Abstract

We have performed seeded preparation experiments on bulk Ge (3%) and P (0.5%) doped fiber preforms with a core region 1.5 mm in diameter. The experiments revealed no measurable changes in the second-harmonic background until the IR average power reached a peak intensity of ~9.5 GW/cm² at the focal spot in the preform. This critical-intensity behavior has also been observed in highly controlled preparation experiments on fibers. This threshold behavior has been explained in fibers in terms of an optical delocalization mechanism.¹ Sidelight studies on the preform revealed a sharp increase in the second harmonic over a 1 mm region, giving further evidence for the existence of a threshold. Using the effective length contributing to phase-matched SHG in the preform and a conversion efficiency of 2 10-7, we find an effective (2) 5 10-16 m/V.

© 1990 Optical Society of America