REFRACTIVE-INDEX PROFILING OF GRADED-INDEX PLANAR WAVE-GUIDES FROM EFFECTIVE INDEXES MEASURED FOR BOTH MODE TYPES AND AT DIFFERENT WAVELENGTHS

It is well known that, under the WKB approximation, the refractive-ind ex profile of a graded-index planar waveguide can be calculated from t he corresponding effective-index function, which can be found approxim ately by least-squares fitting of a set of measured effective indexes. In the previous work, effective indexes measured for a particular typ e of modes (the TE or TM modes) at a single wavelength are used. This requires that the waveguide supports at least three modes of the same type. In this paper, techniques of combining the effective indexes mea sured for both mode types and at different wavelengths are proposed an d demonstrated with examples. With these techniques, single-mode and t wo-mode waveguides can be profiled.