Ultrafast fiber lasers mode-locked by carbon nanotube and graphene saturable absorbers: review and prospects [Invited]

Carbon nanotube (CNT) and graphene-based saturable absorbers (SAs), with broadband operation, low saturation intensity, and simple fabrication and integration with fibers, have been widely used for mode-locking of ultrafast fiber lasers. Since their first demonstrations, CNT/graphene mode-locked fiber lasers have been reported intensively, spanning wide wavelength ranges, diverse configurations, and different operation regimes. This review systematically summarizes the evolution of CNT/graphene SAs, their fabrication and fiber-integration approaches, and the major milestones achieved in ultrafast fiber laser development, as well as recent new achievements. Finally, we discuss current challenges and prospect future chances for CNT/graphene SAs.