Bandwidth-tunable add-drop filter with a wide FSR based on a π-phase-shifted antisymmetric Bragg grating resonator and Mach-Zehnder interferometers.

We propose a bandwidth-tunable add-drop filter (ADF) with a wide free spectral range (FSR) based on a π-phase-shifted antisymmetric Bragg grating (π-ASBG) resonator and Mach-Zehnder interferometers (MZI) on the silicon-on-insulator (SOI) platform. The π-ASBG forms a traveling-wave-like Fabry-Pérot (F-P) resonator that inherently enables a single-resonance response over a broad wavelength range. By incorporating the MZI configuration, the 3 dB bandwidth of the ADF can be actively tuned. The 3 dB bandwidth is tunable from 0.77 to 0.07 nm. The insertion loss (IL), the extinction ratio (ER), and the side lobe suppression ratio (SLSR) are dependent on the 3 dB bandwidth. Calculated variation ranges of the IL, ER, and SLSR are from 0.36 to 3.04 dB, from 28.97 to 10.64 dB, and from 30.62 to 12.23 dB, respectively. The wide FSR (>50nm) characteristic is preserved under all tuning configurations. We believe the proposed ADF offers a promising building block for future reconfigurable optical communication systems, on-chip optical computing, and high-resolution optical sensing.