We present the results of the experimental study and comparison of Yb-free, Er-doped, all-fiber, alignment free, single frequency (SF) fiber amplifiers operating under 980-, 1470- and 1530-nm pumping for the core- and clad-pumping architectures. In the single-mode core-pumped configuration Er- doped fiber amplifiers demonstrated 52% and 60% pump to output efficiencies for 980 and 1480 nm pump wavelength, respectively, producing over 140 mW of SF output power at seed wavelength approximately 1560 nm and over 180 mW at seed wavelength 1605 nm for 300 mW of pump power. At the same time, when clad pumped, Er-doped 20/125 DC LMA gain fiber demonstrates laser efficiencies of 22.4% pumped at 980 nm - up to 20 W of fiber-coupled diode laser pumping. The same LMA fiber demonstrates 33% optical-to-optical efficiency (46% slope efficiency versus absorbed power) when cladding-pumped with 1520-1530-nm fiber-coupled laser diode modules. Detailed analysis of these experiments is presented.
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