RESEARCH ON A RICE FIELD METHANE DETECTION SYSTEM USING HOLLOWCORE PHOTONIC CRYSTAL FIBRE BASED ON TDLAS TECHNIQUE

A methane gas detection system has been developed based on the infrared absorption method. The system can be deployed in dry rice field for real-time detection. It consists of self-developed circuits and essential optical parts. A distributed feedback laser has been chosen as the optical source of the system. Hollow-core photonic crystal fibre is also applied as a part of the gas cell. The major circuit boards include laser driver circuit, laser temperature control circuit, digital lock-in amplifier circuit and linear power circuit. The laser diode can be effectively controlled by using the above circuits. The laser driving current step is 1 mA and the temperature fluctuation is less than ± 0.02 ℃. Based on the TDLAS technique, spectroscopy test shows that the proposed laser driving circuits has accurate control capability. The detection error is about 2.3% by performing the full-scale detection experiments. Further gas detection experiments using standard gas under 600 ppm also demonstrate the effectiveness and stability of the proposed system. By replacing the optical source and essential driving circuits of the system, the system can be applied to detect other trace gases.