Composition-engineered quantum dashes for high-speed C-band VCSELs

Abstract

We present a comprehensive multi-physics analysis of composition-engineered InAs/InGaAsP quantum-dash (Qdash) active regions for high-speed C-band wafer-fused vertical-cavity surface-emitting lasers (VCSELs). By integrating cavity eigenmode simulations, eight-band k⋅p electronic-structure modeling, and a travelling-wave time-domain laser dynamics framework, we evaluate how bandgap engineering, strain redistribution, and confinement-layer design collectively influence Qdash emission and modulation performance. Slight P alloying of the Qdash, combined with an InP first capping layer and a 1.10Q InGaAsP second capping layer, enables management of blue shifting of the ground-state transition while permitting increased Qdash height. This design enhances conduction-band offsets, strengthens electron confinement, and significantly improves optical transition strength. Device-level simulations show an ∼16% enhancement in differential gain and an increase of −3 dB modulation bandwidth from 11.2 to 13.4 GHz, accompanied by markedly improved large-signal non-return to zero eye quality. The results demonstrate that coordinated bandgap and strain engineering provide a practical pathway toward high-speed, energy-efficient C-band VCSELs suitable for next-generation optical interconnects and integrated photonic platforms.