JPH02184546A - Production apparatus of optical fiber - Google Patents

Abstract

PURPOSE:To form a dense and uniform carbon coating film on the surface of an optical fiber by using a CVD reaction furnace constructed of a plurality of reaction tubes connected in series and connecting each reaction tube to an exhaust tube and a feed tube to feed a raw material compound which deposits a carbon coating layer by thermal decomposition. CONSTITUTION:A CVD reaction furnace 3 is constructed by connecting a plurality of reaction tubes 5 in series and connecting each reaction tube to an exhaust tube 8 and a feed tube 7 to feed a raw material compound (e.g. benzene) which deposits a carbon coating layer by thermal decomposition. An optical fiber preform is heated and spun in a spinning furnace 2 and the obtained bare optical fiber 1 is successively introduced into each reaction tube 5 of the CVD reaction furnace 3. At the same time, the raw material compound is introduced through the feed pipe 7 and heated with a heater 6 to effect the thermal decomposition and form a carbon coating film on the surface of the bare optical fiber 1. The carbon radical generated by the thermal decomposition of the raw material compound has short residence time in each reaction tube 5 and, accordingly, the polymerization of the carbon radical can be prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an apparatus for forming a carbon film on the surface of an optical fiber, and the present invention relates to an apparatus for forming a carbon film on the surface of an optical fiber. By connecting them to form a CVD reactor, it was possible to obtain a uniform and dense carbon film at a high deposition rate.

[Prior Art] When a silica-based optical fiber comes into contact with hydrogen, absorption loss due to the molecular vibration of hydrogen molecules diffused into the fiber increases, and PtOs, which is contained as a dopant, increases.
G eot, Bto 3, etc. react with hydrogen to form 01(i
Since the OH groups are incorporated into the fiber glass, there is a problem in that transmission loss due to absorption of OH groups also increases.

In order to deal with such adverse effects, a method of filling an optical cable with a liquid composition having hydrogen absorption ability (Japanese Patent Application No. 1983) was proposed.
-251808), but the effect is not sufficient and the structure is complicated, resulting in economical problems.

In order to solve the above problem, it has recently been announced that a carbon film can be formed on the surface of an optical fiber by the CVD method, thereby improving the hydrogen resistance of the optical fiber. This manufacturing method uses bare optical fiber spun from a spinning furnace.
Thermal CV along with raw material compounds mainly consisting of hydrocarbon compounds
The raw material compound is supplied into the D reactor and heated to thermally decompose the raw material compound to deposit a carbon film on the surface of the bare optical fiber.

[Problems to be Solved by the Invention] The deposition rate of a carbon film is controlled by the contact time between carbon radicals generated by thermal decomposition of a raw material compound and a bare optical fiber. Therefore, in order to increase the deposition rate, it is necessary to slow down the spinning speed of the optical fiber or increase the length of the CVD reactor in order to lengthen the contact time.

On the other hand, carbon radicals generated by thermal decomposition of a raw material compound tend to polymerize when heated for a long time.

Therefore, if the length of the CVD reactor is increased, the carbon radicals in the furnace will be widely distributed from those with low molecular weight to those with high molecular weight, making it impossible to obtain a carbon film with uniform quality. Furthermore, it is known that the carbon film formed by the precipitation of polymerized carbon radicals is not dense, so the hydrogen permeation blocking effect is low, and the hydrogen properties of the obtained optical fiber are also poor.

Therefore, conventionally, it has not been possible to obtain an optical fiber having a dense and uniform carbon film formed on its surface at a high spinning speed.

This invention was made in order to solve the above problem, and by arranging CVD reactors with short furnace lengths in multiple stages, it is possible to prevent carbon radicals from becoming polymers and to keep the inside of the CVD reactor constantly low. The object of the present invention is to provide an apparatus that forms a dense and uniform carbon film on the surface of a bare optical fiber at a high deposition rate by filling the surface with molecular weight carbon radicals.

[Means for Solving the Problems] In the optical fiber manufacturing apparatus of the present invention, a reaction tube is provided in which a raw material compound supply pipe for supplying a raw material compound capable of depositing a carbon film by thermal decomposition and an exhaust pipe are respectively connected. The solution was to use a CVD reactor equipped with a plurality of CVD reactors connected in series.

[Function] Since the CVD reactor is constructed by connecting a plurality of reaction tubes in series, each having a raw material compound supply pipe and an exhaust pipe connected to each other, carbon radicals generated by thermal decomposition of the raw material compound are absorbed in each reaction tube. Since the residence time of carbon radicals is shortened, polymerization of carbon radicals can be prevented.

Furthermore, by connecting multiple reaction tubes in series, CV
Since the reactor D has a longer furnace length, the carbon film can be deposited efficiently.

The present invention will be described in detail below.

FIG. 1 shows an embodiment of the optical fiber manufacturing apparatus of the present invention. In FIG. 1, reference numeral 1 indicates a bare optical fiber. The bare optical fiber 1 is obtained by heating and spinning an optical fiber preform (not shown) in an optical fiber spinning furnace 2.The bare optical fiber 1 is spun, and at the same time, the optical fiber is placed in the lower stage of the spinning furnace 2. It is designed to be supplied into a CVD reactor 3 provided therein. This CVD reactor 3 is made up of a plurality of reactors 4 connected in series to maintain airtightness, and each reactor 4 carries out a CVD reaction inside. It consists of a generally cylindrical reaction tube 5 which is advanced to form a carbon film on the surface of the bare optical fiber 1, and a heating element 6 which heats the reaction tube 5. A raw material compound supply pipe 7 for supplying the raw material compound is attached to the upper part of each reaction tube 5, and an exhaust pipe 8 for exhausting unreacted gas and the like is attached to the lower part. Reaction tube 5... and heating element 6 for heating it...
・Can be selected appropriately depending on the heating temperature, etc.
In addition to using a resistance heating furnace, an induction heating furnace, an infrared heating furnace, etc., the heating element 6 can also be one that generates plasma using high frequency waves or microwaves to ionically decompose the raw material compound. Can be used. Furthermore, seal gas supply pipes 9.9 are installed at the upper and lower parts of the CVD reactor 3, respectively, and inert gases such as helium and nitrogen are supplied into the CVD reactor 3 through these seal gas supply pipes 9.9. It is designed to keep the interior airtight by supplying it to the inside. Furthermore, in the lower stage of this CVD reactor 3, there is a resin liquid coating device IO and a curing device! 1 are provided continuously, so that a protective coating layer can be formed on the carbon film formed on the surface of the bare optical fiber 1 in the CVD reactor 3.

In order to form a carbon film on the surface of a bare optical fiber using such a manufacturing apparatus, the following steps are performed.

The optical fiber preform is heated and spun in the optical fiber spinning furnace 2, and the C
Reaction tube 5 of VD reactor 3..., resin liquid coating device 1O1
It is inserted into the curing device 11 and fed so as to run on these central axes at a predetermined linear speed. Next, the heating elements 6 are made to generate heat to heat the inside of each reaction tube 5 to a predetermined temperature, and the seal gas and raw material compounds are supplied into the CVD reactor 3 from the seal gas supply pipes 9 and 9. A raw material compound for forming a carbon film is supplied into each reaction tube 5 from the tubes 7 . The raw material compound supplied from the raw material compound supply pipe 7 is not particularly limited as long as it is a carbon compound that can be thermally decomposed to form a carbon film, but from the viewpoint of the properties of the carbon film formed and its precipitation rate, Carbon number 15
The following hydrocarbons or halogenated hydrocarbons are preferred. These raw material compounds can be supplied in a gaseous state or diluted with an inert gas, etc.
The feeding rate is appropriately selected depending on the type of raw material compound, heating temperature, etc., but is usually 0.2 to 1. (Approximately 500 H!/min is suitable.The heating temperature of the heating element 6 is appropriately selected depending on the type of the raw material compound mentioned above.
~1200°C is suitable. If the heating temperature is lower than 500℃, the thermal decomposition of the raw material compound will not proceed;
If this is done, a large amount of by-product soot will be generated, and the structure of the carbon film formed on the surface of the bare optical fiber 1 will become close to a graphite structure and become brittle, which is not preferable. Furthermore, in order to prevent the generation of soot as a by-product, it is preferable that the heating temperature be kept slightly lower than the thermal decomposition temperature of the raw material compound. The bare optical fiber l on which the carbon film has been formed in this manner is introduced into a resin liquid coating device 10 provided at the lower stage of the CVD reactor 3, and then inserted into a curing device 11 for curing the resin liquid. The bare optical fiber 1 inserted into the resin liquid coating device IO is coated with an ultraviolet curable resin or a thermosetting resin to form a protective coating layer, and then subjected to curing conditions suitable for the applied resin liquid. A protective coating layer is formed by curing in a curing device 11 having a curing device II.

In this way, a CVD reactor 3, a plurality of reactors 4...
When configured by connecting them in series, the contact time between carbon radicals and bare optical fibers in each reactor 4 is short, but the contact time is longer for the CVD reactor 3, so high-quality A carbon film can be efficiently deposited. Therefore, the spinning speed of the optical fiber can be made faster than before.

Also, among the carbon radicals generated in each reactor 4..., those that did not precipitate on the surface of the bare optical fiber 1 are immediately removed from the exhaust pipe 8 attached to each reactor 4...
Since the carbon radicals are discharged to the outside, the carbon radicals are not polymerized in the reaction tube 5. Therefore, the carbon film deposited on the surface of the bare optical fiber 1 is made of low-molecular carbon radicals, has a uniform and dense structure, and has a high ability to block hydrogen permeation.

In addition, in the above apparatus, the carbon coating is formed directly on the surface of the bare optical fiber 1 in the uppermost reactor 4, but in the subsequent reactors 4, the carbon film is formed in the upper stage. Since a new carbon film is formed on the carbon film, even if there are pinholes in the carbon film formed in the upper reactor 4, a new carbon film will be deposited on the pinholes. This will prevent pinholes from growing. Therefore, compared to the conventional case where a thick carbon film is formed in one step, fewer pinholes are generated, and higher hydrogen permeation blocking ability can be obtained.

In addition, in the manufacturing apparatus shown in FIG. 1, there are three reactors 4.
Although the manufacturing apparatus of the present invention is not limited to this example, it is sufficient to connect two or more reactors 4... in series, and the number of connected reactors 4... It can be appropriately selected depending on the raw material compound to be used, the spinning speed of the optical fiber, etc.

Furthermore, in the apparatus shown in FIG. 1, the CV
Although the D reaction furnace 3 is provided separately, the spinning furnace 1 and the CVD reaction furnace 3 are connected to each other in an airtight manner, and the resin liquid coating device 10 and the curing device il are also connected to each other in an airtight manner. Needless to say, it's okay to do so.

[Example] (Example) Three infrared heating furnaces each having an inner diameter of 50 mm and a length of 100 mm were connected in series to the lower stage of a spinning furnace for spinning bare optical fibers from an optical fiber base material, as shown in Fig. 1. A spinning device was installed in the upper stage of this optical fiber manufacturing device, and an optical fiber mother having an outer diameter of 30 mm and having a core impregnated with G e Oy as a dopant was prepared. The material was installed.

This optical fiber preform was heated to 2000° C. and spun into a single mode fiber having an outer diameter of 125 μm at a spinning speed of 20 m/min, and the spun fiber was inserted into the above manufacturing apparatus. At this time, the inside of the CVD reactor was heated to 1200°C, and 1,1.2 diluted with argon gas to about 5 vol.
Trichloroethane gas was supplied into each reaction tube from the raw material compound supply port at a flow rate of 3 f2/min, and each exhaust tube was evacuated at an exhaust pressure of 14 mml-1 tO to form a carbon film on the surface of the bare spun fiber. Furthermore, urethane acrylate resin liquid (Young's modulus 70 kg/mI", elongation 6
An optical fiber coated with a carbon film is inserted into a die spot for UV resin coating sealed with 0%), and a resin liquid is applied to it, and the resin liquid is cured using a UV lamp to form a protective coating. A 300 μm optical fiber was used.

(Example 2) An optical fiber was manufactured in the same manner as in Example 1 except that benzene was used as the raw material compound.

(Example 3) An optical fiber was manufactured in the same manner as in Example 1 except that the spinning speed was 40 m/min.

(Example 4) The optical fiber manufacturing apparatus used in Example 1, which consisted of three reaction tubes, was changed to an apparatus consisting of four reaction tubes, and the spinning speed was changed to 6.
An optical fiber was manufactured in the same manner as in Example 1 except that the speed was 0 m/min.

(Comparative Example 1) Example! Example 1 was carried out in exactly the same manner as in Example 1, except that two of each of the three raw material supply pipes and three exhaust pipes in the optical fiber manufacturing apparatus used in Example 1 were closed, and one raw material supply pipe and one exhaust pipe were used. Manufactured optical fiber.

(Comparative Example 2) The furnace length of the CD reactor of the optical fiber manufacturing equipment used in Comparative Example 1 was 300 mm (300 mm of the furnace length of the manufacturing equipment of Example 1).
An optical fiber was manufactured in exactly the same manner as in Comparative Example 1, except that the optical fiber was increased (2 times).

(Test Example 1) After measuring the thickness of the carbon coating formed on the surface of each optical fiber obtained in Examples 1 to 4, Comparative Example 1, and Comparative Example 2, these were measured to have a diameter of 150+ nm,
Formed into a bundle with a length of 1 km, hydrogen partial pressure 1 stm, temperature 80
The sample was left in a pressurized container at ℃ for 48 hours, and the increase in absorption loss due to hydrogen was measured as the increase in transmission loss at a wavelength of 1.24 μm. The results are shown in Table 1.

Table 1 From Table 1, it can be seen that the optical fiber manufacturing apparatus of the present invention can spin at a high spinning speed regardless of the type of raw material compound.
It was confirmed that a carbon film with sufficient thickness could be formed.

Furthermore, the amount of increase in transmission loss was small, and it was confirmed that the formed carbon film was not dense.

(Test Example 2) The apparatus used in Example 1 (three reaction tubes are connected and the furnace length is 1)
00 mm), the device used in Comparative Example 1 (furnace length 100 mm),
Two of the three raw material supply pipes and three exhaust pipes of the device of Example 1 of n+m were blocked, and one raw material supply pipe and one exhaust pipe were closed.
1,1.1 trichloroethane was supplied as a raw material compound at a rate of 312/min to the equipment used in Comparative Example 2 (the equipment used in Comparative Example 1 with a furnace length of 300 mm). and the spinning speed was 20 m/min, 4
The thickness of the carbon film formed on the surface of the bare optical fiber was confirmed by SEM photography while changing the speed to 0 m/min and 60 m/min. The results are shown in FIG. In FIG. 2, the solid line represents the case where the apparatus of Example 1 is used, the dotted line represents the case where the apparatus of Comparative Example 1 is used, and the -dotted chain line represents the case where the apparatus of Comparative Example 2 is used.

From FIG. 2, it is confirmed that the manufacturing apparatus of Example 1, which is an embodiment of the manufacturing apparatus of the present invention, can form a carbon film with a thickness sufficient to exhibit hydrogen permeation blocking effect even when the spinning speed is increased. did it.

[Effects of the Invention] As explained above, the optical fiber manufacturing apparatus of the present invention includes a raw material compound supply pipe that supplies a raw material compound capable of depositing a carbon film by thermal decomposition, and an exhaust pipe that are connected to each other. Since it is equipped with a CVD reactor in which a plurality of reaction tubes are connected in series, the residence time of carbon radicals generated by thermal decomposition of raw material compounds in each reaction tube is shortened, so that the polymerization of carbon radicals is reduced. It is possible to prevent the formation of a dense and uniform carbon film on the surface of the bare optical fiber.

In addition, since multiple reaction tubes are installed in series, the length of the CVD reactor can be increased, and the contact time between carbon radicals and bare optical fibers can be increased, increasing the deposition rate of the carbon film. Therefore, optical fiber can be spun at high speed.

Furthermore, in each reaction tube that makes up the CVD reactor, a new carbon film is deposited on the carbon film formed in the upper reaction tube, so pinholes etc. are formed in the carbon film formed in the upper reaction tube. Even if this occurs, a new carbon film is formed on the pinhole, preventing further growth of the pinhole, and the resulting carbon film has a high hydrogen permeation blocking ability.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of an optical fiber manufacturing apparatus of the present invention, and FIG. 2 shows optical fibers when using the optical fiber manufacturing apparatus of the present invention and when using a conventional manufacturing apparatus. It is a graph showing the relationship between the fiber spinning speed and the thickness of the carbon coating formed. Figure 2 ■... Bare optical fiber, 3... CVD reactor, 4... Reactor, 5... Reaction tube, 7... Raw material supply pipe, 8... Exhaust pipe. space/l (m/min)

Claims (1)

[Claims] An apparatus for forming a carbon film on the surface of an optical fiber, in which a plurality of reaction tubes are connected in series to a raw material compound supply pipe that supplies a raw material compound capable of depositing a carbon film by thermal decomposition, and an exhaust pipe, respectively. Optical fiber manufacturing device characterized by comprising a connected CVD reactor