Flexible and reconfigurable integrated optical filter based on tunable optical coupler cascaded with coupled...

Reconfigurable optical filter can satisfy diverse filtering requirements in different application scenarios and shorten development cycle. However, it is still challenging to achieve multi-functional filtering richness with high performance. Here, based on a tunable optical coupler cascaded with a coupled resonator optical waveguide (CROW), a highly flexible and reconfigurable integrated optical filter is proposed and demonstrated on the low-loss silicon nitride platform. Both single injection and double injection configurations can be deployed to obtain rich spectral responses. For the single injection configuration, flat-top bandpass filter was experimentally achieved, whose shape factor could be as low as 1.648 and extinction ratio (ER) can be 37.5 dB with a bandwidth tuning range from 2.12 to 4.01 GHz. For the double injection configuration, Lorentz, triangular, sinusoidal, square, tangent-like, and interleaver spectral responses have been reconfigured by controlling seven phase shifters. Moreover, both single and double free spectral ranges (FSR) can be obtained for a fixed ring perimeter in the double injection configuration. The measured ER for the notch filter of Lorentz responses with double FSR is 36.8 dB. We believe that the proposed device has great potential for reconfigurable photonic filtering and microwave photonic signal processing.