Extraordinary optical transmission (EOT) is the phenomenon of greatly enhanced transmission of light through a subwavelength aperture in an otherwise opaque metallic film which has been patterned with a regularly repeating periodic structure. Generally when light of a certain wavelength falls on a subwavelength aperture, it is

diffracted Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

isotropically in all directions evenly, with minimal

far-field The near field and far field are regions of the electromagnetic (EM) field around an object, such as a transmitting antenna, or the result of radiation scattering off an object. Non-radiative ''near-field'' behaviors dominate close to the ant ...

transmission. This is the understanding from classical aperture theory as described by Bethe. In EOT however, the regularly repeating structure enables much higher transmission efficiency to occur, up to several orders of magnitude greater than that predicted by classical aperture theory. It was first described in 1998. This phenomenon that was fully analyzed with a microscopic scattering model is ''partly'' attributed to the presence of

surface plasmon Surface plasmons (SPs) are coherent delocalized electron oscillations that exist at the interface between any two materials where the real part of the dielectric function changes sign across the interface (e.g. a metal-dielectric interface, such ...

resonances and

constructive interference In physics, interference is a phenomenon in which two waves combine by adding their displacement together at every single point in space and time, to form a resultant wave of greater, lower, or the same amplitude. Constructive and destructiv ...

. A surface plasmon (SP) is a collective excitation of the electrons at the junction between a conductor and an insulator and is one of a series of interactions between light and a metal surface called

Plasmonics Plasmonics or nanoplasmonics refers to the generation, detection, and manipulation of signals at optical frequencies along metal-dielectric interfaces in the nanometer scale. Inspired by photonics, plasmonics follows the trend of miniaturizing opt ...

. Currently, there is experimental evidence of EOT out of the optical range. Analytical approaches also predict EOT on perforated plates with a perfect conductor model. Holes can somewhat emulate

plasmons In physics, a plasmon is a quantum of plasma oscillation. Just as light (an optical oscillation) consists of photons, the plasma oscillation consists of plasmons. The plasmon can be considered as a quasiparticle since it arises from the quantiz ...

at other regions of the

electromagnetic spectrum The electromagnetic spectrum is the range of frequencies (the spectrum) of electromagnetic radiation and their respective wavelengths and photon energies. The electromagnetic spectrum covers electromagnetic waves with frequencies ranging fro ...

where they do not exist. Then, the plasmonic contribution is a very particular peculiarity of the EOT resonance and should not be taken as the main contribution to the phenomenon. More recent work has shown a strong contribution from overlapping evanescent wave coupling, which explains why

surface plasmon resonance Surface plasmon resonance (SPR) is the resonant oscillation of conduction electrons at the interface between negative and positive permittivity material in a particle stimulated by incident light. SPR is the basis of many standard tools for measu ...

enhances the EOT effect on both sides of a metallic film at optical frequencies, but accounts for the terahertz-range transmission. Simple analytical explanations of this phenomenon have been elaborated, emphasizing the similarity between arrays of particles and arrays of holes, and establishing that the phenomenon is dominated by

diffraction Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

Applications

EOT is expected to play an important role in the creation of components of efficient photonic integrated circuits (PICs). Photonic integrated circuits are analogous to electronic circuits but based upon photons instead of electrons. One of the most ground-breaking results linked to EOT is the possibility to implement a Left-Handed

Metamaterial A metamaterial (from the Greek word μετά ''meta'', meaning "beyond" or "after", and the Latin word ''materia'', meaning "matter" or "material") is any material engineered to have a property that is not found in naturally occurring materials. ...

(LHM) by simply stacking hole arrays. EOT-based chemical and biological sensing (for example, improving ELISA based antibody detection) is another major area of research. Much like in a traditional

sensor, the EOT efficiency varies with the wavelength of the incident light, and the value of the in-plane wavevector component. This can be exploited as a means of transducing chemical binding events by measuring a change in the local

dielectric constant The relative permittivity (in older texts, dielectric constant) is the permittivity of a material expressed as a ratio with the electric permittivity of a vacuum. A dielectric is an insulating material, and the dielectric constant of an insula ...

(due to binding of the target species) as a shift in the spectral location and/or intensity of the EOT peak. Variation of the hole geometry alters the spectral location of the EOT peak such that the chemical binding events can be optically detected at a desired wavelength. EOT-based sensing offers one key advantage over a Kretschmann-style SPR chemical sensor, that of being an inherently nanometer-micrometer scale device; it is therefore particularly amenable to miniaturization.

References

{{reflist, 2 Quantum optics Electromagnetism Plasmonics Metamaterials