JPH05201739A - Radiation resistant optical fiber, image fiber and manufacturing method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide an optical fiber with high NA having excellent radiation resistance. [Constitution] The core of the optical fiber does not contain chlorine,
And GeO in which Ge-bonding defects are compensated by fluorine
_The core is made of ₂ -F glass and the clad is made of SiO ₂ -F glass, which contains no chlorine, and is Ge.
-Because the coupling defects are compensated for, deterioration of radiation characteristics is prevented. Since the refractive index of GeO ₂ is 10% higher than the refractive index of silica glass, the difference in relative refractive index between the core and the cladding can be increased, and the conventional characteristic that an optical fiber with high NA can be obtained is not impaired.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to an improvement of the optical fiber, the image fiber, and methods for their preparation having a core composed mainly of GeO _2, provides excellent radiation resistance in a simple manner To do.

[0002]

_2. Description of the Related Art Pure GeO ₂ cores are used as optical fibers and image fibers for sensors and light guides. The reason is ultra-high NA
This is because the fiber of the image fiber can be obtained.
In the light guide, a large amount of light is efficiently transmitted.

[0003]

However, in recent years, the chances of using various fibers in a radiation atmosphere have increased, and expectations for the use of the above GeO ₂ core fibers have also increased. However, this GeO ₂ glass itself is Ge.
Radiation characteristics tend to deteriorate if there is an O-bonding defect, etc. Furthermore, since GeO ₂ glass is usually obtained by flame hydrolysis of GeCl ₄ , chlorine is contained in the glass, and this chlorine also has radiation characteristics. Since it causes deterioration, there is a problem that it cannot be used because it is colored with a relatively low dose of γ-rays.

[0004]

The present invention has been made from the above viewpoints, and the invention according to claim 1 is characterized in that it does not contain chlorine and the Ge-O defects are compensated by fluorine. The radiation resistant optical fiber comprises a GeO ₂ -F core and a SiO ₂ glass clad formed around the core. Further, the invention according to claim 2 is characterized in that a chlorine-free alkoxygermanium is used as a starting material, which is synthesized at a low temperature to obtain pure GeO ₂
To obtain a soot preform, which is then vitrified into a transparent glass in a fluorine atmosphere to form a GeO ₂ -F core rod.
This is a method for producing a radiation resistant optical fiber in which an iO ₂ -based glass clad layer is formed to form a core-clad type optical fiber preform and the preform is melt-drawn from one end. Further, the invention according to claim 3 is characterized in that, in an image fiber in which a large number of pixels are fused and integrated with each other, the core forming the pixels does not contain chlorine, and G is formed by fluorine.
The radiation resistant image fiber is made of GeO ₂ -F in which eO defects are compensated and the cladding is made of SiO ₂ glass. A fourth aspect of the invention is a radiation resistant image in which a large number of optical fibers obtained by the method of the second aspect are packed in a quartz tube to form an image fiber base material, and the base material is melt-drawn from one end. It is in a method of manufacturing a fiber. As the alkoxy germanium containing no chlorine, Ge (CH 2
₃ O) ₄ , Ge (C ₂ H ₅ O) _{4 and the} like.

[0005]

[Operation] Ge, which is one of the factors that deteriorate the radiation characteristics
Since the presence of chlorine in O ₂ is excluded from the starting material itself, which is the source of GeO ₂ generation, chlorine is not contained, and another cause of deterioration of radiation characteristics is G.
Since the defect of e-O bond was compensated by the addition of fluorine,
It becomes an optical fiber and an image fiber having excellent radiation characteristics even though it is a core containing GeO ₂ as a main component.

[0006]

【Example】

Example 1 FIG. 1 is a sectional view of an optical fiber according to the present invention, in which 1 is a chlorine-free GeO ₂ -F core. Its refractive index is 1.60. Reference numeral 2 is a fluorine-doped SiO ₂ clad having a refractive index of 1.44. Thus, the relative refractive index difference Δ between the core and the cladding is 10%, which is an extremely high NA. In addition, the γ-ray characteristics were excellent and did not change even after irradiation for 10 hours at a dose rate of 10 ⁶ R / H. An example of the manufacturing method of this fiber will be given. First, a GeO ₂ soot preform is manufactured by a normal VAD method. Specifically, Ge (CH ₃ O) ₄ is placed at the center of the concentric multi-tube burner.
Of 200 sccm, and H ₂ gas of 400 sccc in the second layer
200 sccm of N ₂ gas for the 3rd layer and O _{2 for the} 4th layer
A soot preform having a diameter of 60 mm and made of pure GeO ₂ containing no chlorine is deposited on the tip of the quartz rod as a starting member by supplying 1000 sccm of gas by low temperature synthesis. Maximum temperature of this preform is 1100
Put in a heating furnace of ℃, SiF ₄ gas 50c in this furnace
c) Gradient sintering is performed while being supplied to obtain a transparent core base material having a refractive index of 1.60. Next, a soot layer of SiO _{2 having} a thickness of 20 mm was formed around the transparent base material by an external attachment method, and the soot layer was put in a heating furnace having a maximum temperature of 1500 ° C. and SiF was placed in the furnace.
A core-clad rod with an outer diameter of 30 mm having a SiO ₂ clad layer having a refractive index of 1,44 and doped with transparent fluorine was gradient-sintered while supplying ₄ cc of 100 gas (relative refractive index difference Δ = 10%). The rod thus obtained was introduced into a drawing furnace, and its tip was set to 1600.
An optical fiber having a diameter of 200 μm was formed by heating the fiber to ℃.

Embodiment 2 FIG. 2 is a sectional view of the image fiber of the present invention.
Is a quartz-based image circle, and 12 is a quartz jacket surrounding the image circle. Reference numeral 20 denotes a large number of pixels forming an image circle, and a fluorine-doped quartz glass clad 2 around a GeO ₂ -F core 22 containing no chlorine.
4 are formed, and adjacent clads are fused and integrated. It should be noted that the refractive index of the core 22 is about 0.02 lower than that of pure GeO ₂ due to fluorine doping, and the refractive index of the clad is also less than that of pure SiO ₂ due to fluorine doping. It is reduced by about 0.02, and the relative refractive index difference between the core and the clad is eventually set to about 10%. This image fiber was produced by the following method. Up to the point of obtaining the image fiber strand, it was the same as in Example 1, except that the obtained strand diameter was 300 μm. This 2200 image fiber strands were put into a quartz glass tube with an inner diameter of 15 mm and an outer diameter of 17 mm to form an image fiber base material, which was introduced into a drawing furnace and the tip was heated to 1600 ° C. The image fiber was 125 μm. This image fiber has a relative refractive index difference between the core and the clad that is about 30% larger than that of the conventional image fiber. Therefore, even if the overall diameter is reduced by about 20%, a clear image can be obtained. Also, this image fiber was irradiated with 10 ³ R / H of γ-ray, but the deterioration of the image was small and the image fiber was sufficiently usable.

[0008]

Since the optical fiber and the image fiber according to the present invention have a core made of GeO ₂ -F glass containing no chlorine, the radiation characteristic is deteriorated by chlorine and the Ge—O bond defect is eliminated by fluorination. It is possible to provide the one excellent in radiation resistance without impairing the original advantage that the deterioration of the above can be prevented and thus the relative refractive index difference between the core and the clad can be made large. In addition, the manufacturing method is quite simple, since the core base material and the clad layer around the core base material are exactly the same as in the conventional method except that chlorine germanium-free alkoxygermanium is used as the GeO ₂ generation source gas.

[Brief description of drawings]

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

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

[Explanation of symbols]

1 GeO ₂ -F core containing no chlorine 2 Fluorine dove SiO ₂ clad 10 Image circle 12 Jacket 20 Pixel 22 GeO ₂ -F core containing no chlorine 24 Fluorine dove quartz clad

Claims (4)

[Claims] 1. Ge containing no chlorine and containing fluorine
A radiation resistant optical fiber comprising a GeO ₂ -F core in which -O defects are compensated and a SiO ₂ -based glass clad formed around the core. 2. Use of chlorine-free alkoxygermanium as a starting material and synthesizing it at low temperature to obtain pure Ge
A soot preform made of O ₂ was obtained, and this soot preform was transparent vitrified in a fluorine atmosphere to form a GeO ₂ -F core rod, and then a SiO ₂ glass clad layer was formed around the core rod. A method for producing a radiation resistant optical fiber, which comprises a core-clad type optical fiber preform and melt-draws the preform from one end. 3. An image fiber in which a large number of pixels are fused and integrated with each other, wherein the core forming the pixels is free of chlorine and is composed of GeO ₂ -F in which Ge—O defects are compensated by fluorine. A radiation resistant image fiber, wherein the cladding is made of SiO ₂ glass. 4. A radiation resistant image fiber, comprising a plurality of optical fibers obtained by the method according to claim 2 packed in a quartz tube to form an image fiber base material, and the base material is melt-drawn from one end. Production method.