Layered NbOCl₂ as a Nonlinear Platform for Ultrafast and Excitable Fiber Lasers

Layered van der Waals materials have attracted increasing interest as a nonlinear optical component for advanced laser systems. Here, we demonstrate layered NbOCl₂ as a nonlinear platform enabling ultrafast and excitable fiber laser operation in the telecommunication band. High-quality NbOCl₂ crystals synthesized by chemical vapor transport can be exfoliated into few-layer flakes exhibiting saturable absorption with low saturation intensity. By incorporating NbOCl₂ 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 NbOCl₂ as a nonlinear optical platform for ultrafast and excitable fiber lasers and indicate its potential relevance for spike-based photonic neuromorphic systems.