The spectral analysis and mode structure of ultrabroad InAs/InAlGaAs quantum dash laser

We demonstrate the widened broadband emission of self-assembled quantum dash laser using impurity-free vacancy induced disordering (IFVD) technique. The 100 nm blueshifted lasers exhibit higher internal quantum efficiency and lower threshold current densities than the as-grown devices. The laser emission from multiple groups of quantum-dash (Qdash) families convoluted with multiple orders of subband energy levels within a single Qdash ensemble is experimentally observed. However, the suppression of laser emission in short wavelength and the progressive redshift of peak emission with injection current from devices with short cavity length occur. These effects have been attributed to the nonequilibrium carrier distribution and energy exchange among different sizes of Qdash ensembles. In addition, we perform the far-field lateral mode measurements from the fabricated as-grown Qdash laser. The analysis of mode patterns indicate that Qdash lasers exhibit gradual broadening of beam divergence (FWHM of 3.4° to 10.8°) with increasing injection current. However, these beam divergence angles are still narrower than the quantum well (QW) laser (FWHM ~13°) at an injection up to 2.5 x J_th. Qdash laser exhibits an improved output beam quality, therefore reduced filamentation, as compared to the QW laser, owing to the inherent characteristics from quantum-dot (Qdot) laser, where injected carriers are confined by the lateral energy barriers as Qdots are disconnected laterally and are cladded by larger bandgap materials. Our results imply a highly attractive wavelength trimming method, well suited for improved performance, and monolithic Qdash integration of optoelectronics components.