Hierarchical construction of higher-order exceptional points

TL;DR

This paper introduces a hierarchical method for designing photonic structures with higher-order exceptional points (HOEPs), making them easier to fabricate and more resistant to imperfections, demonstrated through PT-symmetric microring resonators.

Contribution

A novel hierarchical approach for engineering HOEPs in photonic systems that enhances robustness and simplifies implementation compared to existing methods.

Findings

HOEPs can be achieved without uniform coupling profiles.

The proposed method shows resilience to fabrication imperfections.

Full-wave simulations confirm the effectiveness of the approach.

Abstract

The realization of higher-order exceptional points (HOEPs) can lead to orders of magnitude enhancement in light-matter interactions beyond the current fundamental limits. Unfortunately, implementing HOEPs in the existing schemes is a rather difficult task, due to the complexity and sensitivity to fabrication imperfections. Here we introduce a hierarchical approach for engineering photonic structures having HOEPs that are easier to build and more resilient to experimental uncertainties. We demonstrate our technique by an example that involves parity-time (PT) symmetric optical microring resonators with chiral coupling among the internal optical modes of each resonator. Interestingly, we find that the uniform coupling profile is not required to achieve HOEPs in this system -- a feature that implies the emergence of HOEPs from disorder and provides resilience against some fabrication errors. Our results are confirmed by using full-wave simulations based on Maxwell's equation in realistic optical material systems.