Very narrow spectral filters with multilayered grating-waveguide structures

Promising configurations for grating-waveguide structures are presented. In these structures, the grating layer, which is normally adjacent to the waveguide layer, is displaced by means of an intermediate layer, resulting in significant reduction of losses and weaker coupling. This leads to very narrow spectral bandwidths and high contrast ratios. Experimental results reveal that the spectral bandwidths can be as low as 0.1 nm with contrast ratios greater than 1000, suggesting that these grating-waveguide structures could be useful for optical communication networks.