In this work, a heavily Er-doped fiber with an 8 µm core diameter and a numerical aperture of 0.13 was prepared by the modified chemical vapor deposition (MCVD) technique combined with the sol-gel method. The background loss and absorption coefficient at 1530 nm were measured to be 20 dB/km and 128 dB/m, respectively. Thanks to the sol-gel method, the fiber showed a good doping homogeneity, which was confirmed through unsaturable absorption measurement. The net gains of three 25, 45, and 75-cm-long fibers were measured in the range of 1520 to 1600 nm, and the highest gain reached above 23 dB at both 1530 and 1560 nm in 25 and 75-cm-long fibers, respectively. The short-cavity laser performance was measured using centimeter-scale fibers. The maximum output power of 12 mW was demonstrated in a 6.5-cm-long active fiber with a slope efficiency of 20.4%. Overall, the prepared heavily Er-doped silica fiber is a promising item to be applied in a high-repetition-rate or single-frequency fiber laser.

A highly transparent Eu3+-doped CaGdAlO4 (CGA) single crystal is grown by the floating zone method. The segregation coefficient, x ray diffraction, and x ray rocking curve are detected, and the results reveal that the single crystal is of high quality. The f–f transitions of Eu3+ in the host lattice are discussed. The D05–F72 emission transition at 621 nm (red light) is dominant over the D05–F71 emission transitions at 591 and 599 nm (orange light), agreeing well with the random crystal environment of Eu3+ ions in a CGA crystal. The decay time of Eu:D05 is measured to be 1.02 ms. All the results show that the Eu:CGA crystal has good optical characterization and promises to be an excellent red- fluorescence material.