Effect of Electrode Reversal on Induced Nonlinearity in Specialized Silicon Structures

Abstract

Silica glass is a centrosymmetric material that does not support even-ordered nonlinearity. Despite the fact, its vast importance in photonic systems motivated researchers to develop techniques to break the centrosymmetric structure. However, to this day the effective nonlinearity in silica glass remains too low for practical applications in active nonlinear devices. In this study, a model of sub-dividing glass samples into multiple, alternating doped and undoped silica layers is investigated for its ability to enhance nonlinearity in silica glass. The glass samples are fabricated using a standard PECVD process. The dopant in the layers is germanium. Nonlinearity is induced in the samples using corona poling and the samples are characterized using Maker fringe measurements. The primary focus of this research is to analyze the distinctive properties of the nonlinearity profile that emerge due to certain alterations in the poling conditions. The following two steps introduce the alterations. In the first step, a set of two identical samples are poled with a positive voltage, but one of the samples is oriented in the opposite orientation inside the poling setup. One can alternatively think of it as a reversal of the electrodes. In the next step, another identical set of samples is poled in the same manner, but with a negative poling voltage. Thus, four glass samples are produced that possess unique nonlinearity profiles as shown by the Maker fringe measurements. It is observed that the intensity of SHG from the samples increases as the square of the intensity of the applied laser beam. The nonlinearity was stable and permanent for months. Different dopant types affect the Maker fringe patterns. A MATLAB hypothesis suggested that the modulation fringes for certain samples occur due to the formation of two nonlinear regions near the electrodes, each of width 5 µm. The samples which did not show modulation fringes only have a single nonlinear layer of width 9 µm. The findings of this research project can be implemented to understand the charge migration mechanism due to poling, thus enhancing the optimization capability of inducing nonlinearity in silica glass.ii