JP2001281272A - Current/magnetic field measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a current/magnetic field measuring apparatus utilizing the Faraday effect which permits measurement at a higher accuracy by eliminating effect of external magnetic fields along with a higher dynamic range. SOLUTION: A laser diode 1 is driven by an LD driver 2 to supply exciting light to a fiber laser. The light is guided to a coupler 4 with a transmission fiber 3 and further to a ring resonator 5 of a ring laser with the coupler 4. The ring resonator 5 is composed of an optical fiber containing a laser medium having a light amplifying action and wound on the circumference of a primary conductor 6 to be measured. Beat frequency generated in the ring laser by the Faraday effect is determined thereby obtaining a current value of the primary conductor 6.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measuring device for measuring a change in a physical quantity by using a change in a polarization characteristic of an optical element, and more particularly to a Faraday measurement device having a ring-shaped optical path such as a ring laser. Current using effect
The present invention relates to a magnetic field measuring device.

[0002]

2. Description of the Related Art Hitherto, there have been proposed various optical applied measuring devices for measuring a change in a physical quantity by utilizing a change in a polarization characteristic of an optical element. Since this optical applied measuring device is hardly affected by electric noise and can achieve a higher dynamic range than an electric measuring device, there is a strong expectation for its development. Above all, an optical fiber current measuring device (hereinafter referred to as an optical CT) has attracted attention as a compact optical applied measuring device.

In the optical CT, an optical fiber is arranged as a sensor close to a conductor through which a current to be measured flows, and a linearly polarized light is passed through the sensor, and a Faraday effect in which a polarization plane is rotated by a magnetic field generated by the current to be measured. It is used to measure current, and it can be composed of an insulator, has high linearity because there is no saturation, can measure from DC to high frequency, and has the features of being compact.

As a method for extracting the Faraday effect as a signal, a polarization plane rotation method and an interference method have been conventionally proposed. In this polarization plane rotation method, light whose polarization plane has been rotated due to the Faraday effect is extracted using a polarizer and converted into an intensity signal by extracting only one polarization component. For example, Masao Takahashi et al. "Optical Current Transformer
for Gas Insulated Switchgear using Silica Optical
Fiber "IEEE Transactions on Power Delivery V01.1
2, No. 4, p1422, the method is disclosed and has already been put to practical use.

On the other hand, the above-mentioned interference method utilizes the fact that the propagation time of right-handed and left-handed circularly polarized light is generated due to the Faraday effect, and causes right-handed and left-handed light to interfere with each other. For calculating the current value, for example, SX Shor "Im
perfect Quater-Waveplate Compensation in Sagnac In
terferometer-Type Current Sensor "Journal of Light
The embodiment is disclosed in wav Technology, Vol 16, No. 7, P1212.

[0006] Since both the polarization plane rotation method and the interference method use light, they are hardly affected by electric noise.
Although a high dynamic range can be expected for electrical measuring instruments, the use of intensity signals limits the dynamic range due to electrical noise and drift at the detector. It has been demanded.

On the other hand, researches have been made to improve the accuracy by using the difference in the oscillation frequency of the laser instead of the intensity signal as the output signal of the optical CT. This is Myung Lae Le
e et al "A polarimetric current sensor using an orthogo
nally polarized dual-frequency fiber laser "Meas.
Sci. Technol., Vol. 9, p 952 discloses the method. FIG. 9 shows the configuration of an optical CT using this fiber laser.

[0010] That is, in the optical CT shown in FIG.
The fiber laser 29 is configured so that the excitation light is input through the coupler 26 into the fiber amplifier 11 wound in a coil around the primary conductor 6 to be measured. The fiber laser 29 includes a resonator including a fiber amplifier 11, a rear mirror 27 including a Faraday rotating mirror, and an output mirror 28. Laser oscillation is performed at a resonance frequency determined by the optical length of the resonator. Generates clockwise and counterclockwise circularly polarized light around the primary conductor 6.

When a current is applied to the primary conductor 6 to be measured, a magnetic field is applied to the fiber laser, and the refractive index changes between clockwise circularly polarized light and counterclockwise circularly polarized light due to the Faraday effect. Will be done. The optical length of the resonator is n · l (n: refractive index, l: fiber resonator length)
Therefore, there is a difference in the resonator length between the clockwise circularly polarized light and the counterclockwise circularly polarized light. As a result, the output light transmitted through the polarizer 15 generates a beat signal of both oscillation frequencies. Is observed. Since the beat frequency is proportional to the magnitude of the applied magnetic field (current), the current can be obtained by measuring the beat frequency. In general, a frequency signal is more likely to obtain a higher dynamic range than an intensity signal. Therefore, the optical CT shown in FIG. 9 is a method in which current measurement in a high dynamic range is expected.

[0010]

However, the conventional optical CT as described above has problems to be solved as described below. That is, the optical CT using the intensity signal
Therefore, the dynamic range cannot be increased in principle, and a high dynamic range can be expected in the optical CT using the oscillation frequency. However, due to the configuration, it is difficult to arrange the rear mirror 27 and the output mirror 28 at exactly the same position. Difficult, and errors due to inability to completely close
There is a problem that it is difficult to achieve high accuracy under the influence of an external magnetic field.

The present invention has been proposed to solve the above-mentioned drawbacks of the prior art, and has as its object the purpose of achieving a high dynamic range and eliminating the influence of an external magnetic field to achieve high precision. It is an object of the present invention to provide a current / magnetic field measuring device using the Faraday effect that enables measurement.

[0012]

In order to achieve the above object, the invention of claim 1 is characterized in that a ring laser is used as a current / magnetic field detection sensor. According to the first aspect of the present invention, the current or the magnetic field is measured by utilizing the Faraday effect generated in the ring laser disposed near the object to be measured, so that the resonator as the current or magnetic field sensor is completely looped. With this structure, measurement can be performed without being affected by an external magnetic field.

According to a second aspect of the present invention, a laser beam is generated in two directions which propagate countercurrently in a ring laser, and the laser beam in the two directions is generated by the Faraday effect acting between the laser beam in the two directions and the object to be measured. It is characterized in that a current or a magnetic field to be measured is measured based on a beat frequency generated from a difference in oscillation frequency between light beams. According to the second aspect of the present invention, due to the Faraday effect, the optical path length of the ring laser has an optical path difference between right-handed circularly polarized light and left-handed circularly polarized light, and the resonance frequency thereof is different. Also oscillate at different oscillation frequencies for clockwise and counterclockwise circularly polarized light. Therefore, a beat is generated between the clockwise circularly polarized light and the counterclockwise circularly polarized light, and the beat frequency is proportional to the current value applied to the measurement target.
By determining the beat frequency, the current value of the measurement target can be determined.

According to a third aspect of the present invention, in the current / magnetic field measuring apparatus according to the second aspect, the ring laser is provided with a plurality of current or magnetic field measurement value detectors, and each of the plurality of detectors detects a ring laser. It is characterized in that the laser light circulating inside is taken out of the ring laser. According to the invention described in claim 3, the fact that an output can be obtained from an arbitrary point on the measuring device is used,
Signals can be supplied to a plurality of devices using the output of the measuring device with minimum wiring.

According to a fourth aspect of the present invention, in the current / magnetic field measuring apparatus according to the first, second, or third aspect, the ring laser is constituted by an optical fiber. According to the fourth aspect of the present invention, since the ring laser is composed of fibers, the optical path is always stable, and high-precision measurement can be performed without being affected by instability due to disturbance such as temperature.

According to a fifth aspect of the present invention, in the current / magnetic field measuring apparatus according to the fourth aspect, the optical fiber constituting the ring laser is twisted. According to the fifth aspect of the present invention, by twisting the optical fiber serving as the sensor, the natural propagation mode of the fiber can be circularly polarized light, and the accuracy of the measuring instrument using the change in the refractive index of the circularly polarized light can be improved. Can be increased.

According to a sixth aspect of the present invention, in the current / magnetic field measuring apparatus according to the fourth aspect, at least a part of the optical fiber constituting the ring laser is constituted by a fiber having an optical amplification function. And According to the invention of claim 6, since it is not necessary to dope a laser medium into the sensor section which receives the Faraday effect,
The type of fiber material that can be used is not limited, and the design of a current measuring device having an arbitrary sensitivity is facilitated.

The invention according to claim 7 is based on claim 1, claim 2,
The current / magnetic field measuring apparatus according to claim 3, 4, 5, or 6, wherein a Faraday element comprising an optical fiber is provided in a part of an optical path of the ring laser. . According to the seventh aspect of the present invention, since only a part of the ring laser is a Faraday element, by arranging the measurement target close to the part, the other part is detected by the Faraday effect. Errors can be reduced.

The invention according to claim 8 is based on claim 1, claim 2,
Claim 3, Claim 4, Claim 5, Claim 6, or Claim 7
In the current and magnetic field measurement device according to the above, a part of the optical path of the ring laser is configured from a polarization maintaining fiber,
A phase difference plate is provided on both sides of the Faraday element. According to the eighth aspect of the invention, by configuring the optical path other than the sensor portion with the polarization maintaining fiber, the rotation of the polarization plane due to the Faraday effect other than the sensor is prevented, and highly accurate measurement is possible. .

The invention of claim 9 is the invention of claim 7 or 8.
Wherein the polarizer is provided on at least a part of the optical path of the ring laser, and a phase difference plate is provided on both sides of the Faraday element. According to the ninth aspect of the present invention, by arranging retardation plates at both ends of the sensor, the sensor portion transmits circularly polarized light, the other fiber portions transmit linearly polarized light, and further transmits a part of the ring laser. By inserting a polarizer, this linearly polarized light becomes elliptically polarized light due to birefringence, and the component rotated by Faraday rotation other than the sensor is removed. Only the polarized light component which is obtained is taken out, and high precision measurement becomes possible.

According to a tenth aspect of the present invention, in the current / magnetic field measuring apparatus according to the eighth or ninth aspect, a phase difference generated by the phase difference plate is ４λ. According to the tenth aspect, by setting the phase difference generated by the phase difference plate to 円 · λ, linearly polarized light can be accurately converted to circularly polarized light, and high-precision measurement is possible. is there.

According to the eleventh aspect of the present invention, there is provided an electric power supply according to any one of the first, second, third, fourth, sixth, seventh, eighth, ninth and tenth aspects. In the magnetic field measuring apparatus, at least two or more Faraday elements are provided in the optical path of the ring laser, and a means for connecting the Faraday elements in series is provided. Is characterized in that the transmittance has a polarization dependency so that the light is transmitted or attenuated. According to the eleventh aspect of the present invention, at least two or more Faraday elements are provided in the ring resonator, and means for coupling light in series between the Faraday elements is provided, and the Faraday elements are connected in series. The means is characterized by having a polarization dependence of transmittance so that only a specific polarized light is transmitted or attenuated. When measuring the sum current and the difference current of two or more Faraday elements, The effect of the change in polarization between the elements can be eliminated by using a means for extracting only a certain polarization component.

According to a twelfth aspect of the present invention, a ring-shaped optical path having two or more Faraday elements is used, and the Faraday effect of a Faraday element arranged at a position affected by a magnetic field induced by a current to be measured is used. Then, in a photocurrent measuring device that measures the intensity of current from the phase difference between two light waves propagating in the Faraday element, a light source, two or more Faraday elements, and light guided from the light source are separated by two.
Means for separating the two lights into two, means for connecting the two separated lights to the Faraday element, means for connecting the respective Faraday elements in series, and recombination of the two lights emitted from the Faraday element. And a means for measuring the intensity of the recombined light, wherein the means for coupling the Faraday elements in series has a polarization dependence of transmittance so that only specific polarized light is transmitted or attenuated. It is characterized by the following. According to the twelfth aspect of the invention, the sum or difference current can be measured with high accuracy in the interference-type current measurement device, as in the twelfth aspect of the invention.

According to a thirteenth aspect of the present invention, in the photocurrent measuring device according to the eleventh or twelfth aspect, a polarizer is disposed in the means for connecting the Faraday elements in series. According to the thirteenth aspect, since the extinction ratio of the polarizer can be easily obtained, for example, about 60 dB, it is possible to sufficiently remove the change in the polarization and perform the measurement with high accuracy.

According to a fourteenth aspect, in the photocurrent measuring device according to the thirteenth aspect, the polarizer is arranged near the Faraday element. According to the fourteenth aspect of the present invention, since the polarizer is disposed near the Faraday sensor, the disturbance of polarization between the polarizer and the Faraday element is minimized, and high-precision measurement is possible.

According to a fifteenth aspect of the present invention, in the photocurrent measuring device according to the twelfth, thirteenth or fourteenth aspect,
In the means for coupling the Faraday elements in series,
The polarization plane is not preserved by the polarization plane preserving fiber. According to the fifteenth aspect of the present invention, since the polarization maintaining fiber is not used for the means for connecting the Faraday elements in series, the trouble of adjusting the axis of the polarization maintaining fiber to the polarization and the angle at this time are eliminated. An error in current measurement due to a setting error can be eliminated.

According to a sixteenth aspect of the present invention, in the photocurrent measuring device according to the twelfth, thirteenth, fourteenth, or fifteenth aspect, a means for coupling the Faraday elements in series includes a depolarizer. It is characterized by being arranged. According to the sixteenth aspect, by using the depolarizer and the polarizer, a linearly polarized light having a stable light amount propagates between the Faraday elements, and high-precision measurement can be performed.

[0028]

Embodiments of the present invention (hereinafter, referred to as embodiments) will be specifically described below with reference to the drawings.

(1) First Embodiment FIG. 1 is a schematic diagram showing the configuration of a first embodiment of a current measuring device according to the present invention. That is, the laser diode 1
Are driven by the LD driver 2 to supply excitation light to the fiber laser. And
This light is guided by the transmission fiber 3 to the coupler 4, and further introduced into the ring resonator 5 of the ring laser by the coupler 4. The ring resonator 5 is composed of an optical fiber including a laser medium having a function of amplifying light by entering excitation light, such as neodymium or erbium, and is wound around a primary conductor 6 to be measured. Has been turned. In this case, in this embodiment,
The ring resonator 5 is composed of a single material optical fiber containing a laser medium, and has an optical amplifying action over the entire length of the ring. Further, as the optical fiber, one having no linear birefringence is used, and one in which the oscillated laser light is circularly polarized is used.

In the ring laser having such a configuration,
When sufficient excitation light is given to the ring resonator 5 composed of an optical fiber via the transmission fiber 3 and the coupler 4, the ring laser oscillates at a resonance frequency determined by the optical path length L of the ring resonator 5, Clockwise and counterclockwise laser light (circularly polarized light) circulates in the ring resonator 5.

Under such a condition, when a current is applied to the primary conductor 6 disposed at the center of the ring resonator 5, the optical path length of the ring laser becomes right-handed circularly polarized light and left-handed due to the Faraday effect. An optical path difference occurs between the surrounding circularly polarized lights, and the optical path lengths are L + δ and L−δ, respectively. For this reason, the clockwise and counterclockwise circularly polarized light has different resonance frequencies,
Since the oscillation frequency of the ring laser also oscillates at different oscillation frequencies for right-handed and left-handed circularly polarized light, a beat occurs between right-handed and left-handed circularly polarized light. Since the beat frequency is proportional to the value of the current supplied to the primary conductor 6, the current value of the primary conductor 6 can be determined by determining the beat frequency. That is, the oscillated light is extracted from the coupler 4, guided to the detector 8 by the light receiving fiber 7, photoelectrically converted by the detector 8, amplified by the amplifier 9, and then the beat frequency is measured by the spectrum analyzer 10. I have.

As described above, in the current measuring device of the present embodiment, since the beat frequency is used as the output signal, it is easy to obtain a large dynamic range, and the sensor portion which receives the Faraday effect has a loop structure. Since it is closed completely, it is not affected by an external magnetic field in principle, and high precision can be achieved. In addition, since the optical fiber is used as the sensor, it is easy to use all the optical paths as fibers or waveguides. is there.

When a medium having a large photoelastic effect is used for an optical fiber used as a sensor, linear birefringence is generated by winding the fiber in a loop. In a fiber with such a large linear birefringence, the propagation mode of the optical fiber is two orthogonal linearly polarized lights that coincide with the axis of the linear birefringence. Even if optical rotation due to the Faraday effect is added, circularly polarized waves will propagate. However, as a result, only the frequency difference between two orthogonal linearly polarized lights is observed as the beat frequency, and the frequency does not change even if a current is applied to the primary conductor.

As a method of removing the influence of such linear birefringence, it is known that twisting the fiber is effective. When the fiber is twisted, the propagation mode becomes circular birefringence, and the optical rotation due to the Faraday effect can be effectively captured. The optical fiber used at this time may be a fiber having no linear birefringence or a high birefringence fiber, and by applying a sufficient twist to the linear birefringence, the propagation mode can be circularly polarized. .

(2) Second Embodiment FIG. 2 is a schematic diagram showing the configuration of a second embodiment of the current measuring device according to the present invention. In FIG. 2, from the laser diode 1 to the spectrum analyzer 10,
The description is omitted because it is the same as FIG. That is, in the current measuring device of the present embodiment, the plurality of couplers 4 are provided in the ring resonator 5, and the light is extracted to the plurality of detectors 8.

In the present embodiment having such a configuration, even if a plurality of light extraction ports are provided in the ring resonator 5, the beat frequency that can be extracted does not change, and the same high precision as in the first embodiment is obtained. Measurement is possible. That is,
In the conventional photocurrent measuring device, the light outlet from the sensor is always one point, and when it is desired to provide a plurality of detectors, it is necessary to separately lay optical fibers from there. Was causing an increase. However, according to the current measuring device of the present embodiment, it is possible to extract light of an arbitrary number of branches from an arbitrary point in the ring resonator, which simplifies the configuration, reduces cost and improves reliability. Becomes possible.

(3) Third Embodiment FIG. 3 is a schematic diagram showing the configuration of a third embodiment of the current measuring device according to the present invention. In FIG. 3, from the laser diode 1 to the spectrum analyzer 10,
The description is omitted because it is the same as FIG.

In the current measuring devices of the first and second embodiments, the ring resonator is composed of an optical fiber of a single material and has an optical amplification function over the entire length of the ring. In the current measuring device described above, an optical fiber amplifier 11 having an optical amplifying function is arranged near the entrance of the coupler 4. Further, a Faraday element 14 composed of an optical fiber having a Faraday effect is provided in a part of the optical path of the ring laser.
Since the Faraday element 14 needs to propagate a circularly polarized wave, a ４λ plate 13 as a phase difference plate is provided at both ends of the Faraday element 14.

As the optical fibers other than the optical fiber amplifier 11 and the sensor section, the polarization maintaining fiber 1
2 is used. Therefore, in this ring laser, the laser oscillates with light of two orthogonal polarizations that match the axis of birefringence of the polarization-maintaining fiber 12.

In the current measuring device of this embodiment having such a configuration, it is not necessary to dope a laser medium into the sensor section which is subjected to the Faraday effect. This facilitates the design of a current measurement device having However, in this case, since the Faraday effect in portions other than the sensor section is observed as an error, it is necessary to contrarily avoid the Faraday effect. Therefore, in the present embodiment, the fiber length of the optical fiber amplifier 11 is set shorter than the length of the ring resonator to reduce the Faraday effect in the amplifier section.

Since the polarization preserving fiber 12 is used as an optical fiber other than the amplification section and the sensor section, two orthogonal polarization axes which coincide with the birefringence axis of the polarization preserving fiber in this ring laser. The laser oscillates with the light of the wave. Further, the Faraday element 14 as a sensor unit is formed of an optical fiber having a Faraday effect and is configured to measure a current flowing through the primary conductor 6. At this time, the Faraday element 1
Since it is necessary for the Faraday element 4 to propagate a circularly polarized wave, １ ／ λ plates 13 are arranged at both ends of the Faraday element 14, the linearly polarized light emitted from the polarization plane preserving fiber 12 is converted into a circularly polarized light, Has been propagated to.

In this embodiment, in order to reduce the influence of the other phase magnetic field, the primary conductor 6 is wound only around the Faraday element instead of disposing the primary conductor 6 at the center of the ring laser. It is also effective to rotate the current to make it circulate. Further, the measuring device of the present embodiment can also be used as a magnetic field measuring device as it is, and can be used for measuring a magnetic field at the Faraday element.

(4) Fourth Embodiment FIG. 4 is a schematic diagram showing the configuration of a fourth embodiment of the current measuring device according to the present invention. In FIG. 4, from the laser diode 1 to the spectrum analyzer 10,
As shown in FIG. 1, a fiber amplifier 11, a polarization preserving fiber 12, a λλ plate 13, a Faraday element 14
Are the same as those in FIG.

The present embodiment is characterized in that at least one or more polarizers 15 are inserted into the ring resonator 5. Note that the polarizer 15 is disposed so as to coincide with the birefringent axis direction of the polarization-maintaining fiber 12.
One of the two orthogonal linearly polarized lights is cut to make a single linearly polarized light.

In the ring resonator 5, two fiber couplers 4 are provided on both sides of the fiber amplifier 11 so as to extract clockwise light and counterclockwise light, respectively, as described later. Have been. Further, a beam combining coupler 16 is provided between the two fiber couplers 4 and the detector 8, and the right-handed light and the left-handed light extracted by the two fiber couplers 4 are combined to generate a propagation time difference. It is configured to be able to measure a beat frequency proportional to.

The present embodiment having the above configuration has
It works as follows. That is, since the polarizer 15 is provided, the light incident on the Faraday element 14 is only clockwise (or counterclockwise) light, and no beat due to the Faraday effect occurs in this state. However, the light turning clockwise and the light turning counterclockwise in the ring laser are respectively rotated clockwise and counterclockwise in the Faraday element 14 by the action of the １４λ plates 13 arranged on both sides of the Faraday element 14. , And a propagation time difference occurs due to the Faraday effect. Therefore, when the clockwise light and the counterclockwise light are combined, a beat frequency proportional to the propagation time difference is observed.

As described above, in this embodiment, since both the light propagating clockwise and the light propagating counterclockwise through the ring resonator are used, two fiber couplers 4 are arranged in the ring resonator. And clockwise and counterclockwise light, respectively. These two lights are combined by a beam combining coupler 16 for combining another beam, and a beat is generated. Further, according to the present embodiment, even if crosstalk occurs between the two propagation modes of the polarization-maintaining fiber 12 due to the birefringence of the fiber, the crosstalk component is removed by the polarizer 15 to increase the crosstalk. Accurate current measurement can be realized.

(5) Fifth Embodiment FIG. 5 is a schematic diagram showing the configuration of a fifth embodiment of the current measuring device according to the present invention. The current measuring device according to the present embodiment includes:
As shown in FIG. 5, the plurality of Faraday elements 14, 14
Are connected in series, and the plurality of Faraday elements 14,
14 is to measure the current at a plurality of measurement objects 6, 6 (points) by winding the primary conductors 6, 6 which are the measurement objects around each of the measurement objects 14, and to measure the sum or difference current. It is. In FIG. 5, the components from the laser diode 1 to the beam combining coupler 16 are the same as those in FIG.

That is, in the conventional winding CT, 1
Since the secondary side and the secondary side are electromagnetically coupled, direct series connection cannot be performed. However, in the case of the current measuring device of the present embodiment, series connection can be easily performed. The serial connection in the conventional photocurrent measuring apparatus is described, for example, by Tomohiro Soso et al.
The method is disclosed in the 1999 National Conference of the Institute of Electrical Engineers of Japan, Kiyoshi Kurosawa et al., "Basic Study of Current Differential Protection System Applying Optical CT Technology," PSR-99-8, the Institute of Electrical Engineers of Japan. ing.

As in the case of such a conventional photocurrent measuring apparatus, direct series connection can also be performed in this embodiment using a ring laser. However, the problem with the serial connection is that the influence of the linear birefringence of the sensor increases as the number of sensors (the number of Faraday elements 14) increases. Also in the case of the present embodiment, crosstalk occurs between two polarized lights propagating in the ring laser due to the linear birefringence of the sensor, resulting in an error in current measurement. Therefore, in the present embodiment, the crosstalk component is cut using the polarizer 15 as in the fourth embodiment.

(6) Sixth Embodiment FIG. 6 is a schematic diagram showing the configuration of a sixth embodiment of the current measuring device according to the present invention. In this embodiment, means for connecting the Faraday elements 14 in series is provided, and only a specific polarized light is transmitted by connecting a depolarizer or a polarizer to an optical fiber connecting the Faraday elements in series. Alternatively, by attenuating, the polarization dependence of the transmittance is provided, and the two or more Faraday elements 14 are connected without using a polarization-maintaining fiber. The fiber used at this time is, for example,
Single mode fiber for communication. FIG.
In FIG. 5, the components from the laser diode 1 to the beam combining coupler 16 are the same as those in FIG.

In this embodiment, the ring resonator of the ring laser is constituted by a single mode fiber. However, if the light propagated through the single mode fiber is used as it is, the polarization plane becomes unstable. 1
The first depolarizer 20 is arranged at the exit of the single mode fiber 17 to make the light non-polarized, and then pass through the polarizer 15 to obtain linearly polarized light. In this case, the same effect can be obtained only with the polarizer 15, but the intensity of light transmitted through the polarizer changes depending on the state of polarization, and the polarization direction of the transmitted light of the polarizer is 90 °.
When the linearly polarized light is incident on the polarizer, the transmitted light amount of the polarizer becomes 0, and there is a possibility that the measurement cannot be performed. In this embodiment, the first single mode fiber 17 has the first The depolarizer 20 is arranged.

In this embodiment, the linearly polarized light transmitted through the polarizer 15 disposed adjacent to the first depolarizer 20 becomes circularly polarized light through the １ ／ λ plate 13, and is converted by the Faraday element 14 into Faraday light. Received the effect, 1 /
The light becomes the linearly polarized light again by the 4λ plate 13, and the second Faraday element 1
Light is guided up to 4. In this case, the light that has passed through the second single mode fiber 18 is similarly depolarized by the second depolarizer 21 and then is depolarized by the second depolarizer 2.
The light becomes circularly polarized light by the polarizer 15 and the ４λ plate 13 which are disposed adjacent to the light-receiving element 1, and is subjected to the Faraday effect by the Faraday element 14. This light is again linearly polarized by the ４λ plate 13 and the polarizer 15, and the third single mode fiber 19
Light propagates toward.

As described above, since the ring resonators are connected by the single mode fiber, connection between the modules becomes easy, and an angle error when the polarization maintaining fiber is connected causes an error in current measurement. Problems can also be avoided, and highly accurate current measurement can be realized.

In the configuration of the present embodiment shown in FIG. 6, the 1 / 4.lambda. Plates 13 are arranged on both sides of the Faraday element 14, but this configuration is simplified to, for example, as shown in FIG. 1/4 on only one side of the Faraday element 14
Even when the λ plate 13 and the polarizer 15 are arranged,
For the incident light, it acts so that the light incident on the Faraday element becomes clockwise (counterclockwise) circularly polarized light, and for the outgoing light, of the light transmitted through the Faraday effect, the Faraday element The same effect can be obtained because it works so as to transmit only the component turned into the left-handed (right-handed) circularly polarized light.

(7) Seventh Embodiment FIG. 8 shows an example in which the configuration shown in FIG. 6 is applied to an interference type current measuring device. In this interference type current measuring device, a light source is provided outside the ring-shaped optical path, and the optical length is changed between light propagating clockwise and light propagating counterclockwise through the ring-shaped optical path. The Faraday effect is used in a current measuring device as a means for changing the optical length as a means for changing the optical length.
A super luminescent diode 24 is used as a light source. This super luminescent diode 24
Is driven by a driver 25, and light is guided by the transmission fiber 3 to a ring-shaped optical path. This light is split by the coupler 4 into light propagating clockwise and counterclockwise through the ring optical path.

First, the light turning clockwise will be described.
This clockwise light is guided by the first single mode fiber 17, is once depolarized by the first depolarizer 20, is then linearly polarized by the polarizer 15, and is １ ／ λ
The light is turned into clockwise circularly polarized light by the plate 13, and the Faraday element 14
Receives the phase difference due to the Faraday effect, and
Then, the light passes through the polarizer 15, propagates through the second single-mode fiber 18, is made unpolarized by the second depolarizer 21, and then becomes linearly polarized by the polarizer 15, After becoming clockwise circularly polarized light by the λλ plate 13, further receiving a phase difference due to the Faraday effect by the Faraday element 14, and becoming linearly polarized light by the ４λ plate 13,
The light passes through the polarizer 15 and returns to the coupler 4 via the third single mode fiber 19.

On the other hand, the light propagating counterclockwise propagates through each element in exactly the reverse order of the light propagating clockwise. However, in the Faraday element 14, a counterclockwise circle opposite to the clockwise light is generated. It will propagate with polarized light. For this reason, the phase difference θ due to the Faraday effect between the clockwise light and the counterclockwise light becomes plus or minus, and the intensity of the interference light changes in proportion to sin2θ. Therefore, the current can be obtained by converting the interference light intensity into an electric signal by the detector 8 and obtaining an arc sine by the signal processing circuit.

As described above, even in the interference type current measuring device, it is possible to connect the Faraday elements with the single mode fiber and measure the sum or difference current.

[0060]

As described above, according to the present invention, it is possible to provide a current / magnetic field measuring apparatus capable of achieving a high dynamic range and eliminating the influence of an external magnetic field to enable high-precision measurement. Can be.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a configuration of a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a configuration of a third embodiment of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a fourth embodiment of the present invention.

FIG. 5 is a schematic diagram showing a configuration of a fifth embodiment of the present invention.

FIG. 6 is a schematic diagram showing a configuration of a sixth embodiment of the present invention.

FIG. 7 is a schematic diagram showing a configuration of a modification of the sixth embodiment of the present invention.

FIG. 8 is a schematic diagram showing a configuration of a seventh embodiment of the present invention.

FIG. 9 is a schematic diagram showing a configuration of a conventional photocurrent sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laser diode 2 ... LD driver 3 ... Transmission fiber 4, 16 ... Coupler 5 ... Ring resonator 6 ... Primary conductor 7 ... Light receiving fiber 8 ... Detector 9 ... Amplifier 10 ... Spectrum analyzer 11 ... Fiber amplifier 12 ... Polarization plane Storage fiber 13: 1 / 4λ plate (phase difference plate) 14: Faraday element 15: Polarizer 16: Coupler for beam combining 17: First single mode fiber 18: Second single mode fiber 19: Third single mode Fiber 20 first depolarizer 21 second depolarizer 22 signal processor 23 output 24 superluminescent diode 25 driver 26 WDM coupler 27 rear mirror 28 output mirror 29 fiber laser

Continued on the front page (72) Inventor Masao Hori 1-1-1, Shibaura, Minato-ku, Tokyo F-term in Toshiba head office (reference) 2G017 AA01 AB01 AD12 AD15 2G025 AA11 AB10 AB12 AC06 2G035 AA08 AA17 AB00 AC02 AD33

Claims (16)

[Claims] 1. A current / magnetic field measuring device using a ring laser as a current / magnetic field detection sensor. 2. An oscillation frequency between two laser beams in a ring laser due to a Faraday effect acting between the laser beams in the two directions and an object to be measured. A current / magnetic field measuring apparatus for measuring a current or a magnetic field of a measurement target based on a beat frequency generated from a difference between the current and the magnetic field. 3. The ring laser according to claim 1, wherein a plurality of current or magnetic field measurement value detectors are provided, and a laser beam circulating in the ring laser is extracted from each of the plurality of detectors to the outside of the ring laser. Item 3. A current / magnetic field measurement device according to item 2. 4. The current / magnetic field measuring apparatus according to claim 1, wherein the ring laser is constituted by an optical fiber. 5. The current / magnetic field measuring apparatus according to claim 4, wherein the optical fiber constituting the ring laser is twisted. 6. The current / magnetic field measuring apparatus according to claim 4, wherein at least a part of the optical fiber constituting the ring laser is constituted by a fiber having no optical amplification action. 7. The ring laser according to claim 1, wherein a Faraday element comprising an optical fiber is provided in a part of the optical path of the ring laser. The current / magnetic field measuring device according to claim 6. 8. The ring laser according to claim 1, wherein a part of an optical path of the ring laser is composed of a polarization preserving fiber, and retardation plates are provided on both sides of the Faraday element. The current / magnetic field measuring apparatus according to claim 3, 4, 5, 5, 6, or 7. 9. The ring laser according to claim 7, wherein a polarizer is provided on at least a part of an optical path of the ring laser, and a phase difference plate is provided on both sides of the Faraday element. Current and magnetic field measuring device. 10. A phase difference caused by the phase difference plate is 1
10. The current / magnetic field measuring apparatus according to claim 8, wherein the current / magnetic field is / 4λ. 11. At least two light beams in an optical path of a ring laser.
The above-mentioned Faraday element and a means for connecting each Faraday element in series are provided, and the means for connecting the Faraday elements in series is provided with a polarization dependency of transmittance so that only a specific polarized light is transmitted or attenuated. The current / magnetic field according to claim 1, 2, 3, 4, 7, 6, 7, 8, 9, or 10, wherein measuring device. 12. A Faraday device having a ring-shaped optical path having two or more Faraday elements and utilizing the Faraday effect of a Faraday element disposed at a position affected by a magnetic field induced by a current to be measured. A photocurrent measuring device for measuring current intensity from a phase difference between two light waves propagating in an element, a light source, two or more Faraday elements, and means for separating light guided from the light source into two. Means for coupling the two separated lights to the Faraday element; means for coupling the respective Faraday elements in series; means for recombining the two lights emitted from the Faraday element; Means for measuring the intensity of the combined light, wherein in the means for coupling the Faraday elements in series,
A photocurrent measuring device characterized in that the transmittance has a polarization dependency so that only a specific polarized light is transmitted or attenuated. 13. A polarizer is provided in the means for connecting the Faraday elements in series.
Or the photocurrent measuring device according to claim 12. 14. The photocurrent measuring device according to claim 13, wherein said polarizer is arranged near said Faraday element. 15. The photocurrent measuring device according to claim 12, wherein the polarization plane is not preserved by the polarization plane preserving fiber in the means for connecting the Faraday elements in series. . 16. The photocurrent measuring apparatus according to claim 12, wherein a depolarizer is arranged in the means for connecting the Faraday elements in series. .