Compensation for surface contamination in a D-fiber evanescent wave methane sensor

The effects of surface contamination on the performance of a D-fiber evanescent wave methane sensor are discussed. Contamination on the flat surface of the D-fiber will modify both the scale factor of the methane detection system and the birefringence of the D-fiber. The birefringence variation can be monitored and used to compensate for the scale factor variation, through one of the two compensation models which will be described in the text. The models are found to be fairly accurate, and for the D-fiber used in our experimental tests, the maximum relative error for scale factor correction is about /spl plusmn/5%, for both models. >