Hybrid plasmonic structures based on CdS nanotubes: A novel route to low-threshold lasing on the nanoscale

Nanowires and nanotubes could become important building blocks in advanced photonic systems owing to their fascinating optoelectronic properties and high compatibility with versatile chemical synthetic methods. Many intriguing studies have been enabled by applying these nanostructures in the construction of various types of active and passive photonic components. Successful examples are the recent demonstration of semiconductor and plasmonic lasers based on CdS nanowires (Duan et al 2003 Nature 421 241-5, Oulton et al 2009 Nature 461 629-32, Ma et al 2010 Nature Mater. 10 110-13), which generate and deliver intense coherent light down to and even below the diffraction-limited scale. Here in this paper, by carrying out a numerical investigation of a novel hybrid plasmonic structure that consists of a CdS nanotube sitting above a metal substrate separated by a nanometric MgF₂ layer, we show theoretically that nanotube-based plasmonic structures can also act as highly efficient lasing sources. Optical properties of such a laser configuration including modal behaviour and the lasing threshold is investigated with regard to the variation of key geometrical parameters. Simulation results reveal that the employment of a CdS nanotube may result in improved optical performance compared with the conventional CdS-nanowire-based plasmon laser. Reduced lasing threshold with mitigated modal loss can be achieved simultaneously under carefully engineered geometries. We also explore the feasibility of combining nanowire- and nanotube-based active and passive components for on-chip integrations. As a simple demonstration, monolithic integration of a CdS nanotube laser with a CdS-nanowire-based passive component is shown numerically on a single chip. We expect that these studies could lay the foundations for nanotube- and nanowire-based hybrid integrated photonic components and circuits.