Modeling of photoinduced charge separation in germanosilicate optical fibers during UV-excited poling

We report numerical solutions of a proposed model for charge separation and trapping during poling of germanosilicate fiber in the presence of ultraviolet (UV) light. The model was solved quantitatively in the steady state to determine the space-charge field distribution after UV-excited poling of a germanosilicate optical fiber with internal electrodes. The resulting internal electric field was found to be up to an order of magnitude higher than the initial poling field, sufficient to produce an effective second-order nonlinearity consistent with experimental observations by the internal field acting on the inherent third-order nonlinearity. The effects of core-cathode spacing, nonuniform defect distributions, and photo-electron recombination rate on the induced χ _eff ⁽²⁾ were also investigated. It is shown that a small core-cathode spacing is advantageous. Our UV-poled field solutions may also apply to thermal poling, provided we swap the anode and cathode designations. The results suggest that it is optimal to have the core located in the depletion region regardless of poling method.