Dual-sideband heterodyne of dispersion spectroscopy based on phase-sensitive detection.
A methane sensor based on dispersion spectroscopy is presented in this paper. A standard Mach-Zehnder modulator working in carrier suppression mode is adopted to generate a spectrum of a carrier and two sidebands. We aim at detecting the phase shift of the beatnote generated by the two sidebands in a methane concentration evaluation process. We put forward an analytical model to describe the dual-sideband heterodyne scheme and carry out experiments to demonstrate the model. Long-term tests show that the sensor has a minimum detection limit of 0.4  ppm·mHz<sup>-0.5</sup> at an average time of 1 s. And in the condition of 1 atm and room temperature, a linear measurement range from 0.4 to 44955  ppm·m is achieved.