Localized guided-mode resonance-enabled highly angle-insensitive optical filtering.

Angle sensitivity to incident light remains a fundamental limitation in conventional Fabry-Pérot (F-P) and guided-mode resonance (GMR) filters due to the angular dependence of the transverse wave vector. In this work, we propose a compact planar notch filter based on localized guided-mode resonance (LGMR) by embedding a metallic grating within a tri-layer SiO2-Si-SiO2 structure. The design achieves three-dimensional (3D) confinement of the transverse wave vector, effectively suppressing angular dispersion and stabilizing the resonance condition. Numerical simulations based on the finite-difference time-domain (FDTD) method demonstrate a flat stop band near 1.55 µm with a minimal wavelength shift of only 7.4 nm over a broad angular range of 0°-70°. Spectral tunability in the near-infrared (NIR) region is realized through controlled adjustment of the grating period. The proposed LGMR notch filter provides a robust and integrable solution for angle-insensitive spectral filtering in applications such as Raman spectroscopy and optical communication.