In this work, we discuss a novel architecture for an all-fiber linearly polarized counter-pumped linear amplifier utilizing an 85 μm core diameter rod fiber. Signal light is launched directly into the core region of the rod fiber with high coupling efficiency via a monolithic Mode-Field Adapter (MFA) splice. The free-space coupling optics and alignment for counter-pumping the amplifier are contained and fixed in a small, ruggedized packaging. Both the monolithic MFA splice and fixed free-space optics lock the signal and pump coupling efficiencies, allowing the device to be handled as if it were entirely monolithic. Over 18 dB of gain was achieved during power testing as a single-stage linear amplifier. Methodologies for advancing this architecture into a multistage linear amplifier to achieve higher peak and average powers are discussed. Simulations and models are used to define the signal power, pump power, gain fiber geometries, and gain stage lengths required to achieve 1 mJ pulse energies in 1 ns pulse durations, as well as predict the resulting B-integral, Amplified Spontaneous Emission (ASE) levels, and unabsorbed pump power. The feasibility of realizing such an amplifier architecture is then discussed as a conclusion.
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