JPS62165133A - Optical fiber temperature sensor - Google Patents

Abstract

PURPOSE:To detect the lengthwise temperature distribution of an optical fiber with high sensitivity by providing a metallic coating layer which has no hysteresis loop on the external surface of the optical fiber. CONSTITUTION:The glass fiber 1 for optical transmission and the metallic coating layer 2 on the external surface of the fiber 1 are provided. The coating layer 2 is heated and cooled alternately in advance so as to vary in internal stress, i.e. expand or contract with its ambient temperature with high sensitivity. This means a heat cycle in which the coating layer 2 is cooled and heated lengthwise alternately and uniformly. This heat cycle is repeated plural times so that the metal of the coating layer 2 is work-hardened and the internal stress of the coating layer 2 varies with the ambient temperature without drawing any hysteresis loop. This is determined properly according to the material forming the coating layer 2, etc. Thus, the lengthwise temperatur distribution of the optical fiber is detected with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a temperature sensor using a metal-coated optical fiber, and particularly to a highly sensitive sensor cord-shaped optical fiber C II.
It is related to sensors.

[Prior art]

Optical fiber temperature sensors are often in the form of a sensor element in which the optical fiber itself functions as a temperature sensor because it can detect the temperature distribution in the longitudinal direction of the optical fiber. Some sensor element type optical fiber temperature sensors include a metal coating layer provided on the outer surface of the optical fiber. In this device, the stress inside the metal coating layer changes depending on the surrounding temperature change, and the local loss change that occurs in the optical fiber due to this internal stress change is taken as a transmission parameter such as the amplitude (intensity) of light, and temperature change is detected. It is something to detect.

(Problems to be Solved by the Invention) However, in such an optical fiber temperature sensor, the internal stress of the metal coating layer caused by temperature changes is
As shown in the figure, the temperature changes by drawing a hysteresis curve, which has a hysteresis loop due to plastic deformation.

This hysteresis loop plots stress on the vertical axis and humidity on the horizontal axis. In this case, the transmission loss partially generated within the optical fiber due to the above stress change will also change in response to the above temperature change, drawing a hysteresis loop. Therefore, accurate temperature changes can be determined based on the loss change in the optical fiber. There was a problem that it could not be detected.

[Means for solving problems]

Therefore, the optical fiber temperature sensor of the present invention solves the above problems by using a metal coating layer that does not have a hysteresis loop.

[Effect]

In this optical fiber temperature sensor, when the ambient temperature in the longitudinal direction of the optical fiber changes, the internal stress of the metal coating layer does not draw a hysteresis loop in response to the above temperature change, and the stress increases as shown in Figure 3. It changes with the rising curve and the falling curve of . Furthermore, this stress change causes a partial change in the core diameter, refractive index, etc. within the optical fiber, and this change causes a partial loss change in the optical fiber, which does not have hysteresis with respect to the stress change. As a result, changes in optical fiber loss are captured as transmission parameters such as amplitude, and temperature changes are detected accordingly.

〔Example〕

FIG. 1 shows the configuration of an optical fiber temperature sensor A according to the present invention, in which reference numeral 1 indicates a glass fiber for optical transmission, and 2
is a metal coating layer provided on the outer surface of the optical fiber 1. Here, for the optical fiber 1, quartz glass or the like having excellent transmission characteristics is selected.

The metal coating layer 2 perceives changes in ambient temperature as changes in internal stress such as expansion or contraction, and this layer has been subjected to heating and cooling treatment in advance in order to react with high sensitivity to changes in ambient temperature. They are applied alternately. Here, the above treatment means a heat cycle in which cooling and heating are alternately repeated uniformly along the longitudinal direction of the metal coating layer 2. The temperature range of this heat cycle is determined in consideration of the type of metal of the metal coating layer 2, its coating thickness, and the stress amplitude caused by temperature changes, which will be described later, to a degree that does not cause metal destruction.
The temperature is usually in the range of -80 to 100°C, but is not limited to this range. The number of cycles of this heat cycle is equal to or greater than the number of times that the metal of the metal coating layer 2 is work-hardened and the stress inside the metal coating layer 2 changes without drawing a hysteresis loop in response to changes in the surrounding temperature. It is determined as appropriate depending on the material forming the metal coating layer 2, which will be described later. Furthermore, as the material for forming the metal coating layer 2, a material with a large coefficient of linear expansion is selected, and specifically, aluminum, nickel, tin, bismuth, etc. are preferably used, and the film thickness is 10 to 10. The range is approximately 50 μm.

If it is less than 10 μm, it is too thin, so the amount of change in internal stress due to changes in ambient temperature will be small, and therefore the loss change in the optical fiber 1 due to changes in internal stress will also be small, resulting in the above temperature change. This results in the inconvenience that it is not possible to accurately detect the In addition, if the thickness exceeds 50 μm, it is too thick and the heat associated with a 4 degree change in the surroundings becomes difficult to be transmitted from the surface of the metal N layer 2 to the inside, resulting in inconveniences such as the inability to accurately detect temperature changes. occurs. In addition, metal coating 1l1 is applied for protection.
2, a resin coating can be applied on top. In this case, as the coating resin, 711
A material having a smaller Young's modulus than m metal is selected, and specifically, silicone resin, urethane acrylate resin, etc. are preferably used.

Next, we will introduce an optical fiber temperature sensor △ consisting of such a configuration.
An example of a method for manufacturing will be explained. First, an optical fiber base material made of quartz glass is heated in a spinning furnace, and an optical fiber 1 obtained by melt-spinning by a conventional method is passed through, for example, an aluminum melting tank, and the above-mentioned aluminum is coated on the surface thereof, and the above-mentioned Excess aluminum is squeezed out by passing it through a die provided in the tank to obtain an aluminum coated optical fiber. Next, this aluminum-coated optical fiber is spirally wound and placed in a cooling and heating furnace.
The metal coating) layer 2 is heated to a predetermined temperature, left to cool, and then cooled to a predetermined temperature.

The heating and cooling operations for this aluminum coated optical fiber are repeated a predetermined number of times to obtain the desired optical fiber temperature sensor A shown in FIG.

Next, the optical fiber temperature sensor A obtained in this way
Explain how to use. For example, if the outermost layer is the aluminum coat layer 2 as described above, in this temperature sensor,
As the ambient temperature rises, the aluminum coat layer 2 expands and internal stress changes, and at the same time, the core diameter and refractive index of the optical fiber 1 partially change due to the change in internal stress, resulting in a change in transmission loss. . This change in transmission loss is used as a change in the amplitude of light by an optical time dom connected to one end of this temperature sensor.
einllefractometry). In addition to such a detection method, there is also a method of detecting a change in transmission loss as a change in phase using interference.

Such an optical fiber temperature sensor has a metal coating layer 2 on the outer surface of the optical fiber 1 that has been subjected to heat work-hardening treatment, so that the metal coating layer 2 is resistant to changes in ambient temperature.
vJ2 is elastically deformed, and the stress generated by this deformation changes without drawing a hysteresis loop. Roughly speaking, the transmission loss changes with this stress change, and as a result, it is possible to accurately match the temperature change to the loss change of the optical fiber. Therefore, with this temperature sensor, it is possible to detect the temperature distribution in the longitudinal direction of the optical fiber with iH sensitivity.

Hereinafter, the effects of this invention will be clarified by showing experimental examples.

[Experiment example]

An optical fiber base material made of quartz glass is melt-spun using a conventional method, and an aluminum coat layer with a thickness of 25 μm is provided on the outer peripheral surface.
℃ and 8000 cycles to obtain an optical fiber temperature sensor. In addition to the aluminum coating layer, a temperature sensor with a metal coating layer of nickel, tin, and bismuth was also manufactured.

Regarding these four types of temperature sensors, the temperature accuracy before and after heat cycle treatment was compared.

For this temperature accuracy comparison test, a 0T
DR3 was used. This 0TDR3 measures the change in light intensity by capturing the loss change in the optical fiber as the reflected light intensity. In addition, 8 in the figure is a normal transmission optical fiber with a length of 1000 m, one end of which is connected to 0TDR3.
A metal-coated fiber with a length of 200 m was connected to the other end with a temperature sensor A, and a 50 m portion of the fiber was spirally wound and placed in the heating furnace 4. The furnace temperature of the heating furnace 4 was set, and the error between the set temperature and the temperature actually measured by the optical fiber temperature sensor was defined as the temperature accuracy, and is shown in Table 1.

Furthermore, since the heat cycle treatment conditions for the temperature sensors provided with the metal coating layers of nickel, tin, and tin are different from each other, these conditions are also listed in Table 1.

Table 1 As is clear from the results, the optical fiber temperature sensor of the present invention has a metal coating layer that is alternately heated and cooled on the outermost layer, so it is highly sensitive and has significantly improved temperature accuracy. It turns out that it is a sensor.

〔Effect of the invention〕

As explained above, the optical fiber temperature sensor of the present invention has a metal coating layer that does not have a hysteresis loop on the outer surface of the optical fiber, so it can accurately respond to changes in the ambient temperature and changes in the loss of the optical fiber. It becomes something that makes you do something.

Therefore, with this temperature sensor, it is possible to detect the temperature distribution in the longitudinal direction of the optical fiber with high sensitivity.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of the optical fiber temperature sensor of the present invention, FIG. 2 is a schematic view showing an experimental example using the optical fiber temperature sensor of the present invention, and FIG. 3 is a schematic cross-sectional view showing an example of the optical fiber temperature sensor of the present invention. FIG. 4 is a graph showing a temperature non-hysteresis curve for a metal coating layer to explain the effects of the conventional optical fiber temperature sensor. This is a graph showing. A...Optical fiber temperature sensor, 1...
Glass fiber for optical transmission, 2...metal coating layer.

Claims (2)

[Claims] (1) An optical fiber temperature sensor comprising a metal coating layer provided on the outer surface of a glass fiber for optical transmission, characterized in that the metal coating layer does not have a hysteresis loop. (2) The optical fiber temperature sensor according to claim 1, wherein the metal coating layer has a hysteresis loop removed by a heat cycle.