Spatial Filtering with Nonlocal Non-Hermitian Metasurfaces

TL;DR

This paper introduces compact, robust nonlocal non-Hermitian metasurfaces for optical spatial filtering, offering a highly aligned-insensitive alternative to bulky traditional filters with potential for widespread application.

Contribution

The authors design a novel non-Hermitian metasurface based on a resonant waveguide grating that achieves effective spatial filtering with high robustness and ease of manufacturing.

Findings

Operates over a ~1 degree angular range

Ultrathin and insensitive to misalignment

Easy to manufacture and integrate

Abstract

Spatial filtering of optical fields has widespread applications ranging from beam shaping to optical information processing. However, conventional spatial filters are bulky and alignment-sensitive. Here, we present nonlocal non-Hermitian metasurfaces that can act as exceptionally effective optical spatial filters while being highly compact and insensitive to both lateral and longitudinal displacements. The metasurface design is based on a resonant waveguide grating in which radiative losses of the modes are tailored to realize a symmetry-protected bound state in the continuum in the middle of a non-Hermitian flat band. Using this design, we propose a compact spatial filtering device operating over an angular range of approximately 1 degree around normal incidence. In addition to being ultrathin and robust against translational misalignment, the proposed metasurfaces are easy to manufacture, which makes them an attractive alternative to conventional spatial filters, holding a potential to become a widely used optical component.