EXTRAORDINARY OPTICAL-TRANSMISSION THROUGH SUBWAVELENGTH HOLE ARRAYS

The desire to use and control photons in a manner analogous to the con trol of electrons in solids has inspired great interest in such topics as the localization of light, microcavity quantum electrodynamics and near-field optics(1-6). A fundamental constraint in manipulating ligh t is the extremely low transmittivity of apertures smaller than the wa velength of the incident photon, While exploring the optical propertie s of submicrometre cylindrical cavities in metallic films, we have fou nd that arrays of such holes display highly unusual zero-order transmi ssion spectra (where the incident and detected light are collinear) at wavelengths larger than the array period, beyond which no diffraction occurs, In particular, sharp peaks in transmission are observed at wa velengths as large as ten times the diameter of the cylinders. At thes e maxima the transmission efficiency can exceed unity (when normalized to the area of the holes), which is orders of magnitude greater than predicted by standard aperture theory, Our experiments provide evidenc e that these unusual optical properties are due to the coupling of lig ht with plasmons-electronic excitations-on the surface of the periodic ally patterned metal film, Measurements of transmission as a function of the incident light angle result in a photonic band diagram, These f indings may find application in novel photonic devices.