Design of High-Q-Gradient Dielectric Nanoparticle Chain Surface Plasmonic Cavities

Surface plasmonic cavities consisting of dielectric nanoparticle chains directly placed on a metal substrate are designed and studied, including a periodic nanoparticle chain (PNC) cavity and several different surface plasmon trap (SPT) cavities. The SPT cavities are designed by adjusting the nanoparticle sizes and the spacing between nanoparticles. Among them, the nanoparticle sizes range from 10 nm to 140 nm, and the spacings between the nanoparticles range from 200 nm to 280 nm. Compared to the PNC cavity, the SPT cavities support a single mode operation with higher Q factors within a relatively wide bandwidth. In particular, when the particle size and the spacing between the particles of the chain are set to vary in a parabolic gradient profile, the Q factor of the SPT cavity can be improved up to 85% compared to the PNC cavity. Our designs can be applied in the development of high-Q-factor plasmonic nanolasers.