JP2002236159A - Optical fiber magnetic sensor - Google Patents

Abstract

(57) [Problem] To provide an optical fiber magnetic sensor capable of performing stable magnetic detection without being affected by a change in characteristics of a sensor. SOLUTION: A magnetic detecting element 15 which takes in magnetic information detected in an optical signal transmitted through an optical fiber, and a reference magnetic field applying device 1 which applies a reference magnetic field to the magnetic detecting element 15
And a calibration means for separating a reference magnetic field component and a detection target magnetic component from the magnetic information captured by the magnetic detection element 15 and calibrating the detection target magnetic component with the reference magnetic field component to obtain detection target magnetic information. 101.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber magnetic sensor for detecting magnetism (magnetic field) by using an optical fiber and a magnetic detecting element. The present invention relates to an optical fiber magnetic sensor capable of performing stable magnetic detection without receiving it.

[0002]

2. Description of the Related Art A conventional optical fiber magnetic sensor obtains magnetic information to be detected, such as geomagnetism, by a magnetic detecting element inserted into an optical fiber. For example, as shown in FIG. It includes a Mach-Zehnder interferometer in which the magnetic detection element 3 is incorporated in an arm branched and coupled by 2, 5 and a photodetector 6 for converting an optical output of the Mach-Zehnder interferometer into an electric signal.

Light emitted from a light source 1 is split by a coupler 2 and passes through two arms to be multiplexed by a coupler 5. The magnetic detecting element 3 is inserted into one of the two arms,
The magnetic sensing element 3 converts a change in the sensed magnetism into a change in the optical path.

The modulator 4, the modulator 7, the oscillator 10, and the synchronous detector 11 perform control to keep the optical path difference between the two arms of the Mach-Zehnder interferometer constant at all times. That is, the oscillator 1
The AC signal from 0 is applied to the modulator 4 of one arm, and the modulated light is multiplexed by the coupler 5 with the light of the other arm. At this time, interference occurs according to the optical path difference between the two arms, and the light having the interference is converted into an electric signal by the light receiver 6. A modulation component is extracted from the electric signal by the synchronous detector 11, and a signal is added to the modulator 7 so that the modulation component output becomes constant. In this way, control is performed so that the optical path difference between the two arms of the Mach-Zehnder interferometer is always constant.

On the other hand, an AC signal having a frequency different from that described above is applied to the magnetic detecting element 3 by an oscillator 8. Magnetic information is taken into this frequency component. When the light having the frequency component in which the magnetic information is captured is combined with the light of the other arm that does not have the frequency component, interference occurs in accordance with the frequency component. In step 6, it is converted into an electric signal. A magnetic change component (magnetic information) is extracted from the electric signal by the synchronous detector 9,
It is output as a magnetic signal.

[0006]

In the prior art, the control of the optical path difference between the two arms of the Mach-Zehnder interferometer is controlled to be constant, but the output of the light source 1 and the interference length change, The magnetic signal output fluctuated even if the same magnetic field was detected due to the fluctuation of the loss of the magnetic field, the temperature characteristic of the magnetic detecting element 3 and the aging.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and to provide an optical fiber magnetic sensor capable of performing stable magnetic detection without being affected by a change in characteristics of the sensor.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a magnetic detecting element for capturing magnetic information detected in an optical signal transmitted through an optical fiber, and applying a reference magnetic field to the magnetic detecting element. A reference magnetic field applying device, and a reference magnetic field component and a detection target magnetic component are separated from the magnetic information captured by the magnetic detection element, and the detection target magnetic component is calibrated with the reference magnetic field component and the detection target magnetic information and Calibration means for performing the calibration.

[0009] The magnetic detecting element may be incorporated in a Mach-Zehnder interferometer.

[0010] The reference magnetic field applied by the reference magnetic field applying device may be an alternating magnetic field.

[0011]

An embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

As shown in FIG. 1, an optical fiber magnetic sensor according to the present invention has a magnetic detecting element 15 for taking in magnetic information detected in an optical signal transmitted through an optical fiber. A reference magnetic field application device (reference magnetic field generation device) 14 for applying a magnetic field, and a reference magnetic field component and a detection target magnetic component are separated from the magnetic information captured by the magnetic detection element 15, and the detection target magnetic component is separated from the reference magnetic field component. Calibrating means 101 for calibrating by means of magnetic information to be detected
And

More specifically, the optical fiber magnetic sensor comprises a light source 12, a coupler 13 forming one end of a Mach-Zehnder interferometer, a magnetic detecting element 15 inserted into one of two arms branched by the coupler 13, and Magnetic detection element 1
The modulator 16 provided on the arm into which the antenna 5 is inserted, the modulator 19 provided on the other arm, the coupler 17 forming the opposite end of the Mach-Zehnder interferometer, and the light that has caused interference in the Mach-Zehnder interferometer Light receiver 1 for converting to electric signal
8, an oscillator 20 for applying an AC signal of a predetermined frequency for capturing magnetic information to the magnetic detection element 15,
A synchronous detector 21 for synchronously detecting an electric signal from the detector 8 to extract magnetic information, an oscillator 22 for applying an AC signal to the modulator 16, and a modulator for synchronously detecting an electric signal from the optical receiver 18 and outputting the modulator. 19 and a reference magnetic field applying device 14 provided near the magnetic detecting element 15.
And an oscillator 24 for supplying an AC current for generating an AC magnetic field to the reference magnetic field applying device 14, and magnetic information extracted by the synchronous detector 21 is synchronously detected by an AC signal of the oscillator 24 to generate a reference magnetic field component (amplitude). A synchronous detector 25 to be separated; a phase shifter 26 for matching the phase of the AC signal of the oscillator 24 with the phase of the same frequency component as the AC signal of the oscillator 24 included in the output signal of the synchronous detector 21; A multiplier 27 for reproducing the reference magnetic field component (AC signal) by multiplying the reference magnetic field component (amplitude) by the obtained AC signal, and subtracting the product signal from the magnetic information extracted by the synchronous detector 21 to detect the target magnetic field It comprises a subtraction means 102 for separating the components and a divider 28 for calibrating the magnetic component to be detected by dividing the difference signal by a reference magnetic field component (amplitude).

The operation of the optical fiber magnetic sensor shown in FIG. 1 will be described. The description of the same operation as in the related art is omitted, but the synchronous detector 21 outputs the magnetic information sensed by the magnetic detection element 15. The magnetic detecting element 15 is provided with a reference magnetic field applying device 1 for applying external magnetism (magnetic field) to be detected originally.
Since the reference magnetic field generated by No. 4 is superimposed, the output of the synchronous detector 21 also superimposes the reference magnetic field component on the magnetic component to be detected.

The output of the synchronous detector 21 is output to the synchronous detector 2
5, when the synchronous detection is performed by the AC signal of the oscillator 24, the amplitude value of the reference magnetic field component is obtained. This amplitude value corresponds to the light source 12
If the output / interference length changes, the loss of the optical system changes, the temperature characteristics of the magnetic detection element 15 and the secular change occur, the change occurs in proportion to the magnetic component to be detected originally intended to be detected.

In order to remove this frequency component (reference magnetic field component) from the magnetic information signal output of the synchronous detector 21 including an AC reference magnetic field component, first, a phase shifter 26 outputs a signal from the oscillator 24. Synchronous detector 2
One signal output is made to coincide with the phase of the same frequency component as the AC signal of the oscillator 24. Further, the AC signal from the phase shifter 26 is multiplied by the reference magnetic field component amplitude value from the synchronous detector 25 by the multiplier 27 to reproduce an AC signal to be subtracted from the signal output of the synchronous detector 21.

From the signal output of the synchronous detector 21, the multiplier 2
The reference magnetic field component reproduced in step 7 is subtracted, and the difference signal is separated as a magnetic component to be detected. When the divider 28 divides the detection target magnetic component by the reference magnetic field component amplitude value from the synchronous detector 25, magnetic information of the detection target in which the detection target magnetic component is calibrated is obtained.

Next, a specific embodiment will be described with reference to FIG.

In the optical fiber magnetic sensor shown in FIG.
A metal-coated fiber coil 34 is used as a magnetic detecting element. The metal film fiber coil 31 for the reference optical path is for reducing the optical path difference between the two arms of the Mach-Zehnder interferometer. Further, a reference magnetic field generating coil 37 is used as a reference magnetic field applying device.

Light source 29, coupler 30, modulator 32, coupler 33, modulator 35, light receiver 36, oscillator 38, oscillator 39, oscillator 40, synchronous detector 41, synchronous detector 42,
Synchronous detector 43, phase shifter 44, multiplier 45, subtraction means 1
03 and the divider 46 are all the same as those described with reference to FIG. 1 and have the same connection relationship.

The oscillator 38 is connected to the metal-coated fiber coil 34.
Is supplied with an alternating current. At this time, when an external magnetic field (a detection target) is generated and the external magnetic field is applied to the metal-coated fiber coil 34, the metal-coated fiber coil 34 expands or contracts due to electromagnetic force, and the metal-coated fiber coil 34 The length changes, and the change in the magnetic field translates into fiber stretching.

A constant alternating current from an oscillator 39 is applied to the reference magnetic field generating coil 37 to
4 is given a constant alternating magnetic field.

As described above, when multiplexing is performed by the coupler 33, interference occurs according to the optical path difference between the two arms, and the light having the interference is converted into an electric signal by the light receiver 36. From this electric signal, the synchronous detector 41 can extract magnetic information sensed by the metal-coated fiber coil 34. Then, the reference magnetic field component and the detection target magnetic component are separated from the magnetic information, and the detection target magnetic component is calibrated with the reference magnetic field component to output the detection target magnetic information (magnetic signal).

Next, a configuration modified from the embodiment of FIG. 2 will be described.

The optical fiber magnetic sensor shown in FIG. 3 includes a light source 47, a coupler 48, a metal film fiber coil 50, a reference magnetic field generating coil 53, a modulator 51, a coupler 49, a light receiver 52, an oscillator 54, an oscillator 55, and an oscillator. 56, synchronous detector 58, adder 57, synchronous detector 59, synchronous detector 6
0, a phase shifter 61, a multiplier 62, a subtraction means 104, and a divider 63. Members in the same arrangement as in FIG. 2 are the same members as those in FIG. This optical fiber magnetic sensor removes the metal film fiber coil 31 for the reference optical path and the modulator 32 from the optical fiber magnetic sensor of FIG. 2, adds the signal output of the synchronous detector 60 to the AC signal of the oscillator 56, and modulates the modulator 51. Is provided with an adder 57 to be applied to.

The reference signal for adjusting the optical path difference supplied from the oscillator 56 and the control signal for stabilizing the optical path difference supplied from the synchronous detector 60 are added by an adder 57, and the sum is added. The modulator 51 is driven by this signal.

With this configuration, the number of components of the optical system can be reduced, the sensor can be simplified, and the cost can be reduced.

In the above embodiment, the optical fiber magnetic sensor is constituted by using the magnetic detecting element composed of the metal-coated fiber coil, but other types of sensors are also used.
The present invention can achieve the same effect.

[0029]

The present invention exhibits the following excellent effects.

(1) Even if the sensitivity of the magnetic detection element changes due to the influence of temperature, or the output or interference value of the light source changes, a stable magnetic signal output can be obtained by calibrating with the reference magnetic field component. can get. Therefore, the operating temperature range of the sensor can be expanded, and the range of application can be expanded.

(2) Since a change in sensor characteristics due to aging can be calibrated, the life of the product is prolonged.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical fiber magnetic sensor according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of an optical fiber magnetic sensor according to another embodiment of the present invention.

FIG. 3 is a configuration diagram of an optical fiber magnetic sensor showing another embodiment of the present invention.

FIG. 4 is a configuration diagram of a conventional optical fiber magnetic sensor.

[Explanation of symbols]

14, 37, 53 Reference magnetic field applying device (Reference magnetic field generating device) 15, 31, 34, 50 Magnetic detecting element 101, 103, 104 Calibration means

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yukio Ikeda 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Within the Opto-System Research Laboratory, Hitachi Cable, Ltd. (72) Inventor Shuichi Sunahara 1 Toyota-cho, Toyota-shi, Aichi Prefecture Address Toyota Motor Corporation F term (reference) 2G017 AD12 BA03 BA05 BA11 BA13 2G025 AA08 AB10

Claims (3)

[Claims] 1. A magnetic detecting element for capturing magnetic information detected in an optical signal transmitted through an optical fiber, a reference magnetic field applying device for applying a reference magnetic field to the magnetic detecting element, and a magnetic field captured by the magnetic detecting element. An optical fiber magnet comprising: a calibration unit that separates a reference magnetic field component and a detection target magnetic component from information, and calibrates the detection target magnetic component with the reference magnetic field component to obtain detection target magnetic information. Sensor. 2. The optical fiber magnetic sensor according to claim 1, wherein said magnetic detecting element is incorporated in a Mach-Zehnder interferometer. 3. The optical fiber magnetic sensor according to claim 1, wherein the reference magnetic field applied by the reference magnetic field applying device is an alternating magnetic field.