PERFORMANCE LIMITATION OF FIBER OPTIC METHANE SENSORS DUE TO INTERFERENCE EFFECTS

We model interference effects in fiber optic methane sensors and predi ct the influence on the sensitivity. System sensitivity in terms of mi nimum detectable methane concentration is expressed as a function of b irefringence, spectral transmission characteristics and polarization d ependent 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 d ata. The model predicts that the interference effects may be minimized by using a depolarized broadband source (say, 30-50 nm) with a Gaussi an spectral lineshape, together with a birefringence balanced sensor c onfiguration.