WAVE-PROPAGATION IN A SLAB OF TRANSVERSALLY INHOMOGENEOUS-MEDIUM, WITH GAIN OR LOSS VARIATIONS

The modal wave propagation in a slab of transversally inhomogeneous complex medium, surrounded by a (generally complex) homogeneous medium, is investigated both by an exact method of solution of the wave equation, and by several approximate approaches. Eigenvalues and eigenfunctions are determined for both the fundamental and the first higher-order even mode, in the case of an active parabolic medium, as a function of the ″convergence″ of the medium. Particular attention is devoted to the so-called no-boundry approximation, which is quite attractive in its simplicity but does not allow the determination of modal gain and losses.