Integrable nonlinear parity-time symmetric optical oscillator
  The nonlinear dynamics of a balanced parity-time symmetric optical microring arrangement are analytically investigated. By considering gain and loss saturation effects, the pertinent conservation laws are explicitly obtained in the Stokes domain-thus establishing integrability. Our analysis indicates the existence of two regimes of oscillatory dynamics and frequency locking, both of which are analogous to those expected in linear parity-time symmetric systems. Unlike other saturable parity time symmetric systems considered before, the model studied in this work first operates in the symmetric regime and then enters the broken parity-time phase. 
Absar U. Hassan, Hossein Hodaei, Mohammad-Ali Miri, Mercedeh   Khajavikhan, Demetrios N. Christodoulides
physics.optics