Guided modes in non-Hermitian optical waveguides

We study guided modes in non-Hermitian optical waveguides with dielectric layers having either gain or loss. For the case of a three-layer waveguide, we describe stationary regimes for guided modes when gain and loss compensate each other in the entire structure rather than in each layer. We demonstrate that, by adding a lossless dielectric layer to a double-layer waveguide with the property of parity-time (PT) symmetry, we can control a ratio of gain and loss required to support propagating and nondecaying optical guided modes. This novel feature becomes possible due to the modification of the mode structure, and it can allow using materials with a lower gain to balance losses in various optical waveguiding structures. In addition, we find a non-PT-symmetric regime when all guided modes of the system have their losses perfectly compensated.