JPS61222940A - Optical fiber - Google Patents

Abstract

PURPOSE:At least one of the core and the clad of an optical fiber in which at least the core is composed of quartz is doped with GeO2 and F to improve the hydrogen resistance and radiation resistance of the optical fiber. CONSTITUTION:In the above-mentioned doping, the concentration of GeO2 is lower than 12mol% and the concentration molar ratio of GeO2 to F is more than 4. The effect cited above is similarly obtained in an optical fiber which is composed of quartz in both the core and the clad.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an optical fiber having excellent hydrogen resistance and radiation resistance.

[Prior art]

In recent years, optical fiber cables have been introduced at a rapid pace. The optical fibers used in this cable are generally made of quartz glass, and representative examples include those with SS10t-G1110 core/Si0g cladding and those with 5ift core/SiOg-F cladding. . However, the former 5iO1-GeOz core/Si0g cladding has good radiation resistance but poor hydrogen resistance. On the other hand, Sing core/5iOx-F craft has good hydrogen resistance but poor radiation resistance. That is, a silica glass optical fiber with excellent hydrogen resistance and radiation resistance has not yet been obtained.

[Purpose of the invention]

In view of the above problems, an object of the present invention is to provide an optical fiber having excellent hydrogen resistance and radiation resistance.

[Structure of the invention]

In order to achieve the above object, the optical fiber of the present invention is characterized in that at least the core of the optical fiber is made of quartz glass and the cladding is small (both of which are doped with GeO or F).

[Embodiments of the invention]

Embodiments of the present invention will be described in detail with reference to the drawings.

The present inventors first developed a conventionally common 5iOz-Gem,
It was confirmed that when an optical fiber having a core/5iOz kraft structure is doped with ~1 mol % of fluorine F, the increase in transmission loss due to hydrogen can be suppressed (see Fig. 4), but the radiation resistance deteriorates as shown in the table below.

Table 1 (at 1.3 μm) The radiation resistance is γ-ray 1.8 x 10' r*
++ is the value after irradiation.

Next, when an optical fiber having a 5ift core/SiO□ clad structure is doped with fluorine F, the hydrogen resistance is good, but the radiation resistance is also deteriorated, as shown by the values at the bottom of Table 1 above. Based on the above results, the present inventors added GeOx and F to an optical fiber consisting of a quartz glass core (outer diameter 125 μm) and a silicone cladding (outer diameter 380 μm, refractive index 1.41). Characteristics were evaluated while varying the doping amount. Through this series of experiments, the results shown in FIGS. 1 to 3 were found.

First, the quartz glass core (outer diameter 125 μm) and the silicone cladding (outer diameter 380 μm, refractive index 1.4
After heating the optical fiber of 1) to 200'C in a hydrogen atmosphere and doping it with F, the transmission loss amount was measured in the 1.44 μm and 1.55 μm bands, and the results were as shown in FIG. That is, as the content of fluorine F increases, the transmission loss decreases. Moreover, when the value is 0°4+mol% or more, it is stable, and there is no difference in the effect even if the doping is done more than that.

Next, the 5iO1 optical fiber and the Sing optical fiber doped with 3.6so1% of GeO□ were each doped with fluorine F at O to I, 0slo 1%, and the radiation resistance at that time was determined. tested for sex. The irradiated radiation was a gamma ray of 1 x lO'r*+tt/hr, and when the irradiation dose reached 6 x 10 r@Rt, the transmission loss of the optical fiber was measured. This result is shown in Figure 2.
As shown in this figure, the transmission loss of the 5iO2-F glass optical fiber increases in proportion to the amount of fluorine F doped. However, in the case of a material doped with GeO□, as shown by curve B, the increase in transmission loss can be significantly reduced. Furthermore, the transmission loss is smaller than when the fluorine F is not doped until the fluorine F doping amount reaches about 0.801%. That is, by doping with Ge01, the radiation resistance is significantly improved, and the fluorine F doping amount reaches approximately 0.8mol%.
This has the effect of suppressing the deterioration of radiation resistance caused by.

Next, as shown in Figure 3, 0.4 m of fluorine F is contained in the glass.
The presence of about 1.0 ol % is sufficient to suppress the increase in transmission loss due to hydrogen. Therefore, the radiation resistance was investigated when the amount of fluorine F was fixed at 0.4n+o1% and the amount of Ge0t doped was varied. The measurement results are shown in Figure 1.

From this figure, it can be seen that initially as the amount of Ge01 increases, the transmission loss due to radiation decreases, but when GeO□ is 0 and 5 mo
On the contrary, it increases when it exceeds 1%, and furthermore, GeO□
Two points were found: when the GeO2 content exceeds 12111o1%, the radiation resistance deteriorates compared to the case where the GeO2 is not doped.

By the way, the mechanism by which the results shown in FIGS. 1 and 2 are produced will be inferred below.

(A) (B) (C) There are structural defects as shown in (A) above in the optical fiber,
The vicinity of this defect is positively charged. Therefore, if a hydrogen molecule exists near this point, the structure becomes polarized and easily reacts. As a result, the following reaction occurs, and an increase in transmission loss due to hydrogen occurs.

However, when this is doped with fluorine F, as shown in (B) above, the positively charged portions are neutralized by F- and the structural defects disappear. That is, doping with fluorine F suppresses the polarization of hydrogen, thereby suppressing transmission loss due to hydrogen. However, conversely, due to the fluorine F doping, a portion occurs where the normal 5t-0 bond is weakened. This means that the ionic radius of F- is 1.36 people,
Although the valence of O is almost equal to 1.40, the valence is different, so when a bond between Si and F occurs, the 0 atom that should originally enter the space where the F atom exists is shown in (B) above. In other words, the bond angle changes, or the distance between Si and 0 becomes thicker, making the bond weaker (as shown in (C)) due to radiation exposure. As a result, transmission loss increases.

On the other hand, we showed that doping fluorine-doped quartz glass with Ge0t improves its radiation resistance, and the reason for this is
The ionic radius of Si" is 0.41 arc, and that of Ge'° is 0.53 arc, which is about 20% larger for Ge". Therefore, when GeO2 is doped, the glass network is expanded (the distance between Gs and 0 is larger than the distance between 5i and 0).
5t due to doping with fluorine F as shown in B)
-0 bond distortion can be relaxed and absorbed.

However, as mentioned above, G e 4 * and Si0 have different ionic radii, so if too much GeO□ is doped, 5i
The connection between -0 and Ge-0 bonds (considered to be Si-0-Ge) is shifted, and as a result, the bonds are easily broken due to radiation exposure, and as shown in Figure 1, Ge01 is 5wo1%
Above that, the radiation resistance will be adversely affected.

From the above reasoning, GeO1 and fluorine F are doped at a certain ratio or higher to maintain the hydrogen resistance due to fluorine F doping and remove the strain in the 5i-0 bond, while GeO!
G weaker than the 5i-0 bond by regulating the maximum value of
It is thought that it is possible to prevent an increase in e-0 bonding and thereby improve radiation resistance.

Therefore, from Fig. 1, when the GeOz concentration is about 12no1% or less, the radiation exposure loss is smaller than that of the Stow-F glass, and the meaning of GeOt doping comes out.
The concentration of 01 is 12+wo1% or less. Also, from Figure 2, when the concentration of fluorine F is about 0.8Ilo1% or less, the radiation exposure loss is smaller than that of Sing-Ge0g glass, so it makes sense to dope fluorine F. Ratio GeO1mol%/Fll
o1% is (GeOt/F) = 3.610.8≧
It becomes 4. Therefore, at least one of the core and cladding of an optical fiber whose core is made of silica glass,
An optical fiber characterized in that it is doped with Ge0z and F, in particular, the concentration ratio Ge01a of Ge0t and F is
When +o1%/PIlo1% is 4 or more and the GeO2 concentration is 12 mol% or less, it is possible to obtain an optical fiber with the best hydrogen resistance and radiation resistance. In the experiments of the present invention, an optical fiber whose core is made of quartz glass and whose cladding is made of silicone is used for ease of testing, but similar results could be obtained with an optical fiber whose core and cladding are both made of silica glass. Obtainable.

〔Effect of the invention〕

As described above (according to the present invention), by doping with Ge and F, an optical fiber having excellent hydrogen resistance and radiation resistance can be obtained.

[Brief explanation of drawings]

FIGS. 1 and 2 are graphs showing radiation resistance, and FIGS. 3 and 4 are graphs showing hydrogen resistance. Figure 2 FIL turtle ((2) 1%) Figure 3

Claims (3)

[Claims] (1) An optical fiber characterized in that at least one of the core and cladding of an optical fiber whose core is made of silica glass is doped with GeO_2 and fluorine F. (2) Concentration ratio of GeO_2 and F above GeO_2 mol%
The optical fiber according to claim 1, wherein /Fmol% is 4 or more. (3) The GeO_2 concentration is 12 mol% or less and GeO
The concentration ratio of _2 and F GeO_2 mol%/F mol% is 4
An optical fiber according to claim 1, characterized in that the above is the case.