Influence of optical feedback on harmonic pulsating solutions of long-cavity mode-locked VECSELs

TL;DR

This paper investigates how optical feedback influences the stability and selection of harmonic pulsating solutions in long-cavity mode-locked VECSELs, combining experimental and theoretical analysis.

Contribution

It provides new insights into the role of optical feedback as a solution discriminator and identifies asymmetrical resonance effects caused by gain depletion.

Findings

Feedback can reinforce or hinder specific harmonic solutions.

Experimental results match theoretical predictions.

Asymmetrical resonance tongues are due to gain depletion effects.

Abstract

We analyse the effect of optical feedback on the dynamics of external-cavity mode-locked semiconductor lasers operated in the long cavity regime. Depending on the ratio between the cavity round-trip time and the feedback delay, we show experimentally that feedback acts as a solution discriminator that either reinforces or hinders the appearance of one of the multiple coexisting mode-locked harmonic solutions. Our theoretical analysis reproduces well the experiment. We identify asymmetrical resonance tongues due to the temporal symmetry breaking induced by gain depletion.