Customization of evanescent near fields on freestanding plasmonic nanomembranes

Abstract

For a very long time optical evanescent near fields have been considered useless for practical applications and remained a theoretical curiosity. However, with advances in micro and nanotechnologies and the decreasing sizes of the photonic devices there came a need to overcome diffractive limit which sparked a practical interest in these previously overlooked field components. With the discovery of Surface Plasmon Polaritons (SPP), bound surface modes propagating along interfaces between materials with different signs of relative dielectric permittivity and being evanescent in the direction perpendicular to the interface a path was open to actively design spectral and spatial properties of near fields. Now plasmonic metamaterials and evanescent near fields are used not just for imaging beyond diffractive limit but also in transformation optics, biochemical sensing, cloaking devices, photonic integrated circuits, etc. Freestanding plasmonic nanomembranes are fairly simple and yet highly versatile structures which can be utilized in practically any of the fields of application of plasmonics, making them an ideal platform to build upon. In this paper we present a novel structural design as a means for customizing and tailoring the near field response of multilayer freestanding nanomembranes. To this purpose ellipsoidal diffractive "bumps" are built into the nanomembrane as the coupling elements between freely propagating and evanescent modes.