Apparatus for dehydrating and consolidating an optical fiber preform and method of the same

A method of dehydrating and consolidating an optical fiber preform, comprising:

• arranging said optical fiber preform in a dehydration and consolidation furnace having a first muffle tube constructed of a first hollow cylinder, a first cover member, and a first bottom member and a second muffle tube constructed of a second hollow cylinder, a second cover member, and a second bottom member, which are arranged coaxially in a furnace body such that the whole circumference of said first muffle tube is surrounded by said second muffle tube and an intermediate room is formed therebetween;
• maintaining the pressure of an intermediate room formed between said first muffle tube and said second muffle tubes to be lower than both a pressure in said first muffle tube and a pressure outside said second muffle tube;
• and
• performing a gas supply and exhaust of said intermediate room independent of the gas supply and exhaust of the first muffle tube and a furnace body room.