JPS5925733B2 - Manufacturing method of optical transmission line - Google Patents

Description

[Detailed description of the invention] The present invention relates to optical transmission lines (optical fibers).

(hereinafter also simply referred to as fiber).
A known method for manufacturing optical fibers is to first create a central rod-shaped preform (preformed material), and then stretch this preform into a linear shape using an electric furnace or an oxygen/hydrogen torch to form a fiber. .

Recently, CVD (Chemical) is used to create preforms.
How to use alVaporDeposHion) (
The CVD method (hereinafter referred to as CVD method) is widely used. CV
Method D involves bringing a reaction gas (or a mixed gas of a carrier gas and a reaction gas) into contact with the surface of the target solid in a reaction tube kept at high temperature, and depositing products from the chemical reaction of the reaction gas on the solid surface. This is a method of forming a surface thin film layer. In the case of producing the above preform by such a CVD method, for example, a SiO2 glass layer is deposited as a cladding layer on the inside of a commercially available standard size quartz glass tube, and then a core layer having a refractive index higher than that of the cladding layer is made of, for example, GeO2. The added SiO2 glass layer is deposited, and the glass tube is formed into a central rod shape using a glass lathe or the like while rotating and heating to form a preform. When a preform produced by the CVD method is spun into a fiber by the method described above, the dimensions of the fiber are determined by the following relational expression based on the law of conservation of matter.

2Lf to Dp2 (-)=(□) =1 ・・・・・・・・・・・・(1
) Df'fL, where Dp = outer diameter of preform Df = outer diameter of fiber rp ■ Core radius of preform rf = core radius of fiber L ■ Length of preform Lf = length of fiber Transforming equation (1) The following equation is obtained.

”=−L・・・・・・・・・・・・(2) (or −=−) In other words, when producing a fiber with a certain predetermined outer diameter and core diameter, the outer diameter of the preform It is necessary to define the diameter and core diameter in advance so that the above equation (2) holds true.

Furthermore, extremely high precision is required for the outer diameter of the fiber, and for this purpose, it is necessary to increase the precision of the outer diameter of the preform. In order to adjust the outer diameter and core diameter of the preform and to adjust the outer diameter dimension accuracy, conventionally, a cladding layer and a core layer (hereinafter abbreviated as deposited layer) are deposited on the inner surface of the glass tube or the outer surface of the glass rod during preform manufacturing. A method is used to adjust the thickness of the

However, since preforms made by CVD or flame hydrolysis are created by applying a deposited layer to a glass tube or glass rod and then deforming it, it is difficult to precisely define the thickness of the deposited layer in advance. In practice, it has been very difficult to obtain a predetermined outer diameter and core diameter. Furthermore, since the outer diameter of the preform is also subjected to mechanical deformation force during molding, it is generally difficult to improve dimensional accuracy. Therefore, in view of the above-mentioned circumstances, it is an object of the present invention to extremely easily adjust the outer diameter and core diameter of a preform, as well as adjust the outer diameter dimensional accuracy, and to achieve dimensional accuracy that has the desired outer diameter and core diameter. The object of the present invention is to provide an improved method that allows easy production of high quality optical transmission lines.

The method according to the present invention is a method for manufacturing a fiber from a preform, in which the outer circumferential surface of the preform is processed and the outer diameter dimension D is adjusted to the core diameter 2r of the preform.
In this method, the outer diameter Df and core diameter 2rf of the fiber to be manufactured are adjusted so that D,/Df-RP/Rf holds, and then the fiber is spun.

That is, the method of the present invention adjusts the outer diameter and core diameter of the fiber and adjusts the dimensional accuracy of the outer diameter of the fiber by processing and finishing the outer diameter of the preform to desired dimensions and accuracy. . Hereinafter, the present invention will be described in detail based on specific examples with reference to the accompanying drawings.

The figure simply shows an example of a fiber manufacturing process that utilizes the CVD method during preform manufacturing.

To briefly explain this, first, a SlO2 glass cladding layer 2 of an appropriate thickness is coated on the inner surface of a support glass tube 1 by CVD. A preform 4 is formed by depositing a SiO2-GeO2 glass core layer 3 and deforming it into a solid rod shape.
The preform 4 is then spun into a fiber 6. As an example, a commercially available fused silica glass tube (diameter 17 to 20φ) is used as the glass tube 1, and the outer diameter D of the preform 4 and the diameter of its SlO2 to GeO2 glass core portion 5 (hereinafter referred to as core diameter ) 2r is P D = 10 ± 1.0 mm φ P 2r = 3.5 ± 0.11 Lm φ p .

The above-mentioned accuracy of outer diameter 2r can be easily achieved for a preform manufactured by the CVD method. When a fiber with a standard outer diameter of 125 μmφ is manufactured from the above preform by the conventional method, the outer diameter of the fiber is Dfl and the core diameter is 2r.
From the above equation (2), f is Df-125±12.5 μmφ 2rf-44±1.3 μmφ.

The dimensional accuracy of the outer diameter of this fiber is as follows:
It is well known that this value is insufficient when a light emitting source such as a light emitting diode (light emitting diode) or a laser is coupled to a light receiving section, or when fibers are coupled together for practical use. Accordingly, the present invention relates to a method of improving the dimensional accuracy of the outer diameter of a fiber and also making the core diameter a desired size, by adjusting the preform outer diameter D. Next, a specific example will be given. [First example] Df
=125±2μmφ2rf−85±2.5μmφ (method) From the above formula (2), the preform outer diameter is D −
5.15±0.08m7! Adjust to Lφp.

In this case, the specific adjustment method is to first apply force to the outer peripheral surface of the preform by a chemical etching method using hydrogen fluoride (HF), for example, by melting the SiO2 glass, or by a mechanical polishing method such as sandblasting. The outer diameter D is approximately 5.27F! ! After adjusting to φ, the outer diameter D is further adjusted to 5.1 by precision polishing such as centerless polishing.
It is advantageous to use a method that achieves a finish of 0.08 Ttmφ (indicated by a virtual line A in the figure).

[Second example] When using a fiber of Df-125±2μmφ 2rf30±0.9μmφ (method) From the above formula (2), the preform outer diameter is D,
=14.58±0.23mmφ.

As adjustment methods in this case, two methods as shown below are possible.

(b) After finishing the outer surface of the preform to a diameter of 10±0.1 muφ using the method described in [Example 1] above, cover the preform with a commercially available quartz glass tube of an appropriate size, and use, for example, an oxygen-hydrogen torch to heat the preform. Weld together with the quartz glass tube.

Next, the outer diameter of the preform is adjusted and finished to 14.58±0.23 mmφ (indicated by imaginary line B in the figure) using the same method as in [Example 1].

(b) SlO2 fine powder (soot) on the outer surface of the preform
This is heated and melted in an electric furnace or an oxygen-hydrogen torch to vitrify it, and the outer diameter of the preform is finished to 14.58±0.23 mmφ using the method described in [Example 1].

Incidentally, although not shown in specific numbers, when it is desired to manufacture fibers with different outer diameters, the preform outer diameter D is determined by the above formula (2), and the above p [first example] and [
Adjustment can be made using the method explained in [Second Example].

Further, the preform is not limited to a glass tube, and may be one in which a low refractive index glass layer serving as a coating layer is adhered to the outer periphery of the central rod. As is clear from the above description, according to the present invention, by adjusting the outer diameter of the preform, the outer diameter, core diameter, and outer diameter dimensional accuracy of the fiber can be arbitrarily and easily selected.

Further, when carrying out this method, the adjustment can be performed using a very simple method, so it can be said that it has extremely high practical value.

[Brief explanation of the drawing]

This figure is a schematic diagram of the optical transmission line manufacturing process using the CVD method. Explanation of symbols, 1...Glass tube, 2...
cladding layer, 3... core layer, 4... preform, 5... core section, 6... optical fiber.

Claims (1)

[Claims] 1 Using a glass tube as a base, a glass layer containing the core of the optical transmission line is formed and deposited on the inner wall of the tube by a chemical reaction, and then the whole is formed into a solid rod-shaped preform, and then the outside of the preform is formed. After adjusting the outer diameter of the preform so that the ratio between the diameter and the diameter of the planned core portion is equal to the ratio between the outer diameter and the core diameter of the optical transmission line to be manufactured, the preform is spun into an optical transmission line. Features: A manufacturing method for optical transmission lines.