JPS62191432A - Preform of optical fiber with reduced defects - Google Patents

Abstract

PURPOSE:The areas which do not have effect on light transmission loss are made of a glass which has higher viscosity than that of the glass in the areas which have effect on the emission loss to produce a preform which gives optical fiber with reduced defects and hardly increasing transmission loss. CONSTITUTION:The objective preform for optical fiber is obtained by forming an area B which do not effect the light transmission loss on the outer surface of the area A which effect light transmission loss. In the preform, the area A is composed of the pure quartz core and the fluorine-containing quartz clad. In the meantime, the area B is composed of a glass which contains N, Zr and has higher viscosity, preferably double or more as high as that the glass in area A and pure quartz glass at the temperature at which the preform is drawn into filaments. Thus, the tension in the filament drawing is almost loaded to the area B whereby the titled preform which gives optical fibers with reduced increase in transmission loss by radiation such as gamma-rays.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to the improvement of preforms for optical fibers, and more specifically to the improvement of preforms for optical fibers, and more specifically to the improvement of preforms for optical fibers, and more specifically to the improvement of preforms for optical fibers. Regarding renovation.

[Conventional technology]

Optical fibers are smaller and lighter than copper wire cables, and can be manufactured in large quantities.
Because it enables low transmission loss and high-bandwidth transmission, it is gradually being incorporated into communication lines in place of conventional copper wire cables.

However, it is known that transmission loss of optical fibers increases when exposed to gamma rays or in a hydrogen atmosphere. Furthermore, it is known that this increase in transmission loss is caused by defects in glass or quartz, and the fewer defects there are, the lower the transmission loss will be.

Here, certain defects are caused by drawing tension. Pure silica glass, which does not contain additives, has essentially few defects, and the core is pure quartz and the cladding is doped with fluorine.
The in2 optical fiber exhibits relatively good characteristics. However, even this type of fiber has the problem of defects due to drawing. Conventionally, the generation of these defects has been suppressed by reducing the drawing speed and increasing the drawing temperature.

[Problem that the invention seeks to solve]

However, reducing the drawing speed reduces productivity, and raising the drawing temperature to extremely reduce the viscosity causes the furnace body to wear out faster and makes it difficult to draw the wire stably. There were drawbacks.

The present invention has been made for the purpose of solving the problem of defects caused by drawing tension and obtaining an optical fiber preform that can produce optical fibers with fewer defects and less increase in transmission loss.

[Means to avoid problem decomposition method]

The present invention provides an optical fiber preform consisting of a part that affects optical transmission loss and a part on the outer periphery that does not affect optical transmission loss, wherein the viscosity of the glass in the latter part at the drawing temperature of the preform is This is an optical fiber preform characterized in that the former part is higher than that of glass and pure silica glass.

Particularly preferred embodiments of the invention include the method described above, in which the core is pure quartz glass and the cladding is quartz glass containing at least fluorine.

Conventionally, pure silica glass or glass made of the same material as the cladding has been used for the outer layer of an optical fiber that has a core and cladding, etc., where light does not pass through, that is, an area that does not affect optical transmission loss. In place of these, the present invention uses a glass whose viscosity when drawn is higher than the viscosity of pure silica glass when drawn, in a region that affects optical transmission loss in the fiber. Here, the area that affects or does not affect optical transmission as referred to in the present invention is defined as an area where 99.9999% of the light used passes through A (where the former is defined as the area B) and the latter is defined as B.
(The amount of light seeping out is 10-4% or less), ■ The density of the light used is in the relationship of the minimum value in A ≧ the maximum value in B, the above ■ or ■ and ■ A and B that satisfy the following.

The present invention uses a glass in the region CB+ that does not affect optical transmission loss, which has a higher viscosity when drawn than the viscosity of glass in the region CAI, which affects optical transmission loss, and pure silica glass. By using glass with
A larger portion of the tension during drawing is received by the above-mentioned areas where light does not pass, and as a result, many defects are generated in these areas, but defects are less likely to be generated in areas involved in optical transmission. Moreover, the increase in transmission loss due to γ-ray irradiation can be suppressed to a low level. FIG. 1 is a graph showing the radial viscosity distribution of an example of the preform of the present invention.

In the figure below, 1 and 2 are areas that affect optical transmission (
4) It rains the area that does not affect the 3rd optical transmission. At this time, if A consists of a core 1 and a cladding 2, where the core 1 is pure silica glass and the cladding 2 is quartz glass containing at least fluorine, the effect is even better.

Furthermore, as shown in FIG. 2, a thin glass layer with low viscosity may be added as the outermost layer 4 to the structure shown in FIG. In this way, the Φ scratches on the glass surface disappear during drawing, which is effective in improving the strength.

Note that FIGS. 3 to 5 are graphs showing the viscosity distribution of conventional products.

In the present invention, examples of the glass that can be used for the region affecting optical transmission include pure SiO, Be,
Examples include glasses containing any one of P, F, B, Fb, etc. as a main additive. In addition, examples of glasses that can be used in the region 03) that do not affect optical transmission include N, Zr, La, Os, Pr, N (1°P
m, am, Mu, G (1, TI), D7. E
IO, Fir, Tm, Yb, Lu and a little A
/ (up to 14% by weight) as the main additive.

The viscosity of the region B of the preform of the present invention constructed using the glass described above is, for example, 10 to 10 g.
The viscosity of the area (4) is about 108 Boise, and the viscosity of the region (4) is normally lower than this (a fraction of the viscosity of Bl, but it is preferable to keep it as low as possible. In other words, the larger the difference in viscosity between Bl and 031, the larger it is. It is more preferable for the purpose of the present invention to have a viscosity difference of (5) and CBI, although even a small difference in viscosity is effective, it is preferable that the difference is twice or more.

By the way, in the case where the viscosity of the outer circumference of an optical fiber preform is high, if i) the drawing temperature and ii) the drawing tension are fixed, the drawing temperature (iii) becomes high. Although these :) to (11) cannot be controlled independently, according to the present invention, better results than conventional products can be obtained in either case of fixing the temperature and tension, or fixing the tension and speed. . As a method that faithfully corresponds to the technical idea of the present invention, it is preferable to fix the tension and drawing speed, but since it is technically difficult, in the following examples, the tension and temperature are fixed. By fixing it.

Furthermore, the present invention is effective when applied to either a single mode fiber preform or a multimode fiber preform.

〔Example〕

Hereinafter, the optical fiber preform of the present invention and its effects will be specifically explained with reference to Examples.

Example 1 A preform consisting of a pure silica core with a diameter of 5 fi and a fluorine-doped silica cladding with an outer diameter of 7 and a fluorine content of 3% by weight was coated with silica glass containing CL3 weight of nitrogen at a thickness of 2.75+m. It was attached externally using the plasma method.

The optical fiber preform obtained above was heated to 21°C.
An optical fiber was obtained by drawing at 00° C. under a tension of 15 f. At this time, the viscosity was as follows: outer periphery, core, and cladding.

The resulting optical fiber with an outer diameter of 125μ and a core diameter of 50μ was irradiated with Co0r radiation at a dose rate of 10'R/H for 1 hour, and after one week, the transmission loss at wavelength Q and 65μ was measured and it was 554B. /km.

Comparative Example 1 The same procedure as in Example 1 was carried out except that pure silica glass was attached externally to the silica glass sill containing 0.5% by weight of nitrogen. cL of the obtained optical fiber after γ-ray irradiation
The transmission loss at 63 μ inertia is 77 aB/km in Example 1.
It was bigger.

Example Z Pure silica core with a diameter of 1.6118 and its outer diameter of 19
．． 2. On the outer periphery of a preform made of a fluorine-doped silica cladding having a fluorine content of 1% by weight, silica glass containing α5% by weight of nitrogen was externally attached to a thickness of z9cm by a plasma method.

The optical fiber preform obtained above was heated to 21°C.
The fiber was drawn at 00° C. and under a tension of 15 f to obtain a single mode optical fiber. The transmission loss of this fiber at 1.5 μm was (L, a OdB/km).

The obtained fiber was irradiated with Co gamma rays at a dose rate of 106R/H for 1 hour, and one week later, the transmission loss at a wavelength of 1.3μ was measured and found to be α51clB/41an.

Comparative Example λ The same procedure as in Example 2 was carried out except that pure silica glass was externally attached instead of the silica glass containing Q and 5% by weight of nitrogen. The initial transmission loss of the obtained optical fiber at 1.3μ was 1.58 dB/b, which was almost the same as in Example 2. The transmission loss after one week of γ-ray irradiation is a 64 d
B/km was higher than that of Example 2.

Although the above examples have shown high viscosity layers made of silica glass containing nitrogen, it is also a particularly preferred embodiment to use glass to which Zr is added instead of nitrogen.

〔Effect of the invention〕

When the optical fiber preform of the present invention is drawn to obtain an optical fiber, it is possible to obtain an excellent optical fiber with less characteristic deterioration even under radiation exposure or hydrogen atmosphere compared to conventional products. Make the most of your efforts.
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[Brief explanation of drawings]

1 to 5 are diagrams showing the cross-sectional structure of an optical fiber preform and the radial viscosity distribution during drawing, and FIGS. 1 and 2 show the optical fiber preform of the present invention. , Figures 3 to 5 are for conventional products.

Claims (2)

[Claims] (1) An optical fiber preform consisting of a part that affects optical transmission loss and a part on its outer periphery that does not affect optical transmission loss, where the viscosity of the glass in the latter part at the drawing temperature of the preform is lower than that of the former. A preform for an optical fiber, characterized in that the preform is higher than that of glass and pure silica glass. (2) The optical fiber preform according to claim (1), wherein the core is pure silica glass and the cladding is quartz glass containing at least fluorine.