L-band dual-comb based on gain-switched lasers for CO2 monitoring

This paper reports the development of a dual-comb spectroscopy system based on gain-switched single-mode laser diodes emitting at 1572 nm. The switching is performed by a train of short electrical pulses at a repetition rate of 100 MHz while the lasers are subjected to external optical injection. Under these conditions, broad and Hat optical frequency combs (OFC) are generated, showing 500 tones within 10 dB and a line spacing fix ed by the repetition rate of the swi tching pulses. The dual-comb gene rated by th e interference of two such combs with slightly different line spacing, is used for measuring the absorption line of CO2 at 1572.02 nm. The transmission spectrum is analyzed and fitted to a Voigt profile. A deviation of 3% in the residuals of the fitting is obtained, denoting the high spectral performance of the spectroscopy system.