Relaxation oscillations and damping factors of 1.3 μm In(Ga)As/GaAs quantum-dot lasers

In(Ga)As/GaAs quantum-dot (QD) lasers with emission wavelength at 1295 nm at room temperature are fabricated. The laser active region contains a threefold stack of QD layers with surface dot density of 4.56 × 1010 cm−2. The laser structure is aluminum-free with InGaP as cladding layers. Threshold current density of a narrow stripe laser of 8 μm wide and 3.5 mm long is 152.5 A/cm2. The highest relaxation oscillation frequency measured at room temperature is 1.8 GHz, corresponding to a modulation bandwidth of 2.8 GHz due to the small damping factor. From the above measurement, the differential gain and gain compression factor were extracted to be 4.3 × 10−16 cm2 and 3.4 × 10 −17 cm 3, respectively. Using these parameters, the maximum modulation bandwidth f3 dB max is estimated as 7.9 GHz.