength. As an example, as shown by the broken line in FIG. 6, the peak of the wavelength of the light returned from the fiber Bragg grating portion fbg is 1531 nm. Conversely, when a compressive strain is generated in the object to be measured and the FBG sensor 201 is compressed in the longitudinal direction, the period length Λ of the fiber Bragg grating portion fbg is also reduced, so that the wavelength of the return light from the fiber Bragg grating portion fbg λb shifts to the short wavelength side. As an example, as shown by the dashed line in FIG. 6, the peak of the wavelength of the return light from the fiber Bragg grating portion fbg of the FBG sensor 201 is 1529 nm.

  As shown in FIG. 7A, the dielectric multilayer film 34f1 has a transmittance of about 60% for light having a wavelength of 1531 nm. Therefore, when the peak of the wavelength of the return light from the FBG sensor 201 is shifted to 1531 nm, about 60% of the P-polarized light incident on the dielectric multilayer film 34f1 passes through the dielectric multilayer film 34f1, and the remaining About 40% is reflected by the dielectric multilayer film 34f1. Therefore, the ratio between the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light is about 6: 4. The calculating unit 40 calculates the return light from the FBG sensor 201 based on the comparison result that the ratio between the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light is about 6: 4. It is determined that the wavelength peak is 1531 nm.

  Similarly, when the peak of the wavelength of the return light from the FBG sensor 201 is shifted to 1529 nm, about 40% of the P-polarized light incident on the dielectric multilayer film 34f1 passes through the dielectric multilayer film 34f1, and the remaining Is reflected by the dielectric multilayer film 34f1. Therefore, the ratio between the voltage signal corresponding to the amount of transmitted light and the voltage signal corresponding to the amount of reflected light is approximately 4 to 6, and the calculation unit 40 determines the return light from the FBG sensor 201 based on this comparison. It is determined that the wavelength peak is 1529 nm.

  The calculation unit 40 can measure the amount of strain generated in the FBG sensor 201 based on the wavelength of the return light from the FBG sensor 201 obtained as described above. Further, the calculation unit 40 can also measure the amount of strain generated in the FBG sensors 202 and 203 by the same method as described above with the FBG sensor 201 as an example.

  As described above, the amount of distortion is measured by separating the return light from the FBG sensors 201, 202, and 203 by the filter prism 34, but the polarization direction of the light incident on the filter prism 34 is adjusted by the polarizing prism 32. By doing so, more accurate measurement is realized.

  FIG. 8 shows the filter characteristics of the dielectric multilayer film 34f1 used in the present embodiment with respect to non-polarized incident light. Comparing the filter characteristics shown in FIG. 8 with the filter characteristics of the same dielectric multilayer film 34f1 for the P-polarized incident light (FIG. 7A), the filter characteristics of the dielectric multilayer film 34f1 for the P-polarized incident light are as follows. While the transmittance changes linearly and steeply with a predetermined wavelength width (at least 5 nm), the filter characteristic of the dielectric multilayer film 34f1 with respect to the unpolarized incident light is such that the transmittance changes only in a curve. is there.

  Therefore, when the peak of the wavelength of the return light from the FBG sensor 201 shifts from the center wavelength of 1530 nm, if the incident light is P-polarized light, the amounts of the transmitted light and the reflected light are proportional to the shift amount of the wavelength of the incident light. Although it changes linearly, if the incident light is unpolarized, the amounts of the transmitted light and the reflected light show a random change without being proportional to the shift amount of the wavelength of the incident light. Therefore, by inputting the P-polarized light to the filter prism 34 by using the polarizing prism 32, the slope can be made linear in the filter characteristic of the dielectric multilayer film 34f1, and the measurement target by the calculation unit 40 can be obtained. Measurement of the strain of the object can be facilitated. Similarly, by inputting the P-polarized light to the filter prism 34 using the polarizing prism 32, the slope can be made linear in the filter characteristics of the dielectric multilayer films 34f2 and 34f3. The measurement of the strain of the object to be measured by the method can be facilitated.

  The effects of the detection unit 30 of the present embodiment and the interrogator including the same will be summarized below.

  In the detection unit 30 of the present embodiment, the light reflected by the dielectric multilayer film 34f1 of the filter prism 34 is reflected again by the reflection surface 34r1, and is parallel to the transmitted light transmitted through the dielectric multilayer film 34f1. Therefore, the transmitted light transmitted through the dielectric multilayer film 34f1 and the reflected light reflected by the dielectric multilayer film 34f1 are detected using only the detection surface DS1 of the first photodetector PD1, which is a single photodetector. be able to. The detection unit 30 of the present embodiment does not need to detect the transmitted light and the reflected light from the dielectric multilayer film 34f1 using two photodetectors, and thus can have a compact configuration. Further, the production becomes easy, and the production cost can be suppressed.

  In the detection unit 30 of the present embodiment, the first region DS11 that receives the transmitted light from the dielectric multilayer film 34f1 and the second region DS12 that receives the reflected light from the dielectric multilayer film 34f1 are on the same plane. It is defined. Therefore, according to the detection unit 30 of the present embodiment, the calculation of the wavelength of the return light from the FBG sensor 201 in the calculation unit 40 can be simplified, and the calculation accuracy can be improved. In addition, since the adjustment of the first area DS11 and the adjustment of the second area DS12 can be performed collectively, the adjustment of the detection unit 30 is also simplified and facilitated.

  In the detection unit 30 of the present embodiment, the detection surfaces DS1 to DS3 of the first to third photodetectors PD1 to PD3 are arranged on the same plane, and the detection surfaces DS1 to DS3 from the dielectric multilayer films 34f1, 34f2, and 34f3. The transmitted light and the reflected light are all received on the same plane. Therefore, according to the detection unit 30 of the present embodiment, a compact configuration is possible, and the calculation of the wavelength of the return light from the FBG sensors 201, 202, and 203 can be simplified, and the calculation accuracy can be improved.

  In the detection unit 30 of the present embodiment, the dielectric multilayer film 34f1 and the reflection surface 34r1 are integrally formed using the prism pair PP1. Similarly, the dielectric multilayer film 34f2 and the reflection surface 34f2 are formed integrally using the prism pair PP2, and the dielectric multilayer film 34f3 and the reflection surface 34f3 are formed integrally using the prism pair PP3. . The detection unit 30 of the present embodiment is formed integrally with the dielectric multilayer film functioning as an optical filter and the reflection surface, and has a compact overall configuration.

  The dielectric multilayer films 34f1, 34f2, 34f3 included in the detection unit 30 of the present embodiment are formed on the inclined surface of the right-angle prism by sputtering, vapor deposition, or the like. Therefore, the filter characteristics of the dielectric multilayer films 34f1, 34f2, and 34f3 do not change due to temperature changes, and it is possible to suppress the occurrence of errors due to temperature changes in strain measurement using the FBG sensors 201, 202, and 203.

  The beam splitter 33 of the detection unit 30 of the present embodiment converts the P-polarized light from the polarizing prism 32 including a plurality of return lights from a plurality of FBG sensors into a first film 33f1 functioning as a low-pass filter and a P-polarized light functioning as a high-pass filter. Wavelength division is performed using the two films 33f2. In this manner, a plurality of return lights belonging to different wavelength bands are wavelength-divided without attenuating their energies, so that light having sufficient energy to calculate the wavelength of the return light is filtered by the plurality of filter prisms 34. The light can be sent to each of the optical filters (dielectric multilayer film), and highly accurate detection of each return light can be performed.

  The detection unit 30 of the present embodiment uses the polarizing prism 32 to cause only the P-polarized light to enter the filter prism 34. Therefore, the slope becomes linear in the filter characteristics of the dielectric multilayer films 34f1, 34f2, and 34f3, and the calculation for calculating the wavelength of the return light from the FBG sensors 201, 202, and 203 in the calculation unit 40 is easy.

  Since the interrogator of the present embodiment includes the detection device 30 of the present embodiment, the same effect as the detection device 30 of the present embodiment can be obtained.

  In addition to those specifically described in the above embodiment, the following modified embodiments can be adopted.

  In the above embodiment, the polarizing prism 32, the beam splitter 33, and the filter prism 34 are three compound prisms separated from each other. However, as shown in FIG. 9, a single compound prism CP integrating these is used. Is also good. Further, the first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 may be arranged on the composite prism by bonding or contacting. According to this configuration, the detector 30 can be made more compact. Note that only the polarizing prism 32 and the beam splitter 33 may be integrated into a single composite prism, or only the beam splitter 33 and the filter prism 34 may be integrated into a single composite prism.

  In the above embodiment, it is assumed that the strain is measured at three places on the object using three FBG sensors 201, 202, and 203, and the detector 30 also converts the P-polarized light from the polarizing prism 32 into three lights. It has the beam splitter 33 for splitting and the filter prism 34 having the three prism pairs PP1 to PP3, but is not limited thereto. The number y of measurement points on the object to be measured may be an arbitrary number including 1, and the measurement can be performed using y FBG sensors and the detector 30 corresponding thereto. Specifically, the corresponding detector 30 is a detector having a beam splitter that wavelength-divides the P-polarized light from the polarizing prism 32 into at least y light beams, and a filter prism having at least y prism pairs. . When y = 1, no beam splitter is required.

  In the above embodiment, the polarizing prism 32 is a cube-shaped polarizing beam splitter in which two right-angle prisms are combined. Instead, an arbitrary polarizing beam splitter such as a flat plate-shaped polarizing beam splitter is used. You can also. Further, in the above-described embodiments and modified examples, the polarizing prism 32 may be omitted.

  In the above embodiment, the beam splitter 33 wavelength-divides the P-polarized light from the polarizing prism 32 by the first film 33f1 functioning as a low-pass filter and the second film 33f2 functioning as a high-pass filter. I can't. The beam splitter 33 may perform wavelength division using only a low-pass filter, may perform wavelength division using only a high-pass filter, or may use a band-pass filter. That is, the beam splitter 33 may have any configuration as long as it can appropriately split the wavelength of the return light from the plurality of FBG sensors.

  The beam splitter 33 may use a half mirror, instead of a wavelength division filter such as a low-pass filter or a high-pass filter, to separate return lights from a plurality of FBG sensors. In this case, the energy of the light transmitted through the half mirror or the light reflected by the half mirror is halved compared to before transmission or reflection, so that when returning light is separated by a beam splitter using a half mirror, Although not limited, for example, when the first photodetector PD1, the second photodetector PD2, and the third photodetector PD3 can detect light having energy of about 1/10 of the light output from the light source 10, measurement is performed. It is desirable that the number of points (ie, the number of FBG sensors) be less than about three. As described above, even when return light from a plurality of FBG sensors is separated by the half mirror, each of the separated light includes all return light. By separating and detecting the light amounts of the transmitted light and the reflected light, a desired return light wavelength can be calculated.

  In the above embodiment, the prism pairs PP1 to PP3 reflect the reflected light reflected by the dielectric multilayer films 34f1, 34f2, and 34f3 on the reflecting surfaces 34r1, 34r2, and 34r3, respectively, and make the transmitted light and the reflected light parallel. Was not limited to this. Each of the prism pairs PP1 to PP3 may have a configuration in which the transmitted light transmitted through the dielectric multilayer films 34f1, 34f2, and 34f3 is reflected by a reflection surface to make the transmitted light and the reflected light parallel. This configuration can be specifically realized, for example, by providing a dielectric multilayer film on one of the opposing surfaces of the parallelogram prism and providing a reflective surface on the other.

  In the above embodiment, the filter prism 34, which is a composite prism in which the three prism pairs PP1 to PP3 are integrated, is used. However, the present invention is not limited to this. Instead of the filter prism 34, a plurality of prism pairs separated from each other can be used. Further, in this case, it is not essential to arrange a plurality of prism pairs so that the dielectric multilayer films of the prism pairs spread on the same plane, and it is also possible to arrange the reflection surfaces of these pairs so as to spread on the same plane. Not required. For example, in FIG. 2, a configuration in which the prism pairs PP1 to PP3 are separated from each other is possible, and a configuration in which each of the prism pairs PP1 to PP3 is rotated by 90 ° about the optical axis direction is also possible. Even with such a configuration, the transmitted light and the reflected light from the dielectric multilayer films 34f1, 34f2, and 34f3 can be made parallel, so that the detection unit 30 can be made compact.

  Alternatively, the dielectric multilayer films 34f1, 34f2, 34f3 may be formed as flat optical filters, and the reflecting surfaces 34r1, 34r2, 34r3 may be formed as flat mirrors. Even with such a configuration that does not use the prism pair, the transmitted light and the reflected light from the optical filter can be made parallel. In this case, since the number of components increases as compared with the configuration using the prism pair, the number of measurement points (that is, the number of FBG sensors) is desirably set to about two or less in order to prevent the detection unit 30 from being enlarged. However, the preferred number of measurement points varies depending on the size of the flat optical filter and the mirror, and is not necessarily limited to two or less.

  In the above-described embodiment, the transmitted light and the reflected light from the dielectric multilayer films 34f1, 34f2, and 34f3 are each detected by a single photodetector. However, the present invention is not limited to this. For example, instead of the first photodetector PD1, a transmitted light detector that receives transmitted light from the dielectric multilayer film 34f1 and a reflected light detector that receives reflected light from the dielectric multilayer film 34f1 are used. Is also good. The same applies to the second photodetector PD2 and the third photodetector PD3. Also in this case, since the transmitted light detector and the reflected light detector can be arranged on the same substrate, the detection unit 30 can be made compact.

  Alternatively, a single photodetector is used instead of the first photodetector PD1 to the third photodetector PD3, and the transmitted light and the reflected light from the dielectric multilayer films 34f1, 34f2, and 34f3 are used as the single photodetectors. Light may be received in different regions on one light receiving surface. Further, the first region DS11 and the second region DS12 do not have to be on the same plane. The same applies to the first area DS21 and the second area DS22, and to the third and first areas DS31 and the second area DS32.

  In the above embodiment, the center wavelengths of the FBG sensors 201, 202, and 203 are 1530 nm, 1550 nm, and 1570 nm, respectively, but are not limited thereto. The wavelengths of the FBG sensors used for measurement are arbitrary as long as they are different from each other.

  In the above embodiments and modifications, the transmitted light transmitted through the dielectric multilayer films 34f1, 34f2, 34f3 and the reflected light reflected by the dielectric multilayer films 34f1, 34f2, 34f3 are parallel. The present invention is not limited to this, and the transmitted light transmitted through the dielectric multilayer films 34f1, 34f2, 34f3 may be substantially parallel to the reflected light reflected by the dielectric multilayer films 34f1, 34f2, 34f3. Here, “substantially parallel” means, for example, a case where the angle between the traveling direction of the transmitted light and the traveling direction of the reflected light is about 5 ° or less.

  In this specification, the surface of the prism that functions as an optical filter is called a light separation surface. The function of the optical filter may be provided by forming a dielectric multilayer film as in the above-described embodiments and modified examples, or a diffraction grating or the like may be formed as a light separating surface.

  As long as the features of the present invention are maintained, the present invention is not limited to the above-described embodiment, and other forms that can be considered within the technical idea of the present invention are also included in the scope of the present invention. .

  Since the detection device, the interrogator, and the strain detection system of the present invention are compact, the user can easily transport and install them and perform desired measurement.

Reference Signs List 10 light source 20 coupler 30 detecting unit 32 polarizing prism 32f polarizing film 33 beam splitter 33f1 first film 33f2 second film 33r reflecting surface 34 filter prisms 34f1, 34f2, 34f3 dielectric multilayer film 34r1, 34r2, 34r3 reflecting surface 40 calculating unit 100 Interrogator 200 FBG sensor DS1 DS2, DS3 Light receiving surface PD1 First photodetector PD2 Second photodetector PD3 Third photodetector PP1, PP2, PP3 Prism pair

Claims (17)

A detection device for respectively detecting the wavelengths of a plurality of return lights from a plurality of FBG sensors arranged in series in an optical fiber,
A beam splitter that divides the plurality of return lights into a plurality of light beams,
A plurality of light separation surfaces each of which separates each of the plurality of light beams into transmitted light and reflected light, and a plurality of reflection surfaces each of which reflects the transmitted light or the reflected light and makes the transmitted light and the reflected light substantially parallel to each other; And the prism of
A plurality of transmitted light receiving units that respectively receive the transmitted light from the plurality of prisms,
A plurality of reflected light receiving units that respectively receive the reflected light from the plurality of prisms,
The transmittance of the light separating surface of the plurality of prisms has been changed in regions of different wavelength widths ,
Among the plurality of transmitted light receiving units and the plurality of reflected light receiving units, a pair of transmitted light receiving units and a reflected light receiving unit that receive a pair of the transmitted light and the reflected light from each of the plurality of prisms are , Detection devices arranged on the same plane . The detection device according to claim 1, wherein the pair of transmitted light receiving units and reflected light receiving units are defined on a single light receiving surface of a single photodetector. The detection device according to claim 1, further comprising a polarization separation surface that separates the plurality of return lights into P-polarized light and S-polarized light, and that enters the P-polarized light into the beam splitter. A detection device for respectively detecting the wavelengths of a plurality of return lights from a plurality of FBG sensors arranged in series in an optical fiber,
  A beam splitter that divides the plurality of return lights into a plurality of light beams,
  A plurality of light separation surfaces for separating each of the plurality of light beams into transmitted light and reflected light, and a plurality of reflection surfaces each of which reflects the transmitted light or the reflected light and makes the transmitted light and the reflected light substantially parallel to each other; Prism and
  A plurality of transmitted light receiving units that respectively receive the transmitted light from the plurality of prisms,
  A plurality of reflected light receiving units that respectively receive the reflected light from the plurality of prisms,
  The transmittance of the light separating surface of the plurality of prisms is changed in regions of different wavelength widths,
  A detection apparatus further comprising: a polarization separation surface that separates the plurality of return lights into P-polarized light and S-polarized light, and that enters the P-polarized light into the beam splitter. The polarization splitting surface is formed in a prism, the beam splitter is formed as a prism, the beam splitter, the prism on which the polarization splitting surface is formed, the plurality of prisms, and the plurality of transmissions. The detection device according to claim 3, wherein the light receiving unit and the plurality of reflected light receiving units are integrally joined. The light separating surface of each of the plurality of prisms is provided with a dielectric multilayer film, and the change in transmittance of each of the light separating surfaces is linear. Detection device. The detecting device according to claim 1, wherein the plurality of prisms are integrally joined. The detection device according to any one of claims 1 to 7, wherein the beam splitter includes a wavelength division surface, and divides the plurality of return lights into a plurality of light beams. A light source for irradiating the FBG sensor with broadband light;
A detection device according to any one of claims 1 to 8,
An interrogator comprising: a plurality of transmitted light receiving units; and a calculating unit that calculates a wavelength of each of the plurality of return lights based on detection signals from the plurality of reflected light receiving units. A detection device for detecting the wavelength of the return light from the FBG sensor,
A light separating surface for separating the return light into transmitted light and reflected light,
A reflecting surface that reflects one of the transmitted light or the reflected light to make the transmitted light and the reflected light substantially parallel,
A transmitted light receiving unit that receives the transmitted light from the light separation surface,
A reflected light receiving unit that receives the reflected light from the light separation surface,
The transmittance of the light separating surface is changed in a region of a predetermined wavelength width ,
A detecting device, wherein the transmitted light receiving unit and the reflected light receiving unit are arranged on the same plane . A detection device for detecting the wavelength of the return light from the FBG sensor,
  A light separating surface for separating the return light into transmitted light and reflected light,
  A reflecting surface that reflects one of the transmitted light or the reflected light to make the transmitted light and the reflected light substantially parallel,
  A transmitted light receiving unit that receives the transmitted light from the light separation surface,
  A reflected light receiving unit that receives the reflected light from the light separation surface,
  The transmittance of the light separating surface is changed in a region of a predetermined wavelength width,
  A detection device further comprising a polarization separation surface that separates the return light into P-polarized light and S-polarized light, and that enters the P-polarized light into the light separation surface. The detection device according to claim 11, wherein the transmitted light receiving unit and the reflected light receiving unit are arranged on the same plane. The detection device according to claim 10, wherein the transmitted light receiving unit and the reflected light receiving unit are defined on a single light receiving surface of a single photodetector. 14. The detection device according to claim 13, wherein the light separation surface and the reflection surface are defined in the same prism. A light source for irradiating the FBG sensor with broadband light;
  The detection device according to any one of claims 10 to 14,
  An interrogator comprising: the transmitted light receiving unit; and a calculating unit that calculates a wavelength of the return light based on a detection signal from the reflected light receiving unit. The interrogator according to claim 9, wherein the calculation unit obtains a distortion amount of the FGB sensor based on the calculation result. An FBG sensor,
  A strain detection system comprising the interrogator according to any one of claims 9, 15, and 16.

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