Improved propagation-mode near-field method for refractive-index profiling of optical waveguides

Experimental and theoretical improvements to the propagation-mode near-field technique for refractive-index profiling have been made. The measured near-field profile is deconvoluted with the transfer function of the optical imaging system in order to recover the actual near-field profile. Anew equation is also derived in order to use these data to reconstruct the refractive-index profile of the waveguide under consideration. The improved method, which is valid for all relevant wavelength ranges, is demonstrated in the determination of the refractive-index profiles of two single-mode planar waveguides.