Photonic spin Hall effect in gap–plasmon metasurfaces for on-chip chiroptical spectroscopy

Abstract

Chiral structures possessing differential optical responses to light circular polarization are very common in biological and organic compounds. Attaining chiroptical effects is of great biochemical importance, yet requires complicated structures. Circular dichroism (CD) spectrometers measuring the differential absorption between left- (LCP) and right-circular (RCP) polarizations involve complex hardware to switch laser polarization and manage data acquisition sequentially. Here, we present compact and power-efficient metasurface-based chiroptical spectroscopy solutions based on gap–plasmon metasurfaces (GPMSs). First, a minimalistic design of a real-time CD spectrometer is obtained by using the photonic spin Hall effect (PSHE) in a single GPMS, which spatially separates LCP and RCP spectra. It is the smallest CD spectrometer to our knowledge. Another GPMS-based device built with the same approach rotates light polarization by 45° through adding a phase shift between LCP and RCP. Thus, PSHE in GPMS can provide efficient solutions to vital applications including biosensing, DNA structural analysis, and stereochemistry.