Efficient waveguide-coupling of metal-clad nanolaser cavities

Many remarkable semiconductor-based nanolaser cavities using metal have been reported in past few years. However, the efficient coupling of these small cavities to waveguides still remains a large challenge. Here, we show highly efficient coupling of a semiconductor-based metal-clad nanolaser cavity operating in the fundamental dielectric cavity mode to a silicon-on-insulator waveguide. By engineering the effective refractive index and the field distribution of the cavity mode, a coupling efficiency as high as 78% can be achieved for a metal-clad nanolaser with a modal volume of 0.28 (λ/n)³ while maintaining a high optical quality factor of > 600.