Two-dimensional silicon nanoring array enabled polarization-independent narrow spectral linewidth optical filter

Abstract

In this paper, we investigate a new, to the best of our knowledge, type of guided-mode resonance optical filter with polarization-independence at normal incidence and relatively narrow spectral linewidth in the near-infrared regime. The new optical spectral filter consists of a 2D array of silicon nanorings on silicon film on silica substrate. Using finite difference time domain (FDTD) simulations, it is found that the spectral linewidth of the optical filter is primarily controlled by nanoring width and is tolerant to the variations of the size and height of silicon nanorings. FDTD simulations also reveal that the excited guided mode is more tightly confined in the nanoring structures with smaller ring widths. It is explained that the narrow spectral linewidth of the nanoring structure filter is due to the smaller scattering cross-section of the silicon nanorings and tighter confinement of the guided mode. Our optimally designed optical reflection filter exhibits a 2.4 nm spectral linewidth with nearly 100% peak reflectance at the resonance wavelength.