State-of-Polarization-Based Refractive Index Sensing Using Dielectric Metasurfaces

The resonance wavelength, amplitude, and state-of-polarization (SOP) of dielectric metasurfaces are intrinsically dependent on their dielectric environment, making them suitable for passive refractive index (RI) sensing. Metasurface-based RI sensors typically utilize a colorimetric sensing modality, relying solely upon a shift in resonance wavelength or intensity, which necessitates broadband illumination and detection, which can limit the sensor's signal-to-noise ratio (SNR). We report the scalable fabrication of TiO₂ metasurfaces with varying structural anisotropy using a facile, one-step nanocrystal ink-based nanoimprinting process, and the experimental demonstration of SOP as a modality for RI sensing. We structurally characterize the fabricated metasurfaces and measure their transmission and polarization ellipticity spectra in different RI environments, demonstrating monochromatic humidity sensing and proving the viability of this SOP-based RI sensing even for metasurfaces with very small resonance wavelength shifts.