Two-Stage Performance of Polarization-Maintaining Holmium-Doped Fiber Amplifiers

We report the experimental demonstration and record performance of two-stage broadband, high gain polarization-maintaining (PM) Ho-doped fiber amplifiers (HDFAs) at a signal wavelength of λ
_s
= 2051 nm. We begin by presenting a new PM Ho-doped fiber with core diameter 8 μm, a PANDA structure, a cutoff wavelength of 1650 nm, and a peak absorption of 57 dB/m at 1951 nm. Next, we consider architectures for high gain PM HDFAs. Here we demonstrate G = 60 dB with a dynamic range of >40 dB and noise figures as low as 10 dB. We then investigate configurations for high output power PM HDFAs. With one stage, we measure P
_out
= 3.45 W and an optical-optical slope efficiency η = 69%. With two stages, we obtain P
_out
= 6.7 W and η = 80%. The potential bandwidth of the high power PM HDFA is BW = 100 nm (7.5 THz). An optical signal-to-noise ratio of 58 dB/0.1 nm is achieved, and the polarization extinction ratio is >20 dB. Initial comparisons of simulations of gain and output power with our experimental results show relatively good agreement.