Performance limitation of fiber optic methane sensors due to interference effects

We model interference effects in fiber optic methane sensors and predict the influence on the sensitivity. System sensitivity in terms of minimum detectable methane concentration is expressed as a function of birefringence, spectral transmission characteristics and polarization dependent loss of the fiber system, and the polarization and coherence characteristics of the light source. The sensitivity is calculated for various system arrangements and compared with existing experimental data. The model predicts that the interference effects may be minimized by using a depolarized broadband source (say, 30-50 nm) with a Gaussian spectral lineshape, together with a birefringence balanced sensor configuration.