Thermal poling of femtosecond laser-written waveguides in fused silica.

Thermal poling of femtosecond laser written waveguides was investigated using second-harmonic microscopy under three approaches: (1) pre-poling and (2) post-poling in which fused silica substrates were poled before or after waveguide formation, respectively, and (3) double poling in which poling was applied both before and after laser writing. Effective nonlinear waveguide interaction strength was assessed relative to the mode profile and the assessments demonstrated an erasure effect of 81% in pre-poling and an ion migration blocking effect of 26% in post-poling. Double poling was found to recover the nonlinearity over the modal zone, overcoming prior difficulties with combining laser processing and thermal poling, opening up a future avenue for creating active devices through femtosecond laser writing of nonlinear optical circuits in fused silica.