Interferometric optical magnetic field sensor device

Abstract

To provide an interference type optical magnetic field sensor device that can suppress distortion of a waveform of an electric signal indicative of a magnetic field to be detected.SOLUTION: An interference type magnetic field sensor device 1 has: a first magnetic field sensor element 50A and a second magnetic field sensor element 50B upon which first linear polarization and second linear polarization are incident, and which cause the first linear polarization and the second linear polarization to be changed in accordance with a magnetic field to be applied, and emit third linear polarization and fourth linear polarization; and an optical path unit 40 that has a first optical path propagating the first linear polarization and the fourth linear polarization, and a second optical path propagating the second linear polarization and the third linear polarization, and a branch coupler demultiplexing each of the first linear polarization and the second linear polarization to emit the first linear polarization and the second linear polarization to the first magnetic field sensor element and the second magnetic field sensor element, multiplexing each of the third linear polarization and the fourth linear polarization incident respectively from the first magnetic field sensor element and the second magnetic field sensor element to emit the multiplexed third linear polarization to the second optical path, and emit the multiplexed fourth linear polarization to the first optical path.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to an interferometric optical magnetic field sensor device. [Background technology]

[0002] An interferometric optical magnetic field sensor device is known that uses a magnetic field sensor element equipped with a Faraday rotor at the tip of an optical fiber, and generates a detection signal corresponding to the magnetic field applied to the Faraday rotor by photoelectric conversion of light transmitted through the magnetic field sensor element (see, for example, Patent Document 1). The interferometric optical magnetic field sensor device described in Patent Document 1 (hereinafter also referred to as the sensor device) can suppress the influence of an external magnetic field on the measured value of the detected magnetic field by detecting the magnetic field using a pair of magnetic field sensor elements that can be placed in a predetermined magnetic field with the conductor to be measured in between. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-025794 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, in the sensor device described in Patent Document 1, the first linearly polarized CW1 and the second linearly polarized CCW1 are sequentially incident via a PANDA fiber connecting the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. In the sensor device described in Patent Document 1, the time it takes for the first linearly polarized CW1 and the second linearly polarized CCW1 to pass through the PANDA fiber becomes a time difference in magnetic field detection, which may cause distortion of the waveform of the electrical signal indicating the magnetic field. Distortion of the waveform of the electrical signal indicating the magnetic field caused by the time difference in magnetic field detection due to the time it takes to pass through the PANDA fiber becomes a factor in detection errors when operating in the high frequency band of several MHz or higher. In particular, the longer the sensor fiber length, the more detection errors occur from the lower frequency band.

[0005] The present invention aims to provide an interferometric optical magnetic field sensor device capable of suppressing waveform distortion of the electrical signal indicating the magnetic field to be detected. [Means for solving the problem]

[0006] The interference-type optical magnetic field sensor device according to the present invention includes a light-emitting unit that emits first linearly polarized light, a first optical element that emits first linearly polarized and second linearly polarized light in response to incident first linearly polarized light, and emits second linearly polarized light in response to incident third linearly polarized and fourth linearly polarized light, a first magnetic field sensor element and a second magnetic field sensor element that receive first linearly polarized and second linearly polarized light, and change the first linearly polarized and second linearly polarized light in response to the applied magnetic field to emit the third linearly polarized and fourth linearly polarized light, a first optical path for propagating first linearly polarized and fourth linearly polarized light, a second optical path for propagating second linearly polarized and third linearly polarized light, and first linearly polarized light The optical path section includes an optical path section having a branching coupler that separates the first and second linearly polarized light and emits them to the first and second magnetic field sensor elements, respectively, and combines the third and fourth linearly polarized light incident from the first and second magnetic field sensor elements, respectively, to emit the combined third linearly polarized light to the second optical path and the combined fourth linearly polarized light to the first optical path; a detection signal generation section that receives the two components of the second linearly polarized light and converts them into an electrical signal to output a detection signal corresponding to the magnetic field; and an optical branching section that transmits the first linearly polarized light to the first optical element and branches the second linearly polarized light to the detection signal generation section.

[0007] Furthermore, it is preferable that the interference-type optical magnetic field sensor device according to the present invention further includes a yoke arranged to surround the conductor to be measured and to hold the first magnetic field sensor element and the second magnetic field sensor element.

[0008] Furthermore, the interference-type optical magnetic field sensor device according to the present invention further comprises a first polarization-maintaining fiber that optically connects a branch coupler and a first magnetic field sensor element, and a second polarization-maintaining fiber that optically connects the branch coupler and a second magnetic field sensor element, wherein the lengths of the first polarization-maintaining fiber and the second polarization-maintaining fiber are preferably equal.

[0009] Furthermore, in the interference-type optical magnetic field sensor device according to the present invention, it is preferable that the second polarization-maintaining fiber rotates the polarization planes of the first linear polarization, second linear polarization, third linear polarization, and fourth linear polarization by 90°.

[0010] Furthermore, in the interference-type optical magnetic field sensor device according to the present invention, the second polarization-maintaining fiber is preferably formed by a pair of polarization-maintaining fibers that are fused together after rotating the slow axis and the fast axis by 90°. [Effects of the Invention]

[0011] The interference-type optical magnetic field sensor device according to the present invention can suppress distortion of the waveform of the electrical signal indicating the detected magnetic field. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram of the sensor device according to the embodiment. [Figure 2] Figure 1 is a schematic diagram of the first magnetic field sensor element and the second magnetic field sensor element. [Figure 3] This is a partially enlarged plan view of the area indicated by arrow A in Figure 1. [Figure 4] Figure 1 shows the circuit diagram of the first photodetector, the second photodetector, and the signal processing circuit. [Figure 5] This is a diagram (part 1) illustrating the operation of the sensor device shown in Figure 1. [Figure 6] This is a diagram (part 2) illustrating the operation of the sensor device shown in Figure 1. [Figure 7] (a) is a diagram (part 3) illustrating the operation of the sensor device shown in Figure 1, and (b) is a diagram (part 4) illustrating the operation of the sensor device shown in Figure 1. [Figure 8] (a) is a diagram showing the connection relationship between the PBS and the magnetic field sensor of the sensor device according to the comparative example, and (b) is a diagram showing the timing at which an electrical signal indicating the detected magnetic field is output at each of the magnetic field sensor elements shown in (a). DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0013] Hereinafter, an interferometric optical magnetic field sensor device will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, and extends to the invention described in the claims and equivalents thereof.

[0014] Figure 1 is a block diagram of the sensor device 1.

[0015] The sensor device 1 is an example of an interferometric optical magnetic field sensor device, and includes a light emitting unit 10, a circulator 20, a 1 / 2 wavelength plate 30, and an optical path unit 40. The sensor device 1 further includes a first magnetic field sensor element 50A, a second magnetic field sensor element 50B, a first polarization maintaining fiber 51, a second polarization maintaining fiber 52, a yoke 53, and a detection signal generation unit 60. The optical paths between the light emitting unit 10, circulator 20, 1 / 2 wavelength plate 30, optical path unit 40, and detection signal generation unit 60 are formed by PANDA (Polarization-maintaining AND Absorption-reducing) fiber. Note that the optical paths between the 1 / 2 wavelength plate 30, optical path unit 40, and detection signal generation unit 60 may be formed by a polarization maintaining fiber such as a Bow-tie fiber or an Elliptical Jacket fiber.

[0016] The light-emitting unit 10 includes a light-emitting element 11, an isolator 12, and a polarizer 13. The light-emitting element 11 is, for example, a semiconductor laser or a light-emitting diode, and is preferably a Fabry-Perot laser, a superluminescent diode, etc. The isolator 12 protects the light-emitting element 11 by allowing light emitted from the light-emitting element 11 to pass to the circulator 20 side, and by preventing light incident from the circulator 20 to the light-emitting unit 10 from passing to the light-emitting element 11 side. The isolator 12 is, for example, a polarization-dependent optical isolator, or it may be a polarization-independent optical isolator. The polarizer 13 is an optical element for converting the light emitted from the light-emitting element 11 into linearly polarized light, and its type is not particularly limited. The first linearly polarized light obtained by the polarizer 13 is incident on the circulator 20.

[0017] The circulator 20 is an example of an optical splitting unit, which transmits the first linearly polarized light emitted from the light-emitting unit 10 to the half-wave plate 30 and splits the second linearly polarized light emitted from the half-wave plate 30 to the detection signal generation unit 60. The circulator 20 is formed, for example, by a Faraday rotor, a half-wave plate, a polarizing beam splitter, or a reflective mirror.

[0018] The half-wave plate 30 is an example of a first optical element, and is positioned so that its azimuth angle is 22.5° with respect to the polarization plane of the first linearly polarized light incident from the circulator 20, and rotates the polarization plane of the first linearly polarized light by 45° before emitting it to the optical path section 40. The first linearly polarized light emitted from the half-wave plate 30 has a first linearly polarized light CW1 which is P-polarized and a second linearly polarized light CCW1 which is S-polarized and orthogonal to the first linearly polarized light CW1. The half-wave plate 30 also rotates the polarization plane of the second linearly polarized light incident from the optical path section 40 by 45° before emitting it to the circulator 20.

[0019] The optical path section 40 includes a PBS (polarizing beam splitter) 41, a branching coupler 42, a first optical path 43, a second optical path 44, and a phase adjustment element 45.

[0020] PBS41 separates the first linearly polarized light incident from the half-wave plate 30 into a P-polarized component and an S-polarized component, and emits the first linearly polarized CW1 into the first optical path 43 and the second linearly polarized CCW1 into the second optical path 44. PBS41 also receives the third linearly polarized CW2 from the second optical path 44 and the fourth linearly polarized CCW2 from the first optical path 43, combines them, and emits them back into the half-wave plate 30. The third linearly polarized CW2 and the fourth linearly polarized CCW2 are mutually orthogonal polarization components of the second linearly polarized light emitted into the half-wave plate 30. PBS41 is, for example, a prism-type beam splitter, but may also be a planar beam splitter or a wedge-type beam splitter.

[0021] The branching coupler 42 is a fused or filter-type optical fiber coupler having polarization-independent characteristics, and is optically connected to the first optical path 43, the second optical path 44, the first polarization-maintaining fiber 51, and the second polarization-maintaining fiber 52. The branching coupler 42 demultiplexes the first linearly polarized CW1 incident from the first optical path 43 and the second linearly polarized CCW1 incident from the second optical path 44, and outputs them to the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52, respectively. The branching coupler 42 demultiplexes the first linearly polarized CW1 and the second linearly polarized CCW1 in a 50:50 ratio. One of the first linearly polarized CW1 and the second linearly polarized CCW1 demultiplexed by the branching coupler 42 is incident on the first magnetic field sensor element 50A via the first polarization-maintaining fiber 51. The other of the first linearly polarized CW1 and the second linearly polarized CCW1, which are separated by the branching coupler 42, is incident on the second magnetic field sensor element 50B via the second polarization-maintaining fiber 52.

[0022] The branch coupler 42 combines the third linearly polarized light CW2 incident from the first magnetic field sensor element 50A via the first polarization-maintaining fiber 51 and the third linearly polarized light CW2 incident from the second magnetic field sensor element 50B via the second polarization-maintaining fiber 52. The branch coupler 42 emits the combined third linearly polarized light CW2 into the second optical path 44. The branch coupler 42 combines the fourth linearly polarized light CCW2 incident from the first magnetic field sensor element 50A via the first polarization-maintaining fiber 51 and the fourth linearly polarized light CCW2 incident from the second magnetic field sensor element 50B via the second polarization-maintaining fiber 52. The branch coupler 42 emits the combined fourth linearly polarized light CCW2 into the first optical path 43.

[0023] The first optical path 43 is a PANDA fiber with one end optically connected to PBS 41 and the other end optically connected to a branch coupler 42. The first optical path 43 leads the first linearly polarized CW1 introduced from PBS 41 to the branch coupler 42, and also leads the fourth linearly polarized CCW2 introduced from the branch coupler 42 to PBS 41. The second optical path 44 is a PANDA fiber with one end optically connected to PBS 41 and the other end optically connected to a branch coupler 42. The second optical path 44 leads the second linearly polarized CCW1 introduced from PBS 41 to the branch coupler 42, and also leads the third linearly polarized CW2 introduced from the branch coupler 42 to PBS 41. The optical path between the branch couplers 42 is also a PANDA fiber. Note that the first optical path 43, the second optical path 44, and the optical path between the branch couplers 42 may be polarization-maintaining fibers such as bowtie fibers or elliptical jacket fibers.

[0024] The phase adjustment element 45 includes quarter-wave plates 46 and 47 and a 45-degree Faraday rotator 48. The phase adjustment element 45 is an example of a second optical element and is positioned in the second optical path 44 to adjust the phases of the second linearly polarized CCW1 and the third linearly polarized CCW2 so that the phase difference between the third linearly polarized CCW2 and the fourth linearly polarized CCW2 is 90°. The quarter-wave plate 46 is positioned with its optical axis tilted at 45° with respect to the slow and fast axes of the PANDA fiber forming the second optical path 44, and converts linearly polarized light to circularly polarized light and circularly polarized light to linearly polarized light. The quarter-wave plate 47 is positioned with its optical axis tilted at -45° with respect to the slow and fast axes of the PANDA fiber forming the second optical path 44, and converts circularly polarized light to linearly polarized light and linearly polarized light to circularly polarized light.

[0025] The 45-degree Faraday rotator 48 is positioned between the quarter-wave plates 46 and 47 and changes the phase of the circularly polarized light incident on them. The 45-degree Faraday rotator 48 changes the phase of the incident light such that the phase of the second linearly polarized light CCW1 emitted from the quarter-wave plate 47 is shifted by 45° from the phase of the second linearly polarized light CCW1 incident on the quarter-wave plate 46. The 45-degree Faraday rotator 48 also changes the phase of the incident light such that the phase of the third linearly polarized light CW2 emitted from the quarter-wave plate 46 is shifted by -45° from the phase of the third linearly polarized light CW2 incident on the quarter-wave plate 47.

[0026] Figure 2 is a schematic diagram of the first magnetic field sensor element 50A and the second magnetic field sensor element 50B.

[0027] The first magnetic field sensor element 50A and the second magnetic field sensor element 50B are a pair of elements having the same configuration, and each includes a quarter-wave plate 54, a Faraday rotor 55, and a mirror element 56.

[0028] The first magnetic field sensor element 50A and the second magnetic field sensor element 50B can be positioned within a predetermined magnetic field with the conductor to be measured 100 in between, and are integrally formed with a certain distance between them. The relative position of the first magnetic field sensor element 50A with respect to the second magnetic field sensor element 50B is fixed, and the distance between the first magnetic field sensor element 50A and the second magnetic field sensor element 50B remains unchanged even if the sensor device 1 moves during measurement. The first magnetic field sensor element 50A and the second magnetic field sensor element 50B are light-transmitting and change the phase of transmitted light according to the magnetic field applied to the Faraday rotator 55. Both the first magnetic field sensor element 50A and the second magnetic field sensor element 50B are incident on first linearly polarized CW1 and second linearly polarized CCW1, and emit third linearly polarized CW2 and fourth linearly polarized CCW2 in response to the incident first linearly polarized CW1 and second linearly polarized CCW1.

[0029] The quarter-wave plate 54 is positioned with its optical axis tilted at 45° with respect to the lagging and leading axes of the branch coupler 42 or the first polarization-maintaining fiber 51 and second polarization-maintaining fiber 52 that optically connect to the branch coupler 42. The quarter-wave plate 54 converts linearly polarized light incident from the branch coupler 42 into circularly polarized light, and also converts the circularly polarized light reflected from the Faraday rotator 55 into linearly polarized light.

[0030] The Faraday rotator 55 is a granular film having a dielectric 550 and nano-order magnetic particles 551 dispersed in the dielectric 550 in a stably phase-separated state from the dielectric 550, and is positioned on the end face of the quarter-wave plate 54. The magnetic particles 551 may be oxides in a very small part, such as the outermost layer, but throughout the Faraday rotator 55 they are dispersed individually in the thin film without forming compounds with the dielectric that acts as a binder. The distribution of magnetic particles 551 within the Faraday rotator 55 does not have to be perfectly uniform and may be somewhat biased. If a highly transparent dielectric 550 is used, the Faraday rotator 55 will be light-transmitting because the magnetic particles 551 in the dielectric 550 are smaller than the wavelength of light.

[0031] The Faraday rotor 55 is not limited to a single layer; it may also be a multilayer film in which granular films and dielectric films are alternately stacked. By making the granular film a multilayer, a larger Faraday rotation angle can be obtained due to multiple reflections within the granular film.

[0032] The dielectric 550 is preferably a fluoride (metallic fluoride) such as magnesium fluoride (MgF2), aluminum fluoride (AlF3), or yttrium fluoride (YF3). Alternatively, the dielectric 550 may be an oxide such as tantalum oxide (Ta2O5), silicon dioxide (SiO2), titanium dioxide (TiO2), disiniobium pentoxide (Nb2O5), zirconium dioxide (ZrO2), hafnium dioxide (HfO2), or aluminum trioxide (Al2O3). For good phase separation between the dielectric 550 and the magnetic particles 551, fluorides are preferred over oxides, and magnesium fluoride, which has high transmittance, is particularly preferred.

[0033] The material of the magnetic particles 551 is not particularly limited, as long as it produces the Faraday effect, but examples of materials include ferromagnetic metals such as iron (Fe), cobalt (Co), and nickel (Ni), and their alloys. Examples of Fe, Co, and Ni alloys include FeNi alloy, FeCo alloy, FeNiCo alloy, and NiCo alloy. The Faraday rotation angle per unit length of Fe, Co, and Ni is nearly two to three orders of magnitude larger than that of magnetic garnet used in conventional Faraday rotors. In addition, conventional transparent magnetic materials such as magnetic garnet and ferrite may be used as the material of the magnetic particles 551.

[0034] The mirror element 56 is formed on the side of the Faraday rotor 55 opposite to the quarter-wave plate 54, and reflects light that has passed through the Faraday rotor 55 back towards the Faraday rotor 55. For the mirror element 56, for example, a silver (Ag) film, a gold (Au) film, an aluminum (Al) film, or a dielectric multilayer mirror can be used. In particular, Ag films with high reflectivity and Au films with high corrosion resistance are preferred because they are easy to form. The thickness of the mirror element 56 should be such that a sufficient reflectivity of 98% or more is ensured, and for example, in the case of an Ag film, it is preferable to have a thickness of 50 nm or more and 200 nm or less. By using the mirror element 56 to make light oscillate back and forth within the Faraday rotor 55, the Faraday rotation angle can be increased.

[0035] The first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 are both PANDA fibers of the same length. The first polarization-maintaining fiber 51 optically connects the branch coupler 42 to the first magnetic field sensor element 50A, and the second polarization-maintaining fiber 52 optically connects the branch coupler 42 to the second magnetic field sensor element 50B. The first polarization-maintaining fiber 51 is formed from a single PANDA fiber and derives linearly polarized P-polarized light when linearly polarized P-polarized light is introduced, and linearly polarized S-polarized light when linearly polarized S-polarized light is introduced. The second polarization-maintaining fiber 52 is formed from a pair of PANDA fibers fused at the fusion point Pf with their slow and fast axes rotated by 90°, and derives linearly polarized S-polarized light when linearly polarized P-polarized light is introduced, and linearly polarized P-polarized light when linearly polarized S-polarized light is introduced. The first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 may each be formed from a polarization-maintaining fiber such as a bowtie fiber or an elliptical jacket fiber.

[0036] The first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 receive the first linearly polarized CW1 and the second linearly polarized CCW1, which have been separated by the branch coupler 42. The first polarization-maintaining fiber 51 leads the first linearly polarized CW1 and the second linearly polarized CCW1 introduced from the branch coupler 42 to the first magnetic field sensor element 50A. The second polarization-maintaining fiber 52 rotates the polarization planes of the first linearly polarized CW1 and the second linearly polarized CCW1 introduced from the branch coupler 42 by 90° and leads them to the second magnetic field sensor element 50B.

[0037] The first polarization-maintaining fiber 51 leads the third linearly polarized CW2 and the fourth linearly polarized CCW2 introduced from the first magnetic field sensor element 50A to the branch coupler 42. The second polarization-maintaining fiber 52 rotates the polarization planes of the third linearly polarized CW2 and the fourth linearly polarized CCW2 introduced from the second magnetic field sensor element 50B by 90° and leads them to the branch coupler 42.

[0038] Figure 3 is a partially enlarged plan view of the area indicated by arrow A in Figure 1.

[0039] The yoke 53 has a first yoke 53A and a second yoke 53B. The first yoke 53A and the second yoke 53B are made of a magnetic material with a relative permeability greater than 1, and it is preferable to use a composite material in which soft magnetic particles are dispersed in an insulator such as resin, as this will result in good high-frequency characteristics due to the eddy current suppression effect. A magnetic circuit is formed by the magnetic field generated when an electric current flows through the conductor 100 to be measured, together with the first magnetic field sensor element 50A and the second magnetic field sensor element 50B.

[0040] The first yoke 53A has the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 embedded in it, and together with the second yoke 53B, it holds the first magnetic field sensor element 50A and the second magnetic field sensor element 50B by sandwiching them between them. The second yoke 53B is fixed to the first yoke 53A via a fixing member (not shown).

[0041] The detection signal generation unit 60 includes a PBS 61, a first photodetector 62, a second photodetector 63, and a signal processing circuit 70. The detection signal generation unit 60 separates the second linearly polarized light branched by the circulator 20 into an S-polarized component 64 and a P-polarized component 65. The detection signal generation unit 60 also receives the separated S-polarized component 64 and P-polarized component 65, converts them into electrical signals, and performs differential amplification to output a detection signal Ed corresponding to the magnetic field applied to the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. The PBS 61 is a polarizing beam splitter such as a prism type, planar type, wedge substrate type, or optical waveguide type, and separates the second linearly polarized light branched by the circulator 20 into an S-polarized component 64 and a P-polarized component 65.

[0042] Figure 4 is a circuit diagram of the first photodetector 62, the second photodetector 63, and the signal processing circuit 70.

[0043] The signal processing circuit 70 includes an amplifying element 71, which is, for example, an operational amplifier, and a resistive element 72. The first light-receiving element 62 and the second light-receiving element 63 are, for example, PIN photodiodes, and perform photoelectric conversion to output an electrical signal corresponding to the amount of light received. The anode of the first light-receiving element 62 and the cathode of the second light-receiving element 63 are connected to the negative input terminal of the amplifying element 71, the cathode of the first light-receiving element 62 is connected to a positive power supply +V, and the anode of the second light-receiving element 63 is connected to a negative power supply -V. The first light-receiving element 62 receives the S-polarization component 64 of the combined wave of the third linearly polarized CW2 and the fourth linearly polarized CCW2, and outputs a first electrical signal E1, which is a current proportional to its intensity. The second light-receiving element 63 receives the P-polarization component 65 of the combined wave of the third linearly polarized CW2 and the fourth linearly polarized CCW2, and outputs a second electrical signal E2, which is a current proportional to its intensity.

[0044] The S-polarization and P-polarization components of the third linearly polarized light CW2 incident on the detection signal generation unit 60 are represented by the following equation ECW, and the S-polarization and P-polarization components of the fourth linearly polarized light CCW2 are represented by the following equation ECCW. θ F is the Faraday rotation angle corresponding to the magnetic field applied to the Faraday rotator 55, and j is the imaginary unit.

[0045]

number

[0046] The S-polarization component P0 and P-polarization component P90 of the combined wave of the third linearly polarized CW2 and the fourth linearly polarized CCW2 are expressed from the above ECW and ECCW equations as follows: ECW,0,ECCW,0,ECW,90,ECCW,90 are the S-polarization component of the third linearly polarized CW2, the S-polarization component of the fourth linearly polarized CCW2, the P-polarization component of the third linearly polarized CW2, and the P-polarization component of the fourth linearly polarized CCW2, respectively.

[0047]

number

[0048] The signal processing circuit 70 is an inverting amplifier circuit that inverts and amplifies the differential signal (E1-E2) between the first electrical signal E1 and the second electrical signal E2, thereby outputting a detection signal Ed corresponding to the magnetic field applied to the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. The positive input terminal of the amplifier element 71 is grounded, and the differential signal (E1-E2) is input to the negative input terminal of the amplifier element 71. The differential signal (E1-E2) is proportional to the difference between the S-polarization component P0 and the P-polarization component P90, and the Faraday rotation angle θ F This is an electrical signal corresponding to the light intensity. The detected signal Ed is an electrical signal from which the DC component corresponding to the reference light intensity has been removed.

[0049] Figures 5 to 7 are diagrams illustrating the operation of the sensor device 1. Figures 5 and 7(a) show the propagation states of the first linearly polarized light CW1 and the third linearly polarized light CW2, while Figures 6 and 7(b) show the propagation states of the second linearly polarized light CCW1 and the fourth linearly polarized light CCW2. In Figures 5 to 7, thin arrows indicate the direction of light propagation, and thick arrows 101 to 116 in Figures 5 and 7(a) and thick arrows 201 to 216 in Figures 6 and 7(b) indicate the polarization state at their respective locations. The symbol I indicates the current flowing through the conductor 100 under test, and the symbol H indicates the magnetic field under test.

[0050] First, the first linearly polarized light, which is P-polarized, is emitted from the polarizer 13 of the light-emitting unit 10 (arrows 101, 201), passes through the circulator 20, and enters the half-wave plate 30 (arrows 102, 202). As the first linearly polarized light passes through the half-wave plate 30, its polarization plane rotates by 45°, resulting in light having a first linearly polarized CW1 which is P-polarized and a second linearly polarized CCW1 which is S-polarized (arrows 103, 203). The first linearly polarized CW1 enters the first optical path 43 via PBS 41 (arrow 104), is decoupled by the branching coupler 42, and introduced into the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52, respectively (arrows 105, 106).

[0051] The first linearly polarized CW1 introduced into the first polarization-maintaining fiber 51 is incident on the first magnetic field sensor element 50A from the first polarization-maintaining fiber 51. The first linearly polarized CW1 incident on the first magnetic field sensor element 50A becomes left-rotating circularly polarized by passing through the quarter-wave plate 54, and its phase changes to -θ according to the magnetic field H being measured by passing through the Faraday rotator 55. F The first linearly polarized light CW1 is reflected by the mirror element 56 to become right-rotating circularly polarized light, and then passes through the Faraday rotator 55 again, further changing its phase to -θ according to the magnetic field H being measured. F The polarization is changed. The first linearly polarized CW1 is converted to S-polarized by passing through the quarter-wave plate 54 again and is emitted as the third linearly polarized CW3 to the branch coupler 42 via the first polarization-maintaining fiber 51 (arrow 107). The total phase change at the first magnetic field sensor element 50A is -2θ F It will become.

[0052] The first linearly polarized CW1, which is P-polarized, introduced into the second polarization-maintaining fiber 52, has its polarization plane rotated by 90° at the fusion point Pf of the second polarization-maintaining fiber 52 and is incident on the second magnetic field sensor element 50B as S-polarized (arrow 108). The first linearly polarized CW1 incident on the second magnetic field sensor element 50B becomes left-rotating circularly polarized by passing through the quarter-wave plate 54, and its phase changes to -θ according to the magnetic field H being measured by passing through the Faraday rotator 55. FThe first linearly polarized light CW1 is reflected by the mirror element 56 to become right-rotating circularly polarized light, and then passes through the Faraday rotator 55 again, further changing its phase to -θ according to the magnetic field H being measured. F The polarization is changed. The first linearly polarized CW1 is converted to P-polarized by passing through the quarter-wave plate 54 again and is introduced into the second polarization-maintaining fiber 52 as the third linearly polarized CW3 (arrow 109). At the fusion point Pf of the second polarization-maintaining fiber 52, the polarization plane of the third linearly polarized CW3 is rotated by 90° and emitted from the branch coupler 42 as the third linearly polarized CW2, which is S-polarized (arrow 110). The total phase change at the second magnetic field sensor element 50B is -2θ F It will become.

[0053] The third linearly polarized light CW2 is incident on the phase adjustment element 45 of the second optical path 44 via the branching coupler 42 (arrow 111). In the phase adjustment element 45, the third linearly polarized light CW2 passes through the quarter-wave plate 47, the 45-degree Faraday rotator 48, and the quarter-wave plate 46 in sequence, becoming left-rotating circularly polarized light, changing its phase by -45°, and becoming P-polarized light. The third linearly polarized light CW2 that has passed through the phase adjustment element 45 is converted to S-polarized light via PBS 41 (arrow 112) and emitted to the half-wave plate 30.

[0054] Meanwhile, the second linearly polarized CCW1 is converted to P-polarized light via PBS41 and incident on the second optical path 44 (arrow 204), and then incident on the phase adjustment element 45. In the phase adjustment element 45, the second linearly polarized CCW1 passes through the quarter-wave plate 46, the 45-degree Faraday rotator 48, and the quarter-wave plate 47 in sequence, becoming left-rotating circularly polarized light, changing its phase by 45°, and becoming P-polarized light (arrow 205). The second linearly polarized CCW1 that has passed through the phase adjustment element 45 is decoupled by the branching coupler 42 and introduced into the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52, respectively (arrows 206, 207).

[0055] The second linearly polarized light CCW1 introduced into the first polarization maintaining fiber 51 enters the first magnetic field sensor element 50A from the first polarization maintaining fiber 51. The second linearly polarized light CCW1 incident on the first magnetic field sensor element 50A passes through the 1 / 4 wavelength plate 54 to become left-handed circularly polarized light, and passes through the Faraday rotator 55 to have a phase of -θ according to the measured magnetic field H F change. The second linearly polarized light CCW1 is reflected by the mirror element 56 to become right-handed circularly polarized light, and passes through the Faraday rotator 55 again to further make the phase -θ according to the measured magnetic field H F change, and passes through the 1 / 4 wavelength plate 54 again to be converted into S-polarized light. The second linearly polarized light CCW1 is emitted to the branching coupler 42 via the first polarization maintaining fiber 51 as the fourth linearly polarized light CCW2 (arrow 208). The total phase change amount in the first magnetic field sensor element 50A is -2θ F .

[0056] The second linearly polarized light CCW1, which is S-polarized light introduced into the second polarization maintaining fiber 52, has its polarization plane rotated by 90° at the fusion point Pf of the second polarization maintaining fiber 52 and enters the second magnetic field sensor element 50B as P-polarized light (arrow 209). The second linearly polarized light CCW1 incident on the second magnetic field sensor element 50B passes through the 1 / 4 wavelength plate 54 to become left-handed circularly polarized light, and passes through the Faraday rotator 55 to have a phase of -θ according to the measured magnetic field H F change. The second linearly polarized light CCW1 is reflected by the mirror element 56 to become right-handed circularly polarized light, and passes through the Faraday rotator 55 again to further make the phase -θ according to the measured magnetic field H F change. The second linearly polarized light CCW1 passes through the 1 / 4 wavelength plate 54 again to be converted into S-polarized light, and is introduced into the second polarization maintaining fiber 52 as the fourth linearly polarized light CCW2 (arrow 210). The fourth linearly polarized light CCW2 has its polarization plane rotated by 90° at the fusion point Pf of the second polarization maintaining fiber 52, and is emitted to the branching coupler 42 as the fourth linearly polarized light CCW2 which is P-polarized light (arrow 211). The total phase change amount in the second magnetic field sensor element 50B is -2θ F .

[0057] The fourth linearly polarized CCW2 is introduced into the first optical path 43 via the branching coupler 42 (arrow 212). The fourth linearly polarized CCW2 led into the first optical path 43 is converted to P-polarized light via PBS 41 (arrow 113) and emitted to the half-wave plate 30.

[0058] The third linearly polarized light CW2 and the fourth linearly polarized light CCW2 are combined by PBS41 and their polarization planes rotate by 45° as they pass through the half-wave plate 30. Each of the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 becomes light having a P-polarized component and an S-polarized component (arrows 113, 213), which are split by the circulator 20 and incident on PBS61 (arrows 114, 214). The S-polarized component of the combined third linearly polarized light CW2 and the fourth linearly polarized light CCW2 is incident on the first photodetector 62 (arrows 115, 215), and the P-polarized component is incident on the second photodetector 63 (arrows 116, 216), both via PBS61. In this way, in the sensor device 1, the clockwise polarized light Ecw and the counterclockwise polarized light Eccw are separated into two paths by PBS41, each passing through two magnetic field sensor elements, and finally interfering with each other when passing through the half-wave plate 30.

[0059] In the sensor device 1, linearly polarized light is simultaneously incident on the first magnetic field sensor element 50A and the second magnetic field sensor element 50B, which are positioned on the front and back sides of the conductor 100 to be measured, thereby enabling simultaneous measurement of the magnetic field H on both sides of the conductor 100.

[0060] Figure 8(a) shows the connection relationship between PBS42A and 42B of the sensor device according to the comparative example described in Patent Document 1 and the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. Figure 8(b) shows the timing at which electrical signals indicating the detected magnetic field are output from the first magnetic field sensor element 50A and the second magnetic field sensor element 50B shown in Figure 8(a).

[0061] In the sensor device described in Patent Document 1, the first linearly polarized light CW1 is incident on the first magnetic field sensor element 50A from PBS42A. The first linearly polarized light CW1 is emitted from the first magnetic field sensor element 50A and incident on the second magnetic field sensor element 50B, which is located at an optical distance L from the first magnetic field sensor element 50A, via PBS42A and 42B. The first linearly polarized light CW1 is emitted from the second magnetic field sensor element 50B as a third linearly polarized light CW2.

[0062] The second magnetic field sensor element 50B detects the first linearly polarized light CW1 incident on the first magnetic field sensor element 50A, and the time t corresponds to the optical distance L between the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. L Later, the first linearly polarized light CW1 is incident. Time difference t L As a result, the timing at which the waveforms W101 and W102 of the electrical signals indicating the magnetic field detected by the first magnetic field sensor element 50A and the second magnetic field sensor element 50B are output differs. Because the timing at which the first magnetic field sensor element 50A and the second magnetic field sensor element 50B detect the magnetic field differs, the waveform W103 of the electrical signal indicating the detected magnetic field has a slope in its rising and falling edges, causing waveform distortion.

[0063] On the other hand, in sensor device 1, the first linearly polarized CW1 and the second linearly polarized CCW1 are separated by the branching coupler 42 and simultaneously incident on both the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. In sensor device 1, since the first linearly polarized CW1 and the second linearly polarized CCW1 are simultaneously incident on both the first magnetic field sensor element 50A and the second magnetic field sensor element 50B, the timing of when the first magnetic field sensor element 50A and the second magnetic field sensor element 50B detect the magnetic field coincides. In sensor device 1, since the timing of when the first magnetic field sensor element 50A and the second magnetic field sensor element 50B detect the magnetic field coincides, the electrical signals indicating the magnetic field detected by the first magnetic field sensor element 50A and the second magnetic field sensor element 50B do not have waveform distortion. In sensor device 1, since the electrical signals indicating the magnetic field detected by the first magnetic field sensor element 50A and the second magnetic field sensor element 50B do not have waveform distortion, detection errors can be suppressed when operating at high frequencies.

[0064] Furthermore, the sensor device 1 has a yoke 53 that holds the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. By holding the first magnetic field sensor element 50A and the second magnetic field sensor element 50B with the yoke 53, the sensor device 1 can concentrate the magnetic field on the first magnetic field sensor element 50A and the second magnetic field sensor element 50B, thereby detecting the magnetic field with high accuracy.

[0065] Furthermore, in the sensor device 1, the first magnetic field sensor element 50A and the second magnetic field sensor element 50B are optically connected to the branch coupler 42 by the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52, which have the same length, so the optical distance between them and the branch coupler 42 is equal. In the sensor device 1, since the optical distance between the first magnetic field sensor element 50A and the second magnetic field sensor element 50B and the branch coupler 42 is equal, there is a low risk of differences in the timing of magnetic field detection, and detection errors can be suppressed when operating at high frequencies.

[0066] Furthermore, in the sensor device 1, the second polarization-maintaining fiber 52 rotates the polarization plane of the introduced linearly polarized light by 90°, thereby reversing the direction of Faraday rotation in the second magnetic field sensor element 50B compared to the direction of Faraday rotation in the first magnetic field sensor element 50A. In the sensor device 1, by reversing the direction of Faraday rotation in the second magnetic field sensor element 50B compared to the direction of Faraday rotation in the first magnetic field sensor element 50A, the Faraday rotations of the first magnetic field sensor element 50A and the second magnetic field sensor element 50B can be combined.

[0067] Furthermore, in the sensor device 1, the second polarization-maintaining fiber 52 is formed from a pair of polarization-maintaining fibers that are fused together with their slow and fast axes rotated by 90°. This allows for the simple and highly accurate manufacturing of a structure that rotates the polarization plane of the introduced linearly polarized light by 90°.

[0068] In sensor device 1, the first magnetic field sensor element 50A and the second magnetic field sensor element 50B are fixedly held by a yoke. However, in the sensor device according to this embodiment, the first magnetic field sensor element 50A and the second magnetic field sensor element 50B may be held by a member other than the yoke. Furthermore, in the sensor device according to this embodiment, the first magnetic field sensor element 50A and the second magnetic field sensor element 50B may be movably held by the yoke or a member other than the yoke.

[0069] Furthermore, in sensor device 1, the lengths of the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 are the same, but in the sensor device according to this embodiment, the lengths of the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 may differ to the extent that it does not affect the detection accuracy.

[0070] Furthermore, in the sensor device 1, the second polarization-maintaining fiber 52 is formed by a pair of polarization-maintaining fibers that are fused together with their slow and fast axes rotated by 90°. However, in the sensor device according to this embodiment, it may be formed by a pair of polarization-maintaining fibers arranged to sandwich a half-wave plate. [Explanation of symbols]

[0071] 1. Sensor device 10 Light-emitting part 20. Circulator (optical splitter) 30 1 / 2 wave plate (first optical element) 40 Optical path section 42 Branch coupler 43 1st optical path 44 Second optical path 50A First Magnetic Field Sensor Element 50B Second Magnetic Field Sensor Element

Claims

1. A light-emitting unit that emits first linearly polarized light, An optical element that emits a first linearly polarized light and a second linearly polarized light in response to incident first linearly polarized light, and emits second linearly polarized light in response to incident third linearly polarized light and fourth linearly polarized light, wherein the first linearly polarized light and the second linearly polarized light are mutually orthogonal polarization components of the first linearly polarized light, and the third linearly polarized light and the fourth linearly polarized light are mutually orthogonal polarization components of the second linearly polarized light, A first magnetic field sensor element and a second magnetic field sensor element are incident on the first linearly polarized light and the second linearly polarized light, and the first linearly polarized light and the second linearly polarized light are changed in accordance with the applied magnetic field to emit the third linearly polarized light and the fourth linearly polarized light. An optical path section having a first optical path for propagating the first linearly polarized light and the fourth linearly polarized light, a second optical path for propagating the second linearly polarized light and the third linearly polarized light, and a branching coupler that separates the first linearly polarized light and the second linearly polarized light and outputs them to the first magnetic field sensor element and the second magnetic field sensor element, and combines the third linearly polarized light and the fourth linearly polarized light incident from the first magnetic field sensor element and the second magnetic field sensor element, outputting the combined third linearly polarized light to the second optical path and outputting the combined fourth linearly polarized light to the first optical path, A detection signal generation unit receives the two components of the second linearly polarized light and converts them into an electrical signal to output a detection signal corresponding to the magnetic field, The optical branching unit transmits the first linearly polarized light to the optical element and branches the second linearly polarized light to the detection signal generation unit, An interference-type optical magnetic field sensor device characterized by the following:

2. The interference-type optical magnetic field sensor device according to claim 1, further comprising a yoke arranged to surround a conductor to be measured and holding the first magnetic field sensor element and the second magnetic field sensor element.

3. A first polarization-maintaining fiber optically connects the branching coupler and the first magnetic field sensor element, The system further includes a second polarization-maintaining fiber that optically connects the branching coupler and the second magnetic field sensor element, The interference-type optical magnetic field sensor device according to claim 1 or 2, wherein the lengths of the first polarization-maintaining fiber and the second polarization-maintaining fiber are equal to each other.

4. The interference-type optical magnetic field sensor device according to claim 3, wherein the second polarization-maintaining fiber rotates the polarization planes of the first linearly polarized light, the second linearly polarized light, the third linearly polarized light, and the fourth linearly polarized light by 90°.

5. The interference-type optical magnetic field sensor device according to claim 4, wherein the second polarization-maintaining fiber is formed from a pair of polarization-maintaining fibers that are fused together with their slow and fast axes rotated by 90°.

Images