Tunable nonlinear double-core PT-symmetric waveguides

We propose a scheme for creating a tunable, highly nonlinear defect in a one-dimensional photonic crystal with an embedded atomic cell filled by a mixture of two isotopes of three-level atoms. The defect creates an effective double-core waveguide. The induced refractive index for a probe field can be made parity-time (PT) symmetric by means of a proper combination of a control field and a Stark field; hence the complex defect potential obtained contains double-well real and linear imaginary parts. We also show that it is possible to form various stable nonlinear defect modes supported by the focusing nonlinearity of the system. (C) 2014 Optical Society of America