Wave propagation in a waveguide with a balance of gain and loss

A waveguide problem with a balance between loss and gain has been defined by one of the authors in the COST 240, Working Group 2, to study the mode behaviour in the case of complex refractive index and to compare different approaches. Peculiar wave properties of a waveguide with a balance of gain and loss are described and used to formulate a new beam propagation method (BPM) benchmark test.