Investigation of Chirped InAs/InGaAlAs/InP Quantum Dash Lasers as Broadband Emitters

摘要

In this paper, we assessed the effect of additionally broadened quantum dash (Qdash) optical transitions in the multi-stack dash-in-a-well laser structure at both, material and device level. A broad photoluminescence linewidth of ${sim}{rm 150}~{rm nm}$ demonstrates the formation of highly inhomogeneous InAs-dashes across the stacks. The transmission electron microscopy revealed small (large) average dash height from the Qdash stack with thick (thin) over grown barrier layer. The Fabry–Perot laser diodes fabricated from this chirped structure exhibits unique device physics under the short pulsewidth (SPW) and quasi-continuous wave (QCW) operation. Varying the ridge-width $(W)$ from 2 to 4 $mu{rm m}$ showed quenching of ultrabroad lasing signature in the SPW operation, and consistent even for a wide 15 $mu{rm m}$ oxide strip laser diode. A lasing spectral split with reduced intensity gap in the center is observed in the QCW operation with the gap decreasing with increasing ridge-width. Such atypical lasing operation, influenced by the waveguiding mechanism is qualitatively realized by associating to the reduced vertical coupling effect of the Qdash stacks in the operation of small ridge-width lasers compared with large ridge-width and oxide stripe lasers, and leading to varying non-uniform distribution of carriers among the inhomogeneously broadened Qdash stacks in each case. Our chirped 2$,times,$830 $mu{rm m}$ ridge laser demonstrated marked improvement in the internal quantum efficiency $({sim}{80%})$ and ${-}{rm 3}~{rm dB}$ lasing bandwidth, ${>}{rm 50}~{rm nm}$ centered at ${sim}{1.61}~mu{rm m}$.