NUMERICAL-ANALYSIS OF PASSIVE INTEGRATED-OPTICAL POLARIZATION SPLITTERS - COMPARISON OF FINITE-ELEMENT METHOD AND BEAM-PROPAGATION METHOD RESULTS

We compare results obtained from the application of a scalar finite-element method and a three-dimensional beam-propagation method to passive integrated optical polarization splitters (IOPS's) in Ti-indiffused LiNbO3. A comparison of calculated channel waveguide modes is given. Results reveal good agreement for the two methods. The IOPS is explained in terms of local normal modes. Results obtained by the finite-element and the beam-propagation methods are then used in the two-mode interference picture in order to design several IOPS's. For adiabatic transitions the phase difference of the two lowest-order modes in each polarization at the output of the IOPS is obtained from DELTA-beta as a function of waveguide separation. In the same way the conditions for polarization-independent operation can be obtained. The validity of results obtained by the finite-element ethod with local normal modes for two modes is limited to extremely slowly varying waveguide separations. Otherwise a method is needed that calculates the complete field, including coupling to radiation. Mode coupling, including coupling to radiation modes, is studied in detail for one type of IOPS by means of the beam-propagation method.