“…To achieve high light coupling efficiency between the high power 980-nm semiconductor lasers and the single mode Er 3+ -doped optical fibers, high kink level or kink-free operation of the high power 980-nm semiconductor lasers is needed. To increase the kink level in the ridge structures, lossy metal layers [3], highly resistive regions in both sides of the ridge stripe [4], incorporation of a graded V-shape layer [5], optical antiguiding layers [6,7], separate confinement of carriers and horizontal transverse mode [8], and horizontal coupling of horizontal transverse modes by a groove in the mesa [9] have been studied.…”