Floquet Mode Resonance: Trapping light in the bulk mode of a Floquet topological insulator by quantum self-interference

Floquet topological photonic insulators characterized by periodically-varying Hamiltonians are known to exhibit much richer topological behaviors than static systems. In a Floquet insulator, the phase evolution of the Floquet-Bloch modes plays a crucial role in determining its topological behaviors. Here we show that by perturbing the driving sequence, it is possible to manipulate the cyclic phase change of the system over each evolution period to induce quantum self-interference of a bulk mode, leading to a new topological resonance phenomenon called Floquet Mode Resonance (FMR). The FMR is fundamentally different from other types of optical resonances in that it is cavity-less since it does not require physical boundaries. Its spatial localization pattern is instead dictated by the driving sequence and can thus be used to probe the topological characteristics of the system. We demonstrated excitation of FMRs by edge modes in a Floquet octagon lattice on silicon-on-insulator, achieving extrinsic quality factors greater than 10^4. Imaging of the scattered light pattern directly revealed the hopping sequence of the Floquet system and confirmed the spatial localization of FMR in a bulk-mode loop. The new topological resonance effect could enable new applications in lasers, optical filters and switches, nonlinear cavity optics and quantum optics.