JPH07209396A - Magnetic field sensor - Google Patents

Abstract

PURPOSE:To obtain a magnetic field sensor of which a sensor part has a reduced number of components and of which size can be made small in a large degree and also sensitivity high. CONSTITUTION:The magnetic sensor is equipped with a light source 1, a sensor part 7 having a medium 8 which is so set that two light waves generated from the light source 1 and propagated in reverse directions to each other are transmitted there- through and has a magnetooptical effect, a directional coupler 2 which generates the two light waves by making an emission light from the light source 1 branch and makes the two light waves transmitted through the medium 8 interfere with each other and a photodetector 16 detecting an emission light of the directional coupler 2. A phase shift or a change in a state of polarization to which the light waves are subjected in the medium 8 when a magnetic field is impressed is utilized. Since the light waves propagated through the magnetooptical medium 8 in reverse directions to each other are subjected to the phase shift or conversion of polarization in reverse directions to each other, in other words, an interference output changes in accordance with the phase shift or the change in polarization when the light waves are joined and made to interfere with each other. The strength of the magnetic field is detected from the output.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic field sensor for measuring the strength of a magnetic field generated by a magnetic field component of an electromagnetic wave or a current.

[0002]

2. Description of the Related Art Measurement and transmission of measurement information using light waves are less susceptible to interference due to the influence of electromagnetic induction than other general electric measuring devices, and are also electrically insulated, so they are widely used. In principle, high-precision measurement is possible.

Conventionally, the measurement of the current flowing through an electric wire has been performed by using
Sensors such as those shown in have been developed. This is to measure the strength of the magnetic field generated by the current by utilizing the magneto-optical effect. To be more specific with reference to FIG. 5, light emitted from the light source 1 including a semiconductor laser or a light emitting diode is coupled to the input optical fiber 51 and sent to the sensor unit 50. In the sensor unit 50, the light emitted from the optical fiber 51 becomes parallel light by the lens 11 and becomes linearly polarized light by the polarizer 12, and garnet crystal or BGO (bismuth
It transmits through the magneto-optical medium 13 such as germanium oxide or Bi ₁₂ Ge ₂₀ ) crystal. This transmitted light is taken out by the analyzer 14 only for a specific polarization component, is coupled to the output optical fiber 52 by the lens 15, and is converted into an electric signal by the photodetector 16. In the magneto-optical medium 13, the polarization plane rotates according to the strength of the magnetic field due to the magneto-optical effect (Faraday effect), so the electric output according to the strength of the magnetic field, that is, the current flowing through the electric wire placed near the sensor. Is obtained.

[0004]

However, since the conventional magnetic field sensor shown in FIG. 5 has a large number of constituent parts of the sensor section, the structure is complicated and it is difficult to miniaturize it. Therefore, it is desirable to reduce the number of parts in order to achieve high reliability. Moreover, it cannot be said that the sensitivity is sufficient.

Therefore, a technical object of the present invention is to provide a magnetic field sensor which has a small number of parts in a sensor portion, can be significantly downsized, and can have high sensitivity.

[0006]

According to the present invention, a sensor unit having a light source and a medium having a magneto-optical effect set so that two light waves generated from the light source and propagating in opposite directions are transmitted. And a directional coupler that splits the light emitted from the light source to generate the two light waves and interferes the two light waves transmitted through the medium, and detects the light emitted from the directional coupler. And a photodetector for the magnetic field sensor.

[0007]

The magnetic field sensor of the present invention utilizes the non-reciprocal propagation characteristic of the magneto-optical medium. Specifically, the phase shift or change in polarization state that the light wave undergoes in the medium when a magnetic field is applied is used. That is, since the light waves propagating in the magneto-optical medium in opposite directions undergo phase shifts or polarization conversions in opposite directions, when they are merged and interfered with each other, the interference output is changed according to the received phase shift or polarization change. Change. However, in this case, it is desirable that the two light waves are emitted from one light source in order to cause interference, and the two propagation optical paths need to be substantially the same in order to eliminate unnecessary fluctuations. is there.

Therefore, according to the present invention, as described above, basically, the sensor section does not need a polarizer or an analyzer, and the structure is simpler than the conventional one. Also, when the sensor unit is composed of an optical waveguide, it can be directly connected to an optical fiber, which enables further miniaturization and higher sensitivity.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a schematic configuration diagram of a magnetic field sensor according to Embodiment 1 of the present invention. A light source 1 including a semiconductor laser or a light emitting diode similar to that shown in FIG.
The light emitted from is incident on the prism type directional coupler 2 formed of the semi-transmissive film 17, is split into the counterclockwise optical wave 3 and the clockwise optical wave 4, and is coupled to the optical fibers 5 and 6, respectively. In the sensor section 7, the counterclockwise lightwave 3 is emitted from the optical fiber 5, converted into parallel light by the lens 11, passes through the magneto-optical medium 8 made of YIG garnet crystal, and is coupled to the optical fiber 6 by the lens 15. Similarly, the clockwise light wave 4 passes from the optical fiber 6 through the YIG garnet crystal and is coupled to the optical fiber 5. These light waves return to the directional coupler 2,
Interference on the semi-transmissive film 17 becomes emitted light 18 and the photodetector 1
It is incident on 6. From the photodetector 16, an output corresponding to the strength of the magnetic field applied to the magneto-optical medium 8 is obtained.

(Second Embodiment) FIG. 2 is a schematic configuration diagram of a magnetic field sensor according to a second embodiment of the present invention. A light source 1 including a semiconductor laser or a light emitting diode similar to that shown in FIG.
The light emitted from is incident on a fusion-type directional coupler 22 formed by fusing two optical fibers close to each other, and splits them into a left-handed optical wave 23 and a right-handed optical wave 24, respectively. Guided to 26. In the sensor portion 27, the end faces of the optical fibers 25 and 26 are arranged at a very close distance of about 200 μm or less, and a magneto-optical medium 28 made of garnet crystal or BSO is inserted between both end faces thereof.
Since the distance between the end faces of the optical fiber is small, the counterclockwise optical wave 23 and the clockwise optical wave 24 pass through the magneto-optical medium 28 and are coupled to the optical fibers on the other side with slight loss.
These light waves return to the directional coupler 22, interfere with each other, and their outputs enter the photodetector 16. From the photodetector 16, an output corresponding to the magnetic field strength applied to the magneto-optical medium 28 is obtained. In this embodiment, no lens is required, and the structure is simpler than that of the magnetic field sensor according to the first embodiment. Further, the directional coupler 22 has a small loss because the light wave propagates through the optical fiber as it is, and is stable as an optical system.

(Embodiment 3) FIG. 3 is a schematic configuration diagram of a magnetic field sensor according to Embodiment 3 of the present invention. A light source 1 including a semiconductor laser or a light emitting diode similar to that shown in FIG.
The light emitted from is incident on a fusion-type directional coupler 32 for incident light, which is formed by fusing and adhering two optical fibers to each other, and is split into a left-handed light wave 33 and a right-handed light wave 34, respectively. It is guided to the first and second optical fibers 35 and 36. The sensor unit 37 is a magneto-optical medium YI formed on a GGG (gallium gadolinium garnet) crystal substrate.
The optical waveguide 38 is made of a G (yttrium iron garnet) crystal and has a width of several microns. Optical fibers 35 and 36 are directly coupled to both input and output end faces of the optical waveguide. The basic operation of the magnetic field sensor according to the third embodiment is the same as that of the magnetic field sensors according to the first and second embodiments, but in this third embodiment, another light beam for emitting light is provided between the light source 1 and the directional coupler 32. A fusion-type directional coupler 39 is installed,
The emitted light is guided to the photodetector 16 from there. Further, in order to set the light wave in the optical waveguide 38 to either the TM mode in which the polarization direction is perpendicular to the substrate or the TE mode in which the polarization direction is parallel to the substrate, the optical fibers 35 and 36 are polarization-maintaining optical fibers and the directional couplers 32 and 39 are polarized. A polarizer 40 is inserted between them to remove the excess polarization component. Such a directional coupler 32,
In this embodiment, the bias-like phase difference slightly generated between the counterclockwise light wave 33 and the clockwise light wave 34 is eliminated by adopting a configuration using two 39. The optical waveguide of the third embodiment is, for example, YI formed on a GGG substrate by a liquid phase epitaxial method.
This can be achieved by growing the G crystal to a thickness of several microns and then reducing the film thickness around the optical waveguide by a method such as ion etching. Further, in the third embodiment, since the optical path in the magneto-optical medium can be lengthened by using the sensor portion having the optical waveguide structure, high sensitivity can be obtained.

(Embodiment 4) FIG. 4 is a schematic configuration diagram of a magnetic field sensor according to Embodiment 4 of the present invention. A light source 1 including a semiconductor laser or a light emitting diode similar to that shown in FIG.
The emitted light from the laser passes through the fusion-type directional coupler 39 for outgoing light and is coupled to the sensor substrate 41 by the optical fiber 45. The sensor substrate 41 is composed of an optical waveguide having a width of several microns and made of a YIG (yttrium iron garnet) crystal which is a magneto-optical medium formed on a GGG (gallium gadolinium garnet) crystal substrate similar to that of the third embodiment. The fusion-type directional coupler 3 for incident light.
An optical waveguide 48 for forming a non-reciprocal phase shift due to a magnetic field is formed between the two and the left and right light waves. According to the fourth embodiment, higher sensitivity than that of the third embodiment can be obtained.

In all of the above-mentioned embodiments, an SLD (super luminescent diode) which is less affected by noise due to extra interference can be used as the light source 1 to be used, and between the light waves in both the left and right directions. It is also possible to give an additional phase difference to improve the sensitivity.

[0015]

As described above, according to the present invention, the sensor unit basically does not require a polarizer or an analyzer, and the structure is simpler and smaller than the conventional one. Further, in the present invention,
When the sensor part is composed of an optical waveguide, it can be directly connected to an optical fiber, and it is possible to further reduce the size and increase the sensitivity.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a magnetic field sensor according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a magnetic field sensor according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a schematic configuration of a magnetic field sensor according to a third embodiment of the invention.

FIG. 4 is a diagram showing a schematic configuration of a magnetic field sensor according to Example 4 of the invention.

FIG. 5 is a diagram showing a schematic configuration of a magnetic field sensor according to a conventional example.

[Explanation of symbols]

1 Light Source 2, 22, 32, 39 Directional Coupler 5, 6, 25, 26, 35, 36, 45, 51, 52
Optical fiber 7,27,37 Sensor part 8,13 Magneto-optical medium (YIG garnet crystal) 16 Photodetector 28 Magneto-optical medium 38,48 Optical waveguide

Claims (7)

[Claims] 1. A light source, a sensor unit having a medium having a magneto-optical effect set so that two light waves generated from the light source and propagating in mutually opposite directions are transmitted, and light emitted from the light source is branched. A directional coupler for generating the two light waves and for interfering the two light waves transmitted through the medium, and a photodetector for detecting light emitted from the directional coupler. Characteristic magnetic field sensor. 2. The magnetic field sensor according to claim 1, further comprising an optical fiber connecting between the sensor unit and the directional coupler. 3. The magnetic field sensor according to claim 2, wherein the sensor section is configured by disposing a lens and a magneto-optical medium between two optical fiber end faces. 4. The magnetic field sensor according to claim 2, wherein the sensor unit is configured by inserting a magneto-optical medium between two optical fiber end faces that are close to each other. 5. The magnetic field sensor according to claim 2, wherein the sensor unit is configured by coupling an optical fiber to an end face of an optical waveguide including a magneto-optical medium formed on a substrate. . 6. The magnetic field sensor according to any one of claims 3 to 5, wherein the directional coupler is composed of two optical waveguides or optical fibers that are close to each other. Sensor. 7. The magnetic field sensor according to claim 1, wherein the sensor section and the forward directional coupler are formed on one substrate by an optical waveguide.