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.