JPH01107211A - Environmental resistant optical fiber - Google Patents

Abstract

PURPOSE:To obtain an increase of transmission loss at the time of radiation irradiation and has excellent radiation resistance by decreasing the difference in viscosity at the boundary face between a core and clad. CONSTITUTION:A GeO2 concn. gradient layer in which the concn. at the boundary face is maximized is provided to the periphery of the core-clad boundary face of the F-doped quartz glass clad by which the defects around the boundary face of the clad are filled with Ge while the amt. of the GeO2 to be added is lowered. The generation of strain by a difference in the viscosity at the core-clad boundary face is, therefore, suppressed. The increase of the transmission loss by the radiation irradiation is thereby suppressed and the use in radiation environment is enabled.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a radiation-resistant original fiber whose transmission characteristics are less likely to deteriorate in a radiation environment. The present invention relates to an environmentally resistant original fiber that can be used in environments exposed to radiation.

[Conventional technology]

Recently, there has been an increasing need to use original fibers in radiation environments such as nuclear power generation facilities, and there is a demand for the development of radiation-resistant original fibers.

Conventionally, radiation-resistant original fibers have a core made of high-purity quartz glass and a cladding made of F-doped silica glass ["Sumitomo Electric" No. 123, p. 29 (198
3)], which has a core of high-purity quartz glass and a cladding of quartz glass doped with F and P (Japanese Unexamined Patent Publication No. 61
-174136),? The core is made of quartz glass doped with P and ? Alternatively, FKP Mayu uses quartz glass doped with B as a glass bond (Japanese Unexamined Patent Application Publication No. 1989-1999 L-
242929).

[Problem that the invention seeks to solve]

The present inventors focused on the drawing process of the original fiber and attempted to improve the radiation resistance of the original fiber.

Generally, when drawing the original fiber, the glass base material is heated from the outside, so a temperature distribution is formed in which the outside temperature of the glass matrix phase is high and the inside temperature is low. This temperature difference results in a radial viscosity difference. Furthermore, differences in viscosity arise due to differences in composition between the core and the cladding. In the drawing process, if the viscosity of the core becomes higher than that of the clad to a certain extent, the drawing tension will concentrate on the core and cause distortion at the interface between the two. This distortion is thought to be caused by the formation of defects in the glass due to radiation irradiation, resulting in transmission loss in the original fiber.

Therefore, when we look at the original fiber that has a core of high-purity quartz glass with excellent radiation resistance and a cladding of FBe1 quartz glass, the viscosity of the core and cladding is as follows: Core viscosity (high purity s1o,) > cladding viscosity (F-13
Furthermore, since the temperature during drawing is lower for the core, the viscosity difference becomes even wider, and considerable strain occurs at the interface between the core and the cladding. Despite using quartz glass, an increase in transmission loss during radiation irradiation could not be avoided.

-The present invention utilizes the characteristics of a high-purity silica glass core to reduce the viscosity difference at the interface between the core and cladding, thereby avoiding the occurrence of distortion and achieving radiation resistance that suppresses the increase in transmission loss during radiation irradiation. The aim is to provide excellent original fibers.

[Means for solving problems]

US invention with high purity quartz glass core? The present invention is an environmentally resistant fiber having a cladding containing quartz glass, and is characterized in that a GeO1 concentration gradient layer is provided around the core-cladding interface of the cladding to maximize the GeO1 concentration at the interface.

The interface concentration of the Ge01 (I11 degree gradient layer) depends on the F concentration of the cladding, but the concentration is sufficient to fill the defects in the FBe1 quartz glass around the interface, that is, the number of defects (several ppm) according to Z8R measurement. The refractive index difference Δ+ is preferably 101% or more with respect to the quartz glass containing the cladding. To the extent that no
The difference in refractive index of the 1-containing silica glass in the cladding is approximately 173~
It is preferable to set it to 1/4 or less.

Furthermore, the outer diameter of the geozljk gradient layer is approximately 1.0 mm larger than the core diameter.
2 to 2.0 times is preferable.

Then, the ninth step of doping GeO2 in the cladding is Ge0
Ge compounds such as No. 4 can be used.

Please note that the amount of 1 added to the cladding must be constant in the radial direction to provide a 1m refractive index difference between the core and the cladding necessary for optical transmission, and varies depending on the type of fiber. For example, in a single mode fiber for a wavelength of 1.30 μm, it is necessary to add F so that the refractive index difference is Δ-4n1%, and in a step index fiber, the refractive index difference is f'::t, 0%. In some cases, 1Pt- is added.

In order to dope F into the cladding, carbon fluoride, carbon fluoride chloride, sulfur fluoride, silicon fluoride, sulfur oxyfluoride, silicon oxyfluoride, etc. can be used.

[Function] Ge01 is a substance that increases the refractive index of silica glass, and it is unlikely that it will be added to the cladding part in the past. Also, Ge
Since 02 itself deteriorates the radiation resistance characteristics of the optical fiber, it was not desirable to add it to the environmentally resistant optical fiber.

Furthermore, GeO3 was thought to be a substance that lowers the viscosity of silica glass, so it may be considered a high-purity silica glass core? It was predicted that adding GeO2 to the cladding of the original fiber consisting of the B1 silica glass cladding would not further reduce the viscosity of the cladding, but would widen the viscosity difference between the core and the cladding.

What is the present invention? By providing a GeO2 concentration gradient layer around the core-clad interface of the B-1 silica glass cladding to maximize the concentration at the interface, defects around the interface of the cladding can be removed with Ge while suppressing the amount of GeO2 added. It was also possible to suppress the occurrence of distortion due to the viscosity difference at the core-cladding interface. As a result, the increase in transmission loss due to radiation irradiation was able to be suppressed to a significantly lower level than in the original fiber with no Gems added.

[Example 1] A step-index fiber having the profile shown in FIG. I looked into it.

In the case of the 7-IPA shown in Fig. 1(a), SF, A glass base material is obtained by sintering in a containing gas. This is because the entire glass base material is uniformly doped with F, which corresponds to a refractive index difference of 1.0 degrees with respect to pure silica glass, and an F-containing quartz glass layer that does not contain GeO2 is formed on the outside. On the inside, the above refractive index difference Δ−
= Maximum refractive index difference Δl''t-15 based on toeIb
% of the gray-rad GeO2 concentration gradient region (F
-GeO-51O,) was formed. The center of this glass base material is hollowed out and the inner Ge0. A tube was obtained in which the refractive index difference Δ+ in the maximum concentration region was (108'%).On the other hand,
A pure silica glass rod constituting the core is inserted into the above tube and crushed in an oxygen-hydrogen flame to create a fiber base material.Afterwards, this is drawn to obtain a fiber having the profile shown in Figure 1(a). Ta.

The fiber shown in FIG. 1(0) was prepared in the same manner as above except for the Ge01 concentration gradient layer, having the profile shown in FIG. 1(b).

When we measured the initial characteristics of these original fibers at a wavelength α of 85 μm, we found that the fiber with the first factor (up to) was 2
．． 864 B/-, whereas the fiber of FIG. 1(a) had a power of 2.67 dB/ka+. Next, the dose rate 1
After irradiating with γ-rays of 0' R/Hr for 1 hour, the increase in transmission loss at the above wavelength was measured.
The fiber shown in Figure (a) can reduce the power by a large amount to 1 a OdB/km.

[Example 2] 1K 2 A single mode fiber having the profile shown in Figure 2 (a) was prepared as follows, and its radiation resistance characteristics were investigated by comparing it with a conventional single mode fiber having the profile shown in Figure 2 (b). Ta.

First, the fiber in FIG. 2(a) has a refractive index difference x-1o, ! with respect to pure silica glass. +4? Prepare a quartz glass tube containing 81OL4°SF in the tube.
6-containing gas in a fixed amount, and the amount of G8CL4 added is gradually increased from zero, finally the above refractive index difference Δ-=Il
A glass layer corresponding to the Geo2 concentration gradient layer is formed by the MOVD method while adjusting the refractive index difference Δ+ to be 1108 degrees with reference to B, and then the addition of Ge04 and SF6 is stopped and the core is A pure silica glass layer was formed, and a silicate fiber base material was obtained by solidification treatment. Then, by drawing the base material, a fiber having the profile shown in FIG. 2(a) was obtained.

The fiber shown in FIG. 2(b) was prepared in the same manner as described above except for the Ge01 concentration gradient layer.

When we measured the initial characteristics of these original fibers at a wavelength of 1.30 μm, we found that the fiber shown in Figure 2(b) was (
L 40 dB/kffl, whereas in Fig. 2 (a
The fiber of 1 was α374B/km. Next, after irradiating gamma rays at a dose rate of 10 @R/Hr for 1 hour, the increase in transmission loss at the above wavelength was measured, and the result was shown in Figure 2 (1).
)) fiber is 15. 0 dB/km, whereas the fiber in FIG. 2(a) showed a large reduction of 111 dB/km.

[Example 3] A single mode fiber having the profile shown in Fig. 5(a) was prepared as follows, and its radiation resistance characteristics were investigated by comparing it with a conventional fiber having the profile shown in Fig. 6(1)). Ta.

The fiber in FIG. 3(L) is manufactured by supplying a 5i044-containing gas with a trace amount of Geat4 added around a pure silica glass rod that corresponds to the core to obtain Ge0! Contains S10. By depositing a soot body and sintering it in a SiF4-containing gas, an F--GaO1-containing silica glass layer corresponding to a Ge02# gradient layer was formed around the rod. Therefore, by discontinuing the addition of Ge 04, depositing the 8102 soot body in the same manner as above, and sintering it in the SiF4-containing gas, ? A containing quartz glass layer was formed. This F-containing quartz glass layer has a refractive index difference Δ- of α'3° with respect to the pure silica glass core, and the core interface of the G11101 concentration gradient layer has a refractive index based on the above refractive index difference = 13°. The difference Δ+ was α06chi.

For the fiber shown in FIG. 3(b), a 7-eye fiber having the profile tV shown in FIG. 3(b) was prepared in the same manner as above except for the e02-degree gradient layer.

When we measured the initial characteristics of these original fibers at a wavelength of 1.30 μm, we found that the fiber shown in Figure 3(b) was (
L 56 cLB/km, whereas Fig. 3(a)
The fiber was (L 58 (LB/klll).

Next, after irradiating r@' with a dose rate of 10'R/Hr for 1 hour and measuring the amount of increase in transmission loss at the above wavelength, it is found that the fiber of No. 5 lN(b) is 1&n; On the other hand, 7 Aipa in Figure 3(a) is 12.84B/
The distance has been significantly reduced to km.

〔Effect of the invention〕

By adopting the above configuration, the present invention takes advantage of the radiation resistance properties of the high-purity silica glass core and suppresses the occurrence of distortion at the core-clad interface during wire drawing, thereby increasing transmission loss due to radiation irradiation. It was possible to significantly reduce the amount of radiation, making it possible to use it in radiation environments.

[Brief explanation of the drawing]

Figure 1 (a), Figure 2 (a) and Figure 3 (a) show the profiles of the original fibers obtained in the examples of the present invention.
b), FIG. 2(1)) and FIG. 3(1)) respectively show the profiles of conventional original fibers.

Claims (1)

[Claims] An environmentally resistant fiber having a core of high-purity quartz glass and a cladding of F-containing silica glass, characterized in that a GeO_2 concentration gradient layer is provided around the core-clad interface of the cladding to maximize the GeO_2 concentration at the interface. Environmentally resistant optical fiber.