Mode coupling and output beam quality of 100-400 μm core silica fibers

Propagation and mode coupling within relatively short (similar to 1-10 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 100-400 mu m and lengths of 2m. 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 2m length fiber of 100 mu m core and 660 eta m clad fiber is close to single mode (M-2 - 1.6), while output from a 200 mu m core and 745 mu m clad fiber also has high beam quality. (C) 2011 Optical Society of America