Compact and wideband silicon optical channel-drop filter based on dual-strip waveguide antisymmetric Bragg gratings

We propose and experimentally demonstrate a silicon channel-drop filter based on dual-strip waveguide anti-symmetric gratings, utilizing two Y-junctions to connect conventional multimode strip waveguides and dual-strip waveguides. Since the electric field distributions of the TE0 mode and TE1 mode are well overlapped in the grating corrugation region, the coupling coefficient of the proposed grating is much higher than that of conventional mode-conversion-based Bragg gratings. As a result, a wide bandwidth can be achieved with a short grating length. Experimental results on a silicon-on-insulator (SOI) platform show that the proposed filter can achieve a stopband width of 27.8 nm with a grating length of 60 μm and a stopband width of 44.5 nm with a grating length of 40 μm. Apodization can be realized by controlling the misalignment between different sub-gratings. The measured 3-dB bandwidth and sidelobe suppression ratio of the 60-μm cosine-apodized grating are 20.0 nm and 15.8 dB, respectively. Provided that the design is upgraded to handle both polarizations, we believe the proposed device can be a promising candidate as a filter for coarse wavelength division multiplexing (CWDM) systems, due to its wide bandwidth and compact size.