Relaxation of thermal stresses in double-coated optical fibers

The thermal stresses in double-coated optical fibers are analyzed by the vi scoelastic theory. A closed form solution of the thermal stresses is obtain ed. The thermal stresses are proportional to the temperature change, and ar e a function of the material's properties of the polymeric coatings and the ir thicknesses. The material's properties of the polymeric coatings include the Young's modulus, thermal expansion coefficient, Poisson's ratio, and r elaxation time. The relaxation of thermal stresses is strongly dependent on the relaxation time of the polymeric coating. If the relaxation time of th e polymeric coating is very long, the viscous behavior of the polymeric coa tings will not appear, and the thermal stresses solved by the viscoelastic theory are the same as those solved by the elastic theory. On the other han d, if the relaxation time of the polymeric coating is very short, the relax ation of thermal stresses is very apparent. A compressive radial stress at the interface of the glass fiber and primary coating will result in an incr ease of the microbending losses, and a tensile interfacial radial stress wi ll possibly produce the debond at the interface of the glass fiber and prim ary coating. To minimize this interfacial radial stress, the radii, Young's moduli, thermal expansion coefficients, and Poisson's ratios of polymeric coatings should be appropriately selected, and the relaxation time of the p rimary coating should be decreased. Finally, the thermal stresses in single - and double-coated optical fibers are discussed. (C) 1999 American Institu te of Physics. [S0021-8979(99)06520-2].