Coherent Conversion Between Single‐Frequency and Ultrafast Lasers

Abstract Lasers with high spectral coherence are in high demand for applications requiring high precision. Single frequency (SF) and ultrafast lasers represent two types of highly coherent light sources, each with distinct time‐frequency characteristics. The advent of novel technologies based on electro‐optics and nonlinear optics has bridged the gap between these two types of lasers, enabling coherent conversion between them. This review examines several technologies that enable coherent conversion between SF and ultrafast lasers. The generation of ultrafast pulses by modulation of an SF laser, covering both electro‐optic modulation (EOM) and optic‐optic modulation (OOM) is discussed. With respect to Kerr soliton generation by SF laser‐induced parametric frequency conversion, schemes with and without resonator structure are compared and discussed. The extraction of a single comb line from an ultrafast laser using stimulated Brillouin scattering is also presented. The advent of new technologies using all‐polarization‐maintaining fiber structures has made fiber Brillouin amplification a practical and robust solution for single comb line extraction. These coherent lasers with customizable time and frequency characteristics are poised to become essential building blocks in future photonic technologies.