According to embodiments of the present invention, an optical device is provided. The optical device includes a channel waveguide, and a plurality of optical elements arranged along at least a portion of the channel waveguide to interact with light propagating in the channel waveguide, wherein a period of the plurality of optical elements changes nonlinearly along the portion of the channel waveguide. According to further embodiments of the present invention, a method for forming an optical device is also provided.