To provide an optical fiber durable against long-term use under conditions of high temp. and high humidity by using a polyimide resin having a specified chemical structure as a coating material.
The optical fiber and optical fiber clad are composed of a quartz glass optical fiber. The optical fiber coat consists of a coating material of a polyimide resin having a chemical structure expressed by the formula. In the formula, R1 is a bivalent org. group having ≥2 carbon atoms and (n) is an integer of >1. In this case, fused quartz having the required distribution of refractive index is prepared and then is heated and drawn into a fine optical fiber like thick malt syrup. Thus, the core and the clad are formed at one time. Then the drawn optical fiber is passed through a polyamide acid soln. in dies. After the optical fiber is passed through the soln., the optical fiber is subjected to heat treatment by passing through a heating furnace for a specified time at a required necessary temp. to vaporize the solvent as well as to promote the imidization reaction. Thus, the optical fiber coated with a polyimide is obtd.
MIWA TAKAO
MINAMITANI RINTARO
FUMINO TAKAYUKI
SAKAGUCHI TATSUNORI
WATANABE SHIZUHISA
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