Broadband flat-top SOI add-drop filters using apodized sub-wavelength grating contradirectional couplers.

We report on broadband, flat-top, optical add-drop filters using apodized, sub-wavelength grating contradirectional couplers (SWG CDCs) on a silicon-on-insulator platform. In our device, two asymmetric SWG waveguides, having corrugation-apodized Bragg gratings, are used to couple light contradirectionally between the fundamental and next higher-order transverse electric modes of a two-waveguide system. We demonstrate an apodized, SWG CDC that has a flat-top, drop-port response with a 3 dB bandwidth of 32.6 nm, a sidelobe suppression ratio of 19 dB, and a low ex cess loss of 0.26 dB. We also demonstrate series-cascaded, apodized, SWG CDCs that have square-shaped, drop-port responses with 3 dB bandwidths > 30 n m, sidelobe suppressions >50 dB, and low excess losses <0.85 dB. (C) 2019 Optical Society of America