Abstract

The photosensitivity of Ge-doped fiber allows the fabrication of useful devices like Bragg gratings or intermodal couplers. Nevertheless, the physical mechanism leading to a permanent refractive index change is still not well understood. It has been suggested that the bleaching of an absorption band at 245 nm plays an important role in the process. One signature of this absorption band is the photoluminescence emitted around 400 nm [1]. This photoluminescence can be excited by direct absorption of UV light, and this method has been used previously to characterize the 245 absorption band [1,2]. We show here that the luminescence can also be excited by two-photon absorption of light around 500 nm. By measuring the photoluminescence signal as a function of the input intensity, we have observed significant deviation from the expected quadratic dependence, indicating a saturation of the two-photon absorption. From our measurements, the saturation intensity can be deduced, and the two-photon absorption cross-section can be estimated.

© 1991 Optical Society of America