Abstract

Silica fibers exhibiting high second-order nonlinearities (SON) could be used to develop a new generation of all-fiber electro-optic modulators, switches, tunable filters, and frequency converters. Initial SON's of 1 pm/V and 0.2 pm/V have been reported respectively in thermally poled bulk silica glass¹ and in thermally poled silica fibers.² However, these levels of effective SON in poled fibers were still small compared to those obtained in bulk glass. Fiber with in-built capillaries on either side of the core, suitable for introducing wire electrodes,³ are very attractive for thermal poling. Fujiwara et al. recently reported an electro-optic coefficient as high as 6 pm/V in these fibers, poled under UV excitation.⁴ The applied electric field was only 80 V/µm (800 V across gap of 10 (µm) in these experiments—not sufficient to produce any significant electric field-induced SON via the third-order nonlinearity. It is possible that phenomena other than the Pockel's effect contribute to the high value of coefficient obtained. These phenomena, if they exist, are unlikely to play a role in second-harmonic generation (SHG).

© 1996 Optical Society of America