Electromagnetically Induced Transparency-like Effect in U-Shaped Silicon Metasurfaces and Gap-Mode-Enhanced...

Electromagnetically induced transparency-like effects in silicon metasurfaces have attracted considerable interest due to their capability to manipulate optical resonances and improve sensing performance. In this work, a U-shaped silicon metasurface is proposed, consisting of a horizontal nanopillar supporting bright mode and two vertical nanopillars supporting dark mode. The coupling and coherent interference between the bright and dark modes lead to a pronounced EIT-like effect at specific wavelengths. By introducing nanoscale gaps between the horizontal and vertical silicon pillars, a U-shaped silicon metasurface with gap mode (UG metasurface) is formed, which induces strong near-field enhancement and is associated with reduced radiative losses, thereby improving the quality factor of the EIT-like resonance of UG metasurfaces. Two silicon metasurface samples are fabricated, and their transmission spectra are experimentally measured, showing good agreement with numerical simulations. In addition, the refractive index sensing performance of silicon metasurfaces is numerically investigated. The results show that the UG metasurface design significantly enhances the sensing capability, increasing the figure of merit from 6 RIU^-1 to 60 RIU^-1. The proposed silicon metasurfaces and near-field enhancement with the gap-mode mechanism provide a promising strategy for realizing high-performance optical sensing and offer valuable insights into the manipulation of electromagnetic responses.