Widely Tunable Photonic Filter Based on Equivalent Chirped Four-Phase-Shifted Sampled Bragg Gratings.

We have developed an integrated dual-band photonic filter (PF) utilizing equivalent chirped four-phase-shifted sidewall-sampled Bragg gratings (4PS-SBG) on a silicon-on-insulator platform. Using the reconstruction equivalent-chirp technique, we designed linearly chirped 4PS Bragg gratings with two π-phase shifts (π-PSs) positioned at 1/3 and 2/3 of the grating cavity, introducing two passbands in the + first order channel. Leveraging the significant thermo-optic effect of silicon, dual-band tuning is achieved through integrated microheaters (MHs) on the chip surface. By varying the injection currents from 0 to 85 mA into the MHs, the device demonstrates continuous and wide-range optical frequency division performance, with the frequency interval between the two passbands adjustable from 52.1 to 439.5 GHz. Four notable frequency division setups at 100, 200, 300, and 400 GHz were demonstrated using a 100 GHz, 1535 nm semiconductor passive mode-locked laser as the light source.