Eight-channel reconfigurable microring filters with tunable frequency, extinction ratio and bandwidth.

We demonstrate an eight-channel reconfigurable optical filter on a silicon chip. It consists of cascaded microring resonators and integrated compact heaters. With an embedded Mach-Zehnder (MZ) arm coupling to a microring resonator, the important parameters of a filter such as center frequency, extinction ratio and bandwidth can be controlled simultaneously for purposes of filtering, routing and spectral shaping. Thus our device could potentially be useful in dense wavelength division multiplexing (DWDM) and radio frequency arbitrary waveform generation (RFAWG). Multichannel filter response was successfully tuned to match the International Telecommunication Unit (ITU) grid with 50, 100 and 200 GHz in channel spacing. Programmable channel selectivity was demonstrated by heating the MZ arm, and continuous adjustment of through-port extinction ratio from 0 dB to 27 dB was achieved. Meanwhile, the 3 dB bandwidth in the drop port changed from 0.12 nm to 0.16 nm. The device had an ultra-compact footprint (1200 microm x 100 microm) excluding the metal leads and contact pads, making it suitable for large scale integration.