According to some embodiments a method of processing an optical fiber comprises the steps of: (i) drawing the fiber at a drawing rate of at least 30 m/sec; and (ii) cooling the drawn fiber in a gas at an average cooling rate less than 5000 °C/s, such that said cooling reduces the temperature of the fiber from an entering temperature in the range between 1500 °C and 1700 °C to another temperature in the range between 1200 °C and 1400 °C, the gas being at a temperature between 800 °C and 1500 °C; and the thermal conductivity K of the gas being not greater than 1.5xl0" 4 cal/cm-s-K for at least one temperature within a range of 800 °C to 1500 °C at one atm (atmosphere) pressure absolute.