JP2001033492A - Optical application measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a change in a physical amount such as a current, a magnetic field or the like in an accurately stable state by forming a fiber diffraction grating at one end of an optical fiber to be a sensor as a reflecting mirror. SOLUTION: A light linearly polarized by a polarizer 5 is incident to a sensor fiber 8 through an optical beam splitter 6. A fiber reflecting mirror 9 is disposed at an end of the fiber 8, and a measured light is reciprocated in the fiber by the mirror 9. The light folded in the fiber 8 by the mirror 9 is branched by a non-polarized beam splitter 6, and incident to a polarizing beam splitter (PBS) 10. The PBS 10 is disposed so that an incident polarizing bearing becomes 45 deg. when a Faraday rotation of a polarizing plane is '0', and two-axis intensity light signals perpendicularly crossing are obtained from emitting lights of the fiber 8. These signals are respectively photoelectrically converted by axis detectors 11a, 11b, current values are calculated by an electronic circuit 12 and output as measurement signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical measurement apparatus for measuring a change in a physical quantity such as a current or a magnetic field by using a change in polarization characteristics of an optical element.

[0002]

2. Description of the Related Art Various types of conventional optical applied current measuring devices have been proposed.
Typical examples include those published in a paper (SPIE vol.374 Fiber Optic 83 ') in 1983.

FIG. 6 is a schematic diagram showing the configuration of an optical applied current measuring device according to the above-mentioned paper.

[0006] As shown in FIG. 6, a He—Ne laser beam output from a laser light source 38 is linearly polarized by a polarizer 5 and is incident on a single mode fiber 41 through an objective lens 39. This single mode fiber 41
Causes the light passing through the single mode fiber 41 to undergo Faraday rotation due to a magnetic field generated by the bus current.

The light that has exited the single mode fiber 41 is collimated by an objective lens 39 and enters a Wollaston prism 42. This Wollaston prism 42 is 45 ° with respect to the incident polarization direction when the Faraday rotation is 0.
, And the light emitted from the fiber is defined as a two-component light intensity signal that is orthogonal.

[0006] These lights are photoelectrically converted by the detector 11, and after necessary calculations are performed by the electronic circuit 12, they are output as current values.

Here, assuming that the signals photoelectrically converted by the detector 11 are I1 and I2, (I1-I2) / (I1 + I
By performing the calculation of 2), regardless of the incident intensity,
The Faraday rotation angle can be determined.

A current measuring device using such an optical fiber has a high insulation property and does not cause a decrease in linearity due to saturation.
Furthermore, because of its high-speed response and nonflammability, it has attracted attention as a physical measuring instrument.

However, since the sensor is a single mode fiber, the optical path is several microns, the optical element needs to have a high level of stability, and a linear birefringence is generated by the force applied when the optical component is fixed, and the polarization is good. Because it is difficult to maintain the characteristics, it is difficult to achieve high accuracy,
It has made it difficult to realize a highly accurate current measuring device.

Therefore, as a method of stabilizing the amount of light coupled to a single mode fiber and achieving high precision,
For example, Trevor is an all-optical fiber current measuring device.
Proposed by W.MacDougall et al. (IEEE Transac
tion on Power Delivery, Vol.7, No2, p848 ~).

This current measuring device realizes all paths from the light source to the light receiving device as optical fibers, and the configuration will be described with reference to FIG.

As shown in FIG. 7, the linearly polarized light from the light source 2 passes through the polarization maintaining fiber 33 and is converted into the sensor fiber 8.
Sent to. The polarization maintaining fiber 33 and the sensor fiber 8 are connected by fusion. The polarization maintaining fiber fused to the output side of the sensor fiber behaves as a polarizer, and outputs the rotation of the polarization plane due to the Faraday rotation as a change in the amount of light. The light is photoelectrically converted by the detector 11, and a necessary operation is performed by the electronic circuit 12 to output a current value.

According to the current measuring device having such a configuration, there is no instability of the coupled light amount, but when the fiber shape changes due to external vibration, it appears as the rotation of the polarization plane, which causes an error. . In addition, since the optical rotation due to twisting of the fiber depends on the temperature in order to reduce the linear birefringence of the fiber, as a result, the photocurrent sensor generates an error due to the temperature.

It is known that a fiber can be used for reciprocation in order to prevent such an error. In other words, the rotation of the polarization plane due to torsion or torsion returns to the original polarization plane by reciprocating through the fiber, and only the Faraday rotation can be extracted.

[0015]

The above-described photocurrent detection device has the following problems to be solved.

That is, the effect of birefringence generated by the force applied to the optical component is still large. This is a problem because the birefringence due to the fixing of the sensor fiber is the largest.

In order to eliminate an error due to rotation of the polarization plane due to twisting or twisting of the fiber, it is desirable to use the sensor fiber in a reciprocating manner. In this case, a light separating means for separating the incoming and outgoing light without disturbing the incident polarization state and the outgoing polarization state is required. However, at present, an optical element of a waveguide type capable of separating incoming and outgoing light has not been realized. For this reason, it is necessary to use a bulk element as an optical component,
This has a problem in the stability of the amount of light coupled to the sensor fiber.

The present invention has been made in view of the above circumstances, and has as its object to provide an optical applied measuring device capable of measuring a change in a physical quantity such as a current or a magnetic field with high accuracy and in a stable state. And

[0019]

According to the present invention, in order to achieve the above object, an optical measuring apparatus is constituted by the following means.

According to a first aspect of the present invention, there is provided an optical measuring apparatus for measuring a current or a magnetic field utilizing the Faraday effect of an optical fiber, wherein a fiber diffraction grating is formed as a reflecting mirror at one end of the optical fiber serving as a sensor. is there.

According to the optical measuring apparatus having such a configuration, a reflecting mirror is formed on the end face of the fiber, or the fiber end face is polished in the case of emitting light from the fiber to the space once, or the ferrule is formed. Although it is necessary to adhere firmly, this is not necessary when a fiber diffraction grating is used, and the occurrence of birefringence due to fixing to a ferrule can be eliminated.

According to a second aspect of the present invention, in the optical measuring apparatus according to the first aspect of the present invention, the light reflection portion of the fiber diffraction grating is provided on the incident side of the fixed portion at the end of the fiber. .

According to the optical measuring apparatus having such a configuration, since light does not pass through a portion where birefringence occurs due to fixing of the end of the fiber, the influence of birefringence can be further reduced.

According to a third aspect of the present invention, there is provided a light source, a transmission fiber for transmitting light from the light source, a polarizing element for converting light transmitted by the transmission fiber into linearly polarized light, and a current or a magnetic field. A Faraday element receiving Faraday light; a reflecting mirror provided at the end of the Faraday element for reflecting light back; and a beam separating means for separating light reflected back by the reflecting mirror and transmitted through the sensor again from incident light. And means for measuring the polarization state of the light separated by the beam separating means, wherein the beam separating means uses a fiber coupler using a polarization maintaining fiber.

According to the optical applied measuring device having such a configuration, the optical path leading to the transmission fiber can be constituted only by the fiber, so that the light quantity can be stabilized.

According to a fourth aspect of the present invention, in the optical device according to the third aspect of the present invention, a Faraday rotator is inserted between the fiber coupler and a reflecting mirror provided at the end of the sensor.

According to the optical applied measuring device having such a configuration, the relationship between the Faraday rotation angle and the amount of light transmitted through the polarizer on the light receiving side changes in a sine function, so that the absolute value of the current can be determined as it is. Although the direction cannot be known, by inserting the Faraday rotator, the operating point in a sine function can be shifted, and the direction of the current can be known.

According to a fifth aspect of the present invention, in the optical applied measuring device according to the third or fourth aspect, the angle of rotation of the Faraday rotator is ± ｛(17.5 to 27.5).
7.5) + 90 ° n｝ (n is an integer).

According to the optical measuring apparatus having such a configuration, the light beams I1 and I2 biased ± (35 to 55) ° can be taken out, and by performing (I1−I2) / (I1 + I2), The optical rotation angle can be accurately measured without depending on the change in the light amount.

According to a sixth aspect of the present invention, in the optical measuring apparatus according to the third aspect of the present invention, the means for measuring the polarization state of the light includes a polarization-maintaining fiber coupler, and an output side of each of the fiber couplers. A polarizer whose transmission polarization direction matches the birefringence axis of the fiber coupler, a light receiving element for photoelectrically converting the light transmitted through this polarizer, and necessary calculations based on the electric signal from the light receiving element It is composed of an electronic circuit that performs processing.

According to the optical applied measuring device having such a configuration, a high extinction ratio can be obtained by using the polarizer together.

A seventh aspect of the present invention is the optical applied measuring device according to the sixth aspect, wherein a fiber polarizer is used as the polarizer.

According to the optical apparatus having such a configuration, a measuring instrument with more stable light quantity can be realized by using a fiber as a polarizer.

According to an eighth aspect of the present invention, there is provided a light source, a polarizing element for converting light transmitted by a light transmitting fiber for transmitting light from the light source into linearly polarized light, and a Faraday element receiving Faraday rotation by a current or a magnetic field. Reflected light that reflects light back and forth at the end of the Faraday element, beam separating means that separates light reflected back to the reflected light and transmitted through the sensor again from incident light, and separated by the beam separating means. Means for measuring the polarization state of the reflected light, wherein the beam splitting means uses a branched optical path formed in a waveguide shape.

According to the optical applied measuring device having such a configuration, the optical path leading to the transmission fiber can be constituted only by the fiber, so that the light quantity can be stabilized.

According to a ninth aspect of the present invention, in the optical measuring apparatus according to the eighth aspect of the present invention, a polarizer is formed on a waveguide.

According to the optical measuring apparatus having such a configuration, the main optical element can be formed on one waveguide substrate, so that not only the light amount is stable but also the vibration can be enhanced. In addition, since temperature control such as cooling and heating can be easily performed, stable measurement can be easily performed even when the temperature changes.

[0038]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of an optical applied measuring apparatus according to the present invention.
FIG. 2 is a configuration diagram showing an embodiment.

In FIG. 1, reference numeral 2 denotes a light source driven by a driver 1, and light emitted from the light source 2 is introduced into a transmission fiber 3. The light propagating through the transmission fiber 3 becomes parallel light by the coupling lens 4a, and is guided to the polarizer 5 installed near the sensor.

The light linearly polarized by the polarizer 5 passes through the non-polarizing beam splitter 6 and is incident on the sensor fiber 8 by the coupling lens 4b. The sensor fiber 8 is arranged so as to orbit around the conductor 7 through which the current to be measured flows, and receives Faraday light by a magnetic field generated by the current.

On the other hand, a fiber reflecting mirror 9, which will be described in detail later, is disposed at the end of the sensor fiber 8, and the measuring light reciprocates in the sensor fiber by the fiber reflecting mirror 9.

The light reflected from the sensor fiber by the fiber reflecting mirror 9 is split by the non-polarizing beam splitter 6 and enters a polarizing beam splitter (hereinafter abbreviated as PBS) 10. This PBS
10 indicates that the incident polarization direction is 45 when the Faraday irradiation angle is 0.
And two orthogonal intensity light signals are obtained from the light emitted from the sensor fiber.

This optical signal is supplied to the detector 11 of each axis.
The photoelectric conversion is performed by a and 11b, the current value is calculated by the electronic circuit 12, and this is output as a measurement signal.

Here, an example of the configuration of the end portion of the sensor fiber 8 provided with the fiber reflecting mirror 9 will be described with reference to FIG.

As shown in FIG. 2, a diffraction grating formed by irradiating the single mode fiber with an ultraviolet laser beam is used as a fiber reflecting mirror 9, which is a glass in which the coating on the end side of the sensor fiber 8 is peeled off. The tube portion is connected in the middle of the tube portion by fusion. Then, in order to maintain the shape of the sensor fiber 8 with respect to the portion reflected by the diffraction grating, a fiber reflector 9
Is fixed to a ferrule 16 generally used as an optical fiber connector for communication or the like by bonding. That is, after the adhesive is injected into the center hole of the ferrule 16, the fiber at one end of the fiber reflecting mirror 9 is inserted, and the fiber is heated and bonded.

As described above, by setting the fiber reflecting mirror 9 closer to the light source than the ferrule fixing portion, even if stress is generated due to adhesion and fixing to the ferrule, the polarization characteristics due to linear birefringence do not deteriorate. .

It is desirable to reduce the linear birefringence by protecting the periphery of the fusion fixing portion of the fiber reflecting mirror 9 with a material having a low Young's modulus such as silicone rubber or acrylic resin. Alternatively, a commercially available dedicated coater may be used to cover the fiber around the fusion-fixed portion of the fiber reflector 9 in order to cover the fiber with a protective coat.

As described above, according to the first embodiment, by forming the fiber diffraction grating as a reflecting mirror at the end side of the sensor fiber, a reflecting mirror can be formed on the end face of the fiber, or light can be temporarily transmitted from the fiber to the space. It is not necessary to polish the end face of the fiber or to firmly adhere to a ferrule or the like as in the case of emitting light, and it is possible to eliminate the occurrence of birefringence due to fixing to the ferrule.

Further, by providing the light reflecting portion of the fiber diffraction grating on the incident side of the fixed portion at the end of the fiber, light does not pass through the portion where birefringence occurs due to the fixing of the end of the fiber. The effect can be reduced.

FIG. 3 shows a second embodiment of the optical measuring apparatus according to the present invention.
In the configuration diagram showing the embodiment, the same parts as those in FIG.

In FIG. 3, reference numeral 2 denotes a light source driven by a driver 1, and light emitted from the light source 2 is introduced into a transmission fiber 3. The light that has propagated through the transmission fiber 3 is linearly polarized by the fiber polarizer 18 and sent to the polarization plane maintaining coupler 19.

The polarization-maintaining coupler 19 is coupled so that the axis of the fiber is aligned with the output polarization axis of the fiber polarizer 18, and the light enters the Faraday rotator 24 while maintaining the polarization plane. In the Faraday rotator 24, the light is rotated by 22.5 ° so that the light is incident on the sensor fiber 8.

In this case, the optical rotation angle of the Faraday rotator 24 is set to ± {(17.5 to 27.5) + 90 ° n}.
By setting (n is an integer), ± (35-55)
The two biased lights I1 and I2 can be taken out, and by calculating (I1-I2) / (I1 + I2), the Faraday irradiation angle can be accurately measured without depending on the change in the light amount. In the present embodiment, the optical rotation angle is ±
(22.5 + 90n) °.

The sensor fiber 8 is arranged so as to go around the conductor 7 through which the current to be measured flows, and receives Faraday light by a magnetic field generated by the current. At the end of the sensor fiber 8, a diffraction grating formed in the same manner as in the first embodiment is arranged as a reflection mirror 9, and reciprocates measurement light in the sensor fiber.

The light returning from the end of the sensor fiber 8 passes through the Faraday rotator 24 again, and
The plane of polarization rotates an additional 22.5 °. This light is split by the polarization plane maintaining coupler 19 and split by the PBS 10 into light of two orthogonal polarization components. PBS10
Is set in accordance with the axis of the polarization maintaining coupler 19, and the incident polarization direction is 45 ° when the Faraday irradiation angle is 0.
Becomes The sensor fiber 8 is provided by the PBS 10.
Are obtained from the light emitted from the light source.

This optical signal is supplied to the detector 11 of each axis.
The photoelectric conversion is performed by a and 11b, the current value is calculated by the electronic circuit 12, and this is output as a measurement signal.

As described above, according to the second embodiment, it is possible to use all the optical fibers from the light source 2 to the sensor fiber 8, and there is no portion where the light propagates in the space. And a stable output can be obtained.

The relationship between the Faraday light application angle and the amount of light transmitted through the polarizer on the light receiving side changes sinusoidally by the Faraday rotator 24 provided between the sensor fiber 8 and the polarization plane holding coupler 19. The functional operating point can be shifted, and the direction of the current can be known. In other words, without the Faraday rotator, the direction of the current cannot be known, although the absolute value of the current is known. However, in the present embodiment, the absolute value and the direction of the current can be known.

Further, the polarization maintaining coupler 19 and the sensor fiber 8 can be connected by fusion, and there is an advantage particularly in a fiber using glass which is weak in moisture. In other words, the fiber end face needs to transmit light without reflection, coating can be performed only with a specific material, and becomes a water infiltration path. Water can be prevented from entering.

In the second embodiment, the diffraction grating is formed as a reflecting mirror at the end of the sensor fiber. However, the present invention can be similarly applied to a device in which a reflecting mirror is attached to the end face of the sensor fiber. Needless to say.

FIG. 4 shows a third embodiment of the optical applied measuring apparatus according to the present invention.
In the configuration diagram showing the embodiment, the same parts as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 4, the structure from the light source 2 to the fiber polarizer 18, the polarization maintaining coupler 19, the sensor fiber 8, and the reflecting mirror 9 is the same as that of the third embodiment, and therefore the description thereof is omitted. I do. Here, the fiber polarizer 18 is denoted by reference numeral 18a, and the polarization plane holding coupler 19 is denoted by reference numeral 19a.

In the third embodiment, the output of the polarization-maintaining coupler 19a is incident on a polarization-maintaining coupler 19b provided separately therefrom, and the polarization-maintaining coupler 19b converts the output into two-component polarized light. Branch. Thereafter, a fiber polarizer 18b provided as a receiving fiber,
The signal passes through 18c, is photoelectrically converted by the detectors 11a and 11b, and the electronic circuit 12 calculates a current value to output a measurement signal.

As described above, according to the third embodiment, the polarized light split into two components by the polarization plane holding coupler 19b is photoelectrically converted by the detectors 11a and 11b through the fiber polarizers 18b and 18c, respectively, and the electrons are converted into electrons. Since an all-optical fiber configuration for inputting to the circuit 12 is used, there is no portion where light propagates in space, and a photocurrent sensor with a more stable light quantity can be realized.

In the third embodiment, the polarization maintaining coupler and the polarization splitting couplers 19a and 19b are constituted by fibers, but these may be formed by a waveguide 21 formed on a substrate 20 as shown in FIG. Can be configured.

In general, the optical path of a waveguide formed on a substrate does not become a perfect circle, but forms an optical path having linear and birefringent axes having horizontal and vertical axes on the substrate surface. When a Y-branch coupler is formed on this waveguide, the polarization-maintaining coupler 19 is formed.
Is formed. When a metal is placed near the waveguide,
It functions as the polarizer 18. By attaching the sensor fiber 8, the receiving fiber 18, and the transmitting fiber 3 to this waveguide, a photocurrent sensor can be formed.

With such a configuration, the same operation and effect as those of the third embodiment can be obtained. In addition, since the main optical element can be formed on a single waveguide substrate by forming a polarizer, not only the light amount is stable, but also the vibration becomes strong, and the temperature control such as cooling and heating is easily performed. Since the measurement can be performed, a measurement device that is stable against a temperature change can be easily realized.

[0069]

As described above, according to the present invention, it is possible to provide an optical applied measuring apparatus capable of measuring a change in a physical quantity such as a current or a magnetic field with high accuracy and in a stable state.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an optical applied measurement device according to the present invention.

FIG. 2 is a cross-sectional view showing a configuration example of a terminal end of a sensor fiber provided with a fiber reflecting mirror in the embodiment.

FIG. 3 is a configuration diagram showing a second embodiment of the optical applied measurement device according to the present invention.

FIG. 4 is a configuration diagram showing a third embodiment of the optical applied measurement device according to the present invention.

FIG. 5 is a diagram showing an example of a case where the polarization maintaining coupler and the polarization splitting coupler are configured by waveguides formed on a substrate in the embodiment.

FIG. 6 is a schematic configuration diagram showing an example of a conventional optical applied current measuring device.

FIG. 7 is a configuration diagram when all paths from a light source to a light receiver are realized as optical fibers as a current measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Driver 2 ... Light source 3 ... Transmission fiber 4a, 4b ... Coupling lens 5 ... Polarizer 6 ... Unpolarized beam splitter 7 ... Conductor through which a measured current flows 8 ... Sensor fiber 9 ... Fiber Reflecting mirror 10 Polarizing beam splitter 11a, 11b Detector 12 Electronic circuit 13 Fusion 18 18, 18a, 18b, 18c Fiber polarizer 19, 19a, 19b Polarization maintaining coupler 24 …… Faraday rotator

Continued on the front page (72) Inventor Kiyohisa Terai 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba Hamakawasaki Plant (72) Inventor Sakae Ikuta 2-1 Ukishima-cho, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture East F term (reference) in Shiba Substation Equipment Technology Co., Ltd. 2G017 AA01 AD12 AD14 AD15 2G025 AB10 AB13 AC06 2H079 AA03 BA02 CA11 EA09 EB18 KA05

Claims (9)

[Claims] 1. An optical applied measurement device for measuring a current or a magnetic field using the Faraday effect of an optical fiber, wherein a fiber diffraction grating is formed as a reflecting mirror at one end of an optical fiber serving as a sensor. apparatus. 2. The optical applied measurement device according to claim 1, wherein a light reflection portion of the fiber diffraction grating is provided on the incident side of the fiber end. 3. A light source, a transmission fiber for transmitting light from the light source, a polarization element for converting light transmitted by the transmission fiber into linearly polarized light, and a Faraday element for receiving Faraday light by a current or a magnetic field. A reflecting mirror provided at the end of the Faraday element and reflecting light back, a beam separating means for separating light reflected back by the reflecting mirror and transmitted through the sensor again from incident light, and a beam separating means. Means for measuring the polarization state of the separated light, wherein the beam separating means uses a fiber coupler using a polarization maintaining fiber. 4. The optical applied measuring device according to claim 3, wherein a Faraday rotator is inserted between the fiber coupler and a reflecting mirror provided at the end of the sensor. 5. The optical applied measuring device according to claim 3, wherein the optical rotation angle of the Faraday rotator is ±
(17.5-27.5) + 90 ° n} (n is an integer), wherein the optical applied measurement device is set. 6. The optical applied measuring device according to claim 3, wherein the polarization state maintaining means is a means for measuring the polarization state of light, and is provided on each of the emission sides of the fiber coupler, and a birefringence axis of the fiber coupler. And a light receiving element for photoelectrically converting light transmitted through the polarizer, and an electronic circuit for performing necessary arithmetic processing based on an electric signal from the light receiving element. Characteristic optical measurement equipment. 7. The optical applied measurement device according to claim 6, wherein a fiber polarizer is used as the polarizer. 8. A light source, a polarizing element for converting light transmitted by a light transmitting fiber for transmitting light from the light source into linearly polarized light, a Faraday element receiving Faraday rotation by a current or a magnetic field, and a terminal of the Faraday element Reflected light that reflects light back and forth, beam separating means that separates the light that is reflected back to this reflected light and transmitted through the sensor again from the incident light, and measures the polarization state of the light separated by the beam separating means And a beam splitting unit using a branched optical path formed on a waveguide. 9. The optical applied measurement device according to claim 8, wherein the polarizer is formed on the waveguide.