JPH11352158A - Optical fiber measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize highly accurate measurement by enhancing uniformity of a light in an optical fiber. SOLUTION: An optical application measuring instrument for measuring a physical quantity by a variation of a characteristic of light is provided with an optical fiber sensor 8 disposed in the vicinity of an object to be measured; a light source 12 generating light and transmitting it to the sensor 8; a detector 13 for detecting an outgoing light from the sensor 8; an optical system 18a optically combining the sensor 8 with the light source 12 and the detector 13; and a signal processing portion 14 for processing a signal from the detector 13. Optical fiber twisted in a manufacturing stage is used as the fiber for optical fiber sensor 8 and the optical fiber is further twisted when mounting and is disposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical fiber measuring instrument for measuring a physical quantity by utilizing a change in the characteristics of light, and more particularly to an optical fiber measuring instrument having an improved configuration of an optical fiber sensor.

[0002]

2. Description of the Related Art Hitherto, an optical fiber measuring instrument for measuring a physical quantity by light has been proposed. In particular, an optical fiber current measuring device (for example, an optical current transformer) arranges an optical fiber as a sensor in close proximity to a conductor through which a current to be measured flows, and transmits linearly polarized light to the sensor to generate Faraday generated by the current to be measured. It measures the optical rotation angle of the effect.

FIG. 12 is a configuration diagram showing an optical fiber current measuring device described in US Pat. No. 3,605,013 as an example of a conventional optical fiber current measuring device. As shown in FIG. 12, the optical fiber current measuring device includes a laser 1, a polarizer 2, a transmitting fiber 3, an optical fiber sensor (optical guide) 3 ', a conductor to be measured 4, an analyzer 5, an optical detector 6, The optical fiber sensor 3 ′ is configured such that an optical fiber for a sensor is arranged close to the conductor 4 to be measured so as to be wound therearound.

The light emitted from the laser 1 serving as a light source is
The light is converted into linearly polarized light by the polarizer 2 and guided to the optical fiber sensor 3 ′ through the light transmitting fiber 3. A magnetic field is generated by the current I flowing through the conductor to be measured 4, and this magnetic field causes light propagating in the optical fiber sensor 3 ′ to
Optical rotation based on the Faraday effect occurs. After passing through the optical fiber sensor 3 ′, the light is guided to the analyzer 5 through the light transmitting fiber 3, and only the light component in the direction of the analyzer 5 passes and is guided to the photodetector 6. When the current amount I changes, the Faraday rotation angle changes in accordance with the change, so that the light amount after passing through the analyzer 5 changes, and the output of the photodetector 6 changes accordingly. Therefore, by measuring the output of the photodetector 6, the current I can be obtained.
The obtained result is displayed by the display device 7 also serving as a signal processor.

[0005]

However, FIG.
In a conventional optical fiber current measuring device as shown in Fig. 1, the sensitivity of the sensor optical fiber is reduced due to the birefringence induced in the optical fiber by winding the sensor optical fiber around the conductor to be measured, and the temperature and the like are reduced. There is a problem that the measurement results fluctuate depending on the external environment. In addition, in order to use it in a power system, it is necessary to secure not only high-precision measurement but also long-term reliability.

[0006] Such a problem is not limited to the optical fiber current measuring instrument, and various physical quantities of the object to be measured can be measured by utilizing a change in light passing through an optical fiber sensor arranged near the object to be measured. It is also present in various optical fiber meters configured to measure.

The present invention has been proposed to solve such problems of the prior art, and an object of the present invention is to provide an optical fiber measuring instrument capable of performing high-accuracy measurement and having excellent long-term reliability. It is to be.

[0008]

In order to achieve the above object, an optical fiber measuring device is constituted by the following means. In the invention corresponding to claim 1,
An optical fiber sensor arranged near the object to be measured;
A light source that generates light for measurement and sends the light to the sensor, a detector that detects light emitted from the sensor, an optical system that optically couples the sensor with the light source and the detector, and And a signal processing unit for processing a signal of the optical fiber, wherein the optical fiber measuring device for measuring a physical quantity by a change in the characteristics of light is characterized in that a fiber having optical rotation is always used even in the absence of a magnetic field as the optical fiber sensor. .

According to the first aspect of the present invention, by using an optical fiber having optical rotation at all times even in the absence of a magnetic field as the optical fiber sensor, when the light propagates in the optical fiber sensor, the polarization plane of the light becomes optically rotatory. As a result, the light is averaged by being rotated, thereby reducing the non-uniformity inside the optical fiber sensor as viewed from the light. As a result, the effect of linear birefringence induced in the optical fiber and causing non-uniformity can be suppressed, and highly accurate measurement can be realized.

According to a second aspect of the present invention, there is provided an optical fiber sensor disposed near an object to be measured, a light source that generates measurement light and sends the light to the sensor, and detects light emitted from the sensor. An optical fiber measurement device comprising: a detector, an optical system that optically couples the sensor, the light source, and the detector, and a signal processing unit that processes a signal from the detector, and that measures a physical quantity by changing a characteristic of light. The device is characterized in that a twisted optical fiber is used as the optical fiber for the optical fiber sensor.

The invention corresponding to claim 3 is characterized in that the twisted optical fiber is an optical fiber twisted in a manufacturing stage, a mounting stage, or both stages.

According to the invention corresponding to claim 2 or 3,
By using a twisted spun fiber, an optical fiber with small birefringence can be obtained. That is, since the spun fiber is produced by drawing while rotating the preform as a fiber raw material, the asymmetry of the fiber core portion generated at the time of producing the fiber is eliminated, and a fiber having a small birefringence can be realized. In this case, since the optical fiber is twisted at a high temperature in the manufacturing stage, almost no stress is generated inside the fiber, the optical fiber has almost no optical rotation.

However, even if such a homogeneous optical fiber is used, if the optical fiber is given a curvature at the mounting stage, birefringence is induced in the optical fiber due to the curvature, and the characteristics of the optical fiber are substantially impaired. Become uniform. On the other hand, in the present invention, by forming an optical fiber sensor by applying a twist to the optical fiber at the manufacturing stage or the mounting stage or at both stages, a stress is generated in the twisting direction, and the optical propagating light has an optical rotation. You can have.

Therefore, when light propagates in such an optical fiber sensor, the plane of polarization of the light is averaged by the rotation and rotation of the optical rotation, so that the non-uniformity inside the optical fiber sensor as viewed from the light is eliminated. And high-accuracy measurement can be realized without lowering the sensitivity.

According to a fourth aspect of the present invention, in the optical fiber measuring instrument according to the second aspect, the outer diameter of the cladding of the optical fiber for the optical fiber sensor is 2r (μ).
m), assuming that the number of turns of the optical fiber around the object to be measured is m (turns), the torsion rate n _t (turns / m) applied to the optical fiber in the mounting stage is n _t ≦ (125 / 2r) (8.0-log ₁₀ m).

According to the fourth aspect of the present invention, the torsion rate n applied to the optical fiber for the optical fiber sensor is n.
_By specifically defining the value of _t (times / m) with respect to the cladding outer shape 2r (μm), it is possible to suppress a decrease in life based on mechanical strength due to torsion, and to improve long-term reliability.

According to a fifth aspect of the present invention, in the optical fiber measuring instrument of the second or third aspect, the birefringence amount of the entire length of the optical fiber for the optical fiber is a relationship between the number of twists and the birefringence amount. Is characterized in that the number of twists is set so as to have one of values near 0 ° and near an extreme value.

According to the fifth aspect of the present invention, since the total length of the optical fiber for the optical fiber sensor is near 0 ° or near the extreme value, the change in sensitivity becomes small even when the external environment such as temperature changes. High accuracy can be maintained.

According to a sixth aspect of the present invention, in the optical fiber measuring instrument according to the fifth aspect of the present invention, the direction of the plane of polarization of the light incident on the optical fiber sensor is set with respect to the surface on which the optical fiber is disposed. + 45 °, +135
°, -45 °, or -135 °.

According to the sixth aspect of the present invention, by twisting the optical fiber sensor, the degree of averaging the birefringence induced in the fiber can be increased, and as a result, the twist can be reduced with a small amount of twist. Since the amount of change in sensitivity can be reduced, a reduction in life can be suppressed, and high accuracy can be maintained.

A seventh aspect of the present invention is the optical fiber measuring instrument according to the second or fifth aspect, wherein a quartz fiber is used as the optical fiber for the optical fiber sensor, and the number of twists N over the entire length of the optical fiber is N.
(Times) is a value that satisfies 3.5M-1 ≦ N ≦ 3.5M + 1 (M is an integer other than 0).

According to the seventh aspect of the present invention, the number of twists N (times) over the entire length of the quartz fiber for the optical fiber sensor is specifically defined, whereby the rotation angle of the polarization plane of the light due to the twisting. Can be made an integral multiple of around 90 °, whereby the amount of birefringence of the entire length of the optical fiber for the optical fiber sensor can be made close to 0 °. Therefore, even if the external environment such as temperature changes, the amount of change in the sensitivity is reduced without lowering the sensitivity, so that high accuracy can be maintained.

An eighth aspect of the present invention is the optical fiber measuring instrument according to the second or fifth aspect, wherein a quartz fiber is used as the optical fiber for the optical fiber, and the number of twists N (times) over the entire length of the optical fiber is used.
Is a value within ± 1 of a value satisfying | N | = 1.75 + 3.5M (M is a positive integer).

According to the invention corresponding to claim 8, the number of twists N over the entire length of the quartz fiber for the optical fiber sensor is provided.
By specifically defining (times), the amount of birefringence can be made an extreme value. Therefore, even if the external environment such as the temperature changes, the change amount of the sensitivity becomes small, so that high accuracy can be maintained.

The invention corresponding to claim 9 is the invention according to claims 1 to 8
In the optical fiber measuring device corresponding to any one of the above, the average bending radius of the optical fiber for the optical fiber sensor is R (m), the number of turns of the optical fiber around the object to be measured is m, and the wavelength of light is λ. In this case, the outer diameter 2r (μm) of the cladding of this optical fiber is expressed as: (r / 62.5) ² ≦ (80 / 2mπR / 3.8) (R
/0.25) ² (λ / 0.8).

According to the invention corresponding to claim 9, the cladding outer shape 2r (μ) of the optical fiber for the optical fiber sensor is provided.
By defining m) specifically with respect to the average bending radius R (m) and the number m of turns of the optical fiber, and the wavelength λ of light, birefringence due to bending can be reduced, so that accuracy can be improved. .

[0027] The invention corresponding to claim 10 is claim 1.
8 wherein the average bending radius of the optical fiber for the optical fiber sensor is R (m) and the number of turns of the optical fiber around the object to be measured is m. In addition, the outer diameter 2r (μm) of the cladding of this optical fiber is 2R / 125 ≦ (8.0-log ₁₀ m) × 2mπR /
It is a value that satisfies 3.5.

According to the tenth aspect of the present invention, the cladding outer shape 2r of the optical fiber for the optical fiber sensor is provided.
(Μm) is specifically defined for the average bending radius of the optical fiber with respect to R (m) and the number of turns m, so that even when the bending radius of the optical fiber is small, the birefringence due to bending can be reduced and the twisting occurs during the mounting stage. As a result, it is possible to suppress a decrease in the life due to the mechanical strength, and thus it is possible to improve accuracy and long-term reliability.

The eleventh aspect of the present invention relates to the first to tenth aspects.
In the optical fiber measuring device according to any one of the above, the optical fiber for the optical fiber sensor,
The optical fiber is characterized in that a new coating layer is provided after applying a torsional stress to at least the core portion.

According to the eleventh aspect of the present invention, the twist can be fixed by providing a new coating layer after applying a torsional stress to at least the core portion of the optical fiber sensor. Therefore, the optical fiber does not become entangled due to the twisting, and the mounting becomes easy.
Since the influence of linear birefringence induced in the optical fiber and causing non-uniformity can be suppressed by optical rotation of light due to torsional stress, highly accurate measurement can be realized.

The invention corresponding to claim 12 is based on claims 1 to
In the optical fiber measuring instrument of the invention corresponding to any one of the eleventh aspect, the optical fiber for the optical fiber sensor applies a torsional stress to at least a core portion thereof, and at least both ends are fixed, and becomes an outer jacket. It is an optical fiber provided with a protection pipe.

According to the twelfth aspect of the present invention, by providing at least a core with at least both ends fixed by applying a torsional stress to the core of the optical fiber sensor, a protective pipe serving as a jacket is provided outside the core. The influence of linear birefringence induced in the optical fiber and causing non-uniformity can be suppressed by the optical rotation of light due to torsional stress. Therefore, high-precision measurement can be realized, deterioration of the optical fiber itself can be prevented, and long-term reliability can be ensured.

The invention according to claim 13 is the invention according to claims 2 to 12
In the optical fiber measuring instrument according to the invention corresponding to any one of the above, a part of the optical fiber for the optical fiber sensor is provided with a rotating part for adjusting a twist.

According to the thirteenth aspect of the present invention, the provision of the rotating portion for adjusting the torsion in a part of the optical fiber sensor allows the torsion to be adjusted at the mounting stage. Therefore, the predetermined torsion condition can be easily adjusted, so that even if the external environment such as the temperature changes, the amount of change in sensitivity becomes small, and high accuracy can be maintained.

The invention corresponding to claim 14 is based on claim 13
In the optical fiber measuring device according to the invention, a driving unit such as a pulse motor is provided in the rotating unit.

According to the fourteenth aspect of the present invention, by providing a driving unit such as a pulse motor in the rotating unit, it is possible to adjust the torsion of the optical fiber with high accuracy by remote control and to set the optical fiber to a predetermined number of times. . Therefore, even if the external environment such as temperature changes, the amount of change in sensitivity becomes small,
High accuracy can be maintained.

The invention corresponding to claim 15 is the invention according to claim 13
Or the optical fiber measuring instrument according to the invention, which is characterized in that a fixing portion for fixing rotation is provided to the rotating portion.

According to the fifteenth aspect of the present invention, by providing a fixing portion for fixing rotation to the rotating portion,
The post-torsion state can be fixed at a predetermined number of rotations. Therefore, it is possible to suppress the amount of change in sensitivity and maintain high accuracy over a long period of time.

According to a sixteenth aspect of the present invention, in the optical fiber measuring instrument of the first or second aspect, a fiber guide for loosely fixing an optical fiber for an optical fiber sensor is provided. .

According to the sixteenth aspect, the optical fiber can be loosely fixed by the fiber guide. Therefore, it is possible to prevent the optical fiber from being shifted or entangled, so that high accuracy can be maintained.

A seventeenth aspect of the present invention is the optical fiber measuring instrument according to the first or second aspect, wherein at least one of the optical fiber for the optical fiber sensor and the coupling optical system is kept in a dry state by a flange or a vacuum. It is characterized by being disposed in a drawn container.

According to the seventeenth aspect of the present invention, at least one of the optical fiber and the inside of the coupling optical system is arranged in a flange kept in a dry state or in a vacuum-evacuated container. High-precision measurement that can avoid the influence can be realized for a long time.

According to an eighteenth aspect of the present invention, an optical fiber sensor disposed near an object to be measured, a light source that generates light for measurement and sends the light to the sensor, and detects light emitted from the sensor. An optical fiber measurement device comprising: a detector, an optical system that optically couples the sensor, the light source, and the detector, and a signal processing unit that processes a signal from the detector, and that measures a physical quantity by changing a characteristic of light. In the apparatus, a depolarizer is attached to the light source to supply unpolarized light to the optical system.

According to the eighteenth aspect, since the polarization state of the output light from the light source can be depolarized (randomized), the polarization state can be changed even if an external influence is exerted between the light source and the optical system. It becomes non-polarized, and the polarization state determined by the optical system can be realized without lowering the light output. Therefore, highly accurate measurement that is hardly affected by the external environment can be realized.

The invention corresponding to claim 19 is the invention according to claim 18
In the optical fiber measuring device according to the invention, a polarization maintaining fiber is used as the depolarizer, and a characteristic axis of the polarization maintaining fiber is about 45 ° and about −45 ° with respect to a polarization plane of light emitted from the light source. , About 135 ° or about 135 ° to the light source.

According to the invention corresponding to claim 19, the polarization state of the output light from the light source can be depolarized (randomized), so that the polarization state determined by the coupling optical system is realized without lowering the light output. it can. Therefore, highly accurate measurement that is hardly affected by the external environment can be realized.

According to a twentieth aspect of the present invention, there is provided an optical fiber sensor disposed near an object to be measured, a light source for generating measurement light and sending the light to the sensor, and detecting light emitted from the sensor. An optical fiber measurement device comprising: a detector, an optical system that optically couples the sensor, the light source, and the detector, and a signal processing unit that processes a signal from the detector, and that measures a physical quantity by changing a characteristic of light. The apparatus is characterized in that the light interference of the optical system is measured by using light propagating in the same optical path in opposite directions to each other in order to equalize the influence from the outside.

According to the twentieth aspect of the present invention, an optical fiber measuring instrument capable of performing high-accuracy measurement and having excellent long-term reliability can be realized by detecting a light interference phenomenon of an optical system.

The invention corresponding to claim 21 is claim 1
20. A plurality of optical fiber measuring devices according to the invention corresponding to any one of the twenty optical devices. According to the invention corresponding to claim 21, application of a current differential system or the like becomes possible by comprising a plurality of optical fiber measuring instruments, and high-precision measurement that is hardly affected by an external environment becomes possible.

The invention corresponding to claim 22 is based on claim 21.
In the optical fiber measuring device according to the invention, a plurality of optical fiber measuring devices are connected in series, and at least the optical fiber measuring devices are connected by a low birefringent fiber or a high birefringent fiber (polarization maintaining fiber). It is characterized by.

According to the invention corresponding to claim 22, since at least the optical fiber measuring devices are connected by a low birefringence fiber or a high birefringence fiber, high precision measurement can be realized or a change in the external environment can occur. Difficult measurement can be realized.

[0052]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A plurality of embodiments in which the optical fiber measuring device according to the present invention is applied to an optical fiber current measuring device will be described below with reference to FIGS.
FIG. 1 shows a configuration diagram of a first embodiment according to the present invention. As shown in FIG. 1, in the optical fiber current measuring device according to the present embodiment, the optical fiber sensor 8
It is arranged so as to surround the conductor 4 to be measured.

As shown in FIG. 1, the optical fiber current measuring device according to the present embodiment is roughly divided into a sensor optical unit 9,
It comprises a signal processing unit 10 and a transmission fiber unit 11.

The signal processing unit 10 includes a light source 12 for generating measurement light, a detector 13 for detecting two lights from the sensor optical unit 9 and converting the two lights into an electric signal corresponding to the intensity.
A signal processing circuit 14 that performs arithmetic processing on the signal obtained by the detector 13 and an output terminal 15 that outputs a processing result are provided. The light source 12 is constituted by a laser diode or a super luminescent diode.

The transmission fiber section 11 includes a light transmission fiber 16 for transmitting light from the light source 12 in the signal processing section 10 to the sensor optical section 9, and two detection fibers in the signal processing section 10 from the sensor optical section 9. And two light receiving fibers 17 for transmitting light to the container 13.

On the other hand, the sensor optical section 9 includes a coupling optical section 18.
a and an optical fiber sensor section 18b. The coupling optical unit 18a includes four lenses 19 to 22,
It comprises a polarizer 23, two beam splitters 24 and 25, and two analyzers 26 and 27. Here, of the four lenses 19 to 22, the first lens 19
Is used to convert the light from the light transmitting fiber 16 into a parallel beam, and the second lens 20 receives the light from the optical fiber sensor 18b and receives the light emitted from the optical fiber sensor 18b. Used to
The third and fourth lenses 21 and 22 are used to collect the parallel beams and enter the respective light receiving fibers 17.

The polarizer 23 is used to convert the light into linearly polarized light having a 45-degree direction with respect to the horizontal direction (the plane on which the optical fiber 8 is disposed). The two beam splitters 24 and 25 convert the light into its incident light. Each is used to split transmitted light and reflected light according to the direction. The two analyzers 26 and 27 are used to extract orthogonal polarization components in the x and y directions, respectively, by transmitting linearly polarized light in the horizontal and vertical directions, respectively.

In this case, the coupling optical section 18a transmits the light from the light transmitting fiber 16 to the first lens 19 and the polarizer 2
3. One end of the optical fiber sensor section 18b is sent via the first beam splitter 24 and the second lens 20.

The light in the reflection direction from the optical fiber sensor section 18b is transmitted through the second lens 20 and then reflected by the first lens.
, And is transmitted to the second beam splitter 25 to be split into light in two directions. The one split light is transmitted to the first light receiving fiber 1 via the first analyzer 26 and the third lens 21.
7 The other split light is secondly transmitted to the other light receiving fiber 1 via the analyzer 27 and the fourth lens 22.
7

On the other hand, the optical fiber sensor section 18b is composed of an optical fiber sensor 8 composed of an optical fiber wound around the conductor 4 under measurement through which the current to be measured flows by an integral number of times of 1 or more. 8 has a reflective end 28 at the end thereof. Here, a case where a highly reliable quartz fiber is used as the optical fiber for the optical fiber sensor 8 will be described, but the present invention is not particularly limited to the quartz fiber. Also, the reflection end 2 of the optical fiber sensor 8
Numeral 8 reflects the light propagating in the optical fiber sensor 8, returns the light again into the optical fiber sensor 8, and propagates the light in the opposite direction. At this time, by using the reflection end 28, the input end and the output end of the optical fiber completely coincide with each other. In the drawing, reference numeral 29 indicates such an input / output end, and the input / output end 29 is housed in a structure. The input / output end 29, which is both ends of the optical fiber sensor 8, and the above-described reflection end 28 are arranged close to each other.

FIG. 2 is an explanatory diagram showing details of the optical fiber sensor 8. As an optical fiber for the optical fiber sensor 8, a single mode fiber that always has optical rotation even in the absence of a magnetic field is used, and this optical fiber itself is a (span) fiber twisted in a manufacturing stage. The optical fiber for the optical fiber sensor 8 is composed of a core portion 30 through which light propagates, a cladding layer 31 and a coating layer 32 provided sequentially on the outer periphery thereof, and is mechanically twisted rightward in the mounting stage. I have.

The current measurement of the conductor 4 to be measured by the optical fiber current measurement of FIG. 1 having the above configuration is performed as follows. First, light emitted from the light source 12 of the signal processing unit 10 is transmitted to the coupling optical system 18a of the sensor optical unit 9 through the light transmitting fiber 16.

The light from the light transmitting fiber 16 is converted into a parallel beam by the first lens 19, converted into linearly polarized light by the polarizer 23, and then transmitted through the first beam splitter 24 to be converted into the second beam. And is incident on the starting end of the optical fiber sensor section 18b.

The light incident on the optical fiber sensor section 18b propagates through the optical fiber sensor 8 and is reflected by the reflection end 28, and then returns again into the optical fiber sensor 8, and propagates in the opposite direction to the coupling optical system 18a side. From the incident end, which is the start end of. In this case, the optical fiber sensor unit 1
The polarization plane of the light passing back and forth in 8b rotates due to the Faraday effect induced by the measured current flowing through the conductor 4 to be measured.

The light emitted from the optical fiber sensor 8 is converted into a parallel beam by the second lens 20 of the coupling optical system 18a, then reflected by the first beam splitter 24, and reflected by the second beam splitter 25. It is split into light in two directions.

In this case, one of the split beams from the second beam splitter 25 passes through the third lens 21 and the light receiving fiber 17 after the first analyzer 26 extracts the polarization component in the x direction. Then, it is sent to one detector 13 of the signal processing unit 10. Further, the other split light is obtained by extracting the polarization component in the y direction by the second analyzer 27.
The light is sent to the other detector 13 via the fourth lens 22 and the light receiving fiber 17.

In this manner, the light of the polarization components in the x direction and the y direction is sent to each detector 13 and these detectors 13
The signals of the respective polarization components obtained in (1) are sent to the signal processing circuit 14 where they are subjected to arithmetic processing, and the obtained processing results, that is, the measurement results, are output from the output terminal 15.

The signal flow in the optical fiber current measuring device shown in FIG. 1 has been described above. In particular, the optical fiber sensor 8 has a uniform core portion 30 and the light inside the optical fiber sensor 8 because of its configuration. When propagating, the plane of polarization of the light rotates. This will be described below.

First, the optical fiber for the optical fiber sensor 8 is a single mode fiber that always has optical rotation even in the absence of a magnetic field, and the optical fiber itself is twisted by drawing while rotating the preform in the manufacturing stage. Core fiber 30 produced during fiber fabrication because of
Is eliminated, and the amount of birefringence is reduced.
(<2 ° / m). That is, the core portion 30 is made uniform.

When the optical fiber is bent, a main axis of birefringence is generated in the bending direction, that is, the direction in which the optical fiber is arranged (x-axis) and the direction perpendicular thereto (y-axis). Cause. On the other hand, the optical fiber sensor 8 is mechanically twisted rightward even in the mounting stage.
The light propagating inside rotates. That is, in FIG. 2, when light in a linear direction propagates in the axial direction (z-axis direction) of the optical fiber sensor 8, points A and B
The direction of the polarization plane at the point is shown, and since the optical fiber is twisted and twisted, the polarization plane of the light is A at the point B.
The light is rotated by an angle θ as compared with the point. The same operation can be obtained even when the optical fiber is mechanically twisted to the left.

As described above, when light propagates in the optical fiber sensor 8, the light is averaged due to rotation of the polarization plane of the light, so that the non-uniformity inside the optical fiber sensor 8 as viewed from the light can be eliminated. And high-accuracy measurement can be realized without lowering the sensitivity. Since the optical rotation due to the torsional stress is a fixed ratio to the amount of twist, if the amount of twist is known in advance, the amount of optical rotation can be obtained, and the Faraday effect and the magnetic field generated by the measured current 4 can be obtained. Can be separated. In particular, in the present embodiment, since the optical path is reciprocated using the reflecting mirror 28, the amount of optical rotation due to twisting is reversed in the going and returning directions, and is canceled out. Has the advantage that it can be measured.

Therefore, according to the present embodiment, as a result of imparting optical rotation to the optical fiber, non-uniformity inside the fiber can be eliminated, so that highly accurate current measurement can be realized.

It is needless to say that a similar effect can be obtained even in a configuration having no reflection end. Next, a second embodiment of the optical fiber current measuring device according to the present invention will be described.
Note that this embodiment corresponds to a modification of the above-described first embodiment, and a description of a configuration similar to that of the first embodiment will be omitted.

That is, in the present embodiment, the amount of twist applied to the optical fiber of the optical fiber sensor 8 as shown in FIG. 2 is specified to improve long-term reliability. In particular, the life of the optical fiber sensor 8 is important for applying the optical fiber current measuring device to the power system.

First, the lifetime t _{s of} the optical fiber twisted in the mounting stage is expressed by the following equation (1). _{ln (t s / t pe1)} = ln (P f / L · N p1) -ln (b) -n · ln (σ s / σ p1) b = ln (1 + N p2 / N p1) / ln {1+ ( σ _p2 ) _n · t _pe2 / (σ _p1 ) ⁿ · t _pe1 … (1) In the equation (1), each parameter represents a parameter of the strength test of the optical fiber twisted at the manufacturing stage. t _pe1 and t _pe2 are the first and second proof test times,
P _f is the failure probability, L is the fiber length, N _p1 and N _p2 are 1,
Number of breaks per unit length during the second proof test time, σ
_p1 and _σp2 are stresses at the time of the first and second proof stress tests, and n is a slope obtained by a dynamic fatigue test.

Σ _s is the stress in actual use and is equal to the maximum principal stress of the fiber. That is, it is expressed as follows. σ _s = [σ _zmax + {(σ _zmax ) ² + 4G ² θ ² r ² }
^1/2 ] / 2 where G is the transverse elastic modulus, θ is the twist angle per unit length, and r is the outer radius of the optical fiber cladding layer. Σ _zmax is the maximum stress of bending, and is expressed by the following equation.

Σ _zmax = {r / (R + r)} E where R is the bending radius of the fiber and E is the Young's modulus. Specifically, a quartz fiber is used as the optical fiber for the optical fiber sensor, the fracture establishment P _f = 10 ⁻⁵ , the outer radius of the optical fiber clad r = 62.5 μm, the bending radius of the fiber is 0.5 m, and the number of turns m = 1, When a strength test was performed, n = 20, t _pe1 = 1.2 (s),
b = 0.0492, σ _p1 = 3.196 × 10 ⁵ (P
a), N _p1 = 1.43 (co / m), E = 7.2 × ^{10 10}
(N / m ² ) and G = E / {2 · (1 + 0.2)}. Then, when this result was substituted into the above equation (1), the dependency of the fiber breaking life on the number of twisting of the fiber was obtained as shown in FIG. As is clear from FIG. 3, when the twisting rate is set to 8 times / m or less,
The mechanical life of 25 years or more required for the power system can be secured.

More specifically, the probability of fracture P _f = 10 ^-5
In order to secure a mechanical life of 25 years or more, the following conditional expression is required by further simplifying the expression (1). That is, when the outer diameter of the clad of the optical fiber for the optical fiber sensor is 2r (μm) and the number of turns of the optical fiber around the object to be measured is m (turns), the twisting ratio n added to the optical fiber in the mounting step is n _{If t} (times / m) satisfies the following expression (2), a life of 25 years or more can be secured with a breakage probability P _f = 10 ⁻⁵ .

N _t ≦ (125 / 2r) (8.0−log ₁₀ m) (2) In the equation (2), the bending radius R ≦ 0.
This is a necessary condition that is satisfied when the distance is 5 m, and when R> 0.5 m, the life can be further extended. By the way, if the condition of FIG. 3 is substituted, n _t ≦ 8.0 (times / m)
= 16.0π (radian / m), which is consistent with the result of FIG.

Therefore, by applying a twist that satisfies the condition of the formula (2) to the optical fiber, the optical fiber becomes homogeneous, so that highly accurate measurement can be realized and long-term reliability is improved. Can be.

Next, a third embodiment of the optical fiber current measuring device according to the present invention will be described. Note that this embodiment corresponds to a modification of the above-described first embodiment, and a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the present embodiment, in the optical fiber sensor 8 as shown in FIG. 1, the birefringence of the entire length of the optical fiber is near 0 ° or near the extreme in the relationship between the number of twists and the birefringence. The number of twists is set as described above to ensure high accuracy.

FIG. 4 shows the relationship between the number of twists over the entire length of the optical fiber and the amount of birefringence (arbitrary scale) in the quartz fiber. At this time, the polarization plane of the light incident on the optical fiber sensor 8 is +4 with respect to the direction in which the optical fiber is arranged.
It is close to 5 ° (similar results are obtained near + 135 °, −45 °, and −135 °). Here, the neighborhood is ± 2
A range of 2.5 ° is shown, but if the range is ± 10 °, the effect is even greater. Twist in quartz fiber フ ァ イ バ ー
And the rotation light amount ω are expressed by the following equation.

Ω = 0.073 ° (radian) The coefficient 0.073 slightly changes depending on the temperature. Here, there is a relationship of ξ = 2πN between the number of twists N (times) and the amount of twist ξ. The condition that the amount of twist と す る is set to be a multiple of 3.5 times is expressed by the following equation (3).

2π (3.5M−1) ≦ ξ (= 2πN) ≦ 2π (3.5M + 1) (3) In the equation (3), M is a positive integer, and ξ
A negative value indicates a leftward twist. If the amount of twist ξ is defined as shown in the equation (3), the amount of rotation ω is (π / 2)
M is substantially equal to M, and as shown in FIG. 4, the amount of birefringence over the entire length of the optical fiber is near 0 °.

When the current value is low, there is a relationship between the sensitivity S of the optical fiber current measuring device and the amount of birefringence δ as expressed by the following equation (4). S = sin δ / δ (4) Accordingly, if the amount of birefringence δ is near 0 °, highly sensitive and highly accurate measurement can be performed. Further, even if the amount of rotation is slightly changed due to a temperature change, since the birefringence amount δ is near 0 °,
The sensitivity S hardly changes, and the temperature stability is excellent.

In FIG. 4, the number of twists N (times)
Is near the value obtained by adding 1.75 to a multiple of 3.5 times, and is expressed by the following equation (5). | N | = 1.75 + 3.5M (5) In the equation (5), M is a positive integer. If the number of twists N is defined so as to be close to satisfying the expression (5), that is, within ± 1, the amount of birefringence becomes close to an extreme value as shown in FIG. In this case, the sensitivity S of the measuring device is slightly reduced, but since the amount of birefringence is near the extreme value, the sensitivity does not fluctuate even if the amount of rotation changes slightly due to a temperature change.

As described above, the birefringence of the optical fiber sensor is set to a value close to 0 ° or to an extremum in the relationship between the number of twists and the amount of birefringence. A highly accurate measuring instrument which is hardly affected can be realized. Also, the direction of the plane of polarization of light incident on the optical fiber sensor (the direction of linearly polarized light) is + 45 ° and +135 with respect to the plane on which the optical fiber is arranged.
By setting the angle in the vicinity of °, -45 °, or -135 °, the amount of change in sensitivity can be reduced with a small amount of twist, and a reduction in life can be suppressed.

Next, a fourth embodiment of the optical fiber current measuring device according to the present invention will be described. Note that this embodiment corresponds to a modification of the above-described first embodiment, and a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in this embodiment, the cladding outer diameter 2r (μm) of the optical fiber sensor 8 as shown in FIG.
By defining the average bending radius R (m) and the number of turns m of the optical fiber, and the wavelength λ of the light,
The purpose is to improve the accuracy by reducing birefringence due to bending.

First, an optical fiber sensor 8 having a clad outer diameter of 2r (μm) has an average bending radius R around the conductor 4 to be measured.
When installed in (m), the amount of birefringence Δβ (° / m) due to bending induced in the optical fiber is given by the following (6)
It is expressed by an equation.

Δβ = | (πEc / λ) (r / R) ² × (180 / π) | (6) where E is Young's modulus (= 7.75 × 10 ⁹ kg / m ²⁾
(Quartz)) and c are photoelastic constants (= −3.5 × 10 ⁻¹¹ m)
² / kg), and λ is the wavelength of light.

FIG. 5 shows that, when r = 62.5 μm, the average bending radius R and the amount of birefringence Δβ increase, and the sensitivity of the optical fiber sensor 8 decreases. Therefore,
The amount of birefringence over the entire length of the optical fiber sensor 8 is δ
(°), assuming that the number of turns around the conductor 4 to be measured of the optical fiber sensor 8 is m, the following equation is obtained from the above equation (6).

Δ = 3.8 × (0.25 / R) ² (r / 6
2.5) ² (0.8 / λ) × 2mπR In this case, since the sensitivity S of the optical fiber sensor 8 is expressed by the above equation (4), in order to keep the measurement accuracy within ± 1%, It is desirable that δ ≦ 0.35 radian = 20 °. 4, when the number of twists over the entire length of the optical fiber is set to about 3.5 or more, the amount of birefringence becomes 1/4 or less as compared with the case where the number of twists is zero. Therefore, if fiber parameters are set so as to suppress the amount of birefringence induced by bending to 20 ° × 4 = 80 ° or less,
Measurement accuracy of ± 1% can be easily satisfied.

Therefore, the parameters of the optical fiber sensor 8 according to the present embodiment are set so as to satisfy the condition shown in the following equation (7). (R / 62.5) ² ≦ (80 / 2mπR / 3.8) (R / 0.25) ² (λ / 0.8) (7) In the equation (7), R = 0.1 ( m), m = 10 (times),
Substituting λ = 0.8 (μm), the outer radius r of the cladding of the optical fiber sensor is 45 μm or less.

Also, R ≧ 0.25 (m), m = 1
(Times), when λ = 1.3 (μm) and r <40 (μm), δ <3 °, and even if the number of twists over the entire length of the optical fiber is zero, a predetermined accuracy can be satisfied. further,
If this is twisted about 3.5 turns or more over the entire length of the optical fiber, δ <0.75 °, sensitivity S> 0.999997 can be realized, and an ultra-high-precision optical fiber current measuring device can be realized.

Therefore, according to the present embodiment, the amount of birefringence over the entire length of the optical fiber can be greatly reduced by using the parameters of the optical fiber sensor 8 that satisfies the above equation (7). The accuracy of the vessel can be increased.

Next, an optical fiber current measuring device according to a fifth embodiment of the present invention will be described. Note that this embodiment corresponds to a modification of the above-described first embodiment, and a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in this embodiment, the cladding outer diameter 2r (μm) of the optical fiber sensor 8 as shown in FIG.
Is defined with respect to the average bending radius R (m) and the number of turns m of the optical fiber, the amount of birefringence over the entire length of the optical fiber is reduced, the accuracy is increased, and the reduction in mechanical life is suppressed to ensure long-term reliability. It enhances the character.

The condition for ensuring the mechanical life required for the power system is as follows:
Twist rate n ^t added to the mounting stage for optical fiber
(Times / m). In order to reduce the amount of birefringence over the entire length of the optical fiber to a certain value, as shown in FIG. 4, at least about 3.5 over the entire length of the optical fiber.
Twist more than rotation.

Therefore, if the average bending radius of the optical fiber sensor 8 is R (m), the following equation is established. (125 / 2r) (8.0-log ₁₀ m) × 2mπR ≧
3.5 That is, the optical fiber sensor 8 satisfies the following expression (8).

2r / 125 ≦ (8.0−log ₁₀ m) × 2mπR / 3.5 (8) where r is the outer radius (μm) of the cladding of the optical fiber,
m is the number of turns (turns) of the optical fiber around the conductor 4 to be measured. In this equation (8), m = 1 (times), R =
Substituting 0.05 (m) gives r ≦ 45 (μm).

Therefore, according to the present embodiment,
By using the optical fiber sensor 8 that satisfies the expression (8), even when the bending radius of the optical fiber sensor 8 is small, the amount of birefringence over the entire length of the optical fiber can be reduced, and the optical fiber sensor 8 can be mechanically twisted during mounting. Since a reduction in the life can be suppressed, an optical fiber current measuring instrument excellent in accuracy and long-term reliability can be realized.

Further, as a modified example of the present embodiment,
The condition of the cladding outer diameter 2r of the formula (8) and the cladding outer diameter 2r of the formula (7) described in the fourth embodiment are explained.
r, the outer radius r of the cladding of the optical fiber sensor 8 is less than 40 μm (80 μm
Less). According to this configuration, it is possible to realize an optical fiber current measuring device that is further highly accurate and has excellent long-term reliability.

FIG. 6 is a view showing a sixth embodiment of the optical fiber current measuring device according to the present invention, and is an explanatory view showing the details of the optical fiber sensor 8 in particular. Note that this embodiment corresponds to a modification of the above-described first embodiment, and a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the present embodiment, FIG.
As shown in FIG. 5, torsion stress is applied to these portions by twisting the core portion 30, the cladding layer 31, and the coating layer 32 of the optical fiber sensor 8, and the twisting occurs around the coating layer 32. Is fixed by an external coating layer 33 of acrylic or the like newly provided.

With this configuration, the entanglement of the optical fiber due to the twist can be prevented, the mounting becomes easy, and the influence of the linear birefringence induced in the optical fiber and causing the non-uniformity is reduced. Can be suppressed by optical rotation of light due to stress.

As described above, according to the present embodiment, the core layer 30 of the optical fiber sensor 8 moves from the coating layer 3
By applying a torsional stress to up to two portions and providing an outer coating layer 33 around the portion to fix the torsion, an extremely easy-to-handle and high-precision optical fiber current measuring device can be realized. In addition, it is not always necessary to apply a torsional stress to the entire portion from the core portion 30 to the coating layer 32, and by applying at least a torsional stress to the core portion 30, similarly excellent effects can be obtained. .

FIG. 7 is a diagram showing a seventh embodiment of the optical fiber current measuring device according to the present invention, and is an explanatory diagram showing the details of the optical fiber sensor 8 in particular. Note that this embodiment corresponds to a modification of the above-described first embodiment, and a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the present embodiment, FIG.
As shown in FIG. 7, the sixth embodiment is characterized in that the torsion stress is applied to these portions by twisting the core portion 30, the cladding layer 31, and the coating layer 32 constituting the optical fiber of the optical fiber sensor 8. This is the same as the embodiment, but the method of fixing this torsion is different. In the present embodiment, the torsion is fixed by connectors 34 for fixing both ends of the optical fiber sensor 8, and a protective pipe 35 serving as a jacket is provided outside the optical fiber sensor 8. Also, connectors 3 at both ends
At least one of the four is provided with a torsion fixture 36 for fixing after adjusting the torsion. further,
Although not shown, a guide for the optical fiber sensor 8 may be provided partially or entirely in the pipe 35.

With this configuration, after passing the optical fiber sensor 8 through the pipe 35, the number of twists over the entire length of the optical fiber sensor 8 can be easily determined by rotating one connector 34. Therefore, the entanglement of the optical fiber due to the twist can be prevented, the mounting becomes easy, the number of twists can be easily adjusted in the mounting stage, and the straight line which is induced in the optical fiber and causes the non-uniformity. The influence of birefringence can be appropriately suppressed by optical rotation of light due to appropriate torsional stress.

As described above, according to the present embodiment, the core layer 30 of the optical fiber sensor 8 starts to cover the coating layer 3.
2, a torsion stress is applied to both ends of the optical fiber sensor 8, and a pipe 35
Is provided, it is possible to realize a highly accurate optical fiber current measuring device which is very easy to handle, can prevent deterioration of the optical fiber sensor 8 itself, and can be easily adjusted at the mounting stage.

It is not always necessary to apply a torsional stress to the entire portion from the core portion 30 to the coating layer 32. By applying a torsional stress to at least the core portion 30, similarly excellent effects can be obtained. Things. Further, the means for fixing both ends of the optical fiber sensor 8 is not limited to the configuration of the connector 34 or the torsion fixture 36 or the like, and the specific configuration can be appropriately selected. The general configuration can be appropriately selected.

Further, when the optical fiber sensor 8 described in the sixth embodiment is housed in the protection pipe 35 of the present embodiment, the protection from the outside can be further strengthened, and a high-precision optical fiber current measuring device is realized. it can.

FIG. 8 is a diagram showing an eighth embodiment of the optical fiber current measuring device according to the present invention, and is an explanatory diagram showing the details of the sensor optical unit 9 in particular. Note that this embodiment corresponds to a modified example of the above-described first embodiment, and therefore a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the embodiment, as shown in FIG. 8, the reflection end 28 is connected to the optical fiber sensor 8 coming out of the coupling optical section 18a. Reflection end 2
Reference numeral 8 is connected to a rotating portion 37 fixed to a flange or a container (not shown), and the rotating portion 37 is connected to a driving portion 38 such as a pulse motor that can be driven from the outside. The rotating section 37 is provided with a fixing section 39 such as a screw for fixing the twist of the optical fiber sensor 8. The optical fiber sensor 8 is housed in a flange (not shown) or a square groove of a container,
It is loosely fixed by 0 (here, the optical fiber sensor is wound only once, but may be wound several times). Note that a desiccant 41 packed in a bag is also contained in the flange or the container, and a desiccant is also contained in the coupling optical unit 18a (not shown).

With this configuration, it is possible to adjust the torsion at the mounting stage by the rotating unit 37. If the driving unit 38 which can be driven from the outside is used, further adjustment can be easily and accurately realized. After the adjustment, the twisted state can be fixed by the fixing portion 39. At this time, the sum of the birefringence not only of the optical fiber itself but also of the connectors attached to both ends can be minimized. For this purpose, the output of the optical fiber current measuring device may be adjusted so as to be near the extreme value, especially near the maximum value. The optical fiber sensor 8 is loosely fixed by the fiber guide 40 to prevent the optical fiber from shifting or tangling. In particular, in the case of a plurality of turns, the guides to be passed for each turn are separated to prevent the fibers from becoming entangled. The desiccant 41 in the flange or the container or the desiccant in the coupling optical system 18a can avoid the effects of dew condensation and high humidity on the optical fiber sensor 8 and the optical components in the coupling optical system 18a.

As described above, according to the present embodiment, the rotating unit 37 and the driving unit 3 connected to the optical fiber sensor 8 are used.
8, since the optical fiber sensor 8 can be fixed at a predetermined number of twists by the fixing portion 39, the amount of change in sensitivity can be suppressed and high accuracy can be maintained over a long period of time. In addition, by providing the fiber guide 40, the optical fiber sensor 8 can be loosely fixed, and deviation and entanglement can be prevented, so that high accuracy can be maintained. Furthermore, desiccant 4
The optical fiber sensor 8 or the coupling optical system 1
By arranging at least one of the flanges 8a in a flange kept in a dry state or in a vacuum-evacuated container, it is possible to avoid the effects of dew condensation and high humidity, and to achieve high-accuracy measurement over a long period of time.

Here, the drive unit 38 is adjusted, and then the fixed unit 39 is adjusted.
As a result, even if the rotating portion 37 is fixed and then removed, the same excellent effect can be obtained. The same effect can be obtained even if a gas having a high dew point such as dry air or nitrogen is sealed in order to create a dry state. Further, a hole is made in the coupling optical system 18a,
By improving the air permeability with the flange or the inside of the container, it is possible to avoid the effects of condensation and high humidity.

FIGS. 9A to 9C are views showing a ninth embodiment of the optical fiber current measuring device according to the present invention, and are explanatory diagrams showing details of the light source 12 and the light transmitting fiber. is there. Note that this embodiment corresponds to a modified example of the above-described first embodiment, and therefore a description of a configuration equivalent to that of the first embodiment will be omitted.

That is, in the present embodiment, FIG.
As shown in (a), the light source 12 is connected to the light transmitting fiber 16 via a depolarizer (polarization canceller) 42. The depolarizer 42 is a Rio type depolarizer (Lyot-dep).
olarizer), the two highly birefringent fibers (polarization maintaining fibers) are connected such that the characteristic axes thereof have an angle of 45 °. The ratio of the fiber lengths L1 and L2 is 1: 2.

With this configuration, regardless of the polarization direction of the light emitted from the light source 12, the amount of light in the orthogonal mode of the light emitted from the depolarizer 42 becomes equal, and the phase difference between the orthogonal components becomes greater than the coherent length. Can be.
Therefore, even if there is some change in the external environment of the light transmitting fiber 16, the light output of the polarizer 23 of the coupling optical unit 18a can be kept constant.

By the way, the conditional expression for setting the coherence length or more satisfies the following expression (9). δω · δτ · z ≧ π (9) where δω is the spectrum width of the light source, δτ is the time difference between orthogonal modes, and z is the fiber length L1. Light source 12
Is a Gaussian spectrum, has a spread width (δλ; wavelength width) of 7 nm, and the time difference between the orthogonal modes of the fibers constituting the depolarizer 42 is 1 ns / km, the fiber length L1 becomes 0.5 m or more.

In another embodiment of the present invention, FIG.
As shown in (b), a polarization maintaining fiber (highly birefringent fiber) 43 is provided in the light source 12, and the characteristic axis of the polarization maintaining fiber is about 45 ° with respect to the polarization plane of the light emitted from the light source 12 and about − 45 °, about 135 ° or about -135
Mounted at an angle of °. FIG. 9C shows a state in which the mounting angle is 45 ° (the figure is an elliptical jacket type, but any type such as a panda, a bowtie, an elliptical clad, an elliptical core, a rectangular core, and a four-part core) is shown. Good). n1 and n2 represent the natural axes of the polarization maintaining fiber, and the natural axes of the light emitted from the light source 12 are 45 ° with respect to the polarization plane.

With this configuration, the emission polarization direction of the light source 12 is limited, but the same operation as that of FIG. 9A can be obtained. At this time, the required fiber length may be L1 or more.

In the case of FIG. 9 (a), even if the depolarizer 42 is mounted at an arbitrary position between the light source 12 and the coupling optical system 18a, almost the same operation is obtained. As described above, according to the present embodiment, the depolarizer 42 or the polarization maintaining fiber 4 is disposed between the light source 12 and the coupling optical system 18a.
3, the light source 12 and the coupling optics 18
Since the polarization state becomes non-polarized even if an external influence is applied between a, the polarization state determined by the coupling optical system 18a can be realized without lowering the optical output. Therefore, highly accurate measurement that is hardly affected by the external environment can be realized.

FIG. 10 is a diagram showing a ninth embodiment of the optical fiber current measuring device according to the present invention. This embodiment is an embodiment in which the rotation angle of the polarization plane (polarization plane) of light is measured using the interference of light, while the first embodiment measures the rotation angle of the polarization plane (polarization plane) of light. As shown in FIG. 10, in the optical fiber current measuring device of the present embodiment, the optical fiber sensor 8 is arranged so as to surround the conductor 4 to be measured.

As shown in FIG. 1, the optical fiber current measuring device of the present embodiment is roughly composed of an optical fiber sensor section 44 and a signal control processing section 45. The optical fiber sensor unit 44 includes the optical fiber sensor 8, the λ / 4 elements 46a and 46b (here, fiber type λ / 4 elements), and the polarization maintaining fiber (high birefringence fiber) 47. / 4 element 4
Reference numeral 6 denotes an arrangement for converting linearly polarized light propagated by the polarization maintaining fiber 47 into circularly polarized light. Each element is connected by fusion.

The signal control processing unit 45 includes a light source 12, a detector 13, a signal control processing circuit 48, a fiber polarizer 49,
It comprises a phase modulator 50 and an output terminal 15. The light source 12 is composed of an SLD (super luminescent diode). The signal control processing circuit 48 supplies a modulation signal to the phase modulator 50 and detects the output of the detector 13 to calculate the current value I to be measured. The obtained result is output from the output terminal 15.

The current measurement of the conductor 4 to be measured by the optical fiber current measurement shown in FIG. 10 having the above configuration is performed as follows. First, the light emitted from the light source 12 of the signal control processing unit 45 is transmitted to the transmission fiber 51 and the fiber polarizer 4.
9. The signal passes through the transmission fiber 52 and is divided into two parts.
It is led to 0. In the phase modulator 50, each light undergoes sine wave modulation and sawtooth wave modulation, and propagates through the optical fiber sensor unit 44 clockwise (cw) and counterclockwise (ccw). The clockwise light passes through the polarization maintaining fiber 47,
The light is converted into right-handed circularly polarized light in the traveling direction by the λ / 4 element 46a, propagates through the optical fiber sensor 8 and undergoes the Faraday effect, and is then converted into linearly polarized light by the λ / 4 element 46b to maintain polarization. After passing through the fiber 47, the light enters the side opposite to the side where the phase modulator 50 exits. The counterclockwise light passes through the polarization maintaining fiber 47 and passes through the λ / 4 element 46b.
Is converted into circularly polarized light clockwise with respect to the traveling direction, and is similarly subjected to the Faraday effect in the optical fiber sensor 8. The light is converted into linearly polarized light by the λ / 4 element 46a, passes through the polarization maintaining fiber 47, and enters the phase modulator 50 on the side opposite to that at the time of emission. The two lights that have entered the phase modulator 50 overlap with each other via the transmission fiber 52, pass through the fiber deflector 49, and enter the detector 13.

Assuming that the fiber length of the optical fiber sensor section 44 is L, the modulation frequency fm of the sine wave is fm = c / 2nL (10) to suppress drift. Here, c is the speed of light, and n is the refractive index of the fiber. When the refractive index is different, the modulation frequency fm is determined in consideration of the difference.

At this time, since the clockwise light and the counterclockwise light have different propagation speeds in the optical fiber sensor 8 due to the Faraday effect, a phase difference φs occurs and interference occurs. The relationship between the phase difference φs and the frequency fs of the sawtooth wave modulated by the phase modulator 50 is represented by φs = φ (t + τ) −φ (t) = 2πτfs (11) Here, τ is the optical fiber sensor unit 44
Is the delay time. When the signal obtained by the detector 13 is synchronously detected by the signal control processing circuit 48 at the sine wave fundamental frequency fm, the output P is Psin (φs−2θf) (12). Here, θf is the Faraday optical rotation angle (= V mI,
V: Verde constant, m: number of turns of the optical fiber sensor,
I: current value).

Therefore, the current I to be measured can be measured by adjusting the repetition frequency fs of the sawtooth wave so that P = 0. The above is the signal flow in the optical fiber current measuring device of FIG. 10. In particular, the optical fiber sensor 8 is a (spun) fiber twisted at the manufacturing stage because of its configurational feature, and therefore has a small amount of birefringence and a circular shape. Since it functions as a polarization preserving fiber, it is very suitable for transmitting circularly polarized light through the optical fiber sensor 8 as in this embodiment. Also, when the optical fiber sensor 8 is twisted and used in the mounting stage, it functions as a circularly polarized light preserving fiber, and thus is very suitable.

[0134] These functions are also the same as those of the optical fiber sensor described in the first embodiment, since linearly polarized light is represented by superposition of clockwise circularly polarized light and counterclockwise circularly polarized light.

Therefore, according to this embodiment, as a result of imparting optical rotatory power to the optical fiber, non-uniformity inside the fiber can be eliminated, and the fiber functions as a circularly polarized light preserving fiber, thereby realizing highly accurate current measurement. it can.

In the present embodiment, the serrodyne method has been described as a signal control processing method, but the same effect can be obtained by using the phase modulation method. The phase modulation method is a method of obtaining an output of a sine function by modulating a phase modulator with fm and detecting a fundamental wave. The Faraday rotation angle or the measured current I may be obtained by detecting only the fundamental wave,
Since it depends on the light amount of the light source, it is also possible to detect the second harmonic and take the quotient of the output with the fundamental wave to eliminate the light amount dependency of the light source. Further, in order to improve the accuracy, the phase modulation is performed so that the output of the second harmonic wave is always 0, and if the quotient of the output of the fundamental wave and the output of the fourth harmonic wave is obtained, the output becomes close to the extreme value with respect to the degree of phase modulation. Therefore, the error can be reduced. Also,
The present embodiment may be applied to various applications without using a phase modulator according to the accuracy to obtain the present embodiment.

Further, instead of the λ / 4 element 46b in FIG. 10, a reflection mirror may be provided and a reflection type in the interference system may be employed. An effect equivalent to the loop shape in FIG. 10 can be obtained by utilizing the clockwise (counterclockwise) circular polarization due to the reflection. In this case, the polarization maintaining fiber 47 on the incident side counterclockwise can be eliminated. Therefore,
The cost can be reduced accordingly. As a configuration, a depolarizer is arranged in the middle of the transmission fiber 52 in FIG. 10, and the light in the orthogonal two-polarization mode is phase-modulated through the phase modulator 50. The reflected light in the two-polarization mode passes through the depolarizer again to become linearly polarized light of the same polarization and cause interference. Also in this case, a similar effect is obtained by using the optical fiber sensor 8. further,
This embodiment has described the second example of the interference type system in which light does not propagate in free space but propagates in a fiber or an optical waveguide used in a phase modulator. The same effect can be obtained even if the present invention is applied to a modified system in which light is partially propagated in free space by using a (λ / 4 plate).

FIGS. 11A to 11C are views showing an eleventh embodiment of the optical fiber current measuring device according to the present invention. The present embodiment is different from the first and tenth embodiments described above.
Since it corresponds to a modification of the embodiment, the first and tenth
The description of the same configuration as that of the embodiment is omitted.

That is, in the present embodiment, FIG.
As shown in FIG. 1A, n optical fiber current measuring devices wound around conductors 4a to 4n to be measured are connected in series, and each optical fiber sensor 8 is connected by a low birefringence fiber 53. . Low birefringence fiber 53
May be the same as the optical fiber sensor 8, or the optical fiber shown in FIG. 6 or FIG. 7 may be used. The light emitted from the coupling optical unit 18a passes through the n optical fiber sensors 8, is reflected by the reflection end 28, and is coupled to the coupling optical unit 1a.
8a. The rest is the same as in the first embodiment.

With this configuration, each optical fiber sensor 8
In the medium and low birefringence fibers 53, the birefringence can be reduced and does not adversely affect the polarization plane of the propagating light, so that a differential system of n currents is possible. For example,
If this system is applied to n current lines coming and going from a certain substation equipment, the total incoming current and the total outgoing current always show 0 according to Kirchhoff's law. Become. This is determined by the signal processor, and the protection system is operated. In this case, a certain current is determined, and if a higher current flows, the system is determined to be an accident. At this time, if the signal processor has a function of a protection relay, the operation can be speeded up and the cost of the system can be reduced.

Further, if the low birefringence fiber 53 is covered with a pipe, it can be hardly affected by changes in the external environment.
If covered with a pipe having a magnetic shielding effect, the influence of an external magnetic field can be further suppressed.

In another embodiment of the present embodiment, FIG.
As shown in (b), n optical fiber current measuring devices are connected in a loop in series, and each optical fiber sensor 8
High birefringence fiber (polarization maintaining fiber) 54 between
Connected by The high birefringence fiber 54 may be equivalent to the polarization maintaining fiber 47. The light (clockwise light and counterclockwise light) emitted from the signal control processing unit 45 propagates while changing the polarization plane by the λ / 4 elements 46a and 46b, and the optical fiber sensor 8 rotates clockwise circularly polarized light. In addition, the polarization maintaining fiber 47 and the high birefringence fiber 54 propagate so as to have the same polarization linearly polarized light. The rest is the same as in the tenth embodiment.

FIG. 11C shows an embodiment in which (b) is applied to a reflection type, and each optical fiber sensor 8 is connected by a high birefringence fiber (polarization maintaining fiber) 54. .

With this configuration, each optical fiber sensor 8
High birefringence fiber (polarization maintaining fiber) 54 between
, It can be hardly affected by the change of the external environment and the external magnetic field, and a differential system of n currents can be realized. As the differential system, there is an application example as described above.

Therefore, since a low-birefringence fiber or a high-birefringence fiber (polarization maintaining fiber) is connected between the optical fiber current measuring devices, high-precision measurement or measurement hardly affected by changes in the external environment can be realized. .

In this embodiment, the number of windings of the n optical fiber sensors 8 does not always have to be the same, and the same effect can be obtained even if the winding direction of each optical fiber sensor 8 is reversed. can get. Further, a method of winding around the jth and kth conductors to be measured and then winding around the jth conductor to be measured may be used.

The present invention is not limited to the above-described embodiments, and various other modifications can be made within the scope of the present invention. For example, as described in the above embodiment, the present invention is particularly effective for an optical fiber current measuring instrument, and is suitable for an electric power system in view of long-term reliability. The present invention can be similarly applied to the present invention, and similarly excellent effects can be obtained.

Further, in the above-described embodiment, a case where a quartz fiber is used as the optical fiber sensor has been particularly described. However, the present invention is not limited to this.
For example, optical fibers made of other various materials such as lead glass having a small birefringence without twisting can be applied. In such a case, the same effect as in the above embodiment can be obtained. In particular, the condition of the mechanical life described in the above equation (1) holds for all optical fiber sensors. Regardless of the presence or absence of twisting, the mechanical stress satisfies the optical fiber life t _s ≧ 25 years under this condition. When applied to power grids or other applications, using such optical fiber parameters, all such applications are within the scope of the present invention.

[0149]

As described above, according to the present invention,
By imparting optical rotation to the optical fiber for optical fiber, the homogeneity of light in the optical fiber can be improved, so that it is possible to provide an optical fiber measuring instrument capable of performing highly accurate measurement. In particular, by applying an appropriate twist to the optical fiber, it is possible to provide an optical fiber measuring instrument capable of performing highly accurate measurement and having excellent long-term reliability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical fiber current measuring device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing details of the optical fiber sensor of FIG. 1;

FIG. 3 is a graph showing the relationship between the torsion ratio and the life of an optical fiber sensor according to a second embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the number of twists and the amount of birefringence over the entire length of an optical fiber sensor according to a third embodiment of the present invention.

FIG. 5 is a graph showing a relationship between a bending diameter and a birefringence amount per unit length of an optical fiber sensor according to a fourth embodiment of the present invention.

FIG. 6 is an explanatory diagram showing details of an optical fiber sensor according to a sixth embodiment of the present invention.

FIG. 7 is an explanatory diagram showing details of an optical fiber sensor according to a seventh embodiment of the present invention.

FIG. 8 is an explanatory diagram showing details of a sensor optical unit according to an eighth embodiment of the present invention.

FIG. 9 is an explanatory diagram showing details of a light source and a light transmitting fiber according to an eighth embodiment of the present invention.

FIG. 10 is a configuration diagram showing an optical fiber current measuring device according to a tenth embodiment of the present invention.

FIG. 11 is a configuration diagram showing an optical fiber current measuring device according to an eleventh embodiment of the present invention.

FIG. 12 is a configuration diagram showing an example of a conventional optical fiber current measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 4 ... Conductor to be measured 8 ... Optical fiber sensor 9 ... Sensor optical part 10 ... Signal processing part 11 ... Transmission fiber 18a ... Coupling optical part 18b ... Optical fiber sensor part 30 ... Core part 31 ... Cladding layer 32 ... Coating layer 33 ... External coating Layer 34 Connector 35 Pipe Twisting Fixture 37 Rotating Section 38 Drive Section 39 Fixing Section 40 Fiber Guide 41 Desiccant 42 Depolarizer 43, 47 Polarization Maintaining Fiber 53 Low Birefringence Fiber 54: High birefringence fiber

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yuji Mizutani 2121 Naoyo, Asahi-machi, Mie-gun, Mie Prefecture Inside Mie Plant of Toshiba Corporation (72) Inventor Takeshi Ken Sato 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kawasaki, Kanagawa Prefecture Inside Toshiba Hamakawasaki Plant (72) Inventor Toru Uenishi 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Inside Toshiba Hamakawasaki Plant (72) Inventor Sakae Ikuta 2, Ukishima-cho, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture No. 1 Toshiba Substation Equipment Technology Co., Ltd. (72) Inventor Takeshi Yokota 1-1-1, Shibaura, Minato-ku, Tokyo Inside (72) Inventor Hideki Noda 1-1-1, Shibaura, Minato-ku, Tokyo No. 1 In the head office of Toshiba Corporation (72) Inventor Oleg Shchapanov Russia, 125171 Moscow Se Street 15, 188 (72) Inventor Sergey Morshanev Russia, 141120 Moscow Region Friazino Boksarnaya Street 31, 16 (72) Inventor Victor Izaev Russia, 141120 Moscow Region Friasino Prospect Mira 19, 412 (72) Inventor Yuri Chamorovsky Russia, 141120 Moscow Region Friazino Zabodskaya Street 3, 2

Claims (22)

[Claims] 1. An optical fiber sensor disposed near an object to be measured, a light source that generates light for measurement and sends the light to the sensor, a detector that detects light emitted from the sensor, and the sensor An optical fiber measuring device that optically couples a light source and a detector, and a signal processing unit that processes a signal from the detector, and that measures a physical quantity by changing a characteristic of light. An optical fiber measuring instrument characterized in that an optical fiber having optical rotation is always used even in the absence of a magnetic field. 2. An optical fiber sensor arranged near an object to be measured, a light source that generates light for measurement and sends the light to the sensor, a detector that detects light emitted from the sensor, and the sensor. An optical fiber measuring device that optically couples a light source and a detector, and a signal processing unit that processes a signal from the detector, and that measures a physical quantity by changing a characteristic of light. An optical fiber measuring instrument characterized in that a twisted optical fiber is used as the optical fiber. 3. The optical measuring instrument according to claim 2, wherein the twisted optical fiber is an optical fiber twisted in a manufacturing stage, a mounting stage, or both stages. 4. When the outer diameter of the cladding of the optical fiber for the optical fiber sensor is 2r (μm) and the number of turns of the optical fiber around the object to be measured is m (turns), the optical fiber is added to the optical fiber. The optical fiber measuring device according to claim 2, wherein the torsion rate n _t (times / m) obtained is a value satisfying n _t ≤ (125 / 2r) (8.0-log ₁₀ m). 5. The number of twists so that the amount of birefringence of the entire length of the optical fiber for the optical fiber sensor has a value near 0 ° or near an extreme value depending on the relationship between the number of twists and the amount of birefringence. 3. The method according to claim 2, wherein
Or the optical fiber measuring device according to 3. 6. The direction of the plane of polarization of light incident on the optical fiber sensor is + 45 °, + 135 °, −45 °, or −1 with respect to the plane on which the optical fiber is disposed.
6. The optical fiber measuring device according to claim 5, wherein the optical fiber measuring device is set to be near 35 [deg.]. 7. A quartz fiber is used as the optical fiber for the optical fiber sensor, and the number of twists N (times) over the entire length of the optical fiber is 3.5M-1 ≦ N ≦ 3.5M + 1 (M is an integer other than 0). The optical fiber measuring instrument according to claim 2 or 5, wherein the value is a satisfying value. 8. A quartz fiber is used as the optical fiber for the optical fiber sensor, and the number of twists N (times) over the entire length of the optical fiber satisfies | N | = 1.75 + 3.5M (M is a positive integer). The optical fiber measuring instrument according to claim 2 or 5, wherein the value is within ± 1 of the following. 9. The optical fiber for the optical fiber sensor has an average bending radius of R (m), the number of turns of the optical fiber around the object to be measured is m, and the wavelength of light is λ.
In this case, the outer diameter of the cladding of the optical fiber is 2r.
(Μm) is (r / 62.5) ² ≦ (80 / 2mπR /
10. A value satisfying (3.8) (R / 0.25) ² (λ / 0.8).
The optical fiber measuring instrument according to any one of the above. 10. When the average bending radius of the optical fiber for the optical fiber sensor is R (m) and the number of turns of the optical fiber around the object to be measured is m, the outer diameter of the cladding of the optical fiber is 2r (μm ) Is 2r / 125 ≦ (8.0−log ₁₀ m) × 2mπR /
The optical fiber measuring instrument according to any one of claims 1 to 8, wherein the value satisfies 3.5. 11. The optical fiber for an optical fiber sensor according to claim 1, wherein a new coating layer is provided after applying a torsional stress to at least a core portion thereof. The optical fiber measuring device according to one of the above. 12. The optical fiber for an optical fiber sensor applies a torsional stress to at least a core portion thereof.
12. The optical fiber measurement according to claim 1, wherein at least both ends are fixed by a fixing means, and an optical fiber is provided with a protective pipe serving as a jacket on the outside thereof. vessel. 13. The optical fiber measuring instrument according to claim 2, wherein a rotation part for adjusting a twist is provided in a part of the optical fiber for the optical fiber sensor. . 14. The optical fiber measuring instrument according to claim 13, wherein the rotation unit is configured to be able to adjust the rotation from outside by a driving unit such as a pulse motor. 15. The optical fiber measuring instrument according to claim 13, wherein the rotating section has a fixing section for fixing rotation. 16. The optical fiber measuring instrument according to claim 1, further comprising a fiber guide for loosely fixing the optical fiber for the optical fiber sensor. 17. The optical fiber measurement according to claim 1, wherein at least one of the optical fiber for the optical fiber sensor and the optical system is disposed in a flange kept in a dry state or in a vacuum-evacuated container. vessel. 18. An optical fiber sensor disposed near an object to be measured, a light source that generates light for measurement and sends the light to the sensor, a detector that detects light emitted from the sensor, and the sensor. An optical fiber measuring device that optically couples a light source and a detector, and a signal processing unit that processes a signal from the detector, and that measures a physical quantity by changing a characteristic of light. An optical fiber measuring instrument, wherein a depolarizer is attached to the light source in order to supply unpolarized light. 19. A polarization maintaining fiber is used as the depolarizer, and the intrinsic axis of the polarization maintaining fiber is about 45 ° with respect to the polarization plane of light emitted from the light source, and about −
19. A light source attached to the light source at an angle of 45, about 135 or -135.
An optical fiber measuring instrument as described. 20. An optical fiber sensor arranged near an object to be measured, a light source that generates light for measurement and sends the light to the sensor, a detector that detects light emitted from the sensor, and the sensor. An optical fiber measuring device that includes an optical system that optically couples a light source and a detector and a signal processing unit that processes a signal from the detector, and that measures a physical quantity by changing a characteristic of light. An optical fiber measuring device for measuring interference of light of the optical system using light propagating in the same optical path in opposite directions to each other. 21. An optical fiber measuring device comprising a plurality of the optical fiber measuring devices according to claim 1. 22. The optical fiber measurement device according to claim 21, wherein a plurality of optical fiber measurement devices are connected in series, and at least the optical fiber measurement devices are connected by a low birefringence fiber or a high birefringence fiber. apparatus.