Abstract
The effect of domain inversion shape on the SHG conversion efficiencies of QPM nonlinear waveguide devices is theoretically analyzed. Three domain inversion shapes, namely elliptic , sine and arc , are considered in this analysis. The duty cycle α( x ) is derived for each case and the periodic modification of the nonlinear coefficient is taken as a binary square function. To simplify the calculation of the integral overlap between the domain-inverted regions and the guided modes, a highly confined mode and a Gaussian mode are used. The SHG conversion efficiencies are theoretically plotted against the duty cycle α 0 for various mode width/waist. The results show that the optimal duty cycle α 0 for maximum SHG efficiency is shape-dependent. This implies that, in order to obtain large harmonic intensities, it is necessary to identify the domain inversion shape associated with a particular fabrication process before the QPM structure can be optimized by choosing the appropriate grating duty cycle.