JP2657726B2 - Radiation-resistant optical fiber and image fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION This invention relates to an improvement of the optical fiber and the image fiber for the GeO ₂ core, provides excellent radiation resistance.

[0002]

_2. Description of the Related Art Pure optical fibers having a core of GeO ₂ are used as optical fibers and image fibers for sensors and light guides. The reason is the super high NA
Because of this feature, an image fiber with a very small diameter has been obtained by taking advantage of this feature.
In a light guide, a large amount of light is efficiently transmitted.

[0003]

However, in recent years, the opportunity to use various fibers in a radiation atmosphere has increased, and expectations for the use of the above-mentioned GeO ₂ core fibers have also increased. However, this GeO ₂ glass has a problem in that it has low radiation characteristics, is colored by a relatively low dose of γ-rays, and cannot be used.

[0004]

SUMMARY OF THE INVENTION The present invention has been made from the above viewpoint, and the invention according to claim 1 is characterized in that GeO containing at least 300 ppm of an OH group is used.
_It consists of _two cores. Further, according to the invention described in claim 2, the core constituting the pixel has at least O
It contains 300 ppm of H groups. Here, the reason that the OH group is included at least 300 ppm is that even if the γ-ray is irradiated with 10 ⁶ R, the loss increase amount is 50 dB.
/ Km or less.

[0005]

By including 300 ppm of OH groups in GeO _{2 serving} as a core, radiation characteristics can be improved while maintaining the original feature that a refractive index difference between a core and a clad can be increased.

[0006]

【Example】

Embodiment 1 FIG. 1 is a cross-sectional view of an optical fiber according to the present invention. Reference numeral 1 denotes a core in which GeO ₂ contains 400 ppm of an OH group, and its refractive index is 1,61. 2 is fluorine-doped S
In the iO ₂ cladding, its refractive index is 1,44. Thus, the relative refractive index difference コ ア = 10% between the core and the clad is an extremely high NA. In addition, the γ-ray characteristics are excellent such that the loss increase is 40 dB / km even at a total dose of 10 ⁶ R. An example of a method for producing this fiber will be described. First, a GeO ₂ soot preform is prepared by a normal VAD method. Specifically, the center of the concentric multi-tube burner is GeCl
₄ at 200 sccm, Ar at the second layer at 300 sccm,
1000 sccm of H _{2 in the} third layer and 15 of O _{2 in the} fourth layer.
By feeding at a flow rate of 00 sccm and performing low-temperature synthesis, the tip of a quartz rod as a starting member was made of pure GeO ₂ and had a diameter of 20 m.
Deposit m soot preforms. This preform was placed in a heating furnace having a maximum temperature of 1200 ° C. in a steam atmosphere, and was subjected to gradient sintering to reduce the OH group having a refractive index of 1,66 to 400 pp.
m was used as a transparent core base material. Next, a soot layer of SiO ₂ was formed to a thickness of 15 mm around the transparent base material by an external method, and was placed in a heating furnace having a maximum temperature of 1300 ° C., and 30 cc of SiF ₄ gas was supplied into the furnace. By gradient sintering, a core-clad rod having an outer diameter of 20 mm and a transparent fluorine-doped 30SiO ₂ cladding layer having a refractive index of 1,44 (differential index difference 両 者 = 10%) was obtained. The rod thus obtained was introduced into a drawing furnace,
The tip is heated to 1400 ° C to form a fiber and the diameter is 2
An optical fiber of 00 μm was used. 10 ⁶ R
Γ-rays, the loss increase is 40 dB / k
m.

Embodiment 2 FIG. 2 is a sectional view of an image fiber according to the present invention.
Denotes an image circle, and 12 denotes a quartz jacket surrounding the image circle. Reference numeral 20 denotes a number of pixels constituting an image circle, which is GeO containing 400 ppm of OH groups.
₂ Fluorine dove quartz glass clad 2 around core 22
4 are formed, and the cladding is shown by a dotted line, but actually the adjacent claddings are fused and integrated. The refractive index of the core 22 is 1,61, and the refractive index of the cladding is 1,44 after being doped with fluorine. As a result, the relative refractive index difference between the core and the cladding is about 10
% Has been. This image fiber was produced by the following method. Up to the point where the image fiber is obtained, the same as in the first embodiment.
m. 2500 image fiber strands were placed in a quartz glass tube having an inner diameter of 17 mm and an outer diameter of 19 mm to form an image fiber preform, which was introduced into a drawing furnace.
The tip is heated to 1800 ° C. and drawn to a diameter of 190
A μm image fiber was used. Since the relative refractive index difference between the core and the clad of this image fiber is about 5% larger than that of the conventional fiber, a clear image can be obtained as before even if the entire diameter is reduced by about 30%. . The image fiber was irradiated with 10 ⁶ R γ-rays, and the loss increase was 35 dB / km.

[0008]

The optical fiber and the image fiber according to the present invention have a Ge core whose core contains 300 ppm of OH groups.
Since it is made of O ₂ glass, the radiation resistance can be improved without impairing the original advantage that the relative refractive index difference between the core and the clad can be made large.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical fiber according to the present invention.

FIG. 2 is a cross-sectional view of the image fiber of the present invention.

[Explanation of symbols]

Reference Signs List 1 GeO ₂ core containing OH group 2 Fluorine-doped SiO ₂ clad 10 Image circle 12 Jacket 20 Pixel 22 GeO ₂ core containing OH group 24 Fluorine-doped SiO ₂ clad

Claims (2)

(57) [Claims] 1. G containing at least 300 ppm of an OH group
A radiation-resistant optical fiber comprising an eO ₂ core. 2. A radiation-resistant image fiber, wherein a core constituting a pixel contains at least 300 ppm of an OH group.