Dual spectral filters with multi-layered grating waveguide structures

Promising configurations for dual spectral filters based upon grating-waveguide structures are presented. In these configurations, the parameters of the multimode waveguide and grating are carefully chosen to achieve dual resonances at two different pre-determined wavelengths. Specifically, the grating-waveguide structure resonates for each pre-selected wavelength with a different waveguide mode. Theoretical and experimental results reveal that the resonance wavelengths can be accurately selected and that the resonance spectral bandwidths can be less than 1 nm with high contrast ratios.