Loss-induced suppression and revival of lasing

TLDR

Controlling and reversing loss remains a major challenge in optical systems, as lasers require sufficient gain to overcome losses and reach threshold. The study demonstrates turning losses into gain by steering system parameters near an exceptional point where eigenvalues and eigenstates coalesce. This is achieved by tuning system parameters to approach an exceptional point, where eigenvalues and eigenstates coalesce. In coupled microresonators, EPs manifest as loss‑induced suppression and revival of lasing; below a critical loss value the Raman laser is annihilated, while beyond it lasing recovers despite increasing loss, illustrating counterintuitive EP behavior and offering a novel method to reverse loss effects.

Abstract

Controlling and reversing the effects of loss are major challenges in optical systems. For lasers losses need to be overcome by a sufficient amount of gain to reach the lasing threshold. We show how to turn losses into gain by steering the parameters of a system to the vicinity of an exceptional point (EP), which occurs when the eigenvalues and the corresponding eigenstates of a system coalesce. In our system of coupled microresonators, EPs are manifested as the loss-induced suppression and revival of lasing. Below a critical value, adding loss annihilates an existing Raman laser. Beyond this critical threshold, lasing recovers despite the increasing loss, in stark contrast to what would be expected from conventional laser theory. Our results exemplify the counterintuitive features of EPs and present an innovative method for reversing the effect of loss.