JP2023158963A - Interference type optical magnetic field sensor device - Google Patents

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

The present invention relates to an interferometric optical magnetic field sensor device.

An interferometric optical magnetic field sensor that uses a magnetic field sensor element with a Faraday rotator installed at the tip of an optical fiber, and photoelectrically converts the light that passes through the magnetic field sensor element to generate a detection signal according to the magnetic field applied to the Faraday rotator. Devices are known (see, for example, Patent Document 1). The interferometric optical magnetic field sensor device (hereinafter also referred to as the sensor device) described in Patent Document 1 uses a pair of magnetic field sensor elements that can be placed within a predetermined magnetic field with a conductor to be measured in between. By detecting it, it is possible to suppress the influence of the external magnetic field on the measured value of the detected magnetic field.

Japanese Patent Application Publication No. 2021-025794

However, in the sensor device described in Patent Document 1, the first linearly polarized light CW1 and the second linearly polarized light CCW1 are sequentially transmitted via a PANDA fiber connecting between the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. incident. In the sensor device described in Patent Document 1, the time it takes for the first linearly polarized light CW1 and the second linearly polarized light CCW1 to pass through the PANDA fiber causes a time difference in detecting the magnetic field, which may distort the waveform of the electric signal indicating the magnetic field. Distortion of the waveform of the electrical signal representing the magnetic field due to the time difference in magnetic field detection due to the time it takes to pass through the PANDA fiber becomes a cause of detection error when operating in a high frequency band of several MHz or higher. In particular, the longer the sensor fiber length, the more detection errors occur from low frequency bands.

SUMMARY OF THE INVENTION An object of the present invention is to provide an interferometric optical magnetic field sensor device capable of suppressing waveform distortion of an electric signal indicating a detected magnetic field.

The interferometric optical magnetic field sensor device according to the present invention includes a light emitting section that emits first linearly polarized light, and a light emitting section that emits first linearly polarized light and second linearly polarized light according to the incident first linearly polarized light. a first optical element that emits second linearly polarized light according to the third linearly polarized light and the fourth linearly polarized light; a first magnetic field sensor element and a second magnetic field sensor element that emit the third linearly polarized light and the fourth linearly polarized light by changing the polarized light and the second linearly polarized light; and a first magnetic field sensor element that propagates the first linearly polarized light and the fourth linearly polarized light. an optical path, a second optical path for propagating the second linearly polarized light and the third linearly polarized light, and branching each of the first linearly polarized light and the second linearly polarized light and emitting them to the first magnetic field sensor element and the second magnetic field sensor element; , combining the third linearly polarized light and the fourth linearly polarized light incident from each of the first magnetic field sensor element and the second magnetic field sensor element, and outputting the combined third linearly polarized light to the second optical path, A detection signal corresponding to the magnetic field is generated by receiving two components of the second linearly polarized light and converting them into electrical signals. It has a detection signal generation section that outputs the detection signal, 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.

Further, it is preferable that the interferometric optical magnetic field sensor device according to the present invention further includes a yoke that is arranged to surround the conductor to be measured and holds the first magnetic field sensor element and the second magnetic field sensor element.

Further, the interferometric optical magnetic field sensor device according to the present invention includes a first polarization maintaining fiber that optically connects the branch coupler and the first magnetic field sensor element, and a first polarization maintaining fiber that optically connects the branch coupler and the second magnetic field sensor element. It is preferable that the first polarization maintaining fiber and the second polarization maintaining fiber have the same length.

Further, in the interferometric optical magnetic field sensor device according to the present invention, the second polarization maintaining fiber rotates each polarization plane of the first linearly polarized light, the second linearly polarized light, the third linearly polarized light, and the fourth linearly polarized light by 90 degrees. It is preferable to let

Further, in the interferometric optical magnetic field sensor device according to the present invention, the second polarization-maintaining fiber is formed by a pair of polarization-maintaining fibers that are fused with the slow axis and the fast axis rotated by 90 degrees. is preferred.

The interferometric optical magnetic field sensor device according to the present invention can suppress distortion of the waveform of an electric signal indicating a detected magnetic field.

FIG. 1 is a block diagram of a sensor device according to an embodiment. 2 is a schematic diagram of a first magnetic field sensor element and a second magnetic field sensor element shown in FIG. 1. FIG. FIG. 2 is a partially enlarged plan view of the portion indicated by arrow A in FIG. 1. FIG. 2 is a circuit diagram of a first light receiving element, a second light receiving element, and a signal processing circuit shown in FIG. 1. FIG. FIG. 2 is a diagram (part 1) for explaining the operation of the sensor device shown in FIG. 1; FIG. 2 is a diagram (part 2) for explaining the operation of the sensor device shown in FIG. 1; (a) is a diagram (part 3) for explaining the operation of the sensor device shown in FIG. 1, and (b) is a diagram (part 4) for explaining the operation of the sensor device shown in FIG. 1. (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 output of an electric signal indicating the magnetic field detected in each of the magnetic field sensor elements shown in (a). FIG.

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

FIG. 1 is a block diagram of the sensor device 1. As shown in FIG.

The sensor device 1 is an example of an interferometric optical magnetic field sensor device, and includes a light emitting section 10, a circulator 20, a 1/2 wavelength plate 30, and an optical path section 40. The sensor device 1 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 generating section 60. Furthermore, it has The optical path between the light emitting section 10, the circulator 20, the half-wave plate 30, the optical path section 40, and the detection signal generating section 60 is formed by a PANDA (Polarization-maintaining AND Absorption-reducing) fiber. Note that the optical path between the 1/2 wavelength plate 30, the optical path section 40, and the detection signal generation section 60 is formed by a polarization-maintaining fiber such as a bow-tie fiber or an elliptical jacket fiber. Good too.

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 specifically, preferably a Fabry-Perot laser, a superluminescence diode, or the like. The isolator 12 protects the light emitting element 11 by transmitting the light emitted by the light emitting element 11 to the circulator 20 side and not transmitting the light incident on the light emitting part 10 from the circulator 20 to the light emitting element 11 side. The isolator 12 is, for example, a polarization-dependent optical isolator, or may be a polarization-independent optical isolator. The polarizer 13 is an optical element for converting the light emitted by 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 input to the circulator 20 .

The circulator 20 is an example of a light branching section, and transmits the first linearly polarized light emitted from the light emitting section 10 to the 1/2 wavelength plate 30, and transmits the second linearly polarized light emitted from the 1/2 wavelength plate 30. The wave light is branched to a detection signal generating section 60. The circulator 20 is formed by, for example, a Faraday rotator, a half-wave plate, a polarizing beam splitter, or a reflecting mirror.

The 1/2 wavelength plate 30 is an example of a first optical element, and is arranged 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. The polarization plane of the one linearly polarized light is rotated by 45 degrees and output 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 that is P polarized light and a second linearly polarized light CCW1 that is S polarized light orthogonal to the first linearly polarized light CW1. Further, the half-wave plate 30 rotates the polarization plane of the second linearly polarized light incident from the optical path section 40 by 45 degrees and outputs the second linearly polarized light to the circulator 20 .

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.

The PBS 41 separates the first linearly polarized light incident from the 1/2 wavelength plate 30 into a P polarized light component and an S polarized light component, and sends the first linearly polarized light CW1 to the first optical path 43 and the second linearly polarized light CCW1 to the first optical path 43. The light is emitted to the second optical path 44, respectively. Further, the PBS 41 receives the third linearly polarized light CW2 from the second optical path 44 and the fourth linearly polarized light CCW2 from the first optical path 43, synthesizes them, and outputs them to the half-wave plate 30. The third linearly polarized light CW2 and the fourth linearly polarized light CCW2 are mutually orthogonal polarized components of the second linearly polarized light emitted to the half-wave plate 30. The PBS 41 is, for example, a prism beam splitter, but may also be a planar beam splitter or a wedge beam splitter.

The branching coupler 42 is a fused type or filter type optical fiber coupler having polarization-independent characteristics, and connects the first optical path 43, the second optical path 44, the first polarization-maintaining fiber 51, and the second polarization-maintaining fiber 52 with optical fibers. connected. The branching coupler 42 splits the first linearly polarized light CW1 incident from the first optical path 43 and the second linearly polarized light CCW1 incident from the second optical path 44, and separates them into the first polarization maintaining fiber 51 and the second linearly polarized light CCW1. The light is emitted to each of the polarization maintaining fibers 52. The branch coupler 42 separates each of the first linearly polarized light CW1 and the second linearly polarized light CCW1 at a ratio of 50:50. One of the first linearly polarized light CW1 and the second linearly polarized light CCW1 separated by the branching coupler 42 is input to the first magnetic field sensor element 50A via the first polarization maintaining fiber 51. The other of the first linearly polarized light CW1 and the second linearly polarized light CCW1 separated by the branching coupler 42 is input to the second magnetic field sensor element 50B via the second polarization maintaining fiber 52.

The branching coupler 42 receives the third linearly polarized light CW2 which is input from the first magnetic field sensor element 50A via the first polarization maintaining fiber 51, and the third linearly polarized light CW2 which is input from the second magnetic field sensor element 50B via the second polarization maintaining fiber 52. and the third linearly polarized light CW2. The branching coupler 42 outputs the combined third linearly polarized light CW2 to the second optical path 44. The branching coupler 42 receives the fourth linearly polarized light CCW2 which is input from the first magnetic field sensor element 50A via the first polarization maintaining fiber 51, and the fourth linearly polarized light CCW2 which is input from the second magnetic field sensor element 50B via the second polarization maintaining fiber 52. and the fourth linearly polarized light CCW2. The branching coupler 42 outputs the combined fourth linearly polarized light CCW2 to the first optical path 43.

The first optical path 43 is a PANDA fiber optically connected to the PBS 41 at one end and the branch coupler 42 at the other end. The first optical path 43 guides the first linearly polarized light CW1 introduced from the PBS 41 to the branch coupler 42, and also guides the fourth linearly polarized light CCW2 introduced from the branch coupler 42 to the PBS 41. The second optical path 44 is a PANDA fiber optically connected to the PBS 41 at one end and the branch coupler 42 at the other end. The second optical path 44 guides the second linearly polarized light CCW1 introduced from the PBS 41 to the branch coupler 42, and also guides the third linearly polarized light CW2 introduced from the branch coupler 42 to the PBS 41. The optical path between branch couplers 42 is also a PANDA fiber. Note that the optical path between the first optical path 43, the second optical path 44, and the branching coupler 42 may be a polarization-maintaining fiber such as a bow-tie fiber or an elliptical jacket fiber.

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 arranged in the second optical path 44, and adjusts the second linearly polarized light CCW1 so that the phase difference between the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 becomes 90°. and adjust the phase of the third linearly polarized light CW2. The quarter-wave plate 46 is arranged so that its optical axis is inclined at 45 degrees with respect to the slow axis and the fast axis of the PANDA fiber forming the second optical path 44, and converts linearly polarized light into circularly polarized light. Convert polarized light to linearly polarized light. The quarter-wave plate 47 is arranged so that its optical axis is tilted by −45° with respect to the slow axis and fast axis of the PANDA fiber forming the second optical path 44, and converts circularly polarized light into linearly polarized light. Convert linearly polarized light to circularly polarized light.

The 45-degree Faraday rotator 48 is arranged between the quarter-wave plates 46 and 47, and changes the phase of the circularly polarized light incident thereon. The 45-degree Faraday rotator 48 is configured such that the phase of the second linearly polarized light CCW1 emitted from the quarter-wave plate 47 is shifted by 45 degrees from the phase of the second linearly polarized light CCW1 incident on the quarter-wave plate 46. , changes the phase of the incident light. In addition, the 45-degree Faraday rotator 48 shifts the phase of the third linearly polarized light CW2 emitted from the quarter-wave plate 46 by -45° from the phase of the third linearly polarized light CW2 incident on the quarter-wave plate 47. The phase of the incident light is changed so that

FIG. 2 is a schematic diagram of the first magnetic field sensor element 50A and the second magnetic field sensor element 50B.

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 both include a quarter wavelength plate 54, a Faraday rotator 55, and a mirror element 56.

The first magnetic field sensor element 50A and the second magnetic field sensor element 50B can be placed within a predetermined magnetic field with the conductor to be measured 100 therebetween, and are integrally formed with a constant interval between them. The relative position of the first magnetic field sensor element 50A to the second magnetic field sensor element 50B is fixed, and even if the sensor device 1 moves during measurement, the distance between the first magnetic field sensor element 50A and the second magnetic field sensor element 50B remains constant. Unchanging. The first magnetic field sensor element 50A and the second magnetic field sensor element 50B have optical transparency 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 receive the first linearly polarized light CW1 and the second linearly polarized light CCW1, and respond to the input of the first linearly polarized light CW1 and the second linearly polarized light CCW1. Then, the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 are emitted.

The 1/4 wavelength plate 54 is arranged with respect to the slow axis and the fast axis of the branching coupler 42 or the first polarization maintaining fiber 51 and the second polarization maintaining fiber 52 that optically connect the branching coupler 42. The optical axis is arranged at an angle of 45°. The quarter-wave plate 54 converts the linearly polarized light incident from the branching coupler 42 into circularly polarized light, and also converts the circularly polarized light, which is the return light incident from the Faraday rotator 55, into linearly polarized light.

The Faraday rotator 55 is a granular film having a dielectric material 550 and nano-order magnetic particles 551 dispersed in the dielectric material 550 in a state of stable phase separation from the dielectric material 550. It is arranged on the end face of the plate 54. The magnetic particles 551 may be oxides in a small part, such as the outermost layer, but in the entire Faraday rotator 55, they can be formed into a thin film alone without forming a compound with a dielectric material that serves as a binder. Dispersed. The distribution of the magnetic particles 551 within the Faraday rotator 55 does not have to be completely uniform and may be somewhat biased. If a highly transparent dielectric material 550 is used, the Faraday rotator 55 has optical transparency because the magnetic particles 551 are present in the dielectric material 550 in a size smaller than the wavelength of light.

The Faraday rotator 55 is not limited to a single layer, but may be a multilayer film in which granular films and dielectric films are alternately laminated. By making the granular film a multilayer film, a larger Faraday rotation angle can be obtained due to multiple reflections within the granular film.

The dielectric 550 is preferably a fluoride (metal fluoride) such as magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), or yttrium fluoride (YF ₃ ). Further, the dielectric material 550 is made of tantalum oxide (Ta ₂ O ₅ ), silicon dioxide (SiO ₂ ), titanium dioxide (TiO ₂ ), diniobium pentoxide (Nb ₂ O ₅ ), zirconium dioxide (ZrO ₂ ), or hafnium dioxide. (HfO ₂ ) and dialuminum trioxide (Al ₂ O ₃ ). For good phase separation between the dielectric material 550 and the magnetic particles 551, fluoride is preferable to oxide, and magnesium fluoride, which has high transmittance, is particularly preferable.

The material of the magnetic particles 551 is not particularly limited as long as it produces a Faraday effect, but examples include ferromagnetic metals such as iron (Fe), cobalt (Co), nickel (Ni), and alloys thereof. can be mentioned. Examples of alloys of Fe, Co, and Ni include FeNi alloys, FeCo alloys, FeNiCo alloys, and NiCo alloys. 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 rotators. Note that the material of the magnetic particles 551 may be a conventional transparent magnetic material such as magnetic garnet or ferrite.

The mirror element 56 is formed on the surface of the Faraday rotator 55 opposite to the 1/4 wavelength plate 54, and reflects the light transmitted through the Faraday rotator 55 toward the Faraday rotator 55. As the mirror element 56, for example, a silver (Ag) film, a gold (Au) film, an aluminum (Al) film, a dielectric multilayer mirror, or the like can be used. In particular, an Ag film with high reflectance and an Au film with high corrosion resistance are preferred because they are easy to form. The thickness of the mirror element 56 may be any size that can ensure a sufficient reflectance of 98% or more; for example, in the case of an Ag film, it is preferably 50 nm or more and 200 nm or less. By reciprocating light within the Faraday rotator 55 using the mirror element 56, the Faraday rotation angle can be increased.

Each of the first polarization maintaining fiber 51 and the second polarization maintaining fiber 52 is a PANDA fiber having the same length. The first polarization maintaining fiber 51 optically connects the branch coupler 42 and the first magnetic field sensor element 50A, and the second polarization maintaining fiber 52 connects the branch coupler 42 and the second magnetic field sensor element 50B. Connect optically. The first polarization maintaining fiber 51 is formed of a single PANDA fiber, and when P-polarized linearly polarized light is introduced, it derives P-polarized linearly polarized light, and when S-polarized linearly polarized light is introduced, S Derive the linear polarization of polarized light. The second polarization-maintaining fiber 52 is formed by a pair of PANDA fibers that are fused with the slow axis and fast axis rotated by 90 degrees at the fusion point Pf, and when P-polarized linearly polarized light is introduced, S-polarized linearly polarized light is derived, and when S-polarized linearly polarized light is introduced, P-polarized linearly polarized light is derived. Each of the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 may be formed of a polarization-maintaining fiber such as a bow-tie fiber or an elliptical jacket fiber.

The first linearly polarized light CW1 and the second linearly polarized light CCW1 separated by the branching coupler 42 are introduced into the first polarization maintaining fiber 51 and the second polarization maintaining fiber 52 . The first polarization maintaining fiber 51 guides the first linearly polarized light CW1 and the second linearly polarized light CCW1 introduced from the branching 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 light CW1 and the second linearly polarized light CCW1 introduced from the branching coupler 42 by 90 degrees and outputs them to the second magnetic field sensor element 50B.

The first polarization-maintaining fiber 51 guides the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 introduced from the first magnetic field sensor element 50A to the branching coupler 42. The second polarization-maintaining fiber 52 rotates the polarization planes of the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 introduced from the second magnetic field sensor element 50B by 90 degrees and outputs them to the branching coupler 42.

FIG. 3 is a partially enlarged plan view of the portion indicated by arrow A in FIG.

The yoke 53 includes 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 magnetic permeability greater than 1, and if a composite material in which soft magnetic particles are dispersed in an insulator such as resin is used, high frequency characteristics can be improved due to the effect of suppressing eddy currents. is favorable, which is preferable. A magnetic circuit formed by a magnetic field generated by a current flowing through the conductor to be measured 100 is formed together with the first magnetic field sensor element 50A and the second magnetic field sensor element 50B.

The first yoke 53A has a first polarization maintaining fiber 51 and a second polarization maintaining fiber 52 embedded therein, and by sandwiching the first magnetic field sensor element 50A and the second magnetic field sensor element 50B together with the second yoke 53B, A first magnetic field sensor element 50A and a second magnetic field sensor element 50B are held. The second yoke 53B is fixed to the first yoke 53A via a fixing member (not shown).

The detection signal generation section 60 includes a PBS 61, a first light receiving element 62, a second light receiving element 63, and a signal processing circuit 70. The detection signal generating section 60 separates the second linearly polarized light branched by the circulator 20 into an S polarized light component 64 and a P polarized light component 65. In addition, the detection signal generating section 60 receives the separated S-polarized light component 64 and P-polarized light component 65, converts them into electrical signals, and differentially amplifies them, thereby transmitting the signals to the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. A detection signal Ed is output according to the magnetic field applied to the magnetic field. The PBS 61 is a polarization beam splitter of prism type, planar type, wedge substrate type, optical waveguide type, etc., and separates the second linearly polarized light branched by the circulator 20 into an S polarized light component 64 and a P polarized light component 65.

FIG. 4 is a circuit diagram of the first light receiving element 62, the second light receiving element 63, and the signal processing circuit 70.

The signal processing circuit 70 includes an amplification element 71, which is, for example, an operational amplifier, and a resistance element 72. Each of the first light-receiving element 62 and the second light-receiving element 63 is, for example, a PIN photodiode, and performs photoelectric conversion and outputs an electric signal according 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 the positive power supply +V, and the anode of the second light receiving element 63 is connected to the negative input terminal of the amplifying element 71. is connected to the negative power supply -V. The first light receiving element 62 receives the S-polarized light component 64 of the combination of the third linearly polarized light CW2 and the fourth linearly polarized light CCW2, and outputs a first electrical signal E1 which is a current proportional to the intensity thereof. The second light receiving element 63 receives the P-polarized light component 65 of the combination of the third linearly polarized light CW2 and the fourth linearly polarized light CCW2, and outputs a second electric signal E2 which is a current proportional to the intensity thereof.

The S-polarized light component and the P-polarized light component of the third linearly polarized light CW2 incident on the detection signal generating section 60 are expressed by the ECW of the following equation, and the S-polarized light component and the P-polarized light component of the fourth linearly polarized light CCW2 are expressed by the ECCW of the following equation. be done. θ _F is a Faraday rotation angle according to the magnetic field applied to the Faraday rotator 55, and j is an imaginary unit.

The S-polarized light component P0 and the P-polarized light component P90 of the combination of the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 are expressed as follows from the equations of ECW and ECCW described above. ECW,0, ECCW,0, ECW,90, ECCW,90 are the S polarized light component of the third linearly polarized light CW2, the S polarized light component of the fourth linearly polarized light CCW2, the P polarized light component of the third linearly polarized light CW2, and the third linearly polarized light CW2, respectively. This is the P polarized light component of the four linearly polarized light CCW2.

The signal processing circuit 70 is an inverting amplification circuit, and by inverting and amplifying the differential signal (E1-E2) between the first electric signal E1 and the second electric signal E2, the first magnetic field sensor element 50A and the second magnetic field A detection signal Ed corresponding to the magnetic field applied to the sensor element 50B is output. The plus input terminal of the amplification element 71 is grounded, and the differential signal (E1-E2) is input to the minus input terminal of the amplification element 71. The differential signal (E1-E2) is an electrical signal that is proportional to the difference between the S polarization component P0 and the P polarization component P90 and corresponds to the Faraday rotation angle θ _F. The detection signal Ed is an electrical signal from which a DC component corresponding to the reference light intensity has been removed.

5 to 7 are diagrams for explaining the operation of the sensor device 1. FIG. 5 and 7(a) show the propagation states of the first linearly polarized light CW1 and the third linearly polarized light CW2, and FIGS. 6 and 7(b) show the propagation states of the second linearly polarized light CCW1 and the fourth linearly polarized light CCW2. show. In FIGS. 5 to 7, thin arrows indicate the propagation direction of light, and thick arrows 101 to 116 in FIGS. 5 and 7(a) and thick arrows 201 to 216 in FIGS. 6 and 7(b) indicate the respective locations. shows the polarization state at . The symbol I indicates the current flowing through the conductor 100 to be measured, and the symbol H indicates the magnetic field to be measured.

First, first linearly polarized light, which is P-polarized light, 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). . The first linearly polarized light has a polarization plane rotated by 45 degrees by passing through the half-wave plate 30, and has a first linearly polarized light CW1 that is P polarized light and a second linearly polarized light CCW1 that is S polarized light. (arrows 103, 203). The first linearly polarized light CW1 enters the first optical path 43 via the PBS 41 (arrow 104), is split by the branching coupler 42, and introduced into each of the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52. (arrows 105, 106).

The first linearly polarized light CW1 introduced into the first polarization maintaining fiber 51 is input from the first polarization maintaining fiber 51 to the first magnetic field sensor element 50A. The first linearly polarized light CW1 incident on the first magnetic field sensor element 50A becomes counterclockwise circularly polarized light by passing through the quarter-wave plate 54, and changes to the magnetic field H to be measured by passing through the Faraday rotator 55. to change the phase by -θ _F. The first linearly polarized light CW1 becomes clockwise circularly polarized light by being reflected by the mirror element 56, and passes through the Faraday rotator 55 again to further change the phase by -θ _F in accordance with the magnetic field H to be measured. The first linearly polarized light CW1 is converted into S-polarized light by passing through the quarter-wave plate 54 again, and is emitted as the third linearly polarized light CW3 to the branching coupler 42 via the first polarization-maintaining fiber 51 ( arrow 107). The total amount of phase change in the first magnetic field sensor element 50A is _-2θF .

The first linearly polarized light CW1, which is P-polarized light, introduced into the second polarization-maintaining fiber 52 has its polarization plane rotated by 90 degrees at the fusion point Pf of the second polarization-maintaining fiber 52, and is converted into S-polarized light to the second magnetic field sensor. The light is incident on element 50B (arrow 108). The first linearly polarized light CW1 incident on the second magnetic field sensor element 50B becomes counterclockwise circularly polarized light by passing through the quarter-wave plate 54, and changes to the magnetic field H to be measured by passing through the Faraday rotator 55. to change the phase by -θ _F. The first linearly polarized light CW1 becomes clockwise circularly polarized light by being reflected by the mirror element 56, and passes through the Faraday rotator 55 again to further change the phase by -θ _F in accordance with the magnetic field H to be measured. The first linearly polarized light CW1 is converted into P-polarized light by passing through the quarter-wave plate 54 again, and is introduced into the second polarization-maintaining fiber 52 as the third linearly polarized light CW3 (arrow 109). The plane of polarization of the third linearly polarized light CW3 is rotated by 90 degrees at the fusion point Pf of the second polarization maintaining fiber 52, and the third linearly polarized light CW3 is outputted to the branching coupler 42 as the third linearly polarized light CW2 which is S-polarized light (arrow 110). The total amount of phase change in the second magnetic field sensor element 50B is _-2θF .

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 order, thereby becoming counterclockwise circularly polarized light and changing the phase. It changes by -45° and becomes 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 the PBS 41 (arrow 112), and is emitted to the 1/2 wavelength plate 30.

On the other hand, the second linearly polarized light CCW1 is converted into P-polarized light via the PBS 41, enters the second optical path 44 (arrow 204), and enters the phase adjustment element 45. In the phase adjustment element 45, the second linearly polarized light CCW1 passes through the 1/4 wavelength plate 46, the 45 degree Faraday rotator 48, and the 1/4 wavelength plate 47 in order, thereby becoming counterclockwise circularly polarized light and changing the phase. It changes by 45 degrees and becomes P polarized light (arrow 205). The second linearly polarized light CCW1 transmitted through the phase adjustment element 45 is split 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).

The second linearly polarized light CCW1 introduced into the first polarization maintaining fiber 51 is input from the first polarization maintaining fiber 51 to the first magnetic field sensor element 50A. The second linearly polarized light CCW1 incident on the first magnetic field sensor element 50A becomes counterclockwise circularly polarized light by passing through the 1/4 wavelength plate 54, and responds to the magnetic field H to be measured by passing through the Faraday rotator 55. to change the phase by -θ _F. The second linearly polarized light CCW1 becomes clockwise circularly polarized light by being reflected by the mirror element 56, and by passing through the Faraday rotator 55 again, the phase is further changed by −θ _F according to the magnetic field H to be measured, and the second linearly polarized light CCW1 is turned into clockwise circularly polarized light. The light is transmitted through the quarter-wave plate 54 and converted into S-polarized light. The second linearly polarized light CCW1 is output as the fourth linearly polarized light CCW2 to the branching coupler 42 via the first polarization maintaining fiber 51 (arrow 208). The total amount of phase change in the first magnetic field sensor element 50A is _-2θF .

The S-polarized second linearly polarized light CCW1 introduced into the second polarization-maintaining fiber 52 has its polarization plane rotated by 90 degrees at the fusion point Pf of the second polarization-maintaining fiber 52, and is converted into P-polarized light to the second magnetic field sensor element. 50B (arrow 209). The second linearly polarized light CCW1 incident on the second magnetic field sensor element 50B becomes counterclockwise circularly polarized light by passing through the 1/4 wavelength plate 54, and responds to the magnetic field H to be measured by passing through the Faraday rotator 55. to change the phase by -θ _F. The second linearly polarized light CCW1 becomes clockwise circularly polarized light by being reflected by the mirror element 56, and passes through the Faraday rotator 55 again to further change the phase by -θ _F in accordance with the magnetic field H to be measured. The second linearly polarized light CCW1 is converted into S-polarized light by passing through the quarter-wave plate 54 again, and is introduced into the second polarization-maintaining fiber 52 as the fourth linearly polarized light CCW2 (arrow 210). The plane of polarization of the fourth linearly polarized light CCW2 is rotated by 90 degrees at the fusion point Pf of the second polarization maintaining fiber 52, and the fourth linearly polarized light CCW2 is emitted to the branching coupler 42 as P-polarized light (arrow 211). The total amount of phase change in the second magnetic field sensor element 50B is _-2θF .

The fourth linearly polarized light CCW2 is introduced into the first optical path 43 via the branching coupler 42 (arrow 212). The fourth linearly polarized light CCW2 guided to the first optical path 43 is converted to P-polarized light via the PBS 41 (arrow 113), and is emitted to the 1/2 wavelength plate 30.

The third linearly polarized light CW2 and the fourth linearly polarized light CCW2 are combined by the PBS 41 and transmitted through the 1/2 wavelength plate 30, thereby rotating the plane of polarization by 45°. Each of the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 becomes light having a P polarized light component and an S polarized light component (arrows 113, 213), branches at the circulator 20, and enters the PBS 61 (arrows 114, 214). ). The S polarized light component of the combination of the third linearly polarized light CW2 and the fourth linearly polarized light CCW2 is sent to the first light receiving element 62 (arrows 115, 215), and the P polarized light component is sent to the second light receiving element 63 (arrows 116, 216), respectively. It enters through the PBS 61. 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 the PBS 41, each passing through two magnetic field sensor elements, and finally passing through the 1/2 wavelength plate 30. interfere with each other as they pass.

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 arranged on the front and back sides of the conductor to be measured 100, thereby simultaneously measuring the magnetic field H on the front and back sides of the conductor to be measured 100. can do.

FIG. 8A is a diagram showing a connection relationship between PBSs 42A and 42B, a first magnetic field sensor element 50A, and a second magnetic field sensor element 50B of a sensor device according to a comparative example described in Patent Document 1. FIG. 8(b) is a diagram showing the timing at which electrical signals indicating the magnetic fields detected in each of the first magnetic field sensor element 50A and the second magnetic field sensor element 50B shown in FIG. 8(a) are output.

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 the PBS 42A. The first linearly polarized light CW1 is emitted from the first magnetic field sensor element 50A, and is incident on the second magnetic field sensor element 50B, which is separated by an optical distance L from the first magnetic field sensor element 50A, via the PBSs 42A and 42B. The first linearly polarized light CW1 is emitted from the second magnetic field sensor element 50B as the third linearly polarized light CW2.

The second magnetic field sensor element 50B receives the first linearly polarized light CW1 for a period of time corresponding to the optical distance L between the first magnetic field sensor element 50A and the second magnetic field sensor element 50B after the first linearly polarized light CW1 enters the first magnetic field sensor element 50A. After t _L, the first linearly polarized light CW1 is incident. Due to the time difference t _L , the timings at which the electric signal waveforms W101 and W102 representing the magnetic fields detected by the first magnetic field sensor element 50A and the second magnetic field sensor element 50B are output are different. Because the timing at which the first magnetic field sensor element 50A and the second magnetic field sensor element 50B detect the magnetic field is different, the waveform W103 of the electric signal indicating the detected magnetic field has a slope in the rising waveform and the falling waveform. Distortion occurs.

On the other hand, in the sensor device 1, the first linearly polarized light CW1 and the second linearly polarized light CCW1 are split by the branching coupler 42 and simultaneously enter both the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. In the sensor device 1, the first linearly polarized light CW1 and the second linearly polarized light CCW1 are simultaneously incident on both the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. The timing at which the sensor element 50B detects the magnetic field coincides. In the sensor device 1, the first magnetic field sensor element 50A and the second magnetic field sensor element 50B detect the magnetic field at the same timing, so the first magnetic field sensor element 50A and the second magnetic field sensor element 50B detect the magnetic field. The electrical signal shown has no waveform distortion. In the sensor device 1, the electric signals indicating the magnetic field detected by the first magnetic field sensor element 50A and the second magnetic field sensor element 50B are not distorted in waveform, so detection errors are suppressed when operating at high frequency. can.

The sensor device 1 also includes a yoke 53 that holds the first magnetic field sensor element 50A and the second magnetic field sensor element 50B. The sensor device 1 holds the first magnetic field sensor element 50A and the second magnetic field sensor element 50B by the yoke 53, thereby concentrating the magnetic field on the first magnetic field sensor element 50A and the second magnetic field sensor element 50B, and achieving high precision. Can detect magnetic fields.

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 having the same length. , so that the optical distance between the branch coupler 42 and the branch coupler 42 is equal. In the sensor device 1, the first magnetic field sensor element 50A and the second magnetic field sensor element 50B have the same optical distance from the branch coupler 42, so there is a low possibility that the timing of detecting the magnetic field will be different, and they can operate at high frequency. Detection errors can be suppressed when

In addition, in the sensor device 1, the second polarization maintaining fiber 52 rotates the polarization plane of the introduced linearly polarized light by 90 degrees, thereby changing the rotation direction of the Faraday rotation in the second magnetic field sensor element 50B to the first magnetic field sensor element. The rotation direction of Faraday rotation at 50A can be reversed. In the sensor device 1, the rotation direction of the Faraday rotation in the second magnetic field sensor element 50B is reversed with the rotation direction of the Faraday rotation in the first magnetic field sensor element 50A. Faraday rotation can be synthesized.

In addition, in the sensor device 1, the second polarization-maintaining fiber 52 is formed by a pair of polarization-maintaining fibers that are fused with the slow axis and the fast axis rotated by 90 degrees, so that the linearly polarized light that is introduced is A structure that rotates the plane of polarization by 90 degrees can be easily manufactured with high precision.

In the sensor device 1, the first magnetic field sensor element 50A and the second magnetic field sensor element 50B are fixedly held by the yoke, but in the sensor device according to the 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. Further, in the sensor device according to the 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.

Further, in the 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 the embodiment, the lengths of the first polarization-maintaining fiber 51 and the second polarization-maintaining fiber 52 are the same. The length of the wave-maintaining fiber 52 may vary within a range that does not affect detection accuracy.

Further, 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 the slow axis and the fast axis rotated by 90 degrees. However, the sensor device according to the embodiment may be formed by a pair of polarization-maintaining fibers arranged to sandwich the 1/2 wavelength plate.

1 Sensor device 10 Light emitting section 20 Circulator (light branching section)
30 1/2 wavelength plate (first optical element)
40 Optical path section 42 Branch coupler 43 First optical path 44 Second optical path 50A First magnetic field sensor element 50B Second magnetic field sensor element

Claims (5)

a light emitting unit that emits first linearly polarized light;
A first that emits first linearly polarized light and second linearly polarized light in response to the incident first linearly polarized light, and emits second linearly polarized light in response to the incident third linearly polarized light and fourth linearly polarized light. an optical element;
The first linearly polarized light and the second linearly polarized light are incident, and the first linearly polarized light and the second linearly polarized light are changed according to an applied magnetic field to output the third linearly polarized light and the fourth linearly polarized light. a first magnetic field sensor element and a second magnetic field sensor element,
A first optical path that propagates the first linearly polarized light and the fourth linearly polarized light, a second optical path that propagates the second linearly polarized light and the third linearly polarized light, and each of the first linearly polarized light and the second linearly polarized light. The third linearly polarized light and the fourth linearly polarized light enter from the first magnetic field sensor element and the second magnetic field sensor element, respectively. an optical path including a branching coupler that combines each of the linearly polarized lights, outputs the combined third linearly polarized light to the second optical path, and outputs the combined fourth linearly polarized light to the first optical path; Department and
a detection signal generation unit that outputs a detection signal according to the magnetic field by receiving two components of the second linearly polarized light and converting them into electrical signals;
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 generating section;
An interferometric optical magnetic field sensor device characterized by: The interferometric optical magnetic field sensor device according to claim 1, further comprising a yoke arranged to surround the conductor to be measured and holding the first magnetic field sensor element and the second magnetic field sensor element. a first polarization maintaining fiber optically connecting the branch coupler and the first magnetic field sensor element;
further comprising a second polarization maintaining fiber optically connecting the branch coupler and the second magnetic field sensor element,
3. The interferometric optical magnetic field sensor device according to claim 1, wherein the first polarization-maintaining fiber and the second polarization-maintaining fiber have equal lengths. 4. The interference according to claim 3, wherein the second polarization-maintaining fiber rotates each polarization plane of the first linearly polarized light, the second linearly polarized light, the third linearly polarized light, and the fourth linearly polarized light by 90 degrees. type optical magnetic field sensor device. 5. The interferometric magneto-optical field sensor device according to claim 4, wherein the second polarization-maintaining fiber is formed by a pair of polarization-maintaining fibers that are fused with a slow axis and a fast axis rotated by 90 degrees.

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