## Abstract

Propagation and mode coupling within relatively short ($\sim 1\u201310\text{\hspace{0.17em}}\mathrm{m}$) large core, nominally multimode, fibers are of interest in a number of applications. In this research, we have studied the output beam quality and mode coupling in various fibers with core diameters of $100\u2013400\text{\hspace{0.17em}}\mathrm{\mu m}$ and lengths of $2\text{\hspace{0.17em}}\mathrm{m}$. Output beam quality $({M}^{2})$ and mode-coupling coefficients $(D)$ have been studied for different clad dimensions, numerical apertures, and wavelengths. The mode-coupling coefficients have been determined based on modal power diffusion considerations. The results show that *D* scales approximately as the inverse square of the clad dimension and inverse square root of the wavelength. Output from a $2\text{\hspace{0.17em}}\mathrm{m}$ length fiber of $100\text{\hspace{0.17em}}\mathrm{\mu m}$ core and $660\text{\hspace{0.17em}}\mathrm{\mu m}$ clad fiber is close to single mode (${M}^{2}=1.6$), while output from a $200\text{\hspace{0.17em}}\mathrm{\mu m}$ core and $745\text{\hspace{0.17em}}\mathrm{\mu m}$ clad fiber also has high beam quality.

© 2011 Optical Society of America

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