Some progress has been made toward fabricating EDWAs by
SC-RTA. For example, relative gains of 1.1 dB/cm have been
obtained using Yb–Er-codoped silica–titania, but only in a strip loaded
geometry with fiber coupling and propagation losses so
high that no external gain was observed [10]. In this letter, we
demonstrate the first practical sol-gel EDWA. The device is
based on a buried active core and has low coupling and propagation
loss, strong confinement, and a realistic external gain.