Layered NbOCl ₂ as a Nonlinear Platform for Ultrafast and Excitable Fiber Lasers

ABSTRACT Layered van der Waals materials have attracted increasing interest as a nonlinear optical component for advanced laser systems. Here, we demonstrate layered NbOCl ₂ as a nonlinear platform enabling ultrafast and excitable fiber laser operation in the telecommunication band. High‐quality NbOCl ₂ crystals synthesized by chemical vapor transport can be exfoliated into few‐layer flakes exhibiting saturable absorption with low saturation intensity. By incorporating NbOCl ₂ into an erbium‐doped fiber laser, stable self‐starting mode‐locked operation is achieved at a threshold pump power of 77 mW. The laser generates pulses with pulses centered at 1593 nm, with a 3 dB bandwidth of 2.5 nm, a repetition rate of 4.5 MHz, a signal‐to‐noise ratio exceeding 60 dB, and maintains stable operation over 24 h. Beyond mode‐locked and Q‐switched regimes, the same laser system can be operated in an excitable regime, where isolated optical spikes are generated in response to external perturbations, exhibiting threshold‐like and all‐or‐none spiking behavior. These results highlight the versatility of NbOCl ₂ as a nonlinear optical platform for ultrafast and excitable fiber lasers and indicate its potential relevance for spike‐based photonic neuromorphic systems.