JPH03115136A - Optical fiber preform and its production - Google Patents

Abstract

PURPOSE:To obtain an optical fiber preform having improved dispersion property and bending property which consists of a core, first clad part surrounding the core, and second clad part having larger amt. of chlorine and higher refractive index than the first clad. CONSTITUTION:A gas-state source material of glass is introduced to an oxyhydrogen flame burner to deposite glass finer particles produced by hydrolytic effect of the flame on a carrier body. The obtd. porous glass material is treated at high temp. in He gas atmosphere containing <10mol% Cl2 to obtain transparent glass as a glass rod comprising a core and the first clad. This glass rod is then covered with fine particles of glass produced by the same method as above described to obtain porous glass material having the second clad. Then this base material is treated by heating in He gas atmosphere containing Cl2 gas by the amt. larger than that in the first clad by >=5mol%. Thus, the targetted optical fiber perform can be obtained.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to an optical fiber preform, particularly a day-pressed clad single fiber with improved dispersion characteristics and bending characteristics, in which the refractive index of the cladding portion is adjusted by the amount of chlorine. The present invention relates to a mode optical fiber preform and a manufacturing method thereof.

(Prior art) Figure 1 (a) for a silica-based single mode optical fiber
) shown in Matsushido clad type (hereinafter abbreviated as bingata)
The one shown in Figure 1(b) is usually used.
There is also known a depressed clad type (hereinafter abbreviated as OC type) shown in Figure 1, which has improved dispersion characteristics and bending characteristics.

Therefore, in order to obtain a single mode optical fiber preform with this DC type profile, only the refractive index (n2) of the first cladding part in FIG.
Alternatively, it is necessary to lower both the refractive index (n2) of the first cladding part and the refractive index (n, ) of the second cladding part by adding boron, fluorine, etc. so that n2<n.

(Issues to be solved) When manufacturing an optical fiber base material using the Shitakatte method, VAD method, OVD method, MCVD method, etc., the refractive index of BCl3, BF3, SF, SiF4, etc. is changed during deposition or sintering of this base material. A lowering dopant is used, but if a boron compound is used, it will cause an increase in the transmission loss of the resulting optical fiber, and if a fluorine compound is used, it will increase the transmission loss during synthesis or sintering of the optical fiber base material. There is a problem in that the glass products used for the burner, heating chamber, furnace tube, etc. used are etched.

On the other hand, when obtaining an optical fiber preform by sintering a porous glass base material created by VAD method, OVO method, etc. to make it transparent, heat treatment is also performed in a chlorine gas atmosphere. This chlorine gas has the effect of performing a deOH reaction, but this is only used in the production of the MC type single mode optical fiber shown in Figure 1(a); For example, the refractive index n2 of the cladding part can be set to n2<n with respect to the refractive index n1 of the core part, but as shown in FIG. 1(b)
There is a disadvantage that it is not possible to make a C-type single mode optical fiber as shown in FIG. 2, in which the core, second cladding, and first cladding have refractive indexes of nl>t+3>n2.

(Means for Solving the Problems) The present invention relates to a DC type single mode optical fiber preform that solves such disadvantages and a method for manufacturing the same.
In an optical fiber preform mainly composed of silica glass, which includes a cladding part and a second cladding part surrounding the first cladding part, the chlorine content of the second cladding part is greater than the chlorine content of the first cladding part. The porous glass base material obtained by sending the gaseous glass forming raw material to an oxyhydrogen flame burner and depositing the glass fine particles generated by flame hydrolysis on a carrier using an optical fiber preform characterized by A process of obtaining a glass rod consisting of a core part and a first cladding part by treating it at high temperature in a helium gas atmosphere containing chlorine gas to make it transparent vitrified, and using this glass rod as a starting material, applying the same method as above. A porous glass base material having a second cladding part obtained by depositing the glass fine particles obtained in step 1 is produced, and then this is heat-treated in a helium gas atmosphere containing at least 5 mol% or more chlorine gas than the first cladding part. The present invention relates to the above-described optical fiber preform characterized in that it is obtained by a process and a method for manufacturing the same.

That is, as a result of various studies on DC type single mode optical fiber preforms and methods for manufacturing the same, the present inventors created a porous base material consisting of a core part and a first clad part by a known method, and then heated it with chlorine gas. After sintering into a glass rod in the presence of helium gas and optionally oxygen gas, VAD is placed on the glass rod.
When a second cladding part is created by depositing glass particles by a method such as a method or an OvD method, and then sintered in the presence of chlorine gas or helium gas at a concentration higher than the above-mentioned chlorine gas concentration, this second cladding part The inventors discovered that the refractive index n of the first cladding part is higher than the refractive index n2 of the first cladding part, and therefore a DC type single mode optical fiber preform can be easily obtained, and also studied this manufacturing method and completed the present invention. Ta.

(effect) These will be explained in more detail below.

For the DC type single mode fiber preform of the present invention, first, a quartz glass rod having a core portion and a first cladding portion having the profile shown in FIG. 2 is manufactured.

This rondo is created using the VAD method or the OVD method. In the VAD method, a gaseous glass-forming raw material such as silicon tetrachloride and a topping agent such as germanium tetrachloride are sent from a core burner, and silicon tetrachloride is sent from a first clad burner to cause flame hydrolysis. The glass particles generated here are deposited on a carrier to create a porous glass base material. In addition, in the OVD method, silicon tetrachloride is flame-hydrolyzed by a burner that moves from side to side along the core glass rod while rotating, and the glass fine particles generated here are transferred to the core glass. Layers are deposited around the rod to create a porous glass matrix. The porous glass members thus obtained are then sintered into glass rods in an atmosphere containing chlorine gas, helium gas, oxygen gas, etc.; The gas concentration is 1
The content is less than 0 mol%, preferably 0.5 mol% or more.

Fine glass particles obtained by flame hydrolyzing a gaseous glass-forming raw material such as silicon tetrachloride using a VAD method or an OVD method are placed on the glass rod made of the core portion and the first cladding portion thus obtained. The porous glass base material thus obtained is deposited for the second cladding part and sintered in a mixed atmosphere of chlorine gas and helium with a chlorine gas concentration of 25 mol% or more relative to the first cladding part. According to this, the refractive index n of the second cladding part is higher than the refractive index n2 of the first cladding part D.
An advantage is provided that C-type single mode optical fiber preforms are easily obtained.

That is, in the optical fiber preform of the present invention, the second cladding part is formed in an atmosphere containing a larger amount of chlorine gas than the amount of chlorine gas used to form the first cladding part, g! In other words, the refractive index of the first and second cladding parts is controlled by controlling the concentration of chlorine gas supplied when a porous glass base material is sintered into transparent glass. Since the refractive index of the second cladding part can be made higher than the refractive index of the first cladding part, a DC type single mode optical fiber preform can be easily obtained.

The relationship between the concentration of chlorine gas and the refractive index of quartz glass when this porous glass base material is sintered in an atmosphere containing chlorine gas is shown in FIG.

(Example) Next, examples of the present invention will be given.

Example 1 Oxyhydrogen flame burner 1 for forming the core portion to which germanium tetrachloride gas as a dopant is supplied together with silicon tetrachloride gas, and oxyhydrogen flame burner 2 for forming the first cladding portion to which silicon tetrachloride gas is supplied. , and a refractory carrier 3 for depositing glass fine particles generated by flame hydrolysis in these flame burners.A porous glass base material 5 is prepared by the VAD method in a reactor 4 shown in FIG. After forming the porous glass base material 5, the porous glass base material 5 is sintered as shown in FIG. The rod was placed in a reaction furnace 7 and heated to 1,400° C. in an atmosphere with a chlorine gas concentration of 2 mol %, and sintered into transparent glass to produce a glass rod 8.

Next, this glass rod 8 is placed in a 4° reaction apparatus 10 shown in FIG. 6, which has an oxyhydrogen flame burner 9 for forming a second cladding part to which silicon tetrachloride gas is supplied and an exhaust port, and is subjected to the OVD method. After forming the second cladding part 11 on the glass rod 8, it is placed in the sintering reactor 7 shown in FIG. 1 under gas atmosphere
．． It was sintered at 400°C and made into transparent glass to produce an optical fiber preform.

Next, we measured the refractive index of the core, first cladding, and second cladding of the optical fiber preform obtained in this way, and found that it had a profile as shown in FIG. It was confirmed that it was a DC type single mode optical fiber preform with a relative refractive index difference of .30% and Δ-0.03%.

[Brief explanation of drawings]

Figure 1 shows the profiles of silica-based single mode optical fiber preforms; Figure 1 (a) is a matte clad type, Figure 1 (b) is a depressed clad type, and Figure 2 is a profile of the present invention. Figure 3 is a graph of the relationship between the chlorine gas concentration and the refractive index of silica glass when porous glass base material is sintered, and Figure 4 is a graph of the relationship between the refractive index of silica glass and VAD. Fig. 5 is a vertical cross-sectional view of a sintering reactor for sintering the porous glass base material;
FIG. 6 shows a longitudinal cross-sectional view of the reaction apparatus for forming the second cladding part, and FIG. 7 shows a refractive index graph of the optical fiber obtained in the example.

Claims (1)

[Claims] 1. The main component is quartz glass, which is composed of a core portion, a first cladding portion surrounding the core portion, and a second cladding portion having a higher refractive index than the first cladding portion surrounding the first cladding portion. An optical fiber preform characterized in that the chlorine content of the second cladding part is greater than the chlorine content of the first cladding part. 2. The gaseous glass-forming raw material is sent to an oxyhydrogen flame burner, and the glass particles produced by the flame hydrolysis are deposited on a carrier to form a porous glass base material, which is then treated at high temperature to be sintered and made into transparent glass. A step of obtaining a glass rod consisting of a core part and a first cladding part, using this glass rod as a starting material, depositing glass particles thereon to produce a porous glass base material having a second cladding part, and then 2. The method of manufacturing an optical fiber preform according to claim 1, wherein the preform is heated in a helium gas atmosphere containing at least 5 mol % or more of chlorine gas relative to the first cladding portion to form transparent glass.