# US 9,517,964 B2 · Method for producing optical fiber preform

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 9,517,964 B2
- Document ID: US9517964B2
- Status: Granted
- Kind: B2
- Application number: 13/229,196
- Filed: 2011-09-09
- Published: 2012-01-05
- Granted: 2016-12-13
- Earliest claimed: 2009-03-12
- Assignees: Fujikura Ltd.
- Applicants: Takahiro Hamada
- Inventors: Takahiro Hamada
- Web page: https://patentgrep.com/patent/US9517964B2

## CPC

- C03B 37/01446: {Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering (C03B37/01853 takes precedence)}
- C03B: MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES

## Abstract

Provided is a method for producing an optical fiber preform including a dehydration step and a sintering step. In the dehydration step, a porous glass base material is provided to a furnace core tube of a dehydration-sintering furnace, and the porous glass base material is dehydrated using a dehydration agent added with an argon gas. In the sintering step, the porous glass base material dehydrated in the dehydration step is sintered. Further, in the dehydration step, a temperature of the porous glass base material begins to be increased in a condition such that a high heat conductivity gas, having a heat conductivity higher than a heat conductivity of the argon gas, is remaining inside the porous glass base material.

## Claims

### Claim 1

A method for producing an optical fiber preform, comprising:
providing a porous glass base material to a furnace core tube of a dehydration-sintering furnace, the furnace core tube being filled with air having a heat conductivity higher than a heat conductivity of argon gas;
beginning to replace the air in the furnace core tube with argon gas;
beginning to allow a temperature of the porous glass base material to increase when 30% to 90% of a volume of the air in the furnace core tube is replaced with argon gas so that 70% to 10% of a volume of the air remains in the furnace core tube in a case where a total volume of the air and the argon gas is defined as 100% by volume in the furnace core tube;
heating to dehydrate the porous glass base material using a dehydrating agent, the dehydrating agent being diluted by argon gas; and
sintering the dehydrated porous glass base material.

### Claim 2

A method for producing an optical fiber preform, comprising:
providing a porous glass base material to a furnace core tube of a dehydration-sintering furnace, the furnace core tube being filled with air in the dehydration-sintering furnace;
preparing a high heat conductivity gas having a heat conductivity higher than a heat conductivity of argon gas, the high heat conductivity gas being different from air;
purging the high heat conductivity gas into the air filled furnace core tube and replacing 50% to 95% of a volume of the air presented in the furnace core tube with the high heat conductivity gas, the furnace core tube thus being filed with a mixture gas of the air and the high heat conductivity gas;
beginning to introduce argon gas into the furnace core tube;
beginning to allow a temperature of the porous glass base material to increase when 30% to 90% of a volume of the mixture gas in the furnace core tube is replaced with argon gas so that 70% to 10% of a volume of the mixture gas remains in the furnace core tube in a case where a total volume of the mixture gas and the argon gas is defined as 100% by volume in the furnace core tube;
heating to dehydrate the porous glass base material heated using a dehydrating agent, the dehydrating agent being diluted by argon gas; and
sintering the dehydrated porous glass base material.

### Claim 3 (depends on 2)

The method for producing the optical fiber preform according to claim 2, wherein the high heat conductivity gas is at least one type selected from the group consisting of a helium gas, nitrogen gas, and a neon gas.

### Claim 4 (depends on 2)

The method for producing the optical fiber preform according to claim 2, wherein the temperature of the porous glass base material begins to be increased when 40% to 80% of a volume of the mixture gas in the furnace core tube is replaced with argon gas.