FIBER BRAGG GRATING-BASED WAVELENGTH MODULATION SPECTROSCOPY TECHNIQUE FOR TRACE GAS SENSING

摘要

A novel gas sensing system based on a tunable fiber Bragg grating (FBG) and a Super luminescent light emitting diode (SLED) source is proposed for trace gas sensing. Such a system has been demonstrated for precise detection of acetylene (C_2H_2) using wavelength modulation spectroscopy technique (WMS) based on modulating the Bragg wavelength of FBG within the width of an absorption line of a target gas. The sensing system has been calibrated against specific gas concentrations (ppm) through controlled experiments and the minimum detectable acetylene (C_2H_2) gas concentration is experimentally found to be ～ 80 ppm (0.008% by volume). Furthermore, the detection limit of the system for SNR(3 dB) was estimated to be ～ 7 ppm (0.0007% by volume). The proposed system provides a relatively inexpensive alternative for trace gas sensing based on a well-established FBG technology. Moreover, the proposed system has tremendous potential for simultaneous detection of multiple species through the use of a cascaded set of carefully chosen FBGs.