A modified cross-correlation method for white-light optical fiber extrinsic Fabry-Perot interferometric hydrogen sensors

ABSTRACT An extrinsic Fabry-Perot interferometric (EFPI) optical fiber hydrogen sensor based on palladium silver (Pd-Ag) film is designed for hydrogen leakage detection. A modified cross correlation signal processing method for an optical fiber EFPI hydrogen sensor is presented.As the applying of a speci al correlating factor which ad vises the effect on the fringe visibility of the gap length and waveleng th , the cross correlation method has a hi gh accuracy which is insensitive to light source power drift or changes in attenuation in the fiber, and the segment search method is employed to reduce computation and demodulating speed is fast. The Fabry-Perot ga p length resolution of better than 0.2nm is achieved in a certain concentration of hydrogen. Keywords: optical fiber sensor, extrinsic Fabry-Perot in terferometer, cross-correlation, fringe visibility 1. INTRODUCTION Hydrogen as a source of clean, sustainable, and abundant energy is widely used in numerous research and industrial fields. However, hydrogen has the wide explosion range (4–75%), in addition, it easily leaks out due to the smallest molecule size. Therefore, security syst ems for hydrogen environments require continuous and reliable hydrogen sensors, especially for low concentrations. A number of hydrogen sensors had been proposed and practically applied