Recent advances in long wavelength quantum dot based lasers

This paper presents recent progress in the field of semiconductor lasers based on self-assembled quantum dots grown either on GaAs or InP substrates. Quantum dot (QD) based lasers are attracting a lot of interest owing to their remarkable optoelectronic properties that result from the three dimensional carrier confinement. They are indeed expected to exhibit much improved performance than that of quantum well devices. Extremely low threshold currents as well as high temperature stability have readily been demonstrated in the InAs/GaAs material system. The unique properties of quantum dot based active layers such as broad optical gain spectrum, high saturation output power, ultrafast gain dynamics and low loss are also very attractive for the realization of mode-locked lasers. Recent results in the field of directly modulated InAs/GaAs lasers emitting in the 1.3 μm window are discussed. We report in particular on temperature independent linewidth enhancement factor (or Henry factor α_H) up to 85°C. This is a key parameter which determines many laser dynamic properties. Optical feedback insensitive operation of specifically band-gap engineered devices, compatible with high bit rate isolator-less transmission is also reported at 1.55 μm. Monolithic mode locked lasers based on InAs/InP quantum dashes have been investigated for 1.55 μm applications. Sub-picosecond pulse generation at very high repetition rates (> 100 GHz) is reported for self-pulsating one-section Fabry Perot devices. Specific applications based on these compact pulse generators including high bit rate clock recovery are discussed.