JPH0366263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a novel method for manufacturing quartz glass 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, while natural or synthetic quartz glass is used as the skin pipe, the temperature at which the skin pipe can be drawn is high, e.g. 2000℃
However, at such high temperatures, the above-mentioned optical fiber softens and exhibits great fluidity, 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, fluorine-doped quartz glass pipes and Vycor glass pipes are currently known as commercially available pipes 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 the problem of emitting fluorine contained as a dopant during wire drawing, which corrodes the inner wall of the drawing furnace and the carbon electrode. 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]

The present invention proposes a new manufacturing method capable of manufacturing high-quality multiple fibers with high yield among the above-mentioned conventional techniques, in which both the core and the cladding layer thereon are made of quartz glass containing a dopant. and further has a support layer made of quartz glass with a drawing temperature of at least 1800°C on top of the optical fiber, or a large number of its base material made of quartz glass with a drawing temperature approximately the same as that of the silica glass constituting the support layer. It is characterized in that it is housed in a skin pipe and the skin pipe itself is drawn.

[Specific and detailed description of the invention]

In the present invention, the optical fiber or its base material used as the drawing target is quartz glass in which both the core and the cladding on the core have dopants, and the viscosity is considerably low at the drawing temperature of the skin pipe used in the present invention. Although it exhibits easy-flowing properties, it has a support layer made of quartz glass with a drawing temperature of 1800°C or higher on top of the cladding layer, which surprisingly causes the core and cladding to form during the drawing process. It acts to prevent abnormal deformation, and thus achieves a reduction in cross section while maintaining the structure of the 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 dopants or contains only a small amount of dopants, 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 constitute the skin pipe and the support layer of the optical fiber, 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 contained in the multiple fiber produced according to the present invention have a hexagonal cross-section and a structure in which adjacent optical fibers and support layers are fused to each other. The thickness of the fused support layer in the above fused structure (2
If the total thickness of each support layer of the optical fiber is at least 5 μm, abnormal deformation of the core and cladding can be prevented during drawing.

However, in order to more reliably prevent deformation, the thickness of the support layer of the optical fiber used as the drawing object or its base material, and the diameter reduction rate of the drawing should be adjusted so that the thickness of the fused support layer is at least 1 μm. Just adjust it.

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 obtained by drawing an optical fiber 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 skin pipe at temperature, the outer diameter can be changed, for example.
Multiple fibers of 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〕

A core made of pure silica glass doped with Ge is topped with a cladding layer made of pure silica glass doped with B ₂ O ₃ , and then a drawing temperature of approx.
Optical fiber 20000 with an outer diameter of 300 μm and a support layer of 20 μm thick made of natural quartz glass at 1900°C
After surface cleaning and other treatments, the books were packed in a close-packed array in a skin pipe made of synthetic quartz glass with an inner diameter of 45 mm and a wall thickness of 0.8 mm at a drawing temperature of approximately 1900°C, and while applying ultrasonic waves again, 10% hydrofluoric acid was used. Clean the surface of each optical fiber and the surface of the skin pipe with an aqueous solution, then rinse with water, dry, and then clean the inside of the skin pipe at a distance of 10 ^-4 mm.
The wire is drawn from one end at 2100℃ while being maintained in a high vacuum state of Hg, and the outer diameter is 2 mm, and the number of optical fibers contained is
Obtained 20000 multiple fibers. According to microscopic observation of the cross section of the multifiber, there were no defects where the claddings of adjacent optical fibers were torn and the cores were fused together.

[Comparative example]

A multiple fiber was produced which differed from Example 1 only in that each of the 20,000 optical fibers to be drawn was made of glass having an outer diameter of 300 μm without a support layer. A cross-sectional microscopic observation of the obtained multiple fibers revealed that the cores of adjacent optical fibers were fused in many places.

[Effects of the present invention] When both the core and the cladding are made of silica glass containing a dopant, the difference in refractive index between the two parts can be increased by selecting and adjusting the type and amount of dopant in each part of the core and the cladding. In this way, even if the cladding layer is thin, it can function to prevent light leakage.

This means that it is possible to manufacture multiple fibers with a small outer diameter and excellent flexibility by increasing the cross-sectional diameter reduction ratio by drawing, but the present invention can improve such flexibility. Multiple fibers with excellent image transmission performance can be produced on an industrial scale.

Claims (1)

[Claims] 1. The core and the cladding layer thereon are both made of quartz glass containing a dopant, and furthermore, there is a support layer made of quartz glass whose drawing temperature is at least 1800°C. A method for manufacturing multiple fibers, characterized in that the skin pipes made of quartz glass having approximately the same drawing temperature as the quartz glass constituting the fibers are closely packed in an aligned manner, and the skin pipes are drawn together.