Efficient waveguide-coupling of metal-clad nanolaser cavities

Abstract

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.

Advances in small lasers

“…Recent electrically pumped photonic crystal lasers have indeed exceeded the 10 fJ energy target 59 . Metallic nano-cavity devices are another promising candidate 84 as they can have much smaller active regions than dielectric cavity lasers. Although their low Q factors typically lead to higher threshold currents, some design studies predict that metallic structures coupled to waveguides could offer very small footprint devices with sufficient efficiency for this application (Fig.…”

“…Although their low Q factors typically lead to higher threshold currents, some design studies predict that metallic structures coupled to waveguides could offer very small footprint devices with sufficient efficiency for this application (Fig. 5a) 84 . Furthermore, it is predicted that due to their sub-wavelength sized, low Q factor cavities, metallic devices can provide the highest possible modulation bandwidth 23 .…”

“…(Reproduced from Ref. 84 ) b, Energy can also be coupled to a plasmonic waveguide, but the large losses in these waveguides may require active loss compensation. Schematic of slab plasmon waveguide amplifier with ultra-thin gold film between optically pumped organic semiconductor layers (left).…”

Engineering of metal-clad optical nanocavity to optimize coupling with integrated waveguides

“…To overcome this limitation, researchers have recently explored metallic III-V nanoscale optical cavities and achieved physical and modal sizes on the subwavelength scale, which is sufficiently small to open up new possibilities for implementing higher-performing Si/III-V hybrid optical systems [13][14][15][16][17][18][19][20][21][22][23][24][25]. However, with this approach, one significant problem in practical integration and use arises: Because of the extremely small output aperture of such a cavity, the radiation from the cavity diverges very rapidly, which makes optical coupling between the III-V cavity and integrated Si-waveguides very inefficient [25,26]. To implement practical devices, a more efficient coupling method is highly desired.…”

Metallic subwavelength-cavity semiconductor nanolasers

“…Through 2D simulation (Figure 6b and 6c), we found an evanescent coupling can be efficient if the effective indices of the two waveguides match. Kim et al proposed a similar evanescent coupling scheme 59 to integrate a metallic cavity nanolaser with a silicon-on-insulator waveguide. Simulation shows that a high coupling efficiency can be achieved between the metallic nanocavity and the silicon-on-insulator waveguide underneath.…”