BUTT-COUPLING EFFICIENCY OF VCSELS INTO MULTIMODE FIBERS

We report a detailed study on butt-coupling efficiencies of vertical-c avity surface-emitting lasers (VCSEL's) to standard graded index multi mode silica fibers, Coupling efficiency strongly depends on active las er diameter as well as index guiding and transverse mode spectrum of t he laser. For typical active laser diameters of 16-20-mu m coupling ef ficiencies of about 90% are obtained with weakly index guided proton-i mplanted vertical-cavity lasers (VCL's) whereas stronger index guided oxidized lasers show considerably lower coupling efficiencies between 75% and 55%, depending on driving currents.