JPH05157951A - Optical fiber cable - Google Patents

Abstract

PURPOSE:To decrease the influence of hydrogen in high-temp. environment by allowing an inert gas to flow into a metallic pipe housing a coated optical fiber. CONSTITUTION:The coated optical fiber 1 is housed in the metallic pipe 21 consisting of a stainless steel or the like in a high-temp. part 4 where the temp. is to be measured of the coated optical fiber 1 constituted by forming a resin coating 12 on optical fiber glass 11, by which the optical fiber cable 2 is formed. A branch part 21' of the metallic pipe 21 is provided at one end of the optical fiber cable 2 and the inert gas, such as gaseous nitrogen, is made to flow continuously or intermittently into the metallic pipe 21 from a gas cylinder 3 connected to this part. The taking out port of the coated optical fiber 1 is previously formed with a sealing part 6 of a resin, etc., so as to do not leak the gas. Further, the other end of the metallic pipe 21 is held open in such a manner that the inert gas flowing therein is released. The high-temp. part 4 is open and the optical fiber cable 2 is placed therein and is exposed to the high-temp. state.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber cable containing a metal tube used in a high temperature environment.

[0002]

2. Description of the Related Art In order to improve the heat resistance of an optical fiber cable containing a metal tube, an optical fiber core having an amorphous carbon coating and a polyimide resin coating layer on the optical fiber glass is housed in a metal tube such as stainless steel. However, an example of trying to prevent an increase in transmission loss of the optical fiber due to the action of hydrogen generated in the metal tube at a high temperature on the optical fiber glass is disclosed in, for example, JP-A-3-110508.

[0003]

However, as long as the optical fiber glass is coated with resin, it is not possible to eliminate the generation of hydrogen due to the progress of decomposition of the resin at a high temperature of 300 ° C., for example. Furthermore, in the optical fiber cable with a metal tube, hydrogen generated in the metal tube does not escape to the outside by the metal tube, so even a small amount of hydrogen is likely to affect the optical fiber glass. It is known that the carbon film has a limited hydrogen shielding effect, and its performance deteriorates at higher temperatures.

[0004]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and even when an optical fiber cable in which an optical fiber core wire having at least a resin coating is housed in a metal tube is used in a high temperature environment. The present invention provides an optical fiber cable in which the influence of hydrogen is reduced, and is characterized in that an inert gas is continuously or intermittently poured into a metal tube for use.

[0005]

In the above-described optical fiber cable of the present invention, an inert gas such as nitrogen or helium which suppresses the decomposition of the resin is introduced into the metal tube containing the resin-coated optical fiber core wire at the end of the metal tube. The hydrogen generated in the metal tube was discharged to the outside before it adversely affects the optical fiber core wire.

The flow rate of the inert gas flowing into the metal pipe is
It is determined according to the amount and rate of hydrogen generated, which is assumed from the type of resin used for the optical fiber core, the coating thickness, the inner diameter of the metal tube, the operating temperature, and the like. In addition, it is desirable that the inert gas is continuously supplied, but if the hydrogen generation amount is small, it may be intermittently supplied.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view of an embodiment of the optical fiber cable of the present invention, FIG.
It is an enlarged view of the A section of a figure. This system is an example of a system for measuring a high temperature by an optical fiber temperature distribution measuring device. In the drawing, as shown in FIG. 2, reference numeral 1 denotes an optical fiber core wire in which a resin coating 12 is applied on an optical fiber glass 11, and in the high temperature part 4 and its vicinity where the temperature is to be measured, The wire 1 is housed in a metal tube 21, such as stainless steel, forming an optical fiber cable 2. In this example, a stainless steel SUS316 having an inner diameter of 1.4 mm and an outer diameter of 1.8 mm is used as a metal tube, and an optical fiber core wire having a coating layer of an ultraviolet curable resin having a diameter of 0.25 mm is housed therein.

As shown in FIG. 1B, a branch portion 21 'of a metal pipe 21 is provided at one end of the optical fiber cable 2, and an inert gas such as nitrogen gas is fed into the metal pipe 21 from a gas cylinder 3 connected to the branch portion 21'. Pour into. A sealing portion 6 is formed of resin or the like at the outlet of the optical fiber core wire 1 so that gas does not leak out. The other end of the metal tube 21 is in an open state so that the poured inert gas is released. The high temperature part 4 is an oven of 200 ° C. or higher, and the optical fiber cable 2 is placed therein and exposed to high temperature. In addition, 5 is an optical fiber temperature distribution measuring device.

In the above structure, an increase in transmission loss of the optical fiber was observed at a high temperature of 200 ° C. or higher, and an increase in loss indicating that the cause was hydrogen was confirmed at a wavelength of 1.4 μm. The amount of loss increase was 0.9 dB / km when the generated hydrogen did not escape in the metal tube without pouring the inert gas, and 0.2 dB / km when the inert gas was poured.

[0010]

As described above, in the optical fiber cable of the present invention, the influence of hydrogen in a high temperature environment is reduced by injecting an inert gas into the metal tube containing the optical fiber core wire. Is possible. Therefore, it is expected that the optical fiber temperature distribution measurement system will be applied to high temperature measurement.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of an optical fiber cable of the present invention, FIG. 1 (a) is a configuration diagram, and FIG. 1 (b) is an enlarged view of a portion A in FIG. 1 (a).

FIG. 2 is a cross-sectional view of an optical fiber cable used in an example of the present invention.

[Explanation of symbols]

 1 Optical fiber core wire 11 Optical fiber glass 12 Resin coating 2 Optical fiber cable 21 Metal tube 3 Gas cylinder 4 High temperature part 5 Optical fiber temperature distribution measuring device 6 Sealing part

Claims (1)

[Claims] 1. An optical fiber cable characterized in that a resin-coated optical fiber core wire is housed in a metal tube and an inert gas is continuously or intermittently poured into the metal tube for use.