Quasinormal coupled-mode analysis of dynamic gain in exceptional-point lasers

TL;DR

This paper develops a novel coupled-mode analysis framework to understand the complex dynamic gain behavior in lasers operating near exceptional points, revealing new properties like time-varying scattering and non-reciprocal transmission.

Contribution

It introduces a perturbative coupled-mode theory that captures the spatial-temporal dynamics of near-EP lasers, bridging the gap left by conventional static gain models.

Findings

Demonstrates dynamic population inversion leads to self-modulated laser dynamics.

Establishes a modal interpretation of dynamic gain in near-EP lasers.

Enables exploration of non-reciprocal and time-varying properties in laser systems.

Abstract

One of the key features of lasers operating near exceptional points (EPs) is that the gain medium can support an oscillating population inversion above a pump threshold, leading to self-modulated laser dynamics. This unusual behavior opens up new possibilities for frequency comb generation and temporal modulation. However, the dynamic population inversion couples signals with different frequencies and thus cannot be captured by conventional temporal coupled-mode theory (TCMT) based on static saturable gain. In this paper, we develop a perturbative coupled-mode analysis framework to capture the spatial-temporal dynamics of near-EP lasers. By decomposing discrete frequency generation into multiple excitations of resonant modes, our analysis establishes a minimal physical model that translates the local distribution of dynamic population-inversion into a resonant modal interpretation of laser gain. This work enables the exploration of unique properties in this self-time-modulated systems, such as time-varying scattering and non-reciprocal transmission.