Topological constant-intensity waves.

Topological constant-intensity (TCI) waves are introduced in the context of non-Hermitian photonics. Unlike other known examples of topological defects, the proposed TCI waves exhibit a counterintuitive behavior because a phase difference occurs across space without any accompanying intensity variations. Such solutions exist only on non-Hermitian systems, because the associated nonzero phase difference is directly related to the real and imaginary parts of the potential. The free space diffraction and the existence of such waves in two spatial dimensions are also discussed in detail.