1.48 mum 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 LDs) have been investigated in terms of the beam divergence, threshold current, and differential quantum efficiency. A calculation predicts that narrow beam divergence perpendicular to the junction plane could be obtained by the use of small number of step quaternary layers with wide bandgap. Experimentally, the threshold current increased due to the small optical confinement, although the beam divergence became small. The full width at half maximum (FWHM) of the far-field pattern in the horizontal direction was 20 deg and that in the vertical direction was 25 deg . Output power as high as 208 mW was achieved at a driving current of 1000 mA for a 1-mm-long device. Stable transverse mode operation was confirmed up to the maximum output power. Coupling efficiency of 89% and output power from a single-mode fiber of 185 mW were obtained at 25 deg C