High power, low linewidth enhancement factor gain chip based on the second conduction subband transition.

We demonstrate a high-power InGaAs/GaAs quantum well (QW) gain chip that achieves a suppressed linewidth enhancement factor (α-factor) by utilizing the second conduction subband (E2) transition. The low α-factor is intrinsically enabled by operating the device on the E2 transition, while high-power single-mode operation is ensured by an asymmetric epitaxial waveguide and a J-shaped ridge structure. The device exhibits a gain peak shift from 1050 nm (first conduction subband (E1) transition) to 990 nm (E2 transition) at high current injection, achieving a fundamental transverse-mode output of 180.01 mW, with α-factor suppressed. Compared to the E1 transition, the E2 transition offers a sixfold reduction in α-factor and demonstrates markedly lower sensitivity to carrier fluctuations. Additionally, the E2 transition yields a higher gain than E1, enhancing the potential for high-power scaling. This work validates E2-transition engineering as an effective strategy for high-performance narrow-linewidth light sources.