Reduced-symmetry LMA rod-type fiber for enhanced higher-order mode delocalization

Abstract

We present a novel design of a micro-structured large-pitch, large-mode-area (LMA) asymmetric rod-type fiber. By reducing the cladding symmetry through six high-refractive index germanium-doped silica inclusions, the fiber features strong higher-order mode (HOM) delocalization, leading to a potentially enhanced preferential gain for the fundamental mode in active fibers. In addition, high resolution spatially and spectrally ($S^2$) resolved mode analysis measurements confirm HOM contributions below 1% and ${\mathrm{LP}}_{1\mathrm{m}}$-like HOM contributions below the detection limit. This proposed fiber design enables single-mode operation, with near-diffraction-limited beam quality of $M^2=1.3$ and an effective mode area of $2560{\mathrm{\mu m}}^2$ at 1064 nm. This design opens new insights into improving the threshold-like onset of modal instabilities in high-power fiber lasers and fiber amplifiers by efficiently suppressing ${\mathrm{LP}}_{11}$ modes.

© 2017 Optical Society of America

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