JPH046120A - Preform for image fiber - Google Patents

Abstract

PURPOSE:To suppress the generation of bubbles by forming a glass tube to be used as a supporting layer with a quartz glass contg. a dopant and increasing its softening temp. from the inner part toward the outer part. CONSTITUTION:A quartz glass doped with 30-40 mol% Ge or 10-15 mol% F is used for the inner layer 1 of a supporting-layer glass tube, and a quartz glass free of a dopant is used for an outer layer 2. The softening temp. of the inside of the tube is approached to the softening temp. at 1400-1450 deg.C of the fiber for a picture element, and the softening temp. is increased from the inner part toward the outer part as the dopant content decreases. Many fibers 10 for a picture element are packed into the supporting layer 12 to obtain a preform, the preform is heated to a specified temp., melted and drawn to form an image fiber, the supporting layer is coated with an UV-curing resin to form an outer layer 14, and a high-strength image fiber excellent in picture quality is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a base material for image fibers for image transmission, which suppresses the generation of bubbles that cause problems during manufacturing, and provides high strength and image quality. This allows an excellent image fiber to be obtained.

[Conventional technology]

As shown in FIG. 2, the structure of a typical conventional image fiber includes an image circle 10 (partially omitted) for image transmission consisting of a large number of pixels, and an image circle 10 (partially omitted) provided sequentially around the image circle 10. a support layer 12 made of quartz glass; and a coating layer 14 made of a thermosetting resin or an ultraviolet curing resin.
It is composed of. The manufacturing method is to pack a large number of pre-prepared fiber wires for pixels into a quartz tube as a base material, melt-draw this from one end to form an image fiber, and then apply a resin coating on it.

[Problem to be solved by the invention]

However, since the fiber wire for the pixel is made of quartz glass doped with Ge or F, and the quartz tube serving as the support layer is made of pure silica glass, the former has a lower softening point.

This is not so much of a problem when the fiber for pixels is a low NA fiber with a small amount of dopant, but as the amount of dopant in the fiber gradually increases, the difference in softening point from the surrounding quartz tube increases. If the temperature of the heating furnace is raised sufficiently to melt the quartz tube, the fiber for the pixel in the center will undergo extreme deformation, creating bubbles, which will deteriorate the strength and image quality of the resulting image fiber. Ta.

[Means to solve the problem]

In view of the above, the present invention provides a base material for an image fiber that can suppress the generation of bubbles during manufacturing. In the image fiber base material, the glass tube is made of silica-based glass containing a doping material, and the softening temperature thereof increases from the inside to the outside. It is about becoming.

Here, the softening temperature can be changed by changing the amount of Ge or F doped into the silica glass, and can be obtained by, for example, the MCVD method. That is, while rotating a quartz tube prepared in advance around its axis, the oxyhydrogen burner is traversed along its axial direction. On the other hand, inside this quartz glass tube S iC141Cy e C1
4, and then gradually increasing the supply amount of G e CI 4 (.By doing this, SiO□-GeO2 glass in which the amount of GeO2 is gradually increased on the inner surface of the quartz tube is obtained.

Note that the amount of GeO2 to be supplied is appropriately determined in consideration of the composition of the pixel element wire, that is, its softening temperature. Further, the doping material is not limited to Ge, but may also be FP, CI, etc., and the starting material gas is SF6, POCl3, C
Examples include I□.

[Effect]

The softening temperature of the glass tube that supports the pixel wire is gradually increased from the inside to the outside, and the softening temperature on the inside is set to be similar to the softening temperature of the pixel wire, which is the cause of bubbles during wire drawing. is removed.

〔Example〕

FIG. 1 is a cross-sectional view of a supporting glass tube used in the present invention, which consists of an inner layer 1 made of quartz glass doped with Ge or F, and an outer layer 2 made of pure silica glass containing no dopant. ing. The amount of dopant in the inner layer 1 is greatest on the inside, and is set to be as equal as possible to the softening temperature of the pixel wire, and then the amount of dopant gradually decreases toward the outside.

The softening temperature of the pixel wires currently used is approximately 1400
℃ to 1450℃, and in order to cope with this, Ge
When F is used as a doping material, 30 to 40 mol% is required, and when F is used as a doping material, 10 to 15 mol% is required.

〔Example〕

Pixel element wire diameter 200. crm's Gem2-3 i O
.

6°000 core fluorine-doped Sing thalassod fibers (core clad non-refractive index difference = 4%) were prepared. This was packed into a quartz glass tube with the following structure as a support. In other words, as a quartz-based glass tube, the inner diameter is 18 mm, the outer diameter is 20 nm, and the inner wall thickness is 1 nm.
The material used was doped with e, the amount of which was gradually decreased from the inside to the outside, so that the softening temperature varied from 1400°C to 1500°C.

One end of the base material thus obtained was heated to about 2000° C. and melt-drawn to form an image fiber with a diameter of 500 μm, which was subsequently coated with silicone resin. When the presence of bubbles in this fiber was investigated by changing the outer diameter during drawing, it was found that there was less than one bubble per 100 m.
I was able to drastically reduce it. Moreover, the image quality was also good.

[Effects of the Invention] As described above, this invention uses a quartz-based glass tube whose softening temperature increases from the inside to the outside as the support tube used as the base material for the image fiber η. It is an excellent image fiber whose temperature is not much different from the softening temperature of the pixel element wire, which prevents bubbles from forming inside when drawn, and which has high strength and does not adversely affect image quality. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a support tube used in the image fiber preform of the present invention, and FIG. 2 is a partially omitted sectional view of a typical image fiber. 1: Cross-sectional view of a doped quartz glass tube, 2: Outer layer consisting of pure quartz glass without dopants. : Image circle: Support tube: Outer layer

Claims (1)

[Claims] In an image fiber base material in which a large number of pixel wires are packed in a glass tube serving as a support layer, the glass tube is made of silica-based glass containing a dopant, and the softening temperature thereof increases from the inside to the outside. A base material for an image fiber, which is characterized by a shape that increases toward the target.