Abstract: Disclosed is an optical fiber possible to prevent it from increasing an optical loss occurring during fabrication of a single mode fiber preform and extraction thereof and enhance an optical transmission efficiency, a method of producing the same comprising the steps of forming a first quartz tube having a first thermal conductivity, said first quartz tube being used as a clad; depositing a core layer and a clad layer inside said first quartz tube to form a preliminary perform by heating of said fist quartz tube; forming a second quartz tube having a second thermal conductivity lower than said first thermal conductivity; and depositing said second quartz tube to said preliminary preform by heating to produce said optical fiber preform.

Abstract: Disclosed is an optical fiber capable of preventing an increase in an optical loss from occurring during fabrication and extraction of a single mode fiber preform and enhancement of an optical transmission efficiency, a method of producing the same comprising the steps of forming a first quartz robe having a first thermal conductivity, said first quartz tube being used as a clad; depositing a core layer and a clad layer inside the first quartz robe to form a preliminary perform by heating of the fist quartz robe; forming a second quartz tube having a second thermal conductivity lower than the first thermal conductivity; and depositing the second quartz tube to said preliminary preform by heating to produce the optical fiber preform. On embodiment, uses N overclad layers having thermal conductivites K.sub.x such that K.sub.0 >K.sub.1 >K.sub.2 . . . >K.sub.N and coefficients of viscosity .mu..sub.0 <.mu..sub.1 <.mu..sub.2 . . . <.mu..sub.N.