JPH06123661A - Optical fiber distribution type temperature sensor and apparatus for generating two wavelength light - Google Patents

Abstract

PURPOSE:To correctly measure the temperature distribution along an optical fiber by holding the difference of wavelengths of two input lights lambda1, lambda2 at all times at the Raman shift wavelength, thereby eliminating the dependency on the wavelength of the transmission loss of the optical fiber under the high temperatures or radioactive environment, etc. CONSTITUTION:An exciting light of the wavelength lambda0 from a light source 1 is input to an optical fiber 2 thereby to generate an induced Raman scattering light of the wavelength lambda1. The light of the wavelength lambda1 enters an optical multiplexer/demultiplexer 30 along with the light of the wavelength lambda0. The demultiplexer 30 separaes the light of the wavelength lambda0 from the light of the wavelength lambda1 and sends them to an optical switch 4. The lights are alternately put into a sensor optical fiber 5. When the light of the wavelength lambda0 is introduced, the back scattering light including the Stokes light of the wavelength lambda1 is brought into an optical multiplexer/demultiplexer 31. The demultiplexer 31 sends the light of the wavelength lambda1 generated in the optical fiber 5 to an operating/processing system. If the light of the wavelength lambda1 is input, the back scattering light including the anti-Stokes light of the wavelength lambda0 because of the exciting light of the wavelength lambda1 is sent to the operating/ processing system. Accordingly, the temperature distribution along the optical fiber 5 is obtained according to the OTDR method.

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 distributed temperature sensor for measuring a temperature distribution along an optical fiber by detecting Raman scattered light generated in the optical fiber, and to be used for the same. The present invention relates to a two-wavelength light generator.

[0002]

2. Description of the Related Art As an optical fiber type distributed temperature sensor, a Raman scattered light intensity distance distribution generated in an optical fiber is measured by a method of OTDR (Optical Time Domain Reflectometry), and this information is converted into an optical fiber. A method of obtaining a temperature distribution along the line is known. For example, in Japanese Patent Laid-Open No. 2-276932, a wavelength λ of Raman scattered light generated in an optical fiber using a light source having a wavelength λ ₀ is used.
The Stokes light of _s and the anti-Stokes light of wavelength λ _a are measured, and the fact that the ratio of these is a function of temperature is used to determine the temperature distribution along the optical fiber.

According to this method, even if the transmission loss of the optical fiber changes due to microbending or the like, the transmission loss of the optical fiber at the wavelength λ _s of the Stokes light and the wavelength λ _a of the anti-Stokes light similarly changes. Therefore, the temperature distribution along the optical fiber can be measured without being affected by the microbend or the like. However, it is known that when an optical fiber is used under high temperature or radiation environment, the transmission loss of the optical fiber increases, and the degree of increase depends on the wavelength. In such a case, it has been difficult for the conventional method to accurately measure the temperature distribution.

Therefore, in order to solve such a problem, British Patent GB2181830A uses two kinds of light sources of a wavelength λ ₀ and a wavelength λ ₁ whose wavelength difference corresponds to the Raman shift wavelength. Seeking the temperature distribution along the optical fiber by measuring the wavelength lambda ₀ of the anti-Stokes light generated by the wavelength lambda ₁ of the Stokes light and the wavelength lambda ₁ of the light source generated by the wavelength lambda ₀ of the light source in this manner There is. By doing so, the transmission loss of the optical fiber that influences the Stokes light measurement and the anti-Stokes light measurement is the sum of the transmission losses of the wavelength λ ₀ and the wavelength λ ₁ in both cases. Therefore, no matter how the transmission loss at these wavelengths changes, Stokes light and anti-
The influence on the Stokes light is the same, and even if the transmission loss change has wavelength dependency, the influence on the temperature distribution measurement can be avoided.

[0005]

However, according to the above-mentioned British patent, there is no problem if light sources having different wavelengths λ ₁ and ₂ whose wavelength difference exactly matches the Raman shift wavelength can be prepared. It is difficult to prepare such two light sources. Also, since the wavelength of the light source changes depending on the temperature, when the ambient temperature changes, the wavelength difference between the two light sources is always kept the same. Therefore, precise temperature control for wavelength selection of the light source and wavelength stabilization is required. This has to be done, which is also very difficult. Therefore, when the transmission loss of the optical fiber changes with wavelength dependence under high temperature or radiation environment, it is still difficult to accurately measure the temperature distribution along the optical fiber.

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to meet the optical fiber even when the transmission loss of the optical fiber changes with wavelength dependence under high temperature or radiation environment. It is an object of the present invention to provide a novel optical fiber type distributed temperature sensor capable of measuring a temperature distribution with high accuracy. Another object of the present invention is to provide a two-wavelength light generation device capable of producing two lights having different wavelengths, which always have Raman shift wavelengths and different wavelengths, from a single light source.

[0007]

The optical fiber type distributed temperature sensor of the present invention is configured such that excitation light having a central wavelength λ ₀ output from a light source is incident on an optical fiber for generating stimulated Raman scattered light and and the center wavelength lambda ₁ of the stimulated Raman scattering light generated, two types of light having a wavelength of the center wavelength lambda ₀ of the excitation light is incident on the optical fiber sensor, the sensor optical fiber in the excitation light having a center wavelength lambda ₀ Center wavelength λ ₁ generated at
Of the Stokes light, using a center wavelength lambda ₀ of the anti-Stokes light generated in the optical fiber for the sensor by stimulated Raman scattering light having a center wavelength lambda _1, to measure the temperature distribution along the optical fiber sensor It was done. In addition,
The optical fiber for generating stimulated Raman scattered light can easily generate stimulated Raman scattered light in the optical fiber by increasing the output of the light source, so it does not need to be a special optical fiber. It can be composed of an optical fiber.

Further, the optical fiber type distribution type temperature sensor of the present invention, the center wavelength lambda ₁ and the light source for outputting pumping light having a center wavelength lambda _0, the incidence of the central wavelength lambda ₀ of the excitation light from the light source
Induction and stimulated Raman scattered light generation optical fiber for generating the Raman scattering light, the first of demultiplexing an excitation light of the induced Raman scattering light and the central wavelength lambda ₀ of the center wavelength lambda ₁ emitted from the optical fiber An optical multiplexer / demultiplexer, an optical switch for switching the demultiplexed pumping light having a central wavelength λ ₀ and stimulated Raman scattered light having a central wavelength λ ₁ to alternately enter the sensor optical fiber,
When the excitation light with the center wavelength λ ₀ is incident on the sensor optical fiber, the backscattered light including the Stokes light with the center wavelength λ ₁ generated in the sensor optical fiber is used as the excitation light with the wavelength λ ₀ and the Stokes with the wavelength λ ₁ . When the stimulated Raman scattered light of center wavelength λ ₁ is incident on the optical fiber for sensor,
The anti-center wavelength λ ₀ generated in the optical fiber for sensor
A second optical coupler to anti-Stokes light and demultiplexes the stimulated Raman scattering light and the wavelength lambda ₀ of the wavelength lambda ₁ backscattered light including Stokes light is demultiplexed by the second demultiplexer center wavelength lambda based _first on the Stokes beam and the center wavelength lambda ₀ of the anti-Stokes light is obtained and an arithmetic processing circuit for determining the temperature distribution along the optical fiber for the sensor by OTDR technique. In this case, in order to simplify the configuration, it is preferable that the first optical multiplexer / demultiplexer, the second optical multiplexer / demultiplexer, and the optical switch are integrated into a waveguide.

[0009] 2-wavelength light generating apparatus of the present invention, the center wavelength lambda ₀ of the light source for outputting pumping light, the center wavelength lambda ₁ of the induced Raman scattering light upon incidence of the central wavelength lambda ₀ of the excitation light from the light source the generated, in which a stimulated Raman scattered light generation optical fiber for emitting the excitation light of the induced Raman scattering light and the central wavelength lambda ₀ of the center wavelength lambda _1.

[0010]

According to the present invention, the Stokes light of the wavelength λ ₁ generated by the stimulated Raman scattering phenomenon when the light of the wavelength λ ₀ of high output from the light source is incident on the optical fiber and the light of the wavelength λ ₀ of the original light source. Focusing on the fact that the wavelength difference exactly matches the Raman shift wavelength, the wavelength λ ₀ obtained by using the same or a single light source
And Stokes light and anti-Stokes light are measured using the light having the wavelength of λ ₁ and the temperature distribution along the optical fiber from the measurement results.

That is, when pumping light having a central wavelength λ ₀ large enough to generate stimulated Raman scattered light is made incident on the optical fiber for generating stimulated Raman scattered light from the light source, the central wavelength λ ₁ is introduced into this optical fiber. Stimulated Raman scattered light of
The stimulated Raman scattered light having the central wavelength λ ₁ generated in this optical fiber travels in the optical fiber together with the excitation light having the central wavelength λ ₀ . The first optical multiplexer / demultiplexer demultiplexes this light emitted from the optical fiber into light having a central wavelength λ ₀ and light having a central wavelength λ ₁ , and these lights are transmitted to an optical fiber for sensor via an optical switch. It is incident alternately.

As described above, in order to obtain two kinds of light having the wavelength λ ₀ and the wavelength λ ₁ where the wavelength difference is the Raman shift wavelength, the pumping light having the wavelength λ ₀ and the incident light are incident on the optical fiber. It is obtained from stimulated Raman scattered light. Therefore, it becomes easy to obtain the wavelength λ ₀ and the wavelength λ ₁ whose wavelength difference exactly matches the Raman shift wavelength. Moreover, since the wavelength λ ₀ and the wavelength λ _{1 in} which the wavelength difference exactly matches the Raman shift wavelength are obtained from _one light source, the wavelength difference is always kept the same even if the wavelength of the light source changes depending on the ambient temperature. Therefore, it is not necessary to precisely control the temperature as in the case of using two light sources. Therefore, even when the transmission loss of the optical fiber changes with wavelength dependence under high temperature or radiation environment, the temperature distribution along the optical fiber can be accurately measured.

[0013]

EXAMPLE An example of the present invention will be described with reference to FIG. A light source 1 having a central wavelength λ ₀ is connected to an optical fiber 2 for generating stimulated Raman scattered light. The output of the light source 1 is sufficient to generate stimulated Raman scattered light having a central wavelength λ _{1 in} the optical fiber 2, and, for example, a pulsed semiconductor pumped solid-state laser or the like is used. The stimulated Raman scattered light having the central wavelength λ ₁ generated in the optical fiber 2 travels in the optical fiber 2 together with the excitation light having the central wavelength λ ₀ , and enters the optical multiplexer / demultiplexer 30.

The optical multiplexer / demultiplexer 30 has a wavelength λ ₀ and a wavelength λ ₁
Has a function of demultiplexing the light and outputting it to the optical fiber 61 and the optical fiber 62, respectively. The light having the central wavelength λ ₀ that has entered the optical fiber 61 passes through the optical multiplexer / demultiplexer 31, passes through the optical fiber 64, and enters the optical switch 4. On the other hand, the light of the central wavelength λ ₁ that has entered the optical fiber 62 passes through the optical multiplexer / demultiplexer 32 and enters the optical switch 4 through the optical fiber 65. The optical switch 4 alternately connects the optical fibers 64 and 65 to the sensor optical fiber 5, so that the sensor optical fiber 5 receives the light of the central wavelength λ _{0 and} the light of the central wavelength λ ₁ alternately. Will be done.

When the optical fiber 64 and the sensor optical fiber 5 are connected by the optical switch 4, the light of the central wavelength λ ₀ travels in the sensor optical fiber 5, and as a result, in the optical fiber 5, As shown in FIG. 2 (A), Stokes light having a center wavelength λ ₁ and anti-Stokes light having a center wavelength λ _0a are generated.

Of these, the backscattered light traveling to the side of the optical switch 4 enters the optical multiplexer / demultiplexer 31 via the optical switch 4 and the optical fiber 64. The optical multiplexer / demultiplexer 31 transmits light of wavelength λ _{0 to} the optical fiber 61 and light of wavelength λ _{1 to} the optical fiber 60.
The Stokes light having the center wavelength λ ₁ generated in the sensor optical fiber 5 enters the O / E converter 70 through the optical fiber 60 and is converted into an electric signal. After that, the OTDR waveform of the Stokes light of the sensor optical fiber 5 is obtained by the sampling, A / D conversion, and averaging processing circuit 8.

Similarly, when the sensor optical fiber 65 and the sensor optical fiber 5 are connected by the optical switch 4, as shown in FIG. 2B, the sensor light is excited by the excitation light having the central wavelength λ _1. Stokes light having a center wavelength λ _1s and anti-Stokes light having a center wavelength λ ₀ are generated in the fiber 5, and the optical multiplexer / demultiplexer 32 outputs the light having the wavelength λ ₀ to the optical fiber 63.
In addition, since it has a function of demultiplexing the light of wavelength λ ₁ into the optical fiber 62, the anti-Stokes light of center wavelength λ ₀ is
After passing through the E converter 71, the averaging processing circuit 8 measures the OTDR waveform of the anti-Stokes light of the sensor optical fiber 5. The signal applied from the averaging circuit 8 to the light source 1 is the synchronization signal 81.

OTD of the Stokes light and the anti-Stokes light of the optical fiber for the sensor thus measured
The R waveform can be processed in the temperature distribution calculation circuit 9 to obtain the temperature distribution along the sensor optical fiber 5.

As described above, according to the above embodiment, 1
By using the number of light sources and stimulated Raman scattered light generation optical fiber, is always the wavelength difference is to obtain the excitation light of the scattered light and lambda ₀ of lambda ₁ to be held in the Raman shift wavelength, high temperature and radiation Even when the transmission loss of the optical fiber changes depending on the wavelength under the environment, the temperature distribution along the optical fiber can be accurately measured.

In the above embodiment, the optical multiplexer / demultiplexer 30,
Although 31 and 32 are independent of each other, it is also possible to integrate these functions into an integrated type, and in this case, the optical fibers 61 and 62 for connection become unnecessary. When the sensor optical fiber 5, the stimulated Raman scattered light generating optical fiber 2 connected to the light source, and the optical fibers 60 and 63 connected to the O / E converter are single mode optical fibers, an optical multiplexer / demultiplexer is used. Since 30, 31, and 32 and the optical switch 4 can be formed on the waveguide, these components can be integrated waveguide components.

[0021]

【The invention's effect】

(1) According to the optical fiber type distributed temperature sensor according to any one of claims 1 and 2, the transmission loss of the optical fiber which affects the measurement of Stokes light and anti-Stokes light generated in the sensor optical fiber. Can be made to be exactly the same for the measurement of Stokes light and the measurement of anti-Stokes light, and the influence of the change in the transmission loss of the optical fiber on the temperature distribution measurement accuracy can be eliminated.

Since only one light source is used, 2
Compared to the method using two light sources, the wavelength selection of the light source used and the precise temperature control for wavelength stabilization are not required, and the optical fiber type distributed temperature that is not easily affected by the deterioration of the transmission loss of the optical fiber compared to the conventional method. The sensor can be configured.

(2) According to the optical fiber type distributed temperature sensor of the third aspect, miniaturization is facilitated.

(3) According to the two-wavelength light generating device of the fourth aspect, it is possible to obtain two lights of different wavelengths which always have Raman shift wavelengths, although the wavelength difference is a simple structure.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an optical fiber type distributed temperature sensor according to an embodiment of the present invention.

FIG. 2 is a spectrum diagram of Raman scattered light.

[Explanation of symbols]

 1 light source 2 optical fiber for generating stimulated Raman scattered light 30, 31, 32 optical multiplexer / demultiplexer 4 optical switch 5 optical fiber for sensor 60, 61, 62, 63, 64, 65 optical fiber 70, 71 O / E converter 8 A / D, sampling and averaging processing circuit 9 temperature distribution calculation circuit 81 synchronization signal

Claims (4)

[Claims] _1. A pumping light having a central wavelength λ ₀ output from a light source is incident on an optical fiber for generating stimulated Raman scattered light, and the stimulated Raman scattering light having a central wavelength λ ₁ and the central wavelength λ generated in the optical fiber. ₀ 2 kinds of light of a wavelength of the excitation light is incident on the optical fiber sensor, and the center wavelength lambda ₁ of the Stokes light generated in the optical fiber for the sensor by the excitation light having a center wavelength lambda _0, the central wavelength lambda ₁ The temperature distribution along the optical fiber for sensor is measured by using the anti-Stokes light with the center wavelength λ ₀ generated by the stimulated Raman scattered light of Sensor. 2. A light source for outputting pumping light having a central wavelength λ ₀ ,
An optical fiber for generating stimulated Raman scattered light that generates stimulated Raman scattered light with a central wavelength λ ₁ by the incidence of excitation light with a central wavelength λ ₀ from a light source, and stimulated Raman scattering with a central wavelength λ ₁ emitted from the optical fiber A first optical multiplexer / demultiplexer that demultiplexes the light and the excitation light having the central wavelength λ ₀ , and the demultiplexed central wavelength λ ₀
Of the excitation light of the center wavelength λ _{1 and} the stimulated Raman scattered light of the center wavelength λ ₁ are alternately incident on the sensor optical fiber, and when the excitation light of the center wavelength λ ₀ is incident on the sensor optical fiber, Center wavelength λ generated in optical fiber
_The backscattered light including the Stokes light of ₁ is demultiplexed into the excitation light of wavelength λ ₀ and the Stokes light of wavelength λ ₁ , and when the stimulated Raman scattered light of center wavelength λ ₁ is incident on the sensor optical fiber, the second optical coupler to the central wavelength lambda ₀ anti-Stokes light and the half wave of stimulated Raman scattering light and the wavelength lambda ₀ of the wavelength lambda ₁ of the backscattered light that includes anti-Stokes light generated in use optical fiber If, calculation for obtaining the temperature distribution along the optical fiber for the sensor by OTDR technique based on the second optical coupler in demultiplexed central wavelength lambda ₁ of the Stokes beam and the center wavelength lambda ₀ of the anti-Stokes light An optical fiber type distributed temperature sensor comprising a processing circuit. 3. The optical fiber type distributed temperature sensor according to claim 2, wherein the first optical multiplexer / demultiplexer, the second optical multiplexer / demultiplexer, and the optical switch are formed by a waveguide. 4. A light source which outputs excitation light having a central wavelength λ ₀ ,
Stimulated Raman scattering that generates stimulated Raman scattered light with a central wavelength λ ₁ by incidence of excitation light with a central wavelength λ ₀ from a light source and emits stimulated Raman scattered light with a central wavelength λ ₁ and excitation light with a central wavelength λ ₀ A two-wavelength light generation device including a light generation optical fiber.