Abstract

A dual-core waveguide with balanced gain and loss in different arms and with intermodal coupling is considered. The system is not invariant under the conventional $\mathcal{PT}$ symmetry, but obeys $\mathcal{CPT}$ symmetry where an additional spatial inversion $\mathcal{C}$ corresponds to swapping the coupler arms. We show that second-order dispersion of coupling allows for unbroken $\mathcal{CPT}$ symmetry and supports propagation of stable vector solitons along the coupler. Small-amplitude solitons are found in explicit form. The combined effect of gain-and-loss and dispersive coupling results in several interesting features which include a separation between the components in different arms, nontrivial dependence of stability of a soliton on its velocity, and the existence of more complex stationary two-hump solutions. Unusual decay dynamics of unstable solitons are also discussed.

© 2017 Optical Society of America

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