Method for producing optical fiber preform

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.