Synthesis of mode converters on the basis of the FDTD method

We propose a universal technique for synthesizing mode converters, which is based on numerical integration of the Maxwell equations on a space-time mesh by the FDTD method. The new technique is an iterative algorithm, in which the correction to the converter profile at each iteration is calculated via the fields on the converter surface that are obtained from two conjugate problems, specifically, by direct and inverse (with an inversion of the time-integration direction) solution of the equations for electromagnetic fields. The efficiency of the synthesis algorithm is illustrated by examples that are of practical importance. The technique is compared with that proposed earlier, which used the solution of a system of equations for coupled waves.