JP7023459B2 - Magnetic field sensor element and magnetic field sensor device - Google Patents

Description

Patent Law Article 30 Paragraph 2 Applicable Website address: https: // iap-jp. org / msj / conf_program 2017 / program_download. php? no = 21aB-1 Publication date: September 5, 2017 [Publications, etc.] The 41st Annual Meeting of the Institute of Electrical Engineers of Japan Date: September 21, 2017 [Publications, etc.] The Institute of Electrical Engineers of Japan Materials The Papers of Technical Meeting on "Magnetics", IEE Japan Magnetics Study Group MAG-17-153-159 Publisher: Institute of Electrical Engineers of Japan Publication date: November 10, 2017 [Publications, etc.] Magnetics Study Group held Date: November 10, 2017

The present invention relates to a magnetic field sensor element and a magnetic field sensor device.

A magnetometer device that measures a current magnetic field using light modulation due to the Faraday effect has been proposed. The Faraday effect is a phenomenon in which the plane of polarization rotates when linearly polarized light propagates in parallel with the direction of the magnetic field. In the head portion of such a magnetic field sensor device (magnetic field sensor element), a sensitive element that causes optical modulation according to a magnetic field is arranged. As an example of the sensitive element, iron garnet crystal, lead fiber, high birefringence fiber and the like have been proposed. For example, Patent Document 1 describes a magneto-optical effect type electromagnetic field sensor that utilizes the Faraday effect of a magnetic garnet.

Patent Document 2 comprises a multilayer film made of a magnetic optical material and a dielectric material, which is a multilayer film having a periodic repeating structure and having a repeating period inverted with the center of the multilayer film as symmetrical. A magnetic field sensitive element having the ability to change the transmittance or the reflectance depending on a magnetic field loaded from the outside is described as a multilayer film magnetic field sensitive element.

Further, Patent Document 3 describes a thin film dielectric having a nanogranular structure composed of an insulator matrix and a metal granule having a nm size. Patent Document 4 describes a translucent magnetic material having a nanogranular structure composed of a fluoride matrix and a magnetic metal granule having a size of nm.

International Publication No. 2007/000947 Japanese Unexamined Patent Publication No. 2000-206218 Japanese Unexamined Patent Publication No. 2012-06428 Japanese Unexamined Patent Publication No. 2017-098423

When various optical fibers are used as the sensitive element of the magnetic field sensor device, it is difficult to miniaturize the sensor head because the Verdet constant is small and it is necessary to circulate a large number of times around an electric wire or the like. The Faraday effect type magnetic field sensitive element proposed in Patent Documents 1 and 2 uses a magnetic garnet having a Curie temperature of 200 ° C. to 300 ° C., and the magnetization is greatly reduced in a high temperature environment, so that the temperature characteristics are poor. Further, since the magnetic garnet is a crystalline material, it is difficult to form a film directly on the sensor head (fiber end), and particularly in the magnetic field sensitive element of Patent Document 2, accurate composition control of the compound is required. Although the conventional Faraday effect magnetometer device using light as a probe has high resistance to electromagnetic noise, a compact and lightweight magnetometer device that can operate in a wide temperature range has not yet been realized.

Therefore, an object of the present invention is to provide a magnetic field sensor element and a magnetic field sensor device that detect a magnetic field by utilizing the Faraday effect, which have excellent temperature characteristics, are compact, and have a simple optical system.

An incident optical fiber that propagates incident light, a granular film in which fine particles of ferromagnetic metal having an average particle size of 2 nm or more and less than 10 nm are dispersed in a metal fluoride dielectric, and a granular film that transmits incident light. Provided is a magnetic field sensor element having a reflective film that reflects light transmitted through a film toward a granular film and an optical fiber for emission that is reflected by the reflective film and propagates back light transmitted through the granular film. Ru.

In the above magnetic field sensor element, the light transmittance of the granular film is preferably 20% or more and 30% or less.

In the above magnetic field sensor element, it is preferable that the ferromagnetic metal contains at least one of Fe and Co, and the metal fluoride is MgF ₂ or YF ₃ .

In the above magnetic field sensor element, the ratio M / (M + F) of the volume M of the ferromagnetic metal and the volume F of the metal fluoride in the granular film is preferably larger than 0.2 and less than 0.5.

In the above magnetic field sensor element, it is preferable that the incident optical fiber and the emitted optical fiber are the same optical fiber, the granular film is formed on the end face of the optical fiber, and the reflective film is formed on the granular film.

Alternatively, in the above magnetic field sensor element, the incident optical fiber and the emitted optical fiber are the same optical fiber, and the magnetic field sensor element includes an optical collimeter arranged at the emission end of the optical fiber, an optical collimeter, and a granular film. Further having a λ / 4 plate arranged between the, the granular film is arranged away from the exit end of the optical fiber, and the optical collimeter uses the light propagating through the optical fiber as parallel light in space. It is preferable that the reflected light, which is the spatially propagated light from the reflecting film, is incident on the optical fiber while being emitted.

Alternatively, in the above magnetic field sensor element, the incident optical fiber and the outgoing optical fiber are the same optical fiber, and the magnetic field sensor element further includes a λ / 4 plate inserted in the middle of the path composed of the optical fiber. It is preferable that the granular film is inserted in the middle of the path composed of the optical fiber, and the reflective film is formed on the end face of the optical fiber.

Alternatively, the above-mentioned magnetic field sensor element further has a planar light wave circuit having an optical branch portion and connecting an incident optical fiber and an emitted optical fiber, and a granular film is formed on the end face of the planar light wave circuit to reflect light. It is preferable that the film is formed on a granular film, the optical fiber for emission is a polarization-retaining optical fiber, and is aligned and connected to a planar light wave circuit.

Further, any of the above magnetic field sensor elements, a light emitting device that introduces linearly polarized light as incident light into the incident optical fiber, and return light derived from the emitted optical fiber are separated into an S-polarized component and a P-polarized component. , A magnetic field sensor device comprising a light receiving device that receives an S-polarized component and a P-polarized component, converts them into an electric signal, and processes the electric signal.

The above-mentioned magnetic field sensor element and magnetic field sensor device have excellent temperature characteristics, are small in size, have a simple optical system, and can detect a magnetic field by utilizing the Faraday effect.

It is an overall block diagram of the magnetic field sensor device 1. It is a figure explaining the rotation of the polarization plane in a granular film 30. It is a schematic diagram of a granular film 30. It is a block diagram which shows the example of the signal processing unit 70. It is a perspective view, a sectional view and an exploded sectional view of another magnetic field sensor element 10A. It is a plan view and a sectional view of another magnetic field sensor element 10B. It is a top view of another magnetic field sensor element 10C. It is a graph which shows the temperature characteristic of the magnetization of the granular film 30. It is a graph which shows the relationship between the film formation temperature of a granular film, and the average particle diameter of magnetic particles in a film. It is a graph which shows the temperature characteristic of the magnetization of the granular film which was formed at different temperature, and the cross-sectional photograph of the granular film. It is a graph which shows the relationship between the transmittance of a granular film, and the SN ratio of the output of a magnetic field sensor element.

Hereinafter, the magnetic field sensor element and the magnetic field sensor device will be described with reference to the drawings. However, it should be understood that the invention is not limited to the drawings or embodiments described below.

FIG. 1 is an overall configuration diagram of the magnetic field sensor device 1. The magnetic field sensor device 1 includes a magnetic field sensor element 10, a light emitting device 50, a half mirror 53, and a light receiving device 60. The magnetic field sensor element 10 has an optical fiber 20, a granular film 30, and a reflective film 40. The light emitting device 50 has a light emitting element 51 and a polarizing element 52, and introduces linearly polarized light into the optical fiber 20 as incident light. The light receiving device 60 includes a λ / 2 plate 62, a polarization separating element 64, light receiving elements 66S and 66P, and a signal processing unit 70, and receives return light derived from the optical fiber 20.

In the magnetic field sensor device 1, the end face on the rear end side (light emitting device 50 side) of the optical fiber 20 is optically connected to the light emitting device 50 and the light receiving device 60. The light emitting device 50 emits linearly polarized light, and the linearly polarized light passes through the half mirror 53 and is incident on the optical fiber 20 from the end surface on the rear end side. The linearly polarized light incident on the optical fiber 20 passes through the granular film 30 via the optical fiber 20, is reflected by the reflective film 40, and is transmitted through the granular film 30 again to become return light. This return light propagates through the optical fiber 20 again, passes through the half mirror 53, and enters the light receiving device 60.

FIG. 2 is a diagram illustrating rotation of a polarizing surface in the granular film 30. On the upper side of FIG. 2, the incident light from the light emitting device 50 and the return light reflected by the reflective film 40 are indicated by arrows. A plane orthogonal to the traveling direction of light is defined as an XY plane, and it is assumed that the polarization direction in (A) before being incident on the granular film 30 is the Y direction. The granular film 30 has fine particles 31 of ferromagnetic metal (hereinafter referred to as magnetic particles 31) (see FIG. 1), and when linearly polarized light passes through the granular film 30 in the presence of a magnetic field, (B). ), _The plane of polarization rotates by θ1 due to the Faraday effect. After that, when the incident light is reflected by the reflective film 40 and passes through the granular film 30 again, as shown in (C), the polarizing surface is further rotated by the Faraday effect, and the Faraday rotation angle is larger than θ ₁ . It becomes ₂ .

Since the magnitude of the Faraday rotation angle changes depending on the strength of the magnetic field, the return light is separated into the S-polarized component and the P-polarized component by the light receiving device 60, and the light is received to obtain the intensity of each, so that the ambient magnetic field is obtained. Can be detected. If the magnetic field is generated by a current flowing through a conductor, the current value can be measured.

The optical fiber 20 propagates linearly polarized light, which is incident light from the light emitting device 50, to the granular film 30, and propagates the return light transmitted through the granular film 30 and reflected by the reflective film 40 to the light receiving device 60. The optical fiber 20 is not only an incident optical fiber of the magnetic field sensor element 10 but also an emitted optical fiber. Reference numeral 21 in FIG. 1 is a core of the optical fiber 20, and reference numeral 22 is a cladding of the optical fiber 20. The optical fiber 20 may be a single-mode optical fiber, but is preferably a polarization-retaining optical fiber. If the optical fiber 20 is a polarization-retaining optical fiber, it propagates in a state where linear polarization is maintained at a constant intensity, is incident on the granular film 30, is reflected by the reflective film 40, and returns light transmitted through the granular film 30 again. It can propagate while maintaining a constant intensity. The diameter of the optical fiber 20 is not particularly limited, but one having a diameter of 125 μm is generally used.

FIG. 3 is a schematic diagram of the granular film 30. As shown in FIG. 1, the granular film 30 is formed on the end surface 27 on the distal end side (opposite side of the light emitting device 50) of the optical fiber 20. In the granular film 30, as shown in FIG. 3, nano-order magnetic particles 31 are dispersed in the dielectric 32 in a state of being stably phase-separated from the dielectric 32. For example, an oxide may be formed in a small part of the outermost layer or the like, but in the granular film 30, the magnetic particles 31 as a whole are contained in the thin film alone without forming a compound with the dielectric as a binder. It is dispersed in. The distribution of the magnetic particles 31 in the granular film 30 may not be completely uniform or may be slightly biased. If a highly transparent dielectric 32 is used, the granular film 30 has light transmittance because the magnetic particles 31 are present in the dielectric 32 in a size smaller than the wavelength of light.

The granular film 30 is not limited to a single-layer film, and may be a multilayer film in which a granular film and a dielectric film are alternately laminated. If the granular film 30 is a multilayer film, a larger Faraday rotation angle can be obtained by multiple reflections in the granular film 30.

The material of the magnetic particle 31 is not particularly limited as long as it produces a Faraday effect, but the material of the magnetic particle 31 is iron (Fe), cobalt (Co), and nickel (Ni), which are ferromagnetic metals. ) And these alloys. Examples of the alloy include FeNi alloy, FeCo alloy, FeNiCo alloy, and NiCo alloy. The Faraday rotation angle per unit length of Fe, Co, and Ni is about 2 to 3 orders of magnitude larger than that of the magnetic garnet applied to the conventional Faraday rotator, and is easy to detect.

As the dielectric 32, fluoride (metal fluoride) such as magnesium fluoride (MgF ₂ ), aluminum fluoride (AlF ₃ ), yttrium fluoride (YF ₃ ) is preferable. Alternatively, as the dielectric 32, tantalum oxide (Ta ₂ O ₅ ), silicon dioxide (SiO ₂ ), titanium dioxide (TIO ₂ ), diniobium pentoxide (Nb ₂ O ₅ ), zirconium dioxide (ZrO ₂ ), hafnium dioxide. Oxides such as (HfO ₂ ) and dialuminum trioxide (Al ₂ O ₃ ) may be used. Fluoride is preferable to oxide for good phase separation between the dielectric 32 and the magnetic particles 31, and magnesium fluoride is particularly preferable because it has a high transmittance.

As shown in FIGS. 1 to 3, the reflective film 40 is formed on the granular film 30, and reflects the light transmitted through the granular film 30 toward the granular film 30. As the reflective film 40, for example, an Ag (silver) film, an Au (gold) film, an Al (aluminum) film, a dielectric multilayer mirror, or the like can be used. In particular, an Ag film having a high reflectance and an Au film having a high corrosion resistance are convenient and preferable in terms of film formation. The thickness of the reflective film 40 may be a size that can secure a sufficient reflectance of 98% or more, and for example, in the case of an Ag film, it is preferably 50 nm or more and 200 nm or less. The Faraday rotation angle can be increased by reciprocating light in the granular film 30 using the reflective film 40.

The light emitting element 51 is, for example, a semiconductor laser or a light emitting diode. Specifically, as the light emitting element 51, a Fabry-Perot laser, a superluminescence diode, or the like can be preferably used.

The splitter 52 is an optical element for converting the light emitted by the light emitting element 51 into linear polarization, and the type thereof is not particularly limited. The linear polarization obtained by the splitter 52 is introduced into the optical fiber 20.

The half mirror 53 introduces linear polarization from the light emitting device 50 into the optical fiber 20, and sends the return light from the magnetic field sensor element 10 to the light receiving device 60. The optical element for introducing linear polarization into the optical fiber 20 is not limited to the half mirror 53, and may be an optical coupler for coupling and branching the optical fiber, a beam splitter for splitting light, or an optical circulator.

The λ / 2 plate 62 gives a phase difference of λ / 2 (180 °) between the polarization components of the return light from the magnetic field sensor element 10 and rotates the polarization direction to emit the light. It is located on the front side. As the λ / 2 plate 62, a general one using a birefringent material or the like can be used. Alternatively, the same effect can be obtained by arranging the λ / 4 plate in the magnetic field sensor element 10 instead of the λ / 2 plate 62. In this case, it is desirable to insert the λ / 4 plate between the granular film 30 and the reflective film 40, and then the light reciprocates inside the λ / 4 plate to make the λ / 4 plate reflective. Functions as a λ / 2 plate.

The polarization separation element 64 separates the S polarization component 65S and the P polarization component 65P of the return light phase-modulated by the λ / 2 plate 62. As the polarization separating element 64, a polarization beam splitter (PBS) such as a prism type, a planar type, a wedge substrate type, or an optical waveguide type can be used.

The light receiving element 66S receives the S polarization component 65S, and the light receiving element 66P receives the P polarization component 65P and converts them into electric signals (photoelectric conversion). As the light receiving elements 66S and 66P, for example, a PIN photodiode or the like can be used.

FIG. 4 is a block diagram showing an example of the signal processing unit 70. The signal processing unit 70 has amplifiers 71P and 71S, division circuits (analog ICs) 72 and 73, and differential amplifier circuits 74, and has two polarization components from the electrical signals photoelectrically converted by the light receiving elements 66S and 66P. The intensity of is detected as a difference, and the value is replaced with the current value. The amplifier 71P amplifies the electric signal Ep obtained from the P polarization component 65P having a light quantity Lp by the light receiving element 66P. The amplifier 71S amplifies the electric signal Es obtained from the S polarization component 65S having a light amount Ls by the light receiving element 66S. The division circuit 72 divides the electric signal Es by the amplified electric signal Ep, and inputs the output value to the negative side of the differential amplifier circuit 74. The division circuit 73 divides the electric signal Ep by the amplified electric signal Es, and inputs the output value to the positive side of the differential amplifier circuit 74. The differential amplifier circuit 74 differentially amplifies the output values of the division circuits 73 and 74 and converts them into the final current value.

5 (A) to 5 (C) are perspective views, cross-sectional views, and exploded cross-sectional views of the other magnetic field sensor elements 10A, respectively. FIG. 5B shows a cross section of the magnetic field sensor element 10A along the VB-VB line of FIG. 5A. The magnetic field sensor element 10A is a uniaxial space-coupled sensor element using an optical collimator, and includes an optical fiber 20, a protective member 25, a rotary sleeve 26, a granular film 30, a transparent substrate 33, and λ / 4. It has a plate 34, a reflective film 40, and an optical collimator 80. Of these, the granular film 30 and the reflective film 40 are the same as those of the magnetic field sensor element 10 in FIG. Since the granular film 30 and the reflective film 40 are thin films, they are omitted in FIG. 5B for the sake of easy understanding. In the magnetic field sensor device 1, the magnetic field sensor element 10A may be used instead of the magnetic field sensor element 10.

The optical fiber 20 is an incident optical fiber that propagates linearly polarized light incident from the light emitting device 50, and is also an emitted optical fiber that propagates return light to the light receiving device 60. The protective member 25 is a member that covers the emission end portion of the optical fiber 20 (the end portion opposite to the light emitting device 50 in FIG. 1), and the rotary sleeve 26 is a cylindrical shape attached to one end portion of the protective member 25. It is a member of. Examples of the material of the protective member 25 and the rotary sleeve 26 include glass, ceramic, metal, and synthetic resin.

The optical collimator 80 is arranged so as to be covered with a protective member 25 and a rotary sleeve 26 at the emission end of the optical fiber 20, and has a capillary 81, a lens barrel 82, and a collimator lens 83. The capillary 81 is a member to which the emission end portion of the optical fiber 20 is attached, and the lens barrel 82 is a cylindrical member surrounding the end portion of the capillary 81. The collimated lens 83 is embedded in the end of the lens barrel 82, and the light propagating through the optical fiber 20 is emitted as collimated light (parallel light) into the space inside the rotating sleeve 26, and the reflected light of the emitted light is emitted. Is incident on the optical fiber 20.

The granular film 30 is formed on the transparent substrate 33 and is arranged at the end of the rotary sleeve 26 away from the emission end of the optical fiber 20. Examples of the material of the transparent substrate 33 include glass, quartz, and synthetic resin. The λ / 4 plate 34 is arranged between the optical collimator 80 and the granular film 30, and converts linearly polarized light into circularly polarized light or elliptically polarized light, and converts circularly polarized light or elliptically polarized light into linearly polarized light. The reflective film 40 is formed on the surface of the transparent substrate 33 opposite to the granular film 30. However, unlike the illustrated form, both the granular film 30 and the reflective film 40 may be laminated on one side of the transparent substrate 33. In this case, the reflective film 40 and the granular film 30 are laminated in this order on the surface of the transparent substrate 33 on the protective member 25 side, or the granular film 30 and the reflective film 30 are reflected on the surface of the transparent substrate 33 opposite to the protective member 25. The films 40 may be laminated in this order.

In the magnetic field sensor element 10A, the λ / 4 plate 34, the granular film 30, the transparent substrate 33, and the reflective film 40 are in close contact with each other in this order, and they close the end of the space in the rotating sleeve 26. Further, the reflective film 40 is arranged so as to be aligned with the position of the beam waist W of the spatially propagated light L focused by the collimating lens 83.

In the magnetic field sensor element 10A, the linearly polarized light from the light emitting device 50 propagating through the optical fiber 20 passes through the capillary 81 of the optical collimator 80 and is emitted into the space inside the rotating sleeve 26 via the collimator lens 83. The emitted light is transmitted through the λ / 4 plate 34 and converted into circular polarization, transmitted through the granular film 30 and the transparent substrate 33, reflected by the reflective film 40, and again transmitted through the transparent substrate 33, the granular film 30 and λ / 4. It passes through the plate 34, is converted into linear polarization, passes through the collimating lens 83, and is incident on the optical fiber 20 as return light. When a magnetic field is applied around the magnetic field sensor element 10A, when light passes through the granular film 30, the polarizing surface rotates according to the intensity of the magnetic field.

In the magnetic field sensor element 10A, phase modulation of P wave and S wave is caused by the λ / 4 plate 34 in the linear polarization propagating in the optical fiber 20. In the magnetic field sensor device 1 using the magnetic field sensor element 10A, a state in which the light intensities of the P-polarized component and the S-polarized component received by the light receiving device 60 match is set as the zero point in advance. As a result, when the polarization plane of the granular film 30 is rotated by an external magnetic field, the light intensity of each polarization component changes linearly, so that it is easy to use as a sensor.

6 (A) and 6 (B) are a plan view and a cross-sectional view of another magnetic field sensor element 10B. FIG. 6B shows a cross section of the magnetic field sensor element 10B along the VIB-VIB line of FIG. 6A. The magnetic field sensor element 10B includes a sensor head base material 16, optical fibers 20B, 21B, 22B, a granular film 30, a transparent substrate 33, a λ / 4 plate 34, and a reflective film 40. Of these, the granular film 30 and the reflective film 40 are the same as those of the magnetic field sensor element 10 in FIG. In the magnetic field sensor device 1, the magnetic field sensor element 10B may be used instead of the magnetic field sensor element 10.

The sensor head base material 16 is a member that supports the optical fibers 21B and 22B, the granular film 30, the transparent substrate 33, the λ / 4 plate 34, and the reflective film 40. Examples of the material of the sensor head base material 16 include glass, ceramics, metals, and synthetic resins. The optical fibers 21B and 22B, the granular film 30, the transparent substrate 33, the λ / 4 plate 34, and the reflective film 40 are fixed to the sensor head base material 16 with, for example, an adhesive or a curable resin.

The optical fiber 20B is connected to the optical fiber 21B at the end 28. The optical fiber 20 is an incident optical fiber in which linearly polarized light from the light emitting device 50 is incident on the optical fibers 21B and 22B, and is also an outgoing optical fiber that propagates the return light from the optical fibers 21B and 22B to the light receiving device 60. be. The optical fiber 20B may be a single-mode optical fiber, but is preferably a polarization-retaining optical fiber.

The optical fibers 21B and 22B are single-mode optical fibers having the same characteristics and diameters. It is preferable that the optical fibers 21B and 22B are cut by fixing the optical fibers originally connected to one to the sensor head base material 16. The optical fibers 21B and 22B are fixed to the sensor head base material 16 so that the optical axis C1 of the optical fiber 21B and the optical axis C2 of the optical fiber 22B coincide with each other.

The granular film 30 is provided on the transparent substrate 33 inserted in the middle of the path composed of the optical fibers 21B and 22B. The light incident surface M of the granular film 30 is orthogonal to the optical axes C1 and C2 of the optical fibers 21B and 22B.

The λ / 4 plate 34 is arranged on the opposite side of the reflective film 40 with the granular film 30 interposed therebetween in the middle of the path composed of the optical fibers 21B and 22B. Unlike the illustrated example, the transparent substrate 33 may be omitted and the granular film 30 may be formed on the λ / 4 plate 34. In this case, the number of parts can be reduced, and the thickness of the parts is reduced by the amount of the transparent substrate 33, so that the magnetic field sensor element 10B can be miniaturized, the assembly work becomes simpler, and the light loss is reduced. Further, although the λ / 4 plate 34 and the granular film 30 are in close contact with each other in the illustrated example, they may be separated from each other with the optical fibers 21B and 22B interposed therebetween.

The reflective film 40 is formed on one end face of a path composed of optical fibers 21B and 22B. The reflective film 40 may be provided at least on the end surface 27 of the optical fiber 22B, and may extend to the entire or a part of the tip surface 16E of the sensor head base material 16 formed flush with the end surface 27. ..

In the magnetic field sensor element 10B, the linearly polarized light propagating through the optical fiber 20B enters the optical fiber 21B from the end 28, propagates through the optical fiber 21B, passes through the λ / 4 plate 34, and is converted into circular polarization. .. This circular polarization passes through the granular film 30 and the transparent substrate 33, propagates through the optical fiber 22B, is reflected by the reflective film 40, propagates again through the optical fiber 22B, and propagates through the transparent substrate 33, the granular film 30 and the λ / 4 plate. It passes through 34 and is converted into linear polarization. This linearly polarized light propagates through the optical fiber 21B and is output to the optical fiber 20B as return light. When a magnetic field is applied around the magnetic field sensor element 10B, when light passes through the granular film 30, the polarizing surface rotates according to the intensity of the magnetic field.

The magnetic field sensor element 10B can be easily manufactured because it is not necessary to increase the shape accuracy of each component so as to align the optical axis or to assemble each component with accuracy, and the optical fibers 21B and 22B. Since the optical axes of the above are aligned, the loss of light can be reduced.

FIG. 7 is a plan view of another magnetic field sensor element 10C. The magnetic field sensor element 10C includes a planar light wave circuit 11, an optical fiber 19, an optical fiber 20C, a granular film 30, and a reflective film 40. Of these, the granular film 30 and the reflective film 40 are the same as those of the magnetic field sensor element 10 in FIG. In the magnetic field sensor device 1, the magnetic field sensor element 10C may be used instead of the magnetic field sensor element 10.

The planar light wave circuit 11 is an optical waveguide formed on a base substrate such as glass, and has an optical branch portion 12, optical paths 13, 14, 15, and connection portions 17, 18. In the optical branch portion 12, the optical paths 13, 14 and 15 are branched into each other in a Y shape, the optical path 14 faces one end surface side of the planar light wave circuit 11, and the optical paths 13 and 15 face one end surface thereof. They are arranged on the other end surface side, respectively. The connecting portion 17 is formed at the end of the optical path 13, and the connecting portion 18 is formed at the end of the optical path 15. A granular film 30 and a reflective film 40 are formed on the end faces of the plane light wave circuit 11 on the optical path 14 side (opposite to the connecting portions 17 and 18). The connecting portions 17, 18 and the granular film 30 and the reflecting film 40 are not limited to the facing end faces of the planar light wave circuit 11, and may be provided on adjacent end faces, respectively.

The optical fiber 19 is an incident optical fiber that propagates linearly polarized light from the light emitting device 50 to the planar optical wave circuit 11, and is connected to the planar optical wave circuit 11 by a connecting portion 17 using an adhesive whose refractive index is matched. There is. The optical fiber 19 may be a single-mode optical fiber or a polarization-retaining optical fiber.

The optical fiber 20C is an optical fiber for emission that propagates the return light emitted from the planar light wave circuit 11 to the light receiving device 60 without disturbing the polarization state, and uses an adhesive whose refractive index is matched at the connection portion 18. It is connected to the plane light wave circuit 11. The optical fiber 20C is preferably a polarization-retaining optical fiber, and is aligned and connected to the planar light wave circuit 11.

In the magnetic field sensor element 10C, the optical fiber 20C is rotated in the axial direction with respect to the polarization plane of the return light from the planar light wave circuit 11 at the connection portion 18 in a state where no magnetic field is applied, so that the light receiving device 60 receives light. The light intensities of the P-polarized component and the S-polarized component are adjusted to be equal. Therefore, since it is not necessary to provide the wave plate in the planar light wave circuit 11, the loss that may occur due to the wave plate can be suppressed.

The granular film 30 is formed on the end surface of the planar light wave circuit 11 on the optical path 14 side, and the reflective film 40 is formed on the granular film 30.

In the magnetic field sensor element 10C, the linearly polarized light from the light emitting device 50 enters the optical path 13 from the connection portion 17 via the optical fiber 19 and proceeds in the direction of the arrow in FIG. 7, and the optical branch portion 12 and the optical path It permeates the granular film 30 via 14. At that time, when a magnetic field is applied around the magnetic field sensor element 10C, the polarizing surface rotates according to the strength of the magnetic field. The light transmitted through the granular film 30 is reflected by the reflective film 40, passes through the granular film 30 again, returns to the optical path 14, and exits from the connecting portion 18 via the optical branch portion 12 and the optical path 15. It enters the optical fiber 20C and propagates through the optical fiber 20C.

In the magnetic field sensor element 10C, the plane of polarization is easily maintained even against disturbances due to twisting, bending, or the like, especially in the planar light wave circuit 11, so that the phase modulation generated by the Faraday rotation can be accurately propagated. Further, the linearly polarized light that has entered the planar light wave circuit 11 from the optical fiber 19 can propagate through the planar light wave circuit 11 as it is without being branched by the conventional branch coupler. Further, in the magnetic field sensor element 10C, as described above, since it is not necessary to provide a wave plate in the planar light wave circuit 11, the light intensity can be detected without suffering a loss due to the wave plate.

In the magnetic field sensor elements 10, 10A to 10C, a Faraday effect is generated while the light reciprocates in the granular film 30 in the presence of a magnetic field, which increases the Faraday rotation angle. The light intensity of each polarization component is also increased. As a result, there is no possibility that the polarized light is hidden in the crosstalk during propagation and cannot be detected, so that it is not necessary to arrange an optical element for polarization separation in the vicinity of the granular film 30. Therefore, the head portion of the magnetic field sensor element can be miniaturized, and measurement using the Faraday effect can be realized with a simple optical system.

Since the Curie temperature of the magnetic garnet is about 200 ° C. to 300 ° C., the magnetization is lowered and the Faraday effect is also lowered in a high temperature environment close to the Curie temperature. Therefore, the conventional Faraday effect type magnetic field sensor using the magnetic garnet has low sensitivity in a high temperature environment and becomes difficult to operate. On the other hand, the Curie temperature of the above-mentioned ferromagnetic metal used as the magnetic particle 31 is as high as about 1000 ° C., and the temperature characteristic of the sensor sensitivity depends only on the temperature characteristic of the magnetization of the magnetic particle 31.

FIG. 8 is a graph showing the temperature characteristics of the magnetization of the granular film 30. The horizontal axis of the graph represents the applied magnetic field H (koe), and the vertical axis represents the magnetization M (kG). In FIG. 8, for the granular film of Co-MgF ₂ (magnetic particles are Co, dielectric is MgF ₂ ) formed at 350 ° C., the ambient temperature is set to room temperature (rt), 150 ° C. and 350 ° C. The measurement results are shown in layers. As can be seen from the graph, in the granular film of Co-MgF ₂ , the magnetization fluctuation due to the ambient temperature is small, and the saturation magnetization hardly decreases even when heated to 350 ° C. In particular, since the linear region near the origin of the graph hardly changes depending on the ambient temperature, the magnetic field sensor elements 10, 10A to 10C using the granular film of Co-MgF ₂ do not substantially reduce the sensor sensitivity even in a high temperature environment. ..

The magnetic field sensor elements 10, 10A to 10C are excellent in temperature characteristics, and the sensor sensitivity is kept constant in a wide temperature range in practical use, so that they are suitable for use as a current sensor for a power electronics circuit or the like. Further, the magnetic field sensitive element composed of the granular film 30 can be applied to a magnetic field sensor element (magnetic field sensor device) utilizing the Faraday effect regardless of an optical method such as an interference type or an intensity modulation type.

FIG. 9 is a graph showing the relationship between the film formation temperature of the granular film and the average particle size of the magnetic particles in the film. 10 (A) and 10 (B) are a graph showing the temperature characteristics of the magnetization of the granular film formed at different temperatures and a cross-sectional photograph of the granular film. The horizontal axis of FIG. 9 represents the film formation temperature T (° C.), and the vertical axis represents the average particle size d (nm) of the magnetic particles. The vertical line in FIG. 9 represents the error range of the average particle size. The horizontal axis of FIG. 10A represents the applied magnetic field H (koe), and the vertical axis represents the magnetization M (kG). The granular film can be formed on a substrate by thin film deposition or sputtering, and in FIGS. 9 to 10B, Co and MgF ₂ are set at room temperature (<70 ° C.), 250 ° C., 350 ° C. and 450 ° C. The results are shown for a granular film of Co-MgF ₂ produced by depositing Co-MgF 2 on a substrate.

In the cross-sectional photograph of FIG. 10B, the average particle size of the magnetic particles (Co) in the granular film is also shown. The average particle size (diameter) of Co in the granular film of Co-MgF ₂ prepared at room temperature (<70 ° C.), 250 ° C., 350 ° C. and 450 ° C. was 2.9 nm and 4.0 nm, respectively. It is 6.8 nm and 10.6 nm. These average particle sizes are values obtained by measuring the particle sizes of each magnetic particle on a cross-sectional photograph of a granular film taken by a transmission electron microscope and averaging them. The black part on the cross-sectional photograph corresponds to Co, and the white part corresponds to MgF ₂ . As can be seen from FIG. 10B, the average particle size changes depending on the film formation temperature (the substrate temperature during film formation), and becomes larger as the substrate temperature is higher. The average particle size of the magnetic particles in the granular film can be controlled mainly by adjusting the substrate temperature and the rotational speed of the substrate at the time of film formation, or by post-annealing.

In order to use the granular film as a sensitive element of a magnetic field sensor device, it is desirable that the magnetization changes linearly with respect to the magnetic field when a magnetic field is applied. Further, if there is hysteresis in the temperature characteristic of magnetization, a measurement error occurs when the magnetic field sensor element is used for an AC magnetic field, so it is desirable that there is no hysteresis.

As can be seen from FIG. 10 (A), the lower the film formation temperature, the smaller the hysteresis, but the narrower the linear region of magnetization with respect to the magnetic field. On the other hand, the higher the film formation temperature, the wider the linear region of magnetization with respect to the magnetic field, but the larger the hysteresis. In particular, when the film formation temperature is 450 ° C. or higher and the average particle size is 10 nm or higher, the hysteresis is large, and at high temperatures, the saturation magnetization is reduced and the Faraday effect is also reduced, which is not preferable. Further, since the lower limit of the film formation temperature of the granular film is about 70 ° C., it is difficult to make the average particle size smaller than 2 nm. Therefore, in the case of a Granular film of Co-MgF ₂ , in order to achieve both linearity and soft magnetism (small hysteresis), the average particle size of the magnetic particles dispersed in the film is 2 nm or more and less than 10 nm. It is preferably about 4 nm when the film formation temperature is 250 ° C.

Further, in the case of Co-MgF ₂ , the ratio M / (M + F) of the volume M of the ferromagnetic metal Co and the volume F of the metal fluoride MgF ₂ in the granular film is larger than 0.2 and less than 0.5. Is preferable. When the volume ratio M / (M + F) is 0.5 (that is, M: (M + F) = 1: 2), Co is most densely packed in MgF ₂ , and when the amount of Co is larger than that, the membrane is not a granular film. Therefore, 0.5 is considered to be the upper limit of the volume ratio M / (M + F). When the volume ratio M / (M + F) is less than 0.5, the distance between the Co fine particles becomes large and the transmittance becomes large, so that the transmitted light modulated by the Faraday effect can be effectively taken out. Further, when the volume ratio M / (M + F) is 0.2 or less, the ratio of the ferromagnetic metal is too small and it becomes difficult to detect the Faraday effect, so that it is preferably a larger value.

In the following, the experimental results of producing a plurality of granular films by changing the film formation temperature and the film thickness and measuring their characteristics will be described.

Co and MgF ₂ are vapor-deposited on a substrate kept at room temperature (<70 ° C.) so that the volume ratio M / (M + F) becomes 0.50, and a granular Co-MgF ₂ having a film thickness of 0.25 μm is deposited. A film was prepared. The average particle size of Co in the film is 3.0 nm, and the S / N ratio (SNR) of the output signal of the magnetic field sensor device (signal processing unit 70 in FIG. 1) using this granular film is 0.51. rice field. The values of the S / N ratio shown below are all relative values with the dB value of the S / N ratio in Comparative Example 2 described later as 1. The width of the magnetization curve when the magnetic field is applied alternately in one direction and the opposite direction is ΔH (Oe), and when ΔH is less than 10 Oe, 10 Oe or more and less than 100 Oe, and 100 Oe or more, the hysteresis is “none”, “small”, respectively. When defined as "large", this granular film had no hysteresis.

When light having a wavelength of 1550 nm was incident on this granular film when the magnetization was saturated, the transmittance was 30%. In addition, the figure of merit FOM defined by the ratio θ _F / P _loss of the Faraday rotation angle θ _F (deg / μm) per 1 μm of film thickness and the loss amount P _loss (dB / μm) of transmitted light per 1 μm of film thickness. When (Figure Of Merit) was obtained, it was 0.067 deg / dB. Here, Plus is an amount obtained by _-10 log (I / I ₀ ), where I is the transmitted light intensity and I ₀ is the incident light intensity when light having a wavelength of 1550 nm passes through a thin film having a film thickness of 1 μm. .. For example, in a magnetic field sensor element, when light having a wavelength of 1550 nm is incident at the time of magnetization saturation, if the figure of merit FOM is 0.05 deg / dB or more, the performance as a sensor is sufficient.

Co and MgF ₂ are vapor-deposited on a substrate kept at room temperature (<70 ° C.) so that the volume ratio M / (M + F) is 0.33, and a granular Co-MgF ₂ having a film thickness of 0.75 μm is deposited. A film was prepared. The average particle size of Co in the membrane is 2.9 nm, the S / N ratio in the case of this granular membrane is 0.64, the hysteresis is "none", and the transmittance is under the same conditions as in Example 1. Was 29%, and the figure of merit FOM was 0.089 deg / dB.

Co and MgF ₂ are vapor-deposited on a substrate kept at room temperature (<70 ° C.) so that the volume ratio M / (M + F) is 0.25, and a granular Co-MgF ₂ having a film thickness of 2.00 μm is deposited. A film was prepared. The average particle size of Co in the membrane is 2.5 nm, the S / N ratio in the case of this granular membrane is 0.64, the hysteresis is "none", and the transmittance is under the same conditions as in Example 1. Was 28% and the figure of merit FOM was 0.065 deg / dB.

Co and MgF ₂ are vapor-deposited on a substrate kept at room temperature (<70 ° C.) so that the volume ratio M / (M + F) becomes 0.20, and a granular Co-MgF ₂ having a film thickness of 3.25 μm is deposited. A film was prepared. The average particle size of Co in the membrane is 2.0 nm, the S / N ratio in the case of this granular membrane is 0.29, the hysteresis is "none", and the transmittance is under the same conditions as in Example 1. Was 26% and the figure of merit FOM was 0.035 deg / dB.

Co and MgF ₂ were vapor-deposited on a substrate kept at 250 ° C. so that the volume ratio M / (M + F) was 0.33 to prepare a granular film of Co-MgF ₂ having a film thickness of 0.75 μm. .. The average particle size of Co in the membrane is 4.0 nm, the S / N ratio in the case of this granular membrane is 0.63, the hysteresis is "none", and the transmittance is under the same conditions as in Example 1. Was 23% and the figure of merit FOM was 0.089 deg / dB.

Co and MgF ₂ were vapor-deposited on a substrate kept at 350 ° C. so that the volume ratio M / (M + F) was 0.50 to prepare a granular film of Co-MgF ₂ having a film thickness of 0.25 μm. .. The average particle size of Co in the membrane is 9.0 nm, the S / N ratio in the case of this granular membrane is 0.30, the hysteresis is “small”, and the transmittance is under the same conditions as in Example 1. Was 20% and the figure of merit FOM was 0.030 deg / dB.

Co and MgF ₂ were vapor-deposited on a substrate kept at 350 ° C. so that the volume ratio M / (M + F) was 0.33 to prepare a granular film of Co-MgF ₂ having a film thickness of 2.50 μm. .. The average particle size of Co in the membrane is 6.8 nm, the S / N ratio in the case of this granular membrane is 0.89, the hysteresis is "small", and the transmittance is under the same conditions as in Example 1. Was 25% and the figure of merit FOM was 0.198 deg / dB.

Co and MgF ₂ were vapor-deposited on a substrate kept at 350 ° C. so that the volume ratio M / (M + F) was 0.25 to prepare a granular film of Co-MgF ₂ having a film thickness of 5.00 μm. .. The average particle size of Co in the membrane is 6.0 nm, the S / N ratio in the case of this granular membrane is 0.99, the hysteresis is "small", and the transmittance is under the same conditions as in Example 1. Was 27% and the figure of merit FOM was 0.255 deg / dB.

Fe and MgF ₂ were vapor-deposited on a substrate kept at 350 ° C. so that the volume ratio M / (M + F) was 0.33 to prepare a granular film of Fe-MgF ₂ having a film thickness of 0.75 μm. .. The average particle size of Fe in the membrane is 5.0 nm, the S / N ratio in the case of this granular membrane is 0.55, the hysteresis is “small”, and the transmittance is under the same conditions as in Example 1. Was 29% and the figure of merit FOM was 0.060 deg / dB.

Co and YF ₃ were vapor-deposited on a substrate kept at 350 ° C. so that the volume ratio M / (M + F) was 0.25 to prepare a granular film of Co-YF ₃ having a film thickness of 1.50 μm. .. The average particle size of Co in the membrane is 6.0 nm, the S / N ratio in the case of this granular membrane is 0.74, the hysteresis is "small", and the transmittance is under the same conditions as in Example 1. Was 28% and the figure of merit FOM was 0.132 deg / dB.

(Comparative Example 1) Co _{-MgF 2 having} a film thickness of 1.25 μm is deposited on a substrate kept at 450 ° C. so that the volume ratio M / (M + F) becomes 0.50. A granular film was prepared. The average particle size of Co in the membrane is 11.0 nm, the S / N ratio in the case of this granular membrane is 0.82, the hysteresis is “large”, and the transmittance is under the same conditions as in Example 1. Was 29% and the figure of merit FOM was 0.175 deg / dB.

(Comparative Example _{2) Co-MgF 2 having} a film thickness of 6.00 μm is deposited on a substrate kept at 450 ° C. so that the volume ratio M / (M + F) is 0.33. A granular film was prepared. The average particle size of Co in the film is 10.6 nm, the S / N ratio in the case of this granular film is 1.00 (reference value), the hysteresis is “large”, and the same conditions as in Example 1. Below, the transmittance was 27% and the figure of merit FOM was 0.247 deg / dB.

The results of Examples 1 to 10 and Comparative Examples 1 and 2 described above are summarized in Table 1. As can be seen from Table 1, when the average particle size of the fine particles of the ferromagnetic metal is 2 nm or more and less than 10 nm (particularly 9 nm or less), it is preferable because both linearity of the temperature characteristics of magnetization and soft magnetism can be achieved. Further, the ratio M / (M + F) of the volume M of the ferromagnetic metal and the volume F of the metal fluoride in the granular film is larger than 0.2 and less than 0.5 (particularly 0.25 or more and 0.33 or less). ), The performance index FOM is 0.05 deg / dB or more, and the performance as a sensor is ensured, which is more preferable.

11 (A) and 11 (B) are graphs showing the relationship between the transmittance of the granular film and the SN ratio of the output of the magnetic field sensor element. The horizontal axis of the graph is the transmittance (ratio of transmitted light intensity to incident light intensity) T (%) of the applied light, and the vertical axis is the S of the output signal of the magnetic field sensor device (signal processing unit 70 in FIG. 1). Represents the / N ratio (SNR). As described above, the value on the vertical axis is a relative value with the value of Comparative Example 2 as 1. The curves a to l in the graph are the S / N ratios according to the transmittance (that is, the film thickness) of the granular films prepared under the same conditions as in Examples 1 to 10 and Comparative Examples 1 and 2, respectively. It shows a change.

The smaller the film thickness of the granular film, the higher the transmittance but the smaller the Faraday effect, and conversely, the larger the film thickness, the larger the Faraday effect but the lower the transmittance. That is, the Faraday effect and the transmittance are in an inversely proportional relationship, and it is not preferable whether either of them is extremely large or small. From the graphs shown in FIGS. 11 (A) and 11 (B), the S / N ratio of the sensor output is maximized within the range of the transmittance of about 20% or more and 30% or less under any film forming condition. You can see that. Therefore, it is preferable that the film thickness of the granular film 30 is controlled so that the transmittance (light transmittance) is 20 or more and 30% or less.

1 Magnetic field sensor device 10, 10A to 10C Magnetic field sensor element 19, 20, 20B, 20C, 21B, 22B Optical fiber 30 Granular film 31 Magnetic particle 32 Dielectric 40 Reflective film 50 Light receiving device 60

Claims (10)

Ferromagnetic fine particles with an average particle size of 2 nm or more and less than 10 nm are dispersed in the dielectric of metal fluoride, and a granular film that allows incident light to pass through.
A reflective film that reflects light transmitted through the granular film toward the granular film, and
An optical fiber that propagates the incident light to the granular film and propagates the return light that is reflected by the reflective film and transmitted through the granular film.
A magnetic field sensor element characterized by having. The magnetic field sensor element according to claim 1, wherein the light transmittance of the granular film is 20% or more and 30% or less. The ferromagnetic metal contains at least one of Fe and Co.
The magnetic field sensor element according to claim 2, wherein the metal fluoride is MgF2 or YF3. The magnetic field according to claim 3, wherein the ratio M / (M + F) of the volume M of the ferromagnetic metal and the volume F of the metal fluoride in the granular film is larger than 0.2 and less than 0.5. Sensor element. The granular film is formed on the end face of the optical fiber and is formed on the end face of the optical fiber.
The magnetic field sensor element according to any one of claims 1 to 4, wherein the reflective film is formed on the granular film. The magnetic field sensor element further includes an optical collimator arranged at the emission end of the optical fiber and a λ / 4 plate arranged between the optical collimator and the granular film.
The granular film is arranged so as to be separated from the exit end of the optical fiber.
The optical collimator according to any one of claims 1 to 4, wherein the optical collimator emits the light propagating through the optical fiber into space as parallel light, and causes the reflected light, which is the spatially propagating light from the reflective film, to enter the optical fiber. The magnetic field sensor element according to item 1. The magnetic field sensor element further has a λ / 4 plate inserted in the middle of the path composed of the optical fiber.
The granular film is inserted in the middle of the path composed of the optical fiber, and the granular film is inserted.
The magnetic field sensor element according to any one of claims 1 to 4, wherein the reflective film is formed on an end face of the optical fiber. An incident optical fiber that propagates incident light,
A granular film in which fine particles of a ferromagnetic metal having an average particle size of 2 nm or more and less than 10 nm are dispersed in a dielectric of a metal fluoride and transmit the incident light.
A reflective film that reflects light transmitted through the granular film toward the granular film, and
An optical fiber for emission that is reflected by the reflective film and propagates the return light that has passed through the granular film.
It has a planar light wave circuit having an optical branch portion and connecting the incident optical fiber and the outgoing optical fiber.
The granular film is formed on the end face of the planar light wave circuit and is formed.
The reflective film is formed on the granular film, and the reflective film is formed on the granular film.
The emission optical fiber is a polarization-retaining optical fiber, and is a magnetic field sensor element that is aligned and connected to the planar light wave circuit. The magnetic field sensor element according to any one of claims 1 to 7 .
A light emitting device that introduces linearly polarized light into the optical fiber as the incident light,
A light receiving device that separates the return light derived from the optical fiber into an S-polarized component and a P-polarized component, receives the S-polarized component and the P-polarized component, converts them into an electric signal, and processes the electric signal. ,
A magnetic field sensor device characterized by having. The magnetic field sensor element according to claim 8 and
A light emitting device that introduces linearly polarized light as incident light into the incident optical fiber, and
The return light derived from the emission optical fiber is separated into an S-polarized component and a P-polarized component, and the S-polarized component and the P-polarized component are received and converted into an electric signal to process the electric signal. With the equipment
A magnetic field sensor device characterized by having.

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