JP2014145719A - Optical probe sensor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical probe sensor device having high detection accuracy.SOLUTION: A sensor device 10 includes a light-emitting unit 51 and a light-receiving unit 52, a sensor unit 20, optical fiber cores 42 and 43, and a signal processing unit 60. The sensor unit 20 includes: a magnetic material 21 for producing an in-plane magnetic Kerr effect; and a polarizer 27 for branching reflection light from the magnetic material 21 into an S polarization component and a P polarization component. The optical fiber core 42 propagates light having the S polarization component from the polarizer 27 as an optical signal, and the optical fiber core 43 propagates light having the P polarization component from the polarizer 27 as an optical signal. The light-receiving unit 52 converts the respective optical signals of the optical fiber cores 42 and 43 into a first electric signal and a second electric signal. The signal processing unit 60 includes a first division circuit for dividing the second electric signal by the first electric signal; a second division circuit for dividing the first electric signal by the second electric signal; and a differential amplification circuit for differentially amplifying and outputting respective output values of the first and the second division circuits.

Description

  The present invention relates to an optical probe sensor device, and more particularly to a technique that is effective when applied to an optical probe sensor device that detects a change in current or magnetic field by a change in light.

  The Shinshu University Spin Device Technology Center Activity Report (Non-patent Document 1) states that the in-plane magnetic Kerr effect of a magnetic material is used as a current detection method using light that is not affected by external electromagnetic interference as a probe. An optical probe current sensor utilizing the above is described. In this optical probe current sensor, linearly polarized light is incident on the surface of a magnetic material, and reflected light from the surface of the magnetic material is split into a P-polarized component and an S-polarized component through a quarter-wave plate and a prism beam splitter (PBS). Then, light of each polarization component propagates through the optical fiber and is received by the photodiode.

Makoto Sonehara and 7 others, "Fundamental study on optical probe current sensor using Kerr effect of Fe-Si / Mn-Ir exchange-coupled single domain magnetic thin film", Shinshu University Spin Device Technology Center activity report (2008) Pp. 27-28

  In the optical probe current sensor described in Non-Patent Document 1, the current to be measured and the magnitude of the magnetic field are converted as the amounts of S-polarized light component and P-polarized light component of the reflected light from the magnetic material that causes the in-plane magnetic Kerr effect. The For this reason, the light amounts of the S-polarized light component and the P-polarized light component should not change for reasons other than changes due to the in-plane magnetic Kerr effect of the magnetic material. However, when an external force such as vibration or impact is applied to the optical fiber that propagates light of each polarization component, the amount of light changes, so that the detection accuracy (measurement accuracy) represented by the S (Signal) / N (Noise) ratio or the like Will fall.

  An object of the present invention is to provide an optical probe sensor device with high detection accuracy. The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  An optical probe sensor device according to one solution of the present invention includes a light emitting unit and a light receiving unit, a sensor unit optically connected between the light emitting unit and the light receiving unit, and the sensor unit and the light receiving unit. First and second optical fiber cores to be connected, and a signal processing unit (signal processing circuit) electrically connected to the light receiving unit, wherein the sensor unit has a magnetic body that generates an in-plane magnetic Kerr effect; A polarizer that branches the reflected light from the magnetic material into an S-polarized component and a P-polarized component, and the first optical fiber core propagates the light of the S-polarized component from the polarizer as an optical signal, The second optical fiber core propagates light of the P-polarized component from the polarizer as an optical signal, and the light receiving unit transmits the optical signals of the first and second optical fiber cores to the first and second optical signals, respectively. Converted into an electrical signal, the signal processing unit, Outputs of a first division circuit that divides the second electric signal by one electric signal, a second division circuit that divides the first electric signal by the second electric signal, and outputs of the first and second division circuits, respectively. And a differential amplifier circuit that differentially amplifies and outputs the value.

  According to this, even if an external force such as vibration or impact is applied to the first and second optical fiber cores to change the light amounts of the S-polarized component and the P-polarized component, the light amount change (noise) of each other is changed. It can be reduced by a divide-by-2 circuit. That is, it can be made less susceptible to disturbances caused by vibrations or shocks of the optical fiber, and the detection accuracy of the optical probe sensor device can be increased.

  The optical probe sensor device preferably includes one multi-core fiber, and the first and second optical fiber cores constitute a core of the one multi-core optical fiber.

  According to this, since the first and second optical fiber cores are similarly subjected to disturbances such as vibration and impact, the change in the amount of reflected light (S-polarized component, P-polarized component) due to the disturbance is also the same. Therefore, mutual light quantity change (noise) can be canceled (reduced) by the first and second divider circuits, and the detection accuracy of the optical probe sensor device can be further increased.

  Preferably, the optical probe sensor device includes a third optical fiber core that connects the light emitting unit and the sensor unit, and the third optical fiber core constitutes the core of the one multi-core optical fiber.

  According to this, since the first, second, and third optical fiber cores are similarly subjected to disturbances such as vibration and impact, the change in the amount of incident light and reflected light (S-polarized component, P-polarized component) due to the disturbance is also the same. Become. Therefore, a more accurate S / N ratio can be detected.

  In the optical probe sensor device, it is preferable that a maximum Kerr rotation angle of the magnetic body is 1 ° or less. For example, the magnetic material is an Fe (iron) -Si (silicon) -based alloy (maximum Kerr rotation angle 0.04 °) or an Al (aluminum) -Ni (nickel) -Co (cobalt) -based alloy (maximum Kerr rotation angle). 0.03 °) is preferable. Even when a magnetic material having a small maximum Kerr rotation angle such as these magnetic materials is used, the detection accuracy of the optical probe sensor device can be increased.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows. An optical probe sensor device with high detection accuracy can be provided.

It is the schematic of the structure of the optical probe sensor apparatus in one Embodiment of this invention. It is the schematic of the optical system of the optical probe sensor apparatus shown in FIG. It is a figure explaining the detection principle of the optical probe sensor apparatus shown in FIG. It is a figure explaining the detection principle of the optical probe sensor apparatus shown in FIG. It is a figure explaining the detection principle of the optical probe sensor apparatus shown in FIG. It is a figure explaining the detection principle of the optical probe sensor apparatus shown in FIG. It is a figure explaining the detection principle of the optical probe sensor apparatus shown in FIG. It is a block diagram of the signal processing part of the optical probe sensor apparatus shown in FIG.

  In the following embodiments of the present invention, the description will be divided into a plurality of sections when necessary. However, in principle, they are not irrelevant to each other, and one of them is related to some or all of the other modifications, details, etc. It is in. For this reason, the same code | symbol is attached | subjected to the member which has the same function in all the figures, and the repeated description is abbreviate | omitted.

  In addition, the number of components (including the number, numerical value, quantity, range, etc.) is limited to that specific number unless otherwise specified or in principle limited to a specific number in principle. It may be more than a specific number or less. In addition, when referring to the shape of a component, etc., it shall include substantially the same or similar to the shape, etc., unless explicitly stated or in principle otherwise considered otherwise .

  In the embodiment of the present invention, a case where the present invention is applied to an optical probe current sensor among optical probe sensor devices (hereinafter simply referred to as sensor devices) will be described. FIG. 1 is a schematic diagram of the configuration of the sensor device 10. The sensor device 10 includes a sensor unit 20, a light propagation unit 40, and a main body unit 50.

  The sensor unit 20 is an optical probe that detects a current to be measured (current in the cable 100 indicated by a cross-sectional diameter in FIG. 1) with light, and a magnetic body 21 (for example, a film shape) that generates an in-plane magnetic Kerr effect. Magnetic material). The sensor unit 20 includes a polarizer 22, mirror units 23, 24, and 25, a wave plate 26, and a polarizer 27 as optical components.

  As the polarizer 22, for example, a Glan-Thompson polarizing prism can be applied. In addition, as the mirror portions 23, 24, and 25, those in which a highly reflective metal such as Ag (silver) is coated on the total reflection surface or flat plate surface of the prism can be applied. Further, as the wavelength plate 26, for example, a 1 / 4λ plate or a 1 / 2λ plate can be applied. As the polarizer 27, for example, a PBS or a grand laser prism can be applied.

  The light propagation unit 40 is for propagating light (optical signal), and includes three optical fiber cores (hereinafter simply referred to as cores) 41, 42, and 43. As the light propagation unit 40, for example, a multi-core optical fiber can be applied. At this time, the cores 41, 42, and 43 constitute a core of one multi-core optical fiber.

  The main body 50 receives light reflected from the surface of the magnetic body 21 via the cores 42 and 43, and a light emitting section 51 that emits light that is incident on the surface of the magnetic body 21 via the core 41. A light receiving unit 52 that converts the signal into an electrical signal and a signal processing unit 60 that processes the detection signal. For clarity of explanation, in FIG. 1, an optical path from the light from the light emitting unit 51 reflected by the magnetic body 21 to the light received by the light receiving unit 52 is indicated by an arrow.

  As the light emitting unit 51, for example, a semiconductor laser can be applied. Further, as the light receiving unit 52, photodiodes 52S and 52P (light receiving elements) corresponding to the cores 42 and 43, respectively, can be applied. Further, as the signal processing unit 60, for example, a mounting board (signal processing device) on which various ICs (Integrated Circuits) are mounted can be applied in order to configure a signal processing circuit. In the present embodiment, the photodiodes 52S and 52P are mounted on the mounting board constituting the signal processing unit 60.

  FIG. 2 is a schematic diagram in which the mirror units 23, 24, and 25 in FIG. 1 are omitted in order to clarify the optical system (optical path) of the sensor device 10.

  First, the incident light 101 from the light emitting unit 51 propagates through the core 41 of the light propagation unit 40 and reaches the sensor unit 20. Next, in the sensor unit 20, the incident light 101 is linearly polarized by the polarizer 22 and is incident on the surface of the magnetic body 21. The reflected light 102 (linearly polarized light) reflected from the surface of the magnetic body 21 is converted into circularly polarized light by the wave plate 26. Then, the reflected light 102 (circularly polarized light) is branched by the polarizer 27 into S-polarized component light 102S and P-polarized component light 102P and emitted to the outside of the sensor unit 20.

  The light 102S from the sensor unit 20 propagates through the core 42 of the light propagation unit 40, reaches the photodiode 52S of the light receiving unit 52, and is received and converted into an electrical signal. That is, the photodiode 52S receives the S-polarized component light 102S propagating through the core 42 and converts it into an electrical signal. The light 102P from the sensor unit 20 propagates through the core 43 of the light propagation unit 40, reaches the photodiode 52P of the light receiving unit 52, and is received and converted into an electrical signal. That is, the photodiode 52P receives the P-polarized component light 102P propagating through the core 43 and converts it into an electrical signal. Thus, in the sensor device 10, the reflected light 102 from the magnetic body 21 that causes the in-plane magnetic Kerr effect is branched into the S-polarized component and the P-polarized component, and the light 102S (optical signal) of the S-polarized component is used as an electrical signal. , P-polarized light component 102P (optical signal) is detected as an electrical signal.

  Here, the principle of the sensor device 10 that detects the current to be measured with light will be described. 3 and 4, the magnetic body 21 is disposed in close contact with or close to the cable 100 through which the current to be measured flows, and the incident light 101 incident on the surface of the magnetic body 21 and the reflected light 102 reflected therefrom are also combined. Show. Further, FIG. 5 shows the light amount Lr of the reflected light 102, the light amount Ls of the S-polarized component light 102S, the light amount Lp of the P-polarized component light 102P, and the Kerr rotation angle θk.

  First, the state of the sensor device 10 shown in FIG. 3 is a standard state in which no current flows through the cable 100 and no current magnetic field H (applied magnetic field H) is generated. In FIG. 3, the magnetic body 21 is arranged so that the extending direction of the cable 100 and the direction of the magnetic moment 21M of the magnetic body 21 that generates the in-plane magnetic Kerr effect coincide with each other. When linearly polarized incident light 101 is incident on the surface of the magnetic body 21 in such a state, the reflected light 102 reflected from the magnetic body 21 remains linearly polarized due to the lateral Kerr effect.

  Next, the state of the sensor device 10 illustrated in FIG. 4 is a state in which a current I flows through the cable 100 and a current magnetic field H is generated by the current I. The magnitude of the current magnetic field H varies depending on the amount of the current I. When the linearly polarized incident light 101 is incident on the surface of the magnetic body 21 in such a state, the reflected light 102 reflected from the magnetic body 21 becomes linearly polarized light that has become an extremely small amount of elliptically polarized light due to the longitudinal Kerr effect. In FIG. 4, the reflected light 102 is shown as elliptically polarized light for the sake of clarity.

  When the magnitude of the current magnetic field H changes, the magnetic moment 21M rotates by changing to the change. At this time, the reflected light 102 reflected from the surface of the magnetic body 21 is changed in proportion to the rotational angle of the magnetic moment 21M due to the longitudinal Kerr effect. For this reason, the light amount Lr (intensity) of the reflected light 102 changes, and the light amount Ls of the light 102S that is the S-polarized component and the light amount Lp of the light 102P of the P-polarized component also change.

  FIG. 6 is a graph showing changes in the light quantity Ls of the light 102S and the light quantity Lp of the light 102P with respect to the applied magnetic field H. When the applied magnetic field H is applied from the minus direction to the plus direction after the applied magnetic field H is zero (the applied magnetic field H is changed in direction), the light quantity Ls (see FIG. 5) is plus. The size of the direction gradually decreases, becomes negative, and gradually increases in the negative direction. On the other hand, the light amount Lp (see FIG. 5) is applied in the positive direction after the applied magnetic field H from the minus direction through the time when the applied magnetic field H is zero. It becomes gradually larger in the positive direction.

  FIG. 7 is a graph showing a change in the difference (Ls−Lp) between the light amount Ls and the light amount Lp with respect to the applied magnetic field H obtained with reference to FIG. From this, Ls-Lp with respect to the applied magnetic field H changes so as to draw a magnetization curve (indicated by a wavy line in FIG. 7). Therefore, the sensor device 10 can detect (measure) the magnitude of the applied magnetic field H and further the magnitude of the current I by obtaining the light quantity Ls and the light quantity Lp.

  By the way, in this embodiment, the maximum Kerr rotation angle θkmax. The magnetic body 21 of 1 ° or less is applied. Therefore, as is apparent from FIG. 5, the light quantity Ls of the S-polarized component and the light quantity Lp of the P-polarized component of the reflected light 102 can be approximated as shown in the following equations (1) and (2). .

  Here, when the reflected light 102 passes through the wave plate 26 (¼λ plate or 1 / 2λ plate), the linearly polarized light becomes circularly polarized light. In addition, when the reflected light 102 is a very small amount of elliptically polarized light, it becomes elliptically polarized light whose principal axis is slightly inclined from a perfect circle.

  The light quantity Ls ′ of the light 102S of the S-polarized component and the light quantity Lp ′ of the light 102P of the P-polarized component when passing through the wave plate 26 can be expressed by the following equations (3) and (4).

  Here, the light 102S propagates through the core 42 as an optical signal, but it is also conceivable that the core 42 is subject to disturbances such as vibration and impact. When the change in the light quantity Ls ′ of the light 102S due to the influence of the disturbance is expressed using the disturbance coefficient α, αLs ′ is obtained. Similarly, if the change in the light amount Lp ′ of the light 102P due to the influence of disturbance such as vibration or impact on the core 43 is expressed using the disturbance coefficient β, βLp ′ is obtained.

When an Fe—Si alloy is applied as the magnetic body 20, the maximum Kerr rotation angle θkmax. Is 0.04 °, and when the light quantity Ls = 100, Lp = tan θk from FIG. 5, the light quantity Lp falls within the following range.
0 <Lp <0.07 (0 <θk <π / 2)

Further, when an Al—Ni—Co alloy is applied as the magnetic body 20, the maximum Kerr rotation angle θkmax. Is 0.03 °, and if the light quantity Ls = 100, the light quantity Lp is in the following range.
0 <Lp <0.05 (0 <θk <π / 2)

  As described above, when the magnetic body 20 having the maximum Kerr rotation angle θk of 1 ° or less is used, the light amount Lp is extremely small with respect to the light amount Ls, that is, the light amount αLp ′ is extremely small with respect to the light amount βLs ′. It turns out that the influence of the disturbance on 'will become large.

  Therefore, in the present embodiment, the signal processing unit 60 does not simply input the electric signal Es corresponding to the light amount βLs ′ and the electric signal Ep corresponding to the light amount αLp ′ to the differential amplifier circuit. As will be described below, the circuit configuration can cancel disturbance.

  FIG. 8 is a block diagram of the signal processing unit 60 of the sensor device 10. The signal processing unit 60 includes photodiodes 52S and 52P, amplifiers 61 and 62, division circuits 63 and 64 (analog IC), and a differential amplifier circuit 65. The electric signal Es converted from the light 102S (light quantity βLs ′) by the photodiode 52S is amplified by the amplifier 61. In addition, the electric signal Ep converted from the light 102P (light quantity αLp ′) by the photodiode 52P is amplified by the amplifier 62.

  The amplified electrical signals Es and Ep are input to the minus side of the differential amplifier circuit 65 as an output value of the division circuit 63 that divides the electrical signal Es by the electrical signal Ep. The amplified electrical signals Es and Ep are input to the plus side of the differential amplifier circuit 65 as an output value of the division circuit 64 that divides the electrical signal Ep by the electrical signal Es. Then, the output value of the differential amplifier circuit 65 is obtained. This output value can be expressed as the following equation (5). In equations (5) and (6), in order to clarify the effect of the sensor device 10 that detects a change in current by a change in light, the light amounts βLs ′ and αLp ′ are used instead of the electrical signals Es and Ep. Used.

  According to this, even if an external force is applied to the cores 42 and 43 to change the light amount βLs ′ and the light amount αLp ′, the light amount changes (disturbance coefficients α and β) can be reduced by the divider circuits 63 and 64. . Therefore, the detection accuracy (for example, S / N ratio) of the sensor device 10 can be increased.

  Moreover, in this embodiment, the sensor apparatus 10 applies one multi-core fiber to the light propagation part 40, and the cores 42 and 43 comprise the core of the one multi-core optical fiber.

  According to this, since the cores 42 and 43 are similarly subjected to disturbances such as vibrations and shocks, the changes in the light quantity βLs ′ and the light quantity αLp ′ due to the disturbances are also the same. That is, α = β. Therefore, the mutual light quantity change (noise) can be canceled (reduced) by the divider circuits 63 and 64, and the detection accuracy (for example, S / N ratio) of the sensor device 10 can be further increased. If α = β, the equation (5) can be expressed as the following equation (6) using the equations (3) and (4).

  When α = β using a multi-core fiber, the electrical signal Es corresponding to the light amount βLs ′ and the electrical signal Ep corresponding to the light amount αLp ′ are simply input to the differential amplifier circuit without using the divider circuit, The output corresponds to -√2θk. On the other hand, when the divider circuits 63 and 64 are used and the output is input to the differential amplifier 65, the output is −4θk, and an S / N ratio improvement of 2√2 times is expected.

  Moreover, in this embodiment, the sensor apparatus 10 is provided with the core 41 which connects the light emission part 51 and the sensor part 20, and the core 41 comprises the core of one multi-core optical fiber.

  According to this, since the cores 41, 42, 43 are similarly subjected to disturbances such as vibration and impact, the amount of incident light 101 due to the disturbance, the amount Ls of the S-polarized component of the reflected light 102, and the P-polarized component of the reflected light 102 The change in the amount of light Lp is also the same. Therefore, the detection accuracy (for example, S / N ratio) of the sensor device 10 can be further increased.

  Such a sensor device 10 is used, for example, in order to accurately detect a current referred to in speed control or torque control in an electric vehicle or a hybrid vehicle. Specifically, in the sensor device 10 installed in an engine room such as an electric vehicle, the sensor unit 20 is routed from the main body unit 50 by the light propagation unit 40 to detect a current in the cable 100 at a predetermined location. be able to.

  Although the present invention has been specifically described above based on the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments and can be variously modified without departing from the gist thereof.

  In the above-described embodiment, the case where one multi-core fiber configured by the first and second optical fiber cores connecting the sensor unit and the light receiving unit is used has been described. Not limited to this, the first and second optical fiber cores may be configured as separate single-core optical fibers. In this case, the disturbance coefficients α and β are in the relationship of α ≠ β, but the detection accuracy of the optical probe sensor device is improved by reducing the mutual light quantity change (noise) by the first and second divider circuits. Can do.

  In the embodiment, the case where the third optical fiber core that connects the light emitting unit and the sensor unit is used has been described. Not only this but the structure which attaches a light emission part directly to a sensor part, without using a 3rd optical fiber core may be sufficient. In this case, the detection accuracy of the optical probe sensor device can be improved by eliminating the influence of disturbance caused by the use of the third optical fiber core.

  As another embodiment, the sensor unit may be configured so that linearly polarized incident light is made circularly polarized and then incident on the surface of the magnetic body to obtain circularly polarized reflected light. In addition, the optical axis adjustment can be easily performed in the configuration in which linearly polarized incident light is incident on the surface of the magnetic material and the reflected light is circularly polarized as in the embodiment.

  The optical probe sensor device of the present invention can be used as a current detection sensor or a magnetic field detection sensor for any electronic / electrical equipment, and particularly in a poor electromagnetic noise environment or an environment affected by vibration or impact. It is widely used.

DESCRIPTION OF SYMBOLS 10 Optical probe sensor apparatus 20 Sensor part 21 Magnetic body 21M Magnetic moment 22 Polarizers 23, 24, 25 Mirror part 26 Wave plate 27 Polarizer 40 Light propagation part 41, 42, 43 Optical fiber core 50 Main part 51 Light emission part 52 Light reception Unit 52P, 52S photodiode 60 signal processing unit 61, 62 amplifier 63, 64 division circuit 100 cable 101 incident light 102 reflected light I current H applied magnetic field

Claims (6)

A light emitting part and a light receiving part;
A sensor unit optically connected between the light emitting unit and the light receiving unit;
First and second optical fiber cores connecting the sensor unit and the light receiving unit;
A signal processing unit electrically connected to the light receiving unit,
The sensor unit includes a magnetic body that generates an in-plane magnetic Kerr effect, and a polarizer that branches reflected light from the magnetic body into an S-polarized component and a P-polarized component,
The first optical fiber core propagates light of an S-polarized component from the polarizer as an optical signal,
The second optical fiber core propagates light of a P-polarized component from the polarizer as an optical signal,
The light receiving unit converts the optical signals of the first and second optical fiber cores into first and second electrical signals,
The signal processing unit includes: a first divider circuit that divides the second electric signal by the first electric signal; a second divider circuit that divides the first electric signal by the second electric signal; And a differential amplifier circuit that differentially amplifies and outputs respective output values of the second divider circuit. The optical probe sensor device according to claim 1,
With one multi-core fiber,
The optical probe sensor device, wherein the first and second optical fiber cores constitute a core of the one multi-core optical fiber. The optical probe sensor device according to claim 2,
A third optical fiber core connecting the light emitting unit and the sensor unit;
The optical probe sensor device, wherein the third optical fiber core constitutes a core of the one multi-core optical fiber. In the optical probe sensor device according to any one of claims 1 to 3,
An optical probe sensor device, wherein the maximum Kerr rotation angle of the magnetic material is 1 ° or less. In the optical probe sensor device according to any one of claims 1 to 4,
The optical probe sensor device, wherein the magnetic body is an Fe—Si alloy. In the optical probe sensor device according to any one of claims 1 to 4,
The optical probe sensor device, wherein the magnetic body is an Al—Ni—Co alloy.

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