Multiwavelength GaN-Based Surface-Emitting Lasers and Their Design Principles

Dual-wavelength lasing operations are demonstrated in GaN-based vertical-cavity surface-emitting lasers (VCSELs) comprising ingeniously designed asymmetric InGaN quantum wells (AS-QWs). The dual laser modes show exact positive-correlated polarization dependences with a high degree of polarization of up to 98%. By simply tuning the pump energy, the components and intensity of the laser outputs can be continuously changed, making wavelength selection and switching available for the GaN-based VCSELs. Detailed theoretical analysis and experimental measurements show that the intensity of optical gain and the coupling between the active layer and optical field, namely the electron-photon interaction, as well as carrier tunneling and photon reabsorption play a crucial role in the multiwavelength lasing processes. Moreover, the design principles of the proposed AS-QWs and multistacked size-varied quantum dot (MS-QD) active regions are elaborated to provide guidelines for controllable multiwavelength emissions in GaN-based surface-emitting lasers. These results not only provide better understanding of lasing in nitride-based microcavity systems but also shed insight into the more fundamental issues of electron-photon coupling in such systems. Importantly, such controllable multiwavelength laser operations may extend nitride-based VCSELs to previously inaccessible areas, for example, flip-flop, ultrafast switches, and other functional devices such as Raman lasers and sensors.