OBSERVATION OF SEEDED 2ND HARMONIC-GENERATION IN BULK GERMANOSILICATE FIBER PREFORMS

Simultaneous irradiation of a bulk fiber preform with molar concentrations of 3% Ge and 0.5% P doped silica core region resulted in self-organized second harmonic generation with an effective χ(2) ∼ 1.2×10-16 m/V. The experiments revealed that the bulk preform requires the same critical IR intensity (∼ 10 GW/cm2) as the drawn fibers to prepare. Attempts to self-prepare the preform failed, indicating that self-preparation in fibers is most likely initiated by second harmonic generation associated with the core-cladding interface. © 1990.