JP2000088939A - Detecting apparatus for magneto-optical field - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a detecting apparatus by which light for detection can be transmitted at a long distance by a method wherein a first optical fiber which guides random light from a random light source to a sensor unit is provided and a second optical fiber by which detection light radiated from the sensor unit is guided to a light receiving part is provided. SOLUTION: This apparatus is composed of a sensor unit 1 which is installed in a desired detection point such as a current cable, a transmission line or the like, In addition, it is composed of a high-efficiency random light source 20 which supplies light, for detection, to the sensor unit 1. In addition, it is composed of a light receiving element 3 by which a detection result from the sensor unit 1 is converted into an electric signal, In the high-efficiency random light source 20, a laser light source 2, a polarization cancellation part 5 and a third single-mode optical fiber F3 are provided. Random light which is obtained by the polarization cancellation part 5 comprises a large quantity of light. The sensor unit 1 is coupled to a first single-mode optical fiber F1. In the sensor unit 1, a polarizer 11, a magneto-optical element 12 and an analyzer 13 are provided, Light which is radiated by the analyzer 13 is guided to the light receiving element 3 via a second single-mode optical fiber F2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical magnetic field detecting device used for detecting a current flowing in a power cable or a transmission line.

[0002]

2. Description of the Related Art Conventionally, an optical magnetic field current sensor has been used to detect a current flowing through a power cable or a power transmission line and a state of leakage current from the power cable or the transmission line. The optical magnetic field current sensor utilizes the Faraday effect in which the plane of polarization of light traveling in a specific substance rotates according to the magnitude of a magnetic field in the traveling direction of the light. The specific configuration is a magneto-optical element that generates the Faraday effect, a polarizer and an analyzer respectively disposed on the light incident side and the output side of the magneto-optical element, and a light emitting diode that inputs random light to the polarizer. And a light receiving element that detects light emitted from the polarizer and converts the light into an electric signal. Then, so that the direction of the magnetic field to be detected and the traveling direction of the light match,
A magneto-optical element is arranged.

The light incident on the magneto-optical element from the polarizer changes its polarization direction in accordance with the magnitude of the magnetic field and is incident on the analyzer.
Corresponds to the magnitude of the magnetic field. Therefore, if the magneto-optical element is arranged in accordance with the direction of the magnetic field generated around the power cable according to the so-called right-hand rule, the current flowing through the power cable can be detected.

In order to centrally manage the current detection at a plurality of locations, the magneto-optical current sensor has a sensor unit including a polarizer, a magneto-optical element, and an analyzer arranged at a detection point. , Is arranged on a detection device installed at a location distant from the detection point. That is, a plurality of light emitting diodes and light receiving elements for a plurality of photomagnetic field current sensors are collectively arranged in a detection device, and the detection device and the analyzer and polarizer of each sensor unit are connected by an optical fiber. Have been.

Conventionally, a distributed index (graded index) optical fiber has been used as this optical fiber. It is known that this distributed index optical fiber has a large transmission loss (about 0.6 μm in a wavelength band of 1.3 μm).
dB / km), and long-distance transmission is difficult. On the other hand, the transmission loss of a single mode optical fiber is about 0.3 dB / km, which is about one half of that of a distributed index optical fiber. Is about twice as long.

However, a single mode optical fiber is
Poor coupling efficiency with a general light emitting diode as a light source of random light. Specifically, when the light emitting diode and the single mode optical fiber are coupled, the light intensity becomes extremely low at a maximum of about -35 dBm. Since light-emitting diodes cannot emit strong light due to their properties, the achievable transmission distance is longer when a distributed index optical fiber with relatively good coupling efficiency with the light-emitting diode is used. Become. In other words, in any case, since long-distance transmission is impossible, the distance between the detection point and the detection device cannot be increased.

On the other hand, since the core diameter of the distributed index optical fiber is large (50 μm), various modes of light propagate therein. When external vibration occurs, mode conversion occurs inside the distributed index optical fiber, and the intensity of light emitted from the end face changes accordingly. Since it is difficult to distinguish between a change in light intensity representing a change in the magnetic field corresponding to a change in the current flowing through the power cable and a change in light intensity due to the vibration of the distributed index optical fiber, vibration occurs. In some circumstances, a magneto-optical current sensor using a distributed index optical fiber cannot be used substantially.

Further, the use of the distributed index optical fiber requires time and costly laying work, and furthermore, in order to safely lay the optical fiber along the power cable, a power outage is required. I will be forced. Therefore, as a result, the optical magnetic field current sensor is expensive. On the other hand, for power cables or overhead power lines,
For the purpose of data communication, a single mode optical mode fiber is provided, and if this fiber can be used for an optical magnetic field current sensor, a significant cost reduction can be achieved. The use of existing single-mode optical fibers is no match.

[0009]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned technical problems and to provide an optical magnetic field detecting device which enables long-distance transmission of light for detection.

[0010]

According to the first aspect of the present invention, there is provided a linearly polarized light source for generating linearly polarized light, and a linearly polarized light source generated from the linearly polarized light source. It has a random light source that includes a polarization canceling unit that converts polarized light into random light and emits it, and a magneto-optical element that generates the Faraday effect. A magnetic field detection unit that emits light, a light receiving unit that receives detection light emitted by the magnetic field detection unit and converts the detection light into an electric signal, and a first optical fiber that guides random light from the random light source to the magnetic field detection unit, A second optical fiber for guiding detection light emitted by the magnetic field detection unit to the light receiving unit.

The linearly polarized light source may be a laser light source. According to the above configuration, the linearly polarized light source that easily achieves high output, and the polarization canceling unit that cancels the linearly polarized light of the light from the linearly polarized light source to generate random light, achieve high efficiency randomization. A light source can be realized. Therefore, lengthening the first optical fiber and the second optical fiber,
Since the detection light can be transmitted over a long distance, the detection point where the magnetic field detection unit is to be arranged and the installation point of the linearly polarized light source and the light receiving element can be far apart. As a result, the degree of freedom in installation of the device is increased, and centralized management of magnetic field detection at a plurality of detection points is facilitated.

The invention according to claim 2 is the optical magnetic field detecting device according to claim 1, wherein the first optical fiber and the second optical fiber are single mode optical fibers. The first optical fiber will be coupled to the depolarizer, but the light from the depolarizer will not be diverging light, such as the output light of a light emitting diode. Therefore, even when a small-diameter single mode optical fiber is applied to the first optical fiber, good coupling efficiency can be obtained. Therefore, as the first optical fiber and the second optical fiber,
By using a single-mode optical fiber with a small transmission loss, further long-distance transmission of the light for detection can be realized.

According to a third aspect of the present invention, the random light source further includes a third optical fiber for guiding the linearly polarized light from the linearly polarized light source to the polarization canceller. 3. The optical magnetic field detecting device according to claim 1, wherein the optical magnetic field detecting device is a single mode optical fiber. The beam generated by a linearly polarized light source represented by a laser light source is thin, compared to the divergent light generated by a light emitting diode.
Light collection is much easier. Therefore, the linearly polarized light source and the single mode optical fiber can be coupled with high efficiency. Therefore, according to the present invention, a single-mode optical fiber having a small transmission loss is coupled between the linearly polarized light source and the polarization canceling unit.

When a laser light source and a distributed index optical fiber are coupled, a thin light beam is incident on a large-diameter optical fiber, so that so-called fluctuation noise is generated, and there is a problem in use. Such a problem does not occur if a single mode optical fiber having a small diameter is used. The polarization canceling unit may be arranged at any position between the linearly polarized light source and the magnetic field detecting unit. That is, the third optical fiber may be shortened to shorten the optical transmission distance between the polarization canceling unit and the linearly polarized light source, or the third optical fiber may be elongated and the first optical fiber may be shortened. The fiber may be shortened, and the polarization canceling unit may be arranged near the magnetic detection unit. Of course, the first
Alternatively, both the third optical fiber and the third optical fiber may be lengthened, and the polarization canceling unit may be arranged near the middle between the linearly polarized light source and the magnetic field detecting unit.

Thus, by increasing the length of the first and / or second optical fiber and the third optical fiber,
The light transmission length can be lengthened, and the magneto-optical element and the like and the linearly polarized light source and the light receiving element can be arranged at a long distance. In addition, since a single mode optical fiber cannot theoretically have one mode, if the first to third optical fibers are single mode optical fibers, no mode conversion occurs even if vibration occurs. . Therefore, the magnetic field can be detected well even in an environment with vibration.

In the case where the magneto-optical element is arranged near a power cable or a transmission line, and a current flowing therethrough is indirectly detected by detecting a magnetic field formed around the power cable or the transmission line, the power cable or the transmission cable may be used. A single mode optical fiber attached to the electric wire can be used. This makes it possible to install an optical magnetic field current sensor configured using the optical magnetic field detection device at low cost.

According to a fourth aspect of the present invention, the magnetic field detecting section extracts a specific linearly polarized wave from random light from the first optical fiber and enters the magneto-optical element; 4. An analyzer into which light emitted from the element is incident, and further includes an analyzer that extracts only a specific polarized light component and uses it as detection light.
The optical magnetic field detection device according to any one of the above.

In this case, it is preferable that the magneto-optical element is arranged so that the traveling direction of the incident light from the polarizer is along the direction of the magnetic field to be detected. According to the configuration described in claim 4, the plane of polarization of linearly polarized light from the polarizer rotates according to the magnitude of the magnetic field and enters the analyzer.
From the analyzer, detection light of an amount corresponding to the magnitude of the magnetic field is extracted.

According to a fifth aspect of the present invention, the depolarization section includes a first polarization maintaining fiber having a length of 1 to 50 meters and a second polarization maintaining fiber having a length of 2 to 100 meters.
5. The optical magnetic field detecting device according to claim 1, wherein the polarization maintaining fiber is fused at a fusion angle of 0 to 90 degrees. The polarization maintaining fiber is an optical fiber that propagates light while maintaining linear polarization along the natural polarization direction (main axis direction). When linearly polarized light enters the polarization maintaining fiber, it is separated into two modes polarized in directions orthogonal to each other, and propagates with different propagation constants and group velocities. Therefore, if the length of the polarization maintaining fiber is set to a certain length or more, the difference in the reach between the modes exceeds the coherence length of the light source light, and the crosstalk between these two modes becomes negligible. The two orthogonal polarization modes lose coherence. However, the coherence of the linearly polarized light incident along the main axis is not lost. Therefore,
A fusion angle between the first polarization maintaining fiber and the second polarization maintaining fiber, which is an angle formed by the main axis directions, is 0 to 9 degrees.
When fusion is performed so as to satisfy 0 degree (0 degree <(fusion angle) <90 degrees), and linearly polarized light enters from the first polarization maintaining fiber, any incident light enters from the second polarization maintaining fiber. The random light that has lost the coherence of the orthogonal polarization mode of the polarization angle is emitted.

Based on such a principle, the configuration of the polarization canceller according to claim 5 allows the spectral half width Δλ to be 2
By incidence of linearly polarized light of nm to 5 nm, random light having a fluctuation width of light intensity of 3 dB or less can be obtained in a wavelength band of 1.3 μm. Therefore, in this case, it is preferable that the linearly polarized light source generates linearly polarized light having a spectral half width of 2 nm to 5 nm.

Note that a part of the first polarization maintaining fiber may constitute the third optical fiber,
A part of the second polarization maintaining fiber may constitute the first optical fiber. According to a sixth aspect of the present invention, the length of the first polarization maintaining fiber is about 1.5 meters, and the length of the second polarization maintaining fiber is about 3 meters. Item 6. An optical magnetic field detection device according to item 5.

With this configuration, random light having a fluctuation range of 1 dB or less in light intensity can be obtained in a wavelength band of 1.3 μm by the incidence of linearly polarized light having a spectral half width Δλ of 3 nm. Therefore, in this case, it is preferable that the linearly polarized light source emits linearly polarized light having a spectral half width of about 3 nanometers.

[0023]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing a configuration of a photomagnetic current sensor according to one embodiment of the present invention. The optical magnetic field current sensor includes, for example, a sensor unit 1 (magnetic field detection unit) provided at a desired detection point such as a current cable or a power transmission line, and a high-efficiency random number for supplying detection light to the sensor unit 1. The light source 20 includes a light source 20 and a light receiving element 3 (light receiving unit) such as a photodiode that receives detection light representing a detection result from the sensor unit 1 and converts the light into an electric signal. The optical waveguide from the high-efficiency random light source 20 to the sensor unit 1 is:
It comprises a first single mode optical fiber F1. on the other hand,
The optical waveguide extending from the sensor unit 1 to the light receiving element 3 is constituted by a second single mode optical fiber F2 having both ends coupled to the optical waveguide.

The high-efficiency random light source 20 includes a laser light source 2 such as a semiconductor laser that generates linearly polarized light, a polarization canceling unit 5 that converts the linearly polarized light generated by the laser light source 2 into random light, and a laser light source. And a third single-mode optical fiber F3 for guiding the linearly polarized light generated by the second optical fiber 2 to the polarization canceller 5. Since the laser light source 2 uses stimulated emission, it has a much higher luminous efficiency than a light emitting diode using spontaneous emission, and differs from a light emitting diode that basically generates divergent light. Generates a thin beam light. For this reason, the third single mode optical fiber F3 can be coupled with good efficiency, and a large amount of linearly polarized light can be supplied to the polarization canceller 5. Therefore, the random light obtained by depolarizing by the depolarizing unit 5 can have a large light amount.

The sensor unit 1 is coupled to a first single-mode optical fiber F1, and extracts a linear polarization component in a specific direction from random light incident from the optical fiber F1, and emits the same. The linearly polarized light from the polarizer is incident, and the polarization direction of the linearly polarized light is rotated according to the magnitude of the magnetic field H along the traveling direction of the linearly polarized light (Faraday effect). A magneto-optical element 12 that emits the linearly polarized light thus obtained, and an analyzer 13 that receives the linearly polarized light from the magneto-optical element 12, detects the polarized light component in a specific direction, and emits the polarized light component. . The light emitted by the analyzer 13 is guided to the light receiving element 3 via the second single mode optical fiber F2.

FIG. 2 is an illustrative view showing an arrangement of the above-mentioned magneto-optical current sensor. Around the power cable 100, a magnetic field H in a clockwise direction with respect to the direction of the current I appears along the circumferential direction thereof (right-hand screw rule). A substantially C-shaped magnetic core 101 is arranged along the magnetic field H, and the sensor unit 1 is arranged in a gap G of the magnetic core 101. At this time, the sensor unit 1
Are arranged such that the direction of the magnetic field H and the propagation direction of light in the magneto-optical element 12 match.

With this configuration, the magnetic field H generated around the power cable 100 is concentrated in the gap G where the sensor unit 1 is formed.
2 causes the rotation of the light propagating in the polarization direction to rotate. By detecting the amount of light emitted from the analyzer 13 with the light receiving element 3 in this manner, the current I
Can be detected.

From the sensor unit 1, a first single-mode optical fiber F1 and a second single-mode optical fiber F2 are drawn out, and are drawn into a detection device 150 provided at a remote place. This detection device 150
Inside, a polarization canceling unit 5, a third optical fiber F3, a laser light source 2, and a light receiving element 3 are provided. FIG. 3 is a perspective view illustrating a configuration example of the polarization canceling unit 5. Polarization canceller 5
Is formed by fusing one end of each of a first polarization maintaining fiber 51 and a second polarization maintaining fiber 52 with a fusion portion. The other end of the first polarization maintaining fiber 51 is connected to a third single mode optical fiber F3 on the side of the laser light source 2.
The other end of the second polarization maintaining fiber 52 is connected to the first single mode optical fiber F1 on the sensor unit 1 side via an optical connector.

The first and second polarization maintaining fibers 51,
52 guides light incident from one end while maintaining its polarization state. These polarization maintaining fibers 5
1 and 52, the angles (fusion angles) formed by the main axes A1 and A2, which are the natural polarization directions, are 0 to 90 degrees (more preferably, 40 to 50 degrees), and the optimum value is 45 degrees. ) Are fused to form an angle. The first polarization maintaining fiber 51 has a length L1 of 1 m to 50 m (the optimum value is
1.5 m), and the length L2 of the second polarization maintaining fiber 52 is 2 m to 100 m (the optimal value is 3 m).

When the linearly polarized light from the third single-mode optical fiber F3 enters the first polarization maintaining fiber 51, the light is transmitted to the first polarization maintaining fiber 51 and the natural polarization direction of the first polarization maintaining fiber 51. It splits into two modes with orthogonal directions and propagates at different speeds. The difference ΔL1 between the reach of the two modes when reaching the emission end of the first polarization maintaining fiber 51 having the length L1 is given by the following equation (1).

ΔL1 = cτ _p L1 = B · L1 (1) where c is the light speed, τ _p is the polarization dispersion mode constant, and B is the constant polarization refractive index (B = cτ _p ). Respectively. The coherence length Lc of the laser light source 2 is given by the following equation (2) based on the wavelength λ of the laser light and the spectral half width Δλ.

Lc = λ ² / Δλ (2) Therefore, to satisfy the inequality of the following equation (3),
If the length L1 of the first polarization maintaining fiber 51 is determined, crosstalk between modes is eliminated, and the coherence of the orthogonal polarization mode is lost. cτ _p L1> Lc (3) However, the intrinsic polarization direction A of the first polarization maintaining fiber 51
The coherence of light incident linearly polarized along 1 is not lost. Therefore, in order to lose the coherence of the orthogonal polarization mode at all incident polarization angles, the first polarization maintaining fiber 51
And the second polarization maintaining fiber 52 are fused with each other at a fusion angle of 0 to 90.
Degree (45 degrees is most preferable). The length L2 of the second polarization maintaining fiber 52 is about twice the length of the first polarization maintaining fiber 51. As a result, random light is emitted from the emission end of the second polarization maintaining fiber 52.

With the above configuration, when the spectral half width Δλ of the light generated by the laser light source 2 is 2 nm to 5 nm, the light intensity fluctuation width becomes 3 in the 1.3 μm wavelength band.
Good random light of not more than dB can be obtained. The most preferable configuration is that the length of the first polarization maintaining fiber 51 is 1.5 m.
And the length of the second polarization maintaining fiber 52 is 3 m,
It is obtained by setting the fusion angle to 45 degrees. In this case, the spectrum half width Δλ of the light generated by the laser light source 2
Is 3 nm, good random light having a light intensity fluctuation width of 1 dB or less can be obtained.

As described above, according to the configuration of this embodiment, linearly polarized light is generated from the laser light source 2 which can easily achieve a large light output, and the third polarized light can be coupled to the laser light source 2 with high coupling efficiency. And the third single-mode optical fiber F3
By converting the linearly polarized wave propagating through 3 into random light by the polarization canceller 5, a highly efficient random light source 20 with high intensity and a small light intensity fluctuation width is realized. The propagation of light from the random light source 20 to the polarizer 11 and the propagation of light from the analyzer 13 to the light receiving element 3 are performed by single-mode optical fibers F1 and F2 with small transmission loss.

Thus, while avoiding the problem of low coupling efficiency between a light emitting diode and a single mode optical fiber, which has been generally used as a random light source, a combination of a high output random light source and a low transmission loss optical waveguide is realized. As a result, even if the single mode optical fibers F1 and F2 are long, the magnetic field H can be detected satisfactorily. Accordingly, the distance between the sensor unit 1 and the detection device 150 can be significantly increased as compared with the related art using a distributed index optical fiber. As a result, for example, centralized management of current detection at many detection points is facilitated.

Moreover, the single mode optical fiber F1,
Since F2 and F3 are thin, there is theoretically only one mode, and even if external vibration occurs, there is no possibility that mode conversion will occur due to the influence of this vibration. This enables stable detection even in an environment with vibration. Further, a single mode optical fiber may already be attached to a power cable or a transmission line for the purpose of data communication. In such a case, by using the single mode optical fiber, the work of newly laying the optical fiber can be omitted, so that the installation cost of the optical magnetic field current sensor can be greatly reduced.

While the embodiment of the present invention has been described above, the present invention can be embodied in other forms. For example, in the above-described embodiment, the polarization canceling unit 5 is disposed in the detection device 150. However, the polarization canceling unit 5 is configured to use any one of the paths of the detection light from the detection device 150 to the sensor unit 1. If it is interposed at the position of
For example, it can be arranged near the sensor unit 1.

Further, in the above-described embodiment, an example in which the optical magnetic field detecting device is used to detect the current flowing through the power cable 100 has been described. Needless to say, the present invention can be widely applied to detection of any other physical quantity that can be detected. In addition, it is possible to make various design changes within the technical scope described in the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a photomagnetic current sensor according to an embodiment of the present invention.

FIG. 2 is an illustrative view showing an arrangement mode of the above-mentioned magneto-optical current sensor.

FIG. 3 is a perspective view illustrating a configuration example of a polarization canceling unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Sensor unit 2 Laser light source 3 Light receiving element 5 Depolarization part 11 Polarizer 12 Magneto-optical element 13 Analyzer 20 Random light source F1 1st single mode optical fiber F2 2nd single mode optical fiber F3 3rd single mode optical fiber 51 first polarization maintaining fiber 52 second polarization maintaining fiber

Claims (8)

[Claims] 1. A linearly polarized light source for generating linearly polarized light, a random light source including a polarization canceling unit for converting linearly polarized light generated from the linearly polarized light source into random light and emitting the same, and a Faraday effect. A magnetic field detecting unit having a generated magneto-optical element, receiving random light from a random light source and emitting detection light reflecting an external magnetic field, and receiving the detection light emitted by the magnetic field detection unit and converting it into an electric signal A first optical fiber that guides random light from the random light source to the magnetic field detection unit; and a second optical fiber that guides detection light emitted by the magnetic field detection unit to the light reception unit. An optical magnetic field detection device characterized by the above-mentioned. 2. The optical magnetic field detecting device according to claim 1, wherein said first optical fiber and said second optical fiber are single mode optical fibers. 3. The random light source further includes a third optical fiber for guiding the linearly polarized light from the linearly polarized light source to the polarization canceller, and the third optical fiber is a single mode optical fiber. The optical magnetic field detecting device according to claim 1, wherein: 4. A magnetic field detecting unit comprising: a polarizer that extracts a specific linearly polarized wave from random light from the first optical fiber and enters the magneto-optical element; and an output light from the magneto-optical element. 4. The optical magnetic field detection device according to claim 1, further comprising an analyzer that is incident and extracts only a specific polarization component and uses it as detection light. 5. A polarization canceling unit comprising: a first polarization maintaining fiber having a length of 1 to 50 meters; and a second polarization maintaining fiber having a length of 2 to 100 meters. 5. The optical magnetic field detecting device according to claim 1, wherein the optical magnetic field is fused at a fusion angle of degrees to 90 degrees. 6. The length of the first polarization maintaining fiber is about 1.5 meters, and the length of the second polarization maintaining fiber is about 3 meters. Optical magnetic field detection device. 7. The light according to claim 1, wherein said linearly polarized light source generates linearly polarized light having a spectral half width of 2 nm to 5 nm. Magnetic field detector. 8. An optical magnetic field detecting apparatus according to claim 7, wherein said linearly polarized light source generates linearly polarized light having a spectral half width of about 3 nanometers.