Thermally induced microbending losses in double-coated optical fibers during temperature cycling

The thermally induced microbending losses in double-coated optical fibers d uring temperature cycling are analyzed. The compressive radial stress at th e interface between the glass fiber and primary coating would produce the m icrobending loss. A simplified closed-form formula to calculate the microbe nding loss is obtained by the viscoelastic theory. This formula can be exte nded to calculate microbending losses induced by temperature cycling with a ny number of stages, if the temperature is linearly raised, linearly droppe d, or fixed in each stage of the cycle. Although the temperature change is zero at the end of the temperature cycling, the microbending loss will poss ibly exist. This microbending loss increases with the number of temperature cycles, and finally approaches a constant. To minimize the interfacial rad ial stress between the glass fiber and primary coating, the radius, Young's modulus, thermal expansion coefficient, and Poisson's ratio of polymeric c oatings should be appropriately selected, and the relaxation time of the pr imary coating should be much shorter than the period of the temperature cyc le. The condition for the glass transition temperature range of polymeric c oatings within the temperature cycling is discussed. Additionally, microben ding losses in single-coated optical fibers during temperature cycling are also considered. (C) 2000 American Institute of Physics. [S0021-8979(00)073 20-5].