Realizing Minimally Perturbed, Nonlocal Chiral Metasurfaces for Direct Stokes Parameter Detection.

Recent development in nonlocal resonance based chiral metasurfaces draws great attention due to their abilities to strongly interact with circularly polarized light at a relatively narrow spectral bandwidth. However, there still remain challenges in realizing effective nonlocal chiral metasurfaces in optical frequency due to demanding fabrications such as 3D-multilayered or nanoscaled chiral geometry, which, in particular, limit their applications to polarimetric detection with high-Q spectra. Here, we study the underlying working principles and reveal the important role of the interaction between high-Q nonlocal resonance and low-Q localized Mie resonance in realizing effective nonlocal chiral metasurfaces. Based on the working principles, we demonstrate one of the simplest types of nonlocal chiral metasurfaces which directly detects a set of Stokes parameters without the numerical combination of transmitted values presented from typical Stokes metasurfaces. This is achieved by minimally altering the geometry and filling ratio of every constituent nanostructure in a unit cell, facilitating consistent-sized nanolithography for all samples experimentally at a targeted wavelength with relatively high-Q spectra. This work provides an alternative design rule to realizing effective polarimetric metasurfaces and the potential applications of nonlocal Stokes parameters detection.

Near-flat top bandpass filter based on non-local resonance in a dielectric metasurface.

Localized light matter interaction at a resonant nanostructure facilitates spectrally selective transmission of light, which has led to demonstrations of ultrathin metasurface based optical filters. Unfortunately, due to the nature of Lorentzian spectral line shape in such resonances, it is inevitable to suffer significant spectral crosstalk. In this work, we demonstrate a conceptually new type of spectral filter which exhibits near flat-top bandpass with minimized spectral overlaps. To realize this, we leverage the recent development of non-local resonance in dielectric nanostructure to design a double-layered optical filter with performance comparable to the ideal spectral filters. The designed metasurface shows averaged transmission of more than 90% across the target spectral band and suppressed transmission of less than 10% out of the spectral band.