The Asymmetric Active Coupler: Stable Nonlinear Supermodes and Directed   Transport
  We consider the asymmetric active coupler (AAC) consisting of two coupled dissimilar waveguides with gain and loss. We show that under generic conditions, not restricted by parity-time symmetry, there exist finite-power, constant-intensity nonlinear supermodes (NS), resulting from the balance between gain, loss, nonlinearity, coupling and dissimilarity. The system is shown to possess nonreciprocal dynamics enabling directed power transport and optical isolation functionality. 
Yannis Kominis, Tassos Bountis, and Sergej Flach
physics.optics nlin.CD nlin.PS