The topological edge state (TES) in a one-dimensional optical lattice has exhibited robust field
localization or waveguiding against the structural perturbations that would give rise to fault-tolerant
photonic integrations. However, the zero mode as a kind of TES usually deviates from the exact zero
energy state in a finite Hermitian lattice due to the coupling between these edge states, which inevitably
weaken the topological protection. Here, we first show such a breakup of zero modes in finite Su-Schriffer
Heeger optical lattices and then reveal their recovery by introducing non-Hermitian degeneracies with
parity-time (
PT
) symmetry. We carry out experiments in a finite silicon waveguide lattice, where a passive
PT
symmetry was implemented with carefully controlled lossy silicon waveguides. The experimental
results are fully compatible with the theoretical prediction. Our results show that the topological property of
an open system can be tuned by non-Hermitian lattice engineering, which offers a route to enhance the
topological protection in a finite system.
DOI: 10.1103/PhysRevLett.123.165701
