Chiral Zener tunneling in non-Hermitian frequency lattices.

A waveguide coupler under both phase and intensity modulation is proposed to generate a non-Hermitian Su-Schrieffer-Heeger lattice in frequency dimension. By varying the modulation period and phase, we can manipulate the on-site potential of the lattice and realize anisotropic coupling of the supermodes in waveguides. The artificial electric field associated with the modulation phase can also be introduced simultaneously. Zener tunneling is demonstrated in the non-Hermitian system and manifests an irreversibly unidirectional conversion between odd and even supermodes. The conversion efficiency can be optimized by varying the on-site potential of the waveguides. The study provides a versatile platform to explore non-Hermitian multiband physics in synthetic dimensions, which may find great application in chiral mode converters and couplers.