Twist-induced non-Hermitian skin effect in optical waveguide arrays

A non-Hermitian skin effect (NHSE) dramatically localizes bulk modes at open boundaries, leading to fascinating eigenvalue and wavefunction topologies. However, realizing NHSE typically requires non-reciprocal couplings, which many photonic systems cannot provide. Here, we propose an approach using twisted optical waveguide arrays. The twisting introduces geometrical phase in photon coupling process, effectively acting as artificial gauge fields for photons. By constructing a dissipative Aharonov–Bohm chain of twisted lattices, we achieve NHSE by combining these artificial gauge fields with dissipation. We can control the localization strength and direction of skin modes by tuning the twist. Additionally, we characterize the topological edge modes using Majorana's stellar representation and further propose twisted spectral winding with bipolar NHSE in a trapezoidal lattice. Our work offers an alternative avenue to realize eigenvalue topology and control light localization and transport.