JPS60204641A - Production of core wire of optical fiber - Google Patents

Abstract

PURPOSE:To suppress the occurrence of increase in optical transmission loss in use for a long period and obtain the titled core wire having improved reliability for a long period, by irradiating the core wire with ultraviolet light before and/ or after coating the core wire with a thermosetting silicone resin layer. CONSTITUTION:An optical fiber 1 consisting of a core GeO2-SiO2 and clad SiO2 is drawn by heating a preform is directly passed through an ultraviolet light furnace having built-in ultraviolet lamps of 5-50W/cm or thermosetting silicone resin layer 2 is formed on the resultant drawn optical fiber 1 by applying a thermosetting silicone resin thereto, and baking the resin in a heating furnace is passed through the ultraviolet light furnace and irradiated with ultraviolet light. The thermosetting silicone resin layer 2 is then formed in the same manner as described above or the optical fiber 1 is directly extrusion coated with nylon on the outer periphery thereof to form a nylon coating 3 thereon. Thus, the titled core wire is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing a coated optical fiber that is unlikely to cause an increase in transmission loss under high temperature conditions or during long-term use.

(Conventional technology) FIG. 1 shows a standard wire structure.

An optical fiber 1 having a core Gθo, -5to, and a cladding StO is covered with a thermosetting silicone resin layer 2 and a nylon coating 3. In the manufacturing process of this core wire, first, a preform is heated to draw an optical fiber, and at the same time, thermosetting silicon is applied and baked in a heating furnace. After that, a core wire coating is applied through a nylon extrusion process.

Figure 2 shows the optical transmission loss characteristic curve of the optical fiber having the structure shown in Figure 1. The horizontal axis of the graph is the wavelength [μm], and the vertical axis is the optical transmission loss (14B/km). . The optical fiber core in Figure 1 has the initial characteristics shown by the solid line in the figure, but when this core is heated to 200°C, the optical transmission loss increases rapidly as shown by the dotted line in the figure. .

Although the value of the increase varies depending on the glass material that makes up the optical fiber, it is several dB/
It ranges from km to several tens of a:e/km. The increase in transmission loss at a wavelength of 1.4 μm that occurred in this case remained even after the fiber core was returned to room temperature, confirming that an irreversible change had occurred in the glass material itself. . Such a 200° C. temperature increase test is considered to be an accelerated test for examining general long-term reliability.

(Objective of the Invention) The object of the present invention is to solve the problem of increased optical transmission loss at a temperature of 200°C or higher in a core wire having a thermosetting silicone resin layer and a nylon layer covering the outer periphery of a glass optical fiber as described above. It is an object of the present invention to provide a pretreatment method that suppresses the above-described problems and improves the long-term reliability of the core wire.

(Structure of the Invention) The above-mentioned increase in optical transmission loss is caused by hydrogen molecules or OTT groups existing in the glass moving through the glass due to temperature rise and generating new OH groups in the core of the glass fiber. It is thought that this is the cause. Therefore, in order to prevent these bad molecules and ions from penetrating into the core, the present inventors formed a trap layer on the outer periphery of the optical fiber to trap them before they reach the core. After considering various methods to do this, we came up with a method of irradiating the optical fiber with ultraviolet rays. That is, based on the above reasoning, the present invention adds a new ultraviolet irradiation process as a pretreatment to the conventional fiber manufacturing process, and
The present invention provides a method for producing a cored optical fiber that is unlikely to cause an increase in loss even when heated to 00°C or higher.

That is, the present invention provides a method for manufacturing a cored optical fiber in which at least a thermosetting silicone resin layer is provided on the outer periphery of a glass optical fiber.
Another object of the present invention is to provide a method for producing a cored optical fiber, which comprises performing ultraviolet irradiation treatment at a stage after being coated with the thermosetting silicone resin.

The ultraviolet irradiation treatment is carried out by introducing the fiber into an ultraviolet furnace equipped with an ultraviolet lamp of about 5 to 50 W/ty+, for example, and passing it through it, but the amount of ultraviolet irradiation required depends on the degree of effect and the fiber used. Needless to say, the settings should be made depending on the material.

Since the thermosetting silicone resin is transparent, the ultraviolet irradiation step does not necessarily have to be carried out before coating with the thermosetting silicone resin, but should be carried out on the same line after the drawing line is coated with the thermosetting silicone resin. It's okay. It may also be sprayed before and after coating with thermosetting silicone resin. Alternatively, an ultraviolet irradiation step may be performed completely independently after the wire drawing step is completed and before the opaque secondary coating is applied.

The ultraviolet irradiation described above is performed on an optical fiber coated with a thermosetting silicone resin, and the purpose is not to oxidize the resin but to change the quality of the glass material.

The present invention will be specifically illustrated below based on Examples.

(Example) Heating a multimode glass fiber preform,
A multimode fiber with a core diameter of 5011 m' and a fiber diameter of 125 μm was drawn, and at the same time, a thermosetting silicone resin was applied and baked in a heating furnace to provide a thermosetting silicone resin layer with a diameter of 400 pm. Thereafter, a nylon-coated core wire having a diameter of 900 pm was obtained through a nylon extrusion process.

This core wire was used as a comparative example.

Figure 2 shows the initial characteristics (actual I%) of the obtained core wire and the characteristics (dotted line) when the core wire is heated at 200°C for about 4 hours.In this case, at wavelength i, 4 pm, The increase in optical transmission loss is approximately F3 dB/km.

Example 1゜Exactly the same design as used in Figure 2 (core Ge01-g
A cored optical fiber was fabricated using lOl, cladding sto,). However, in the process of drawing the fiber, the silicone resin was baked and hardened before being irradiated with ultraviolet light. In the case of irradiation, irradiation was performed for 0002 seconds using an ultraviolet oven with output 1 and Off. Thereafter, nylon coating was performed in a nylon extrusion process.

Figure 3 shows the initial characteristics of this core (shown by the solid line) and the 200
The characteristics (dotted line) are shown 4 hours after heating to °C.

In this case, the wavelength is 14 μn! The increase in optical transmission loss at 5 d
B/km, and it is clear that the high temperature characteristics were improved by ultraviolet irradiation.

Example 2 An optical fiber core having exactly the same design as that used in FIG. 2 was prepared. However, a new step was added between the drawing step and the next nylon extrusion step, in which the optical fiber is irradiated with ultraviolet light while being re-wound. Ultraviolet irradiation requires output 1. Use OKW's ultraviolet oven for 001 seconds.

Figure 4 υD, initial characteristics of this core (solid line) and 200℃
The characteristics (dotted line) are shown after heating to 4 hours and holding for 4 hours. In this case, the increase in optical transmission loss at a wavelength of 1.4 μm was only 1.5 dB/km.

Example 1. It is thought that the effect of stabilizing high-temperature properties is greater because the amount of ultraviolet irradiation is larger than in the case of .

(Effects of the Invention) As is clear from the above examples, the present invention provides a core wire in which a thermosetting silicone resin layer and a nylon break are provided on the outer periphery of a glass fiber, which is necessary for resin curing. This is a simple and effective method for improving the 200° C. high-temperature properties and general long-term reliability of the core wire by using an ultraviolet irradiation process, which is not considered to be the case. It is believed that the principle by which the method of the present invention improves high-temperature properties and general long-term reliability is that the glass itself is altered by ultraviolet irradiation to form a trap layer.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of an optical fiber core, FIGS. 2 to 4 are diagrams showing the optical transmission loss characteristics of the core with the structure shown in FIG. 1, and FIG. In this case, FIGS. 5 and 4 show the cases of the core wires according to Examples 1 and 2 of the present invention. In addition, the solid lines in Figures 2 to 4 indicate the initial characteristics, and the dotted lines indicate the 20
High temperature characteristics at 0°C are shown. Agents 1) Akira Agent Hagiwara Sale - Oni 2 Diagram Wavelength Eμ几〕 Spread Cp, m〕) Skin Long Litel 'J

Claims (1)

[Claims] In a method for manufacturing a cored optical fiber, the method comprises providing at least a thermosetting silicone resin layer on the outer periphery of a glass optical fiber,
1. A method for producing an optical fiber core wire, comprising performing ultraviolet irradiation treatment before coating with a thermosetting silicone resin layer and/or at a stage after coating with the thermosetting silicone resin.