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Low linewidth enhancement factor and chirp and suppressed filamentation in tunnel-injection In0.4Ga0.6As self-assembled quantum dot lasers

We report measurements of the near-field pattern of ridge-waveguide tunnel injection In0.4Ga0.6As/GaAs self-assembled quantum dot lasers and have compared the results with similar strained quantum well lasers. While no filamentation is observed in the quantum dot devices, significant filamentatin and side lobes are observed in the quantum well lasers. The trend is corroborated by measured linewidth enhancement factor, α, of the two types of devices. Values of α~3.8 are measured in the quantum well lasers, while α is ≤0.7 in the quantum dot lasers, suggesting a very small refractive index change with injection in the active region. Chirp ≤0.6Å is measured in the tunnel injection devices, while it varies in the 1.6-3 Å range in the quantum well lasers.