JPS60141628A - Preparation of quartz glass doped with fluorine - Google Patents

Abstract

PURPOSE:To prepare quartz glass doped with fluorine having smaller refractive index than conventional products by using PF3 as precursor of dopant. CONSTITUTION:Soot of SiO2 is prepd. by burning a gaseous mixture comprising SiCl4, H2, and O2. PF3 is allowed to contact with the soot and then vitrified, or a gaseous mixture consisting of SiCl4, PF3 and O2 is heated at ca. 800- 1,600 deg.C to form soot of SiO2 doped with P and F, and the SiO2 layer contg. P and F is vitrified. By either of both methods, quartz glass doped with F having <=1.445 refractive index is obtd. The quartz glass prepd. by this method is doped with P in addn. to F, and existence of P effects to increase the refractive index of the quartz glass, however, the degree is not so large as to affect severaly the influence of F for decreasing remarkably the refractive index. Therefore, the titled glass having smaller refractive index than conventional product using BF3, etc. is obtd.

Description

[Detailed description of the invention] do.

It is known that doping quartz glass with fluorine lowers the refractive index of the quartz glass, and such fluorine-doped quartz glass is used, for example, as a material for the cladding of silica glass optical fibers.

Silica glass-based optical fibers are known to have a composition consisting of a core and a fluorine-doped silica glass cladding that has a smaller refractive index than the core, and utilizes the difference in refractive index between the core and the cladding (80) and transmits light. The larger Δn is, the more light leakage can be reduced and the number of openings can be increased. However, the core that transmits light must have as little light transmission loss as possible, and from that point of view, high-purity quartz glass is preferable. Therefore, in order to increase Δn, fluorine-doped quartz glass with a low refractive index is used as a cladding. It is used as

As a method for manufacturing such fluorine-doped quartz glass, SL
A method of manufacturing fluorine-boron doped quartz glass by heating a mixed gas consisting of C#4, a fluoride such as BF3, and oxygen is known.

However, since the fluorine-boron doped quartz glass obtained by this method is heavily doped with fluorine and boron, there are various problems caused by boron.
For example, it has problems such as an increase in the coefficient of thermal expansion, and a practical fluorine-boron doped silica glass has a refractive index of at most 1.4465 (the refractive index of pure silica glass (1
, 4585> (80), only 0.012> can be obtained.

As a result of intensive research to create a practical fluorine-doped quartz glass with an even lower refractive index, the inventors found that PFs
They have discovered that when producing fluorine-doped quartz glass using fluorine-doped quartz glass as a dopant precursor, the refractive index of the obtained fluorine-doped quartz glass can be further reduced, and the present invention has been completed.

PFs used in the present invention has a melting point of -93.8°C and a boiling point of -84°C.
It is a gaseous compound at room temperature of 4°C, molecules @ 126.

In the method of the invention, St
a? Approximately 800 ml of mixed gas consisting of forming agent, PFs, and oxygen
St heated to ~1600°C and doped with phosphorus and fluorine
S which forms the soot of at and further contains phosphorus and fluorine
L Opi! may be vitrified, or St CI
5LOt by burning a mixed gas consisting of 4, hydrogen and oxygen
A soot may be formed, and then the soot may be brought into contact with PFs and then vitrified. In either method, fluorine-doped quartz glass having a refractive index of 1.445 or less can be obtained.

When using a mixed gas containing a St 02 forming agent such as St CI 4 and PFs, 1.5 tOt forming agent 10
0.05 to 1 part by volume of PFs may be mixed per 0 part by volume. In addition, when PFs is brought into contact with SL 02 soot, the temperature is about 100 to 1000°C, preferably about 300 to 8°C.
PFs may be brought into contact with St Ot soot at a temperature of 00° C. for about 5 to eO minutes.

The quartz glass obtained by the method of the invention is doped not only with fluorine but also with phosphorus. Although this phosphorus acts to increase the refractive index of silica glass, the degree of this action is very small compared to the refractive index lowering effect of fluorine, and does not significantly impair the refractive index lowering effect of fluorine.

Note that, since PFs is decomposed by water, it is preferable to use it in a system free of water as much as possible.

The fluorine-doped quartz glass obtained by the method of the present invention is effective as the cladding of a silica glass optical fiber, the cladding of an image guide, an optical lens, and a prism. When used as the cladding of a silica glass-based optical fiber, the difference in refractive index (80) with the high-purity silica glass of the core should be set to 0.
02 or more, therefore, the thickness of the cladding can be further reduced and the numerical aperture can be increased.

Furthermore, image guides using silica glass optical fibers are usually manufactured by fusing a large number of optical fibers together due to manufacturing constraints, and have the problem of poor flexibility. The cladding can be made thinner when
The outer diameter of the image guide can be reduced, and its flexibility can be greatly improved. It is not clear why the refractive index is significantly lower than that of conventional fluorine-doped silica glass when PFs is used as a precursor with Dovan, but it is a Lewis acid with a strong PF%, It is presumed that when the skeleton becomes 1, phosphorus is incorporated into the glass skeleton together with 1 to 3 fluorine atoms.

Next, the present invention will be explained in detail by giving examples.
The present invention is not limited to such embodiments.

Example 1 SL CI 4 was placed in a quartz glass tube heated to 600°C.
A mixed gas of PFs and oxygen (SL (Ja: PF
s:0p-1:0, 3:2, molar ratio) was doped with phosphorus and fluorine by continuously contacting them for 10 minutes.
A soot of t 02 was formed. Then, the quartz glass was heated to 1200°C to form the SiO! The soot was vitrified to obtain fluorine-doped quartz glass. The refractive index of the obtained fluorine-doped quartz glass was 1,438.

Example 2 SL CI < and mixed gas of hydrogen and oxygen (SLC&a
: Ha: 0, -1: 10: 25, molar ratio) was burned and blown onto quartz glass to form Stoe's soot.

The soot was then maintained at 600° C., contacted with PFs for 10 minutes, and then heated to 1200° C. to vitrify it to obtain phosphorus-fluorine doped quartz glass. The refractive index of the obtained fluorine-doped quartz glass was 1.432.

Claims (1)

[Claims] A method for producing fluorine-doped quartz glass, characterized in that I PFs is used as a Dovan i- precursor.