Long-wavelength (1.3-1.5 micron) quantum dot lasers based on GaAs

Abstract

The molecular beam epitaxy of self-assembled quantum dots (QDs) has reached a level such that the principal advantages of QD lasers can now be fully realized. We overview the most important recent results achieved to date including excellent device performance of 1.3 µm broad area and ridge waveguide lasers (J th <150A/cm 2 , I th =1.4 mA, differential efficiency above 70%, CW 300 mW single lateral mode operation), suppression of non-linearity of QD lasers, which results to improved beam quality, reduced wavelength chirp and sensitivity to optical feedback. Effect of suppression of side wall recombination in QD lasers is also described. These effects give a possibility to further improve and simplify processing and fabrication of laser modules targeting their cost reduction. Recent realization of 2 mW single mode CW operation of QD VCSEL with all-semiconductor DBR is also presented. Long-wavelength QD lasers are promising candidate for mode-locking lasers for optical computer application. Very recently 1.7-ps-wide pulses at repetition rate of 20 GHz were obtained on mode-locked QD lasers with clear indication of possible shortening of pulse width upon processing optimization. First step of unification of laser technology for telecom range with QD-lasers grown on GaAs has been done. Lasing at 1.5 µm is achieved with threshold current density of 0.8 kA/cm 2 and pulsed output power 7W.

Continuous wave terahertz radiation from an InAs/GaAs quantum-dot photomixer device

“…They exhibit many curious optoelectronic properties, which are fully configurable during MBE by altering deposition factors such as: dot size, density, material/s, multi-layer periodicity, and density-ofstates. 9 QD's have been shown to exhibit ultrafast recovery times, [10][11][12] and InAs QD layers integrated into bulk GaAs can act analogously to mid-gap carrier trapping sites. This allows a severe reduction in charge carrier lifetimes with a comparatively small reduction in average carrier mobility 13 as the vast majority of the bulk lattice volume may be of high crystalline quality, unlike that of LT-GaAs.…”

Compact ultrafast lasers based on quantum-dot structures

“…Interestingly, practical devices exhibit the predicted outstandingly low thresholds 4,5 , but the spectral bandwidths of such lasers are significantly broader than those of conventional quantum-well lasers 6 . This characteristic is attributable to inhomogeneous broadening with its dependence on the dot size distributions.…”

Recent advances in VECSELs

“…From QD-based gain chips one mainly expects a realization of low laser thresholds and high characteristic temperatures (Kovsh et al 2004), given the peculiarities of the density of states for low-dimensional structures. However, the inherently strong inhomogeneous gain broadening, their ultrafast carrier dynamics and low-absorption saturation are also considered beneficial when it comes to the realization of ultrashort pulses under ML operation (Rafailov et al 2007).…”