Effect of InGaAsP intermediate layer in 1.3 μm AlGaInAs strain-compensated multiple quantum well laser diodes

The effect is investigated of introducing a linearly graded-index separate-confinement-heterostructure InGaAsP intermediate layer between the InGaAs cap layer and the InP cladding layer to improve the characteristics of 1.3 μm AlGaInAs strain-compensated multiple-quantum-well laser diodes (LDs). With the InGaAsP intermediate layer, 3 μm-ridge-strip LDs without facet coating under CW operation exhibit a threshold current of 16mA, a resistance of 5.8 Ω, a characteristic temperature of 75 K in the range 20-70°C and 41 K at 70-100°C, a differential quantum efficiency of 50% and a low slope efficiency drop of -1.3 dB between 20 and 70°C. These characteristics are better than those of LDs without the InGaAsP intermediate layer. A wavelength swing of 0.48 nm/°C for LDs operated at 50 mA is achieved.