The degenerate band edge laser: a new paradigm for coherent light-matter interaction

TL;DR

This paper introduces a new type of laser based on a fourth order exceptional point of degeneracy called the degenerate band edge, enabling low-threshold, single-frequency lasing in lossless structures with a novel scaling law.

Contribution

It presents the concept of the degenerate band edge laser, a lossless, gainless structure that achieves single-frequency lasing with unprecedented threshold scaling and mode selectivity.

Findings

Lower lasing threshold compared to regular band edge lasers.

Achieves single-frequency operation even without mirror reflectors.

Exhibits a fifth power inverse scaling law of the threshold with cavity length.

Abstract

We propose a novel class of lasers based on a fourth order exceptional point of degeneracy (EPD) referred to as the degenerate band edge (DBE). EPDs have been found in Parity-Time-symmetric photonic structures that require loss and/or gain, here we show that the DBE is a different kind of EPD since it occurs in periodic structures that are lossless and gainless. Because of this property, a small level of gain is sufficient to induce single-frequency lasing based on a synchronous operation of four degenerate Floquet-Bloch eigenwaves. This lasing scheme constitutes a new paradigm in the light-matter interaction mechanism that leads also to the unprecedented scaling law of the laser threshold with the inverse of the fifth power of the laser-cavity length. The DBE laser has the lowest lasing threshold in comparison to a regular band edge laser and to a conventional laser in cavities with the same loaded quality (Q) factor and length. In particular, even without mirror reflectors the DBE laser exhibits a lasing threshold which is an order of magnitude lower than that of a uniform cavity laser of the same length and with very high mirror reflectivity. Importantly, this novel DBE lasing regime enforces mode selectivity and coherent single-frequency operation even for pumping rates well-beyond the lasing threshold, in contrast to the multifrequency nature of conventional uniform cavity lasers.