Silicon Add-Drop Filter Based on Multimode Grating Assisted Couplers

We demonstrate the design, fabrication, and characterization of a two-mode silicon add-drop filter, which is based on multimode grating-assisted contra-directional couplers. The mode conversions between two asymmetry strip waveguides are realized by using spatially periodic corrugations in one side wall of a multimode waveguide at the phase-match condition. Experimental results show that the fundamental mode of a single-mode waveguide is successfully coupled to the first two modes of the multimode waveguide in the opposite direction. The corresponding mode conversion bandwidths and extinction ratios are also measured. The demonstrated add-drop filter may find their applications in a hybrid multiplexing system by combing wavelength-division multiplexing technology and mode-division multiplexing technology for on-chip optical interconnect.