Optical remote monitoring of CH4 gas using low-loss optical fiber link and InGaAsP light-emitting diode in 1.33-μm region

Purely optical remote monitoring of low-level CH4 gas is realized for the first time by the method employing a 2-km long-distance, low-loss silica optical fiber link and a compact absorption cell in conjunction with a high radiant InGaAsP light-emitting diode (LED) at 1.33 μm. Based on the present experiment, the detection limit of CH4 in air was confirmed to be approximately 2000 ppm, i.e., 4% of the lower explosion limit of CH4. This result supports the conclusion that the fully optical remote sensing system incorporating ultralow loss optical fiber networks and near infrared LEDs or laser diodes can be extensively used for the detection and surveillance of various inflammable and/or explosive gases in industrial and mining complexes as well as in residential areas.