Inspection device and inspection method

Abstract

To provide an inspection device and an inspection method, which allow for inspecting performance of an FRM after assembly.SOLUTION: An inspection device for inspecting an FRM (Faraday Rotator Mirror) comprising a Faraday rotator and a mirror is provided, the inspection device comprising a processor configured to repetitively detect intensity of a component of light reflected by the FRM having the same electric field oscillation direction as that of incident light to the FRM.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an inspection device and an inspection method for inspecting the performance of an FRM (Faraday Rotator Mirror). [Background technology]

[0002] Conventionally, optical fiber sensors equipped with FRMs are known. Non-Patent Document 1 discloses an optical fiber hydrophone equipped with an FRM. The optical fiber hydrophone of Non-Patent Document 1 suppresses polarization fading and noise that occur due to changes in the polarization state of interfering light by providing an FRM in a sensing interferometer that detects underwater sounds.

[0003] The FRM consists of a Faraday rotator and a mirror, and is considered to be in a normal state when the polarization rotation angle of the Faraday rotator is 90° in both directions. Non-Patent Document 2 proposes a method for measuring the polarization rotation angle. In the device described in Non-Patent Document 2, linearly polarized light propagating through the air is passed through a retardation plate and a rotating polarizer, and the angle of the rotating polarizer and the transmission intensity are measured to measure the error in the polarization rotation angle of the retardation plate. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Japanese Journal of Applied Physics 52,2013,012501, “Expansion of Dynamic Range in Interferometric Fiber Optic Hydrophone” [Non-Patent Document 2] Applied Physics, 1981, Vol. 50, No. 7, "Technical Note (Method of Measuring Magneto-Optical Effect)", P727-728 Summary of the Invention [Problem to be solved by the invention]

[0005] Due to aging of the magnetism of the FRM or the influence of surrounding magnetism, the polarization rotation angle of the Faraday rotator may change after the FRM or the optical fiber sensor is assembled. However, the method described in Non-Patent Document 2 can measure the polarization rotation angle of the Faraday rotator alone, but cannot measure the polarization rotation angle after the FRM or the optical fiber sensor is assembled. Therefore, there is a problem in that it is not possible to inspect abnormalities that occur after the FRM or the optical fiber sensor is assembled.

[0006] The present invention has been made in view of the above-mentioned problems, and has an object to provide an inspection device and an inspection method capable of inspecting the performance of an FRM after assembly. [Means for solving the problem]

[0007] The inspection device according to the present invention is an inspection device for inspecting an FRM (Faraday Rotator Mirror) having a Faraday rotator and a mirror, and measures the intensity of the component of the light reflected by the FRM whose electric field oscillation direction is the same as that of the input light to the FRM. and the intensity of the component in the direction perpendicular to the input light and the electric field oscillation direction Repeated detection The ratio of the intensity of the component in the same direction as the input light and the electric field oscillation direction to the intensity of the component in the direction perpendicular to the input light and the electric field oscillation direction is repeatedly calculated. The device is equipped with a processor. Another inspection apparatus according to the present invention is an inspection apparatus for inspecting an interferometer having two FRMs, each having a Faraday rotator and a mirror, and includes a processor that repeatedly calculates the polarization angle difference between the two FRMs based on light reflected by the interferometer. The inspection method according to the present invention is a method for inspecting an FRM having a Faraday rotator and a mirror, and measures the intensity of a component of light reflected by the FRM that has the same electric field oscillation direction as the input light to the FRM. and the intensity of the component in the direction perpendicular to the input light and the electric field oscillation direction Repeated detection steps repeatedly calculating a ratio between an intensity of a component in a direction in which the input light and the electric field oscillation direction are the same and an intensity of a component in a direction in which the input light and the electric field oscillation direction are perpendicular to each other; Includes. Another inspection method according to the present invention is an inspection method for inspecting an interferometer having two FRMs, each having a Faraday rotator and a mirror, and includes a step of repeatedly calculating the polarization angle difference between the two FRMs based on light reflected by the interferometer. Effect of the Invention

[0008] According to the inspection device and inspection method of the present invention, the performance of an assembled FRM can be inspected by repeatedly determining the intensity of the component of light reflected from the FRM whose electric field oscillation direction is the same as the input light to the FRM, or the polarization angle difference between two FRMs. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of an inspection device according to a first embodiment. [Diagram 2] 4 is a display example of the Poincaré sphere of input light of the inspection device according to the first embodiment. [Diagram 3] 4 is a display example of the Poincaré sphere of reflected light of the sensing interferometer according to the first embodiment. [Figure 4] FIG. 11 is a schematic configuration diagram of an inspection device according to a second embodiment. [Diagram 5] 13 is a diagram illustrating calculation of a polarization angle difference by a polarization angle calculation section according to the second embodiment. FIG. [Figure 6] FIG. 11 is a schematic configuration diagram of an inspection device according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Embodiment 1 1 is a schematic configuration diagram of an inspection device 1 according to embodiment 1. The inspection device 1 of this embodiment inspects the performance of an FRM (Faraday Rotator Mirror) provided in a sensing interferometer 2.

[0011] The sensing interferometer 2 detects a physical quantity from a strain occurring in a sensing fiber 24. As shown in FIG 1, the sensing interferometer 2 includes optical fibers 21a, 21b, and 21c, an optical coupler 22, a first FRM 23a, a second FRM 23b, and a sensing fiber 24.

[0012] The optical coupler 22 is connected to the inspection device 1 via an optical fiber 21a. The optical coupler 22 is also connected to the first FRM 23a via an optical fiber 21b, and to the second FRM 23b via an optical fiber 21c. The sensing fiber 24 is provided in the optical fiber 21c that connects the optical coupler 22 to the second FRM 23b.

[0013] The optical coupler 22 splits the input light from the inspection device 1 into two lights, and outputs one to the sensing fiber 24 and outputs the other to the first FRM 23a. The optical coupler 22 also outputs the reflected light reflected by the first FRM 23a and the second FRM 23b to the inspection device 1.

[0014] The first FRM 23a includes a Faraday rotator 231 and a mirror 232. After passing through the Faraday rotator 231, the input light from the inspection device 1 is reflected by the mirror 232, passes through the Faraday rotator 231, and returns to the optical coupler 22.

[0015] 1, the second FRM 23b includes a Faraday rotator 231 and a mirror 232, similar to the first FRM 23a. The phase of the input light from the inspection device 1 changes in response to the physical quantity detected by the sensing fiber 24. The light output from the sensing fiber 24 passes through the Faraday rotator 231 of the second FRM 23b, is reflected by the mirror 232, passes through the Faraday rotator 231 and the sensing fiber 24, and returns to the optical coupler 22.

[0016] The optical fiber 21b and the first FRM 23a are a reference arm in which no change in strain or refractive index occurs due to measurement, and the optical fiber 21c, the sensing fiber 24, and the second FRM 23b are a measurement target arm in which a change in strain or refractive index occurs due to measurement. By converting the change in the optical path difference between the reference arm and the measurement target arm into a change in light intensity due to optical interference, the physical quantity detected by the sensing fiber 24 can be measured.

[0017] As shown in FIG. 1, the inspection device 1 of this embodiment includes a pulsed light source 11, a half mirror 12, a polarization controller 13, a lens 14, a polarizing beam splitter 15, O / E converters 16a and 16b, and a processor 17.

[0018] The pulse light source 11 outputs linearly polarized pulse light with a constant frequency as input light to the sensing interferometer 2. The direction in which the electric field of the linearly polarized light output from the pulse light source 11 changes is defined as the X-axis. The half mirror 12 transmits the light input from the pulse light source 11 and outputs it to the polarization controller 13. The half mirror 12 also reflects the light input from the polarization controller 13 and outputs it to the polarization beam splitter 15.

[0019] The polarization controller 13 changes the polarization state of the input light. The polarization controller 13 of this embodiment includes a 1 / 2 wavelength plate 131 and a 1 / 4 wavelength plate 132. The 1 / 2 wavelength plate 131 is a birefringent plate whose birefringence retardation is 1 / 2 wavelength, and the 1 / 4 wavelength plate 132 is a birefringent plate whose birefringence retardation is 1 / 4 wavelength. The polarization controller 13 can change the polarization state of the light passing therethrough by rotating the 1 / 2 wavelength plate 131 and the 1 / 4 wavelength plate 132. The light output from the polarization controller 13 passes through the lens 14 and enters the optical fiber 21a.

[0020] The rotation control of the half-wave plate 131 and the quarter-wave plate 132 in the polarization controller 13 will be described. FIG. 2 is a display example of the Poincaré sphere of the input light of the inspection device 1 according to the first embodiment. It is known that when the Stokes parameters S1, S2, and S3 are expressed in three-dimensional orthogonal coordinates, all polarization states can be expressed on the surface of a sphere centered on the origin O. This display method is called Poincaré sphere display. The polarization controller 13 of this embodiment changes the polarization state of the input light so that the plots representing the polarization state of the pulse on the Poincaré sphere shown in FIG. 2 are not concentrated in one part, but exist on the spherical surface without bias. If the polarization state of the input light is biased on the spherical surface and a wide gap is formed on the Poincaré sphere, an error will occur in the measurement of the error of the polarization rotation angle of the FRM in the inspection units 174a and 174b described later. The presence or absence of bias in the polarization state of the input light can be confirmed based on the output of the polarization controller 13.

[0021] 3 is a display example of the Poincaré sphere of the reflected light of the sensing interferometer 2 according to the first embodiment. The polarization controller 13 rotates the half-wave plate 131 and the quarter-wave plate 132 so that each of the Stokes parameters S1, S2, and S3 obtained from the reflected light of the sensing interferometer 2 varies within a range of ±α. α is expressed by the following formula (1). The Stokes parameters S1, S2, and S3 are each calculated from one pulse. By controlling the rotation of the half-wave plate 131 and the quarter-wave plate 132 in this way, the polarization state of the input light can be changed so that the plot showing the polarization state of the pulse on the Poincaré sphere shown in FIG. 2 exists on the spherical surface without bias.

[0022]

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[0023] The polarizing beam splitter 15 is a separation means that separates the input light into two components whose polarization states are orthogonal to each other and outputs the two components. The polarizing beam splitter 15 of this embodiment separates the input light into a Y component whose electric field oscillation direction is orthogonal to the input light and an X component whose electric field oscillation direction is the same as the input light, and outputs the two components to the O / E converters 16a and 16b, respectively. The O / E converter 16a converts the input Y component optical signal into an electric signal and outputs it to the processor 17. The O / E converter 16b converts the input X component optical signal into an electric signal and outputs it to the processor 17.

[0024] The processor 17 has pulse extraction units 171a and 171b, division units 172a and 172b, maximum value extraction units 173a and 173b, and inspection units 174a and 174b. Each unit of the processor 17 is realized by a dedicated processing circuit. Alternatively, the processor 17 may be configured with a CPU and a memory, and the electrical signals output from the O / E converters 16a and 16b may be converted into digital signals so that the processor 17 executes a program to realize the functions of each unit.

[0025] The pulse extraction unit 171a extracts the intensity I of the Y component of the reflected light from the first FRM 23a from the Y component electrical signal input from the O / E converter 16a. 1Y and the intensity I of the Y component of the reflected light from the second FRM 23b 2Y Furthermore, the pulse extraction unit 171b extracts a pulse corresponding to the intensity I of the X component of the reflected light from the first FRM 23a from the electrical signal of the X component input from the O / E converter 16b. 1X and the intensity I of the X component of the reflected light from the second FRM 23b 2X The extracted pulses are output to division units 172a and 172b.

[0026] The division unit 172a divides the intensity of the X component of the reflected light of the first FRM 23a by the intensity of the Y component orthogonal to the X component based on the input pulse, and obtains the ratio of the X component intensity to the Y component intensity (hereinafter referred to as "X / Y ratio"). The division unit 172b divides the intensity of the X component of the reflected light of the second FRM 23b by the intensity of the Y component based on the input pulse, and obtains the X / Y ratio. The division units 172a and 172b repeatedly obtain the X / Y ratio of the first FRM 23a and the X / Y ratio of the second FRM 23b for each pulse light. The repeatedly obtained X / Y ratios are output to the maximum value extraction units 173a and 173b.

[0027] The maximum value extraction unit 173a extracts the maximum value of the X / Y ratio of the first FRM 23a that is repeatedly obtained. The maximum value extraction unit 173b extracts the maximum value of the X / Y ratio of the second FRM 23b that is repeatedly obtained. The maximum values ​​extracted by the maximum value extraction units 173a and 173b are output to the inspection units 174a and 174b.

[0028] The inspection unit 174a inspects whether the first FRM 23a is normal based on the maximum value of the X / Y ratio of the first FRM 23a. The inspection unit 174b inspects whether the second FRM 23b is normal based on the maximum value of the X / Y ratio of the second FRM 23b. The first FRM 23a is normal when the polarization rotation angle in the first FRM 23a is exactly 90° round trip or within the allowable range. When the first FRM 23a is in the best condition, the polarization state of the reflected light from the first FRM 23a is rotated by 90° from the polarization state of the input light to the first FRM 23a. Therefore, when the first FRM 23a is normal, the repeatedly calculated X / Y ratio is always zero. On the other hand, when the polarization rotation angle of the first FRM 23a is out of 90° round trip, the maximum value of the X / Y ratio increases from zero.

[0029] Therefore, the inspection unit 174a measures the error of the polarization rotation angle of the first FRM 23a from the maximum value of the X / Y ratio of the first FRM 23a, and judges whether or not the error is within a tolerance required for suppressing polarization fading. The tolerance is assumed to be determined in advance by an experiment or the like and stored. If the error is within the tolerance, the inspection unit 174a judges that the first FRM 23a is normal. On the other hand, if the error is not within the tolerance, the inspection unit 174a judges that the first FRM 23a is not normal. The inspection unit 174b inspects whether or not the second FRM 23b is normal using a method similar to that of the inspection unit 174a. The inspection units 174a and 174b may output the inspection result to a display device provided in the inspection device 1 or an external device.

[0030] The method of inspecting the first FRMs 23a and 23b will be described in detail below. First, the electric field E0 of the pulsed light output from the pulsed light source 11 and transmitted through the half mirror 12, the electric field E1 of the pulsed light reflected by the first FRM 23a and returned to the half mirror 12, and the electric field E2 of the light reflected by the second FRM 23b and returned to the half mirror 12 are expressed by the Jones vectors of the following equations (2) and (3).

[0031]

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number

[0032] where i is 1 or 2, and E 0X is the X component of E0. Also, A i is a coefficient expressing the loss from transmitting through the half mirror 12 to being reflected by the first FRM 23a or the second FRM 23b and returning to the half mirror 12, and J i is the Jones matrix that describes the change in polarization state. J i is expressed by the following equation (4).

[0033]

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[0034] Here, a i , b i , c i , d i is an element of the Jones matrix that represents the change in the polarization state from when the light passes through the half mirror 12 until it reaches the first FRM 23a or the second FRM 23b. i is the polarization rotation angle of the light that has traveled back and forth through the Faraday rotator 231 of the first FRM 23a or the second FRM 23b. i J when is π / 2 i is expressed by the following equation (5).

[0035]

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[0036] Furthermore, if the polarization dependent loss from the time when the light passes through the half mirror 12 until the time when the light reaches the first FRM 23a or the second FRM 23b can be ignored, J i is expressed by the following equation (6).

[0037]

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[0038] In the case where the polarization dependent loss from the time when the light passes through the half mirror 12 until the time when the light reaches the first FRM 23a or the second FRM 23b can be ignored, θ i E when is close to π / 2 i can be approximated by the following equation (7).

[0039]

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[0040] The pulsed light output from the half mirror 12 is separated into an X component and a Y component by the polarizing beam splitter 15. The intensity of the pulsed light is I ix and I iY is expressed by the following equations (8) and (9).

[0041]

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[0042]

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[0043] Here, E * is the complex conjugate of E. The X / Y ratio converted into electrical signals by the O / E converters 16a and 16b and calculated by the processor 17 is expressed by the following formula (10).

[0044]

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[0045] In formula (10), (a i 2 +c i 2 ) 2 fluctuates due to changes in the polarization state after passing through the half mirror 12 until reaching the first FRM 23a or the second FRM 23b. Here, the polarization state of the pulsed light repeatedly output from the pulse light source 11 is changed by the polarization controller 13, the X / Y ratio of the pulsed light corresponding to the first FRM 23a or the second FRM 23b is repeatedly calculated, and the maximum value is extracted, whereby (a i 2 +c i 2 ) 2 is 1. Therefore, the X / Y ratio is θ i 2 Then, by taking the square root, we get θ i By finding the maximum value of the X / Y ratio, an index representing the amount by which the polarization rotation angles of the first FRM 23a and the second FRM 23b deviate from 90° round trip can be obtained, and the performance of the first FRM 23a and the second FRM 23b can be inspected based on this index.

[0046] As described above, the inspection device 1 of the present embodiment can measure the error in the polarization rotation angle of the internal FRM without disassembling the sensing interferometer 2. This makes it possible to inspect for degradation in the performance of the FRM due to the influence of surrounding magnetism after assembly or aging of the magnetism of the FRM.

[0047] Moreover, stable measurement can be achieved even if the loss in the sensing interferometer 2 or the optical transmission path varies by calculating the intensity ratio between the X component and the Y component of the reflected light separated by the polarizing beam splitter 15. Furthermore, the polarization state of the pulsed light input to the sensing interferometer 2 is actively changed using the polarization controller 13, thereby shortening the measurement time.

[0048] Embodiment 2 4 is a schematic configuration diagram of an inspection apparatus 1A according to embodiment 2. The inspection apparatus 1A of this embodiment inspects an inspection object 200 including two sensing interferometers 2a and 2b.

[0049] 4, the inspection target 200 includes two sensing interferometers 2a and 2b, optical fibers 201a, 201b, 201c, 201d, 201e, and 201f, a branching optical coupler 202, a coupling optical coupler 203, and a delay fiber 204. The configurations of the sensing interferometers 2a and 2b are the same as that of the sensing interferometer 2 of the first embodiment.

[0050] The branching optical coupler 202 is connected to the inspection device 1A by an optical fiber 201a. The branching optical coupler 202 is also connected to the sensing interferometer 2a by an optical fiber 201b, and is connected to the sensing interferometer 2b by an optical fiber 201c. The branching optical coupler 202 branches the input light from the inspection device 1A and outputs it to the sensing interferometer 2a and the sensing interferometer 2b.

[0051] The coupling optical coupler 203 is connected to the inspection device 1A via an optical fiber 201f. The coupling optical coupler 203 is also connected to the sensing interferometer 2a via an optical fiber 201d, and is connected to the sensing interferometer 2b via an optical fiber 201e. The coupling optical coupler 203 combines the reflected light from the sensing interferometers 2a and 2b, and outputs the combined light to the inspection device 1A.

[0052] The delay fiber 204 is provided in the optical fiber 201e that connects the coupling optical coupler 203 and the sensing interferometer 2b. The delay fiber 204 generates a delay in the transmission time of the pulse light passing through the delay fiber 204. In the inspection object 200 of this embodiment, the outgoing path for transmitting the input light and the return path for transmitting the reflected light are configured by separate optical fibers 201a and 201f.

[0053] The inspection device 1A of this embodiment includes a pulsed light source 11, a polarization controller 13A, a Stokes spectrometer 18, O / E converters 16c, 16d, 16e, and 16f, and a processor 17A. The configuration of the pulsed light source 11 is the same as that of the first embodiment, and outputs linearly polarized pulsed light parallel to the X-axis as input light.

[0054] The polarization controller 13A is a module that changes the polarization state of the input light, similar to the polarization controller 13. The polarization controller 13A includes a plurality of oscillators 133 for vibrating the optical fiber 201a wound in a coil shape. In the polarization controller 13A of this embodiment, each oscillator 133 generates a vibration, and the optical fiber 201a wound around each oscillator 133 expands and contracts, thereby changing the magnitude of the birefringence of the optical fiber 201a, and changing the polarization state of the input light according to the change in the birefringence. If only one oscillator 133 is included, the polarization state is biased. However, by vibrating a plurality of oscillators 133 facing different directions on the XY plane at different frequencies as in this embodiment, the bias of the plot representing the polarization state is reduced, and the polarization state can be changed so that it exists on the Poincaré sphere without bias. As a method of checking whether or not there is a bias in the polarization state of the input light, in addition to the method of checking the output of the polarization controller 13A like the polarization controller 13 in the first embodiment, in the case of this embodiment, it is possible to confirm that there is no bias in the polarization state by replacing the first FRM 23a or the second FRM 23b of the sensing interferometer 2a or 2b with a mirror and checking that the error in the polarization rotation angle in the first FRM 23a or the second FRM 23b is close to the maximum of 90°. The error in the polarization rotation angle in the first FRM 23a or the second FRM 23b will be described later.

[0055] The Stokes spectrometer 18 divides the input pulsed light into X component I X (t), Y component I Y (t), 45° component I 45 (t) and the 45° component I passed through a quarter-wave plate Q45 The O / E converters 16c to 16f split the input I X (t), I Y (t), I 45 (t) and I Q45 The optical signals (t) are converted into electrical signals and output to the processor 17A.

[0056] The processor 17A includes a Stokes parameter calculator 175, pulse extractors 176a, 176b, 176c, and 176d, polarization angle calculators 177a and 177b, maximum value extractors 178a and 178b, and inspectors 179a and 179b. Each part of the processor 17A is realized by a dedicated processing circuit. Alternatively, the processor 17A may be configured with a CPU and a memory, and the electrical signals output from the O / E converters 16c to 16f may be converted into digital signals, and the processor 17A may execute a program to realize the functions of each part.

[0057] The Stokes parameter calculation unit 175 calculates the intensity I X (t), I Y (t), I 45 (t), I Q45 Based on (t), Stokes parameters S1(t), S2(t) and S3(t) are calculated and output to pulse extraction units 176a to 176d.

[0058] The pulse extraction units 176a to 176d extract pulses corresponding to the Stokes parameters of the first FRM 23a and the second FRM 23b of the sensing interferometers 2a and 2b, respectively. Specifically, the pulse extraction unit 176a extracts pulses corresponding to the Stokes parameters S1(a1), S2(a1), and S3(a1) of the first FRM 23a of the sensing interferometer 2a. The pulse extraction unit 176b extracts pulses corresponding to the Stokes parameters S1(a2), S2(a2), and S3(a2) of the second FRM 23b of the sensing interferometer 2a. The pulse extraction unit 176c extracts pulses corresponding to the Stokes parameters S1(b1), S2(b1), and S3(b1) of the first FRM 23a of the sensing interferometer 2b. The pulse extraction unit 176d extracts pulses corresponding to the Stokes parameters S1(b2), S2(b2), and S3(b2) of the second FRM 23b of the sensing interferometer 2b. The pulses extracted by the pulse extraction units 176a to 176d are output to the polarization angle calculation units 177a and 177b.

[0059] The polarization angle calculation unit 177a calculates the polarization angle difference between the first FRM 23a and the second FRM 23b in the sensing interferometer 2a based on the Stokes parameters of the first FRM 23a and the second FRM 23b in the sensing interferometer 2a. The polarization angle calculation unit 177b calculates the polarization angle difference between the first FRM 23a and the second FRM 23b in the sensing interferometer 2b based on the Stokes parameters of the first FRM 23a and the Stokes parameters of the second FRM 23b in the sensing interferometer 2b. The polarization angle calculation units 177a and 177b repeatedly calculate the polarization angle difference in the sensing interferometer 2a and the polarization angle difference in the sensing interferometer 2b for each pulse light.

[0060] FIG. 5 is a diagram for explaining the calculation of the polarization angle difference by the polarization angle calculation units 177a and 177b according to the second embodiment. In FIG. 5 and the following description, the Stokes parameters are defined as (S k (i), S2 k (i), S3 k The symbol k indicates the order of the FRM, such as the first FRM 23a and the second FRM 23b. The sensing interferometers 2a and 2b are not distinguished here. The Stokes parameters (S11(i), S21(i), S31(i)) of the first FRM 23a and the Stokes parameters (S12(i), S22(i), S32(i)) of the second FRM 23b are displayed on the Poincaré sphere as shown in FIG. 5. The polarization angle calculation units 177a and 177b calculate the polarization angle difference d(i) for each pulse from the Stokes parameters of the first FRM 23a and the Stokes parameters of the second FRM 23b.

[0061] The polarization angle difference d(i) between the first FRM 23a and the second FRM 23b is displayed as an angle difference on the Poincare sphere, which is a double angle change. That is, the angle difference on the Poincare sphere is 2d(i). As shown in FIG. 5, the angle difference 2d(i) on the Poincare sphere is an angle between the Stokes parameters of the first FRM 23a and the Stokes parameters of the second FRM 23b and the origin O. The polarization angle calculation units 177a and 177b calculate the angle difference on the Poincare sphere from the Stokes parameters (S11(i), S21(i), S31(i)) of the first FRM 23a and the Stokes parameters (S12(i), S22(i), S32(i)) of the second FRM 23b, and set the angle difference on the Poincare sphere display to 1 / 2 as the polarization angle difference d(i). The polarization angle difference d(i) is expressed by the following equation (11).

[0062]

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[0063] The maximum value extraction unit 178a extracts the maximum value of the repeatedly obtained polarization angle difference d(i) of the sensing interferometer 2a. The maximum value extraction unit 178b extracts the maximum value of the repeatedly obtained polarization angle difference d(i) of the sensing interferometer 2b. The maximum values ​​extracted by the maximum value extraction units 178a and 178b are output to the inspection units 179a and 179b.

[0064] The inspection unit 179a inspects whether the sensing interferometer 2a is normal based on the maximum value of the polarization angle difference d(i) of the sensing interferometer 2a. The inspection unit 179b inspects whether the sensing interferometer 2b is normal based on the maximum value of the polarization angle difference d(i) of the sensing interferometer 2b. Even if the polarization rotation angle of the FRM is exactly 90° round trip, if the outward and return paths are different, the polarization state changes due to the influence of birefringence of the transmission path. However, since the light reflected by the two FRMs of the same sensing interferometer passes through the same transmission path, the polarization angle difference is zero if the polarization rotation angles of both the first FRM 23a and the second FRM 23b are exactly 90° round trip. On the other hand, if the polarization rotation angle of either the first FRM 23a or the second FRM 23b deviates from 90° round trip, the maximum value of the polarization angle difference increases.

[0065] Therefore, the inspection unit 179a measures the sum of the errors in the polarization rotation angles of the first FRM 23a and the second FRM 23b from the maximum value of the polarization angle difference d(i) of the sensing interferometer 2a, and judges whether it is within the tolerance required for suppressing polarization fading or the like. The polarization angle difference d(i) of the sensing interferometer 2a changes according to the error in the polarization rotation angle of the first FRM 23a of the sensing interferometer 2a and the error in the polarization rotation angle of the second FRM 23b. The maximum value of the polarization angle difference d(i) of the sensing interferometer 2a is equal to the sum of the errors in the polarization rotation angles of the first FRM 23a and the second FRM 23b of the sensing interferometer 2a. When the polarization rotation angles of the first FRM 23a and the second FRM 23b are both 90°, the sum of the errors in the polarization rotation angles of the FRMs is zero, and the maximum value of the polarization angle difference d(i) is also zero.

[0066] If the sum of the errors in the polarization rotation angles of the first FRM 23a and the second FRM 23b is within the allowable range, the inspection unit 179a determines that the sensing interferometer 2a is normal. On the other hand, if the sum of the errors is not within the allowable range, the inspection unit 179a determines that the sensing interferometer 2a is not normal. The inspection unit 179b inspects whether the sensing interferometer 2b is normal or not using the same method as the inspection unit 179a.

[0067] In addition, even if the polarization rotation angle of both the first FRM 23a and the second FRM 23b of the sensing interferometer 2a or 2b deviates from 90° round trip, the sum of the polarization rotation angle errors of the first FRM 23a and the second FRM 23b is measured, so that it is possible to check whether it is within the tolerance range required for suppressing polarization fading, etc.

[0068] According to this embodiment, by making a judgment based on the maximum value of the polarization angle difference of the light reflected from two FRMs (first FRM 23a and second FRM 23b) of the same sensing interferometer 2a, it is possible to measure the error in the polarization rotation angle of the internal FRM without disassembling the inspection object 200 even if the outward and return paths of the inspection object 200 are separated. This makes it possible to inspect the deterioration of the performance of the FRM due to the influence of the surrounding magnetism after assembly or the aging of the magnetism of the FRM. In addition, the measurement time can be shortened by changing the polarization state of the light input to the FRM using the polarization controller 13A.

[0069] Embodiment 3 6 is a schematic configuration diagram of an inspection apparatus 1B according to embodiment 3. The inspection apparatus 1B of this embodiment inspects an inspection object 200A including a sensing interferometer 2.

[0070] The inspection object 200A in this embodiment is an interferometric optical fiber sensor. As shown in Fig. 6, the inspection object 200A includes a sensing interferometer 2, optical fibers 211a and 211b, a pulsed light source 212, a delay compensation interferometer 213, an optical coupler 214, an O / E converter 215, an A / D converter 216, and a demodulator 217. The configuration of the sensing interferometer 2 is the same as that of the first embodiment.

[0071] The pulse light source 212 outputs pulse light with a constant frequency as input light. The delay compensation interferometer 213 has an optical coupler, an optical frequency shifter, and a delay compensation fiber, none of which are shown. The pulse light input to the delay compensation interferometer 213 is split into two by the optical coupler, one of the pulse light is delayed by the delay compensation fiber, and the optical frequency of the other pulse light is shifted by the optical frequency shifter. The pulse light output from the delay compensation fiber and the pulse light output from the optical frequency shifter are merged into the optical fiber 211a by the optical coupler, and are output to the sensing interferometer 2.

[0072] The optical coupler 214 branches the reflected light from the sensing interferometer 2 and outputs it to the O / E converter 215 and the inspection device 1B. The O / E converter 215 converts the input pulsed light into an electric signal and outputs it to the A / D converter 216. The A / D converter 216 converts the electric signal converted by the O / E converter 215 into a digital signal and outputs it to the demodulator 217. The demodulator 217 demodulates the signal detected by the sensing fiber 24 of the sensing interferometer 2 from the digital signal converted by the A / D converter 216 and outputs it.

[0073] The inspection device 1B of this embodiment includes a connector 19, a Stokes spectrometer 18, O / E converters 16c, 16d, 16e, and 16f, and a processor 17B. The inspection device 1B is connected to an inspection target 200 via the connector 19, and reflected light from the sensing interferometer 2 branched by the optical coupler 214 is input to the Stokes spectrometer 18 via the connector 19.

[0074] In the present embodiment, the configurations and functions of the Stokes spectrometer 18 and the O / E converters 16c to 16f are the same as those in the second embodiment. Moreover, the processor 17B in the present embodiment includes a Stokes parameter calculator 175, pulse extractors 176a and 176b, a polarization angle calculator 177a, a maximum value extractor 178a, and an inspector 179a. The configurations and functions of the components in the processor 17B are the same as those in the second embodiment. However, in the present embodiment, since the polarization controller 13 is not provided, the polarization state cannot be actively changed, and the polarization angle calculator 177a repeatedly calculates the polarization angle difference until the polarization state changes due to a temperature change or bending stress in the optical transmission path of the inspection target 200A.

[0075] According to this embodiment, it is possible to inspect whether the sensing interferometer 2 is normal or not while it is in operation, without removing the sensing interferometer 2 from the inspection target 200A. This makes it possible to inspect the performance degradation of the FRM due to the influence of surrounding magnetism after assembly, or due to aging of the magnetism of the FRM. In addition, since the inspection target 200A and the inspection device 1B can be detached, multiple inspection targets can be inspected with one inspection device 1B.

[0076] The above is an explanation of the embodiment of the present invention, but the present invention is not limited to the configuration of the above embodiment, and various modifications and combinations are possible within the scope of the technical concept. For example, in the above embodiment, an example of inspecting the FRM after the sensing interferometer 2 is constructed is shown, but the inspection device 1 can also be used to inspect the FRM alone before the sensing interferometer 2 is constructed. In this case, a light source that outputs continuous light instead of the pulse light source 11 is used, and the maximum value of the continuous signal output from the O / E converter is extracted to determine whether the FRM is normal or not.

[0077] In addition, in the first and second embodiments, examples of polarization controllers 13 and 13A in which half-wave plate 131 and quarter-wave plate 132 are rotated, or an optical fiber is wound in a coil shape around oscillator 133 and vibrated, are shown, but polarization controllers 13 and 13A may have other configurations as long as they change the polarization state.

[0078] In addition, in the first embodiment, an example is shown in which the X / Y ratio between the X component intensity and the Y component intensity separated by the polarizing beam splitter 15 is used, but if the loss is stable, a polarizer may be used to extract the maximum value of the X component. That is, by repeatedly detecting the intensity of the component of the light reflected by the FRM of the sensing interferometer 2, whose electric field oscillation direction is the same as that of the input light to the FRM, the error in the polarization rotation angle of the FRM can be measured. Note that the input light to the FRM includes not only the light at the entrance of the light of the FRM, but also the light that passes through the optical fiber, optical coupler, etc. and then inputs to the FRM before entering the optical fiber, optical coupler, etc.

[0079] In addition, in the processor 17 of the first embodiment, an example has been shown in which the X / Y ratio is calculated after the pulse is extracted, but the pulse may be extracted after the X / Y ratio is calculated. In addition, in the processor 17A of the second and third embodiments, an example has been shown in which the Stokes parameters are calculated before the pulse is extracted, but the Stokes parameters may be calculated after the pulse is extracted.

[0080] In the Stokes spectrometer 18 and the processor 17A of the second embodiment, the intensity I X (t), I Y (t), I 45 (t), I Q45 Although the Stokes parameters are calculated from the light (t) in the above example, the polarization state may be calculated based on other spectroscopic methods or parameters.

[0081] In addition, in the inspection units of the inspection devices 1 to 1B in the above-described embodiments, the maximum value of the X / Y ratio or the polarization angle difference is extracted, but a value related to the maximum value may be extracted. For example, an index indicating an increase or spread of a numerical value, such as an average value or a standard deviation, may be used.

[0082] Furthermore, the processor of the inspection devices 1 to 1B of the above-mentioned embodiments may be configured not to have an inspection unit. In this case, the maximum value of the X / Y ratio or the polarization angle difference extracted by the maximum value extraction unit is output from the inspection devices 1 to 1B, and a separately provided processing device performs the same inspection as the inspection unit. [Explanation of symbols]

[0083] 1, 1A, 1B inspection device, 2, 2a, 2b sensing interferometer, 11 pulse light source, 12 half mirror, 13, 13A polarization controller, 14 lens, 15 polarizing beam splitter, 16a, 16b, 16c, 16d, 16e, 16f O / E converter, 17, 17A, 17B processor, 18 Stokes spectrometer, 19 connector, 21a, 21b, 21c optical fiber, 22 optical coupler, 23a first FRM, 23b second FRM, 24 sensing fiber, 131 1 / 2 wave plate, 132 1 / 4 wave plate, 133 oscillator, 171a, 171b pulse extraction unit, 172a, 172b division unit, 173a, 173b maximum value extraction unit, 174a, 174b inspection unit, 175 Stokes parameter calculation unit, 176a, 176b, 176c, 176d pulse extraction unit, 177a, 177b polarization angle calculation unit, 178a, 178b maximum value extraction unit, 179a, 179b inspection unit, 200, 200A inspection object, 201a, 201b, 201c, 201d, 201e, 201f optical fiber, 202 branching optical coupler, 203 coupling optical coupler, 204 delay fiber, 211a, 211b optical fiber, 212 pulse light source, 213 delay compensation interferometer, 214 optical coupler, 215 O / E converter, 216 A / D converter, 217 demodulator, 231 Faraday rotator, 232 mirror.

Claims

1. An inspection device for inspecting a Faraday Rotator Mirror (FRM) having a Faraday rotator and a mirror, An inspection device comprising a processor that repeatedly detects the intensity of components of light reflected by the FRM whose electric field vibration direction is the same as the input light to the FRM and whose electric field vibration direction is perpendicular to the input light, and repeatedly calculates the ratio between the intensity of the components whose electric field vibration direction is the same as the input light and the intensity of the components whose electric field vibration direction is perpendicular to the input light.

2. a light source that outputs the input light to the FRM; a beam splitter that separates the light reflected by the FRM into a component having an electric field oscillation direction in the same direction as the input light and a component having an electric field oscillation direction perpendicular to the input light; The processor includes: Repeatedly calculating the ratio based on a component having an electric field oscillation direction that is the same as that of the separated input light and a component having an electric field oscillation direction that is perpendicular to that of the input light; 2. The inspection apparatus according to claim 1, wherein the maximum value, the average value or the standard deviation of the ratio is extracted.

3. The processor includes: Measure the error of the polarization rotation angle of the FRM from the maximum value, average value, or standard deviation of the ratio; The inspection apparatus according to claim 2 , further comprising a step of determining whether the error is within an allowable range.

4. An inspection apparatus for inspecting an interferometer including two FRMs (Faraday Rotator Mirrors), each of which has a Faraday rotator and a mirror, comprising: An inspection apparatus comprising a processor that repeatedly calculates the polarization angle difference between the two FRMs based on light reflected by the interferometer.

5. The processor includes: Calculating the Stokes parameters of the light reflected by the interferometer; The inspection apparatus according to claim 4 , wherein the polarization angle difference is calculated based on the Stokes parameters.

6. The processor includes: Measure the sum of the errors in the polarization rotation angles of the two FRMs from the maximum value, average value, or standard deviation of the polarization angle difference; 6. The inspection apparatus according to claim 4, further comprising a step of determining whether or not the sum of the errors is within an allowable range.

7. 7. The inspection device according to claim 4, further comprising a connector connected to an interferometric optical fiber sensor including the interferometer and a light source that inputs light to the interferometer.

8. 8. The inspection device according to claim 1, wherein the input light to the FRM is a pulsed light.

9. 9. The inspection apparatus according to claim 1, further comprising a polarization controller that changes the polarization state of the input light to the FRM.

10. 1. A method for inspecting an FRM having a Faraday rotator and a mirror, comprising the steps of: Repeatedly detecting the intensity of a component of the light reflected by the FRM, the component having an electric field oscillation direction that is the same as that of the input light to the FRM, and the component having an electric field oscillation direction that is perpendicular to the input light; and repeatedly calculating a ratio between an intensity of a component in a direction that is the same as the input light and an electric field oscillation direction and an intensity of a component in a direction that is perpendicular to the input light and the electric field oscillation direction.

11. 1. A method for inspecting an interferometer including two FRMs, each having a Faraday rotator and a mirror, comprising the steps of: The inspection method includes a step of repeatedly calculating a polarization angle difference between the two FRMs based on light reflected by the interferometer.

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