Investigation of PPLN Waveguide Uniformity via Second Harmonic Generation Spectra

Alan C. Gray  ; Sam A. Berry  ; Lewis G. Carpenter ; James C. Gates  ; Peter G. R. Smith ; Corin B. E. Gawith

Abstract

Experimental data collection methods and a corresponding numerical model are presented to investigate the quality of waveguide fabrication in nonlinear optics. The method utilises white light interferometry and standard image recognition techniques to calculate a waveguide propagation constant function. This enables comparison of a numerical second harmonic spectrum in quasi-phasematched materials, such as periodically poled lithium niobate, with the waveguide's experimental phasematching spectrum. Using the presented method, a 3rd order polynomial fit to waveguide ridge width is demonstrated to be in good agreement with experimental phasematching spectra. The presented technique provides a nondestructive route to discriminate between issues in fabrication steps in nonlinear waveguide design.