Modeling an evanescent field absorption optical fiber sensor

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Abstract
Using the weakly guiding and exact field solutions of an optical fiber, we wrote a FORTRAN program to determine the fractional power that reaches the end of an optical fiber with an absorptive cladding. We have assumed that each mode of the fiber is equally excited. This corresponds to incoherent source excitation. The results were compared to a previous approximations published in the literature. We have found that, at low V-numbers, V < 20, Payne and Hale's approximation deviate by more than 20% from the weakly guiding solution. At high V-numbers, the approximation deviated by less than 10%. When compared to Payne and Hale's approximation, both the weakly guiding and exact solutions are closer to the data points obtained experimentally by Degrandpre and Burgess. Although closer than Payne and Hale's approximation, our solution still deviates from Degrandpre and Burgess' results. The difference may be due to the assumption that all modes were excited equally. Another possibility was the fact that we have neglected leaky modes in our treatment.

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