Solitons in a PT-symmetric χ coupler.

We consider the existence and stability of solitons in a χ coupler. Both the fundamental and second harmonics (SHs) undergo gain in one of the coupler cores and are absorbed in the other one. The gain and loss are balanced, creating a parity-time (PT) symmetric configuration. We present two types of families of PT-symmetric solitons having equal and different profiles of the fundamental and SHs. It is shown that the gain and loss can stabilize solitons. The interaction of stable solitons is shown. In the cascading limit, the model is reduced to the PT-symmetric coupler with effective Kerr-type nonlinearity and the balanced nonlinear gain and loss.