JPH01260331A - Distribution type temperature measuring apparatus - Google Patents

Abstract

PURPOSE:To measure temperature with high accuracy, by using a wave dividing plate of two diffraction lattices and arranging two diffraction lattices so that the planes each containing incident light and diffracted light thereof cross at a right angle each other. CONSTITUTION:The back scattering light generated in an optical fiber sensor part is guided to a wave dividing unit 4 by a coupler. The wave dividing unit 4 is composed of two diffraction lattices 4a, 4b each of which is formed by providing a large number of unidimensional grooves to a metal or glass plane cyclically and the two diffraction lattices 4a, 4b are arranged so that the respective groove directions cross each other at a right angle. Backwardly scattered light is divided into Stokes light, Rayleigh scattering light and anti-Stokes light by the two diffraction lattices 4a, 4b.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] This invention relates to a distributed temperature measuring device using Raman backscattered light, which efficiently receives backscattered light generated within an optical fiber sensor section, It is designed to separate the three waves of scattered light, Stokes light, and anti-Stokes light with low crosstalk.

[Prior Art] Generally, when a pulsed wave of wavelength λ is input into an optical fiber, most of the input pulsed light is transmitted through the optical fiber in the direction of incidence, but a part of the pulsed light is transmitted backward. Ray scattering occurs such that it returns to the input end of the optical fiber as scattered light (wavelength λ). By sequentially detecting the intensity of this Ray scattered light at each point from the time when the pulsed light enters the optical fiber, it is possible to determine the temperature of the environment where the fiber is placed, the surface condition of the optical fiber, strain, stress, etc. It is possible to measure physical quantities.

In addition, in recent years, 0TDR devices for temperature measurement that utilize Raman backscattered light generated by injecting pulsed light into an optical fiber have been put into practical use. It is possible to detect the temperature distribution over a distance of about I km (approx.
Wavelength λ. -λi), it is possible to measure temperature distribution that is not affected by optical fiber transmission loss, microbent loss, etc., and is therefore useful as a maintenance system device for power equipment, etc. The 0TDr (device) for temperature measurement separates the Stokes light and anti-Stokes light into Stokes light and anti-Stokes light by using interference filters, diffraction gratings, etc. that are compatible with the Stokes light and anti-Stokes light returning from the optical fiber. By measuring the intensity ratio, the environmental temperature where the tip fiber was placed was determined.

[Problems to be Solved by the Invention] However, in the conventional 0TDR device for temperature measurement using Raman backscattered light, the intensity of the Raman backscattered light is extremely small compared to the Ray scattering light. It has been difficult to obtain sufficient measurement accuracy by separating Stokes light and anti-Stokes light, which are two components of scattered light, using an interference filter, a diffraction grating, or the like and measuring them simultaneously.

In addition, since the wavelength difference (λi) between Leh scattered light and Stokes light and anti-Stokes light is extremely small, it is necessary to ensure sufficient wavelength separation accuracy and maintain low crosstalk when separating and detecting these lights. It was also difficult.

Therefore, this invention solves the above-mentioned problems and efficiently and efficiently generates three waves (Ray scattering light, Stokes light,
The purpose of the present invention is to provide a distributed temperature measuring device that can measure temperature with high accuracy from the intensity ratio of Stokes light and andestokes light.

[Means for Solving the Problems] The present invention includes an optical fiber sensor section that guides a pulse wave emitted by a light source to produce a Raman effect, and an optical fiber sensor section that is arranged between the light source and the optical fiber sensor section to generate a Raman effect. It has a coupler that guides the Raman backscattered light generated in the fiber sensor section into the demultiplexing unit together with the Ray scattered light, and a demultiplexing unit that separates the Raman scattered light into Stokes light and Andes-Stokes light and detects them. In the distributed temperature measuring device, the demultiplexing unit is composed of two diffraction gratings, and the planes of the two diffraction gratings containing the incident light and the diffracted light are orthogonal to each other. This was the solution.

[Function] In this way, by configuring the demultiplexing unit with two diffraction gratings and arranging the two diffraction gratings orthogonally to each other, even if the respective lights to be separated are weak, they can be It is possible to separate Stokes light and anti-Stokes light with high separation and low crosstalk, and therefore, the temperature at which the optical fiber sensor section is placed can be accurately measured from the intensity ratio of these lights.

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 shows an example of a temperature measuring device according to the present invention.

Reference numeral 1 in FIG. 1 indicates a light source that emits pulsed light. The light source 1 is composed of a laser capable of producing stable coherent light and an interference filter, and the pulsed light emitted from the light source 1 is guided into the optical fiber sensor section 2 to be measured. Here, in order to obtain strong Raman scattering light with good directivity, the laser for light source l includes continuous wave ion lasers such as YAG lasers, semiconductor lasers, and argon lasers that can emit strong coherent light, as well as pulsed lasers such as nitrogen lasers. A laser or the like is used. The optical fiber sensor section 2 to be measured is used as a sensor section for measuring the temperature of the environment in which it is placed, and is used by being buried or placed along the location where the temperature is to be measured. For this optical fiber sensor section 2, either a step index type or graded index type multimode fiber may be used, or a single mode fiber may be used. A coupler 3 is disposed between the light source 1 and the optical fiber sensor section 2, and the light source 1 and the optical fiber sensor section 2 are connected to the input end and output side light guide section of the coupler 3c3, respectively. For the coupler 3, an ordinary optical fiber power brake made by fusing parts of two optical fibers in the longitudinal direction is preferably used, but a glass plate, semi-transparent film, reflective dichroic mirror, etc. A beam splitter or the like may also be used. In addition, a demultiplexing unit 4 is connected to the other light guide portion on the input side of the coupler 3, and the backscattered light (Leh scattering light, Raman scattering light) from the optical fiber 2 is
can be guided into the demultiplexing unit 4. Here, the demultiplexing unit 4 is a device that demultiplexes the backscattered light generated in the above-mentioned optical fiber to be measured into three waves, each of which is a component, and simultaneously monitors the two waves, as shown in FIG. It is composed of two diffraction gratings 4a and 4b. Here, the two diffraction gratings 4a and 4b each have a large number of one-dimensional periodic grooves on a metal or glass plane, and the two diffraction gratings 4a and 4b each have a direction of the grooves. are arranged so that they are orthogonal to each other. In other words, the planes having the incident light and the diffracted light of each diffraction grating are oriented orthogonal to each other, so the first diffraction grating 4a and the second diffraction grating 4b have different separation directions. It is possible to separate the waves into three waves with high separation accuracy.

The thus demultiplexed Lehry scattered light, Stokes light, and anti-Stokes light are each detected by a photodetection system 5.6.
Detected by The photodetection systems 5 and 6 detect low-intensity Stokes light and anti-Stokes light, so they each include an amplifier such as a photodiode or an avalanche photodiode, and an amplifier for integrating and processing the low-intensity light. , a signal averager, a computer, etc.

Hereinafter, a measurement method using the temperature measuring device of the present invention will be explained.

Wavelength λ emitted from light source l. The pulsed light is coupler 3
The light passes through and enters the optical fiber sensor section 2 to be measured. Most of the light incident on the optical fiber sensor section 2 travels through the optical fiber, but some of it is backscattered together with Ray scattered light as Raman backscattered light due to the Raman effect, and returns to the coupler 3. come. At this time, the Raman backscattered light includes Stokes light (wavelength λ.+λi) shifted to the longer wavelength side than the fundamental wave (Lehley scattered light) and anti-Stokes light (wavelength λ.-λi) shifted to the shorter wavelength side. is occurring. This mixed light of the Raman backscattered light and the Ray scattered light is guided into the demultiplexing unit 4 by the coupler 3.

Here, when the mixed light obliquely enters the diffraction grating plane in the demultiplexing unit 4, the diffraction angle of the diffracted light differs depending on the wavelength, so it is separated into separate lights for each wavelength. When such separation is performed sequentially by changing the separation direction using the two diffraction gratings 4a and 4b, the light is separated into three waves, namely, Ray scattered light, Stokes light, and anti-Stokes light, with high accuracy. Subsequently, these lights enter a photodetection system 5.6, are detected and integrated, and the intensity at each wavelength is measured. As a result, the temperature of the optical fiber sensor section 2 can be calculated from the intensity ratio of the Stokes light and the anti-Stokes light.

According to the device described above, the backscattered light generated within the optical fiber sensor section 2 is guided into the demultiplexing unit 4 by the coupler 3, and the two fibers disposed in the demultiplexing unit 4 are arranged orthogonally to each other. Since the backscattered light can be split into three waves by the diffraction gratings 4a and 4b, it is possible to efficiently receive the backscattered light and separate the waves with high separation accuracy and low crosstalk.

[Example] Pulsed light was oscillated using an IOW pulse laser with a center wavelength of 905 nm as a light source. A graded index optical fiber with a core diameter of 200 μm and a cladding diameter of 250 μm and a relative refractive index difference of 2.8% between the core and cladding and a transmission loss of 8 dB/km was prepared and used as an optical fiber to be measured. Inside the optical fiber, Stokes light with a wavelength of 940 nm and anti-Stokes light with a wavelength of 870 nm are generated as Raman backscattered light, and mixed light including Rayleigh backscattered light with the same wavelength as the oscillation wavelength is backscattered and returns to the coupler. This mixed light was guided into the demultiplexing unit using a coupler. Inside the demultiplexing unit, two diffraction gratings were arranged so that the planes containing the incident light and the diffracted light were orthogonal to each other. The mixed light that entered the demultiplexing unit first enters the two diffraction grating surfaces sequentially, and is divided into three waves (Ray scattering light (904 nm), Stokes light (940 nm), and anti-Stokes light (870 nm).
m)) and were then simultaneously detected by a photodetection system.

When the crosstalk value of the detected light was measured, it was -6
It showed a very small value of less than 0 dB, indicating that the signals could be separated accurately with low crosstalk. Furthermore, integration processing was performed using a photodetection system to obtain a desired temperature signal.

[Effects of the Invention] As explained above, the present invention includes an optical fiber sensor section that guides a pulse wave emitted by a light source to produce a Raman effect, and an optical fiber sensor section that is disposed between the light source and the optical fiber sensor section, a coupler that guides the Raman backscattered light generated within the optical fiber sensor section into the demultiplexing unit together with the Raman scattered light;
In a distributed temperature measuring device comprising a demultiplexing unit that separates and detects Raman scattered light into Stokes light and anti-Stokes light, the demultiplexing unit is composed of two diffraction gratings, and the two The diffraction gratings are arranged so that the planes containing the incident light and the diffracted light are orthogonal to each other, so the backscattered light is efficiently received and the intensity is extremely low compared to Leh scattered light. Stokes light and anti-Stokes light, which are components of Raman scattered light, can be separated with high precision and low crosstalk and detected simultaneously, making it possible to measure temperature with high precision.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a distributed temperature measurement device of the present invention, and FIG. 2 is a configuration diagram showing an example of a branching unit of the temperature measurement device of FIG. 1. 1...Light source, 2...Optical fiber sensor section, 3...Coupler, 4...Demultiplexing unit.

Claims (1)

[Claims] An optical fiber sensor section that guides a pulse wave emitted by a light source to produce a Raman effect; A distributed temperature measuring device comprising: a coupler that guides backscattered light together with Rayleigh scattered light into a demultiplexing unit; and a demultiplexing unit that separates and detects Raman scattered light into Stokes light and anti-Stokes light, A distributed temperature type characterized in that the demultiplexing unit is composed of two diffraction gratings, and the planes containing the incident light and diffracted light of the two diffraction gratings are arranged in such a direction that they are orthogonal to each other. Measuring device.