Methods of making an optical fiber, and optical fiber

A method of processing an optical fiber comprising:

• (i) providing the fiber drawn at a draw rate greater than 30 m/sec;
• (ii) cooling the fiber at a first cooling rate, said first cooling rate being greater than 5000° C./s, said cooling at the first cooling rate reducing fiber temperature from a first temperature T1 to a second temperature T2, such that T2<T1, the first temperature T1 being in the range from 1800° C. to 2100° C. and the second temperature T2, being in the range from 1600° C. to 1800° C.;
• and
• (iii) cooling said fiber in a gas at a second cooling rate, at a gas temperature between 800° C. and 1500° C., the second cooling rate being less than 5000° C./s, said cooling at said second cooling rate reducing the temperature of said fiber from a third temperature T3 to a fourth temperature T4, wherein T3≤T2, the third temperature T3 being in the range from 1500° C. to 1700° C. and the fourth temperature T4 being in the range from 1200° C. to 1400° C.;
• and wherein the thermal conductivity κ of the gas is not greater than 1.6×10−4 cal/cm-s-K, for all temperatures between 800° C. and 1500° C. at 1atm pressure absolute.

The method of manufacturing an optical fiber comprising:

• (i) heating a fiber preform above its softening point,
• (ii) drawing the optical fiber from the heated preform at a draw rate of at least 30 m/sec;
• and
• (iii) passing the optical fiber through two treatment stages, such that
• a. the fiber enters a first treatment stage at a temperature between 1800° C. and 2100° C. and experiences an average cooling rate greater than 5000 ° C./s in the first treatment stage;
• b. the optical fiber exits the first treatment stage at a temperature between 1600° C. and 1800° C.;
• c. the optical fiber enters a second treatment stage downstream from the first treatment stage at a temperature between 1500° C. and 1700° C. and experiences an average cooling rate less than 5000° C./s in the second treatment stage in a gas or gas mixture having
• i. a temperature between 800° C. and 1500° C. and
• ii. a thermal conductivity κ that is not greater than 1.6×10−4 cal/cm-s-K for all temperatures within a range of 800° C. to 1500° C. at 1 atm pressure absolute, and
• d. the optical fiber exits the second treatment stage at a temperature between 1200° C. and 1400° C.