Surface Plasmon Polaritons Emission with Nanopatch Antennas: Enhancement by Means of Mode Hybridization

We theoretically study the emission of surface plasmon polaritons (SPPs) in cylindrical nanopatch antennas with sub-10 nm dielectric gaps. The eigenmodes of a nanopatch antenna can be classified as gap modes or antenna modes. We show that these two families of modes possess very different intrinsic properties regarding the emission of SPPs. Gap modes have an extremely large Purcell factor, which allows overcoming quenching, but a weak efficiency to radiate SPPs. On the other hand, antenna modes have a weaker Purcell factor but a larger efficiency to radiate SPPs. The coupling between gap modes and antenna modes results in the formation of hybrid modes. We evidence that these hybrid modes have the advantage to provide both a large Purcell factor and a large SPP efficiency. Working with such hybrid modes allows enhancing the SPP emission. We show that the mode hybridization results in an enhancement of 2 orders of magnitude of the power radiated into propagating SPPs at lambda = 800 nm and an overall SPP efficiency of 15% for a gap thickness of 1 nm. Moreover, increasing the refractive index of the host medium surrounding the nanopatch further improves the SPP emission.