A highly Yb-doped polarization-maintaining fiber has been developed. Optimization of the aluminophosphosilicate core composition made it possible to achieve a high gain (comparable with that of phosphate glasses), simultaneously with high pump-to-signal conversion efficiency. Codoping the core with germanium oxide provided high photosensitivity and made it possible to record highly reflective fiber Bragg gratings directly in the active fiber. Single-frequency fiber lasers have been designed based on the developed fiber, which generate in a single polarization mode with a record-short cavity length, equal to 14 mm. The pump-to-signal conversion efficiency was shown to be 22% for a polarized single-frequency laser at a wavelength of 1064 nm and 17% for a polarized single-frequency laser at 976 nm.
Semenov et al. (Mon,) studied this question.