JP4868310B2 - Photocurrent sensor - Google Patents

Description

  The present invention relates to a photocurrent sensor using the Faraday effect, and in particular, in a photocurrent sensor using an optical fiber, a reflection type photocurrent sensor that makes light incident from one end side of the photocurrent sensor and reflects it at the other end side. It is about improvement.

  A photocurrent sensor using the Faraday effect in which the plane of polarization of light rotates by the action of a magnetic field is known, and such a photocurrent sensor has an advantage that it is not affected by electromagnetic noise. It is used for measuring current in an insulated switchgear.

  There are various types of photocurrent sensors. Among these, a type has been filed in which an optical fiber is used as a sensor section and is wound around the outer circumference of a conductor through which a current to be measured flows (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 10-319051 (page 3-6, FIG. 1)

As shown in FIG. 24, the photocurrent sensor 100 of Patent Document 1 has an optical fiber 102 installed around the conductor 101 through which the current to be measured flows, and is incident from one end side of the optical fiber 102. The basic principle is to measure the Faraday rotation angle of linearly polarized light that is rotated by the magnetic field of the current to be measured when the linearly polarized light is reflected at the other end. A first nonreciprocal polarization plane rotating element (first ferromagnetic Faraday rotator) 103 and a first birefringent element (first calcite) 104 are provided on one end side of the optical fiber 102. The non-reciprocal polarization plane rotation element 103 is a light transmission type that rotates the polarization plane of linearly polarized light by 22.5 degrees.

  On the incident side of the first birefringent element 103, a prism 105 and one end side of the polarization plane preserving optical fiber 106 are arranged. The other end side of the polarization plane preserving optical fiber 106 is disposed on the optical axis of the second nonreciprocal polarization plane rotation element (second ferromagnetic Faraday rotator) 107. The second nonreciprocal polarization plane rotation element 107 rotates the polarization plane of linearly polarized light by 45 degrees. On the incident side of the second nonreciprocal polarization plane rotation element 107, a second birefringence element (second calcite) 108 is disposed.

  Furthermore, the other end side of the polarization plane preserving optical fiber 109 is connected to the light source 110. The light emitted from the light source 110 is transmitted through a polarizer (not shown), so that linearly polarized incident light enters the polarization plane preserving optical fiber 109. The component denoted by reference numeral 111 calculates the sum of the modulation factors by multiplying the ratio of the direct current component to the alternating current component of each electrical signal output from the two light receivers (photoelectric conversion elements) 112 and 113. (The arithmetic processing device that performs such arithmetic processing is referred to as a division circuit).

  In the photocurrent sensor 100 configured as described above, the linearly polarized light propagated from the light source 110 is incident on the second birefringent element 108 in a state where the polarization state is maintained by the polarization plane preserving optical fiber 109, and birefringence is achieved. Then, the light is transmitted through the second non-reciprocal polarization plane rotation element 107 without causing any incident. The polarization plane of the linearly polarized light incident on the second nonreciprocal polarization plane rotation element 107 is rotated 45 degrees and incident on the polarization plane preserving optical fiber 106, and this polarization state is maintained, and the first birefringence element 104 is maintained. Incident light is transmitted therethrough without causing birefringence, and is incident on the first nonreciprocal polarization plane rotating element 103.

  The polarization plane of the linearly polarized light that has entered the first nonreciprocal polarization plane rotating element 103 is further rotated by 22.5 degrees, enters the optical fiber 102, is reflected by the reflecting mirror 114 around the outer periphery of the conductor 101, and the reflected light is reflected. Then, it enters the first nonreciprocal polarization plane rotation element 103 again.

  The reflected light is incident on the first birefringence element 104 with the polarization plane rotated by 22.5 degrees by the first nonreciprocal polarization plane rotation element 103. As a result, the reflected light Lout incident on the first birefringent element 104 is the polarization plane of the linearly polarized light Lin before entering the first nonreciprocal polarization plane rotating element 103, excluding the Faraday rotation angle due to the current to be measured. It has been rotated 45 degrees in total. For this reason, the reflected light Lout undergoes birefringence when passing through the first birefringent element 104, and is separated into reflected light Lout1 and reflected light Lout2 each having an intensity of 1/2.

  One separated reflected light Lout1 enters the light receiving element 112 via the prism 105 and the multimode optical fiber 115, is converted into an electric signal, and the output signal is input to the arithmetic processing unit 111. One reflected light Lout2 is incident on the second non-reciprocal polarization plane rotation element 107 via the polarization plane preserving optical fiber 106, and the polarization plane is rotated again by 45 degrees, and is incident on the second birefringence element 108. To do.

  As a result, the reflected light Lout2 incident on the second birefringent element 108 is rotated by a total of 90 degrees from the polarization plane of the linearly polarized light Lin, excluding the Faraday rotation angle due to the current to be measured. For this reason, the reflected light Lout2 causes birefringence when passing through the second birefringent element 108, and all of it is directed toward the prism 116 side. The reflected light Lout2 that has passed through the prism 116 enters the light receiver 113 via the multimode optical fiber 117, is converted into an electrical signal, and the output signal is input to the arithmetic processing unit 111.

  Thereafter, the magnitude of the current to be measured is obtained by performing predetermined signal processing in the arithmetic processing unit 111 that has received the output signals from the light receivers 112 and 113. In the photocurrent sensor 100, even if the Faraday rotation ability of the two non-reciprocal polarization plane rotating elements 103 and 107 has temperature dependency, signal processing is performed by using the sum of the modulation degrees of the two signals as the system output. It is explained that the influence can be reduced.

However, as described above, in the photocurrent sensor 100, the two non-reciprocal polarization plane rotating elements 103 and 107 have temperature dependency, so that signal processing is performed with the sum of the modulation degrees of the two signals as the system output. However, the effect of temperature dependence cannot be completely eliminated. Therefore, since the temperature dependence of the entire photocurrent sensor is not eliminated, some kind of temperature compensation device is required.

  Furthermore, since the incident light from the light source is converted into linearly polarized light and propagated, the entire optical system of the photocurrent sensor 100 has polarization dependency. Accordingly, the polarization plane preserving optical fibers 106 and 109 must be used. However, due to the structure of the polarization plane preserving optical fiber, propagation loss becomes large in long-distance light propagation. Therefore, even if there is a request for long distance correspondence of the photocurrent sensor, it was impossible to realize it.

  In addition, it is difficult to operate the dividing circuit used for the photocurrent sensor 100 at a high frequency, and if an attempt is made to increase the frequency, the arithmetic processing unit becomes expensive. For this reason, it is difficult to speed up the operation of the entire photocurrent sensor 100.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to perform temperature compensation without providing any temperature compensation device, and perform computation processing that is polarization-independent and performs computation processing. It is an object of the present invention to provide a photocurrent sensor capable of realizing simplification and high speed of the apparatus and capable of stably operating a light source.

The invention according to claim 1 of the present invention comprises an optical fiber arranged to circulate around a conductor through which a current flows, and a photoelectric conversion unit having a light source and a light receiver, and receives incident light from the light source. In a photocurrent sensor that propagates in a fiber and measures the current flowing in the conductor using the Faraday effect generated in the propagation light in the optical fiber,
An optical circuit unit including at least two birefringent elements, two non-reciprocal polarization plane rotation elements having rotation angles of 45 degrees and 22.5 degrees, and a polarization plane rotation element;
From the photoelectric conversion unit side, the polarization plane rotation element, one of the birefringence elements, the non-reciprocal polarization plane rotation element having a rotation angle of 45 degrees, the other birefringence element, and the rotation angle of 22.5 degrees Arrange in the order of non-reciprocal polarization plane rotation element,
Two optical fibers are arranged around the conductors so as to be opposite to each other, and incident light from the light source is separated into two polarization components by the optical circuit unit, and each light component is separated by each polarization component. Separating the incident light into four polarization components by propagating into the fiber and separating each polarization component emitted from the optical fiber after propagation into ordinary and extraordinary rays by the birefringence element;
Further, in the birefringent element in which the incident light is separated into the four polarized light components, polarized light components that are ordinary rays or polarized light components that are extraordinary rays are combined, and the combined light is detected by the receiver as detection light. It is a photocurrent sensor characterized by receiving light.

  The invention according to claim 2 of the present invention is the photocurrent sensor characterized in that the number of the light receivers is one.

  Further, according to a third aspect of the present invention, the electrical signal output from the light receiver upon receiving the detection light is branched into a direct current component and an alternating current component by a filter connected to the output side of the light receiver. The photocurrent sensor operates the light source by feeding back only the direct current component to the light source.

  Furthermore, in the invention according to claim 4 of the present invention, at least two birefringent elements are arranged on an optical path from the light source to the optical fiber, and the shift amount of each extraordinary ray in the two birefringent elements is 4. The photocurrent sensor according to claim 1, wherein each of the birefringent elements is configured to be equal to each other.

  According to the photocurrent sensor of the first aspect of the present invention, the light output from the light source is separated into four polarization components, and the ordinary light or the extraordinary light is combined into detection light, and the detection light is Detect with receiver. As a result, even if an angle shift due to the temperature dependence of the nonreciprocal polarization plane rotation element occurs in the rotation angle of the current to be measured due to the magnetic field, temperature compensation can be performed. Accordingly, it is not necessary to separately provide a temperature compensation device for the photocurrent sensor, and thus the photocurrent sensor can be reduced in size, simplified, and reduced in cost.

  Furthermore, since the photocurrent sensor can be operated even when non-polarized light is incident from the light source, the photocurrent sensor can be configured without using the polarization plane preserving optical fiber, and the photocurrent sensor can be used for a long distance. The request can be realized.

  According to the photocurrent sensor of claim 2 of the present invention, it is possible to simplify the arithmetic processing device and speed up the arithmetic operation by configuring the photocurrent sensor arithmetic processing device with a single light receiver. Is possible.

  Furthermore, according to the photocurrent sensor according to claim 3 of the present invention, the speed of the calculation operation is established, the light output from the light source is detected by the light receiver, and the electrical signal of the DC component of the detected light is detected. Is fed back to the light source, so that the light source can be stably operated. Therefore, deterioration of the measurement accuracy of the photocurrent sensor can be prevented.

  Further, according to the photocurrent sensor of claim 4 of the present invention, the fluctuation amount of the forward optical path in the optical circuit unit is eliminated by making the shift amounts of the two polarization components in the forward direction the same. It is possible to suppress the loss fluctuation of the entire photocurrent sensor.

<First Embodiment>
Hereinafter, a first embodiment according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic plan view showing the configuration of the photocurrent sensor 1 according to the first embodiment, and FIG. 2 is an outline of only the optical fibers 2a and 2b and the lens 8 extracted from the photocurrent sensor 1 shown in FIG. Figure
FIG. 3 is a schematic plan view in which only the optical circuit unit 4 is extracted from the photocurrent sensor 1 shown in FIG. 1 and the optical path state in the forward direction is entered. FIG. It is the schematic plan view which filled in the optical path state. FIG. 5 is a perspective view showing the configuration of the optical circuit unit 4, and FIG. 6 is a perspective view showing the arrangement of optical elements constituting the optical circuit unit 4 and the polarization state of propagating light in the forward direction. FIG. 7 is a perspective view showing the arrangement of the optical elements of the optical circuit unit 4 and the polarization state of the propagation light in the reverse direction.

  FIG. 8 is a schematic diagram showing only the optical fibers 19a and 19b and the lens 16 extracted from the photocurrent sensor 1 shown in FIG. 1, and FIG. 9 is a ferrule 7 for inserting and holding the optical fibers 2a, 2b, 19a and 19b. , 18 and FIG. 10 is a diagram showing a modification of FIG. 11A to 11E are diagrams showing polarization states of forward light in the optical circuit unit 4 in FIG. 3, and FIGS. 12F to 12K are optical circuits in FIG. FIG. 6 is a diagram illustrating a polarization state of light in the reverse direction in the unit 4. (A) to (K) in FIGS. 11 and 12 correspond to the polarization states in the respective optical path sections indicated by reference numerals (A) to (K) in FIGS. 3 and 4. Furthermore, FIG. 13 shows an enlarged view of the polarization component of FIG. 3 to 7, the lenses 8 and 16 are not shown. In the present invention, the optical path from the light source 5 to the optical fibers 2a and 2b is defined as “forward direction”, and the optical fiber 2a. , 2b are defined as “reverse directions” respectively.

  The photocurrent sensor 1 according to the first embodiment includes optical fibers 2a and 2b, a photoelectric conversion unit 3, and an optical circuit unit 4, and propagates incident light from the light source 5 into the optical fibers 2a and 2b. The magnitude of the current is measured using the Faraday effect generated in the propagation light in the optical fibers 2a and 2b by the magnetic field of the external current. The optical fibers 2a and 2b are arranged so as to circulate around the conductor 6 through which the current to be measured flows, and as shown in FIG. 1, the two optical fibers 2a and 2b are opposite to each other. In addition, they are arranged around the conductor 6 with the same length and the same number of turns. Further, the optical fibers 2 a and 2 b on the side extending toward the optical circuit unit 4 are held by the two-core ferrule 7. The optical fibers 2a and 2b used as the sensor unit are optimally capable of propagating linearly polarized light, such as lead glass fiber and quartz glass fiber.

  As shown in FIG. 2, the lens 8 and the ferrule 7 are positioned and positioned so that the optical axis oa of the lens 8 and the center point C of the ferrule 7 are on the same straight line in the z-axis direction. By arranging the lens 8 and the ferrule 7 in this way, the center point (same position as the center point C) of each optical fiber 2a, 2b and the optical axis oa of the lens 8 are arranged on the same straight line. The optical axis oa of 8 is held by the ferrule 7 so that the central axes fc of the optical fibers 2a and 2b are equidistant.

  The optical fibers 2a and 2b are of the same material, the same structure, and the same mode. Also, a reflection film 15 is provided as a reflection member at the end of each optical fiber 2a, 2b. Instead of the reflective film 15, for example, gold, silver, copper, chromium, aluminum, or the like, a metal with low absorptivity and high reflectivity for light, or a multilayer film with low absorptivity and high reflectivity was used. A reflection mirror may be used.

  The optical circuit unit 4 is configured so that the linearly polarized light of each polarization component of ordinary light and extraordinary light is incident on the optical fibers 2a and 2b, and the rotation angle of the polarization plane of each polarization component emitted from the optical fibers 2a and 2b. Is a circuit unit for coupling linearly polarized ordinary rays or extraordinary rays affected by the magnetic field of the current to be measured. As shown in FIGS. 1 to 5, the optical circuit section has at least two or more birefringent elements (in this embodiment, composed of three elements of 9, 10, and 11), and rotation angles of 45 degrees and 22.5 degrees. Two non-reciprocal polarization plane rotation elements 12 and 13, one polarization plane rotation element 14, and lenses 8 and 16 are provided.

  The two non-reciprocal polarization plane rotating elements 12 and 13 are light transmission type Faraday rotators each having a magnet 17 provided outside, and the polarization plane of the incident linearly polarized light is 45 degrees or 22.5 degrees in a predetermined direction, respectively. Rotate. As the material, garnet, TBIG, GBIG, etc. are optimal, and materials that are as thin as possible with a rotation angle of about 45 degrees or 22.5 degrees in the wavelength band used are used. The rotation directions of the nonreciprocal polarization plane rotating elements 12 and 13 are set to be counterclockwise when viewed in the z-axis direction as shown in FIG. 3 to 7, the illustration of the magnet 17 that applies magnetism to the nonreciprocal polarization plane rotating elements 12 and 13 is omitted.

  The three birefringent elements 9, 10, and 11 are made of a light transmission type uniaxial single crystal, and include rutile (TiO2), calcite (CaCO3), quartz (SiO2), yttrium osobanadate (YVO4), and alpha barium vodate. (ΑBaB2O4) or the like is used. Each birefringent element 9, 10, 11 selected from such materials is processed into a flat plate shape so that two opposing optical surfaces are parallel to each other.

  The direction of the crystal axis X92 (see FIG. 5) of the first birefringent element 9 with respect to the normal of the optical surface is about 42 to 50 degrees with respect to the normal of the optical surface so as to obtain the maximum separation width ( Most preferably, it is set to 47.8 degrees), and the direction of the crystal axis X91 on the optical surface is set parallel to the y-axis direction. Further, the crystal axis X102 direction of the second birefringent element 10 with respect to the normal of the optical surface is set to about 42 to 50 degrees (most preferably 47.8 degrees) with respect to the normal of the optical surface. The direction of the crystal axis X101 on the optical surface is set to be inclined by 45 degrees with respect to the x-axis direction. Accordingly, the two birefringent elements 9 and 10 are arranged such that the directions of the crystal axes X91 and X101 on the optical surfaces are different by 45 degrees. The direction of the crystal axis X112 (see FIG. 5) with respect to the optical surface of the third birefringent element 11 is set parallel to the z-axis direction, and the direction of the crystal axis X111 on the optical surface is the x-axis direction. Set to parallel.

  The polarization plane rotating element 14 rotates the polarization plane of incident linearly polarized light by 90 degrees in a predetermined direction, and is composed of an optical element having an effect of rotating the polarization plane of linearly polarized light, such as a half-wavelength element. The When a half-wave element is used, a phase element whose crystal axis X141 direction is inclined by 45 degrees with respect to the x-axis as shown in FIG. 5 is optimal.

The lenses 8 and 16 collimate or converge incident light. The lens 8 is disposed between the non-reciprocal polarization plane rotating element 13 and the two-core ferrule 7, while the lens 16 is coupled with the photoelectric conversion unit 3 and the third. They are respectively installed between the birefringent elements 11. As shown in FIG. 2 or FIG. 8 , each imaging point in the lenses 8 and 16 is set at the core portion of the end face of each optical fiber 2a, 2b, 19a, 19b. As the lenses 8 and 16, an aspheric lens, a ball lens, a plano-convex lens, a distributed refraction lens, or the like can be used. In the present embodiment, an aspheric lens is used.

  The photoelectric conversion unit 3 includes a light source 5, a single light receiver 20, an LPF (Low Pass Filter) 21, and a lens 22. The light receiver 20 includes a photoelectric conversion element such as a photodiode that converts received light into an electric signal. Furthermore, an LPF 21 which is a kind of filter is connected to the electrical signal output side of the light receiver 20, and the electrical signal output from the light receiver 20 is branched for each component, and only a desired electrical signal component is a light source. 5 is fed back. The light source 5 is a semiconductor laser, a light emitting diode, a super luminescent diode, or the like. Further, the lens 22 converges incident light, and is installed between the light source 5 and the optical fiber 19a, and its image point is set at the core of the end face of the optical fiber 19a.

  SMF and MMF are used for the optical fibers 19a and 19b used as waveguides connecting the photoelectric conversion unit 3 and the optical circuit unit 4. The end faces on the one end side of the two optical fibers 19a and 19b are on the same plane and are held by a ferrule 18 having a two-core structure with a predetermined gap therebetween. The optical axis oa of the lens 16 and the center point C of the ferrule 18 are positioned with respect to each other so as to be on the same straight line in the z-axis direction as shown in FIG. By disposing the lens 16 and the ferrule 18 in this way, the center point of the optical fibers 19a and 19b (the same position as the center point C) and the optical axis oa of the lens 16 are disposed on the same straight line. Is held by the ferrule 18 so that the central axes fc of all the optical fibers 19a and 19b are equidistant from the optical axis oa.

  Furthermore, the light incident / exit end faces of the optical fibers 2a, 2b (or 19a, 19b) are formed obliquely at the same inclination angle φ as shown in FIG. However, the inclination angle may be changed between the optical fibers 2a, 2b and 19a, 19b. In FIG. 9, the ferrule 7 (or 18) tip is processed into a conical shape so that the light incident / exit end surfaces of the optical fibers 2a and 2b (19a and 19b) are formed obliquely at the same inclination angle φ. It was. Alternatively, as shown in FIG. 10, the optical fibers 2a and 2b (19a and 19b) are projected from the end surface of the ferrule 7 (18), and only the input and output end surfaces of the optical fibers 2a and 2b (19a and 19b) are polished. Then, they may be formed obliquely at the same inclination angle.

  The operation of the photocurrent sensor 1 configured as described above will be described with reference to FIGS. 1, 2, 6 to 8 and 11 to 13. 11 and 12, the horizontal direction is the x-axis, the vertical direction is the y-axis, and the direction toward the paper surface is the z-axis. For convenience of explanation, the polarization component in each optical path cross section is divided into four parts in both the vertical and horizontal directions. Indicates the propagation position.

The non-polarized light emitted from the light source 5 is incident on the end face of the optical fiber 19a by the lens 22, propagates through the optical fiber 19a, and is emitted from the light incident / exit end face formed obliquely. At the time of emission, the emitted light is emitted obliquely according to the inclination angle φ, and propagates across the optical axis oa of the lens 16 while expanding the beam diameter at a constant spread angle θ≈λ / (πω0). Is incident on the surface of the lens 16. The light incident on the lens 16 is refracted outward from the optical axis oa by the convex curved surface on the left side of the lens 16 shown in FIG. 8, and is emitted from the lens 16 so that the light axis IBa is parallel to the z axis. (See FIGS. 3 and 11A). The emitted light IB is converted into collimated light or convergent light and emitted to the first birefringent element 9 and is orthogonal to the crystal axis X91 by the birefringent element 9 as shown in FIGS. The ordinary polarized light and the parallel extraordinary light are separated into two polarization components P1 and P2.

  The separated polarization components P1 and P2 are incident on the nonreciprocal polarization plane rotation element 12 (see FIG. 6). When the polarization components P1 and P2 are transmitted through the nonreciprocal polarization plane rotating element 12, the polarization directions are rotated by 45 degrees in the same direction as shown in FIG. 11C. By being rotated by the nonreciprocal polarization plane rotation element 12, the polarization plane direction of one polarization component P2 is aligned in parallel with the crystal axis X101 direction of the second birefringence element 10. Therefore, when each of the polarization components P1 and P2 is incident on the second birefringent element 10, the polarization component P2 is shifted obliquely upward as shown in FIGS. 6 and 11D.

  The polarization components P1 and P2 transmitted through the second birefringent element 10 are then incident on the nonreciprocal polarization plane rotation element 13. When the polarization components P1 and P2 pass through the nonreciprocal polarization plane rotation element 13, the polarization directions are rotated by 22.5 degrees in the same direction, as shown in FIGS. 6 and 11E. As shown in FIG. 2, the polarization components P1 and P2 whose polarization planes are rotated are refracted inward from the right convex curved surface of the lens 8 and further refracted inward by the convex curved surface on the left of the lens 8. Then, the light is emitted from the lens 8 while being converged obliquely so as to cross the optical axis oa toward the light incident / exit end faces of the optical fibers 2a and 2b.

  Each polarization component P1, P2 coupled to the light incident / exit end faces of the optical fibers 2a, 2b is refracted at the light incident / exit end faces, propagates through the optical fibers 2a, 2b, and reaches the other end face. Therefore, the light is reflected by the reflecting film 15 and propagated while maintaining the linearly polarized state. After propagation, the light is again emitted from the end faces of the optical fibers 2a and 2b to the lens 8. As described above, since the optical fibers 2a and 2b are arranged so as to circulate around the conductor 6 through which the current to be measured flows, the polarization planes of the polarization components P1 and P2 are affected by the current magnetic field during propagation. And rotated according to the magnitude of the current to be measured.

  As described above, the two optical fibers 2a and 2b are arranged around the conductor 6 in the opposite directions, the same length, and the same number of turns. Accordingly, the propagation optical path length in the optical fibers 2a and 2b and the circular integral of the magnetic field of the current to be measured are equal for each polarization component P1 and P2, so that the phase between the two polarization components P1 and P2 is the optical fiber. Even after exiting from 2a and 2b, they are set in phase.

  The light re-entering the lens 8 is refracted outward from the optical axis oa on the convex curved surface on the right side of the lens 8 as shown in FIG. 2, so that the light axes ba1 and ba2 are parallel to the z-axis. 8 is emitted. The emitted polarization components P1 and P2 are converted into collimated light or convergent light, and are incident on the nonreciprocal polarization plane rotation element 13 again (see FIGS. 7 and 11E). When the polarization components P1 and P2 pass through the nonreciprocal polarization plane rotation element 13 again, the polarization plane is further rotated by 22.5 degrees (see FIGS. 7, 12 (F), and 13). Therefore, after passing through the non-reciprocal polarization plane rotating element 13 in the reverse optical path and the polarization plane of each polarization component P1, P2 before transmitting through the non-reciprocal polarization plane rotating element 13 in the forward optical path A deviation of 45 degrees from the polarization plane of each of the polarization components P1 and P2 occurs. The reason why the plane of polarization is rotated 45 degrees in this way is to determine how much the final detection light has been rotated by the influence of the current magnetic field, to determine its rotation angle, and to calculate the measured current value from this rotation angle. .

  By shifting the polarization plane by 45 degrees, the measurement range of the photocurrent sensor 1 can be maximized. However, if it is determined that the function of the photocurrent sensor 1 is sufficiently secured even if the measurement range is somewhat narrow, the nonreciprocal polarization plane rotating element 13 may be replaced with an element having a rotation angle other than 22.5 degrees. good.

  The polarization components P1 and P2 whose polarization planes are rotated by 22.5 degrees by the nonreciprocal polarization plane rotation element 13 are incident on the second birefringence element 10. The polarization planes of the respective polarization components P1 and P2 incident on the second birefringent element 10 are shifted by α degrees with respect to the polarization plane not considering the influence of the current magnetic field and exhibit states such as P1 ′ and P2 ′ ( α degree is the rotation angle affected by the current being measured and the temperature dependence of the non-reciprocal polarization plane rotating elements 12 and 13). For this reason, as shown in FIGS. 7 and 13, the polarization planes of the polarization components P1 and P2 are the ordinary rays P1Ro and P2Ro of the polarization planes orthogonal to each other by the second birefringent element 10, and the extraordinary rays P1Re, Separated into P2Re. Thus, the incident light incident from the light source 5 is separated into four polarization components P1Ro, P2Ro, P1Re, and P2Re.

  The ordinary rays P1Ro and P2Ro and the extraordinary rays P1Re and P2Re separated by the second birefringent element 10 have an average intensity ratio if the rotational angles of the two nonreciprocal polarization plane rotating elements 12 and 13 are not temperature dependent. Becomes 1: 1. However, since the rotation angle of the polarization plane of the Faraday rotator has temperature dependency, the rotation angle fluctuates due to the temperature dependency. As a result, the polarization components P1 and P2 in the second birefringent element 10 are changed. At the time of separation, the intensity ratio of the ordinary rays P1Ro and P2Ro and the extraordinary rays P1Re and P2Re does not correspond to 1: 1, and the intensity varies as shown in FIG.

In the second birefringent element 10, the ordinary rays P1Ro and P2Ro are not shifted because they are perpendicular to the direction of the crystal axis X101, and are emitted while maintaining the same optical path. One extraordinary ray P1Re, P2Re is emitted is shifted towards obliquely downward a crystal axis X101 a direction parallel to the direction (see FIGS. 7 and 12 (G)).

  Next, the polarization components P1Ro, P2Ro, P1Re, and P2Re incident on the nonreciprocal polarization plane rotating element 12 are rotated by 45 degrees in the same direction as shown in FIGS. The polarization planes of the polarization components P1Re and P2Re that are extraordinary rays in the birefringent element 10 are aligned in parallel with the crystal axis X91 direction of the first birefringent element 9. Therefore, when each polarization component P1Ro, P2Ro, P1Re, P2Re is incident on the first birefringent element 9, the polarization components P1Re, P2Re are shifted downward as shown in FIG. 7 and FIG. 12 (I). The On the other hand, the polarization planes of the polarization components P1Ro and P2Ro are aligned parallel to the direction of the crystal axis X111 of the third birefringent element 11.

  Next, each polarization component P1Ro, P2Ro, P1Re, P2Re is propagated to the polarization plane rotation element 14. However, since the size of the polarization plane rotating element 14 is set so as to transmit only one ordinary ray P2Ro and arranged on the optical path, only the polarization plane of the ordinary ray P2Ro is rotated by 90 degrees (FIG. 7, FIG. Propagated to the third birefringent element 11 (see FIG. 12J).

  The size of the third birefringent element 11 is set so as to transmit only the ordinary rays P1Ro and P2Ro, and is arranged on the optical path. Further, due to the rotation of the polarization plane by the polarization plane rotating element 14, the polarization direction of the ordinary ray P1Ro is set parallel to the crystal axis X111 direction, and the polarization direction of the ordinary ray P2Ro is set perpendicular to the crystal axis X111 direction. Accordingly, only the ordinary ray P1Ro is shifted in the third birefringent element 11, and the polarization components P1Ro and P2Ro that are ordinary rays in the second birefringent element 10 are combined (FIGS. 7 and 12K). reference).

  The combined light DB obtained by combining the ordinary rays P1Ro and P2Ro is converged by the lens 16 as shown in FIG. 8, and is incident on the end face of the optical fiber 19b so as to cross the optical axis oa of the lens 16. The coupled light DB incident on the optical fiber 19b is refracted at its light incident / exit end face, propagates through the optical fiber 19b, is received by the light receiver 20 as detection light, and is converted into an electrical signal.

  The electric signal output from the light receiver 20 is input to the LPF 21 and branched into a DC component and an AC component. The AC component is input from the LPF 21 to an arithmetic processing unit (not shown), and the magnitude of the current to be measured is obtained by performing a predetermined calculation. The amplitude of the AC component is the current value, and the frequency is the frequency of the current to be measured flowing through the conductor 6 as it is. On the other hand, the DC component is input from the LPF 21 to the light source 5.

  The lens 16 is positioned so that the optical axis oa of the lens 16 is positioned between the incident light IB and the detection light DB as indicated by a point A1 in FIG. 12K when viewed in the z-axis direction. And Further, the optical axis oa of the lens 8 is positioned so as to be on the middle of the change components P1 and P2, as indicated by a point A2 in FIG. 11E when viewed in the z-axis direction. To do.

  The photocurrent sensor 1 of the present invention can be variously changed based on its technical idea. For example, as shown in FIGS. 14 to 16, the polarization plane rotating element 14 is placed on the optical path of one of the extraordinary rays P1Re and P2Re. The third birefringent element 11 is arranged on the optical path of the two extraordinary rays P1Re and P2Re, and the two extraordinary rays P1Re and P2Re are coupled to each other. The light DB may be changed so that the combined light DB is received by the light receiver 20 as detection light. 14 is a modified example of FIG. 4, and (F) to (K) in FIG. 14 and (F) to (K) in FIG. 16 correspond to each other.

  Since only the light in the reverse direction is transmitted through the polarization plane rotating element 14, the polarization plane rotating element 14 may be replaced with a Faraday rotator having a rotation angle of 90 degrees.

  As described above, in the photocurrent sensor 1 of the first embodiment, the light IB output from the light source 5 is separated into the four polarization components P1Ro, P2Ro, P1Re, and P2Re, and the ordinary rays P1Ro, P2Ro, or extraordinary rays are separated. P1Re and P2Re are combined and detected by the light receiver 20. As a result, even if an angle shift due to the temperature dependence of the nonreciprocal polarization plane rotation elements 12 and 13 occurs in the rotation angle of the current to be measured due to the magnetic field, temperature compensation is performed. Accordingly, it is not necessary to separately provide a temperature compensation device, and the photocurrent sensor 1 can be reduced in size, simplified, and reduced in cost.

  Furthermore, since the photocurrent sensor 1 can be operated even when non-polarized light is incident from the light source 5, it is possible to configure the photocurrent sensor without using a polarization plane preserving optical fiber. Therefore, it is possible to realize a long distance requirement of the photocurrent sensor.

  Further, since the light receiver 20 of the arithmetic processing device of the photocurrent sensor 1 can be constituted by one, the arithmetic processing device can be simplified and the arithmetic operation speed can be increased.

  Furthermore, after establishing a high-speed operation, the light source 5 is stabilized by detecting the light IB output from the light source 5 with the light receiver 20 and feeding back the electric signal of the DC component of the detected light to the light source 5. It is possible to prevent the measurement accuracy from deteriorating.

<Second Embodiment>
Next, a second embodiment according to the present invention will be described in detail with reference to FIGS. In addition, the same number is attached | subjected to the same location as 1st Embodiment, and the overlapping description and figure are abbreviate | omitted or simplified and shown. FIG. 17 is a perspective view showing the configuration of the optical circuit unit 4 of the photocurrent sensor according to the second embodiment, and FIG. 18 is an excerpt of only the optical circuit unit 4 of the second embodiment, and the optical path state in the forward direction. 19 is a schematic plan view in which only the optical circuit portion 4 is extracted and the optical path state in the reverse direction is entered. FIG. 20 is a perspective view showing the arrangement of optical elements constituting the optical circuit unit 4 of the second embodiment and the polarization state of propagating light in the forward direction. FIG. It is a perspective view which shows the arrangement | positioning of an element, and the polarization state of the propagation light in a reverse direction.

  FIGS. 22A to 22E are diagrams showing polarization states of light in the forward direction in the optical circuit unit 4 of FIG. 18, and FIGS. 23F to 23K are diagrams of FIGS. FIG. 3 is a diagram illustrating a polarization state of light in the reverse direction in the optical circuit 4. (A) to (K) in FIGS. 22 and 23 correspond to the polarization states at the cross sections of the optical paths indicated by reference numerals (A) to (K) in FIGS. 18 and 19. Note that the lenses 8 and 16 are not shown in FIGS.

  The photocurrent sensor according to the second embodiment differs from the photocurrent sensor 1 of the first embodiment in that the second birefringence element 10 ′, the polarization plane rotation element 14 ′, and the third birefringence. The configuration of the element 11 ′. First, the second birefringent element 10 ′ is set so that the shift amount of the polarization component P2 that becomes an extraordinary ray in the second birefringent element 10 ′ is equal to the shift amount of the extraordinary ray P1 in the first birefringent element 9. The birefringent elements 9 and 10 'are configured by setting the material and thickness of'. By adopting such a configuration, the shift amounts of the polarization components P1 and P2 in the two birefringent elements 9 and 10 ′ arranged on the optical path from the light source 5 to the optical fibers 2a and 2b become equal. The shift amounts of the two polarization components P1 and P2 in the direction can be set to be the same. As a result, loss fluctuations in the optical path in the forward direction of the optical circuit unit 4 can be eliminated, so that loss fluctuations in the entire photocurrent sensor can be suppressed.

  Furthermore, the direction of the crystal axis X112 ′ (see FIG. 17) of the third birefringent element 11 ′ with respect to the normal of the optical surface is 42˜about the normal of the optical surface so as to obtain the maximum separation width. It is set to around 50 degrees (most preferably 47.8 degrees), and the direction of the crystal axis X111 ′ on the optical surface is set to be inclined by 22.5 degrees with respect to the x-axis direction.

  The three birefringent elements 9, 10 'and 11' are made of a light transmission type uniaxial single crystal, and the materials include rutile (TiO2), calcite (CaCO3), quartz (SiO2), yttrium osovanadate (YVO4), Alpha barium bodate (αBaB2O4) is used. Each birefringent element 9, 10 ′, 11 ′ selected from such a material is processed into a flat plate shape so that two opposing optical surfaces are parallel to each other.

  Next, the polarization plane rotating element 14 ′ is an optical element that rotates the polarization plane of incident linearly polarized light by 90 degrees in a predetermined direction, and two polarization plane rotating element plates 14′a and 14′b made of half-wavelength elements. It consists of and. The crystal axis X14'a direction of the polarization plane rotation element plate 14'a is inclined 33.75 degrees with respect to the x axis, and the crystal axis X14'b direction of one polarization plane rotation element plate 14'b is relative to the x axis. It is set to tilt 11.25 degrees. The two polarization plane rotating element plates 14'a and 14'b are superposed on each other's joint surface and bonded with an optical adhesive such as an ultraviolet curing type to constitute the polarization plane rotating element 14 '. It is assumed that the adhesive does not protrude from the bonding surface to the optical surface.

  The operation of the photocurrent sensor in which the configuration of the optical circuit unit 4 is changed will be described with reference to FIGS. 22 and 23, the horizontal direction is the x-axis, the vertical direction is the y-axis, and the direction toward the paper surface is the z-axis. For convenience of explanation, the vertical and horizontal directions are divided into four parts and the polarization components in each optical path section are divided. Indicates the propagation position.

  The non-polarized light emitted from the light source 5 propagates from the optical fiber 19a to the first birefringent element 9 and is separated into polarized components P1 and P2, and the polarization direction is 45 degrees by the nonreciprocal polarization plane rotation element 12. It is rotated and incident on the second birefringent element 10 '. When the polarization components P1 and P2 are incident on the second birefringent element 10 ', the polarization component P2 is shifted obliquely upward as shown in FIGS. 20 and 22D. As described above, the shift amount of the polarization component P2 that becomes an extraordinary ray in the second birefringence element 10 ′ is the same as the shift amount of the polarization component P1 that becomes an extraordinary ray in the first birefringence element 9. A second birefringent element 10 'is constructed. Accordingly, as shown in FIGS. 22B and 22D, each polarization component P1, P2 is transmitted through the nonreciprocal polarization plane rotation element 13 in the polarization state where the shift amounts of the polarization components P1, P2 are equal, Coupled to fibers 2a and 2b.

  The polarization planes of the polarization components P1 and P2 coupled to the optical fibers 2a and 2b are rotated under the influence of the magnetic field of the current to be measured, and pass through the nonreciprocal polarization plane rotation element 13 again, and then the second birefringence. Incident on element 10. Since the polarization planes of the polarization components P1 and P2 incident on the second birefringent element 10 cause an angle shift of α degrees as described above, the polarization planes of the polarization components P1 and P2 are shown in FIGS. As shown in (G), the beams are separated into normal rays P1Ro and P2Ro and extraordinary rays P1Re and P2Re that are orthogonal to each other.

  In the second birefringent element 10 ′, the ordinary rays P1Ro and P2Ro are not shifted because they are orthogonal to the crystal axis X101 direction, while the extraordinary rays P1Re and P2Re are obliquely upward in a direction parallel to the crystal axis X101 direction. And is emitted (see FIGS. 21 and 23G).

  Next, each polarization component P1Ro, P2Ro, P1Re, P2Re is rotated 45 degrees by the nonreciprocal polarization plane rotation element 12, and the polarization plane of the polarization components P1Re, P2Re is in the direction of the crystal axis X91 of the first birefringence element 9 Aligned in parallel. Accordingly, the polarization components P1Re and P2Re are shifted downward by the first birefringent element 9.

  Next, each polarization component P1Ro, P2Ro, P1Re, P2Re is propagated to the polarization plane rotation element 14 '. However, the sizes of the polarization plane rotation plates 14'a and 14'b are set on the optical path so as to transmit only the ordinary rays P1Ro and P2Ro, respectively. Accordingly, the polarization plane of the ordinary ray P1Ro is rotated by 22.5 degrees and the polarization plane of the other ordinary ray P2Ro is rotated by 67.5 degrees in opposite directions (see FIGS. 21 and 23J). In the rotated state, each polarization component P1Ro, P2Ro, P1Re, P2Re is then propagated to the third birefringent element 11 '.

  The size of the third birefringent element 11 'is set so as to transmit only the ordinary rays P1Ro and P2Ro and is arranged on the optical path. Further, due to the rotation of the polarization planes at the polarization plane rotation plates 14′a and 14′b, the polarization direction of the ordinary ray P1Ro is parallel to the crystal axis X111 ′ direction, and the polarization direction of the ordinary ray P2Ro is the crystal axis X111 ′ direction. Each is set vertically. Accordingly, only the ordinary ray P1Ro is shifted in the third birefringent element 11 ′, and the polarized components P1Ro and P2Ro that are ordinary rays in the second birefringent element 10 ′ are combined (FIGS. 21 and 23). (See (K)).

  The combined light DB in which the ordinary rays P1Ro and P2Ro are coupled is propagated through the optical fiber 19b, received by the light receiver 20 as detection light, converted into an electric signal, and branched into a DC component and an AC component by the LPF 21. Is done. The AC component is input from the LPF 21 to an arithmetic processing unit (not shown), and the magnitude of the current to be measured is obtained. On the other hand, the DC component is input from the LPF 21 to the light source 5.

  The photocurrent sensor of the second embodiment can be variously changed based on its technical idea. For example, a polarization plane rotating plate in which the crystal axis X14′a is changed in a direction of 78.75 degrees with respect to the x-axis direction. The polarization plane rotating element 14 'is composed of 14'a and the polarization plane rotating plate 14'b whose crystal axis X14'b is changed in the direction of 33.75 degrees with respect to the x-axis direction, and the extraordinary ray P1Re is 22.5 degrees, The extraordinary ray P2Re is rotated 112.5 degrees in the same direction, the two extraordinary rays P1Re and P2Re are combined to form a combined light DB, and the combined light DB is changed to be received by the light receiver 20 as detection light. Also good.

  Since only the light in the reverse direction is transmitted through the polarization plane rotating element 14 ', the polarization plane rotating element 14' may be replaced with a Faraday rotator.

  As described above, according to the photocurrent sensor of the second embodiment, the photocurrent sensor 1 of the first embodiment has temperature compensation, long-distance correspondence, simplification of the arithmetic processing device, and high-speed operation. It is possible to make the shift amounts of the two polarization components P1 and P2 in the forward direction the same, as well as the effect of stabilizing the light source 5 and preventing the deterioration of measurement accuracy. As a result, it is possible to eliminate the loss variation of the forward optical path in the optical circuit unit, and thus it is possible to suppress the loss variation of the entire photocurrent sensor.

  The photocurrent sensor of the present invention is used for a current measuring unit of a protective relay device in a power system of a substation.

1 is a schematic plan view showing a configuration of a photocurrent sensor 1 according to a first embodiment of the present invention. FIG. 2 is a schematic diagram illustrating only the optical fibers 2a and 2b and the lens 8 extracted from the photocurrent sensor 1 shown in FIG. FIG. 2 is a schematic plan view in which only an optical circuit section 4 is extracted from the photocurrent sensor 1 shown in FIG. 1 and a forward optical path state is entered. FIG. 2 is a schematic plan view in which only the optical circuit section 4 is extracted from the photocurrent sensor 1 shown in FIG. 1 and the optical path state in the reverse direction is entered. The perspective view showing the structure of the optical circuit part 4 of the photocurrent sensor 1 shown in FIG. The perspective view which shows arrangement | positioning of each optical element which comprises the optical circuit part 4 of the photocurrent sensor 1 shown in FIG. 1, and the polarization state of the propagation light in a forward direction. The perspective view which shows the arrangement | positioning of each optical element of the optical circuit part 4 of the photocurrent sensor 1 shown in FIG. 1, and the polarization state of the propagation light in a reverse direction. FIG. 2 is a schematic diagram showing only the optical fibers 19a and 19b and the lens 16 extracted from the photocurrent sensor 1 shown in FIG. The block diagram of the ferrules 7 and 18 which insert and hold | maintain the optical fibers 2a, 2b, 19a, and 19b. The block diagram which shows the example of a change of FIG. The figure which shows the polarization state of the light of the forward direction in the optical circuit part 4 of FIG. The figure which shows the polarization state of the light of the reverse direction in the optical circuit part 4 of FIG. The enlarged view of the polarization component of FIG. The schematic plan view which shows the example of a change of FIG. The perspective view which shows the example of a change of FIG. The polarization state presentation figure which shows the example of a change of FIG. The perspective view showing the structure of the optical circuit part 4 of the photocurrent sensor which concerns on the 2nd Embodiment of this invention. FIG. 6 is a schematic plan view in which only an optical circuit unit 4 of the second embodiment is extracted and a forward optical path state is written. FIG. 6 is a schematic plan view in which only the optical circuit unit 4 of the second embodiment is extracted and the optical path state in the reverse direction is entered. The perspective view which shows arrangement | positioning of each optical element which comprises the optical circuit part 4 of 2nd Embodiment, and the polarization state of the propagation light in a forward direction. The perspective view which shows arrangement | positioning of each optical element of the optical circuit part 4 of 2nd Embodiment, and the polarization state of the propagation light in a reverse direction. The figure which shows the polarization state of the light of the forward direction in the optical circuit part 4 of FIG. The figure which shows the polarization state of the light of the reverse direction in the optical circuit 4 of FIG. Schematic which shows the structure of the conventional photocurrent sensor.

Explanation of symbols

1 Photocurrent sensor
2a, 2b, 19a, 19b Optical fiber 3 Photoelectric conversion unit 4 Optical circuit unit 5 Light source 6 Conductor 7, 18 Ferrule 8, 16 Lens 9 First birefringence element
10, 10 'second birefringent element
11, 11 'Third birefringent element
12 First nonreciprocal polarization plane rotation element
13 Second nonreciprocal polarization plane rotation element
14, 14 'Polarization plane rotation element
15 Reflective film
17 Magnet

Claims (4)

An optical fiber arranged to circulate around a conductor through which a current flows, and a photoelectric conversion unit having a light source and a light receiver, and propagates incident light from the light source into the optical fiber. In a photocurrent sensor that measures the current flowing through the conductor using the Faraday effect generated in light,
An optical circuit unit including at least two birefringent elements, two non-reciprocal polarization plane rotation elements having rotation angles of 45 degrees and 22.5 degrees, and a polarization plane rotation element;
From the photoelectric conversion unit side, the polarization plane rotation element, one of the birefringence elements, the non-reciprocal polarization plane rotation element having a rotation angle of 45 degrees, the other birefringence element, and the rotation angle of 22.5 degrees Arrange in the order of non-reciprocal polarization plane rotation element,
Two optical fibers are arranged around the conductors so as to be opposite to each other, and incident light from the light source is separated into two polarization components by the optical circuit unit, and each light component is separated by each polarization component. Separating the incident light into four polarization components by propagating into the fiber and separating each polarization component emitted from the optical fiber after propagation into ordinary and extraordinary rays by the birefringence element;
Further, in the birefringent element in which the incident light is separated into the four polarized light components, polarized light components that are ordinary rays or polarized light components that are extraordinary rays are combined, and the combined light is detected by the receiver as detection light. A photocurrent sensor characterized by receiving light.
  2. The photocurrent sensor according to claim 1, wherein the number of the light receivers is one.   The electrical signal output from the light receiver upon receiving the detection light is branched into a direct current component and an alternating current component by a filter connected to the output side of the light receiver, and only the direct current component is fed back to the light source to provide the light source. The photocurrent sensor according to claim 1, wherein the photocurrent sensor is operated.   At least two of the birefringent elements are arranged on the optical path from the light source to the optical fiber, and each birefringent element is configured so that the shift amounts of the extraordinary rays in the two birefringent elements are equal to each other. The photocurrent sensor according to any one of claims 1 to 3, wherein the photocurrent sensor is characterized in that

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