Dual-Comb Spectroscopy From an Optically Injected Single Gain-Switched Semiconductor Laser Source

In this work an experimental demonstration of dual-comb spectroscopy using a single gain-switched laser source is presented. By externally modulating the repetition rate of a single train of optical pulses with a periodic signal, two broad optical frequency combs (OFCs) are generated. These combs, each with a width of 70 GHz, have different repetition rates close to 250 MHz alternating periodically according to the modulation. Then, after separating the two combs into two different branches and delaying one of them with a fiber spool, both OFCs were used in a dual-comb scheme, resulting in a flat dual comb radio-frequency spectrum. We validate the capability of this system for spectroscopy by measuring the absorption profile of a 100-Torr HCN gas cell with high resolution. This single-laser approach opens the path to using gain-switching dual-comb systems as a simple and cost-effective alternative for high-resolution integrable applications.