Self-injection locking of a gain-switched diode laser for quantum applications

The self-injection locking technique is established as a powerful method for diode laser frequency stabilization and achieving exceptional spectral purity. When a diode laser excites a mode of high-Q microresonator the backscattered wave due to Rayleigh scattering appears and enables the narrowing and frequency stabilization of the laser output. In recent studies there was reported observation of the self-injection locking regime applied to a gain-switched laser diode, revealing a dramatic spectral purification effect where the linewidth of individual comb teeth is reduced to the sub-kHz scale, comparable to a non-switched SIL laser. This configuration enables the generation of high-contrast, electrically tunable optical frequency combs with line spacing tunable over an immense range from 10 kHz to 10 GHz, governed solely by the radio-frequency modulation parameters. We demonstrate that this frequency can be continuously tuned. The unparalleled flexibility in tuning the comb's line spacing and bandwidth, combined with its spectral purity and high power, positions the GS-SIL laser as a compact and versatile technology. This technology is immediately relevant for a multitude of cutting-edge applications, including high-capacity coherent communications, precision spectroscopy, optical atomic clocks, quantum key distribution, biosensing, and LiDAR.