Optical fiber manufacturing method and optical fiber manufacturing apparatus

An optical fiber manufacturing method comprising:

• a first process of passing a glass fiber through a fiber path, the glass fiber being drawn from a glass preform, the fiber path being formed through a cooling tube, and the cooling tube being housed in a first casing and being cooled by a first coolant;
• and
• a second process of leading the glass fiber into a second casing before leading the glass fiber into the first casing,
• wherein the first process includes supplying a first dry gas into a first dry space formed between the first casing and the cooling tube, a dew point of the first dry gas being lower than a temperature of the cooling tube,
• the second process includes supplying a second dry gas into a second dry space foiiiied inside the second casing so as to cause a second air pressure in the second dry space to be higher than a third air pressure in an external space of the first casing and the second casing, a dew point of the second dry gas being lower than a dew point in the external space,
• the first casing is in contact with the second casing,
• a drawing speed of the glass fiber is 1000 m/min or more,
• the first process includes supplying the first dry gas into the first dry space so as to cause a first air pressure in the first dry space to be higher than the third air pressure in the external space, the dew point of the first dry gas being lower than the temperature of the cooling tube, and
• the second process includes supplying the second dry gas into the second dry space so as to cause the second air pressure in the second dry space to be higher than the first air pressure in the first dry space, the dew point of the second dry gas being lower than the dew point in the external space and the temperature of the cooling tube.