A lateral-apodized add-drop filter is demonstrated in a multimode asymmetric waveguide Bragg grating. This design utilizes two individual superposed gratings with the same sidewall corrugation depth. The strong side lobes of the grating filter are efficiently suppressed by mapping the target apodization profile into lateral shifts between the periods of the two gratings. Compared with other apodized technology, this device is easier to be realized. Experimental results show that the side-lobes suppression ratio can reach 18.5 dB, and a bandwidth of 9.5 nm is achieved by a large corrugation width of 150 nm. The insertion loss at the drop port is only 0.8 dB, and the extinction ratio is up to 24 dB at the through port.

We demonstrate a thermally tunable four-channel add/drop demultiplexer based on silicon grating-assisted contra-directional couplers (contra-DCs) for 200 GHz dense wavelength division multiplexing (DWDM) systems. In order to obtain the narrow bandwidth and the rapid roll-off necessary for the DWDM, every wavelength channel is filtered dually by two identical contra-DCs cascaded in parallel. In addition, the phase apodization technique is utilized to suppress sidelobes. With these special designs, passbands of the four drop ports exhibit 3 and 20 dB bandwidths of 0.4 and 0.8 nm, respectively, while isolation between adjacent channels is better than 20 dB. Insertion losses at through and drop ports are 0.6 and ∼2.6 dB, respectively. The maximal wavelength-tunable range is up to 25 nm.

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