Exceptional point proximity-driven mode-locking in coupled microresonators

TL;DR

This paper demonstrates theoretically and numerically that mode-locking can be achieved in coupled microresonators near an exceptional point without traditional saturable absorbers, using an auxiliary cavity as an artificial saturable absorber.

Contribution

It introduces a novel mode-locking method leveraging exceptional point physics and an auxiliary cavity, reducing power requirements and simplifying adjustments.

Findings

Mode-locking feasible without natural saturable absorber.

Exceptional point enhances system Q and modulation.

Auxiliary cavity acts as an artificial saturable absorber.

Abstract

We show theoretically and numerically that mode-locking is feasible with a coupled-cavity system with gain and loss, notably, without any natural saturable absorber. We highlight that in the vicinity of the exceptional point, system $Q$ exhibits substantial modulation even with minor refractive index changes and a minimal Kerr effect contribution. Leveraging this unique behaviour, we propose an unprecedented approach wherein the lossy auxiliary cavity functions as an efficient artificial saturable absorber, thus facilitating mode-locking. This approach is not only novel, but also presents considerable advantages over conventional systems where both gain and saturable absorption are contained within a single microcavity. These benefits include reduced operational power and ease of post-adjustment, achievable through the manipulation of the coupling strength between the two microcavities.