Loss-induced lasing: new findings in laser theory?

TL;DR

Loss-induced lasing, previously thought to be a novel effect related to exceptional points, is actually a well-understood phenomenon in laser physics, specifically in loss-coupled distributed feedback lasers, dating back to the 1970s.

Contribution

The paper clarifies that loss-induced lasing is not a new phenomenon nor necessarily linked to exceptional points, but a known mechanism in laser theory from the 1970s.

Findings

Loss-induced lasing is a known laser mechanism.

It does not depend on exceptional point physics.

The phenomenon predates recent experimental reports.

Abstract

In a recent work, using a coupled microresonator system with tailored gain and loss parameters B. Peng et al. [Science 346, 328 (2014)] have experimentally reported on an apparently counterintuitive effect in laser theory, namely the possibility to enhance lasing by increasing loss in the system. The observed phenomenon was related to the existence of an exceptional point in the system and was presented somehow as an unexpected and novel effect, especially by some reporters and scientific blogs. In this communication it is pointed out that the phenomenon of loss-induced lasing does not come as a surprise in known laser theory and that it is not necessarily related to the physics of exceptional points. Loss-induced lasing is basically the lasing mechanism that occurs in loss-coupled distributed feedback lasers. This mechanism dates back to the 1970's, has a simple physical explanation and does not rely on the physics of exceptional points.