Turn-on delay and jitter of terahertz quantum cascade lasers

Abstract This paper investigates the turn-on delay and jitter characteristics of terahertz quantum cascade lasers (THz QCLs) under external influence. The results demonstrate that both external optical feedback and injection current can significantly influence the turn-on delay of THz QCLs. The delay time decreases with the increase of optical feedback strength and injection current and exhibits an additive effect that higher currents combined with stronger feedback yield shorter delays. The impact of optical feedback on jitter displays nonlinear behavior, i.e., optical feedback introduces additional intensity and phase noise superimposed on spontaneous emission-induced intensity noise. At weak optical feedback level, the jitter increases markedly and decreases after arriving at a maximum. At a moderate optical feedback level, the jitter stabilizes as the feedback intensity increases. At strong optical feedback levels, the jitter exhibits complex behavior. The cavity length of optical feedback exhibits periodic modulation on THz QCLs performance. When the phase of optical feedback aligns or opposes to the emitted phase, phase noise diminishes and jitter is significantly reduced. While for other cases, phase noise dominates at intermediate positions, inducing periodic jitter variations.