JPH03248103A - Optical fiber for image fiber - Google Patents

Abstract

PURPOSE:To prevent generation of bubbles and to obtain the high-strength image fiber by providing the center of the optical fiber with a part to constitute a nucleus of the softening temp. higher than the softening temp. of the periphery of the center. CONSTITUTION:The part to have the high softening temp. to constitute the nucleus is provided at the fiber center. Namely, a fine particle layer of porous glass consisting of GeO2-SiO2 of a GI type is deposited around, for example, a pure silica glass rod by an external deposition method. An SiO2 glass layer for a clad contg. fluorine is formed thereon by a plasma external deposition method. This rod is melt drawn from one end and is formed as the optical fiber. Therefore, the twist of optical core-clad fiber due to lowering softening temp. by contg. much dopant and the confinement of the local space by an intersection is thus prevented. The generation of the bliseter bubbles at a high temp. is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an image fiber wire suitable for obtaining a bubble-free, high-strength image fiber.

(Prior Art) In recent years, image fibers have been used for medical purposes, and are required to have a small diameter and high strength. To explain the refractive index profile of the wire that becomes the pixel, the central core part is doped with germanium Ge, and its refractive index is expressed as the relative refractive index difference with the refractive index of silica: Δn゛=
3%. In addition, the cladding part is doped with F, and the relative refractive index difference with the refractive index of silica is Δn-=1
%. Therefore, the relative refractive index difference between the core and the cladding is Δn=4%. Further, the diameter ratio of the core to the cladding is 2:1. To make an image fiber using this strand, the strand is stuffed into a quartz glass tube without any gaps, used as a base material, and one end of the strand is heated and melted to form an integrated image fiber.

(Problems to be Solved by the Invention) Although the diameter of the thus obtained image fiber has been sufficiently reduced, the strength is not sufficient, and improvement has been desired. The cause is the presence of bubbles within the fiber. Although the mechanism of bubble generation is not clear, it is thought to be as follows.

In other words, when the base material is drawn and melted into one piece, if each wire is melted in an orderly manner, no bubbles will be generated. Because it is quite difficult to pack the core-clad wire, which contains a large amount of dopant and has a low softening temperature, it twists, collapses, or intersects, creating a shape where space is locally confined. It is expected that it will swell and form bubbles at high temperatures.

(Means for Solving the Problems) This invention is based on the knowledge that from the above point of view, it is sufficient to provide a core portion with a high softening temperature at the center of the strand, and the first feature thereof is The claimed invention resides in an image fiber wire in which the softening temperature of the glass near the center is higher than the softening temperature of the glass around the center. Further, the invention of the second claim is characterized in that the softening temperature of the glass near the center is at least 200 points higher than the softening temperature of the glass around the center.
This is in the image fiber wire made with high C.

A third aspect of the invention resides in an image fiber wire comprising a core made of pure silica glass near the center and germania-doped silica glass around the center.

In addition, the diameter of the high softening temperature part at the center, which is the core, is 2.
When the thickness is 00 μm, about 20 μm is sufficient. Also,
The reason why we set the softening temperature of the glass near the center to be at least 200 degrees Celsius higher than the softening temperature of the surrounding area is because if there is a temperature difference of this degree, even if a small amount of dopant is introduced into the center, it can function as a nucleus. It is from.

Furthermore, if the center is pure silica, its softening temperature is 2
．． 000°C, and the surrounding Ge doping amount is Δn1=3
%, there is a difference of about 250°C from the softening temperature of approximately 1750°C, and the function as a core is sufficient.

(Example) A pure silica glass rod with a diameter of 5 cm and a length of 200 cm is surrounded by an externally mounted GT type GeO□-5 inch.

A layer of porous glass particles was deposited to a thickness of 50 mm. At this time, the frit gas was supplied by supplying 5iC1a at a constant rate of 11200sccIll, while
! A method was adopted in which a was initially supplied at 50 sccm and then gradually decreased until it reached zero. Next, this was made into transparent glass to form a rond with an outer diameter of 50III11.

Subsequently, a SiO□ glass layer for cladding containing fluorine and having a thickness of 25 mm was formed thereon by an external plasma method. This rond was melt-drawn from one end to form an image fiber wire. The dimension of this wire is the central S
iO□Nuclear diameter 10μm 1 Core diameter 100μm 1 Clad diameter 2
00 μm, and its refractive index profile was as shown in FIG. In the figure, the relative refractive index difference between the core peak refractive index and the center 5iOz refractive index is Δn゛=3%, and the relative refractive index difference between the cladding and the center SiO□ refractive index is Δn
-=1%, relative refractive index difference between core and cladding is Δn=4%
It is.

The image fiber thus obtained had an outer diameter of 20 m,
6,000 fibers were packed into a quartz tube with an inner diameter of 18 m+ to form an image fiber base material. This base material was drawn to have an outer diameter of 500 μm to form an image fiber with 6000 pixels. The frequency of occurrence of bubbles in this image fiber was 2 per 100 m, which was superior to the 10 in the conventional case.

(Effects of the invention) Since a core portion with a higher softening temperature than the surrounding area is provided at the center of the strands constituting the image fiber base material, twisting or falling occurs when they are bundled and melted and wire-drawn to integrate them. Since there is no cross-over, the generation of bubbles can be prevented.
Therefore, a high-strength image fiber can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the refractive index profile of the image fiber of the present invention.

Claims (3)

[Claims] (1) An image fiber wire in which the softening temperature of the glass near the center is higher than that of the glass around the center. (2) The image fiber strand according to claim 1, wherein the softening temperature of the glass near the center is at least 200° C. higher than the softening temperature of the glass around the center. (3) The strand for an image fiber according to claim 1, comprising a core made of pure silica glass near the center and germania-doped silica glass around the core.