In-Depth Studies of the Spectral Bandwidth of a 25 W 2 μm Band PM Hybrid Ho- and Tm-Doped Fiber Amplifier

We report the broadband spectral performance of a three-stage, high gain, single mode, high output power (25 W) polarization-maintaining (PM) hybrid Ho-doped and Tm-doped fiber amplifier at signal wavelengths of λ _s = 2004-2108 nm. The three-stage amplifier consists of a two stage high gain Ho-doped PM single clad preamplifier stage followed by a Tm-doped PM double clad power amplifier. We employ narrow linewidth (<; 2 MHz), single frequency, discrete mode, packaged InGaAs/InP based laser sources to study the performance of our amplifier in a master oscillator-power amplifier (MOPA) configuration. Measurements are made over a broad wavelength range that is determined by careful selection of the properties of the Ho-doped and Tm-doped fibers in the three amplifier stages. No nonlinear effects, such as stimulated Brillouin scattering (SBS) or stimulated Raman scattering (SRS), are observed at any signal wavelength in our measurements. We compare the experimental results with steady-state simulations of both the Ho-doped preamplifier and the TDFA booster and find good agreement between data and simulations for gain, noise figure, output power, and output optical spectra.