Impact of higher-order dispersion on frequency-modulated combs

Frequency -modulated (FM) combs form spontaneously in free -running semiconductor lasers and possess a vast potential for spectroscopic applications. Despite recent progress in obtaining a conclusive theoretical description, experimental FM combs often exhibit non -ideal traits, which prevents their widespread use. Here we explain this by providing a clear theoretical and experimental study of the impact of the higher -order dispersion on FM combs. We reveal that spectrally dependent dispersion is detrimental for comb performance and leads to a decreased comb bandwidth and the appearance of spectral holes. These undesirable traits can be mended by applying a radio frequency modulation of the laser bias. We show that electrical injection -locking of the laser leads to a significant increase of the comb bandwidth, a uniform -like spectral amplitudes, and the rectification of the instantaneous frequency to recover a nearly linear frequency chirp of FM combs. (c) 2024 Optica Publishing Group