There has been considerable interest in methane sensors based on infrared absorption spectroscopy recently for industrial detection and environment monitoring.A DFB LD in the 1665nm region has been utilized as a light source for differential absorption measurement in the sensing of methane.The light output from the DFB LD is split into two beams by a half mirror.One of the beams is used for sensing methane (sensing light beam) while the other is used for wavelength calibration (reference beam).The sensing light beam has been adjusted to coincide with one of the methane 2v3 absorption lines,and it has been monitored by PbSe PD1 (photo diode) after being passed through the testing cell.The reference beam which is free from absorption has been monitored by PD2.Dividing the sensing signal by the reference is also investigated to increase the sensitivity.The system can detect methane down to 100×10-6,and the response time is about 14 s.