Simulation of a ridge-type semiconductor laser with selectively proton-implanted cladding layers

Abstract

High power 980-nm semiconductor lasers are indispensable for pumping sources of erbium doped optical fiber amplifiers [1]. Generally, 980-nm semiconductor lasers have ridge structures so as not to expose their active regions to air during their fabrication, because the active regions are easily oxidized and degraded in air. In the ridge structures, higher-order transverse modes as well as the fundamental transverse mode are confined. As a result, with an increase in injected current, higher-order transverse modes lase; kinks appear in their current versus light-output (I-L) curves [2]. These kinks are attributed to changes in the local gain profile and refractive index owing to spatial hole burning, the free-carrier plasma effect, and heating. To obtain high fiber-coupled optical power, semiconductor lasers with high kink levels operating in the fundamental transverse mode are required. To date, to increase kink levels, coupling of the optical field to the lossy metal layers outside the ridge [3], highly resistive regions in both sides of ridge stripe [4], and incorporation of a graded V-shape layer [5] have been demonstrated. To increase kink level and decrease the threshold current further, a ridge structure with optical antiguiding layers have been proposed [6], [7], but the fabrication process is fairly complicated.