Abstract

Photorefractive gratings in optical fibers are emerging as a key technology for a wide range of applications, such as fiber lasers, optical filtering and sensing. To date, most of the work on fiber gratings has centered on germania-doped optical fibers, as these fibers show by far the highest photosensitivity to UV radiation. In several applications, however, photorefractive gratings are required in fibers where germania cannot be used as a core dopant. One important example is the erbium:ytterbium fiber laser, the most promising scheme for an efficient ultrashort single-frequency fiber laser at 1550 nm.¹ To obtain efficient energy transfer between the Yb³⁺ and Er³⁺ ions, the fiber core must be doped with large concentrations of P₂O₅ and Al₂O₃ and no GeO₂.² Until recently, we had not been able to form any measurable grating in such fibers, due to their extremely poor photosensitivity, which has limited the performance of our single-frequency fiber lasers.

© 1994 Optical Society of America