Broadband dispersion-engineered Bragg grating mirrors for integrated side-coupled Fabry–Pérot resonators

We present the design and demonstration of silicon nitride side-coupled Fabry-Pérot resonators employing both uniform and apodised distributed Bragg reflectors, for broadband dispersion engineering. By implementing air-gap Bragg gratings, we achieve a broad stopband exceeding 70 nm. Apodised gratings enable enhanced dispersion control, allowing transitions from normal to anomalous integrated dispersion. Furthermore, high-Q resonant modes and enhanced peak reflectivity are demonstrated through co-optimisation of cavity length and waveguide-to-cavity gap. The compact footprint, the enhanced mode selectivity and the spectral bandwidth control, make side-coupled Fabry-Pérot resonators a promising platform for resonant mirrors in hybrid on-chip lasers, as well as for sensing and non-linear photonic systems.