Nonlinear adiabatic optical isolator
  We theoretically propose a method for optical isolation based on adiabatic nonlinear sum frequency generation in a chirped quasi-phase-matching crystal with strong absorption at the generated sum frequency wave. The method does not suffer from limitations of dynamic reciprocity found in other nonlinear optical isolation methods, and can provide tunable optical isolation with ultrafast all-optical switching capability. Moreover, as an adiabatic technique it is robust to variations in the optical design and is relatively broadband. 
Andon Rangelov and Stefano Longhi
physics.optics