Complex propagators for evanescent waves in bidirectional beam propagation method

Summary form only given. Several methods for bidirectional beam propagation have been suggested to treat reflective devices. Accurate and efficient modeling of devices such as Bragg gratings, AR coatings and add-drop multiplexers has been demonstrated. However, a significant weakness remains in current bidirectional BPM techniques-evanescent waves are generated at interfaces but are not propagated correctly by the conventional BPM propagator. This leads both to errors in transmission and reflection coefficients and introduces instabilities to the simulation algorithms. The solution to these inaccuracy and instability problems is to find a better propagator, which does not map the real axis to itself. Our approach is to use a complex-valued reference wave number.