JP7743318B2 - Interference-type optical magnetic field sensor device - Google Patents

Description

The present invention relates to an interference-type optical magnetic field sensor device.

An interferometric optical magnetic field sensor device is known that photoelectrically converts light that has passed through a Faraday rotator placed at the tip of an optical fiber to generate a detection signal that corresponds to the magnetic field applied to the Faraday rotator (see, for example, Patent Document 1). The interferometric optical magnetic field sensor device disclosed in Patent Document 1 inverts and amplifies the differential signal of an electrical signal that is proportional to the intensity of each of the S-polarized and P-polarized components, generating a detection signal from which the DC component has been removed, thereby increasing the signal-to-noise ratio of the detection signal that corresponds to the magnetic field being detected.

Furthermore, a ring interferometer has been reported that has significantly improved resistance to polarization crosstalk caused by temperature changes and bending of the optical fiber (for example, Patent Document 2).

Japanese Patent Application Laid-Open No. 2020-126007 Patent Application No. 2021-045982

However, conventional ring interferometers are not completely resistant to polarization crosstalk. The magnetic field sensor elements, adhesives, wave plates, and optical fibers used in the sensor head are temperature-dependent, resulting in polarization crosstalk. This polarization crosstalk is the same as Faraday rotation. In other words, it is superimposed on the modulation that occurs in the sensor head, and if, for example, a temperature change occurs in the sensor head or bending stress occurs in the optical fiber, there is a risk that the magnetic field detection accuracy will decrease or it will become difficult to detect the magnetic field.

The present invention aims to solve these problems and provide an interference-type optical magnetic field sensor device that can eliminate the effects of polarization crosstalk.

An interference-type optical magnetic field sensor device according to one embodiment of the present disclosure includes a first light-emitting unit that emits first linearly polarized light, a second light-emitting unit that emits unpolarized light, a magnetic field sensor element at least a portion of which can be positioned within a predetermined magnetic field and which emits returned light in response to incident light, a first port into which the first linearly polarized light and unpolarized light are incident, a second port from which the incident light is emitted to the magnetic field sensor element and into which the returned light is incident, a third port and a fourth port from which the first linearly polarized light and a second linearly polarized light orthogonal to the first linearly polarized light are respectively output, and a return port. It is characterized by having an optical unit having a fifth port and a sixth port that respectively emit P-polarized and S-polarized components obtained by splitting unpolarized returning light from the reflected light; a detection signal generation unit that receives the first linearly polarized light and the second linearly polarized light and converts them into electrical signals to output a detection signal corresponding to the magnetic field applied to the magnetic field sensor element; a crosstalk compensation circuit that receives the P-polarized and S-polarized components and converts them into electrical signals to output a disturbance signal corresponding to polarization crosstalk; and a signal processing circuit that receives the detection signal and the disturbance signal and outputs a differential signal between the detection signal and the disturbance signal.

In an interferometric optical magnetic field sensor device according to one embodiment of the present disclosure, it is preferable that the wavelength of the first linearly polarized light is light in a first wavelength band, and the wavelength of the unpolarized light is light in a second wavelength band different from the first wavelength band.

In an interferometric optical magnetic field sensor device according to one embodiment of the present disclosure, it is preferable that the first wavelength band be included in the C-band wavelength band, and the second wavelength band be included in the O-band wavelength band.

In an interferometric optical magnetic field sensor device according to one embodiment of the present disclosure, the optical unit includes a first polarizing element that, in response to incidence of first linearly polarized light, emits third linearly polarized light and fourth linearly polarized light orthogonal to the third linearly polarized light, and emits second linearly polarized light in response to incidence of fifth linearly polarized light and sixth linearly polarized light orthogonal to the fifth linearly polarized light; an optical path section optically connected to the first polarizing element and having a first optical path that propagates the third linearly polarized light and the sixth linearly polarized light, and a second optical path that propagates the fourth linearly polarized light and the fifth linearly polarized light; and an optical path section that, in response to incidence of second linearly polarized light from the first polarizing element, converts the second linearly polarized light into the first linearly polarized light and and a third birefringence element that separates the first linearly polarized light and the fourth linearly polarized light that are orthogonal to each other, and the optical path section preferably includes a first birefringence element that separates the third linearly polarized light and the fourth linearly polarized light that are incident from the first polarizing element into the first optical path and the second optical path, respectively, and combines the fifth linearly polarized light that has propagated through the second optical path and the sixth linearly polarized light that has propagated through the first optical path, and outputs the combined light to the first polarizing element; and a second birefringence element that combines the third linearly polarized light that has propagated through the first optical path and the fourth linearly polarized light that has propagated through the second optical path, and outputs the combined light to the second port, and separates the fifth linearly polarized light and the sixth linearly polarized light that are incident from the second port into the first optical path and the second optical path, respectively.

In an interferometric optical magnetic field sensor device according to an embodiment of the present disclosure, the optical path section preferably further includes a second optical element disposed in the first optical path, which adjusts the phases of the third linearly polarized light and the sixth linearly polarized light so that the phase difference between the fifth linearly polarized light and the sixth linearly polarized light is 90 degrees.

In an interferometric optical magnetic field sensor device according to an embodiment of the present disclosure, it is preferable to further include a third birefringence element that, in response to the second linearly polarized light being incident from the first polarizing element, splits the second linearly polarized light into the first linearly polarized light and a second linearly polarized light that is orthogonal to the first linearly polarized light.

It is preferable that an interferometric optical magnetic field sensor device according to an embodiment of the present disclosure further includes a fourth birefringent element onto which the first linearly polarized light and the second linearly polarized light are incident from the third birefringent element, and that the first linearly polarized light is incident from the fourth birefringent element onto the third port, and the second linearly polarized light is incident from the fourth birefringent element onto the fourth port.

In an interferometric optical magnetic field sensor device according to one embodiment of the present disclosure, the first birefringent element, the second birefringent element, the third birefringent element, and the fourth birefringent element are preferably formed from calcite.

In an interferometric optical magnetic field sensor device according to one embodiment of the present disclosure, the first birefringent element and the second birefringent element are preferably spatially coupled.

An interferometric optical magnetic field sensor device according to one embodiment of the present disclosure can provide an interferometric optical magnetic field sensor device that can eliminate the effects of polarization crosstalk.

1 is a block diagram of an interferometric optical magnetic field sensor device according to an embodiment of the present disclosure. FIG. 2 is a circuit block diagram of a first signal processing circuit of an interferometric optical magnetic field sensor device according to an embodiment of the present disclosure. FIG. 10 is a circuit block diagram of a second signal processing circuit of the interferometric optical magnetic field sensor device according to an embodiment of the present disclosure. FIG. 2 is a plan view of the optical unit shown in FIG. 1 . FIG. 5 is a diagram showing optical characteristics of the first birefringent element shown in FIG. 4 . 5A is a diagram showing the optical path of the first linearly polarized light in the optical unit shown in FIG. 4, and FIG. 5B is a diagram showing the transition of the polarization plane of the first linearly polarized light shown in FIG. 5A is a diagram showing the optical path of the second linearly polarized light in the optical unit shown in FIG. 4, and FIG. 5B is a diagram showing the transition of the polarization plane of the second linearly polarized light shown in FIG. FIG. 10 is a plan view of an optical unit according to a modified example. FIG. 9 is an optical path diagram of a first linearly polarized light in the optical unit shown in FIG. 8 . FIG. 9 is an optical path diagram of a second linearly polarized light in the optical unit shown in FIG. 8 .

The following describes an interference-type optical magnetic field sensor device according to the present invention, with reference to the drawings. However, please note that the technical scope of this disclosure is not limited to these embodiments, but extends to the inventions set forth in the claims and their equivalents.

(Configuration and Function of Interferometric Optical Magnetic Field Sensor Device)
FIG. 1 is a block diagram of an interferometric optical magnetic field sensor device according to an embodiment of the present disclosure.

The interference-type optical magnetic field sensor device 100 has an optical unit 1, a first light-emitting unit 110, a second light-emitting unit 110a, a quarter-wave plate 120, a plano-convex lens 130, a magnetic field sensor element 140, a detection signal generating unit 150, a crosstalk compensation circuit 160, and a signal processing circuit 170, and outputs a detection signal corresponding to the magnetic field applied to the magnetic field sensor element 140.

The first light-emitting unit 110 has a first light-emitting element 111, a first isolator 112, and a polarizer 113, and emits first linearly polarized light. The first light-emitting element 111 is, for example, a semiconductor laser or a light-emitting diode. Specifically, the first light-emitting element 111 may be a Fabry-Perot laser, a superluminescent diode (SLD), or the like. The first light-emitting element 111 emits light with a wavelength of, for example, 1550 nm.

The first isolator 112 protects the first light-emitting element 111 by transmitting light incident from the first light-emitting element 111 toward the optical unit 1 and not transmitting light incident from the optical unit 1 toward the first light-emitting element 111. The first isolator 112 is, for example, a polarization-dependent optical isolator, but may also be a polarization-independent optical isolator.

The polarizer 113 is an optical element that converts the light emitted by the first light-emitting element 111 into linearly polarized light B1, and its type is not particularly limited. The first linearly polarized light B1 obtained by the polarizer 113 is incident on the optical unit 1.

The second light-emitting unit 110a has a second light-emitting element 111a, a second isolator 112a, and a depolarizer 113a, and emits unpolarized light. The second light-emitting element 111a is, for example, a semiconductor laser or a light-emitting diode. Specifically, the second light-emitting element 111a can be a Fabry-Perot laser, a superluminescent diode (SLD), or the like. The second light-emitting element 111a emits light with a wavelength of, for example, 1310 nm.

If the wavelength of the first linearly polarized light emitted by the first light-emitting element 111 is light in a first wavelength band, then the wavelength of the unpolarized light emitted by the second light-emitting element 111a is preferably light in a second wavelength band different from the first wavelength band. Furthermore, it is preferable that the first wavelength band be included in the C-band wavelength band (1530-1565 nm), and the second wavelength band be included in the O-band wavelength band (1260-1360 nm). Because the C-band wavelength band and the O-band wavelength band are close to each other, selecting such wavelength bands allows the optical system for the light emitted by the first light-emitting element 111 and the optical system for the light emitted by the second light-emitting element 111a to be shared.

The second isolator 112a protects the second light-emitting element 111a by transmitting light incident from the second light-emitting element 111a toward the optical unit 1 and not transmitting light incident from the optical unit 1 toward the second light-emitting element 111a. The second isolator 112a is, for example, a polarization-dependent optical isolator, but may also be a polarization-independent optical isolator.

The depolarizer 113a is an optical element that converts the light emitted by the second light-emitting element 111a into unpolarized light, and its type is not particularly limited. The unpolarized light obtained by the depolarizer 113a is incident on the optical unit 1.

Optical unit 1 has a housing 10, a first port 11, a second port 12, a third port 13, a fourth port 14, a fifth port 15, and a sixth port 16. It adjusts the phase of incident light so that the phase difference between the outgoing first linearly polarized light B2P3 and the outgoing second linearly polarized light B2P4 is 90 degrees, and also emits return light when unpolarized light is incident. Housing 10 is a housing section made of a material with high thermal conductivity, such as aluminum, and holds the various optical elements of optical unit 1 in predetermined positions.

The first port 11 is an input port that inputs the first linearly polarized light B1 and unpolarized light, and is located in the center of one longitudinal end face of the housing 10, where the first linearly polarized light B1 is input. The second port 12 is an input/output port that outputs the incident light BI that is incident on the magnetic field sensor element 140, and where the return light BR from the magnetic field sensor element 140 is input, and is located in the center of the other longitudinal end face of the housing 10.

The third port 13 is an output port that outputs the first linearly polarized light B2P3 and is located at one end of one of the longitudinal end faces of the housing 10. The fourth port 14 is an output port that outputs the second linearly polarized light B2P4 and is located at the other end of one of the longitudinal end faces of the housing 10. That is, the third port and the fourth port respectively output a first linearly polarized light obtained by splitting the first linearly polarized light from the returning light and a second linearly polarized light that is orthogonal to the first linearly polarized light.

The fifth port 15 is an output port that outputs return light P', which is the P-polarized component when non-polarized light is incident, and is located at one end of one of the end faces perpendicular to the longitudinal direction of the housing 10. The sixth port 16 is an output port that outputs return light S', which is the S-polarized component when non-polarized light is incident, and is located at the other end face perpendicular to the longitudinal direction of the housing 10. In other words, the fifth port and the sixth port respectively output the P-polarized component and the S-polarized component obtained by splitting the non-polarized return light from the return light.

The quarter-wave plate 120 is made of a birefringent material such as quartz, and is positioned with its optical axis tilted 45 degrees with respect to the direction of the polarization plane of the first linearly polarized light B1. The quarter-wave plate 120 converts the first incident polarized light BIP1 and the second incident polarized light BIP2, which are linearly polarized components of the incident light BI output from the second port 12, into circularly polarized light that is incident on the magnetic field sensor element 140 and output to the plano-convex lens 130. The quarter-wave plate 120 also converts the return light BR, which is incident as circularly polarized light from the magnetic field sensor element 140, into linearly polarized components, return light BRP1 and return light BRP2.

The plano-convex lens 130 focuses the incident light BI emitted from the quarter-wave plate 120 onto the magnetic field sensor element 140, and also focuses the returning light BR emitted from the magnetic field sensor element 140 onto the magnetic field sensor element 140.

The magnetic field sensor element 140 has a Faraday rotator 141 and a mirror element 142, and is an element at least a portion of which can be placed within a predetermined magnetic field. The magnetic field sensor element 140 receives incident light BI from the plano-convex lens 130 and emits return light BR corresponding to the incident light BI back to the plano-convex lens 130.

The Faraday rotator 141 is a granular film containing a dielectric and nano-sized magnetic particles dispersed in the dielectric in a state where they are stably phase-separated from the dielectric. It is positioned away from the plano-convex lens 130 by the focal length of the plano-convex lens 130. The magnetic particles may form oxides in a small portion, such as the outermost layer, but throughout the Faraday rotator 141, the magnetic particles are dispersed independently in the thin film without forming compounds with the dielectric, which acts as a binder. The distribution of the magnetic particles within the Faraday rotator 141 does not need to be completely uniform and may be slightly biased. If a highly transparent dielectric is used, the magnetic particles will be present in the dielectric at sizes smaller than the wavelength of light, making the Faraday rotator 141 optically transparent.

The Faraday rotator 141 is not limited to a single layer, but may be a multilayer film in which granular films and dielectric films are alternately stacked. By forming the Faraday rotator 141 using a multilayer granular film, a larger Faraday rotation angle can be obtained due to multiple reflections within the granular film.

The dielectric is preferably a fluoride (metal fluoride) such as magnesium fluoride ( _MgF2 ), aluminum fluoride ( _AlF3 ), or yttrium fluoride ( _YF3 ). Alternatively, the dielectric may be an oxide such as tantalum oxide ( _Ta2O5 ), silicon dioxide _{( SiO2} ), titanium dioxide ( _TiO2 ), niobium pentoxide ( _Nb2O5 ), zirconium dioxide ( _ZrO2 ), hafnium dioxide ( _HfO2 ), or _aluminum trioxide ( _Al2O3 ). To achieve good phase separation between _the dielectric and the magnetic particles, fluorides are more preferable than oxides, and magnesium fluoride, which has high transmittance, is particularly preferred.

The material of the magnetic particles is not particularly limited as long as it produces the Faraday effect, but examples of the material for the magnetic particles include ferromagnetic metals such as iron (Fe), cobalt (Co), and nickel (Ni), as well as alloys of these. 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 two to three orders of magnitude larger than that of magnetic garnets used in conventional Faraday rotators.

The mirror element 142 is formed on the Faraday rotator 141 and reflects light that has passed through the Faraday rotator 141 back toward the Faraday rotator 141. The mirror element 142 can be made of, for example, a silver (Ag) film, a gold (Au) film, an aluminum (Al) film, or a dielectric multilayer mirror. Ag films, which have high reflectivity, and Au films, which have high corrosion resistance, are particularly preferred for their ease of deposition. The thickness of the mirror element 142 need only be large enough to ensure a sufficient reflectivity of 98% or more. For example, in the case of an Ag film, a thickness of 50 nm or more and 200 nm or less is preferred. By using the mirror element 142 to reflect light back and forth within the Faraday rotator 141, the Faraday rotation angle can be increased.

In the magnetic field sensor element 140, when the incident light BI propagates through the inside of the Faraday rotator 141 toward the mirror element 142, the phase is changed by θ _F in accordance with the magnetic field applied to the Faraday rotator 141. On the other hand, Faraday rotation does not occur for the incident unpolarized light. Furthermore, when the return light BR reflected from the mirror element 142 propagates through the inside of the Faraday rotator 141, the phase is changed by θ _F in accordance with the magnetic field applied to the Faraday rotator 141. The phase difference between the incident light BI and the return light BR is 2θ _F.

The detection signal generating unit 150 has a first light receiving element 151, a second light receiving element 152, and a first signal processing circuit 153, and receives the return light BR that has been split into first linearly polarized light B2P3 and second linearly polarized light B2P4 by the optical unit 1.

Each of the first light receiving element 151 and the second light receiving element 152 is, for example, a PIN photodiode. The first light receiving element 151 receives the first linearly polarized light B2P3, and the second light receiving element 152 receives the second linearly polarized light B2P4. Each of the first light receiving element 151 and the second light receiving element 152 photoelectrically converts the received light and outputs an electrical signal corresponding to the amount of light received. The first signal processing circuit 153 differentially amplifies the electrical signal representing the first linearly polarized light B2P3 and the electrical signal representing the second linearly polarized light B2P4, and outputs a detection signal Ed corresponding to the magnetic field applied to the magnetic field sensor element to a display device such as an oscilloscope.

Figure 2 shows a circuit block diagram of the first signal processing circuit 153. The first signal processing circuit 153 has a first amplifier circuit 154, a second amplifier circuit 155, a first divider circuit 156, a second divider circuit 157, and a differential amplifier circuit 158. The first signal processing circuit 153 detects the difference in intensity between the two polarization components from the electrical signals photoelectrically converted by the first light receiving element 151 and the second light receiving element 152, and converts the detected numerical value into a current value.

Each of the first amplifier circuit 154 and the second amplifier circuit 155 is an analog amplifier circuit formed by an operational amplifier, a resistor element, etc.

The first amplifier circuit 154 receives a first electrical signal Ep1 corresponding to the light amount Lp of the P-polarized component B2P3 from the first light receiving element 151, amplifies the received first electrical signal Ep1, and outputs a first amplified electrical signal Ep2. The second amplifier circuit 155 receives a second electrical signal Es1 corresponding to the light amount Ls of the S-polarized component B2P4 from the second light receiving element 152, amplifies the received second electrical signal Es1, and outputs a second amplified electrical signal Es2.

Each of the first division circuit 156 and the second division circuit 157 is an analog division circuit formed by an operational amplifier, a resistor element, etc.

The first divider circuit 156 divides the first amplified electrical signal Ep2 by the second amplified electrical signal Es2 and outputs a first analog signal (Ep2/Es2) indicating the divided output value to the negative input terminal of the differential amplifier circuit 158. The second divider circuit 157 divides the second amplified electrical signal Es2 by the first amplified electrical signal Ep2 and outputs a second analog signal (Es2/Ep2) indicating the divided output value to the positive input terminal of the differential amplifier circuit 158.

The differential amplifier circuit 158 is, for example, an operational amplifier, and differentially amplifies the first analog signal (Ep2/Es2) input from the first divider circuit 156 and the second analog signal (Es2/Ep2) input from the second divider circuit 157, and outputs the detection signal Ed.

The crosstalk compensation circuit 160 includes a third light-receiving element 161, a fourth light-receiving element 162, and a second signal processing circuit 163. It receives the P-polarized return light P' and the S-polarized return light S' separated by the optical unit 1 and converts them into electrical signals, thereby outputting a disturbance signal corresponding to the polarization crosstalk.

The third light receiving element 161 and the fourth light receiving element 162 are each, for example, a PIN photodiode. The third light receiving element 161 and the fourth light receiving element 162 receive the return light P' and S', respectively, when unpolarized light is incident. The third light receiving element 161 and the fourth light receiving element 162 perform photoelectric conversion on the received light P' and S', and output an electrical signal corresponding to the amount of light received. The second signal processing circuit 163 differentially amplifies the electrical signals generated by the return light P' and S', and outputs a signal corresponding to crosstalk in the optical fiber.

Figure 3 shows a circuit block diagram of the second signal processing circuit 163. The second signal processing circuit 163 has a third amplifier circuit 164, a fourth amplifier circuit 165, a third divider circuit 166, a fourth divider circuit 167, and a differential amplifier circuit 168. The second signal processing circuit 163 detects the difference in intensity between the two polarization components from the electrical signals photoelectrically converted by the third light receiving element 161 and the fourth light receiving element 162, and converts the detected numerical value into a current value.

The third amplifier circuit 164 and the fourth amplifier circuit 165 are each analog amplifier circuits formed by an operational amplifier, a resistor element, etc.

The third amplifier circuit 164 receives a third electrical signal Ep1' corresponding to the amount of light of the P-polarized component P' from the third light receiving element 161, amplifies the received third electrical signal Ep1', and outputs a third amplified electrical signal Ep2'. The fourth amplifier circuit 165 receives a fourth electrical signal Es1' corresponding to the amount of light of the S-polarized component S' from the fourth light receiving element 162, amplifies the received fourth electrical signal Es1', and outputs a fourth amplified electrical signal Es2'.

The third division circuit 166 and the fourth division circuit 167 are each analog division circuits formed by operational amplifiers, resistor elements, etc.

The third divider circuit 166 divides the third amplified electrical signal Ep2' by the fourth amplified electrical signal Es2' and outputs a third analog signal (Ep2'/Es2') indicating the divided output value to the positive input terminal of the differential amplifier circuit 168. The fourth divider circuit 167 divides the fourth amplified electrical signal Es2' by the third amplified electrical signal Ep2' and outputs a fourth analog signal (Es2'/Ep2') indicating the divided output value to the negative input terminal of the differential amplifier circuit 168.

The differential amplifier circuit 168 is, for example, an operational amplifier, and differentially amplifies the third analog signal (Ep2'/Es2') input from the third divider circuit 166 and the fourth analog signal (Es2'/Ep2') input from the fourth divider circuit 167, and outputs the detection signal Ec. The detection signal Ec is a signal generated by crosstalk.

The signal processing circuit 170 receives the detection signal Ed from the detection signal generating unit 150 and the disturbance signal Ec output by the crosstalk compensation circuit 160, and outputs a differential signal between the detection signal Ed and the disturbance signal Ec. Specifically, the signal processing circuit 170 outputs a signal with reduced crosstalk effects based on the difference between the output signal Ed from the first signal processing circuit 153 of the detection signal generating unit 150 and the output signal Ec from the second signal processing circuit 163 of the crosstalk compensation circuit 160. That is, the output signal from the first signal processing circuit 153 contains the detection signal from the magnetic field sensor element 140 and crosstalk, while the output signal from the second signal processing circuit 163 contains only a signal corresponding to the crosstalk. Therefore, by subtracting the output signal from the second signal processing circuit 163 from the output signal from the first signal processing circuit 153, the signal processing circuit 170 can output only the detection signal from the magnetic field sensor element 140 with reduced crosstalk effects.

(Optical unit)
FIG. 4 is a plan view of the optical unit 1. As shown in FIG.

The optical unit 1 further includes a first birefringent element 21, a second birefringent element 22, a third birefringent element 23, and a fourth birefringent element 24. The optical unit 1 further includes a first Faraday rotator 25, a second Faraday rotator 26, a first (½) wave plate 27, a second (½) wave plate 28, a first (¼) wave plate 29, and a second (¼) wave plate 30. The optical unit 1 further includes a first optical element 31, a second optical element 32, a first base 33, a second base 34, and a third base 35. The first birefringent element 21, the second birefringent element 22, the second Faraday rotator 26, the first (¼) wave plate 29, and the second (¼) wave plate 30 form the optical path section 20. The optical elements included in the optical unit 1, the first birefringent element 21 to the second optical element 32, are spatially coupled without using optical fibers.

The first port 11 receives the first linearly polarized light B1 from the first light emitter 110 and outputs the incident first linearly polarized light B1 to the first Faraday rotator 25.

The second port 12 receives incident light BI from the second birefringent element 22 onto the magnetic field sensor element 140 and outputs the incident light BI to the quarter-wave plate 120. The second port 12 also receives return light BR from the quarter-wave plate 120 and outputs the incident return light BR to the second birefringent element 22.

The third port 13 receives the first linearly polarized light B2P3 from the first optical element 31 and outputs the incident first linearly polarized light B2P3 to the first light receiving element 151. The fourth port 14 receives the second linearly polarized light B2P4 from the second optical element 32 and outputs the incident second linearly polarized light B2P4 to the second light receiving element 152.

The first birefringent element 21, the second birefringent element 22, the third birefringent element 23, and the fourth birefringent element 24 are birefringent elements made of, for example, calcite (CaCO ₃ ).

Figure 5 shows the optical characteristics of the first birefringent element 21.

The first birefringent element 21 has a first surface 21a, a second surface 21b, and an optical axis 21c. Polarized light B propagating along a single optical path is input and output from the first surface 21a, and first polarized light BP1 and second polarized light BP2 propagating along two optical paths are input and output from the second surface 21b. The first polarized light BP1 has a polarization plane in the horizontal direction in Figure 5 and is also referred to as an ordinary ray. The second polarized light BP2 has a polarization plane in the vertical direction in Figure 5 and is also referred to as an extraordinary ray. The first birefringent element 21 is positioned so that the optical axis 21c is oriented in a direction that allows the desired first polarized light BP1 and second polarized light BP2 to enter and exit.

When polarized light B is incident on the first surface 21a, the first birefringent element 21 splits the polarized light B into a first polarized light BP1 that propagates along the longitudinal direction of the first birefringent element 21 and a second polarized light BP2 that propagates at an angle oblique to the longitudinal direction of the first birefringent element 21. When polarized light B is incident on the first surface 21a, the first birefringent element 21 emits the first polarized light BP1 and the second polarized light BP2 from the second surface 21b. When the first polarized light BP1 and the second polarized light BP2 are incident on the second surface 21b, the first birefringent element 21 combines the first polarized light BP1 and the second polarized light BP2 and emits polarized light B from the first surface 21a.

The second birefringent element 22, the third birefringent element 23, and the fourth birefringent element 24 have optical characteristics similar to those of the first birefringent element 21, so detailed description will be omitted.

The first birefringent element 21 is positioned so that its first surface 21a faces the second (1/2) wave plate 28 and its second surface 21b faces the first (1/4) wave plate 29. The second birefringent element 22 is positioned so that its first surface 21a faces the second (1/4) wave plate 30 and its second surface 21b faces the second port 12.

The third birefringent element 23 is arranged so that one surface faces the second (1/2) wave plate 28 and the other surface faces the first (1/2) wave plate 27. The fourth birefringent element 24 is arranged so that one surface faces the first Faraday rotator 25 and the other surface faces the first port 11, the first optical element 31, and the second optical element 32.

The first Faraday rotator 25 and the second Faraday rotator 26 are formed from a ferromagnetic material such as bismuth iron garnet and shift the phase of the incident linearly polarized light and circularly polarized light by 45 degrees. The first Faraday rotator 25 is disposed between the fourth birefringent element 24 and the first (1/2) wave plate 27. The second Faraday rotator 26 is disposed between the first (1/4) wave plate 29 and the second (1/4) wave plate 30 and is also referred to as the second polarizing element.

The first (1/2) wave plate 27 and the second (1/2) wave plate 28 are formed from a birefringent material such as quartz, and are positioned with their optical axes tilted 22.5 degrees with respect to the direction of the polarization plane of the first linearly polarized light B1 incident from the first light emitter 110, shifting the phase of the incident linearly polarized light by 45 degrees. The first (1/2) wave plate 27 is positioned between the first Faraday rotator 25 and the third birefringent element 23. The second (1/2) wave plate 28 is positioned between the first birefringent element 21 and the third birefringent element 23, and is also referred to as the first polarizing element.

The first (1/4) wave plate 29 and second (1/4) wave plate 30 are formed from a birefringent material such as quartz, and are positioned with their optical axes tilted 45 degrees with respect to the direction of the polarization plane of the first linearly polarized light B1 incident from the first light emitter 110, converting linearly polarized light into circularly polarized light and circularly polarized light into linearly polarized light. The first (1/4) wave plate 29 is positioned between the first birefringent element 21 and the second Faraday rotator 26. The second (1/4) wave plate 30 is positioned between the second birefringent element 22 and the second Faraday rotator 26.

The first optical element 31 and the second optical element 32 are rhomboid prisms. The first optical element 31 is disposed between the third port 13 and the fourth birefringent element 24 and includes a filter 310. The first linearly polarized light B2P3, which is light with a wavelength of 1550 nm and is output from the fourth birefringent element 24, is reflected by the filter 310 and output to the third port 13. On the other hand, the returning light with a wavelength of 1310 nm is transmitted through the filter 310 and output to the fifth port 15. In this way, the filter 310 separates the light with a wavelength of 1550 nm from the light with a wavelength of 1310 nm. The second optical element 32 is disposed between the fourth port 14 and the fourth birefringent element 24 and includes a filter 320. The second linearly polarized light B2P4, which is light with a wavelength of 1550 nm and is output to the fourth port 14, is reflected by the filter 320 and output to the fourth port 14. On the other hand, the returning light with a wavelength of 1310 nm passes through the filter 320 and is output to the sixth port 16. In this way, the filter 320 separates the light with a wavelength of 1550 nm from the light with a wavelength of 1310 nm.

The first base 33, second base 34, and third base 35 are each fixed to the housing 10. The first base 33 holds the first Faraday rotator 25 and the first (1/2) wave plate 27 between the third birefringent element 23 and the fourth birefringent element 24. The second base 34 holds the second (1/2) wave plate 28 between the third birefringent element 23 and the first birefringent element 21. The third base 35 holds the second Faraday rotator 26, the first (1/4) wave plate 29, and the second (1/4) wave plate 30 between the first birefringent element 21 and the second birefringent element 22.

Figure 6(a) is a diagram showing the optical path of the first linearly polarized light B1 in the optical unit 1, and Figure 6(b) is a diagram showing the transition of the polarization plane of the first linearly polarized light B1 shown in Figure 6(a).

First, as shown by arrow A, first linearly polarized light B1 with a wavelength of 1550 nm is incident from the first light-emitting unit 110 via the first port 11, and unpolarized light with a wavelength of 1310 nm is incident from the second light-emitting unit 110a via the first port 11. The first linearly polarized light B1 will be described below. The unpolarized light travels a similar optical path as the first linearly polarized light B1, except that its wavelength differs from that of the first linearly polarized light B1 and that no Faraday rotation occurs in the magnetic field sensor element 140. Because the first linearly polarized light B1 is an ordinary ray, it propagates within the fourth birefringent element 24 along the longitudinal direction of the fourth birefringent element 24.

Next, as shown by arrow B, the first linearly polarized light B1 is emitted from the fourth birefringent element 24 and enters the first Faraday rotator 25. The first linearly polarized light B1 undergoes a 45-degree phase shift as it propagates through the first Faraday rotator 25, and as shown by arrow C, it is emitted from the first Faraday rotator 25 with a 45-degree phase shift and enters the first (1/2) wave plate 27.

The first linearly polarized light B1 undergoes a phase shift of -45 degrees as it propagates through the first (1/2) wave plate 27, and as shown by arrow D, its polarization plane returns before entering the first Faraday rotator 25, exits the first (1/2) wave plate 27, and enters the third birefringent element 23. Because the first linearly polarized light B1 is an ordinary ray, it propagates through the third birefringent element 23 along the longitudinal direction of the third birefringent element 23.

Next, as shown by arrow E, the first linearly polarized light B1 is emitted from the third birefringent element 23 and enters the second (1/2) wave plate 28. The first linearly polarized light B1 undergoes a 45-degree phase shift as it propagates through the second (1/2) wave plate 28, and as shown by arrow F, it is emitted from the second (1/2) wave plate 28 with a 45-degree phase shift and enters the first birefringent element 21.

When the first linearly polarized light B1 enters the first birefringent element 21, it is split into a third linearly polarized light B1P1, which is an ordinary ray, and a fourth linearly polarized light B1P2, which is an extraordinary ray. Because the first linearly polarized light B1 is an ordinary ray, it propagates within the first birefringent element 21 along the longitudinal direction of the first birefringent element 21.

As indicated by arrow G, the third linearly polarized light B1P1 exits the first birefringent element 21 and enters the first (1/4) wave plate 29. The third linearly polarized light B1P1 is converted into the first circularly polarized light B1C1 as it propagates through the first (1/4) wave plate 29. As indicated by arrow H, the first circularly polarized light B1C1 exits the first (1/4) wave plate 29 and enters the second Faraday rotator 26.

As the first circularly polarized light B1C1 propagates through the second Faraday rotator 26, the phase of the circular polarization is shifted by 45 degrees, and as shown by arrow I, it is emitted from the second Faraday rotator 26 and enters the second (1/4) wave plate 30. As the first circularly polarized light B1C1 propagates through the second (1/4) wave plate 30, it is converted into third linearly polarized light B1P1. As shown by arrow J, the third linearly polarized light B1P1 is emitted from the second (1/4) wave plate 30 and enters the second birefringence element 22.

On the other hand, the fourth linearly polarized light B1P2, which is an extraordinary ray, propagates inside the first birefringent element 21 at an angle inclined from the longitudinal direction of the first birefringent element 21. As indicated by arrow K, the fourth linearly polarized light B1P2 exits the first birefringent element 21 and enters the second birefringent element 22.

In the second birefringent element 22, the third linearly polarized light B1P1 propagates within the second birefringent element 22 along the longitudinal direction of the second birefringent element 22. On the other hand, the fourth linearly polarized light B1P2 propagates within the second birefringent element 22 at an angle inclined from the longitudinal direction of the second birefringent element 22. As shown by arrow L, the third linearly polarized light B1P1 and the fourth linearly polarized light B1P2 are combined and emitted from the second birefringent element 22 as incident light BI. Light BI' produced when unpolarized light is incident also exits the second birefringent element 22.

Figure 7(a) is a diagram showing the optical path of the second linearly polarized light B2 in the optical unit 1, and Figure 7(b) is a diagram showing the transition of the polarization plane of the second linearly polarized light B2 shown in Figure 7(a).

First, as shown by arrow A, return light BR and BR' enter through the second port 12 from the quarter-wave plate 120. The return light BR will be described below. The return light BR' follows the same optical path as the return light BR, except that its wavelength is different from that of the return light BR and it does not undergo Faraday rotation. The return light BR has a fifth linearly polarized light B2P1 and a sixth linearly polarized light B2P2, which is a polarization component orthogonal to the fifth linearly polarized light B2P1.

When the return light BR enters the second birefringent element 22, it is split into fifth linearly polarized light B2P1 and sixth linearly polarized light B2P2. The fifth linearly polarized light B2P1 is an ordinary ray, so it propagates within the second birefringent element 22 along the longitudinal direction of the second birefringent element 22. On the other hand, the sixth linearly polarized light B2P2 is an extraordinary ray, so it propagates within the second birefringent element 22 at an angle oblique to the longitudinal direction of the second birefringent element 22.

As indicated by arrow B, the fifth linearly polarized light B2P1 is emitted from the second birefringent element 22 and enters the second (1/4) wave plate 30. As the fifth linearly polarized light B2P1 propagates through the second (1/4) wave plate 30, it is converted into the third circularly polarized light B2C1. As indicated by arrow C, the third circularly polarized light B2C1 is emitted from the second (1/4) wave plate 30 and enters the second Faraday rotator 26.

As the third circularly polarized light B2C1 propagates through the second Faraday rotator 26, the phase of the circular polarization is shifted by -45 degrees, and as shown by arrow D, it is emitted from the second Faraday rotator 26 and enters the first (1/4) wave plate 29. As the third circularly polarized light B2C1 propagates through the first (1/4) wave plate 29, it is converted into fifth linearly polarized light B2P1. As shown by arrow E, the fifth linearly polarized light B2P1 is emitted from the first (1/4) wave plate 29 and enters the first birefringence element 21.

On the other hand, the sixth linearly polarized light B2P2, which is an extraordinary ray, propagates inside the second birefringent element 22 at an angle inclined from the longitudinal direction of the second birefringent element 22. As indicated by arrow F, the sixth linearly polarized light B2P2 is emitted from the second birefringent element 22 and enters the first birefringent element 21.

In the first birefringent element 21, the fifth linearly polarized light B2P1 propagates within the first birefringent element 21 along the longitudinal direction of the first birefringent element 21. On the other hand, the sixth linearly polarized light B2P2 propagates within the first birefringent element 21 at an angle inclined from the longitudinal direction of the first birefringent element 21. As shown by arrow G, the fifth linearly polarized light B2P1 and the sixth linearly polarized light B2P2 are combined and output from the first birefringent element 21 to the second (1/2) wave plate 28 as the fourth linearly polarized light B2.

When the fourth linearly polarized light B2 propagates through the second (1/2) wave plate 28, its phase is shifted by -45 degrees and it is emitted from the second (1/2) wave plate 28. As indicated by arrow H, the fifth linearly polarized light B2P1 and the sixth linearly polarized light B2P2 each enter the third birefringence element 23 with their phases shifted by -45 degrees.

When the fifth linearly polarized light B2P1 and the sixth linearly polarized light B2P2 propagate through the third birefringent element 23, they are separated into the first linearly polarized light B2P3, which is an extraordinary ray, and the second linearly polarized light B2P4, which is an ordinary ray. Because the first linearly polarized light B2P3 is an extraordinary ray, it propagates through the third birefringent element 23 at an angle oblique to the longitudinal direction of the third birefringent element 23, as shown by arrow I, exits the third birefringent element 23, and enters the first (1/2) wave plate 27.

The first linearly polarized light B2P3 undergoes a phase shift of -45 degrees as it propagates through the first (1/2) wave plate 27, and as shown by arrow J, it exits the first (1/2) wave plate 27 with a phase shift of -45 degrees and enters the first Faraday rotator 25.

The first linearly polarized light B2P3 undergoes a further phase shift of -45 degrees as it propagates through the first Faraday rotator 25, and as indicated by arrow K, it is emitted from the first Faraday rotator 25 with a further phase shift of -45 degrees and enters the fourth birefringent element 24.

Since the first linearly polarized light B2P3 is an ordinary ray, it propagates inside the fourth birefringent element 24 along the longitudinal direction of the third birefringent element 23, as shown by arrow L, exits the fourth birefringent element 24, and enters the first optical element 31. Since the first linearly polarized light B2P3 has a wavelength of 1550 nm, it passes through the first optical element 31, is reflected by the filter 310, and exits from the third port 13. On the other hand, the returning light when unpolarized light is incident has a wavelength of 1310 nm, so it passes through the filter 310 and exits from the fifth port 15.

Since the second linearly polarized light B2P4 is an ordinary ray, it propagates inside the third birefringent element 23 along the longitudinal direction of the third birefringent element 23, as shown by arrow M, exits the third birefringent element 23, and enters the first (1/2) wave plate 27.

The second linearly polarized light B2P4 undergoes a phase shift of -45 degrees as it propagates through the first (1/2) wave plate 27, and as shown by arrow N, it exits the first (1/2) wave plate 27 with a phase shift of -45 degrees and enters the first Faraday rotator 25.

The second linearly polarized light B2P4 undergoes a further phase shift of -45 degrees as it propagates through the first Faraday rotator 25, and as indicated by arrow O, is emitted from the first Faraday rotator 25 with a further phase shift of -45 degrees and enters the fourth birefringent element 24.

Since the second linearly polarized light B2P4 is an extraordinary ray, it propagates through the fourth birefringent element 24 at an angle relative to the longitudinal direction of the third birefringent element 23, as shown by arrow P, before exiting the fourth birefringent element 24 and entering the second optical element 32. Since the second linearly polarized light B2P4 has a wavelength of 1550 nm, it passes through the second optical element 32, is reflected by the filter 320, and exits from the fourth port 14. On the other hand, the return light when unpolarized light is incident has a wavelength of 1310 nm, so it passes through the filter 320 and exits from the sixth port 16.

(Actions and Effects of the Optical Unit According to the Embodiment)
The optical unit 1 employs a birefringent element, which can be made smaller than a beam splitter, as an element that performs splitting and multiplexing processing, so the interferometric optical magnetic field sensor device 100 can be made smaller than an interferometric optical magnetic field sensor device that uses a beam splitter. For example, the length of one side of a beam splitter is about 300 mm to 600 mm, whereas calcite, which is a birefringent element, has a width and height of 30 mm and a length of 100 mm.

In addition, the optical unit 1 and the interferometric optical magnetic field sensor device 100 spatially couple the optical elements without placing an optical fiber in the optical path between the optical elements. By spatially coupling the optical elements, the optical unit 1 and the interferometric optical magnetic field sensor device 100 can be made smaller than an interferometric optical magnetic field sensor device that places an optical fiber in the optical path between the optical elements.

Furthermore, calcite, one of the birefringent elements used in the optical unit 1, has a higher extinction ratio than a beam splitter. By using a birefringent element with a higher extinction ratio than a beam splitter, the optical unit 1 and the interferometric optical magnetic field sensor device 100 have a higher S/N ratio than interferometric optical magnetic field sensor devices that use beam splitters.

(Modification of the optical unit according to the embodiment)
In the optical unit 1, the first port 11, the third port 13, and the fourth port 14 are arranged on one longitudinal surface of the housing 10, the fifth port 15 is arranged on one surface orthogonal to the longitudinal direction of the housing 10, the sixth port 16 is arranged on the other longitudinal surface of the housing 10. However, in the optical unit according to the embodiment, the first to sixth ports 11 to 16 may be arranged on one surface.

Figure 8 is a plan view of an optical unit 2 according to a modified example, Figure 9 is a diagram showing the optical path of the first linearly polarized light B1 in the optical unit 2 shown in Figure 8, and Figure 10 is a diagram showing the optical path of the second linearly polarized light B2 in the optical unit 2 shown in Figure 8.

Optical unit 2 differs from optical unit 1 in that it has a housing 40 instead of housing 10. Optical unit 2 also differs from optical unit 1 in that it has an optical element 41 instead of the second Faraday rotator 26 and the first (1/2) wave plate 27. Optical unit 2 also differs from optical unit 1 in that it has a first optical path prism mirror 51 to a sixth optical path prism mirror 56. Optical unit 2 also differs from optical unit 1 in that it has a first exit prism mirror 61 to a sixth exit prism mirror 66 instead of the first optical element 31 and the second optical element 32.

The configurations and functions of the components of optical unit 2 other than the housing 40, optical element 41, first optical path prism mirror 51 to sixth optical path prism mirror 56, and first exit prism mirror 61 to sixth exit prism mirror 66 are identical to the configurations and functions of the components of optical unit 1 that are assigned the same reference numerals. Therefore, a detailed description of the configurations and functions of the components of optical unit 2 other than the housing 40, optical element 41, first optical path prism mirror 51 to sixth optical path prism mirror 56, and first exit prism mirror 61 to sixth exit prism mirror 66 will be omitted.

In the housing 40, the second port 12, fifth port 15, and sixth port 16 are arranged on the same plane as the first port 11, third port 13, and fourth port 14. The optical element 41 is an integrated element of the second Faraday rotator 26 and the first (1/2) wave plate 27.

The first optical path prism mirror 51 to the sixth optical path prism mirror 56 and the first exit prism mirror 61 to the sixth exit prism mirror 66 are all rectangular prism mirrors. The first optical path prism mirror 51 and the second optical path prism mirror 52 are disposed in the optical path optically connecting the first birefringent element 21 and the first (1/4) wave plate 29, and reverse the optical path.

The third optical path prism mirror 53 to the sixth optical path prism mirror 56 are arranged on the optical path optically connecting the first birefringent element 21 and the second birefringent element 22. The third optical path prism mirror 53 and the fourth optical path prism mirror 54 invert the optical path between the first birefringent element 21 and the second birefringent element 22. The fifth optical path prism mirror 55 and the sixth optical path prism mirror 56 shift the optical path between the first birefringent element 21 and the second birefringent element 22 inward in the short direction of the housing 40.

The first exit prism mirror 61 and the second exit prism mirror 62 optically connect the fourth birefringent element 24 and the third port 13, similar to the first optical element 31. The first exit prism mirror 61 and the fifth exit prism mirror 65 optically connect the fourth birefringent element 24 and the fifth port 15, similar to the first optical element 31. The third exit prism mirror 63 and the fourth exit prism mirror 64 optically connect the fourth birefringent element 24 and the fourth port 14, similar to the second optical element 32. The third exit prism mirror 63 and the sixth exit prism mirror 66 optically connect the fourth birefringent element 24 and the sixth port 16, similar to the second optical element 32.

The optical unit 1 also includes optical elements, such as a third birefringent element 23 and a fourth birefringent element 24, that split the second linearly polarized light B2 into a first linearly polarized light B2P3 and a second linearly polarized light B2P4. However, the optical unit according to the embodiment does not necessarily have to include an optical element that splits the second linearly polarized light B2.

Furthermore, while the optical unit 1 splits the second linearly polarized light B2 using two birefringent elements, the third birefringent element 23 and the fourth birefringent element 24, the optical unit according to the embodiment may split the second linearly polarized light B2 using a single birefringent element or three or more birefringent elements.

Furthermore, in the optical unit 1, the first birefringent element 21 to the second birefringent element 22 are formed from calcite, but in the optical unit according to the embodiment, the birefringent elements may be formed from a birefringent material other than calcite.

For example, in the optical unit according to the embodiment, the birefringent element may be formed of quartz (SiO ₂ ), rutile (TiO ₂ ), and corundum (sapphire, Al ₂ O ₃ ). When light having a wavelength of 589.3 nm is incident, the refractive index of calcite is 1.6584 for the ordinary ray and 1.4864 for the extraordinary ray. On the other hand, when light having a wavelength of 589.3 nm is incident, the refractive index of quartz is 1.5443 for the ordinary ray and 1.5534 for the extraordinary ray. When light having a wavelength of 589.3 nm is incident, the refractive index of rutile for the ordinary ray is 2.6160 and the refractive index of the extraordinary ray is 2.903. When light having a wavelength of 589.3 nm is incident, the refractive index of corundum for the ordinary ray is 1.768 and the refractive index of the extraordinary ray is 1.7600.

1, 2 Optical unit 10 Housing 11 First port 12 Second port 13 Third port 14 Fourth port 15 Fifth port 16 Sixth port 21 First birefringent element 22 Second birefringent element 23 Third birefringent element 24 Fourth birefringent element 25 First Faraday rotator 26 Second Faraday rotator (second polarization element)
27 First (1/2) wave plate 28 Second (1/2) wave plate (first polarizing element)
REFERENCE SIGNS LIST 100 Interference type optical magnetic field sensor device 110 First light emitting unit 110a Second light emitting unit 120 Quarter wave plate 130 Plano-convex lens 140 Magnetic field sensor element 150 Detection signal generating unit 160 Crosstalk compensation circuit 170 Signal processing circuit

Claims (9)

a first light emitting unit that emits first linearly polarized light;
a second light emitting unit that emits unpolarized light;
a magnetic field sensor element, at least a portion of which can be placed within a predetermined magnetic field, which emits return light in response to incident light;
an optical unit having a first port into which the first linearly polarized light and the unpolarized light are incident, a second port that emits the incident light to the magnetic field sensor element and into which the returned light is incident, a third port and a fourth port that respectively emit first linearly polarized light and second linearly polarized light orthogonal to the first linearly polarized light obtained by splitting the first linearly polarized light from the returned light, and a fifth port and a sixth port that respectively emit P-polarized component and S-polarized component obtained by splitting the unpolarized returned light from the returned light;
a detection signal generating unit that receives the first linearly polarized light and the second linearly polarized light and converts them into electrical signals, thereby outputting a detection signal corresponding to a magnetic field applied to the magnetic field sensor element;
a crosstalk compensation circuit that receives the P-polarized component and the S-polarized component and converts them into electrical signals to output a disturbance signal corresponding to the polarization crosstalk;
a signal processing circuit that receives the detection signal and the disturbance signal and outputs a difference signal between the detection signal and the disturbance signal;
An interference type optical magnetic field sensor device comprising: the wavelength of the first linearly polarized light is light in a first waveband,
the wavelength of the unpolarized light is light in a second wavelength band different from the first wavelength band;
2. The interference type optical magnetic field sensor device according to claim 1. the first wavelength band is included in the C-band wavelength band,
The second wavelength band is included in the O-band wavelength band.
3. The interference type optical magnetic field sensor device according to claim 2. The optical unit comprises:
a first polarizing element that, in response to the first linearly polarized light being incident thereon, emits third linearly polarized light and fourth linearly polarized light orthogonal to the third linearly polarized light, and that, in response to the fifth linearly polarized light and sixth linearly polarized light orthogonal to the fifth linearly polarized light being incident thereon, emits second linearly polarized light;
an optical path unit optically connected to the first polarizing element, the optical path unit having a first optical path that propagates the third linearly polarized light and the sixth linearly polarized light, and a second optical path that propagates the fourth linearly polarized light and the fifth linearly polarized light;
a third birefringence element that, in response to the second linearly polarized light being incident from the first polarizing element, demultiplexes the second linearly polarized light into a first linearly polarized light and a second linearly polarized light orthogonal to the first linearly polarized light,
The optical path section includes:
a first birefringence element that separates the third linearly polarized light and the fourth linearly polarized light incident from the first polarization element into the first optical path and the second optical path, respectively, and combines the fifth linearly polarized light that has propagated through the second optical path and the sixth linearly polarized light that has propagated through the first optical path, and outputs the combined light to the first polarization element;
a second birefringence element that combines the third linearly polarized light that has propagated through the first optical path and the fourth linearly polarized light that has propagated through the second optical path and outputs the combined light to the second port, and that separates the fifth linearly polarized light and the sixth linearly polarized light that have entered from the second port into the first optical path and the second optical path, respectively.
4. The interference type optical magnetic field sensor device according to claim 1. The interferometric optical magnetic field sensor device of claim 4, wherein the optical path section further includes a second optical element disposed in the first optical path and configured to adjust the phases of the third linearly polarized light and the sixth linearly polarized light so that the phase difference between the fifth linearly polarized light and the sixth linearly polarized light is 90 degrees. The interferometric optical magnetic field sensor device of claim 4 or 5, further comprising a third birefringence element that, in response to the second linearly polarized light being incident from the first polarizing element, splits the second linearly polarized light into a first linearly polarized light and a second linearly polarized light orthogonal to the first linearly polarized light. a fourth birefringent element onto which the first linearly polarized light and the second linearly polarized light are incident from the third birefringent element,
the first linearly polarized light is incident on the third port from the fourth birefringent element,
the second linearly polarized light is incident on the fourth port from the fourth birefringent element;
7. An interference type optical magnetic field sensor device according to claim 6. The interferometric optical magnetic field sensor device of claim 7, wherein the first birefringent element, the second birefringent element, the third birefringent element, and the fourth birefringent element are formed of calcite. An interferometric optical magnetic field sensor device according to any one of claims 4 to 8, wherein the first birefringent element and the second birefringent element are spatially coupled.