Fabrication and characterization of waveguide-grating filters

Experimental results on guided-mode resonance filters with a range of grating parameters are presented along with a detailed fabrication process. Surface-relief filters consisting of a photoresist grating on silicon nitride waveguide layer deposited on a fused silica substrate have been fabricated. Resonance efficiencies as high as 76% in transmission and 40% in reflection have been measured. Embedded filters having silicon nitride grating as the middle layer with a photoresist cover layer have also been fabricated. A resonance efficiency of 25% in transmission is measured and weak reflection resonance observed. The observed angular resonance locations for a fixed incident wavelength and the wavelength resonance locations for a fixed incident angle are close to those predicted by the guided-mode resonance analysis developed from the rigorous coupled-wave theory. This is true for both TE and TM waves. Angular and wavelength linewidths at resonance, sideband shapes, and other resonance properties also agree with theory.