Manipulation of lasing modes in a deformed octagonal microcavity laser

We have demonstrated a deformed octagonal microcavity semiconductor laser with manipulated lasing modes for bistable operation and direct modulation. There are two sets of degenerated four-bounced modes, S₀₁ and S₀₂, in the octagonal microcavity, and the degeneracy between them is broken by introducing a square hole into the center of the cavity. In the deformed octagonal microcavity laser, mode S₀₁ dominates the lasing process during the current rising process. However, mode S₀₂ also lases when the current decreases and interacts nonlinearly with S₀₁, which is caused by the non-uniform distribution of the refractive index induced by the square-ring-shaped current injection. We observe a counterclockwise bistable hysteresis loop with continuous injection current ranging from 31 to 13 mA at 288 K. We also study the small-signal modulation response of the laser at high and low states with different injection currents. By utilizing the photon-photon resonance effect between modes S₀₁ and S₀₂, we effectively increased the 3-dB bandwidth of the laser from 12 GHz to 16.2 GHz.