JPH02113205A - Optical fiber - Google Patents

Abstract

PURPOSE:To obtain the low-loss fiber by forming a core part which constitutes a rod for the optical fiber to the viscosity lower by at least one than the viscosity of the other part. CONSTITUTION:This optical fiber has the quartz glass core contg. the halogen ions to increase the refractive of the quartz glass and the 1st quartz glass clad formed of fluorine to the refractive index lower than the refractive index of the core. Further, the fiber consists of the 2nd quartz glass clad which is equal in the refractive index to or slightly larger than the 1st quartz glass clad and the quartz glass jacket formed by doping the halogen ions to increase the refractive index of the quartz glass at the ratio higher than the ratio at which the halogen ions are incorporated in the core. The core when the fiber is formed is then eventually solidified after at least the part of the high viscosity and the remaining of stresses in the core is obviated. The low-loss fiber is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a silica glass-based optical fiber, and provides a low-loss fiber.

(Prior Art) As a general method for manufacturing silica glass optical fibers, there is a method of manufacturing a core clad type base material using a VAD or external attachment method, and then drawing the base material to form a fiber.

(Problems to be Solved by the Invention) The ultimate value of the transmission loss of an optical fiber is around a wavelength of 1.55μ for optical fibers whose main component is silica glass.
Theoretically, it is said to be about 0.14 dB/km. However, the transmission loss of actual optical fibers is affected by various losses, and in industrial production, the average value is 0.18 dB/k.
In reality, it is about m. It has been found that various residual stresses exist as one of the reasons why the loss is not stabilized.According to the study of the present inventors, it has been found that
□In the case of an optical fiber consisting of a glass core F-doped Sing glass cladding, it was found that it is very disadvantageous from the viewpoint of this residual stress. The reason may be as follows. Considering the state in which an optical fiber base material is melted and drawn into a thin optical fiber, when the molten glass solidifies, the core glass, which has a high viscosity, solidifies first. Generally, the cross-sectional area of the core is very small, so most of the drawing tension is applied to the core. At this time, since the clad glass is still in a molten state, no tension is applied to it, and as the fiber is pulled downward, the temperature decreases and the clad glass also solidifies. However, the clad glass merely solidifies and hardly shares the drawing tension, because the core already shares most of the drawing tension.

When abnormal stress is generated in the core glass in this way, various problems are expected. One problem is that the refractive index of the core glass decreases due to tensile stress, making it impossible to maintain the relative refractive index difference between the core and cladding, which is set in advance so that the fiber can operate normally as an optical fiber. In particular, in a single mode optical fiber, if the difference in refractive index between the far claddings is not sufficient, even a slight bend in the optical fiber may cause propagating light to leak to the outside. moreover,
Such residual stress may increase microscopic fluctuations in the refractive index of the core glass and increase scattering of propagating light.

(Means for Solving the Problems) From the above points of view, the present invention first aims to distribute the residual stress during drawing, which tends to concentrate on the core glass of an optical fiber, to other parts. The composition of the optical fiber base material is considered in terms of viscosity.

That is, a quartz glass core containing halogen ions that increase the refractive index of silica glass, a silica glass cladding whose refractive index is lowered by fluorine, and the amount of halogen ions that increase the refractive index of silica glass are as described above. The optical fiber is composed of a silica glass-based jacket doped with a smaller amount than that contained in the core.

In addition, by making the thermal expansion coefficient of the cladding that makes up the optical fiber larger than that of the core, even if the core solidifies earlier than other parts during drawing and residual stress occurs in the core, it is possible to When the cladding solidifies, it contracts to offset the residual stress generated in the core.

That is, a silica glass core containing halogen ions that increases the refractive index of silica glass, a first silica glass cladding whose refractive index is lowered by fluorine, and a first silica glass cladding containing fluorine and phosphorus whose refractive index is Is it equivalent to the silica glass cladding in No. 1?

a second quartz glass cladding made slightly larger;
An optical fiber was constructed from a silica glass jacket doped with a larger amount of halogen ions, which increase the refractive index of silica glass, than the amount contained in the core.

Note that halogen ions that increase the refractive index of quartz glass include chlorine and bromine. The relative difference between the amount of halogen ions contained in the core and the amount of halogen ions contained in the silica glass jacket is 0.1% by weight.
The absolute amount may be adjusted so that the former contains 0.3% by weight or more and the latter contains 0.2% by weight or less.

(Example) First, by the VAD method shown in FIG.
5iC14 in lOOsccm, Ot in 5SLM
, Ha is supplied by l OSLM, and the obtained SiO□ glass fine particles are deposited on the lower end of the starting member l to a diameter of 4 cm.
, 5iOi glass particle sintered body 3 with length 25 cra
Then, this sintered body 3 was introduced into a furnace maintained at 1200° C. and subjected to dehydration treatment. At this time, there is SOC in the furnace.
100 cc of lm for 7 minutes, 5.000 c of He
c Supplied for 7 minutes. Subsequently, the furnace temperature was raised to a maximum temperature of 1.550°C, and this dehydrated sintered body 3 was introduced into the furnace to a diameter of 20 a+a+ and a length of 130 a.
It was made into a transparent glass rod for the core of rm. At this time, there are 5
200 cc of OC1* was supplied for 7 minutes, and He was supplied for 5.000 α' minutes. In this way, a core rod containing 0.5% by weight of chlorine was obtained. 6 Next, this core rod was made to have a diameter of 4o + diameter.

After stretching it to a thickness of 60 mm, fine glass particles made of SiO□ were deposited around it by an external method to a thickness of 150 mm.
It was introduced into a fluorine-containing gas furnace maintained at 20 f.
A transparent glass gland layer with a thickness of f1 m was formed.

Next, glass fine particles of 5iOi were deposited again around this core clad rod to a thickness of 5i1m by the external method, and then made into transparent glass to form a jacket layer. At this time, the maximum temperature inside the furnace is 1520℃, and the SO
Clg was supplied at 50 cc/min and He was supplied at 5.000 cc/min for 7 minutes. The jacket layer thus contained 0.2% by weight chlorine. The core clad thus obtained
The jacket type base material was made into fiber. FIG. 2 shows the refractive index distribution of the obtained fiber, and FIG. 3 shows the loss wavelength characteristics of the fiber and the conventional fiber. As is clear from the figure, it can be seen that the fiber according to the present invention has a lower loss of 20% or more compared to the conventional fiber, and exhibits excellent characteristics.

(Example 2) A base material was made and fiberized in the same manner as in Example 1, except that a second cladding was formed between the cladding and the jacket in Example 1 before forming the jacket. The second method of forming the cladding is the external method, and SiO□ (90% by weight) -P is formed around the previously formed core cladding rod.
ies (t 0% by weight)
01101 thickness and introduced into a fluorine-containing gas furnace maintained at 1400°C to form a second 10m+a thick film.
g A transparent glass crat having a Pa5s-F composition was used.

The refractive index of this second cladding is slightly smaller than that of SiO
B/ka+ (wavelength: 1.55 μm), showing excellent characteristics.

(Effects of the Invention) As described above, the viscosity of the core portion constituting the rod for an optical fiber is made smaller than that of the other portions, so that when it is made into a fiber, the core portion has at least one viscosity. This solidification occurs later than the high viscosity part, and no stress remains inside the core, making it possible to obtain a fiber with low loss.Furthermore, the cladding is made of two layers, one of which is If the coefficient of thermal expansion is made larger than that of the core, even if the core solidifies first and stress remains inside, the cladding, which has a larger coefficient of thermal expansion, will shrink when solidified. This relatively compresses the core, resulting in a low-loss fiber because the residual stress in the core is offset.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing one step in the embodiment of the present invention, Fig. 2 is a graph showing the refractive index distribution of the fiber according to the first embodiment of the invention, and Fig. 3 is the loss of the same fiber and a conventional fiber. FIG. 4 is a graph showing wavelength characteristics, and FIG. 4 is a graph showing a refractive index distribution of a fiber according to a second embodiment of the present invention. In the figure, l: starting member, 2: burner, 3: SiO□
Glass fine particle sintered body. zu7i, 1 figure

Claims (2)

[Claims] (1) A silica glass core containing halogen ions that increase the refractive index of silica glass, a silica glass cladding whose refractive index is lowered by fluorine, and an amount of halogen ions that increase the refractive index of silica glass. An optical fiber comprising a silica glass-based jacket doped in a smaller amount than the amount contained in the core. (2) a silica glass core containing halogen ions that increase the refractive index of silica glass; a first silica glass cladding whose refractive index is lowered by fluorine; A second silica glass cladding is equal to or slightly larger than the first silica glass cladding, and is doped with a smaller amount of halogen ions that increase the refractive index of the silica glass than the amount contained in the core. An optical fiber comprising a quartz glass jacket.