1.48-MU-M HIGH-POWER GAINASP-INP GRADED-INDEX SEPARATE-CONFINEMENT-HETEROSTRUCTURE MULTIPLE-QUANTUM-WELL LASER-DIODES

High-power 1.48 mum graded-index separate-confinement-heterostructure multiple-quantum-well laser diodes (GRIN-SCH MQW LD's) have been inves tigated in terms of the beam divergence, threshold current, and differ ential quantum efficiency. A calculation predicts that narrow beam div ergence perpendicular to the junction plane could be obtained by the u se of small number of step quaternary layers with wide band-gap. Exper imentally, at the same time, the threshold current increased due to th e small optical confinement, although the beam divergence became small . We optimized the GRIN-SCH layers for a narrow and circular output be am with maintaining low threshold current. The full width at the half maximum (FWHM) of the far-field pattern in the horizontal direction wa s 20-degrees and that in the vertical direction was 25-degrees. The ma ximum output power, as high as 208 mW, was achieved at a driving curre nt of 1000 mA for a 1 mm long device with an antireflection and high-r eflection (2%/95%) coated facets. Stable transverse mode operation was confirmed up to the maximum output power. Due to high-power operation with a stable narrow and circular beam, an extremely high coupling ef ficiency of 89% and a record high output power from a single-mode fibe r of 185 mW were obtained at 25-degrees-C.