JP2506690Y2 - Distributed Optical Fiber-Temperature Sensor- - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a distributed optical fiber temperature sensor.

[Prior Art] FIG. 3 shows a block diagram of a conventional distributed optical fiber temperature sensor, and FIGS. 4 and 5 show an example of a conventional detection unit. A laser pulse emitted from a light source 1 such as a semiconductor laser (LD) passes through an optical directional coupler 2 and an optical fiber 3 to be measured.
Is incident on. From the measured optical fiber 3, the incident light causes Raman scattered light to return in a direction opposite to the incident direction. The Raman scattered light passes through the directional coupler 2 again, and this light is split into an optical fiber on the light source 1 side and an optical fiber on the detection section side. The light emitted from the optical fiber on the detector side is divided into anti-Stokes and Stokes components, detected by different detectors 4, and then signal-processed. Here, 5 is an amplifier, 6 is a signal processor for averaging the signals, and 7 is a computer for further analyzing the measured data and displaying it on a display. Details of the detector are shown in FIGS. 4 and 5. Two examples are given as examples.

In either case, for convenience of adjustment, after the Stokes and anti-Stokes light splitting, the light is guided to the detection unit using the optical fiber 8. Here, 8 is an optical fiber, 9 is a filter for demultiplexing Stokes light and anti-Stokes light, 10 is a condenser lens, 11 is a narrow band filter, 12 is a detector such as avalanche photodiode (APD), 13 is 1 × 2 Optical fiber coupler.

[Problems to be Solved by the Invention] In the case of the conventional example, there are two problems, and one is that the loss is large due to transmission by the optical fiber 8.
Secondly, if some external disturbance such as pressure or temperature change is applied to the optical fiber 8, the light receiving level of the detector 12 will fluctuate.

In the example of FIG. 4, the loss due to the coupling of the optical fiber 8 after the demultiplexing of the Stokes light and the anti-Stokes light is 50%, and the coupling loss at the front surface of the detector 15 is 20%, so that only a coupling efficiency of about 40% can be obtained.

Also in the example of FIG. 5, the branching ratio of the 1 × 2 optical fiber coupler 13 is 1: 1 (50%: 50%), but because of the coupling by the optical fiber 8, it is almost the same as the example of FIG. The optical fiber 8 is devised so that no disturbance is applied in the system, but if the change in loss due to temperature change or the like is different between the Stokes light and the anti-Stokes optical fiber, there is a problem in stability.

[Means for Solving the Problems] The present invention has been made to solve the above-described problems, and guides a light source for injecting a laser pulse to an optical fiber to be measured and a return light from the optical fiber to be measured to a measuring device. An optical directional coupler that emits light, a measuring device that detects Stokes light and anti-Stokes light contained in the return light, and measures the temperature distribution related to the optical fiber to be measured and the distance around it from the intensity ratio and delay time thereof. In the distributed optical fiber temperature sensor consisting of, the space between the demultiplexer and the detector of Stokes light and anti-Stokes light is spatially propagated, and the demultiplexer and the detector are subdivided into a plurality of parts, and each subdivided section A distributed light, characterized in that a container having an opening only in a light transmitting portion is arranged in the container, and at least one optical component and / or a detector is housed in the container. A fiber temperature sensor is provided.

 FIG. 1 shows the structure of the detection unit in the present invention.

The configuration of the detection unit includes Stokes light and anti-Stokes light, a demultiplexing unit 30, a narrow band filter unit 31, and a detector unit 32 having a detector such as an APD. Here, 20 is an optical fiber, 21 is a condenser lens, 22 is a filter that is a demultiplexer of Stokes light and anti-Stokes light, 23 is a narrow band filter, and 24 is a detector such as an APD.

In this configuration, the distance from the optical fiber 20 to the detector 24 varies depending on the lens used, but it is better to make the distance as short as possible in terms of coupling efficiency, axial misalignment, and the like.

It is preferable that each part 30, 31, 32 has a closed structure having an opening for transmitting a laser beam to prevent air convection so that fluctuation of the laser beam can be minimized.

The narrow band filter can be finely adjusted in angle with a fine adjusting tool such as a micrometer, and the incident light to the filter is preferably parallel light as much as possible in view of the angle.

Since the APD signal amplification circuit etc. becomes a heat source, either reduce the heat generating elements or do not install them too close.

The above configuration is preferable for the above reason.

[Operation] The operation and features of the present invention are as follows: 1) Since the light emitted from the detection port fiber is directly incident on the detector such as APD, it is more efficient than the conventional method.

2) Since the detection system is divided into three parts and air convection is almost eliminated, there is no fluctuation of the laser beam and the detection intensity is stabilized.

3) Since the narrow band filter is adjusted by a fine adjustment mechanism such as a micrometer head, it is possible to easily prevent mechanical misalignment and adjust the captured wavelength.

[Embodiment] An embodiment of the present invention is shown in FIGS. 1 and 2.

When a SELFOC lens (registered trademark) was used as the lens 21 and the distance from the optical fiber to the APD was set to spatial propagation of about 60 mm, the coupling efficiency was 90% or more. Further, if the characteristics of the filter 22 in the demultiplexing unit of the Stokes light and the anti-Stokes light are set as shown in FIG. 2, the coupling efficiency will not be lowered so much.

By setting the initial setting angle of the narrow band filter 23 to about 10 to 13 degrees and changing it with a micrometer in the range of about 0 to 25 degrees, an arbitrary wavelength can be easily obtained.

In the present invention, the Stokes light / anti-Stokes light separation unit 30, the narrow band filter unit 31, and the detector unit 32 are respectively housed in an aluminum container provided with an entrance / exit hole for laser light. As the material of the container, a material having good workability such as metal such as aluminum and iron or plastic can be preferably used. The container may be made of a transparent material and the portion through which the laser light passes is polished into a lens shape, but there is a problem that external light is detected. The distance from the laser beam emitting end of the optical fiber 20 to the detector 24 such as APD is 70m.
Within m is preferable in terms of binding efficiency.

[Advantage of the Invention] The present invention improves the coupling efficiency between the demultiplexing unit for the Stokes light and the anti-Stokes light and the detector, and the detecting unit is subdivided into a plurality of parts and housed in respective containers, so that the external temperature There is an effect that stable detection intensity can be obtained without fluctuation of the laser beam without being affected by air convection due to the change.

[Brief description of drawings]

1 and 2 show an embodiment of the present invention, FIG. 1 is a block diagram of a detection unit for Stokes light and anti-Stokes light, and FIG. 2 is a filter for a demultiplexing unit for Stokes light and anti-Stokes light. 3 to 5 are graphs showing characteristics, FIG. 3 to FIG. 5 show conventional examples, FIG. 3 is a block diagram of a distributed optical fiber temperature sensor, and FIGS. 4 and 5 are block diagrams of a detection unit. 20: Optical fiber 22: Filter for demultiplexing Stokes light and anti-Stokes light 23: Narrow band filter 24: Detector

Claims (1)

(57) [Scope of utility model registration request] 1. A light source for injecting a laser pulse into an optical fiber to be measured, an optical directional coupler for guiding return light from the optical fiber to be measured to a measuring device, and Stokes light and anti-Stokes light contained in the returned light. In a distributed optical fiber temperature sensor consisting of a measuring device for detecting the temperature distribution of the measured optical fiber and its surrounding distance from the intensity ratio and the delay time, and detecting the Stokes light and anti-Stokes light demultiplexer. The space between the devices is spatially propagated, and the space between the demultiplexer and the detector is subdivided into a plurality of parts, and a container in which an opening is opened only in the light transmitting part is arranged in each subdivided section, and the container is placed in the container. At least one optical component and / or
Alternatively, a distributed optical fiber temperature sensor characterized by containing a detector.