A systematic and detailed study of launching light from semiconductor lasers into plane-ended multimode optical fibers has been carried out—we believe for the first time. Three different semiconductor lasers and four multimode fibers having numerical apertures in the 0.16–0.40 range were used. Simple theoretical models developed for the launching efficiency η give good agreement with experimental results. We show how erroneous results can be obtained when considering only the stimulated emission of the lasers in calculating η. The dependence of η on axial, lateral, and angular misalignments is also investigated and explained qualitatively with ray optics.
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