JP2697898B2 - Method for producing hermetic coated optical fiber - Google Patents

Description

The present invention relates to a method for producing a hermetic coated optical fiber known as an optical fiber having high long-term reliability.

[Related Art] An optical fiber is made of glass such as quartz glass, and when left for a long period of time, moisture acts on minute scratches on the surface of the optical fiber, and the scratches gradually increase. The optical fiber is in a state where some stress is applied when laying,
In an atmosphere where moisture is present, long-term reliability is lacking. Further, in a bad environment such as high temperature and high humidity, the action of moisture further increases, and deterioration of the optical fiber is remarkably accelerated.

A hermetic-coated optical fiber having a water-sealed hermetic coating made of a high-density inorganic film or the like on the surface of the optical fiber is known in order to prevent such moisture or moisture-induced hydrogen from entering the optical fiber. I have.

Hermetic coating on such an optical fiber is performed by a coating method, a plasma CVD method, a thermal CVD method, or the like.

Whichever method is used, the hermetic coating needs to be provided as a uniform film in the longitudinal direction of the optical fiber.

FIG. 3 shows an example of an apparatus for carrying out a method of manufacturing a hermetic coated optical fiber by a thermal CVD method, which is known as a method for uniformly providing a hermetic coating in the longitudinal direction among the above-described methods. Things. In this case, the optical fiber preform 1 is heated in a drawing furnace 2 to be softened and drawn to obtain an optical fiber 3. The obtained optical fiber 3 is passed through an outer diameter measuring device 4, the outer diameter of which is measured, and then passed through a reaction tube 5. A source gas such as C ₂ H _{2 and} a diluent gas such as He, N ₂ and Ar are introduced into the reaction tube 5 through a source gas introduction tube 6. These gases are heated in a reaction tube heating furnace 7 such as an electric resistance furnace, an infrared radiation heating furnace, or a high frequency induction heating furnace provided outside the reaction tube 5. Thus, the heat CV in the reaction tube 5
A D reaction occurs, and a hermetic coating 8 made of an inorganic substance such as C is formed on the surface of the optical fiber 3 to obtain a hermetic coated optical fiber 9. Reaction products and unreacted gas that have not adhered to the optical fiber 3 are exhausted to the outside via an exhaust pipe 10.

[Problems to be Solved by the Invention] However, in such a method for producing a hermetic coated optical fiber, the reaction product 11 that has not adhered to the optical fiber 3 adheres and accumulates on the inner wall of the exhaust pipe 10 and the exhaust pipe 10 , The pressure difference between the inside and outside of the reaction tube 5 changes with time. For example, according to the experiment, the differential pressure (= internal pressure−external pressure) of the reaction tube 5 increased by about 0.5 mmH ₂ O within 30 minutes after the start of the experiment. Due to such a phenomenon, the flow of the raw material gas in the reaction tube 5 changes. Therefore, when the long hermetic coated optical fiber 9 is manufactured, the film thickness of the hermetic coating 8 formed on the surface of the optical fiber 3 is reduced. In this case, there is a problem that it is difficult to form a uniform hermetic coating 8 in the longitudinal direction.

An object of the present invention is to provide a method of manufacturing a hermetic coated optical fiber that can easily form a hermetic coating uniformly in a longitudinal direction.

[Means for Solving the Problems] The means of the present invention for achieving the above object will be described. The present invention is directed to a method in which an optical fiber is passed through a reaction tube, and a raw material gas is supplied into the reaction tube. In a method of producing a hermetic coated optical fiber by forming a hermetic coating on the surface of the optical fiber, a differential pressure between the inside and outside of the reaction tube is measured, and the pressure from the reaction tube is measured so that the differential pressure becomes constant. It is characterized by controlling exhaust.

[Operation] As described above, when the differential pressure between the inside and outside of the reaction tube is controlled to be constant, the state of the flow of the raw material gas in the reaction tube is kept constant without changing over time, so that the hermetic coating is applied to the optical fiber. It is possible to easily manufacture a hermetic coated optical fiber that is uniformly formed in the longitudinal direction.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Parts corresponding to those in FIG. 3 are denoted by the same reference numerals.

FIG. 1 shows a first embodiment of the present invention.
In the present embodiment, a differential pressure gauge 12 is connected to the reaction tube 5, and a regulating valve 13 is connected to the exhaust pipe 10. Thus, the differential pressure between the inside and outside of the reaction tube 5 (= internal pressure-external pressure) is measured by the differential pressure gauge 12, and the obtained differential pressure data is input to the controller 14, and the regulating valve is adjusted so that the differential pressure becomes constant. Control to open 13 gradually.

FIG. 2 shows a second embodiment of the present invention.
In this embodiment, a differential pressure gauge 12 is connected to the reaction
Is connected to the intake pipe 15, the adjustment valve 13 is connected to the intake pipe 15,
The differential pressure between the inside and outside of the reaction tube 5 measured by the differential pressure gauge 12 is input to the controller 14, and the regulating valve 13 is controlled so that the differential pressure becomes constant. That is, while the exhaust pipe 10 is depressurized at a constant pressure by a suction means (not shown), as the differential pressure between the inside and outside of the reaction pipe 5 increases, the regulating valve 13 is gradually closed to reduce the amount of air sucked from the intake pipe 15, The suction pressure of the reaction tube 5 is gradually increased to control the pressure difference between the inside and outside of the reaction tube 5 to be constant.

Such a control method allows more precise control than in the first embodiment. Further, a plurality of intake pipes 15 may be provided. By doing so, the control range of the exhaust capacity is widened.

In the above embodiment, the case where the present invention is applied to the thermal CVD method is described.
The present invention can be similarly applied to a method of forming a film by another method such as the D method.

[Effect of the Invention] As described above, the method of manufacturing the hermetic coated optical fiber according to the present invention controls the differential pressure between the inside and outside of the reaction tube to be constant, so that the state of the flow of the source gas in the reaction tube is A long hermetic coated optical fiber having a uniform thickness in the longitudinal direction of the optical fiber, which is kept constant without changing over time, can be easily manufactured.

[Brief description of the drawings]

1 and 2 are longitudinal sectional views showing a schematic configuration of first and second embodiments of an apparatus for implementing a method of manufacturing a hermetic coated optical fiber according to the present invention, and FIG. 3 is a longitudinal section of a conventional apparatus. FIG. DESCRIPTION OF SYMBOLS 1 ... Optical fiber preform, 2 ... Drawing furnace, 3 ... Optical fiber, 4 ... Outer diameter measuring device, 5 ... Reaction furnace, 6 ... Source gas introduction pipe, 7 ... Reaction tube heating furnace , 8 Hermetic coating, 9 Hermetic coated optical fiber, 10 Exhaust pipe, 11 Reaction product, 12 Differential pressure gauge, 13 Regulator valve,
14 ... Controller, 15 ... Intake pipe.

Claims (1)

(57) [Claims] 1. A method for producing a hermetic-coated optical fiber by passing an optical fiber through a reaction tube, supplying a raw material gas into the reaction tube, and forming a hermetic coating on the surface of the optical fiber by a vapor phase growth method. Measuring the pressure difference between the inside and outside of the reaction tube, and controlling the exhaust from the reaction tube so that the pressure difference becomes constant.