Abstract
A new class of optical fiber, the SHARC fiber, is analyzed in a high-power fiber amplifier geometry using the gain-filtering properties of confined-gain dopants. The high-aspect-ratio (~30:1) rectangular core allows mode-area scaling well beyond 10,000 μm2, which is critical to high-pulse-energy or narrow-linewidth high-power fiber amplifiers. While SHARC fibers offer modally dependent edge loss at the wide "semi-guiding" edge of the waveguide, the inclusion of gain filtering adds further modal discrimination arising from the variation of the spatial overlap of the gain with the various modes. Both methods are geometric in form, such that the combination provides nearly unlimited scalability in mode area. Simulations show that for kW-class fiber amplifiers, only the fundamental mode experiences net gain (15 dB), resulting in outstanding beam quality. Further, misalignment of the seed beam due to offset, magnification, and tilt are shown to result in a small (few percent) efficiency penalty while maintaining kW-level output with 99% of the power in the fundamental mode for all cases.
Highlights
High-power and high-energy fiber lasers and amplifiers have greatly benefitted from largemode-area (LMA) fibers [1]
Both methods are geometric in form, such that the combination provides nearly unlimited scalability in mode area
Since LMA fibers are nominally multimode in nature, some sort of mode filtering is required in order to deliver an output beam having the desired beam quality that is provided exclusively by the fundamental mode
Summary
High-power and high-energy fiber lasers and amplifiers have greatly benefitted from largemode-area (LMA) fibers [1]. A semi-guiding high-aspect-ratio-core (SHARC) fiber was recently introduced [8] as a new fiber architecture that combines the beneficial aspects of solid-state slab lasers and fiber lasers. This new class of fiber, which incorporates a rectangular core, was modeled extensively to elucidate its mode-filtering mechanism, to demonstrate its potential as a verylarge mode area (VLMA) fiber, and to understand the limitations of its operation.
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