Computer modelling of coplanar waveguide

As well as the more familiar microwave applications of coplanar waveguide (CPW), the structure is finding increasing utility in integrated optics, where the wide bandwidth enables one to produce optical modulators with bandwidth in excess of 20 GHz. Whilst a sophisticated modelling suite has been developed to analyse and design integrated optical components numerical techniques tend, if anything, to be too flexible. Semianalytic methods, with their scalar approximations and ad hoc correction factors, may lack accuracy and such techniques are usually only valid over some restricted range of structural parameters data. Once a particular structure has been chosen, with a handful of design parameters, one would appreciate the speed and simplicity of a semianalytic technique for general design and optimisation, while retaining the accuracy of a full-blown numerical analysis. The authors have achieved this trade-off by normalising their semianalytic results against finite element modelling. Having identified areas where the agreement was poor, second order effects and tuning factors are introduced to enhance the agreement over the whole range of interest. They present some analysis of CPW on lithium niobate, an anisotropic substrate which is not readily analysed, especially if the buffer layer which normally lies between the CPW electrodes and the substrate is included