JPH03223632A - Light pulse tester - Google Patents

Abstract

PURPOSE:To improve reliability by covering the element wire of optical fiber with a specified resin. CONSTITUTION:Glass fiber 1 is represented by the SM fiber having a core diameter of 10mum and a clad diameter of 125mum or the GI fiber having a core diameter of 50mum and a clad diameter 125mum or a core diameter of 100mum and a clad diameter of 140mum. The glass fiber 1 is covered with a polyimide resin 2. It is preferable to have a constitution wherein the temperature of an element wire becomes equal to the temperature of external environment as quickly as possible. It is preferable that a gap 3 is as narrow as possible and a thin metal tube 4 is made of a material having excellent heat conductivity such as copper, gold, aluminum and their alloys. The optical fiber is not in direct contact with the external environment at low temperature or high tempera ture and can be isolated from the external environment. Thus, the reliability in measurement can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical pulse tester such as a distributed optical fiber temperature sensor.

[Prior Art] A distributed optical fiber temperature sensor, which is a type of optical pulse tester that measures the temperature distribution, break point, etc. of an optical fiber using the 0TDR method, uses the optical fiber to be measured itself as the sensor body, and It detects temperature distribution in real time. The principle is a type of 0TDR, in which a laser pulse is input into an optical fiber to be measured used as a sensor, and the Raman scattering phenomenon that occurs at each point of the fiber as it propagates is captured, and the ratio of Stokes light intensity to anti-Stokes light intensity is calculated. Distance and temperature data is obtained by utilizing the fact that it is a function of temperature and that the delay time from pulse input to detection of Raman scattered light is distance information.

A block diagram of a conventional distributed optical fiber temperature sensor is shown in FIG.

A laser pulse oscillated from a light source unit 13 such as an LD is transmitted to an optical directional coupler 1 such as an optical fiber coupler or an acousto-optic device.
4 and enters the optical fiber 15 to be measured. A part of the Raman scattered light from the optical fiber 15 returns and is guided to the measuring device by the optical directional coupler 14.

The following processing is performed in the measuring device. Stokes light and anti-Stokes light contained in the Raman scattered light are separated by a spectrometer J6 such as an optical filter, and each is separated by a photoelectric converter 17.1.
Detected at 8. After being further amplified by amplifiers 19 and 20, the signal processing unit 21 performs processing such as averaging processing or calculating a one-quality distribution from the intensity ratio of Stokes light and anti-Stokes light.

The optical fiber to be measured for the sensor is made of glass, especially in the case of communication fiber, it is silica-based glass, and in principle it can be used at temperatures ranging from extremely low temperatures such as liquid helium temperature (4.2K) to high temperatures of over 1000 degrees Celsius. Although it is considered possible to measure temperature, it is impractical in terms of strength and reliability in the state of glass wire. Therefore, in the past, the same protection treatment as for communication fibers was applied. That is, Zinocon resin was used as a buffer layer on the wire, and the wire was coated with a resin such as nylon or ETFE (called a core wire).
For general use, it is reinforced with a tension member such as Kevlar and protected with a PvC sheath (called a cord). Due to the heat resistance of the coating material, the upper limit of the environmental temperature for such practical fibers is about 100°C.

Furthermore, on the low temperature side, microbending occurs in the glass wire due to cooling shrinkage of the coating material, resulting in significant transmission loss, and about -20°C is the lower limit of the practical usage environment.

[Problems to be Solved by the Invention] The purpose of the present invention is to enable practical installation using polyimide resin-coated fibers that can be used in a wide temperature range or heat-resistant thin tubes that increase their strength, and to measure temperature distribution in ultra-low and high-temperature environments. The present invention provides a possible optical pulse tester.

Means for Solving Problem E] The present invention provides a light source unit that inputs a laser pulse into an optical fiber to be measured, an optical directional coupler that converts the optical path of the return light from the optical fiber to be measured to a measuring device, and An optical pulse tester comprising a measuring device for detecting light and measuring physical quantities such as temperature distribution of an optical fiber to be measured, characterized in that the optical fiber to be measured is made of a bare wire coated with polyimide resin. It provides equipment.

FIG. 1 shows a cross-sectional view of an optical fiber to be measured for a sensor used in the optical pulse tester of the present invention. 1 is a glass wire, 2 is a polyimide resin layer, 3 is a void, and 4 is a protective metal capillary. Although measurements can be made at low temperatures and with low loss even if the metal thin tube 4 is not used or is left as a wire, it is preferable to use it in terms of strength. The glass wires include 3M fiber with a core diameter of 10 μm and a cladding diameter of 125 μm, a core diameter of 50 μm, a cladding diameter of 125 μm, a core diameter of 100 μm, and a cladding diameter of 140 μm.
Any type of glass fiber may be used, including a μm GI fiber as a typical example.

Further, it is desirable that the temperature of the wire becomes equal to the temperature of the external environment as quickly as possible, that the gap be as narrow as possible, and that the metal tube be made of a material with good thermal conductivity. For example, copper, gold, aluminum, or even an alloy may be used.

Also, other metals can be used by reducing the wall thickness. The heat-resistant thin tube can be made of metal, fluororesin, silicone resin, glass, ceramic, etc., but metal is preferred because it has good heat conductivity and high heat resistance.

[Function J] In the present invention, a heat-resistant thin tube such as a metal thin tube protects the optical fiber to be measured for the sensor and guarantees its strength, and in actual use, the metal thin tube can be laid with the same ease as handling wire. It becomes possible.

[Example] (Example 1) Quartz-based GI with core diameter of 100 μm and cladding diameter of 140 μm
The fiber is coated with polyimide resin to a thickness of 50 μm, and is made of stainless steel (with an inner diameter of 0.8++ on and an outer diameter of 1.2 mm).
Figure 2 shows measurement data for temperature distribution measurement using a protected optical fiber inserted into a thin tube made of SUS304.

There is a low temperature part with a temperature of about -100°C at a distance of about 60 to 130 rr from the light source, and a part with a distance of about 260 to 3 rr from the light source.
There is a high temperature part of 40m with a temperature of about 200℃,
Conventionally, it was impossible to measure the temperature of gases, liquids, solids, etc. from a low temperature of -100℃ to a high temperature of 200℃ using an optical fiber sensor. This has been made possible with high reliability.

The basic configuration of the optical pulse tester of the present invention is the same as that shown in FIG. 3, and the optical fiber 15 has the above-described configuration.

(Example 2) A distributed optical fiber temperature sensor was created in the same manner as in Example 1 using a ceramic thin tube instead of the stainless steel tube in Example 1. ]Ta.

[Effects of the invention] The optical fiber can be isolated from the outside world at low and high temperatures without directly coming into contact with it, allowing for highly reliable measurements and reducing the possibility of breakage due to external force. have Furthermore, it is possible to install optical fibers in liquid or gas.

In addition, the measurable temperature ranges from 77K to 3K, which is the liquid nitrogen temperature.
Temperatures from 00 to 350°C are possible.

[Brief explanation of drawings]

1 and 2 show an embodiment of the present invention5, FIG. 1 is a cross-sectional view of an optical fiber to be measured, and FIG. 2 is a 1101'
This is a graph of data measured from a low temperature part to a high temperature part of N""C,-=200 DEG C., and FIG. 3 is a diagram of a conventional distributed optical fiber temperature sensor. l...Glass wire 2...Polyimide resin 3.
...Gap 4...Metal capillary diagram

Claims (3)

[Claims] (1) A light source unit that injects a laser pulse into the optical fiber to be measured, an optical directional coupler that converts the optical path of the return light from the optical fiber to the measurement device, and a temperature distribution of the optical fiber to be measured that detects the returned light. 1. An optical pulse tester comprising a measuring device for measuring a physical quantity, wherein the optical fiber to be measured is a wire coated with a polyimide resin. (2) The optical pulse tester according to claim 1, wherein the optical fiber to be measured is a wire coated with a polyimide resin, and the wire is further inserted into a heat-resistant capillary tube. (3) A distributed optical fiber temperature sensor using the optical pulse tester according to claim 1 or 2.