JP3139897B2 - Manufacturing method of heat resistant optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a heat-resistant optical fiber.

A heat-resistant optical fiber is used for temperature measurement, optical fiber communication under a high temperature environment, and the like.

[0003]

2. Description of the Related Art Recently, a metal tube-coated optical fiber cable has been used for an optical fiber cable requiring high tensile strength or environmental resistance. This metal tube coated optical fiber cable is obtained by passing one or more optical fiber strands, optical fiber core wires, or optical fiber cords (hereinafter simply referred to as optical fibers) through a metal tube such as a stainless steel tube or a copper tube. Then, the optical fiber is protected by the metal tube.

[0004] In addition, the optical fiber cable may become hot at the time of fire, at the time of measuring the high temperature of a furnace or the like, or at the time of energy transmission. In such a case, when the optical fiber in the metal tube is heated to a high temperature exceeding, for example, 100 ° C.,
If the plastic coating of the optical fiber undergoes heat shrinkage or further exceeds 200 ° C., it decomposes or burns,
Decomposition or combustion gas is generated. The heat shrinkage causes a compressive stress in the bare optical fiber, which bends and increases transmission loss.
In the case of a metal tube whose both ends are closed by a connection device or a small-diameter and long metal tube, the pressure of these generated gases increases in the tube. As a result, the generated gas at a high pressure may damage the connected equipment or damage the metal pipe whose strength has been reduced due to a rise in temperature.

To solve the above-mentioned problem of the metal tube-coated optical fiber cable exposed to a high temperature, Japanese Patent Application Laid-Open No.
There is a heat-resistant optical fiber cable disclosed in Japanese Patent Publication No. 189814. In this heat-resistant optical fiber cable, a bare optical fiber is inserted with an extra length in the metal tube with a gap. Since the heat-resistant optical fiber cable does not have a coating of nylon, polyethylene, or the like, the coating does not decompose or burn even when exposed to a high temperature exceeding 200 ° C. Further, in the heat-resistant optical fiber cable, the coating is removed immediately before inserting the coated strand into the tube, or the bare optical fiber is inserted into the tube immediately after manufacturing. The coating is removed by dissolving or burning with an organic solvent or acid.

Japanese Patent Application Laid-Open No. 63-205623 discloses a method for manufacturing a heat-resistant optical fiber in which an optical fiber core is heated to a temperature higher than a melting temperature or a decomposition temperature of a coating material, and a part or all of the coating is removed. Has been disclosed.

[0007]

As described above, in a conventional heat-resistant optical fiber cable, a bare optical fiber whose coating has been removed is inserted into a tube. Therefore, when the bare optical fiber is inserted into the tube, gas absorption from the atmosphere in the tube and minute surface flaws easily occur in the bare optical fiber. Gas absorption from the atmosphere in the tube causes transmission loss, and a bare optical fiber having a small surface flaw is easily broken by a small tensile force.

As described above, when the optical fiber in the metal tube is heated to a high temperature exceeding 200 ° C., the plastic coating of the optical fiber is decomposed or burned, and the heat-resistant optical fiber having a part of the coating left is decomposed or burned. Combustion gas may be generated.

When the optical fiber is heated to remove the plastic coating, if the heating temperature exceeds 200 ° C., the plastic coating contracts and compressive stress is applied to the bare optical fiber. This compressive stress causes bending of the bare optical fiber,
The reflectance at the core / cladding interface decreases, and the transmission loss increases. In addition, during heating, the plastic coating is thermally decomposed to generate H ₂ O and H ₂ . Of these, H ₂ O combines with the bare optical fiber SiO ₂ to form silica gel.
When silica gel is generated at the interface between the core and the clad, the reflectance at the interface decreases, which causes an increase in transmission loss. H
₂ is absorbed by the glass core or the glass clad, causing an increase in the transmission loss of the bare optical fiber.

An object of the present invention is to provide a method for manufacturing a heat-resistant optical fiber that can prevent damage to the optical fiber and increase in transmission loss.

[0011]

According to a method of manufacturing a heat-resistant optical fiber of the present invention, a heat treatment is performed while tension is applied to an optical fiber, an optical fiber, or an optical fiber cord (hereinafter simply referred to as an optical fiber). Then, the plastic coating is calcined while removing the pyrolysis gas of the plastic coating generated by the heat treatment.

In order to apply tension to the optical fiber, it is preferable to apply the tension while unwinding the optical fiber from the rewind reel and winding the optical fiber around the take-up reel. The magnitude of the tension can be easily adjusted by adjusting the unwinding speed or the winding speed. The magnitude of the tension must be less than the allowable tension of the bare optical fiber.

In order to calcine the plastic coating, an optical fiber is inserted into a heating furnace, a tube, or the like, and then heated in a state where a rapid oxidation reaction is suppressed. For example, heating is performed in an atmosphere in which a slight amount of oxygen gas (about 0.5 to 10%) is mixed with nitrogen gas. When oxygen gas is included in a large amount, the plastic coating is burned and almost burned out. The heating temperature varies depending on the coating material, but is about 100 to 700 ° C. The heating time is about 10 to 60 seconds. The heating generates a pyrolysis gas containing a small amount of H ₂ , NH ₃ , cyan gas, and the like in H ₂ O. Air, nitrogen gas, or the like is sent to a heating furnace, a pipe, or the like to purge the pyrolysis gas.

[0014]

The plastic calcined layer bears part of the stress applied to the heat-resistant optical fiber and reinforces the heat-resistant optical fiber. Therefore, microbending does not occur in the bare optical fiber. Since the surface of the bare optical fiber is protected by a plastic calcined layer, even when friction or impact is applied when the heat-resistant optical fiber is inserted into a metal tube or the like, a small surface flaw is not generated on the bare optical fiber. Also, 200
Exposure of the optical fiber cable to temperatures as high as above 0 ° C. does not generate decomposition gases because the plastic coating has been modified to a plastic calcined layer.

Since tension is applied to the optical fiber during calcination, even if the plastic coating contracts, no compressive stress is applied to the bare optical fiber. In addition, since the pyrolysis gas of the plastic coating is purged with air or the like during calcination, the bare optical fiber does not absorb H ₂ O or H ₂ .

[0016]

EXAMPLE The manufacture of a heat-resistant optical fiber for temperature measurement will be described as an example. FIG. 1 shows an example of an apparatus for manufacturing a heat-resistant optical fiber. As shown in the figure, a heating device 21 and a cooling device 26 are arranged between the rewind reel 11 and the take-up reel 14.

The rewind reel 11 winds the optical fiber 1 and is driven to rotate by a motor 12. The unwinding reel 11 holds the optical fiber 1 at a constant speed so that the optical fiber 1 is heated by the heating device 17 for a required time.
Send out.

The take-up reel 14 is rotated by a motor 15 and calcined.
Take up. The output torque of the motor 15 is detected by the torque sensor 17, and the detected torque is output to the tension controller 1
9 is output. The tension controller 19 controls the rotation speed of the take-up reel 14 based on the detected torque, and applies tension to the optical fiber 1 or the heat-resistant optical fiber 2 between the rewind reel 11 and the take-up reel 14.

In the heating device 21, a heater 23 and a decomposition gas purge nozzle 24 are disposed in a heating chamber 22. The heating device 21 heats the optical fiber 1 passing through the heating chamber 22 to a required temperature and calcinates it. Air is supplied from the fan 30 and nitrogen gas is supplied from the nitrogen gas cylinder 31 to the decomposition gas purge nozzle 24, and the decomposition gas is discharged out of the heating chamber 22.

The cooling device 26 is adjacent to the heating device 21, and a cooling nozzle 28 for blowing a mixed gas of cooling nitrogen gas and air is disposed in the cooling chamber 27. Air is supplied to the cooling nozzle 28 from a fan 30 to cool the calcined optical fiber 1 passing through the cooling chamber 27.

With the manufacturing apparatus configured as described above,
A heat-resistant optical fiber for temperature measurement was produced as follows.
First, a quartz optical fiber having an outer diameter of 0.4 mm and a length of 2000 m was heated at 130 ° C. for 15 seconds by a heating device, and at the same time, a decomposition gas was removed with a mixed gas of nitrogen gas and air.
The coating of the optical fiber is a UV curable resin. The feed speed of the optical fiber was 0.5 m / sec, and the tension was 1.0 kgf. Next, the calcined optical fiber was cooled to produce a heat-resistant optical fiber.

The heat-resistant optical fiber is made of SUS316,
An optical fiber cable for temperature measurement was produced by vibrating and inserting a stainless steel tube having an outer diameter of 1.8 mm × an inner diameter of 1.4 mm and a length of 2000 m. FIG. 2 shows a part of the optical fiber cable 6 for temperature measurement. As shown in the drawing, the temperature measuring optical fiber cable 6 includes a heat-resistant optical fiber 2 and a stainless steel tube 7. The heat-resistant optical fiber 2 has a bare optical fiber 3 covered with a plastic calcined layer 4. Also,
The heat-resistant optical fiber 2 is inserted into the stainless steel tube 7 with undulations (excess length) 8. This optical fiber cable for temperature measurement was set in a soaking furnace, and an ambient temperature of 675 ° C. was measured. As a result, the temperature error was ± 1.5 ° C.

[0023]

According to the method for producing a heat-resistant optical fiber of the present invention, since tension is applied to the optical fiber during calcination, even if the plastic coating shrinks, no compressive stress is applied to the bare optical fiber. The occurrence of bending of the bare optical fiber is prevented, and there is no increase in transmission loss. Further, since the pyrolysis gas of the plastic coating is purged with a mixed gas of nitrogen gas and air during the calcination, the bare optical fiber does not absorb H ₂ O or H ₂ . In the heat-resistant optical fiber manufactured by the method of the present invention, the surface of the bare optical fiber is protected by a plastic calcined layer, and the plastic coating is modified to a plastic calcined layer. For these reasons, damage to the heat-resistant optical fiber and an increase in transmission loss can be prevented.

[Brief description of the drawings]

FIG. 1 is an apparatus configuration diagram showing an example of an apparatus for implementing a method for manufacturing a heat-resistant optical fiber of the present invention.

FIG. 2 is a partially enlarged cross-sectional view of an optical fiber cable for temperature measurement using a heat-resistant optical fiber manufactured by the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical fiber wire 2 Heat resistant optical fiber 3 Bare optical fiber 4 Plastic calcined layer 6 Heat resistant optical fiber cable 7 Metal tube 8 Extra length 11 Rewind reel 12 Motor 14 Winding reel 15 Motor 17 Torque sensor 19 Tension control device 21 Heating Apparatus 23 Heater 24 Decomposition gas purge nozzle 26 Cooling device 28 Cooling nozzle 30 Fan 31 Nitrogen gas cylinder

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Shimizu Yokoi 3-5-4 Tsukiji, Chuo-ku, Tokyo Nippon Steel Welding Industry Co., Ltd. (56) References JP-A-59-73451 (JP, A) JP-A-4-160040 (JP, A) JP-A-63-34504 (JP, A) JP-A-4-21548 (JP, A) JP-A-4-138406 (JP, A) JP-A-63-189814 (JP) , A) JP-A-7-27951 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C03C 25/10 G02B 6/44 301 G02B 6/44 391

Claims (2)

(57) [Claims] Claims: 1. An optical fiber, an optical fiber, or an optical fiber cord is subjected to a heat treatment under tension.
A method for producing a heat-resistant optical fiber, comprising calcining a plastic coating while removing pyrolysis gas of the plastic coating generated by heat treatment. 2. An optical fiber, an optical fiber, or an optical fiber between the two reels while rewinding the optical fiber, the optical fiber, or the optical fiber cord from the rewinding reel and winding the optical fiber on the take-up reel. The method for producing a heat-resistant optical fiber according to claim 1, wherein the optical fiber cord is calcined by applying tension.