Gas detection based on optical correlation spectroscopy using a single light source

Abstract

An alternative method of gas detection using optical correlation spectroscopy (OCS) has been investigated. A semiconductor optical amplifier (SOA) is employed to transmit broadband light through a reference and measurement cell containing the absorbing species, and the required 180° phase shift between the reference and measurement signal is achieved using an optical fibre delay line. The use of a single SOA light source reduces zero point drift errors that arise when two light sources are utilized and provides high compatibility with single mode optical fibre systems. A theoretical minimum detectable concentration of 0.15 ppm.m has been calculated and experimental results have been obtained for varying concentrations of acetylene (C2H2) gas at different pressures. The theoretical system response was determined using absorption data from the HITRAN database and compares well with the experimental results. Signal-to-noise ratio (SNR) analysis has been performed for our experimental system and an ideal system with minimal losses, an optimum filter and longer cell lengths.