Dual-mode and broadband quantum dot lasers

Abstract

Owing to the 3-D confinement and Stranski-Krastanov (S-K) growth mechanism, the InAs/GaAs QDs often exhibits large gain compression factor as well as large inhomogeneous gain spectrum broadening associated with the strain and size dispersion, which makes it a ideal candidate for the broadband and multi-mode laser applications, such as frequency comb and swept source lasers. However, in order to achieve broadband and high output power, the QD gain devices have to be operated at high injection levels to excite the ground and excited state emissions, thus, the gain spectra usually exhibit a dip between the ground state and excited state due to the finite number of density-of-states in the QD structures. In this presentation, we will show several devices applications of the broadband QD gain region, including broadband swept-source laser, dual-mode laser, and mode lock lasers. The InAs quantum dot (QD) heterostructures were grown on (001) GaAs substrates in a Veeco GEN II molecular beam epitaxy (MBE) system. The active region contains 7-stack of InAs QD layers. In order to achieve the broadband gain emission, each InAs QD active region was tuned by carefully changing the QD growth conditions. In-situ annealing under As2 overpressure before and after QD formation was also performed to enhance QD size inhomogeneity. In addition, the as-grown QD heterostructures were annealed in a rapid thermal annealing (RTA) process at 700°C for 60 sec, which can effectively enhance the inter-diffusion between the InAs QD and GaAs capping regions and further increase the emission linewidth. The InAs QDs were characterized by atomic force microscope (AFM) and transmission electron microscope (TEM) measurements. The QD laser devices are setup in external cavity configurations as well as active mode lock configurations. The device characteristics will be discussed in details.