Sensing with exceptional surfaces: combining sensitivity with robustness

TL;DR

This paper introduces a novel photonic design that creates a hypersurface of Jordan exceptional points, balancing sensitivity with robustness by allowing certain perturbations to shift the system along the surface, maintaining stability.

Contribution

The authors propose a new photonic structure with a hypersurface of Jordan EPs that enhances robustness against fabrication errors while preserving high sensitivity to specific perturbations.

Findings

Design exhibits robustness by shifting along the exceptional surface.

Perturbations due to scattering enhance sensitivity.

Implementation is feasible with standard photonics components.

Abstract

Exceptional points (EPs) are singularities that arise in non-Hermitian physics. Current research efforts focus only on systems supporting isolated EPs characterized by increased sensitivity to external perturbations, which makes them potential candidates for building next generation optical sensors. On the downside, this feature is also the Achilles heel of these devices: they are very sensitive to fabrication errors and experimental uncertainties. To overcome this problem, we introduce a new design concept for implementing photonic EPs that combine the robustness required for practical use together with their hallmark sensitivity. Particularly, our proposed structure exhibits a hypersurface of Jordan EPs (JEPs) embedded in a larger space, and having the following peculiar features: (1) A large class of undesired perturbations shift the operating point along the exceptional surface (ES), thus leaving the system at another EP which explains the robustness; (2) Perturbations due to back reflection/scattering force the operating point out of the ES, leading to enhanced sensitivity. Importantly, our proposed geometry is relatively easy to implement using standard photonics components and the design concept can be extended to other physical platforms such as microwave or acoustics.