JP3107986B2 - Optical fiber magnetic sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an interference type optical fiber magnetic sensor which suppresses noise caused by temperature fluctuation of a sensing unit.

[0002]

2. Description of the Related Art An interference type optical fiber sensor is a sensor for detecting physical quantities such as magnetism and acceleration. Conventionally, as an interference type optical fiber sensor for detecting such magnetism, for example, “Frank Bucholtz, KP Ko”
o, George H Sigel, Jr. , And
Anthony Dutchridge, “Optimi
Zation of the Fiber / Metal
lic Glass Bond in Fiber-o
optic Magnetic Sensors, ”Jo
urnal of Lightwave Techno
logic, vol. LT-3. No. 4, August
1985, pp 814-817 ". In particular, FIG. 1 of this document discloses a schematic configuration diagram of an interference type optical fiber sensor.

After injecting light output from a laser light source into an optical fiber sensor, the light is split into two by an optical coupler, one of which is used as sensing light, the other is used as reference light, and a sensing fiber through which sensing light passes is made of a magnetostrictive material. [In the above document, an amorphous magnetostrictive material (Metallic Gl
ass) is used]. Therefore,
When the magnetic field applied to the magnetostrictive material changes, the magnetostrictive material is distorted, so that the sensing fiber expands and contracts, and the phase of the sensing light passing through the sensing fiber changes. If the sensing light and the reference light that have passed through the sensing fiber interfere with each other and undergo O / E conversion, the phase of the O / E output also changes in proportion to the magnetic field, and this is demodulated to detect the magnetic field.

[0004]

However, in the above-mentioned conventional optical fiber magnetic sensor, even if the temperature of the sensing fiber and the reference fiber fluctuates or the linear expansion of the magnetostrictive material, the phase of the sensing light and the reference light greatly changes. In particular, when the frequency band of the magnetic field to be detected is the same as the frequency band of the temperature fluctuation of the sensor, the phase change due to the magnetic field to be detected is masked by the phase change due to the temperature fluctuation, and the detection may not be possible. Was.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical fiber magnetic sensor which eliminates the above problems, suppresses noise caused by temperature fluctuations of the sensing unit, and has high sensitivity.

[0006]

According to the present invention, there is provided an optical fiber magnetic sensor comprising: a magnet for applying at least a bias magnetic field; and a magnet for applying the bias magnetic field in opposite directions. A closed magnetic circuit having a pair of magnetostrictive materials disposed and a pair of optical fibers of the same length individually bonded to the pair of magnetostrictive materials are provided.

(2) In the optical fiber magnetic sensor according to the above (1), the optical fiber is a coil wound around the magnetostrictive material. (3) In the optical fiber magnetic sensor according to (1), the magnet is a permanent magnet or an electromagnet. (4) In the optical fiber magnetic sensor according to (1), the magnetic circuit includes a magnet, a magnetostrictive material, and a ferromagnetic material.

[0008]

According to the present invention, in an optical fiber magnetic sensor, a magnetic circuit closed by a magnetostrictive material or a magnetostrictive material and a ferromagnetic material is formed, a bias magnetic field is applied by a permanent magnet or an electromagnet, and a magnetic field is applied in a direction opposite to the magnetostrictive material. A structure in which a pair of optical fibers of approximately the same length is bonded to the part where the bias magnet is applied, the push-pull operation is performed only for the magnetic signal, thereby suppressing the influence of disturbance such as temperature fluctuation. it can.

In particular, since the first and second fiber coils are configured so that the fiber lengths thereof are substantially uniform, phase changes due to temperature fluctuations occurring in the two optical fiber coils are in the same direction in the same amount. Become. Therefore, when the phase difference between the lights passing through the two optical fiber coils is detected, the phase change due to the temperature fluctuation is suppressed.

Further, the sensitivity of the magnetic signal is doubled because the phases of the two lights change in opposite directions.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an overall configuration diagram of an optical fiber magnetic sensor according to a first embodiment of the present invention. As shown in this figure, a magnetic circuit 1 is composed of a U-shaped magnetostrictive material 2 and a cubic permanent magnet 3. U-shaped magnetostrictive material 2
Is composed of a magnetostrictive portion 2c common to the first magnetostrictive portion 2a and the second magnetostrictive portion 2b forming two parallel sides. A first magnetostrictive portion 2a forming two parallel sides of the U-shaped magnetostrictive material 2
The first optical fiber coil 4 and the second optical fiber coil 5 are bonded to the first and second magnetostrictive portions 2b, respectively.

Here, the first optical fiber coil 4 and the second
The fiber length of the optical fiber coil 5 is made substantially uniform.
Optical couplers 6 and 7 are connected to both ends of the first and second optical fiber coils 4 and 5, respectively. One optical coupler 6 is an output of the laser light source 11, and the other optical coupler 7 is an O / E converter 12
Connect to the input of. The output of the O / E converter 12 is connected to a passive homodyne demodulator 13.

FIG. 2 is a diagram showing the principle of operation of the magnetic sensing unit of the optical fiber magnetic sensor according to the first embodiment of the present invention. The operation principle of the magnetic sensing unit 10 (see FIG. 1) composed of two optical fiber coils 4 and 5 and two optical couplers 6 and 7 will be described with reference to FIG. When a magnetic circuit is formed by the U-shaped magnetostrictive material 2 and the permanent magnet 3,
A bias magnetic field is applied to the region A of the first magnetostrictive portion 2a and the region B of the second magnetostrictive portion 2b, which form two parallel sides of the U-shaped magnetostrictive material 2, by the permanent magnet 3 in opposite directions. I have.

Therefore, when a magnetic signal is applied to the U-shaped magnetostrictive material 2, one of the magnetic fields in the regions A and B becomes stronger and the other becomes weaker by the same amount. At this time, due to the magnetostriction of the U-shaped magnetostrictive material 2, one of the first optical fiber coil 4 and the second optical fiber coil 5 is distorted in the direction of extension and the other is contracted in the direction of contraction. Then, the light output from the laser light source 11 is split into two by the optical coupler 6, one passes through the first optical fiber coil 4 and the other passes through the second optical fiber coil 5. The phases of the light passing through the two optical fiber coils 4 and 5 change in opposite directions with a magnitude proportional to the magnetic signal due to distortion of the optical fiber. When light passing through the two optical fiber coils 4 and 5 is caused to interfere by the second optical coupler 7 and O / E converted by the O / E converter 12,
The phase difference of the light passing through the two optical fiber coils appears in the phase of the output. By demodulating this phase difference with the passive homodyne demodulator 13, a magnetic signal can be detected.

FIG. 3 is an overall configuration diagram of an optical fiber magnetic sensor according to a second embodiment of the present invention. As shown in this figure, two rod-shaped magnetostrictive materials, that is, a first rod-shaped magnetostrictive material 22a and a second rod-shaped magnetostrictive material 22b are arranged in parallel, and U-shaped permanent magnets 23a and 23b are applied to both ends thereof. Thus, the magnetic circuit 21 is configured. First rod-shaped magnetostrictive material 22
a, the first optical fiber coil 24 is bonded to the second rod-shaped magnetostrictive material 22b, and the second optical fiber coil 25 is bonded to the second rod-shaped magnetostrictive material 22b.

Here, the fiber lengths of the first optical fiber coil 24 and the second optical fiber coil 25 are made substantially uniform. Optical couplers 26 and 27 are connected to both ends of the first and second optical fiber coils 24 and 25, respectively. One optical coupler 26 is the output of the laser light source 31 and the other optical coupler 27 is
Are connected to the input of the O / E converter 32, respectively. O /
A passive homodyne demodulator 33 is connected to the output of the E converter 32.

When magnetic signals are applied to the two rod-shaped magnetostrictive materials 22a and 22b to which bias magnetic fields are applied in opposite directions by the U-shaped permanent magnets 23a and 23b, for example,
The magnetic field in the first rod-shaped magnetostrictive material 22a becomes weaker, and the magnetic field in the second rod-shaped magnetostrictive material 22b becomes stronger by the same amount. That is, the magnetic field in the magnetostrictive material is stronger on one side and weaker on the other side.

Then, due to the magnetostriction of the magnetostrictive material, one of the optical fiber coils is distorted in the direction of extension and the other is distorted in the direction of contraction. Therefore, the light output from the laser light source 31 is divided into two by the optical coupler 26, and one of the lights is divided into the first optical fiber coil 24 and the other is divided into the second optical fiber coil 2.
Pass 5 These two optical fiber coils 24, 2
The phase of the light passing through 5 changes in opposite directions with a magnitude proportional to the magnetic signal due to distortion of the optical fiber. The light that has passed through the two optical fiber coils 24 and 25 is caused to interfere by the second optical coupler 27, and the O / E converter 32 performs O / E conversion.
When the E-conversion is performed, a phase difference between the lights passing through the two optical fiber coils 24 and 25 appears in the output phase. The phase difference is demodulated by a passive homodyne demodulator 33 to detect a magnetic signal.

In the first embodiment, a U-shaped magnetostrictive material and a cubic permanent magnet are provided in the magnetic sensing unit, and in the second embodiment, two bar-shaped magnetostrictive materials and two U-shaped permanent magnets are provided. Although explained, it is not limited to this,
The shape of the magnetostrictive material or the permanent magnet can be appropriately changed, and a magnetic circuit closed with the permanent magnet and the magnetostrictive material or the permanent magnet, the magnetostrictive material and the ferromagnetic material may be formed.

Further, in the first and second embodiments, the optical fiber coil is wound in the longitudinal direction of the magnetostrictive material and is bonded, but the circumference of the magnetostrictive material (in the case of the cylindrical magnetostrictive material, the circular shape is used). It is also possible to use a material wound in the circumferential direction) and bonded. Furthermore, in the above-described first and second embodiments, an example in which the optical fiber coil is bonded to the magnetostrictive material has been described, but the optical fiber may not be wound in a coil shape.

In the above embodiment, the bias magnetic field is applied by the permanent magnet, but an electromagnet may be used instead. Further, in the first and second embodiments, an example has been described in which demodulation is performed by the passive homodyne method. However, other demodulation methods such as an active homodyne method and a heterodyne method may be used.

It should be noted that the present invention is not limited to the above embodiment, and various modifications are possible based on the gist of the present invention, and they are not excluded from the scope of the present invention.

[0023]

As described above, according to the present invention, the following effects can be obtained. In the optical fiber magnetic sensor, a magnetic circuit closed with a magnetostrictive material or a magnetostrictive material and a ferromagnetic material is formed, a bias magnetic field is applied with a permanent magnet or an electromagnet, and a portion where a bias magnet is applied in a direction opposite to the magnetostrictive material, With a structure in which a pair of optical fibers having substantially the same length are bonded, a push-pull operation is performed only on a magnetic signal, so that the influence of disturbance such as temperature fluctuation can be suppressed.

In particular, since the fiber lengths of the first fiber coil and the second fiber coil are configured to be substantially uniform, phase changes due to temperature fluctuations occurring in the two optical fiber coils are generated in the same direction in the same amount. Become. Therefore, when the phase difference between the lights passing through the two optical fiber coils is detected, the phase change due to the temperature fluctuation is suppressed. In addition, the sensitivity is doubled because the phases of the two lights change in opposite directions with respect to the magnetic signal.

Further, since no electric circuit is used in the magnetic sensing unit, it is suitable for magnetic detection under bad conditions such as deep sea. In addition, since a low-loss optical fiber is used for the transmission line between the light source and the sensing unit and between the sensing unit and the O / E converter, it is suitable for magnetic detection in a remote place.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating an operation principle of a magnetic sensing unit of the optical fiber magnetic sensor according to the first embodiment of the present invention.

FIG. 3 is an overall configuration diagram of an optical fiber magnetic sensor according to a second embodiment of the present invention.

[Explanation of symbols]

 1,21 Magnetic circuit 2 U-shaped magnetostrictive material 2a First magnetostrictive portion 2b Second magnetostrictive portion 2c Common magnetostrictive portion 3 Permanent magnet 4,24 First optical fiber coil 5,25 Second optical fiber coil 6, 7, 26, 27 Optical coupler 10 Magnetic sensing unit 11, 31 Laser light source 12, 32 O / E converter 13, 33 Passive homodyne demodulator 22a First rod-shaped magnetostrictive material 22b Second rod-shaped magnetostrictive material 23a, 23b U-shaped permanent magnet

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-156178 (JP, A) JP-A-1-274804 (JP, A) JP-A-64-74477 (JP, A) JP-A-2- 293680 (JP, A) JP-A-9-54148 (JP, A) JP-A-8-248107 (JP, A) JP-A-8-223924 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 33/00-33/18

Claims (4)

(57) [Claims] 1. A closed magnetic circuit comprising: (a) a magnet for applying at least a bias magnetic field; and a pair of magnetostrictive materials arranged so that the bias magnetic field is applied in opposite directions; and (b) the pair of magnetostrictions. An optical fiber magnetic sensor comprising: a pair of equal length optical fibers individually bonded to a material. 2. The optical fiber magnetic sensor according to claim 1, wherein said optical fiber is a coil wound around said magnetostrictive material. 3. The optical fiber magnetic sensor according to claim 1, wherein said magnet is a permanent magnet or an electromagnet. 4. The optical fiber magnetic sensor according to claim 1, wherein the magnetic circuit has a magnet, a magnetostrictive material, and a ferromagnetic material.