Saturable absorber characteristics in quantum dot lasers

A full evaluation of the performance of InGaAs quantum dots as saturable absorbers in multi-contact lasers emitting at a wavelength of 1 μm has been carried out. The light-current curves of the two-section quantum dot laser have been measured at 300K with varying levels of reverse bias applied to the absorber section and are compared with a quantum well control sample. This measurement indicates that the quantum confined stark effect (QCSE) is very different for the quantum dots, and this is confirmed by measurements of differential loss spectra as a function of reverse bias. Up to voltages of 6V there is no shift in the absorption edge of the quantum dots showing that the QCSE is weak for this OD system. Dynamic measurements show that self-pulsation in these lasers is highly temperature dependent, and completely ceases below 150K. We have also measured the absorber recovery time, which is found to increase from 40ps at 300K to 600ps at 50K, demonstrating that a high loss condition cannot be achieved quickly enough at low temperature for self-pulsation to occur.