JPH0220805A - Fiber for light transmission - Google Patents

Abstract

PURPOSE:To obtain the single mode fiber for light transmission having a stable structure with less absorption losses by incorporating GeO2 and F into a core and incorporating only the F at the same concn. as the concn. thereof in the core into a clad in the amt. enough to lower the refractive index without incorporating P2O5 therein. CONSTITUTION:The refractive index distribution shown in the figure is attained by incorporating the GeO2 and the F into the core and incorporating only the F into the clad without adding the P2O5 thereto. Namely, the compsn. of the core is GeO2-F-SiO2 and the compsn. of the clad is SiO2-F. The F is incorporated into the both the core and the clad. The wavelength at which total dispersion is zero is, therefore, nearer the actual use wavelength and the total dispersion thereof is decreased. The single mode fiber having the less losses and dispersion is obtd. in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a fiber for single mode optical transmission using the MAD method.

[Background technology] A single mode optical transmission fiber using the conventional MAD method is
As shown in Fig. 1, a fine particle aggregate (porous base material) consisting of a core 3 and a cladding 4 is formed by a plurality of burners 1.2.
It is made by a process that involves simultaneously depositing the crystals in the rotating axial direction, then converting them into transparent vitrification in a He atmosphere containing chlorine-based gas, stretching them, covering them with quartz pipes, and drawing them into wire. There is.

At this time, for the preparation of the porous base material, 5IC1,
and GeCl4 as raw materials, and 5IC14 as raw material for the cladding, and as a result, the resulting glass composition has a core of 5
The 102-GeO2 cladding becomes S+O, and a refractive index distribution with characteristics as shown in FIG. 2 is obtained. On the other hand, in recent years, a structure as shown in FIG. 3 has been proposed as a new refractive index distribution structure for a fiber for single mode optical transmission. (The Be-11 System Tec
hnicaIJournal Voj, B1. Na2
．． P2B2-26 [see i, 1982] The glass composition of the fiber according to this proposal is as shown in Fig. 4, with a core of GeO3-5ho and a cladding of 5I0.
2-F-P2O5, and the manufacturing method is MCY
This is based on method D.

In the structure shown in FIG. 4, the core glass composition is made of 5I02-GeOQ, but this glass composition is unstable in terms of glass structure based on defects appearing in the ultraviolet absorption spectrum. This is evident from absorption peaks and coloring caused by radiation. Needless to say, defects in the glass structure also have an adverse effect on the near-infrared wavelength band in which optical transmission fibers are used.

Next, the presence or absence of addition of P and OIS in the composition of the cladding will be described. In the conventional MCVD method, in order to avoid manufacturing difficulties such as shrinkage of the quartz tube due to high temperatures, it was essential to add P2O3, which provides physical properties of low viscosity.

However, P2O5 is unnecessary from an optical point of view, and on the contrary, a P atom with a coordination number of 5 is unstable in a glass structure, so it can be said that it is not favorable optically.

[Disclosure of the Invention] Based on the viewpoints explained above, the present invention has a refractive index distribution shown in FIG. 3 containing Gem and F in the core, and P2 in the cladding.
The purpose is to provide a single mode fiber for optical transmission with a new structure containing only F without adding Ol5, and as shown in FIG. The composition of the core is GeO□-F'-5IO□, and the composition of the cladding is SIO□-F, and one feature is that both the core and the cladding contain F.

In addition to loss, a single mode fiber has dispersion as a characteristic, and shortening the ultraviolet absorption edge tends to bring about favorable results in dispersion characteristics as well. The wavelength most commonly used in optical communication systems today is 1.3++m, and the total dispersion of a single mode fiber at this wavelength is a finite value in the case of the refractive index distribution shown in Figures 2 and 3. It is known that the wavelength at which the total dispersion becomes zero is longer than 1.3J11.

The total dispersion of a single mode fiber is determined by the sum of material dispersion and structural dispersion, and material dispersion is fixed to the wavelength of the refractive index. The theory is that the wavelength dependence of absorption and refractive index are not independent of each other, but are linked by the Kramers-Kronitzg relationship (mathematically known as the Hilbert curve r9i). Therefore, by incorporating F into the core, the wavelength at which the total dispersion is almost zero is the wavelength actually used.
, 311m, and the total dispersion is less than 1.31111. For this reason, Gem is added to the core composition.
Including F in addition to 2 works to benefit both loss and dispersion.

Next, regarding the composition of the cladding, for the reasons already mentioned, it does not contain P2O6 and only F is contained in 5I02.

Next, the manufacturing method will be explained.

Generally speaking, if F is introduced in the same process as the 8102 synthesis, highly volatile fluoride gases such as HF and 5IF4 can be introduced.
The generation of 5I02 suppresses the nucleation of 5I02, reducing the glass formation rate, resulting in a method with extremely low productivity. Therefore, in the present invention, the core is made of 5I02-GeO2 glass and the cladding is made of 5I02-GeO2 glass by the method shown in
A porous base material consisting of IO2 was prepared by a fire hydrolysis method, and this was placed in an electric furnace in an atmosphere of ■e+CI2+SFo, with ffe: 10! /mm, C10: 50cc/
am, 5Fa (100cc/+us) to make it transparent. At this time, the temperature was about 1500°C, and the dimensions of the base material were about 45φ x 200mm. In such a porous matrix state, sufficient F is infiltrated into the cladding and the core at substantially the same concentration to lower the refractive index.

be able to. This was stretched to 10 mmφ, a commercially available pure quartz tube was used as a jacket, and the outer diameter was +25 mm.
It was made into an ugly fiber.

Regarding the optical fiber prototyped as described above, the glass composition SIO, -060, in which the core does not contain F! An ultraviolet absorption spectrum test was conducted on a material made of SIO□-F-GeO2 of the present invention and a material made of SIO□-F-GeO2 of the present invention. The results are shown in FIG. 6, and it is clear that the absorption according to the present invention is small.

The microscopic mechanism of stabilizing the glass structure by adding and containing F is still not clear, but oxides such as 5I02 and GeO Easy to become and F
This is thought to be caused by the fact that the gas enters the glass as anions instead of oxygen.

Furthermore, the ease with which defects occur due to GeO□ is correlated with the radiation resistance properties, and it is expected that the radiation resistance properties will be improved by incorporating F.

Further, as shown in FIG. 7, in the refractive index distribution, a decrease of 0.2% in terms of the relative refractive index difference between the core and the cladding was observed. The loss of this optical fiber is 0.45 dB/1 km (
1.3 μm) and the atmospheric dispersion wavelength was 1.305 μm.

[Effects] As explained above, the optical transmission fiber of the present invention has a core containing CeO3 and F, and a cladding containing P20! By containing enough F to lower the refractive index at the same concentration as the core without containing F, it is possible to obtain a single mode fiber for optical transmission with little absorption loss and a stable structure. .

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a method for manufacturing a porous preform for an optical transmission single mode fiber using a conventional VAD method. FIG. 2 is a refractive index distribution diagram of a conventional optical fiber. FIG. 3 is a newly proposed refractive index distribution diagram. FIG. 4 is a glass composition diagram of an optical fiber structure corresponding to the distribution diagram of FIG. 3. FIG. 5 is a diagram of the glass composition of the present invention. FIG. 6 shows the ultraviolet absorption spectra of glasses with and without F. FIG. 7 is a refractive index distribution diagram of an example of the present invention. 1... Burner for core 2... Burner for cladding 3... Porous core portion glass, 4... Porous cladding portion glass. Figure 4 f-Table (nm)

Claims (1)

[Claims] (1) SiO_2 whose core contains both Fe and GeO_2
SiO_ consisting of glass, the cladding containing F at substantially the same concentration as the core and sufficient to lower the refractive index.
1. A fiber for optical transmission, characterized in that the fiber is made of two glasses and further has a jacket of pure silica glass on the outside of the cladding.