JP2016023929A - Optical fiber temperature distribution measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber temperature distribution measuring device capable of integrating an exciter even in a comparatively small space which is approximately similar to a conventional case, and measuring an accurate temperature distribution by removing a higher mode.SOLUTION: In an optical fiber temperature distribution measuring device using an optical fiber as a sensor, and constituted so as to measure a temperature distribution along the optical fiber by utilizing Raman back-scattered light, an exciter is constituted by two-dimensionally wiring the optical fiber.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an optical fiber temperature distribution measuring device using an optical fiber as a sensor, and more particularly to an exciter structure.

  As one type of distributed measurement apparatus using an optical fiber as a sensor, there is an optical fiber temperature distribution measurement apparatus configured to measure a temperature distribution along an optical fiber as described in Patent Document 1. This technique uses backscattered light generated in an optical fiber. In the following description, the optical fiber temperature distribution measuring device is also referred to as DTS (Distributed Temperature Sensor) as necessary.

  Backscattered light includes Rayleigh scattered light, Brillouin scattered light, and Raman scattered light, but temperature-dependent back Raman scattered light is used for temperature measurement. Measure. The back Raman scattered light includes anti-Stokes light AS generated on the short wavelength side with respect to the wavelength of incident light and Stokes light ST generated on the long wavelength side.

  The optical fiber temperature distribution measuring device measures the intensity Ias of the anti-Stokes light and the intensity Ist of the Stokes light, calculates the temperature from the intensity ratio, and displays the temperature distribution along the optical fiber. It is used in fields such as facility temperature management, disaster prevention research and research, and air conditioning in power plants and large buildings.

  FIG. 5 is a block diagram illustrating a basic configuration example of the optical fiber temperature distribution measuring apparatus. In FIG. 5, a light source 1 is connected to an incident end of an optical demultiplexer 2, an optical fiber 3 is connected to an input / output end of the optical demultiplexer 2, and a photoelectric is connected to one output end of the optical demultiplexer 2. A converter (hereinafter referred to as an O / E converter) 4 st is connected, and an O / E converter 4 as is connected to the other emission end of the optical demultiplexer 2.

  The output terminal of the O / E converter 4st is connected to the arithmetic control unit 7 via the amplifier 5st and the A / D converter 6st, and the amplifier 5as and the A / D converter are connected to the output terminal of the O / E converter 4as. It is connected to the arithmetic control unit 7 via 6as. The arithmetic control unit 7 is connected to the light source 1 via the pulse generation unit 8.

  For example, a laser diode is used as the light source 1 and emits pulsed light corresponding to the timing signal from the arithmetic control unit 7 input via the pulse generator 8. The optical demultiplexer 2 receives the pulsed light emitted from the light source 1 at the incident end thereof, emits the pulsed light emitted from the incident / exited end to the optical fiber 3, and the rear Raman generated in the optical fiber 3. Scattered light is incident from its input / output end and wavelength-separated into Stokes light ST and anti-Stokes light AS. The optical fiber 3 receives the pulsed light emitted from the optical demultiplexer 2 from the incident end, and emits backward Raman scattered light generated in the optical fiber 3 toward the optical demultiplexer 2 from the incident end. .

  For example, a photodiode is used as the O / E converters 4st and 4as, and the Stokes light ST emitted from one emission end of the optical demultiplexer 2 is incident on the O / E converter 4st, and O / E conversion is performed. The anti-Stokes light AS emitted from the other emission end of the optical demultiplexer 2 is made incident on the optical demultiplexer 4 and outputs an electrical signal corresponding to the incident light.

  The amplifiers 5st and 5as amplify the electric signals output from the O / E converters 4st and 4as, respectively. A / D converters 6st and 6as convert the signals output from amplifiers 5st and 5as into digital signals, respectively.

  Based on the digital signals output from the A / D converters 6st and 6as, the arithmetic control unit 7 calculates the temperature from the two components of the backscattered light, that is, the intensity ratio of the Stokes light ST and the anti-Stokes light AS. Based on the series, the temperature distribution along the optical fiber 3 is displayed on the display means (not shown). The arithmetic control unit 7 stores in advance the relationship between the intensity ratio and the temperature in the form of a table or an expression. The arithmetic control unit 7 also sends a timing signal to the light source 1 to control the timing of the light pulse emitted from the light source 1.

  The principle of temperature distribution measurement will be described. When the signal strengths of the Stokes light ST and the anti-Stokes light AT are expressed as a function of time with reference to the light emission timing in the light source 1, the speed of light in the optical fiber 3 is known. It can be replaced with a function of distance along. That is, it can be regarded as the intensity of Stokes light ST and anti-Stokes light AS generated at each distance position of the optical fiber, that is, the distance distribution, with the horizontal axis as the distance.

  On the other hand, the anti-Stokes light intensity Ias and the Stokes light intensity Ist both depend on the temperature of the optical fiber 3, and the intensity ratio Ias / Ist of both lights also depends on the temperature of the optical fiber 3. Therefore, if the intensity ratio Ias / Ist is known, the temperature at the position where the Raman scattered light is generated can be known. Here, since the intensity ratio Ias / Ist is a function Ias (x) / Ist (x) of the distance x, the temperature distribution T (x along the optical fiber 3 from this intensity ratio Ias (x) / Ist (x). ).

  By the way, in optical loss measurement of GI (Graded-Index) type optical fiber cable using a material whose refractive index of light continuously changes concentrically from the central axis, there are multiple propagation modes in the measurement light. Therefore, an exciter is used for making the incident condition constant so that the power distribution of each light does not fluctuate.

  By inserting the exciter, many higher-order modes generated at the connection point can be removed, and a stable measurement value can be obtained.

  Further, since light in a steady mode distribution state is incident into the measured optical fiber, transmission loss can be measured in a state close to the characteristics when the measured optical fiber is used as an actual transmission line.

  When light is incident on the GI optical fiber from the light source, a plurality of modes start to propagate. However, depending on the coupling method with the light source and the type of the light source, the modes may not be distributed evenly. If an exciter is inserted in such a case, mode mixing can be sufficiently generated therein, and light can be evenly distributed to the propagation modes.

  Further, by removing unnecessary modes from the incident light of the GI type optical fiber, measurement in a steady mode becomes possible.

JP-A-5-264370

  When attention is paid to the Raman scattered light returning from the near end of the sensor optical fiber of the multimode optical fiber, the light intensity of the higher mode is included. The light intensity of this higher-order mode is attenuated by stress such as bending applied to the optical fiber, but there is a wavelength difference in the attenuation due to bending, so the Stokes light and anti-Stokes of the Raman scattered light returning from the optical fiber for the sensor A difference occurs in the light, resulting in a measurement temperature error of the optical fiber for the sensor.

  As a method for removing higher order modes, for example, there is a method in which an optical fiber is wound around a mandrel at a constant diameter (for example, 15 mm) a plurality of times (for example, 5 times) to form an exciter. The necessary amount of space must be secured.

  The present invention solves such a problem, and an object of the present invention is to incorporate an exciter even in a relatively small space similar to the conventional one, and to eliminate a higher-order mode to obtain a more accurate temperature distribution. An object of the present invention is to provide an optical fiber temperature distribution measuring apparatus capable of measuring.

In order to achieve such a problem, the invention according to claim 1 of the present invention is:
In an optical fiber temperature distribution measuring device configured to measure a temperature distribution along the optical fiber using Raman backscattered light using an optical fiber as a sensor,
The optical fiber is two-dimensionally wired to constitute an exciter.

The invention according to claim 2
In the optical fiber temperature distribution measuring device according to claim 1,
The exciter is formed in a planar shape by forming an optical fiber in a wave shape with a predetermined radius and forming a circular shape.

The invention described in claim 3
In the optical fiber temperature distribution measuring device according to claim 1 or 2,
The exciter is formed in one layer of a multilayer optical fiber sheet constituting the temperature reference portion.

  According to the present invention, an exciter can be added to the optical fiber temperature distribution measuring apparatus with almost no increase in space, and more accurate temperature distribution measurement can be performed by removing higher-order modes with this exciter.

It is a configuration explanatory view showing an embodiment of the present invention. FIG. 6 is a characteristic measurement example diagram of the number of wiring circumferences and insertion loss of the optical fiber 10; It is a temperature distribution measurement result example figure based on the presence or absence of the higher-order mode measured in the state where the temperature of the optical fiber for sensors is constant. It is structure explanatory drawing of the temperature reference part to which the exciter was added. It is a block diagram which shows the basic structural example of an optical fiber temperature distribution measuring apparatus.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIGS. 1A and 1B are configuration explanatory views showing an embodiment of the present invention, in which FIG. 1A is a plan view and FIG. 1B is an enlarged view of an arc portion a surrounded by a broken line in FIG. As shown in FIG. 1 (A), one end of the optical fiber 10 is drawn out from the protective tube 11, and is formed as an arc-shaped corrugation having a constant radius R (for example, 8 mm) on a substrate 12 using, for example, an aluminum plate. Wiring is performed with the number of laps (for example, 10 times).

  In the arc portion a, for example, an outward optical fiber 10a is provided inside the radius R, and a return optical fiber 10b is provided outside.

  Specifically, the corrugated optical fiber wiring is formed in a circular arc shape, and is folded back in the manner of a single stroke, thereby being configured as a planar exciter. This exciter is integrally configured as one layer of a temperature reference portion composed of a multilayer optical fiber sheet.

  FIG. 2 is a characteristic measurement example diagram of the number of times of wiring around the optical fiber 10 and the insertion loss. As shown in FIG. 2, the insertion loss is proportional to the number of turns at a certain number of turns (for example, three times) or more, and the higher-order mode is removed.

  FIG. 3 is an example of a temperature distribution measurement result based on the presence or absence of a higher order mode measured with the temperature of the optical fiber for the sensor being constant. A solid line A indicates a temperature distribution characteristic with a higher order mode, and a broken line B indicates a higher order mode. The temperature distribution characteristics without mode are shown. When the higher-order mode is present as indicated by the solid line A, a phenomenon in which the near-end temperature distribution bends low occurs to cause a measurement temperature error. However, by removing the higher-order mode, the error is reduced as indicated by the broken line B. Not correct temperature distribution can be measured.

  4A and 4B are configuration explanatory views of a temperature reference portion to which an exciter is added, in which FIG. 4A is a plan view and FIG. 4B is a side sectional view. In FIG. 4, on the aluminum plate 12, for example, an optical fiber 13 having a length of about 60 m that constitutes the temperature reference portion is laminated to a thickness of about 1.6 mm, for example, in four layers. An optical fiber 10 having a length of about 0.5 m for excitation is additionally laminated with a thickness of about 0.4 mm.

  The outer diameter dimension of the added excitation part is the same as the temperature reference part provided at the lower part, and the increase in thickness due to the addition of the excitation part is as thin as about 0.4 mm. If a similar arrangement space can be secured, an exciter can be added without difficulty.

  The exciter based on the present invention constituted by wiring optical fibers two-dimensionally is not limited to an optical fiber temperature distribution measuring device, but can be applied in a wide range as an optical wiring component with an excitation function that does not take up space. it can.

  In the above embodiment, an example in which the substrate is an aluminum plate has been described. However, the substrate is not limited to the aluminum plate as long as the optical fibers can be arranged in a desired pattern.

  As described above, according to the present invention, an exciter can be added to the optical fiber temperature distribution measuring device with almost no increase in space, and the higher-order mode is removed by this exciter, thereby more accurate temperature distribution measurement. An optical fiber temperature distribution measuring device capable of performing the above can be realized.

10, 13 Optical fiber 11 Protection tube 12 Substrate

Claims (3)

In an optical fiber temperature distribution measuring device configured to measure a temperature distribution along the optical fiber using Raman backscattered light using an optical fiber as a sensor,
2. An optical fiber temperature distribution measuring apparatus, wherein the optical fiber is two-dimensionally wired to constitute an exciter.   The optical fiber temperature distribution measuring device according to claim 1, wherein the exciter is formed in a planar shape by forming an optical fiber in a wave shape with a predetermined radius and forming it in a circular shape.   3. The optical fiber temperature distribution measuring device according to claim 1, wherein the exciter is formed in one layer of a multilayer optical fiber sheet constituting the temperature reference portion.