JP6017169B2 - Photocurrent detection device and method of manufacturing photocurrent detection device - Google Patents

Description

  Embodiments described herein relate generally to a photocurrent detection device and a method for manufacturing the photocurrent detection device.

  One of the photocurrent sensors as the photocurrent detection device is, for example, a sagnac interferometer type current sensor. This sagnac interferometer type current sensor makes circularly polarized light incident and propagates from both one end and the other end to the current detection coil, and interferes with both lights having a phase difference and is applied from the change in light intensity. The current that generated the generated magnetic field is measured.

  At this time, if the optical fiber has birefringence, the circularly polarized light collapses and current cannot be measured correctly. Therefore, it is important to prevent the birefringence of the optical fiber and to propagate the circularly polarized light correctly.

  Up to now, it has been possible to reduce the birefringence by improving the technology of the sensor portion of the optical fiber, and to achieve a photocurrent detection accuracy of about 1% accuracy.

Japanese Patent Laid-Open No. 10-10378

  However, in recent years, higher accuracy, such as 0.2% accuracy or 0.1% accuracy, is required for the photocurrent sensor, and it is still insufficient for reducing birefringence.

  The problem to be solved by the present invention is to provide a photocurrent detection device capable of reducing the birefringence of an optical fiber and improving the accuracy of current detection, and a method for manufacturing the photocurrent detection device.

The photocurrent detection device of the embodiment is a photocurrent sensor that measures current using the Faraday effect of an optical fiber, and includes a cylindrical member, a support member, and a fixing member. The cylindrical member has a cylindrical portion whose inner diameter is larger than the outer diameter of the optical fiber, and the optical fiber is accommodated in the cylindrical portion. The support member is disposed along the longitudinal direction of the cylindrical member, and has a thermal expansion coefficient equal to or at least smaller than that of the cylindrical member. The support member is formed of a material having a thermal expansion characteristic equivalent to that of the optical fiber. The fixing member fixes the support member and the cylindrical member.

It is a figure which shows the circuit structure of the photocurrent sensor of embodiment. It is sectional drawing which shows the structure of the current detection coil of 1st Embodiment. It is sectional drawing which shows the structure of the current detection coil of 2nd Embodiment. It is sectional drawing which shows the structure of the current detection coil of 3rd Embodiment. It is sectional drawing which shows the structure of the current detection coil of 4th Embodiment. It is sectional drawing which shows the structure of the current detection coil of 5th Embodiment.

Hereinafter, embodiments will be described in detail with reference to the drawings.
(First Embodiment) FIG. 1 is a diagram showing a configuration of a photocurrent sensor according to an embodiment.

  As shown in FIG. 1, the photocurrent sensor of this embodiment is a device for measuring current using the Faraday effect of an optical fiber, and includes a first optical splitter 2, a first polarizing filter 3, and a second light. It has a branching device 4, a phase modulator 5, a current detection coil 6, a light receiver 7, a synchronous detector 8, an oscillation circuit 9, a first quarter wavelength plate 16, a second quarter wavelength plate 17, and the like.

  The first optical splitter 2, the first polarizing filter 3, and the second optical splitter 4 send light emitted from the light source 1 into the current detection coil 6 as counterclockwise light and clockwise light.

  The phase modulator 5 phase-modulates the left-handed light and the right-handed light, and enters the current detection coil 6 through the corresponding quarter wavelength plate 16 (or 17). The phase modulator 5 phase-modulates, for example, counterclockwise light, and enters the current detection coil 6 through the first quarter-wave plate 16. For example, the phase modulator 5 performs phase modulation on the clockwise light that has passed through the first quarter-wave plate 16, and causes the second optical splitter 4, the first polarizing filter 3, and the first optical splitter 2 to be modulated. The light passes through and is received by the light receiver 7.

  The current detection coil 6 is arranged so as to be wound around the cable through which the current I to be detected flows. The current detection coil 6 detects a phase difference due to the Faraday effect. In the current detection coil 6, the light incident from the first quarter wavelength plate 16 and the second quarter wavelength plate 17 circulates and propagates in the respective directions, and sequentially, the second optical splitter 4. The light passes through the first polarizing filter 3 and the first optical branching device 2 and reaches the light receiving device 7 to be received.

  The light receiver 7 receives the light that has passed through the first optical branching device 2. The light receiver 7 photoelectrically converts the received light into an electrical signal. The oscillation circuit 9 oscillates a reference signal. The synchronous detector 8 obtains a detection output having a phase difference proportional to the magnetic field applied to the current detection coil 6 using the signal supplied from the oscillation circuit 9 as a reference signal.

Here, a first embodiment of the current detection coil 6 will be described with reference to FIG.
As shown in FIG. 2, in the current detection coil 6 of the first embodiment, a cladding 62 layer having a slightly lower refractive index than the core 61 is formed around the core 61 where light is actually propagated. , A light guide optical fiber 63 as a sensor, a cylindrical member 64 having rubber elasticity formed of, for example, silicone rubber and the like, and a reinforcing member disposed along the longitudinal direction of the cylindrical member 64 An optical fiber 65 as a support member (reinforcing member) and an adhesive 66 as a fixing member for fixing the optical fiber 65 and the tubular member 64 are provided.

  The optical fiber 63 which is a sensor has a core or clad made of, for example, quartz or glass. The adhesive 66 bonds the optical fiber 65 and the cylindrical member 64 partially or over the entire facing part. The cylindrical member 64 is preferably formed of a material having a sufficiently small Young's modulus with respect to quartz or glass because the shape of the cylindrical member 64 is restrained by the support member. In this example, the reinforcing support member uses an optical fiber 65 having the same (equivalent) thermal expansion characteristics as the optical fiber 63.

  As the reinforcing support member, in addition to the optical fiber 65, one having the same thermal expansion characteristic as that of the optical fiber 63, that is, the one having the same thermal expansion coefficient can be applied.

  The cylindrical member 64 has a cylindrical portion whose inner diameter is larger than the outer diameter of the optical fiber 63, and the optical fiber 63 is accommodated in the cylindrical portion. The optical fiber 63 is housed inside the tubular member 64 (tubular portion) with a gap from the inner wall surface of the tubular member 64, and is protected (held) from being affected by the outside.

  In other words, the cylindrical member 64 has a larger inner diameter than the outer diameter of the optical fiber 63, and a space (gap) is provided in the inside thereof, and has a hollow structure. With such a hollow structure, when an impact such as vibration is applied, the impact can be absorbed by the outer cylindrical member 64 to protect the optical fiber 63 inside.

  For example, if the periphery of the optical fiber 63 is filled with silicone rubber or the like, a force (pressure) for compressing the optical fiber 63 is applied by impact, but in the case of a hollow structure like this embodiment, No pressure is applied to the optical fiber 63.

The function of the photocurrent sensor of this embodiment will be described.
In this embodiment, a material having rubber elasticity such as silicone rubber is used for the cylindrical member 64. Such a material having rubber elasticity generally has a thermal expansion coefficient much larger than that of the optical fiber 63, and applies a force in the expansion / contraction direction to the optical fiber 63 due to expansion / contraction due to temperature change.

  In order to prevent this, it is conceivable that the inner diameter of the cylinder is made larger than the expansion and contraction due to the temperature, but in this case, the original function of holding the optical fiber 63 cannot be performed. In this case, the optical fiber 63 is held in a meandering manner in the cylinder, and birefringence due to bending of the optical fiber 63 occurs. Furthermore, since the shape of the optical fiber 63 is not stable, birefringence also becomes unstable.

  Another measure for preventing the optical fiber 63 from applying a force in the direction of expansion and contraction is to align the thermal expansion of the tubular member 64 with that of the optical fiber 63. Since there is no material having both, the measures with the cylindrical member 64 itself cannot be taken.

  Therefore, in this embodiment, a function for preventing the compressive force from being applied to the optical fiber 63 is realized by newly providing a mechanism for aligning the expansion and contraction of the cylindrical member 64 having rubber elasticity with that of the optical fiber 63. ing.

  That is, in the first embodiment, the reinforcing optical fiber 65 is disposed on the tubular member 64 side, and the tubular member 64 and the optical fiber 65 are fixed (coupled) with the adhesive 66.

  In this case, it is ideal to apply the adhesive 66 over the entire length (longitudinal direction) of the tubular member 64 to couple the optical fiber 65 and the tubular member 64, but the tubular member 64 is not bent. Even if the adhesive 66 is scattered and applied to the extent that the cylindrical member 64 and the optical fiber 65 are fixed (coupled), there is no practical problem.

  As described above, according to the first embodiment, the reinforcing optical fiber 65 is disposed along the longitudinal direction of the cylindrical member 64 in which the optical fiber 63 is accommodated, and the optical fiber 65 and the cylindrical member 64 are fixed by the adhesive 66 ( And the expansion and contraction due to the temperature change is prevented from occurring in the cylindrical member 64, so that no pressure is applied to the optical fiber 63 inside the cylindrical member 64, and the birefringence of the optical fiber 63 can be reduced. As a result, the current detection accuracy can be further increased.

Next, a second embodiment will be described with reference to FIG.
In the first embodiment, the same optical fiber 65 as the optical fiber 63 serving as a sensor is used as the reinforcing support member. However, the reinforcing support member is not necessarily the same as the optical fiber 63.

  That is, the reinforcing support member may be any member having a thermal expansion coefficient that is the same as or close to that of the optical fiber 63 (optical fiber 63 or more) and has a smaller thermal expansion coefficient than that of the tubular member 64.

  Therefore, in the second embodiment, as shown in FIG. 3, a large-diameter multimode fiber 70 is used as a reinforcing support member.

  That is, the current detection coil 6 of the second embodiment is a sensor in which a cladding 62 layer having a refractive index slightly smaller than that of the core 61 is formed around the core 61 where light is actually propagated. As an optical fiber 63 for light guide, a cylindrical member 64 having rubber elasticity formed of, for example, silicone rubber, and a supporting member (reinforcing member) for reinforcement arranged along the longitudinal direction of the cylindrical member 64 Multimode fiber 70 and an adhesive 66 as a fixing member for fixing the multimode fiber 70 and the cylindrical member 64 to each other.

  When the optical fiber 63 as a sensor is, for example, a fiber made of quartz (quartz fiber) or the like, the outer diameter of the single mode fiber is a standard quartz outer diameter such as 125 μm, whereas the multimode fiber 70 is used. Can be produced with a large diameter such as 250 μm to 400 μm.

  By using such a large-diameter multimode fiber 70 as a support member, the fiber is difficult to bend, and when formed into a coil shape, a beautiful circular shape can be formed with substantially the same radius of curvature over the entire length. it can.

  Since the large-diameter multimode fiber 70 is difficult to bend, the bending radius of the fiber is not reduced. The optical fiber 63 accommodated in the cylindrical member 64 reinforced with the large-diameter multimode fiber 70 is The birefringence can be kept to a minimum because it is kept in a beautiful circular shape with no small bending radius.

  As described above, according to the second embodiment, the cylindrical member 64 can be further reinforced by using the multimode fiber 70 as a reinforcing support member, and birefringence can be kept to a minimum.

Next, a third embodiment will be described with reference to FIG.
In the first embodiment, one optical fiber 65 is used as a reinforcing support member for restraining the contraction of the cylindrical member 64. However, the number of the members is not necessarily one, for example, FIG. As shown in FIG. 6, a plurality of optical fibers 65 may be disposed around the cylindrical member 64 and fixed (coupled) to the cylindrical member 64 with an adhesive 66. In this example, four optical fibers 65 are arranged around the cylindrical member 64 at an interval of approximately 90 °, and are bonded to the cylindrical member 64 with an adhesive 66.

  According to the third embodiment, it is possible to make the expansion and contraction due to the temperature change of the tubular member 64 stronger and stronger than the first embodiment, and the birefringence of the optical fiber 63 can be reduced. As a result, the current detection accuracy can be further increased.

Next, a fourth embodiment will be described with reference to FIG.
In the said 1st Embodiment, although the optical fiber 63 which is a sensor was shown accommodated in the hollow cylindrical member 64, this 4th Embodiment demonstrates the example which integrated these.

  That is, the current detection coil 6 of the fourth embodiment is a sensor in which a layer of a clad 72 having a refractive index slightly smaller than that of the core 71 is formed around the core 71 where light is actually propagated. A light guide optical fiber 73, a primary coating 74 formed on the optical fiber 73, a secondary coating 75 formed on the primary coating 74, and a gap above the secondary coating 75 A sensor fiber having a tertiary coating 77 formed with a gap therebetween, an optical fiber 65 as a support member (reinforcing member) for reinforcement disposed along the longitudinal direction of the sensor fiber, and the optical fiber 65 and the tube And an adhesive 66 as a fixing member for fixing the shaped member 64.

  When forming the sensor fiber, a twist is applied to the optical fiber 73 subjected to the primary coating, and a secondary coating 75 for fixing the twist is formed around the twist.

  In the fourth embodiment, since a gap 76 is provided between the secondary coating 75 and the tertiary coating 77, the optical fiber 73 side is affected by thermal expansion when the tertiary coating 77 is formed. Therefore, the tertiary coating 77 harder than the secondary coating 75 can be formed.

  Therefore, the Young's modulus of the primary coating 74 can be lowered to minimize the stress applied to the optical fiber 73, and the secondary coating 75 that affects the thermal expansion on the optical fiber 73 side can fix the twist. By making the required degree of hardness and protecting from external force with a harder tertiary coating 77, it is possible to more reliably prevent the occurrence of wavelength dispersion and birefringence and damage.

  According to the fourth embodiment, an integrated sensor fiber coated in multiple layers is provided on the optical fiber 73, and the optical fiber 65 is fixed (bonded) to the sensor fiber with an adhesive as in the first embodiment. On the other hand, the expansion and contraction due to the temperature change of the tertiary coating 77 is constrained by the optical fiber 65, while the expansion due to the temperature change is the same as the optical fiber 65, so that the birefringence is further stabilized and the current can be measured with high accuracy. become able to.

  Further, as in the first embodiment, the gap 76 provided between the secondary coating 75 and the tertiary coating 77 functions as a buffer layer when an external force such as vibration is applied, so that the external force is reduced. Without being transmitted to the optical fiber 73 as it is, low birefringence can be maintained.

Next, a fifth embodiment will be described with reference to FIG.
In the fifth embodiment, the cylindrical member 64 is not restrained (also fixed or fixed) by the reinforcing optical fiber 65 and the adhesive 66 as in the first embodiment. Instead of this, the quartz member 64 is made of quartz. A cylindrical member having a silicone coating 81 formed on the front and back surfaces of the capillary 80 is formed, and an optical fiber 63 having a small outer diameter is housed in a space inside the silicone coating 81 of the cylindrical member to constitute the current detection coil 6. Yes. That is, this example also has a hollow structure in the cylindrical member.

  For example, in the case where the gap between the optical fiber 63 as a sensor and the quartz capillary 80 is filled with silicone or the like, an external force such as vibration is transmitted to the optical fiber 63 as a contraction force. In this case, the low birefringence can be maintained by providing a space inside the cylindrical member 82.

  This hollow structure can be easily realized by previously applying a silicone coating to the quartz capillary 80 and then passing the optical fiber 63 through the cylinder. The coating is not limited to silicone rubber, and the same effect can be obtained as long as the material has a sufficiently small Young's modulus relative to quartz, such as a resin such as polyimide.

  Although the embodiment of the present invention has been described, this embodiment is presented as an example and is not intended to limit the scope of the invention. The novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  In the above embodiment, the adhesive 66 is used as the fixing member. However, the adhesive 66 is not limited to the adhesive 66. For example, an adhesive tape or the like may be wound around the cylindrical member 64 and fixed (fixed). That is, the optical fiber 65 and the cylindrical member 64 are integrally wrapped and fixed with an adhesive tape.

  DESCRIPTION OF SYMBOLS 1 ... Light source, 2 ... Optical splitter, 3 ... 1st polarizing filter, 4 ... 2nd optical splitter, 5 ... Phase modulator, 6 ... Current detection coil, 7 ... Light receiver, 8 ... Synchronous detector, DESCRIPTION OF SYMBOLS 9 ... Oscillator circuit, 16 ... 1st 1/4 wavelength plate, 17 ... 2nd 1/4 wavelength plate, 61, 71 ... Core, 62, 72 ... Cladding, 63, 73 ... Optical fiber, 64 ... Cylindrical member , 65 optical fibers, 66 adhesives, 70 multimode fibers, 74 primary coatings, 75 secondary coatings, 76 gaps, 77 tertiary coatings, 80 quartz capillaries, 81 silicone coatings.

Claims (4)

In a photocurrent sensor that measures current using the Faraday effect of an optical fiber,
A cylindrical member having an inner diameter larger than the outer diameter of the optical fiber, and a cylindrical member that houses the optical fiber in the cylindrical part;
A support member that is disposed along the longitudinal direction of the cylindrical member and has a thermal expansion coefficient equal to or at least smaller than that of the cylindrical member;
A fixing member for fixing the support member and the tubular member ;
The support member is
A photocurrent sensor formed of a material having a thermal expansion characteristic equivalent to that of the optical fiber . The support member, the optical current sensor fiber der Ru請 Motomeko 1 wherein. 3. The photocurrent sensor according to claim 1, wherein the fixing member is an adhesive that adheres the support member and the cylindrical member partially or in an entire region facing each other . 4. The anchoring member is an optical current sensor according to any one of claims 1 or 2 is a pressure-sensitive adhesive tape for fixing wrapped with the tubular member and the support member.

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