Narrow-Band Add-Drop Filter Based on Cladding-Modulated Apodized Multimode Bragg Grating

A narrow-band add-drop filter based on an anti-symmetric cladding-modulated multimode Bragg grating (CMMBG) is demonstrated on the silicon-on-insulator (SOI) platform. The CMMBG is implemented by using periodic placements of silicon cubes along a multimode waveguide. The coupling strength is varied by changing the distance between the cubes and the multimode waveguide. An unlimited free-spectral range (FSR) and weak coupling strengths for TE0-TE1modes conversion are achieved. Sidewall-misalignment-modulation (SMM) apodization is applied to achieve a high sidelobe suppression ratio (SLSR). The experimental results show that the designed filtering device has a 3-dB bandwidth of 0.8 nm, an insertion loss of -0.65 dB and a SLSR of 20.3 dB. The devices with different grating duty cycles and multimode waveguide widths were also fabricated and analyzed. Our devices are promising for on-chip applications that require narrow bandwidths such as WDM channel filters.