High-sensitivity electro-optic CO<sub>2</sub> gas sensing based on absorption spectroscopy

Abstract

We reported a high-sensitivity CO2 gas sensing system based on wavelength scanning absorption spectroscopy. A distributed feedback (DFB) laser was used as the light source in the system, whose wavelength was thermally tuned, by a thermoelectric cooler (TEC), to scan around one CO2 absorption line near 1572nm. Scanning of the absorption line spectrum is performed over a glass CO2 gas cell, 16.5 cm long with collimated optical fiber connectors. Different concentrations of CO2 were prepared by a high-precision gas flow control meter and sealed within the gas cell. A self-designed detection and amplification circuit was employed for absorption spectrum detection. The circuit implements background-cancellation with a two tier amplification scheme. By cancelling the high background signal, we can improve the CO2 sensitivity by about two orders of magnitude compared with commonly used direct detection methods with high background signals. Reducing the high DC signal permits isolated amplification of the absorption line spectrum. Absorption spectra of different CO2 concentrations were measured, and the results demonstrated sensing capability of 100% to l0.1% concentrations of CO2. This sensing system is expected to be used in conjunction with a wireless CO2 sensor network for large area CO2 monitoring. Given the very lower power consumption of the DFB laser and the detection circuit this sensing system offers a solution for affordable long term CO2 monitoring for reliable storage in carbon sequestration.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.