Two methods of coupling a multimode fibre to a GaAs double-heterostructure laser are investigated: firstly direct coupling into a plane fibre end face, and secondly coupling via a cylindrical glass fibre lens. The power coupled into the fibre was measured for three different lasers (and with one laser as a function of its bias current). The measured coupling efficiency was compared with theoretical considerations. Optical feedback effects due to reflection of the fibre end face have been observed. These cause an oscillation of the coupled power, when the separation between the laser and the fibre end face is varied by only a few tenths of a micron. The alignment tolerances using a fibre lens were, as expected, more critical than for direct coupling.
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