All-Polarization-Maintaining One- and Two-Stage Holmium-doped Fiber Amplifiers at 2051 nm

We report the performance of one- and two-stage single clad polarization-maintaining (PM) Ho-doped fiber amplifiers (HDFAs) at λ
_s
= 2051 nm, pumped at λ
_p
≈ 1950 nm. We show that the Ho-doped fiber has a slope efficiency η = 70 %, and demonstrate an output power P
_out
of 3.5 W and a gain G = 43 dB.