# Enhanced response of non-Hermitian photonic systems near exceptional points

## TL;DR

This paper explores how non-Hermitian photonic systems near exceptional points exhibit unique, non-Lorentzian responses with potential for enhanced optical applications, supported by theoretical and numerical analysis.

## Contribution

It provides a detailed theoretical and numerical analysis of the response characteristics of non-Hermitian photonic systems near exceptional points, highlighting non-Lorentzian line shapes and response enhancement.

## Key findings

- Response peak intensity inversely proportional to the fourth power of decay rate
- Significant response enhancement achievable with optical gain
- Numerical verification using microring cavity simulations

## Abstract

This paper theoretically and numerically studies the response characteristics of non-Hermitian resonant photonic systems operating near an exceptional point (EP), where two resonant eigenmodes coalesce. It is shown that a system near an EP can exhibit a non-Lorentzian frequency response, whose line shape and intensity strongly depend on the modal decay rate and coupling parameters for the input waves, unlike a normal Lorentzian response around a single resonance. In particular, it is shown that the peak intensity of the frequency response is inversely proportional to the fourth power of the modal decay rate and can be significantly enhanced with the aid of optical gain. The theoretical results are numerically verified by a full wave simulation of a microring cavity with gain. In addition, the effects of the nonlinear gain saturation and spontaneous emission are discussed. The response enhancement and its parametric dependence may be useful for designing and controlling the excitation of eigenmodes by external fields.