Crosstalk analysis of a TDM fiber gas sensor array using wavelength modulation of the DFB laser

The results of an investigation on the performance of a time-division addressed fibre optic gas sensor array using wavelength modulation of the DFB laser are reported. The system performance is found to be limited seriously by the extinction ratio of the optical switch used for pulse amplitude modulation. Formulas that relate the crosstalk level to the extinction ratio of the switch, the modulation parameters of the DFB laser and the optical path difference between sensing channels are derived. Computer simulation shows that a methane gas sensor array of 20 sensors with a detection sensitivity of 2000ppm (10cm gas cell) for each individual sensor may be realised using present commercial available single Mach-Zehnder type amplitude modulator (-35dB extinction ratio). An array of 100 sensors with 100ppm detection sensitivity for each sensor may be realised ifa double Mach-Zehnder type amplitude modulator is used.