Spoof surface plasmon photonics

In undergraduate courses on classical electromagnetism, it is taught that a perfect conductor expels the electromagnetic (EM) field, and hence its surface is not able to support the propagation of bound EM waves. However, when the surface of a perfect conductor is structured at a length scale much smaller than the operating wavelength, geometrically induced surface EM modes can be supported. Owing to their similarities with the surface plasmon polaritons (SPPs) in the optical regime, these surface EM modes were named spoof surface plasmons. The concept of spoof surface plasmons has opened up a new line of research within plasmonics with the aim of transferring all the potentialities of SPPs in the optical regime to lower frequencies (microwave, terahertz, and midinfrared regimes) in which a metal behaves as a quasiperfect conductor. In recent years, several research groups have extended this concept from planar surfaces to waveguides, and eventually to resonators, covering the entire range of structures studied in standard plasmonics. This review provides a detailed perspective on the recent developments in spoof surface plasmon photonics from both the fundamental and applied sides.