We propose a novel subwavelength metallic InP/InGaAs laser with a capsule-shaped cavity. By introducing curved metallic facets at the both ends, resonant modes can be strongly confined inside the center of this capsule-shaped cavity, which not only improves the confinement factor and the Q factor, but also reduces the cavity volume. As an example case, we numerically demonstrate that this new structure can decrease the plasmonic loss and improve the Q factor from 197 to 297 and reduce the current threshold from 291μA down to 60μA with a cavity dimension of 1.1 μm × 0.84μm × 1.4μm. In addition, we demonstrate that there exists an optimal cavity width to minimize the current threshold.
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