JPS63205623A - Production of heat resistant optical fiber - Google Patents

Abstract

PURPOSE:To prevent generation of surface flaws of a glass fiber strand and generation of microbending therein by preparing an optical fiber core formed by coating said strand with a coating material, removing the coating material of the optical fiber core and inserting the core into a metallic pipe. CONSTITUTION:The optical fiber core 7 formed by coating the strand 8 with the coating material is prepd. and after the coating material of the core 7 is removed, the core 7 is inserted into the metallic pipe 1. Since the strand 7 is a glassy material consisting of the core 8a and clad 8b, the strand is liable to be flawed during the time after the production of the strand 7 before the insertion thereof into the pipe 1. The coating material is, therefore, removed just before the optical fiber core 7 coated with the coating material is inserted into the pipe 1, then the core 7 is heated to the melting or decomposing temp. of the coating material or above or the coating material is dissolved by a solvent and is thereby removed. The surface defects such as rubbing flaws of the strand are thereby prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing a heat-resistant optical fiber, particularly a heat-resistant optical fiber in which the optical fiber is inserted into a metal tube with a gap and an extra length.

(Prior Art) Optical communication cables that have become widely used in recent years require optical fibers coated with metal tubes because optical fibers are weak in strength. For example, optical fibers that are extended overhead, under the sea, underground, etc.
It is used by covering it with a metal tube to prevent excessive tension or to provide environmental resistance. Further, when the covering is a metal tube, there is an advantage that a tension member is not required and the wire can be extended with a large span since the overhead wire has little slack.

Further, an optical fiber core wire inserted into a metal tube generally consists of a strand, a primary coat, and a reinforcing coat. Silicone is mainly used as the primary coat material, and nylon or polyethylene is used as the reinforcing coat material. These primary coats and reinforcing coats prevent surface scratches and microbending that occur during handling before the optical fiber is inserted into the metal tube.

Note that when an optical fiber in a metal tube is heated or stretched under tension, the optical fiber is is longer than the length of the metal tube. This extra length is called extra length. The extra length is formed by meandering or undulating the optical fiber.

Conventionally, as a method for manufacturing an optical fiber line in which an optical fiber is inserted into a tube such as a metal tube, a tape forming-welding method (for example, Japanese Patent Laid-Open No. 60-46869) is known. In this method, a metal tape is formed into a tubular shape, and both edges of the tape are welded to manufacture the tube, while an optical fiber is inserted.

In addition, another method is the tube insertion method (for example, JP-A-58-
25606) is known. In this method, f
After manufacturing an aluminum tube into which an IA wire is inserted, the diameter of the tube is reduced, and then the steel wire inside the tube is replaced with an optical fiber.

(Problems to be Solved by the Invention) Optical fibers may become hot in the event of a fire, when measuring high temperatures in a furnace or the like, or during energy transmission. However, since the optical fiber core wire inserted into the conventional metal tube is coated with a coating material made of silicone, nylon, polyethylene, etc., if it is exposed to high temperatures exceeding 200°C, the coating material may decompose or It burns and deteriorates the wire. Further, if the metal tube does not have an opening in the longitudinal direction, the generated gas increases the pressure inside the tube and blows out from both ends of the optical fiber, destroying the connection part or, in severe cases, destroying the metal tube itself.

By the way, since there has been no heat-resistant optical fiber that can withstand high temperatures exceeding 200° C., the above-mentioned publication (or other documents) does not suggest at all the manufacture of heat-resistant optical fibers.

Furthermore, it is difficult to manufacture high-quality heat-resistant optical fibers simply by using the conventional optical fiber manufacturing methods disclosed in these publications. The reason for this is that there is a risk of surface scratches and microbending of the wire.

(Means for Solving the Problems) The method for manufacturing a heat-resistant optical fiber of the present invention manufactures a heat-resistant optical fiber in which a glass fiber strand consisting of a core and a cladding is inserted into a metal tube with a gap and an extra length. In this method, a coated optical fiber whose strands are coated with a coat material is prepared, the coating material of the coated optical fiber is removed, and the coated wire is inserted into a metal tube.

The strands are made of quartz-based, multicomponent-based, etc. glass. The metal tube may be made of steel, aluminum or other desired material, and may be a seamless tube, a TIG welded tube, a high frequency welded tube, or a forge welded tube. The outer diameter and wall thickness of the metal tube are determined by taking into consideration the breakage during tube drawing, the outer diameter, strength, and elongation of the final product, the heat-resistant optical fiber. The inner diameter is at least 0.1 mII+ than the outer diameter of the strand.
It has to be big. Furthermore, when a long heat-resistant optical fiber is required, a plurality of metal tubes are connected in the longitudinal direction to obtain the required length.

The size of the extra length is determined by the difference in coefficient of thermal expansion and modulus of longitudinal elasticity between the metal tube and the wire, and the usage conditions of the heat-resistant optical fiber.

Since the wire is made of glass and consists of a core and a cladding, it is easily damaged during the period from when the wire is manufactured until it is inserted into a tube. Therefore, the coating material is removed immediately before inserting the optical fiber coated with the coating material into the tube. The coat material is removed by heating the optical fiber to a temperature higher than the melting or decomposition temperature of the coat material, or by dissolving it with a solvent.

In addition, when inserting the core wire into the tube, in order to prevent scratches on the core wire surface and to make it easier to insert, use powdered solid lubricants such as carbon, talc, and molybdenum disulfide, or Jffi lubricating oil (silicone oil, etc.). It is desirable to attach it to the surface of the wire. In this case, the atmosphere inside the tube is changed to N2 to prevent the lubricant and oil attached to the core wire from burning. It is desirable to replace the gas with an inert gas such as Ar.

Note that the core wire after the coating material has been removed may be coated with a heat-resistant material. Metal, ceramic, carbon, or cermet is used as the heat-resistant material.

(Function) In the method for producing a heat-resistant optical fiber of the present invention, the coating material made of silicone, nylon, polyethylene, etc. is removed, so even if the obtained optical fiber is exposed to high temperatures exceeding 200°C, the coating material will decompose. There is no possibility of burning or burning. Furthermore, since the coating material on the optical fiber core is removed immediately before insertion into the tube, surface defects such as scratches will not occur on the wire.

(Example Work) FIG. 1 is an enlarged sectional view showing an example of a heat-resistant optical fiber manufactured by the method of the present invention. The metal tube 1 has an outer diameter of 10.
3mm, wall thickness 0.9mm seamless stainless steel pipe (S
US304) raw metal pipe is expanded to an outer diameter of 1.0 mm,
The pipe is finished with a wall thickness of 0, 10m and a length of 1000m. The optical fiber before being inserted into tube 1 is a silica-based glass optical fiber (diameter +25 um) coated with silicone as a primary coat and polyethylene as a reinforcing coat with a diameter of 0.711II11.
belongs to.

The optical fiber strand 8 was inserted into the metal tube 1 by the vibration insertion method developed by the present inventors, which will be described later. Immediately before inserting the optical fiber into the metal tube 1, the coating material is removed by heating.
The strand 8 was made up of only a core 8a and a cladding 8b.

Furthermore, carbon powder 8C was applied as a lubricant to the surface of the wire 8 immediately before insertion into the tube.

Embodiments of the present invention will be described below based on the drawings. FIG. 2 is an overall view of an apparatus for implementing the present invention, and FIG. 3 is a plan view of a vibration table.

The pedestal 11 is firmly fixed to the floor surface 9 so as not to vibrate. Coil springs 18 for supporting the vibration table are attached to the four corners of the upper surface of the pedestal 11.

A square plate-shaped vibration table 14 is placed on the pedestal 11 via a support spring 18 . Vibration table 14
A support frame 15 extends downward from the lower surface of.

A pair of vibration motors 2] and 22 are attached to the support frame 15 of the vibration table 14. Vibration motor 2
2, the vibration motor 21 is connected to the center axis 6 of the vibration table 14.
It is in a position and attitude rotated 180 degrees around. Also,
The vibration motors 21 and 22 are arranged such that their rotation axes are parallel to a vertical plane including the central axis C, and are inclined at 75 degrees in opposite directions with respect to the vibration table surface. The vibration motors 21 and 22 have unbalanced weights 24 fixed to both ends of the rotating shaft, and apply an excitation force in an oblique direction to the surface of the vibration table 14 by centrifugal force caused by the rotation of the unbalanced weights 24. . This pair of vibration motors 21,
22 are driven such that their frequencies and amplitudes match each other, and their excitation directions are shifted by 180 degrees from each other. Therefore, when the vibrations caused by the pair of vibration motors 21 and 22 are combined, the vibration table 14 vibrates along a spiral whose central axis coincides with the central axis C of the vibration table 14.

The bobbin 27 is fixed on the vibration table 14 such that the bobbin axis coincides with the center axis C of the vibration table 14. A tube 1 through which the wire 8 is inserted is wound in a coil around the bobbin 27, and the wire 8 is supplied into the tube from the lower end of the coil 5 of this tube. The bobbin 27 has a vibration motor 21,
the lower flange 2 of this to ensure that it receives the vibration of 22.
The outer peripheral edges of 9 are respectively fixed to the vibration table 14 by the fixing jig 31.
is fixed. As shown in FIG. 4, the bobbin 27 is provided with a groove 30 by shaper processing in the circumferential direction of the body 28 so that the unevenness is continuous in the direction of the bobbin axis.
The tube 1 is brought into close contact with the tube 1. When the tube 1 is brought into close contact with the groove 30 of the body of the bobbin 27 in this way, the vibration of the bobbin 27 can be transmitted to the tube 1 with good granularity, and the vibration insertion of the strand 8 can be carried out smoothly and efficiently.

A supply spool 34 of an optical fiber supply device 33 is arranged on the side of the bobbin 27. The supply spool 34 is rotatably supported on a bearing stand 35. The supply spool 34 lets out the optical fiber core 7 wound around it,
It is supplied to the coiled tube 1 via a coat removing device 51.

A drive motor 38 is arranged adjacent to the supply spool 34 , and the supply spool 34 and the drive motor 38 are operatively connected via a belt transmission 40 .

The supply spool 34 is rotationally driven by a drive motor 38.
Then, the optical fiber core 7 is let out, and the coat removing device 5
The optical fiber 7 is supplied to the tube 1 which is wound around the bobbin 27 via the tube 1 .

A holding guide 43 is provided close to the optical fiber feeding position of the supply spool 34 . The holding guide 43 consists of a short tubular main body 44 and a stand 45 that horizontally supports the main body 44, and holds the optical fiber core 7 fed out from the supply spool 34.

Following the holding guide 43, the optical fiber feeding state detection device 4
7 is placed. Optical fiber feeding state detection device 47
consists of a support column 48 and an optical fiber height position detector 49 attached to the support column 48. The optical fiber height position detector 49 is composed of an image sensor and a light source disposed opposite to the image sensor, and is located at a position where the optical fiber coated wire 7 passes, and detects the degree of slack in the optical fiber coated wire 7. A CCD line sensor is used as the image sensor.

A rotation speed control device 50 is connected to the optical fiber feeding state detection device 47, and the rotation speed control device 50 controls the voltage of the power source of the drive motor 38 based on a signal from the detection device 47. That is, the rotational speed of the drive motor 38, that is, the feeding speed of the optical fiber coated wire 7 is controlled according to the height position at which the optical fiber coated wire 7 blocks the optical fiber height position detector 49 from the light source.

During the insertion of the strand 8 into the tube 1, the insertion speed of the strand 8 is not necessarily constant and may vary depending on the resonance phenomenon and the conditions of the inner surface of the tube and the surface of the strand. Therefore, if the speed of the strand 8 in the tube 1 fluctuates, it will affect the feeding state of the optical fiber core 7 outside, and if this feeding speed cannot follow the insertion speed of the strand 8, the optical fiber core Unnecessary slack in the wire 7 or wire breakage due to excessive tension may occur, which may impede the smooth supply of the wire 8. However, the supply spool 34 is driven to rotate as described above, and the supply spool 34 is
By changing the rotational speed or stopping it as the case may be, the strands 8 can always be supplied within the required supplying speed range. In other words, the optical fiber core 7 is not too stretched or too sagging, and is in the best condition (second
It can be maintained in a slightly sagging state (as shown in the figure). As a result, the strand 8 can be inserted into the tube 1 without any hindrance without placing any burden on the strand 8 itself, that is, without providing any resistance to the insertion of the strand 8. By the way, the diameter is 0.4
When inserting a strand of wire 8 into a steel pipe with an inner diameter of 0.5 mm, the force applied to the strand 8 toward the optical fiber supply side is 20 g.
f or more, the wire 8 will not enter the pipe.

A coat removal device 51 is disposed following the optical fiber feeding state detection device 47. FIG. 5 shows details of the coat removal device 51. As shown in the drawings, the coat removal device 51 includes a heating chamber 52, and a heating coil 54 is provided within the heating chamber 52. A guide path 56 is connected to the crater side of the 1 gal #8 chamber 52, which serves as a passage for the wire 8 inside the heating coil 54, and nitrogen gas is supplied to the guide path 56 from a nitrogen gas supply pipe 57. Supplied. A nitrogen gas supply pipe 59 is connected to the center of the heating chamber 52 via a stop valve 60, an exhaust pipe 62 is attached to the top via a stop valve 63, and a tap 65 is attached to the bottom. . A collection tank 66 for collecting molten coating material is arranged below the tap 65. Note that the pressure and temperature within the heating chamber 52 are adjusted to appropriate values based on the detected values of the pressure detector 68 and the temperature detector 69.

A cooling path 71 is connected to the exit side of the heating chamber 52, and cooled nitrogen gas is supplied to the cooling path 71 from a nitrogen gas supply pipe 73. The supplied nitrogen gas passes through the stop valve 76 and is exhausted from the exhaust pipe 75. The pressure inside the cooling path 71 is detected by a pressure detector 78, and the pressure inside the cooling path 71 is detected by a pressure detector 78.
The pressure inside the cooling passage 71 is adjusted so that it does not become lower than the internal pressure of the cooling passage 71. This is to prevent the solution vapor flowing back from the melting chamber 81 to the heating chamber 52 through the cooling path 71 from exploding in the heating chamber 52 .

A melting chamber 81 is provided following the cooling path 71 .

The bottom of the dissolution chamber 81 is a dissolution liquid storage tank 82 , and the dissolution liquid storage tank 82 is connected to the dissolution path 83 via a communication pipe 84 . A solution is pumped into the solution path 83 from the solution storage tank 82 by a pump 85 . A supply pipe 8 is provided in the solution storage tank 82.
Clean solution is supplied from 6, and polluted solution is discharged from drain pipe 87. Steam generated by melting passes through a stop valve 89 and is discharged from an exhaust pipe 88 . The pressure in the melting chamber 81 is detected by a pressure detector 90, and the pressure in the melting chamber 81 is adjusted so that steam does not flow out to the upstream and downstream sides.

A washing chamber 91 is connected to the outlet side of the dissolution chamber 81, and a nozzle 92 for spraying washing water is arranged in the washing chamber. A water supply pipe 93 is connected to the nozzle 92 via a stop valve 94. The polluted wash water is discharged through a drain pipe 96. Further, the pressure inside the washing chamber 91 is detected by a pressure detector 97, and the pressure inside the chamber monitors the pressure in the dissolving chamber 81.

A drying path 101 is connected to the outlet side of the washing chamber 91.
Heated nitrogen gas is supplied to the drying path 101 from a nitrogen gas supply pipe 102 . The supplied nitrogen gas is removed from the stop valve 1.
04 and is discharged from the exhaust pipe 103. dry road 101
The pressure inside the melting chamber 8 is detected by the pressure detector 106.
The pressure inside the drying path 101 is adjusted so that it does not become lower than the internal pressure of the drying path 101.

Next, a method for inserting the wire 8 into the tube 1 using the apparatus configured as described above will be explained.

In advance, the tube 1 is wound in a coil around the bobbin 27 to form the coil 5, and the optical fiber core 7, which is a strand 8 coated with a coating material, is also wound around the supply spool 34.

Note that the tube 1 is not limited to being wound in one layer around the bobbin 27, but is often wound in multiple layers. In this case, the first layer comes into close contact with the groove 30 of the bobbin body 28, but the second and subsequent layers fit between the tubes 1 of the previous layer. Next, the bobbin 27 around which the tube 1 is wound is fixed on the vibration table 14 so that the coil axis and the central axis C of the vibration table 14 coincide.

Then, the optical fiber core 7 is pulled out from the supply spool 34, and the holding guide 43 and the optical fiber feeding state detection device 4 are pulled out.
7 and the coat removing device 51, the tip of the strand 8 is inserted into the pipe entrance from the anti-damage guide 99.

When the optical fiber core 7 enters the coat removal device 51, it is first heated to about 550° C. in the heating chamber 52, and a portion of the polyethylene 7a and silicone 7b is melted or decomposed. Then, after being cooled down to about 30° C. or lower in the cooling path 71, the remaining silicone 7b is dissolved in a sodium hydroxide solution (25!K) in the dissolution chamber 8I. The wire 8 leaving the dissolution chamber 81 passes through a washing chamber 91 and is dried in a drying path +01, and then is inserted into the tube 1 through a scratch-proof guide 99.

The tube inlet end 2 is located at the lowest end of the tube coil 5, so that the strand 8 is inserted into the tube 1 along a substantially tangential direction of the tube coil 5. The strand 8 is initially pushed into the coiled tube by 5 to 30 m. As a result, sufficient conveyance force is applied to the strand 8 by the inner surface of the tube due to the vibration of the tube, and the strand 8 reliably enters the inside of the tube. Note that the pushing length (initial insertion length) is determined by the inner diameter of the tube, the outer diameter of the wire, and the coefficient of friction between the wire and the inner wall surface of the tube. In the initial insertion, if the wire 8 is inserted while applying vibration to the tube, the insertion becomes easier.

Further, in order for the wire 8 to enter the tube smoothly, a certain amount of clearance is required between the wire 8 and the tube, and it is desirable that the clearance be 0.1 mm or more.

Next, when the vibration motors 21 and 22 are driven, since the vibration motors 21 and 22 are attached to the vibration table 14 in the positions and postures described above, the vibration motors 21 and 22 are driven.
is subjected to a torque about the central axis C and a force in the direction of the central axis. As a result, any point on the vibration table vibrates along the spiral H shown in FIG. This vibration is transmitted from the vibration table 14 to the wire 8 through the fixing fitting 31, the bobbin 27, and the tube coil 5 in this order.

It is thought that the movement of the strand changes depending on the type of vibration, the physical properties of the strand, the inner diameter of the tube, etc., or that the strand moves through the tube in the following manner.

As shown in FIG. 6, the bottom surface of the inner wall of the tube is vibrating at a vibration V centering on O. The vibration angle is θ, and the maximum acceleration is n times the acceleration of gravity g (nsjnθ>1). Since it is difficult to imagine that the strands are in contact with the bottom surface of the pipe inner wall over the entire length, it is assumed that they are in contact at pitch L. Let the contact point be a. Contact point a occurs when the vertical acceleration of the bottom of the inner wall of the tube becomes downward equal to g, that is, the separation line 2. It leaves and is released at the above breakaway point PI. The released strand starts flying at the current speed v2 and radiation angle θ.

On the other hand, since the non-contact point a is not a rigid body, the contact point a
Do a different exercise. That is, the upward force of the contact point a cannot be obtained by the vibration V, and after being released above the separation line 1, the downward force generated as the contact point a moves is received.

As a result, the vehicle lands on the landing line f12 at a new contact point S, which is different from the first contact point a. If the vibration (2) of the bottom surface of the tube inner wall at this time is in the upward direction, it continues to rise and is emitted on the separation line ILI. If you land when the vibration V is in the downward direction, once you have descended to the lowest position, you will begin to ascend and move to the departure line 2. released above. Such waviness motion is repeated for each vibration or every several vibrations, and the strand moves through the tube. The most efficient condition is the landing line 1 during the rise of each vibration. coincides with the departure line 12, and the wire starts flying at the same time as it lands.

Strictly speaking, friction phenomena, repulsion phenomena, etc. between the bottom surface of the tube inner wall and the strands should be taken into consideration. Needless to say, when the flying strand comes into contact with the upper surface of the pipe inner wall, the progress state is different.

In addition, when n sin θ≦1, the wire does not fly,
Depending on the state of friction between the bottom surface of the tube inner wall and the wire, the wire may slide and advance.

The strands 8 are propelled by the coil circumferential component of the force received from the inner wall of the tube 1 as described above, and enter the tube. Since the coil axis and the central axis C of the vibration table 14 coincide, the strands 8 in the tube move in a circular motion (
In the example of FIG. 3, a circular motion in the counterclockwise direction P is performed.

The explanation will be given by returning to FIG. 2 again.

When the above-mentioned spiral vibration is applied to the tube coil 5 through the vibration table 14, the strands 8 supplied from the tube entrance end 2 below the coil 5 continuously enter the tube 1 due to the article conveying force of the vibration. Go. That is, the optical fiber core 7 is unwound from the supply spool 34, and the holding guide 43, the optical fiber feeding state detection device 47, the coat removal device 51, the damage prevention guide 99, the tube entrance end 2, the coiled tube 1, The tube outlet end 3 is moved in this order by the vibration of the coil 5, and is inserted through the entire coil 5 after a predetermined time.

During the insertion of the strand 8, if the tube insertion speed changes due to some factor, this will affect the feeding state of the optical fiber core 7 at the position of the optical fiber height position detector 49, This is immediately detected by the detector 49. That is, if the optical fiber height position detector 49 detects that the optical fiber core 7 is over-tensioned, the signal is sent to the drive motor 38 to increase the spool rotation speed and increase the supply speed of the optical fiber core 7. do. Further, if excessive slack in the optical fiber coated wire 7 is detected, the drive motor 38 is similarly controlled to slow down the supply speed of the optical fiber coated wire 7. In this way, an abnormal transport state of the optical fiber core 7 is immediately detected, corrected, and restored to a normal transport state.

The strands were inserted into the steel pipe using the apparatus shown in FIG. 2 under the following conditions.

Vibration conditions: Vibration angle of the coil with respect to the horizontal plane 15 degrees Frequency 20 2 Vertical component of total amplitude 1.55 mm There were no surface scratches on the wire inserted into the steel pipe, and a heat-resistant optical fiber of good quality could be obtained.

(Example ■) The metal tube is a seamless stainless steel pipe (SUS304) with an outer diameter of 10.3 mm and a wall thickness of 0.9 mm, and is expanded to have an outer diameter of 1.011101 mm, a wall thickness of 0.1 On+m, and a length of It has been finished into a 1000m long tube. The optical fiber before insertion into tube 1 is a silica-based glass optical fiber (diameter 125 μm)
It has a diameter of 0.7 mm and is coated with silicone as a primary coat and polyester as a reinforcing coat.

The equipment used and the vibration conditions for fiber insertion were the same as in the example.

The coating material was removed as follows.

First, the core wire 7 is heated to about 300° C. in the heating chamber 52 to melt and decompose the polyester 7a, and then heated to about 300° C. in the cooling chamber 71.
Cooled below ℃. Then, the remaining polyester 7a was dissolved in the dissolution chamber 81 using benzene. As a result, the strand 8
A core wire coated with silicone 7b was obtained, and this was inserted into the steel pipe.

There were no surface scratches on the core wire inserted into the steel tube, and a high-quality heat-resistant optical fiber could be obtained.

This invention is not limited to the above embodiments. Combustion methods, peeling methods, etc. can be applied as methods for removing the coating material. Further, as the insertion method, the above-mentioned pushing method, exchanging method, method using flow of pressurized fluid, etc. may be used. The supply of optical fibers into the pipe is not limited to just one, but may also include a plurality of optical fibers depending on the pipe inner diameter and the optical fiber diameter. In the above description, the pipe through which the optical fiber is inserted is a steel pipe, but of course this combination is not limited, and various specific examples can be considered, such as the optical fiber being inserted into a metal pipe made of aluminum pipe, steel pipe, or the like.

(Effects of the Invention) The heat-resistant optical fiber obtained by the manufacturing method of the present invention has at least no reinforcing coat such as nylon or polyethylene, and is covered with a metal tube, so
The coating material will not decompose or burn and the optical fiber will not deteriorate even if exposed to high temperatures exceeding Further, even if the metal tube does not have an opening in the longitudinal direction, the internal pressure of the tube does not increase due to the generated gas, so the connecting portion of the metal tube or the metal tube itself will not be destroyed. Therefore, even if the optical fiber is exposed to high temperatures during a fire or when measuring the temperature inside a furnace, it is possible to transmit signals reliably or accurately.

Furthermore, since the coating material on the optical fiber core is removed immediately before insertion into the tube, surface defects such as scratches will not occur on the wire. Therefore, a high quality heat-resistant optical fiber can be obtained.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view showing an example of a heat-resistant optical fiber manufactured by the method of the present invention, FIG. 2 is a side view showing an example of the device for inserting the optical fiber of the present invention, and FIG. 3 is a side view of the device. FIG. 4 is a plan view of the vibration table; FIG. 4 is a front view showing an example of a bobbin attached to the vibration table; FIG.
The figure is a detailed view of the coat removing device 51 provided in the above-mentioned apparatus, and FIG. 6 is a diagram illustrating the principle of conveying the strands within the tube. DESCRIPTION OF SYMBOLS 1... Metal tube, 5... Tube coil, 7... Optical fiber core wire, 8... Fiber wire, 11... Frame, +
4--Vibration table, 21.22--Vibration motor, 27--Bobbin, 33--Optical fiber supply device,
38... Drive motor, 43-... Holding guide, 47-
...Speed difference detection device, 50...Control device, 51...
Coat removal device, 52... Heating chamber, 54... Heating coil, 71... Cooling path, Old... Melting chamber, 91...
Washing room, 101...drying path.

Claims (3)

[Claims] (1) In a method for manufacturing a heat-resistant optical fiber in which the optical fiber core is inserted into a metal tube with a gap and an extra length, an optical fiber core in which a glass fiber strand consisting of a core and a cladding is coated with a coating material. A method for producing a heat-resistant optical fiber, which comprises preparing a wire, removing part or all of the coating material of the optical fiber core, and inserting the core into a metal tube. (2) A method for producing a heat-resistant optical fiber according to claim 1, wherein part or all of the coating material is removed by heating the optical fiber core to a temperature higher than the melting or decomposition temperature of the coating material. (3) The method for manufacturing a heat-resistant optical fiber according to claim 1, wherein part or all of the coating material is removed by dissolving the coating material with a solvent.