Tunable flat spectra based on Floquet exceptional points with linear quasienergy bands in frequency lattices
Phys. Rev. A 114, 023504 – Published 4 August, 2026
DOI: https://doi.org/10.1103/t4mx-cr7h
Abstract
Periodic driving greatly expands the physical scope and tunability of non-Hermitian systems, giving rise to rich dynamical phenomena that have no static counterpart. Here we construct a periodically quenched non-Hermitian Su-Schrieffer-Heeger frequency lattice by two coupled ring resonators with periodically dynamic complex modulations. We prove that the quenched lattice is parity-time symmetric as the two durations are equal, and Floquet exceptional points (EPs) will arise with suitable driving period. Meanwhile, the quasienergy bands are approximately linear around the Floquet EPs. With theoretical analysis and numerical simulations, we demonstrate that a flat spectrum with uniformly increasing width can emerge in the quenched frequency lattice, which stems from the linear band structures near the Floquet EPs. The spectrum evolution governed by Floquet EPs shows periodicity and possesses intricate dynamic. Moreover, the broadening speed and power of the flat-top frequency comb can be adjusted by the amplitudes of modulation conveniently, rendering the frequency spectrum more flexible and tunable. This study reveals the intriguing physical phenomena arising from Floquet EPs and demonstrates that the periodically quenched frequency lattice can have applications on spectral manipulation and flat-top microcombs generation.
