Control of Timing Stability, and Suppression in Delayed Feedback Induced Frequency-Fluctuations by Means of Power Split Ratio and Delay Phase-Dependent Dual-Loop Optical Feedback

Abstract

We experimentally demonstrated a power split ratio and optical delay phase dependent dual-loop optical feedback to investigate the suppression of frequency-fluctuations induced due to delayed optical feedback. The device under investigation is self-mode-locked (SML) two-section quantum-dash (QDash) laser operating at ∼21 GHz and emitting at ∼1.55 m. The effect of two selective combinations of power split ratios (Loop-I: −23.29 dB and Loop-II: −28.06 dB, and Loop-I and Loop-II: −22 dB) and two optical delay phase settings ((i) stronger cavity set to integer resonance and fine-tuning the weaker cavity, (ii) weaker cavity set to integer resonance and fine-tuning of stronger cavity) on the suppression of cavity side-bands have been studied. Measured experimental results demonstrate that delayed optical feedback induced frequency-fluctuations can be effectively suppressed on integer resonance as well as on full delay range tuning (0–84 ps) by adjusting coupling strength −22 dB through Loop-I and Loop-II, respectively. Our findings suggest that power split ratio and delays phase-dependent dual-loop optical feedback can be used to maximize the performance of semiconductor mode-locked lasers.

All Optical Stabilizations of Nano-Structure-Based QDash Semiconductor Mode-Locked Lasers Based on Asymmetric Dual-Loop Optical Feedback Configurations

“…For single-loop optical feedback, there is an increase in the system memory, which directly corresponds with the reduction in the timing jitter [20][21][22][23][24][25][26]. With improved timing jitter, single-loop optical feedback produces additional cavity sidebands around the main frequency in the power spectrum [20][21][22][23][24][25][26][27]. Recently, we have proposed the asymmetric dual-loop optical feedback scheme with equal feedback ratio through each loop, to suppress the first sideband around the fundamental frequency; however, the second appears unsuppressed (modal overlap) [22].…”