Dual-Optical Frequency Comb Generation for Gas Spectroscopy Using a Single Gain-Switched Externally-Injected Semiconductor Laser

An optical frequency comb (OFC) generator is a laser source that emits an equally-spaced narrow and coherent array of comb-like tones. OFC generation in semiconductor lasers has attracted much attention due to its strong potential for integration in photonic integrated circuits (PICs) [1]. Gain-switching (GS) has become one of the most popular approaches for OFC generation in semiconductor lasers due to its simplicity, flexibility and versatility, capable of producing high-quality OFCs at low frequencies [2], an essential requirement for spectroscopic applications. Dual-comb spectroscopy (DCS) has proven to be a very effective tool for gas spectroscopy [3]. This technique relies on the use of two OFCs, one acting as signal and the other as local oscillator. High-quality OFCs can be generated by a combination of GS and external optical injection, offering a good performance in terms of resolution and sensitivity [4]. In general, these combs are generated by different laser sources and propagated along two different branches, which can potentially increase instabilities between both combs. Although multiple techniques have been proposed in order to counteract this effect, such as in [5], where the author used time-multiplexing with two OFCs generated by external electro-optical modulation, the costs of the laser system remain high, making it challenging to implement such solutions in cost-sensitive applications.