Two-period contra-directional grating assisted coupler.

We present the design, analysis, and experimental characterization of a novel integrated add-drop filter capable of filtering simultaneously two independent channels that is based on a contra-directional grating assisted coupler with two different periods. The device performance is explained using Fourier analysis and confirmed with numerical simulations using the eigenmode expansion method. The devices were fabricated using electron-beam lithography on a silicon-on-insulator wafer with a 220 nm thick device layer. The Fourier analysis, simulations and experimental results are in agreement and show that the drop port response of the two-period configuration is the superposition of the drop port responses of two single-period gratings. Therefore, the output channels at drop port can be designed independently and can have different bandwidths.