Thermally induced optical effects in optical fibers by inverse methodology

Abstract

A conjugate gradient method based on an inverse algorithm is applied in this study to estimate the unknown time-dependent convection heat transfer coefficient and microbending loss in carbon-coated optical fibers by reading the transient temperature measurement data at the fiber surface, when the optical fibers are subjected to transient thermal loading. No prior information is available on the functional form of the unknown convection heat transfer coefficient in the present study; thus, it is classified as the function estimation in inverse calculation. The accuracy of the inverse analysis is examined by using the simulated exact and inexact temperature measurements. Results show that an excellent estimation on time-dependent convection heat transfer coefficient, temperature distributions, and thermally induced microbending loss can be obtained for all the test cases considered in this study. The individual effect of the thickness, Young’s modulus, Poisson’s ratio, and thermal expansion coefficient of the carbon coating on the transient microbending loss of the optical fiber is also investigated. According to the numerical results, there exists an optimum value for the thickness of the carbon coating to reduce the transient microbending loss and to sustain the mechanical force at the same time.