Compact tunable photonic comb filter on a silicon platform.

We propose and demonstrate a compact wavelength- and bandwidth-tunable photonic comb filter on a silicon platform. It is a Fabry-Perot (FP) cavity fabricated on silicon-on-insulator, which is composed of two cascaded Sagnac loop mirrors (SLMs) with multimode-interferometer-assisted Mach-Zehnder interferometer (MZI) couplers. The effective length of the FP cavity and the reflectivity of the SLMs can be dynamically changed based on thermal-optical effects by tuning three phase shifters along the cavity length and MZI arms, leading to center wavelength tuning and bandwidth tuning of the comb filter. Three tuning cases are investigated. By independently or simultaneously tuning three microheaters, center wavelength tuning with a tuning efficiency of ∼0.017  nm/mW and bandwidth tuning from 4.37 to 27.6 GHz are achieved in the experiment.