Evidence of space-charge effects in thermal poling

The in situ thermal poling processes in germanosilicate fibers for positive and negative poling voltages are significantly different. Thermal poling of silica fibers consists of two processes: the faster linear process of charge migration and the subsequent single exponential process of charge ionization. Both the shielding electrical field due to charge migration and the ionization electrical field due to charge ionization are able to be frozen-in at room temperature and lead to the residual linear electrooptic effects. The observations support that the mechanism of the induced electrooptic effects is based on space charge electrical fields instead of dipole/bond orientation.