Fused silica are common fiber materials which have macroscopic central symmetry without second-order nonlinearity. Studies have shown that thermal poling of fused silica fibers can destroy this macroscopic central symmetry, resulting in second-order nonlinearity or linear electro-optical effects. In this paper, a new type of double-hole optical fiber is designed. A two-dimensional (2D) numerical model is used to simulate the movement of ions and the formation of space charge region by finite element analysis. It is found that the single round square hole structure of the new double-hole fiber promotes the thermal poling process. The effective second-order nonlinear coefficient χ eff ( 2 ) of the new double-hole poled fiber is 0.28 pm/V at the core center, which is 0.05 pm/V higher than that of the circular double-hole poled fiber. In the fiber core, the radial distribution of the internal electric field and of χ eff ( 2 ) is calculated and analyzed. The results of this paper are of great significance for the application of thermally poled fibers on nonlinear all-fiber devices.
Humidity effect on the decay of second-order nonlinearity in thermally poled fused silica
