Improving optical confinement in nanostructures via external mode coupling.

We demonstrate the formation of long-lived resonances via external coupling in open nanostructures. In the examples of three dielectric nanorods or strips, external coupling of modes is induced by tuning of the rod spacing and increases the lifetime over an order of magnitude. Such an enhancement results from the destructive interference of fields that minimizes light leakage. Our results illustrate an effective way of storing light in nanostructures, and have potential applications to nanoscale photonic devices.