JP7472066B2 - Optical unit and interference type optical magnetic field sensor device - Google Patents

Description

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

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

JP 2020-126007 A

However, the interference-type optical magnetic field sensor device described in Patent Document 1 uses a beam splitter and an optical fiber having a predetermined length to form an optical path through which S-polarized light and P-polarized light pass, so it is not easy to miniaturize it.

The present invention aims to solve these problems and provide an optical unit that can reduce the size of an interference-type optical magnetic field sensor device.

The optical unit according to the present invention includes a first port into which a first linearly polarized light is incident, a first polarizing element that outputs the first linearly polarized light and a second linearly polarized light orthogonal to the first linearly polarized light in response to the first linearly polarized light being incident, and outputs the second linearly polarized light in response to the third linearly polarized light and a fourth linearly polarized light orthogonal to the third linearly polarized light being incident, an optical path section that is optically connected to the first polarizing element and has a first optical path that propagates the first linearly polarized light and the fourth linearly polarized light, and a second optical path that propagates the second linearly polarized light and the third linearly polarized light, and and a second port into which the fourth linearly polarized light is incident, and the optical path section has a first birefringence element that splits the first linearly polarized light and the second linearly polarized light incident from the first polarizing element into the first optical path and the second optical path, respectively, and combines the third linearly polarized light propagated through the second optical path and the fourth linearly polarized light propagated through the first optical path, and outputs the combined light to the first polarizing element, and a second birefringence element that combines the first linearly polarized light propagated through the first optical path and the second linearly polarized light propagated through the second optical path, and outputs the combined light to the second port, and splits the third linearly polarized light and the fourth linearly polarized light incident from the second port into the first optical path and the second optical path, respectively.

Furthermore, in the optical unit according to the present invention, it is preferable that the optical path section further includes a second optical element arranged in the first optical path and adjusting the phase of the first linearly polarized light and the fourth linearly polarized light so that the phase difference between the third linearly polarized light and the fourth linearly polarized light is 90 degrees.

Furthermore, it is preferable that the optical unit according to the present invention further includes a third birefringent element that splits the second linearly polarized light into a fifth linearly polarized light and a sixth linearly polarized light orthogonal to the fifth linearly polarized light in response to the second linearly polarized light being incident from the first polarizing element.

Furthermore, it is preferable that the optical unit according to the present invention further includes a fourth birefringent element to which the fifth linearly polarized light and the sixth linearly polarized light are incident from the third birefringent element, a third port to which the fifth linearly polarized light is incident from the fourth birefringent element, and a fourth port to which the sixth linearly polarized light is incident from the fourth birefringent element.

Furthermore, in the optical unit according to the present invention, it is preferable that the first birefringent element and the second birefringent element are spatially coupled.

The interference-type optical magnetic field sensor device according to the present invention includes a light-emitting unit that emits a first linearly polarized light, a magnetic field sensor element at least a part of which can be arranged in a predetermined magnetic field and that emits a return light in response to the incidence of incident light, an optical unit having a first port into which the first linearly polarized light is incident, a second port into which the incident light is emitted and into which the return light is incident, and a third port and a fourth port into which the return light is split and that emit a fifth linearly polarized light and a sixth linearly polarized light obtained by splitting the return light, and a detection signal generating unit that receives the fifth linearly polarized light and the sixth linearly polarized light and converts them into an electrical signal to output a detection signal in response to the magnetic field applied to the magnetic field sensor element, and the optical unit includes a first polarizing element that emits the first linearly polarized light and a second linearly polarized light orthogonal to the first linearly polarized light in response to the incidence of the first linearly polarized light, and emits the second linearly polarized light in response to the incidence of the third linearly polarized light and a fourth linearly polarized light orthogonal to the third linearly polarized light. a third birefringent 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 fifth linearly polarized light and a sixth linearly polarized light orthogonal to the fifth linearly polarized light, and a third birefringent 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 fifth linearly polarized light and a sixth linearly polarized light orthogonal to the fifth linearly polarized light, and the optical path section splits the first linearly polarized light and the second linearly polarized light incident from the first polarizing element into a sixth linearly polarized light and a fifth linearly polarized light. The optical fiber has a first birefringence element that splits the light into the first and second optical paths, and combines the third linearly polarized light propagated through the second optical path and the fourth linearly polarized light propagated through the first optical path, and outputs the combined light to the first polarizing element; and a second birefringence element that combines the first linearly polarized light propagated through the first optical path and the second linearly polarized light propagated through the second optical path, and outputs the combined light to the second port, and splits the third linearly polarized light and the fourth linearly polarized light incident from the second port into the first and second optical paths.

By using the optical unit according to the present invention, the interference type optical magnetic field sensor device can be made smaller.

FIG. 1 is a block diagram of an interference type optical magnetic field sensor device according to an embodiment. FIG. 2 is a plan view of the optical unit shown in FIG. 1 . 3 is a diagram showing optical characteristics of the first birefringent element shown in FIG. 2. 3A is a diagram showing the optical path of a first linearly polarized light in the optical unit shown in FIG. 2, and FIG. 3B is a diagram showing the transition of the polarization plane of the first linearly polarized light shown in FIG. 3A is a diagram showing the optical path of the second linearly polarized light in the optical unit shown in FIG. 2, and FIG. 3B is a diagram showing the transition of the polarization plane of the second linearly polarized light shown in FIG. 2 is a diagram showing the relationship between output intensity and noise of the interference type optical magnetic field sensor device shown in FIG. 1 and an interference type optical magnetic field sensor device according to a comparative example; FIG. FIG. 13 is a plan view of an optical unit according to a modified example. 9 is an optical path diagram of a first linearly polarized light in the optical unit shown in FIG. 8 . 9 is an optical path diagram of a second linearly polarized light in the optical unit shown in FIG. 8 .

The optical unit and interference-type optical magnetic field sensor device according to the present invention will be described below 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 described in the claims and their equivalents.

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

The interference type optical magnetic field sensor device 100 has an optical unit 1, a light emitting section 110, a quarter-wave plate 120, a plano-convex lens 130, a magnetic field sensor element 140, and a detection signal generating section 150, and outputs a detection signal according to the magnetic field applied to the magnetic field sensor element 140.

The light-emitting unit 110 has a light-emitting element 111, an isolator 112, and a polarizer 113. The light-emitting element 111 is, for example, a semiconductor laser or a light-emitting diode. Specifically, a Fabry-Perot laser, a superluminescence diode, or the like can be preferably used as the light-emitting element 111.

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

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

The optical unit 1 has a housing 10, a first port 11, a second port 12, a third port 13, and a fourth port 14, and adjusts the phase of the incident light so that the phase difference between the outgoing fifth linearly polarized light B2P3 and sixth linearly polarized light B2P4 is 90 degrees. The housing 10 is a storage section made of a material with high thermal conductivity such as aluminum, and the various optical elements of the optical unit 1 are arranged in predetermined positions.

The first port 11 is an input port for inputting the first linearly polarized light B1, and is located at the center of one end face in the longitudinal direction of the housing 10, and the first linearly polarized light B1 is input thereto. The second port 12 is an input/output port for outputting the incident light BI that is input to the magnetic field sensor element 140, and for inputting the return light BR from the magnetic field sensor element 140, and is located at the center of the other end face in the longitudinal direction of the housing 10.

The third port 13 is an output port that outputs the fifth 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 sixth linearly polarized light B2P4 and is located at the other end of one of the longitudinal end faces of the housing 10.

The quarter-wave plate 120 is formed of a birefringent material such as quartz, and is arranged 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 the linearly polarized components of the incident light BI output from the second port 12, into circularly polarized light that is input to the magnetic field sensor element 140, and outputs it to the plano-convex lens 130. The quarter-wave plate 120 also converts the return light BR, which is input as circularly polarized light from the magnetic field sensor element 140, into return light BRP1 and return light BRP2, which are linearly polarized components.

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 return 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 part 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 to the plano-convex lens 130 in response to the incident light BI.

The Faraday rotator 141 is a granular film having a dielectric and nano-order magnetic particles dispersed in the dielectric in a state of stable phase separation from the dielectric, and is arranged at a distance from the plano-convex lens 130 by the focal length of the plano-convex lens 130. The magnetic particles may form oxides in a very small part, such as the outermost layer, but in the entire Faraday rotator 141, the magnetic particles are dispersed alone in the thin film without forming a compound with the dielectric that serves as a binder. The distribution of the magnetic particles in the Faraday rotator 141 does not have to be completely uniform, and may be somewhat biased. If a highly transparent dielectric is used, the magnetic particles exist in the dielectric at a size smaller than the wavelength of light, and the Faraday rotator 141 has optical transparency.

The Faraday rotator 141 is not limited to a single layer, but may be a multi-layer film in which granular films and dielectric films are alternately stacked. By forming the Faraday rotator 141 by forming a multi-layer 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 ). The dielectric may also be an oxide such as tantalum oxide ( _Ta2O5 ), silicon dioxide ( _SiO2 ), titanium dioxide ( _TiO2 ), diniobium pentoxide ( _Nb2O5 ), zirconium dioxide ( _ZrO2 ), hafnium dioxide ( _HfO2 ), or dialuminum trioxide ( _Al2O3 ). For good phase separation between the dielectric and the magnetic particles, fluorides are more preferable than oxides, and _magnesium fluoride, which has a high transmittance, is particularly preferable.

The material of the magnetic particles is not particularly limited as long as it produces the Faraday effect, but examples of the material of 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 the light transmitted through the Faraday rotator 141 toward the Faraday rotator 141. For example, a silver (Ag) film, a gold (Au) film, an aluminum (Al) film, or a dielectric multilayer mirror can be used as the mirror element 142. In particular, an Ag film with high reflectivity and an Au film with high corrosion resistance are preferable because they are easy to form. The thickness of the mirror element 142 may be any thickness that can ensure a sufficient reflectivity of 98% or more. For example, in the case of an Ag film, the thickness is preferably 50 nm or more and 200 nm or less. The Faraday rotation angle can be increased by using the mirror element 142 to make the light go back and forth within the Faraday rotator 141.

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 response to the magnetic field applied to the Faraday rotator 141. Also, 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 response to 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 signal processing circuit 153, and receives the return light BR that has been split into the fifth linearly polarized light B2P3 and the sixth linearly polarized light B2P4 in 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 fifth linearly polarized light B2P3, and the second light receiving element 152 receives the sixth 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 signal processing circuit 153 differentially amplifies the electrical signal indicating the fifth linearly polarized light B2P3 and the electrical signal indicating the sixth 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 is a plan view of the optical unit 1.

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 (1/2) wave plate 27, a second (1/2) wave plate 28, a first (1/4) wave plate 29, and a second (1/4) 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 (1/4) wave plate 29, and the second (1/4) wave plate 30 form an optical path section 20. Each of the optical elements included in the optical unit 1, the first birefringent element 21 to the second optical element 32, is spatially coupled without using an optical fiber.

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

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

The third port 13 receives the fifth linearly polarized light B2P3 from the first optical element 31 and outputs the fifth linearly polarized light B2P3 to the first light receiving element 151. The fourth port 14 receives the sixth linearly polarized light B2P4 from the second optical element 32 and outputs the sixth 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 3 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, and inputs and outputs polarized light B propagating through a single optical path from the first surface 21a, and inputs and outputs the first polarized light BP1 and the second polarized light BP2 propagating through two optical paths from the second surface 21b. The first polarized light BP1 has a polarization plane in the horizontal direction in FIG. 3, and is also called an ordinary ray. The second polarized light BP2 has a polarization plane in the vertical direction in FIG. 3, and is also called an extraordinary ray. The first birefringent element 21 is arranged so that the optical axis 21c faces 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 from 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 outputs 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 outputs the 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 here.

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

The third birefringent element 23 is arranged so that the first surface 21a faces the second (1/2) wave plate 28 and the second surface 21b faces the first (1/2) wave plate 27. The fourth birefringent element 24 is arranged so that the first surface 21a faces the first Faraday rotator 25 and the second surface 21b 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 made of 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 of a birefringent material such as quartz, and are arranged with their optical axes tilted by 22.5 degrees with respect to the direction of the polarization plane of the first linearly polarized light B1 incident from the light emitting unit 110, shifting the phase of the incident linearly polarized light by 45 degrees. The first (1/2) wave plate 27 is arranged between the first Faraday rotator 25 and the third birefringent element 23. The second (1/2) wave plate 28 is arranged 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 the second (1/4) wave plate 30 are formed of a birefringent material such as quartz, and are arranged 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 light emitting unit 110, converting linearly polarized light into circularly polarized light and converting circularly polarized light into linearly polarized light. The first (1/4) wave plate 29 is arranged between the first birefringent element 21 and the second Faraday rotator 26. The second (1/4) wave plate 30 is arranged 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 outputs the fifth linearly polarized light B2P3 output from the fourth birefringent element 24 to the third port 13. The second optical element 32 is disposed between the fourth port 14 and the fourth birefringent element 24, and outputs the sixth linearly polarized light B2P4 output from the fourth birefringent element 24 to the fourth port 14.

The first base 33, the second base 34, and the 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 4(a) is a diagram showing the optical path of the first linearly polarized light B1 in the optical unit 1, and Figure 4(b) is a diagram showing the transition of the polarization plane of the first linearly polarized light B1 shown in Figure 4(a).

First, as shown by arrow A, the first linearly polarized light B1 is incident from the light emitting unit 110 through the first port 11. Since the first linearly polarized light B1 is an ordinary ray, it propagates inside 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 phase shift of 45 degrees 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 phase shift of 45 degrees 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, the polarization plane returns before entering the first Faraday rotator 25, is emitted from the first (1/2) wave plate 27, and enters the third birefringent element 23. Since 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 the first linearly polarized light B1P1, which is an ordinary ray, and the second linearly polarized light B1P2, which is an extraordinary ray. Since the first linearly polarized light B1 is an ordinary ray, it propagates inside the first birefringent element 21 along the longitudinal direction of the first birefringent element 21.

As indicated by arrow G, the first linearly polarized light B1P1 exits the first birefringent element 21 and enters the first (1/4) wave plate 29. The first 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.

When 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 output from the second Faraday rotator 26 and enters the second (1/4) wave plate 30. When the first circularly polarized light B1C1 propagates through the second (1/4) wave plate 30, it is converted into the first linearly polarized light B1P1. As shown by arrow J, the first linearly polarized light B1P1 is output from the second (1/4) wave plate 30 and enters the second birefringent element 22.

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

In the second birefringent element 22, the first linearly polarized light B1P1 propagates inside the second birefringent element 22 along the longitudinal direction of the second birefringent element 22. On the other hand, the second linearly polarized light B1P2 propagates inside the second birefringent element 22 at an angle to the longitudinal direction of the second birefringent element 22. As shown by the arrow L, the first linearly polarized light B1P1 and the second linearly polarized light B1P2 are combined and output from the second birefringent element 22 as incident light BI.

Figure 5(a) is a diagram showing the optical path of the second linearly polarized light B2 in the optical unit 1, and Figure 5(b) is a diagram showing the transition of the polarization plane of the second linearly polarized light B2 shown in Figure 5(a).

First, as shown by arrow A, the return light BR is incident from the quarter-wave plate 120 through the second port 12. The return light BR has a third linearly polarized light B2P1 and a fourth linearly polarized light B2P2, which is a polarization component orthogonal to the third linearly polarized light B2P1.

When the return light BR enters the second birefringent element 22, it is split into a third linearly polarized light B2P1 and a fourth linearly polarized light B2P2. The third linearly polarized light B2P1 is an ordinary ray, and therefore propagates inside the second birefringent element 22 along the longitudinal direction of the second birefringent element 22. On the other hand, the fourth linearly polarized light B2P2 is an extraordinary ray, and therefore propagates inside the second birefringent element 22 at an angle to the longitudinal direction of the second birefringent element 22.

As indicated by arrow B, the third linearly polarized light B2P1 is emitted from the second birefringent element 22 and enters the second (1/4) wave plate 30. As the third 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.

When 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 output from the second Faraday rotator 26 and enters the first (1/4) wave plate 29. When the third circularly polarized light B2C1 propagates through the first (1/4) wave plate 29, it is converted into the third linearly polarized light B2P1. As shown by arrow E, the third linearly polarized light B2P1 is output from the first (1/4) wave plate 29 and enters the first birefringence element 21.

On the other hand, the fourth linearly polarized light B2P2, which is an extraordinary ray, propagates inside the second birefringent element 22 at an angle to the longitudinal direction of the second birefringent element 22. As shown by the arrow F, the fourth 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 third linearly polarized light B2P1 propagates inside the first birefringent element 21 along the longitudinal direction of the first birefringent element 21. On the other hand, the fourth linearly polarized light B2P2 propagates inside the first birefringent element 21 at an angle to the longitudinal direction of the first birefringent element 21. As shown by the arrow G, the third linearly polarized light B2P1 and the fourth linearly polarized light B2P2 are combined and output from the first birefringent element 21 to the second (1/2) wave plate 28 as the second linearly polarized light B2.

When the second 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 shown by the arrow H, the third linearly polarized light B2P1 and the fourth linearly polarized light B2P2 each enter the third birefringence element 23 with a phase shift of -45 degrees.

When the third linearly polarized light B2P1 and the fourth linearly polarized light B2P2 propagate through the third birefringent element 23, they are split into a fifth linearly polarized light B2P3, which is an extraordinary ray, and a sixth linearly polarized light B2P4, which is an ordinary ray. Since the fifth linearly polarized light B2P3 is an extraordinary ray, it propagates through the third birefringent element 23 at an angle 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 fifth 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 is emitted from the first (1/2) wave plate 27 with a phase shift of -45 degrees and enters the first Faraday rotator 25.

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

Since the fifth 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 the arrow L, exits the fourth birefringent element 24, and enters the first optical element 31. The fifth linearly polarized light B2P3 is output from the third port 13 via the first optical element 31.

Since the sixth 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 the arrow M, exits the third birefringent element 23, and enters the first (1/2) wave plate 27.

The sixth 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 the arrow N, it is emitted from the first (1/2) wave plate 27 with a phase shift of -45 degrees and enters the first Faraday rotator 25.

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

Since the sixth linearly polarized light B2P4 is an extraordinary ray, as shown by the arrow P, it propagates inside the fourth birefringent element 24 at an angle from the longitudinal direction of the third birefringent element 23, exits the fourth birefringent element 24, and enters the second optical element 32. The sixth linearly polarized light B2P4 is output from the fourth port 14 via the second optical element 32.

(Functions and Effects of the Optical Unit According to the Embodiment)
The optical unit 1 employs a birefringent element that can be made smaller than a beam splitter as an element that performs splitting and multiplexing, so the interference type optical magnetic field sensor device 100 can be made smaller than an interference type 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, while calcite, which is one of the birefringent elements, has a width and height of 30 mm and a length of 100 mm.

In addition, the optical unit 1 and the interference type 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 interference type optical magnetic field sensor device 100 can be made smaller than an interference type optical magnetic field sensor device that places an optical fiber in the optical path between the optical elements.

Furthermore, calcite, which is one of the birefringent elements used in the optical unit 1, has less noise than a beam splitter. The optical unit 1 and the interference type optical magnetic field sensor device 100 use a birefringent element that has less noise than a beam splitter, and therefore have less noise than an interference type optical magnetic field sensor device that uses a beam splitter.

Figure 6 is a diagram showing the relationship between the output intensity and noise of the interference type optical magnetic field sensor device 100 and the interference type optical magnetic field sensor device related to the comparative example. In Figure 6, the horizontal axis represents the output voltage of the light receiving element of the detection signal generation unit, and the vertical axis represents the noise.

In FIG. 6, waveform 700 shows the actual measured noise characteristics of the interference type optical magnetic field sensor device 100. Waveform 701 shows the actual measured noise characteristics of an interference type optical magnetic field sensor device in which optical elements are coupled by optical fiber and a beam splitter is used as a polarization separation element. Waveform 702 shows the actual measured noise characteristics of an interference type optical magnetic field sensor device in which optical elements are spatially coupled without optical fiber and a beam splitter is used as a polarization separation element. Waveform 703 shows the actual measured noise characteristics of an interference type optical magnetic field sensor device in which the arrangement of optical elements is more optimized than that of the interference type optical magnetic field sensor device corresponding to waveform 702. Waveform 704 shows the simulated noise characteristics of the interference type optical magnetic field sensor device 1000.

In addition, since the noise shown in waveform 701 is larger than the noise shown in waveform 702, it can be seen that the noise characteristics are improved by spatially coupling the optical elements without using optical fiber.In addition, since the noise shown in waveforms 702 and 703 is larger than the noise shown in waveform 700, it can be seen that the noise characteristics are improved by using calcite as a polarization separation element instead of a beam splitter.

Note that waveform 700 is approximately identical to waveform 704.

(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 surface in the longitudinal direction of the housing 10, and the second port 12 is arranged on the other surface in the longitudinal direction of the housing 10. However, in the optical unit according to the embodiment, the first port 11 to the fourth port 14 may be arranged on one surface.

Figure 7 is a plan view of an optical unit according to a modified example, Figure 8 is an optical path diagram of the first linearly polarized light B1 in the optical unit shown in Figure 7, and Figure 9 is an optical path diagram of the second linearly polarized light B2 in the optical unit shown in Figure 7.

Optical unit 2 differs from optical unit 1 in that it has a housing 40 instead of housing 10. Also, optical unit 2 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. Also, optical unit 2 differs from optical unit 1 in that it has a first optical path prism mirror 51 to a sixth optical path prism mirror 56. Also, optical unit 2 differs from optical unit 1 in that it has a first exit prism mirror 61 to a fourth exit prism mirror 64 instead of the first optical element 31 and the second optical element 32.

The configurations and functions of the components of the optical unit 2 other than the housing 40, the optical element 41, the first optical path prism mirror 51 to the sixth optical path prism mirror 56, and the first exit prism mirror 61 to the fourth exit prism mirror 64 are the same as those of the optical unit 1 with the same reference numerals. Therefore, detailed explanations of the configurations and functions of the components of the optical unit 2 other than the housing 40, the optical element 41, the first optical path prism mirror 51 to the sixth optical path prism mirror 56, and the first exit prism mirror 61 to the fourth exit prism mirror 64 will be omitted here.

The housing 40 has the second port arranged on the same plane as the first port 11, the third port 13, and the fourth port 14. The optical element 41 is an element that integrates 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 fourth exit prism mirror 64 are all right-angle prism mirrors. The first optical path prism mirror 51 and the second optical path prism mirror 52 are disposed in an optical path that optically connects 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 disposed on an optical path that optically connects 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 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 optical unit 1 also has optical elements, such as the third birefringent element 23 and the fourth birefringent element 24, that split the second linearly polarized light B2 into the fifth linearly polarized light B2P3 and the sixth linearly polarized light B2P4. However, the optical unit according to the embodiment does not need to have optical elements that split the second linearly polarized light B2.

In addition, 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, but 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.

In addition, 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 the ordinary ray of calcite is 1.6584, and the refractive index of the extraordinary ray is 1.4864. On the other hand, when light having a wavelength of 589.3 nm is incident, the refractive index of the ordinary ray of quartz is 1.5443, and the refractive index of the extraordinary ray is 1.5534. In addition, when light having a wavelength of 589.3 nm is incident, the refractive index of the ordinary ray of rutile is 2.6160, and the refractive index of the extraordinary ray is 2.903. In addition, when light having a wavelength of 589.3 nm is incident, the refractive index of the ordinary ray of corundum is 1.768, and the refractive index of the extraordinary ray is 1.7600.

1, 2 Optical unit 11 First port 12 Second port 13 Third port 14 Fourth 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 polarizing 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 Light emitting unit 120 Quarter wave plate 130 Plano-convex lens 140 Magnetic field sensor element 150 Detection signal generating unit

Claims (6)

A housing and
a first port to which a first linearly polarized light is incident;
a first polarizing element that, in response to the first linearly polarized light being incident thereon, emits a first linearly polarized light and a second linearly polarized light orthogonal to the first linearly polarized light, and that, in response to the third linearly polarized light and a fourth linearly polarized light orthogonal to the third linearly polarized light being incident thereon, emits the second linearly polarized light;
an optical path section optically connected to the first polarizing element, the optical path section having a first optical path that propagates the first linearly polarized light and the fourth linearly polarized light, and a second optical path that propagates the second linearly polarized light and the third linearly polarized light;
a second port for outputting the first linearly polarized light and the second linearly polarized light and for receiving the third linearly polarized light and the fourth linearly polarized light,
The optical path portion is
a first birefringence element that splits the first linearly polarized light and the second linearly polarized light incident from the first polarizing element into the first optical path and the second optical path, respectively, and combines the third linearly polarized light propagated through the second optical path and the fourth linearly polarized light propagated through the first optical path, and outputs the combined light to the first polarizing element;
a second birefringent element that outputs the first linearly polarized light propagated through the first optical path and the second linearly polarized light propagated through the second optical path to the second port, and outputs the third linearly polarized light and the fourth linearly polarized light incident from the second port to the first optical path and the second optical path, respectively ;
An optical unit , wherein the first birefringent element and the second birefringent element are spatially coupled . The optical unit according to claim 1, 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 first linearly polarized light and the fourth linearly polarized light so that the phase difference between the third linearly polarized light and the fourth linearly polarized light is 90 degrees. The optical unit according to claim 1 or 2, further comprising a third birefringent element that splits the second linearly polarized light into a fifth linearly polarized light and a sixth linearly polarized light orthogonal to the fifth linearly polarized light in response to the second linearly polarized light being incident from the first polarizing element. a fourth birefringent element onto which the fifth linearly polarized light and the sixth linearly polarized light are incident from the third birefringent element;
a third port to which the fifth linearly polarized light is incident from the fourth birefringent element;
a fourth port to which the sixth linearly polarized light is incident from the fourth birefringent element;
The optical unit according to claim 3 , further comprising: The optical unit according to claim 4, wherein the first birefringent element, the second birefringent element, the third birefringent element, and the fourth birefringent element are formed of calcite. a light emitting unit that emits a first linearly polarized 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 is incident, a second port from which the incident light is output and into which the return light is input, and a third port and a fourth port from which fifth and sixth linearly polarized light beams obtained by splitting the return light are output;
a detection signal generating unit that receives the fifth linearly polarized light and the sixth linearly polarized light and converts them into electrical signals to output a detection signal corresponding to a magnetic field applied to the magnetic field sensor element,
The optical unit includes:
a first polarizing element that, in response to the first linearly polarized light being incident thereon, emits a first linearly polarized light and a second linearly polarized light orthogonal to the first linearly polarized light, and that, in response to the third linearly polarized light and a fourth linearly polarized light orthogonal to the third linearly polarized light being incident thereon, emits the second linearly polarized light;
an optical path section optically connected to the first polarizing element, the optical path section having a first optical path that propagates the first linearly polarized light and the fourth linearly polarized light, and a second optical path that propagates the second linearly polarized light and the third linearly polarized light;
a third birefringence element that splits the second linearly polarized light into a fifth linearly polarized light and a sixth linearly polarized light orthogonal to the fifth linearly polarized light in response to the second linearly polarized light being incident from the first polarizing element,
The optical path portion is
a first birefringence element that splits the first linearly polarized light and the second linearly polarized light incident from the first polarizing element into the first optical path and the second optical path, respectively, and combines the third linearly polarized light propagated through the second optical path and the fourth linearly polarized light propagated through the first optical path, and outputs the combined light to the first polarizing element;
a second birefringence element that combines the first linearly polarized light propagated through the first optical path and the second linearly polarized light propagated through the second optical path and outputs the combined light to the second port, and that separates the third linearly polarized light and the fourth linearly polarized light incident from the second port into the first optical path and the second optical path, respectively ;
2. An interference type optical magnetic field sensor device, wherein the first birefringent element and the second birefringent element are spatially coupled .

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