High optical feedback tolerance of InAs/GaAs quantum dot lasers on germanium.

This work experimentally investigates the optical feedback sensitivity of InAs/GaAs quantum dot (Qdot) lasers epitaxially grown on Ge substrate. In comparison with a Qdot laser on GaAs substrate with identical epilayer and cavity structures, the Ge-based laser is found to exhibit lower sensitivity to the optical feedback, although it has a higher epitaxial defect density. Theoretical analysis proves that the high defect density strongly increases the damping factor while slightly reduces the linewidth broadening factor, which lead to high tolerance to the optical feedback. This work suggests the high potential of Qdot lasers on Ge for isolator-free operation in photonic integrated circuits.