Use of multiple-wavelength and/or TE/TM effective-refractive-index measurements to reconstruct refractive-index profiles

A method is presented whereby the refractive-index profile of a planar, surface-dielectric optical waveguide may be reconstructed from sets of effective refractive indices, measured at different wavelengths and/or with sets of effective refractive indices measured with TE and TM polarisation. The index change and the substrate index may be wavelength dispersive and birefringent. The method is compared, both theoretically and experimentally, with a conventional single-wavelength method for a number of index profiles. This technique provides more information about the profile than can be obtained from one measured set and is used to analyse the index profiles of potassium ion exchange guides formed in soda-lime glass. The limitations of the technique are also discussed