Abstract

It is possible to induce second order nonlinear effects in glass systems, such as fibres, films or bulk silica samples by recording a permanent electric field optically, or by poling the samples with high voltages and heat. Characterising the charge distribution is central to understanding the mechanisms involved. We recently imaged frequency doubling gratings in fibres previously prepared for SHG, by etched the fibres until close to the core. Due to the presence of charges, etching is nonuniform, and the period of the grating can be unambiguously identified. Here, we present a simple technique to determine the charge distribution in poled glasses with submicron resolution. An interference pattern was formed by the reflections of a HeNe beam on the faces of a 1 mm thick poled slice of SiO₂(3 KV, 280 °C). One of the faces was etched in HF, while the other was used as a reference, and the intensity of one fringe was monitored in real time. The optical path of the light reflected off the surface being etched was altered. When the glass was not poled, the etching rate was constant and a periodic variation of the fringe intensity was seen. When the glass was poled, a strong frequency modulation was observed. Positive charge resulted in slower etching, and negative charge caused faster etching [1].

© 1996 IEEE