Superluminescent diode is light source for gas sensing

Sensing trace emissions and the proportion of oxygen (O₂) in exhaust gas are important for monitoring the efficiency of power-generation plants and combustion equipment. Rather than taking the standard optical-sensing approach of pairing a tunable IR laser with absorption spectroscopy, a group at the Indian Institute of Technology (Chennai, India) is using a superluminescent diode (SLD) as the source. The advantage is a simple, stable configuration, although at the cost of some sensitivity.

Two different SLDs were used to sense O₂ via its 760 nm absorption lines, and ammonia (NH₃) via its 1530 nm absorption lines. The light was coupled via optical fiber to a spectrum analyzer for O₂ and an optical spectrum analyzer for NH₃. Over an 8 m absorption path, O₂ concentrations were observed over a range from 5 to 150 kPa. Concentrations of NH₃ over a 2 m path at 0, 13.5, and 20.3 kPa were observed. The detection limit for NH₃ was 2 kPa, but with a stronger absorption line could be lowered to 26.8 Pa (300 parts per million), or even further with a longer path length. The broadband nature of the source could enable simultaneous detection of more than one gas. Contact Nilesh Vasa at [email protected].