Yttrium aluminium garnet (YAG) has been widely used as a solid-state laser host because of its superior optical, thermal,
mechanical properties, as well as its plurality in hosting active ions with a wide range of ionic radii. Drawing YAG into
single crystalline fiber has the potential to further scale up the attainable power level with high mode quality. The recent
advancement on the codrawing laser-heated pedestal growth (CDLHPG) technique can produce glass-clad YAG
crystalline fibers for laser applications. The drawing speed can reach 10 cm/min for mass production. The CDLHPG
technique has shown advantages on transition-metal ion doped YAG and short-fluorescent-lifetime ion doped YAG host.
Compared to silica fiber lasers, the crystalline core offers high emission cross section for transition metal ions because of
the unique local matrix. The challenges on the development of
glass-clad YAG fibers, including core crystallinity,
diameter uniformity, dopant segregation, residual strain, post-growth thermal treatment, and the thermal expansion
coefficient mismatch between the crystalline core and glass clad are discussed. Chromium, ytterbium, and neodymium
ions doped YAG fiber lasers have been successfully achieved with high efficiency and low threshold power. Power
scaling with a clad-pump/side-coupling scheme using single clad or double clad YAG fibers is also discussed.
We demonstrate a cascaded Raman fiber laser with a record output power of 104 W at 1480 nm. We achieve
this with an 1117 nm Yb-doped fiber laser pumping a cascaded Raman conversion to 1480nm. Enhanced efficiency is
achieved in the Raman cavity using a fiber with a long wavelength cut-off which prevents further Raman conversion of
1480 nm light and thus allowing for longer cavity lengths. The output is single mode making it a bright source for core
or cladding pumping of erbium-doped fiber lasers.
We report the measurement of photodarkening in single-mode phosphate fibers with a Yb<sup>3+</sup> concentrations of 7.1 × 10<sup>26</sup>
m<sup>-3</sup> and 1.42 × 10<sup>27</sup> m<sup>-3</sup> (6 wt.% and 12 wt.% Yb<sub>2</sub>O<sub>3</sub>).We compare the photodarkening resistance of these phosphate
fibers with that of three single-mode Yb<sup>3+</sup>-doped silica fibers. Our data shows that under strong pumping conditions,
phosphate fibers allow Yb<sup>3+</sup> concentrations that are least 6 times greater than the most photodarkening-resistant silica
fibers to date without the onset of photodarkening at 660 nm.
We report the first measurement of the stimulated Brillouin scattering (SBS) gain coefficient of a phosphate fiber. Using
single-pass amplification of spontaneous Brillouin scattering noise, we measured an SBS gain coefficient of 2.1 × 10<sup>-11</sup>
m/W in a 124.5-cm single-mode Yb<sup>3+</sup>-doped phosphate fiber. This is a factor of two less than the SBS gain coefficient
of silica fiber, which puts phosphate glass fiber at an advantage for high-power applications.