TRANSVERSE-MODES UNDER EXTERNAL FEEDBACK AND FIBER COUPLING EFFICIENCIES OF VCSELS

We report a detailed study on the transverse mode behavior of vertical -cavity surface-emitting lasers (VCSEL's) under strong external feedba ck, Backreflections from a glass-facet result, periodically depending on the feedback phase, in variations of the transverse mode pattern of strongly index guided multitransverse-mode-emitting lasers, As a resu lt, butt-coupling efficiencies of these lasers strongly depend on lase r-fiber distance, For typical active VCSEL diameters around 15-mu m fi ber-coupled powers into standard 50 mu m-core diameter graded-index (G I) silica fibers vary by nearly 10 dB, Even far high-numerical apertur e 100-mu m-core diameter fibers, power variations of up to 2 dB are ob served.