OSA: Measurement of Near to Mid IR Laser for Gas Detection

Global environmental issues are being highlighted and efforts are being made to reduce greenhouse gases. Carbon dioxide (CO2) is often cited as a greenhouse gas, but other gases that worsen the global environment include sulfur dioxide (SO2) and nitrogen dioxide (NO2). In addition, gas leak detection and central monitoring of explosive gases are effective measures for disaster prevention.

The laser absorption spectroscopy is one of the methods to detect minute amount of gas. It detects a certain gas using a distributed feedback Laser diode (DFB-LD), which has a light absorption wavelength specific to the gas. Since light absorption by gas becomes strong in the long wavelength region, near-infrared to mid-infrared DFB-LD exceeding 2000 nm has come to be used for gas detection.

The optical spectral characterization of DFB-LD is very important because the measurement capability of this method is greatly affected by the side mode suppression ratio (SMSR) performance of DFB-LD.

The applicable models are optical spectrum analyzers that can measure near-infrared and/or mid-infrared light. They offer dynamic range wide enough to measure SMSR of 50 dB or more of DFB-LD that cannot be observed with conventional spectroscopes.