JPS60152926A - Optical-fiber temperature sensor - Google Patents

Abstract

PURPOSE:To measure temperature from a room temperature up to about 500 deg.C accurately, by using impurity-doped optical fiber, which indicates absorption characteristic in an ultraviolet-ray region, measuring a loss at the tail part on the side of a long wavelength of the absorption characteristic, and measuring the temperature from the change in said loss. CONSTITUTION:With pure SiO2 as a core, an optical fiber 3, on which GeO2 that yields absorption in an ultraviolet-ray region is doped, is fused and connected to light-signal transmitting optical fibers 1 and 2, which have few characteristic change due to temperature and have less absorption in the ultraviolet-ray region than the sensing optical fiber 3. A nickel layer is attached to a part, where an aluminum layer is removed, at the end part, and heat resistance is improved. Light having a wavelength of, e.g., 0.7mum, is inputted to one end of the fiber 1 through a laser diode 4. The light is outputted from one end of the fiber 2 and received by a light detecting part 7 through an optical system 6. The loss change is 0.1dB/km at 300 deg.C and 1.5dB/km at 450 deg.C. Thus the temperature can be obtained.

Description

[Detailed description of the invention] (b) Industrial application field The present invention relates to a temperature sensor using an optical fiber.

(B) Prior art As temperature sensors using optical fibers, there are conventionally known temperature sensors that use the optical fiber itself as a sensing medium and those that use crystals or other substances instead of optical fibers as the sensing medium. However, the latter has problems such as difficulty in connecting the optical fiber and the sensing medium.

(c) Purpose This invention is an optical fiber temperature sensor that uses the optical fiber itself as a sensing medium, facilitates connection with the optical fiber, and can accurately measure temperature in the temperature range from room temperature to about 500°C. The purpose is to provide

(D) Structure The optical fiber temperature sensor according to the present invention uses an impurity-doped optical fiber that exhibits absorption characteristics in the ultraviolet region, and measures the loss in the long wavelength tail of the absorption characteristics of the optical fiber in the ultraviolet region. The device is characterized in that the temperature is measured based on changes in loss.

(e) Embodiment In FIG. 1, an optical fiber 3 serving as a sensing medium is connected between optical signal transmission optical fibers 1.2.

The optical fiber 1.2 has a core made of pure Sin, for example, and is an optical fiber whose characteristics change little due to temperature and has less absorption in the ultraviolet region than the optical fiber 3. In this example, the outer diameter is 125 gm, and the core diameter is 125 gm. 50pm
A GI type (graded index type) optical fiber with a relative refractive index difference of 1% and an aluminum coating layer with a thickness of 1701 Lm was used as the optical fiber 3. For example, using an optical fiber doped with Gem2 as an impurity,
In this example, the outer diameter is 125 #Lm and the core diameter is 5011. m
, G e Ot in 5i02 optical fiber with a relative refractive index difference of 1%
An aluminum coat layer having a thickness of 170 pLm was provided on an SI type (step index type) optical fiber doped with . and optical fiber 1.2 for 100m
Cut the optical fiber 3 into a length of 1 m.

The aluminum coating layer at the ends is removed by acid, base, electrolysis, etc., and fusion splicing is performed alternately.

After the connection is completed, the aluminum coat layer removed part of the connection part is coated with nickel to a thickness of 0.1JLm by sputtering, and then nickel is coated to a thickness of 8JLm by an electrolytic method. A nickel layer of m was deposited. The reason why the metal is coated in this way is to increase the heat resistance with the coating material. In addition to the above-mentioned aluminum, copper, nickel, etc. can be used as the coating material, and it can be attached by sputtering or dipping. I am made to do so.

This GeO2-doped optical fiber 3 absorbs in the ultraviolet region, but when the loss at the long wavelength side tail (0.6 gm to 1.0 lm) of this ultraviolet region absorption characteristic is determined as 1111, it changes depending on the temperature. I know what to do. Figure 2 is a graph showing the effect of temperature on absorption loss in the ultraviolet region in the optical fiber 3 doped with 15% GeOz by weight.
In the wavelength 0°6ILm region, the wavelength is 300°C to 500°C, and the wavelength is 0.6ILm.
It can be seen that there is an approximately linear relationship between loss and temperature in the 77zm region from 250°C to 500°C and in the 0.8pm wavelength region from 200°C to 500'O. Therefore, by measuring this loss, it becomes possible to measure the temperature.

In this embodiment, light with a wavelength of 0 and 77 Lm is incident on one end of the optical fiber 1 via the optical system 5 from a laser diode 4 (a light emitting diode may also be used) as a light source, and the optical fiber 1.3.2 The optical signal transmitted from one end of the optical fiber 2 is transmitted to a photodetector 7 via an optical system 6.
We decided to receive the light and measure the loss. Then, when the part of the optical fiber 3 was heated to 300°C to 500°C,
The change in loss is O, ldB/km at 300°C, 350'
c o , 3 dB/km, 400°C te 0 , 8 dB/km
km, 450°C-c'x, and 5 dB/km. Therefore, the temperature can be calculated from this loss measurement value using FIG.

Next, a second embodiment will be described with reference to FIG. In this example, optical fibers 8 to 13 for normal optical signal transmission and optical fibers 14 to 18 for sensing are connected alternately, and the loss is measured by the 0TDR method (optical time domain reflectometer method). It is configured to measure temperature at five locations. Optical fibers 8 to 13 used here and optical fiber/<14
-18 are similar to the optical fibers 1.2 and 3 of the previous embodiment, and the former has lengths of Loom and 3, respectively.
The latter were each 20 m long, and the metal layer was removed and interconnected as in the first embodiment, and then the metal layer was attached, resulting in a total length of 7 m.
00m.

The laser diode 21 generates light with a wavelength of 0.7 gm, and is directly pulse-modulated by a pulse oscillator 22.
This pulsed light passes through the directional coupler 23 and is connected to the optical fiber 8.
incident on one end of This pulsed light is transmitted to the optical fiber 8.14.
．． 9, . . . , a Ray scattering phenomenon occurs at each point, and the reflected light caused by this returns in the opposite direction to the traveling direction. This backscattered light is extracted by the directional coupler 23, converted into an electrical signal by the photodetector 24, amplified by the amplifier 25, and then sent to the averaging processing device 26. This averaging processing device 1126 processes and averages the data obtained from each of the plurality of pulsed lights, and the results are displayed on the screen of the CRT 27. In this way, initial characteristics as shown by the solid line in FIG. 4 are first displayed on the screen. Next, optical fiber 14~
18 points respectively at 120℃, 250℃, 40℃, 2
When heated to 00'0.100° C., the loss increased in these optical fibers, and results as shown by the dotted line in FIG. 4 were obtained. Therefore, the loss change at each measurement point can be measured.
From this change in loss, the temperature can be calculated based on the characteristics shown in FIG.

Note that in the above two embodiments, the loss of the sensing optical fiber is measured using the normal loss measurement method and the 0TDR method, but the loss may be measured using other methods.

(F) Effects According to the present invention, it is easy to measure the loss of the optical fiber, and it is also easy to connect to a normal optical fiber for transmitting optical signals, and the temperature can be measured at a large number of points from remote locations. It is extremely convenient because it allows you to measure

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a first embodiment of the present invention, and FIG. 2 is a 5-in.
A graph showing absorption loss in the ultraviolet region with respect to temperature at a wavelength of 0.6 gm to 1.0 #Lm of a dual-optical fiber, Fig. 3 is a block diagram of the second embodiment, and the Aoi diagram is a diagram of the second embodiment. It is a graph showing the measurement results obtained by the 0TDR method. l, 2.8-13... Optical fiber for optical signal transmission 3.1
4-18... Optical fiber for sensing 4.21...
Laser diode 5.6...Optical system 7.24...Photodetector 22...
・Pulse oscillator 23...Directional coupler 25...Amplifier 26...Averaging processing device 27...CRT Applicant Fujikura Electric Wire Co., Ltd. Photo 1 measurement 3 measurement 2 national temperature (6C)

Claims (1)

[Claims] (1) Using an impurity-doped optical fiber that exhibits absorption characteristics in the ultraviolet region, the loss at the long-wavelength tail of the optical fiber's absorption characteristics in the ultraviolet region was measured, and temperature was measured based on this change in loss. An optical fiber temperature sensor characterized by: