JP3415972B2 - Optical fiber sensor and polarizer unit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber type sensor and a polarizer unit utilizing the Faraday rotation effect of linearly polarized light propagating in an optical fiber, and more particularly to an optical fiber type sensor and a polarization unit for measuring current or magnetic field. Regarding the child unit.

[0002]

2. Description of the Related Art An optical fiber type sensor utilizing the Faraday rotation effect of linearly polarized light propagating in an optical fiber utilizes the principle that the direction of linearly polarized light incident on a sensing fiber is rotated by a magnetic field created by an electric current. .

FIG. 6 is a diagram showing the basic principle of such an optical fiber type sensor. In the optical fiber type sensor, the inspection light from the light source 61 is converted into linearly polarized light by the polarizer 62 and introduced into the sensing fiber 63. At this time, the polarizer 62 cancels fluctuations in the intensity of the light source 61 and the like,
The polarization plane direction of the inspection light is provided so as to be inclined by 45 ° with respect to the vertical coordinate axis of the coordinate system in which the sensor is placed.

The inspection light introduced into the sensing fiber 63 undergoes Faraday rotation due to the current I flowing through the conductor 64, and enters the analyzer 65. When no current is flowing through the conductor 64, the analyzer 65 is incident with the polarization direction of the inspection light being inclined by 45 ° with respect to the axis of the analyzer, as in the case of introduction into the sensing fiber 63. It is provided. The analyzer 65 splits the inspection light into two polarization components and sends them to the light receiving elements 66 and 67, respectively. The light receiving elements 66 and 67 are, for example, photodiodes,
Converts the sent light into an electrical signal. The electric signal is further converted into a Faraday rotation angle value by a known signal arithmetic processing circuit. Since the Faraday rotation angle value is proportional to the current flowing through the conductor 64, the target current value can be obtained by knowing this Faraday rotation angle value.

By the way, in a practical optical fiber type sensor, each component does not have a spatial arrangement as shown in FIG. 6, but a module in which a polarizer 62, a sensing fiber 63, an analyzer 65 and the like are integrated is used. ing.

FIG. 7 is a plan view showing the structure of a conventional modularized optical fiber type sensor. In this optical fiber type sensor 70, a polarizer 72 and an analyzer unit 75 are integrally provided on a base. The polarizer 72 is fixed between the input fiber 71 and the sensing fiber 73. Inspection light L11, which is a laser beam, enters from the end of the input fiber 71, is converted into linearly polarized light by the polarizer 72, and is introduced into the sensing fiber 73.
However, here, the plane of polarization of the inspection light L11 is not inclined by 45 ° as in FIG.

The sensing fiber 73 is wound a plurality of times in a ring shape, and the conductor 74 is inserted in the center thereof. The inspection light L11 undergoes Faraday rotation by the magnetic field generated by the current flowing through the conductor 74 in the process of propagating through the sensing fiber 73, and is input to the analyzer unit 75.

The analyzer unit 75 includes a half-wave plate 751 and
It has a birefringent crystal body 752 and an optical path shift prism 753, which are integrally provided in the housing. The half-wave plate 751 can change the polarization plane angle of the inspection light L11 incident on the birefringent crystal 752 by changing the angle around the optical axis. The half-wave plate 751 is installed such that the polarization plane of the inspection light L11 is inclined by 45 ° with respect to the axis of the analyzer when no current flows in the conductor 74.

The polarizer 72 determines the inclination of the polarization plane of the inspection light L11.
Instead, the reason why the half-wave plate 751 is used is that the polarization plane direction of the inspection light L11 propagating therethrough may be slightly changed due to the twist or deformation of the sensing fiber 73. By adjusting the polarization plane direction of the inspection light L11 after passing through the sensing fiber 73,
Accurate inspection can be performed.

Inspection light L1 that has passed through the half-wave plate 751.
Two components orthogonal to each other are separated by a birefringent crystal body 752, one of which goes straight and is output as a signal T through a light receiving fiber 76, and the other of which is an optical path shift prism 753.
The optical path is adjusted by and is sent to the light receiving fiber 77, and is output as a signal R via the light receiving fiber 77.

The two signals T and R are converted into an electric signal by a light receiving element (not shown), whereby
The value of the current flowing through the conductor 74 is detected as described with reference to FIG.

[0012]

However, the analyzer unit 75 using the half-wave plate 751 as described above has the following problems. (1) When the surface of the half-wave plate 751 is not perpendicular to the optical axis, when the half-wave plate 751 is rotated around the optical axis, the optical path is deviated and the half-wave plate 751 before and after the half-wave plate 751 The coupling efficiency of the optical fiber fluctuates, and an error occurs in the measured value. (2) Since the half-wave plate 751 is made of a crystal such as quartz, the phase difference varies depending on its temperature characteristic, and the emitted light is slightly elliptical. For this reason, highly accurate measurement cannot be expected in an environment where the temperature changes. (3) Since the half-wave plate 751 is a thin plate, it is difficult to attach the half-wave plate 751 and its angle is difficult to adjust.

The present invention has been made in view of the above circumstances, and it is easy to adjust the reference azimuth of the inspection light to a desired angle with respect to the axis of the analyzer without using a half-wave plate. It is an object of the present invention to provide an optical fiber type sensor that can be accurately and accurately made and have a simple structure.

[0014]

In order to solve the above problems, the present invention provides an optical fiber type sensor utilizing the Faraday rotation effect of linearly polarized light propagating in an optical fiber,
The optical input fiber and the sensing fiber are integrally coupled via a polarizer, and the polarizer unit is provided so as to be rotatable about the direction connecting the optical input fiber and the sensing fiber as a rotation axis, and the analyzer. An optical fiber type sensor is provided, which comprises: an analyzer unit that separates and outputs the light emitted from the sensing fiber into two polarization components orthogonal to each other.

In such an optical fiber type sensor, since the polarizer is integrally coupled between the optical input fiber and the sensing fiber, the direction connecting the optical input fiber and the sensing fiber is used as the rotation axis. It can be easily rotated. Therefore, the polarization plane azimuth of the inspection light can be adjusted to a desired angle by rotating the polarizer with respect to the optical axis. At this time, the inspection light hardly shifts in direction in the optical input fiber and the sensing fiber, so the polarization plane direction changes by an angle according to the rotation angle of the polarizer unit.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of the polarizer unit of this embodiment. The polarizer unit 10 is entirely covered with a cylindrical pipe 11 made of stainless steel.
Thin film type polarizer 12 and optical connector ferrules 13 and 1
4 and 4 are integrally provided. They sandwich the polarizer 12 with optical connector ferrules 13 and 14 and use an adhesive to optically and physically bond it and to the sleeve 15
It is configured by wrapping with. An input fiber 16 is coupled to the optical connector ferrule 13, while a sensing fiber 17 is coupled to the optical connector ferrule 13.

The polarizer 12 is a prismatic polarizer such as a polarization beam splitter, a laminated thin film polarizer in which an optically transparent dielectric material and a conductor such as metal are alternately laminated, or a transparent material such as glass. Further, a fine particle orientation dispersion type polarizer in which flat or spheroidal fine particles made of a metal such as silver or copper are orientation-dispersed can be used. Since the laminated thin film polarizer and the fine particle orientation dispersion type polarizer are very small, the entire polarizer unit 10 can be downsized, which is also advantageous for sealing.

FIG. 2 is a diagram showing a schematic configuration of an experimental system for measuring the extinction ratio of the polarizer unit 10 of FIG. From the light source 21, for example, 850n as the inspection light L0
m laser light is output. This inspection light L0 is 1/4
After passing through the wave plate, it becomes linearly polarized light by the polarizer 23 and is condensed by the lens 24. The condensed inspection light L0 is incident on the input fiber 16. Here, the input fiber 16 is a silica glass fiber.

Inspection light L incident on the input fiber 16
Polarization plane azimuths of 0 are changed by the polarizer unit 10 and emitted through the sensing fiber 17. here,
The sensing fiber 17 is a lead glass fiber, and the core glass contains SiO ₂ and PbO, and the weight of SiO ₂ is 5 to 35% and the weight of PbO is 65 to 85%. As a result, the photoelastic constant of the sensing fiber 17 is ± 3 × 10 ⁻⁹ cm ² / kg or less.

The inspection light L0 emitted from the sensing fiber 17 is collimated by the lens 25, separated into two polarization components by the analyzer 26, and each of them is separated by the lens 2.
The light is sent to the light receiving elements 28 and 30 via 7, 29.

By the way, the input fiber 16, the polarizer unit 10, and the sensing fiber 17 are supported by the rotating mechanism portions 31, 32, and 33, respectively. The rotating mechanism portions 31, 32, and 33 can rotate the entrance end of the input fiber 16, the entire polarizer unit 10, and the exit end of the sensing fiber 17, respectively, and fix them at a desired rotation angle. it can.

In such a device, first, the polarizer unit 10 is fixed, the emitting end of the sensing fiber 17 is rotated to twist the fiber, and the polarization plane direction and extinction ratio of the inspection light emitted in that state. An experiment was performed to measure As a result, even if the emitting end of the sensing fiber 17 is rotated, the rate of change of the polarization plane orientation with respect to the rotation angle is about 0.
001 and 0.045 ° for a rotation angle of 45 °
It was a level, which was practically negligible. Also,
The extinction ratio was 35 dB or more, and it was shown that the induced birefringence was extremely small.

For comparison, a similar experiment was carried out using the sensing fiber 17 as a silica glass fiber. As a result, the change of the polarization plane orientation with respect to the rotation angle was as large as about 0.1. Also, the extinction ratio changed indefinitely depending on the degree of rotation.

Next, an experiment was conducted in which the emission end of the sensing fiber 17 was fixed and the polarizer unit 10 was rotated to measure the polarization plane direction and extinction ratio of the emitted inspection light. As a result, the polarization plane direction of the inspection light was rotated by the angle at which the polarizer unit 10 was rotated.

FIG. 3 is a plan view showing the structure of an optical fiber type sensor using the polarizer unit 10 of this embodiment. In this optical fiber type sensor 40, the polarizer unit 10 is provided on the base in a state of being fixed to the fixing unit 41. As will be described later, the polarizer unit 10 is rotationally adjusted and fixed with a direction connecting the optical input fiber and the sensing fiber as a rotation axis. Further, an analyzer unit 43 is provided on the base. A sensing fiber 17 is provided between the polarizer unit 10 and the analyzer unit 43. The sensing fiber 17 is wound a plurality of times in a ring shape, and the conductor 42 is inserted in the center thereof.

From the end of the input fiber 16, the inspection light L1 which is a laser light is incident from a light source (not shown). The inspection light L1 is converted into linearly polarized light by the polarizer unit 10 and introduced into the sensing fiber 17. The inspection light L1 undergoes Faraday rotation by the magnetic field generated by the current flowing through the conductor 42 in the process of propagating through the sensing fiber 17, and then is input to the analyzer unit 43.

The analyzer unit 43 has an analyzer 431 and an optical path shift prism 432, which are integrally provided in the housing. Sensing fiber 1
The inspection light L1 emitted from 7 enters the analyzer 431 of the analyzer unit 43, where two polarization components orthogonal to each other are separated, and one of them goes straight and is output as a signal T via the receiving fiber 44. And the other is the optical path shift prism 43.
The optical path is adjusted by 2 and sent to the light receiving fiber 45, and is output as a signal R via the light receiving fiber 45.
The two signals T and R are converted into an electric signal by a light receiving element (not shown), whereby the value of the current flowing through the conductor 42 is detected.

4A and 4B are views showing the structure of the fixing unit 41. FIG. 4A is a plan view, FIG. 4B is a side view seen from the arrow X direction, and FIG. 4C is a side view seen from the arrow Y direction. is there. The fixed unit 41 includes a base 411 and a fixed unit 2
It is composed of individual pressing plates 412 and 413. The base 411 has a V-shaped groove 411a as shown in FIG.
Are formed. The polarizer unit 10 is placed in the groove 411a.

Since the polarizer unit 10 is formed in a cylindrical shape, it can be easily rotated on the groove 411a. When the polarizer unit 10 is rotated by a desired angle, the pressing plates 412 and 413 are covered from above and the screws 412a, 412b, 413a and 413b are respectively tightened to fix the polarizer unit 10 in that state. You can Alternatively, the pressing plates 412 and 413 are previously set.
The screws 412a, 412b, 413a, 413b.
The rotation angle of the polarizer unit 10 is adjusted in a state where the screws are loosely tightened, and then the screws 412a, 412b, 413a, 4
You may make it strongly tighten 13b.

FIG. 5 is a diagram showing the measurement results of the amount of light output from the analyzer unit 43 with respect to the rotation angle of the polarizer unit 10 of this embodiment. In the figure, the characteristics P and Q indicate the intensity characteristics of the two polarization components separated by the analyzer unit 43. As can be seen from the figure, by appropriately rotating the polarizer unit 10, the two polarization components are separated by 1: 1,
That is, the direction of the emitted light can be adjusted in the angle direction of 45 ° with respect to the axis of the analyzer 431. Therefore, a large stress that breaks the input fiber 16 and the sensing fiber 17 is not applied.

As described above, in this embodiment, since the polarizer 12 is integrally formed with the input fiber 16 and the sensing fiber 17 as the polarizer unit 10, it is not necessary to rotate the polarizer 12 itself. . Therefore, since the optical axis of the inspection light does not change and the fiber coupling efficiency does not change, the polarization plane direction of the inspection light can be easily and accurately adjusted without using the half-wave plate. Also,
The number of parts of the optical fiber type sensor is reduced, and the manufacturing cost and the manufacturing efficiency are improved. Furthermore, the polarizer 12 can be easily sealed and can be miniaturized, and the miniaturization can shorten the optical path, thereby improving reliability.

Further, in this embodiment, since the polarizer unit 10 is fixed by the fixing unit 41, the fixing to the optical fiber type sensor 40 can be easily and surely performed.

The optical fiber has a property called photoelasticity. Photoelasticity is a phenomenon in which the stress applied to a material causes anisotropy in the refractive index of the material, causing birefringence in light propagating in the material. Due to this phenomenon, when the optical fiber is physically twisted with the light beam direction as the central axis, stress is generated and the direction of the polarization plane is also twisted.

Therefore, in this case, the change of the polarization plane azimuth is not always equal to the rotation angle of the polarizer unit, and when the stress changes due to a temperature change or the like, the polarization plane azimuth changes and causes a measurement error. Become. Further, due to birefringence in the fiber, the inconvenience that the inspection light, which should originally be linearly polarized light, is changed to elliptically polarized light, often occurs.

Therefore, in the present embodiment, lead glass is used as the material of the sensing fiber 17, and its photoelastic constant is ±.
Since it is set to 3 × 10 ⁻⁹ cm ² / kg or less, the twist of the polarization plane due to the twist of the sensing fiber 17 when the polarizer unit 10 is rotated can be reduced to a negligible level. Yes, more accurate adjustment is possible.

In this embodiment, the polarization plane azimuth is adjusted by the polarizer unit 10 in which the polarizer 12 is integrated with the fiber. However, by integrating the analyzer 431 with the fiber, the analyzer unit can be adjusted. It is possible to adjust the polarization plane direction by. Analyzer 4 at this time
As the material of 31, an analyzer using a crystal such as calcite or quartz, or a prism type analyzer such as a polarization beam splitter, a Glan-Thompson prism, a Glan-laser prism, or the like can be used.

Further, in the present embodiment, as the optical fiber type sensor 40, the example in which the polarizer unit 10 is used to measure the value of the current flowing through the conductor 42 has been shown, but it is possible to measure the magnitude of the magnetic field instead of the current. Can also be used.

[0038]

As described above, in the present invention, the polarizer is integrally coupled between the optical input fiber and the sensing fiber, so that the direction of connecting the optical input fiber and the sensing fiber is changed. It can be easily rotated as a rotating shaft. Therefore, the polarization plane of the inspection light can be adjusted to a desired direction by rotating the polarizer unit with respect to the optical axis. Therefore, since the optical axis of the inspection light does not change and the fiber coupling efficiency does not change, the polarization plane direction of the inspection light can be easily and accurately adjusted without using the half-wave plate. Moreover, the number of parts of the optical fiber type sensor is reduced, and the manufacturing cost and the manufacturing efficiency are improved. Furthermore, sealing of the polarizer is easy, and miniaturization can be achieved. Since the miniaturization can shorten the optical path, reliability is improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a polarizer unit of the present embodiment.

2 is a diagram showing a schematic configuration of an experimental system for measuring an extinction ratio of the polarizer unit of FIG.

FIG. 3 is a plan view showing a configuration of an optical fiber type sensor using the polarizer unit of the present embodiment.

4A and 4B are diagrams showing a configuration of a fixing unit, FIG. 4A is a plan view, FIG. 4B is a side view seen from an arrow X direction, and FIG. 4C is a side view seen from an arrow Y direction.

FIG. 5 is a diagram showing a measurement result of an output light amount from an analyzer unit with respect to a rotation angle of a polarizer unit of the present embodiment.

FIG. 6 is a diagram showing a basic principle of an optical fiber type sensor.

FIG. 7 is a plan view showing a configuration of a conventional modularized optical fiber type sensor.

[Explanation of symbols]

10 Polarizer unit 11 Cylindrical pipe 12 Polarizer 13,14 Optical connector ferrule 15 sleeves 16 input fiber 17 Sensing fiber 40 Optical fiber type sensor 41 Fixed unit 42 conductor 43 Analyzer unit 431 Analyzer 44.45 Receiving fiber

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-7-248338 (JP, A) JP-A-4-153619 (JP, A) JP-A-61-36725 (JP, A) JP-A-6- 242149 (JP, A) JP-A-1-244376 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01R 15/00-15/26 G02B 27/00-27/64

Claims (10)

(57) [Claims] 1. An optical fiber type sensor utilizing the Faraday rotation effect of linearly polarized light propagating through an optical fiber, wherein an optical input fiber and a sensing fiber are integrally coupled via a polarizer, and the optical input fiber is provided. And a polarizer unit that is rotatably provided with a direction connecting the sensing fiber as a rotation axis, and an analyzer that separates and outputs the light emitted from the sensing fiber into two polarization components orthogonal to each other by the analyzer. An optical fiber type sensor comprising: a unit; 2. In the polarizer unit, a light input fiber and a sensing fiber are bonded to the polarizer with an adhesive via ferrules, and a sleeve is provided around the polarizer and the ferrule. The optical fiber sensor according to claim 1, wherein the sleeve is covered with a housing. 3. The optical fiber type according to claim 2, further comprising: a base on which the polarizer unit is mounted, and a fixing member that fixes the polarizer unit to the base. Sensor. 4. The optical fiber type sensor according to claim 3, wherein a V-shaped groove is formed on the base. 5. The optical fiber type sensor according to claim 1, wherein the sensing fiber has a photoelastic constant of ± 3 × 10 ⁻⁹ cm ² / kg or less. 6. The sensing fiber contains SiO ₂ and PbO in a core glass, and the weight of SiO ₂ is 5 to 3.
The optical fiber type sensor according to claim 1, wherein the weight of PbO is 5% and the weight of PbO is 65 to 85%. 7. An optical fiber sensor utilizing the Faraday rotation effect of linearly polarized light propagating in an optical fiber, a polarizer provided between an optical input fiber and a sensing fiber, the sensing fiber and a light receiving element. The light receiving fiber on the side is integrally coupled via an analyzer, and the analyzer unit is provided so as to be rotatable about the straight traveling direction of the light emitted from the sensing fiber as a rotation axis. Optical fiber type sensor. 8. The optical fiber type sensor according to claim 7, wherein the sensing fiber has a photoelastic constant of ± 3 × 10 ⁻⁹ cm ² / kg or less. 9. The sensing fiber contains SiO ₂ and PbO in a core glass, and the weight of SiO ₂ is 5 to 3.
The optical fiber type sensor according to claim 7, wherein the weight of PbO is 5% and the weight of PbO is 65 to 85%. 10. A polarizer unit for converting light from a light source into linearly polarized light, wherein an optical input fiber and a sensing fiber are integrally coupled via a polarizer, and the optical input fiber and the sensing fiber are connected to each other. A polarizer unit, wherein the polarizer unit is rotatably provided with a connecting direction as a rotation axis.