Non-Hermitian skin effect and quasiperiodicity-induced localization in a photonic lattice with staggered on-site potentials

The quasicrystals combined with nonreciprocal and on-site non-Hermiticity provide a unique platform to explore exceptional phenomena arising from the non-Hermitian skin effect (NHSE). Especially, we investigate a non-Hermitian photonic lattice with nonreciprocal hoppings and staggered complex on-site potentials, revealing an energy-dependent bipolar NHSE and a quasiperiodicity driven redistribution from skin states to bulk-localized states. Numerical winding numbers and analytical contact conditions reveal the spectral reconnections underlying the bipolar NHSE, with the sign of the imaginary eigenenergy determining its localization direction. Meanwhile, imaginary quasiperiodic modulation drives a crossover from skin localization to bulk localization, while real and imaginary modulations yield comparable bulk localization at strong modulation. Moreover, Fibonacci-size calculations support persistent skin–bulk coexistence, while a separable two-dimensional extension connects one-dimensional localization directions to corner accumulation and spatial redistribution. These results provide a unified framework for understanding and controlling the interplay between spectral topology and quasiperiodicity in non-Hermitian photonic systems.