TE and TM mode analysis of planar ion-exchanged waveguides

The WKB technique has been used to analyse the measured TE and TM mode spectra of planar optical waveguides produced by silver ion-exchange at 215¿¿ C in an unstirred melt of silver nitrate for fabrication times ranging from 7 min up to 540 min. The effects of slight variations in the fabrication temperature on the repeatability of the process have been investigated. It has been shown that control over the temperature should be within ¿¿0.5¿¿C of the set point in order to maintain reproducible mode-spectra measurements. A Gaussian refractive index profile, where the maximum index value occurs at some depth below the surface of the guiding region, was found to adequately describe the observed mode spectra. Evidence for the existence of `buried¿¿ modes is presented, based on close examination of the m-line structure. Comparison with results predicted by a monotonically decreasing linear refractive-index profile is given.