Determination of Refractive Index Profile and Mode Index from the Measured Mode Profile of Single-Mode LiNbO3-Diffused Waveguides

A refractive index profile and a mode index of single-mode LiNbO3 channel waveguides are simultaneously estimated from the measured near-field intensity distributions. A third-order low-pass Butterworth filter is used to filter the measured amplitude and its double derivative to remove high-frequency spatial noise and impulses. The mode index or effective index of the propagating mode is extracted by matching the index change profile equal to zero at the waveguide boundary. The proposed technique is applicable to any slowly varying, single-mode, integrated-optic waveguide for TE and TM modes and for any operating wavelength within the single-mode regime.