JPS6287907A - Single-mode optical fiber for 1.5mu band - Google Patents

Abstract

PURPOSE:To enable low transmission loss by composing the core of the titled fiber out of quartz incorporated with an additive for decreasing the viscosity, forming the clad with quartz glass added with fluorine and constituting the essential part of the difference in the refractive index between the core and the clad with addition of fluorine. CONSTITUTION:In the single-mode optical fiber for 1.5mu band wherein the zero- dispersion wavelength is in the range 1.5-1.6mu, the core of the fiber is formed with quartz contg. an additive for reducing the viscosity of quartz, the clad is composed of quartz glass added with fluorine and the essential part of the difference in the refractive index between the core and the clad is constituted with addition of fluorine. At least one kind among a group consisting of F, P2O5 and GeO2 is used as the additive for decreasing the viscosity of SiO2. The transmission loss can be improved by the addition of a small amt. of the additive capable of decreasing the viscosity of the glass. Consequently, the single-mode optical fiber for 1.5mu band with reduced transmission loss can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a single mode optical fiber for the 1 and 5 micron band, which has a zero dispersion wavelength between t5 microns and t6 microns and has reduced transmission loss. be.

(Prior Art) A silica-based glass fiber has a minimum transmission loss in a region where the wavelength of light is 1.5 to 1.6 microns. Therefore, in order to maximize the repeater spacing in a transmission system using optical fibers, it is necessary to use light with a wavelength in the 1.5 micron band mentioned above.In this case, if information is to be sent at a high transmission speed, Single-mode fibers are then used, which have a much wider transmission band than multi-mode fibers. Additionally, if information is to be transmitted at very high transmission rates, it is necessary to minimize the dispersion effects of the fiber at the wavelength of the light used. By the way, single mode fibers for a wavelength of 1.3 microns, which are currently commonly used, are designed so that material dispersion and structural dispersion cancel each other out at a wavelength of around t3 microns, and the sum of dispersions becomes zero. wavelength t
There are two methods for using single mode fiber in the 5 micron band and reducing dispersion at this wavelength. One is to design the fiber structure to have zero dispersion in the 1.5 micron band, and the other is to design four light sources with a very narrow spectral width at the working wavelength in the 1.5 micron band. [Literature 1: D9 J I Lion Gai, Electronics Letters, D, J, M!
L170n et, a/, xelectronics
letters, 18 (1982), p.
445-447).

(Problems to be Solved by the Invention) The present invention solves the former of the two methods described in the previous section.
This relates to a single mode fiber designed to have zero dispersion in the 1.5 micron band.〇Single mode fiber VC has a zero dispersion wavelength of 1.5 microns.
To move from 3 microns to t5 microns, refer to the following document 2.
As described in , it is necessary to make the core diameter of the fiber much thinner and to increase the refractive index difference Δn between one core and the cladding.

(Reference 2: L, G, Kuen et al., Electronics Letters, L, G, Oohem et, ajF,
, X1e-Qt! ? 0niC8Letters, 1
5 (1979), p 554-5550) 810. 810. as the cladding. In a normal silica fiber using
Gθ0. It is a well-known phenomenon that transmission loss increases as the amount of addition increases and Δn increases. On the other hand, 810. which has an SIO core and 7 added to the cladding has excellent properties in principle in terms of radiation resistance, hydrogen resistance, initial transmission loss, etc. Even in a fiber where Δn
A similar phenomenon was observed in which the transmission loss increases as the value increases. To address this drawback, the present inventors attempted to reduce the transmission loss from the perspective of residual distortion, and obtained somewhat good results, but the loss was still large compared to the expected theoretical value. .

In view of the current situation, the present invention has been developed with a core of 810 and a clad of 7-810. The present invention aims to provide a 1.5 micron band zero dispersion single mode fiber having lower transmission loss in the system fiber.

(Means for Solving the Problems) The present invention provides a single mode optical fiber for the 1 and 5 micron band with a zero dispersion wavelength between 15 microns and 1.6 microns, in which the core contains an additive that lowers the viscosity of quartz. This is a single mode optical fiber for the 1.5 micron band, in which the quartz contained therein and the cladding are made of quartz glass doped with fluorine, and the main part of the difference in refractive index between the core and the cladding is made by doping with fluorine. A particularly preferred embodiment of the present invention 1c is 810. As an additive to lower the viscosity of
! , p, o, , Gem. -810,
When various prototype T5 micron band zero dispersion single mode fibers were fabricated and examined, the following was found regarding their transmission loss.

That is, it has been found that the transmission loss can be particularly improved by adding a small amount of an additive to the core that does not cause absorption loss in the tS micron wavelength range and can lower the viscosity of the glass.

This phenomenon can be understood as follows. In other words, the core is 1910.・Clad 7-1
110. In the 1.5-micron zero-dispersion single mode fiber, the cladding glass contains a large amount of 1 to increase Δn, so the softening point of the cladding glass is lower than that of the core glass, and when drawn at high temperatures, the softening point of the cladding glass is lower than that of the core glass. , the cladding glass is considerably thicker than the core glass,
The drawing tension is concentrated in the core. In this case, the zero dispersion wavelength is set to 1
．． 5 micron band [Shifted single mode fiber has a smaller core diameter, so the stress applied to the unit cross-sectional area of the core further increases.

On the other hand, when fibers are formed under high tension, many defects occur in the microscopic network structure of the glass, which increases transmission loss.

In other words, a fiber having a thin core structure with sio,.F-810 cladding has a structure in which defects are extremely likely to occur in the core region.

In order to prevent the above defects from occurring, it is basically desirable to reduce the viscosity of the core as well as that of the cladding.
In terms of practical loss characteristics in the Mi/Ron band, even if the cladding has a lower viscosity, it is sufficiently acceptable.

Also, according to the present invention, a method of increasing the viscosity of the cladding layer may be adopted, but this method is preferable from many practical viewpoints. ,P! One example is adding a small amount of 01% Gem, etc. to the core, and the preferable addition amount is as follows:
! Then, Q, 1 to 1.0 mol%, P, O, 0.1
~3.0 molty, Gem is Q, 1 ~ (13 molty).The contribution to the refractive index at this time is summarized in Table 1K as a refractive index ratio with respect to sio. may be used in combination of one or more types.

(Example) A fiber with the specifications shown in Table 2 was created using the VAD method,
We investigated its characteristics. The results are summarized in Table 2.

Table 2 (Effects of the Invention) As is clear from the results of the above examples, the present invention can provide a single mode optical fiber for the 1.5 micron band with reduced transmission loss.

Claims (1)

[Claims] (1) In a single mode optical fiber for the 1.5 micron band with a zero dispersion wavelength between 1.5 micron and 1.6 micron, the core is quartz containing an additive that lowers the viscosity of quartz, and the cladding is fluorine-containing. A single mode optical fiber for the 1.5 micron band, which is made of doped quartz glass, and the main part of the refractive index difference between the core and the cladding is doped with fluorine.