Chaotic relaxation spike suppression in gain-switched semiconductor Fano laser

Fano semiconductor lasers have gained attention for their ultra-narrow linewidths and strong dispersive properties. Among pulse generation methods, gain switching, driven by a short electrical current pulse, is simple and effective. It typically includes an initial spiking phase followed by a quasi-steady state. Here, we numerically study the effect of a pre-pump current applied before the main injection in an InP-based C-band (λ_r = 1554 nm) photonic crystal (PhC) Fano laser and its impact on pulse dynamics. The results show that in higher quality-factor nanocavity (NC) of Fano lasers (Q=1000) effectively reduces the amplitude of the main spike in the cross-port (P_x) nanosecond optical pulse and improves spike suppression output. The simulations further reveal that increasing the injection current from J = 5 to 15×J_th suppresses relaxation spikes, resulting in a nearly square-shaped optical pulse at higher current levels. Additionally, under constant current conditions, increasing the cavity length (from L = 5 to 11 µm), in different Q values, leads to an increase in the main spike amplitude and the emergence of additional spikes due to the longer photon lifetime.