25  W 2  μm broadband polarization-maintaining hybrid Ho- and Tm-doped fiber amplifier

We report the design, evaluation, and performance of a polarization-maintaining (PM) fiber amplifier with a CW output power of >25  W at 2051 nm and a high input signal dynamic range of 34 dB at 25 W. To improve both the output power and dynamic range performance of previous amplifiers, we propose a PM hybrid design with a single-clad Ho-doped preamplifier (HDFA) followed by a double-clad Tm-doped power amplifier (TDFA). The role of the Ho-doped fiber preamplifier is to provide large input signal dynamic range, low noise figure, and moderate output power over an operating bandwidth from ≈2-2.1  μm. The role of the Tm-doped fiber power amplifier is to offer power amplification with good efficiency, taking full advantage of 2-for-1 ion-ion interactions, with the possibility of scaling up the output power to values much higher than 25 W. Our hybrid Ho-Tm-doped design provides a PM fiber amplifier with a combination of large input signal dynamic range, low noise figure, broad operating bandwidth, and high output power. Simulations of the hybrid HDFA/TDFA performance agree relatively well with experimental data.