| Abstract: | An important function of an optical fiber coating is to prevent optical losses due to microbending induced by lateral forces on the fiber. To protect the fiber over a wide temperature range the modulus of the primary and the secondary coating should be low and high, respectively, and temperature independent. However, selecting the most appropriate organic coating materials introduces a new source of optical losses. Since the linear thermal expansion coefficients of silica and the organic coatings differ by about two orders of magnitude, thermal, fluctuations will cause axial stresses. Cooling may then induce bending or buckling of the glass fiber in the soft primary coating, resulting in increased transmission losses. This effect is especially pronounced when a high-modulus secondary coating is selected with a glass transition temperature above 80°C. For this type of coating the difference in radial shrinkage between the buffer and the top coating during cooling from the curing temperature becomes important. The influence of primary coating thickness is discussed. |
