Apparatus for coating optical fibers

1. Field of the Invention A coating die that includes an insert having a high thermal conductivity, which is greater than 1 W/cm*K. Preferably, the insert is made of diamond having a thermal conductivity in the range of 5 to 20 W/cm*K. Use of this highly conductive insert helps to efficiently dissipate the heat produced by viscous losses in the coating as most of these losses occur very close to the inner wall of the die in the land region. It also reduces to negligible level the wall temperature unbalance between opposite sides of the fiber when this fiber is off-centered thus restoring conditions prevailing at low draw rates and subsequent satisfactory centering force.