JPH0372020B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a new method for manufacturing fused silica multiple fibers.

[Prior art]

Silica glass multiple fibers, which are useful as industrial image guides, are basically manufactured by bundling and drawing a large number of silica glass fibers, but the alignment state of the large number of optical fibers that make up the multiple fibers is important. In order to manufacture high-quality multiple fibers with good yield, it has been proposed to house a bundle of optical fibers to be drawn in a skin pipe and draw the entire skin pipe.

However, it has become clear from experiments conducted by the present inventors that the above-mentioned proposal for employing a skin pipe actually involves various problems that need to be solved. For example, when an optical fiber whose core and cladding are both dopant-containing quartz glass is used as the material to be drawn, and a skin pipe is made of natural or synthetic high-purity quartz glass, the temperature is high enough to allow the skin pipe to be drawn. ,for example
Although it is necessary to draw at 2000°C, the above-mentioned optical fiber becomes soft and exhibits great fluidity at such a high temperature, so its structure as an optical fiber is destroyed during the drawing process.

On the other hand, if a skin pipe made of multi-component glass with a low softening point is used, the opposite phenomenon to the above will occur, causing overflow in the skin pipe during drawing, causing abnormalities during drawing of the optical fiber bundle. The skin pipe loses its ability to prevent deformation and cannot perform its original function as a skin pipe.

From the above experimental results, as a skin pipe,
It will be appreciated that glass pipe having approximately the same drawing temperature as the optical fiber being drawn is suitable. By the way, Vycor glass pipe, which is a fluorine-doped quartz glass pipe, is currently known as a commercially available pipe made of such glass.
However, these pipes cannot be put to practical use as skin pipes for the following reasons. That is, the fluorine-doped quartz glass pipe has a problem in that it releases the fluorine contained as a dopant during the wire drawing operation, damaging the inner wall of the drawing furnace and the carbon heater. On the other hand, Vycor glass pipe has a porous structure and therefore has poor mechanical strength, so it cannot be put to practical use as a skin pipe.

[Summary of the invention]

Among the above-mentioned prior art, the present invention has the following features:
The present invention proposes a new manufacturing method capable of manufacturing high-quality multiple fibers with good yield, which is an optical fiber or its matrix having a cladding layer of silica glass with a drawing temperature of at least 1800°C on a silica glass core containing a dopant. This method is characterized in that a large number of pieces of material are housed in a skin pipe made of quartz glass having approximately the same drawing temperature as the quartz glass constituting the cladding layer, and drawn together with the skin pipe.

[Specific and detailed description of the invention]

In the present invention, the core of the optical fiber or its base material used as the drawing target is quartz glass containing a dopant, so even if the core is drawn at a high temperature of 1800°C or higher, the core becomes free-flowing and deformable. However, the outer cladding acts to prevent abnormal flow deformation of the core, thereby achieving a reduction in cross section while maintaining the structure as an optical fiber.

In the present invention, a quartz glass pipe whose drawing temperature is as described above is used as the skin pipe. Since such quartz glass does not contain a dopant, or if it does contain a small amount, it does not suffer from the above-mentioned corrosion problem and has excellent mechanical strength.

Natural or synthetic quartz glass is used as the quartz glass used to construct the skin pipe and the optical fiber cladding, and its drawing temperature can be measured by the following method.

Drawing temperature of quartz glass: A pipe with an inner diameter of 23 mm and an outer diameter of 26 mm is made from the quartz glass to be tested, and this is drawn at a drawing speed of 0.5 m/min to reduce the diameter to a pipe with an inner diameter of 2.3 mm and an outer diameter of 2.6 mm. The temperature of the glass being drawn when the tension required for drawing is 500 g.

The majority of the optical fibers included in the multiple fiber produced according to the present invention have a structure in which adjacent optical fibers and cladding layers are fused together with the cross section deformed into a hexagonal shape. Of course, it is necessary to adjust the diameter reduction rate during drawing so that the cladding layer of each optical fiber has a thickness that can perform its original function of preventing light leakage, and the average thickness of the cladding layer in the above fused structure (Total thickness of cladding layers of two optical fibers)
The minimum value that can perform the above function is usually 0.5 to 1 μm, although it varies depending on the refractive index difference between the core and the cladding.
That's about it. In the present invention, as long as the final thickness of the cladding layer is at least the above value, abnormal deformation of the core during drawing can be prevented.

Regarding the thickness of the skin pipe, it is appropriate that the thickness of the skin layer after drawing the wire is about 10 to 100 μm, and the dimensions of the skin pipe to be used should be determined by taking into account the diameter reduction rate due to drawing. Bye.

Optical fiber base material (for example, one with an outer diameter of about 1 to 5 mm) or an optical fiber obtained by drawing the base material (for example, one with an outer diameter of about 50 to 500 μm)
Fill the skin pipe in an aligned manner, then clean the surface of the filled material by cleaning with hydrofluoric acid using ultrasonic waves, etc., and then heat the skin pipe at a temperature of 1800 to 2200℃ with the inside of the skin pipe deaerated as necessary. By drawing the entire skin pipe at high temperature, multiple fibers having an outer diameter of, for example, about 0.5 to 5 mm can be manufactured.

[Best mode for carrying out the invention]

Next, the present invention will be explained in more detail with reference to Examples and Comparative Examples.

〔Example〕

Optical fiber with an outer diameter of 300 μm and a core made of pure silica glass doped with Ge and having a refractive index η ^20D of 1.473 and a core with an outer diameter of 200 μm and a 50 μm thick cladding layer made of pure silica glass with a purity of 99.999%.
20,000 wires were surface cleaned and drawn at a temperature of approximately 1,900.
Made of ℃ natural quartz glass, inner diameter 44.6mm, wall thickness
Filled in a close-packed manner in a 0.5mm skin pipe,
Clean the surface of each optical fiber and skin pipe with a 10% hydrofluoric acid aqueous solution while applying ultrasonic waves again.
After washing with water and drying, the inside of the skin pipe is constantly maintained in a high vacuum state of 10 ^-4 mmHg, and one end is opened.
By drawing at 2100°C, a multiple fiber with an outer diameter of 2 mm and 20,000 optical fiber strands was obtained. According to microscopic observation of the cross section of the multiple fiber, there were no defects where the cladding of adjacent optical fibers was torn and the cores were fused together.

[Comparative example]

The refractive index η 20D of the cladding layer of each of the 20,000 optical fibers to be drawn is doped with B ₂ O ₃ : ^1.440
A multiple fiber was manufactured which differed from Example 1 only in that it was made of pure silica glass. A cross-sectional microscopic observation of the resulting multiple fibers revealed many spots where the cores of adjacent optical fibers fused together or where gas was trapped between adjacent optical fibers, resulting in dark spots.

[Effects of the Invention] Using an optical fiber consisting of two layers, a core and a cladding, or its base material, it becomes possible to manufacture multiple fibers with excellent image transmission performance on an industrial scale. Since each optical fiber strand included in the multiple fiber has two layers as described above, a multiple fiber with a smaller outer diameter and excellent flexibility can be obtained compared to a multilayer structure with three or more layers. It will be done.

Claims (1)

[Claims] 1. An optical fiber having a cladding layer of quartz glass with a drawing temperature of at least 1800°C on a core of quartz glass containing a dopant, or a large number of its base material with a quartz glass having a drawing temperature approximately the same as that of the silica glass constituting the cladding layer. A method for producing multiple fibers characterized by housing them in a glass skin pipe and drawing them together with the skin pipe.