Abstract
We propose a deep subwavelength plasmonic cavity based on a metal-coated coaxial structure with ${{\rm Ge}_{0.9}}{{\rm Sn}_{0.1}}$ as the active medium. A fundamental surface plasmon polariton mode is strongly confined on the sidewall of the metal core, with the quality factor up to ${5} \times {{10}^3}$ at 10 K. By reducing the cavity dimension to a few nanometers, this cavity mode shows a strong plasmon binding with the mode volume down to ${8}\; \times {{10}^{- 10}}$ ($\lambda /n{)^3}$, and significant size-dependent damping caused by the non-local optical response. The Purcell factor is achieved as high as ${2} \times {{10}^9}$ at 10 K and ${7} \times {{10}^8}$ at 300 K. This cavity design provides a systematic guideline of scaling down the cavity size and enhancing the Purcell factor. Our theoretical demonstration and understanding of the subwavelength plasmonic cavity represent a significant step toward the large-scale integration of on-chip lasers with a low threshold.
© 2021 Optical Society of America
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