This review provides a perspective on the recent developments in the transmission of light through subwavelength apertures in metal films. The main focus is on the phenomenon of extraordinary optical transmission in periodic hole arrays, discovered over a decade ago. It is shown that surface electromagnetic modes play a key role in the emergence of the resonant transmission. These modes are also shown to be at the root of both the enhanced transmission and beaming of light found in single apertures surrounded by periodic corrugations. This review describes both the theoretical and experimental aspects of the subject. For clarity, the physical mechanisms operating in the different structures considered are analyzed within a common theoretical framework. Several applications based on the transmission properties of subwavelength apertures are also addressed.

http://digital.csic.es/bitstream/10261/47904/1/Light%20passing.pdf

Light passing through subwavelength apertures

This Colloquium analyzes the interaction of light with two-dimensional periodic arrays of particles and holes. The enhanced optical transmission observed in the latter and the presence of surface modes in patterned metal surfaces is thoroughly discussed. A review of the most significant discoveries in this area is presented first. A simple tutorial model is then formulated to capture the essential physics involved in these phenomena, while allowing analytical derivations that provide deeper insight. Comparison with more elaborated calculations is offered as well. Finally, hole arrays in plasmon-supporting metals are compared to perforated perfect conductors, thus assessing the role of plasmons in these types of structures through analytical considerations. The developments that have been made in nanophotonics areas related to plasmons in nanostructures, extraordinary optical transmission in hole arrays, complete resonant absorption and emission of light, and invisibility in structured metals are illustrated in this Colloquium in a comprehensive, tutorial fashion.

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Colloquium: Light scattering by particle and hole arrays

Have you ever felt that the very title, Progress in Optics, conjured an image in your mind? Don’t you see a row of handsomely printed books, bearing the editorial stamp of one of the most brilliant members of the optics community, and chronicling the field of optics since the invention of the laser? If so, you are certain to move the bookend to make room for Volume 16, the latest of this series. It contains seven chapters on widely diverging topics, written by well-known authorities in their fields. These are: 1) Laser Selective Photophysics and Photochemistry by V. S. Letokhov, 2) Recent Advances in Phase Profiles (sic) Generation by J. J. Clair and C. I. Abitbol, 3 ) Computer-Generated Holograms: Techniques and Applications by W.-H. Lee, 4) Speckle Interferometry by A. E. Ennos, 5 ) Deformation  Invariant, Space-Variant Optical  Pattern Recognition by D. Casasent and D. Psaltis, 6) Light Emission from High-Current Surface-Spark Discharges by R. E. Beverly, and 7) Semiclassical Radiation  Theory within a  QuantumMechanical Framework by I. R. Senitzkt. The  breadth of topic  matter  spanned  by  these  chapters makes it impossible, for this reviewer at least, to pass judgement on the comprehensiveness, relevance, and completeness of every chapter. With an editorial board as prominent as that of Progress in Optics, however, it seems hardly likely that such comments should be necessary. It should certainly be possible to take the authority of each author as credible. The only remaining judgment to be  made on these chapters is their readability. In short, what are they like to read? The first sentence of the first chapter greets the eye with an obvious typographical error: “The creation of coherent laser light source, that have tunable radiation, opened the . . . .” Two pages later we find: “When two types of atoms or molecules of different isotopic composition ( A and B ) have even one spectral line that does not overlap with others, it is pos-

Progress in optics

Optical coatings usually consist of many multilayers of thin films to achieve the desired properties A new approach using interference effects between an absorbing dielectric film and a metallic substrate now enables ultrathin optical coatings that could also find applications as thin solar cells or photodetectors

Nanometre optical coatings based on strong interference effects in highly absorbing media

BACKGROUND Future high-performance portable and wearable optical devices and systems with small footprints and low weights will require components with small form factors and enhanced functionality. Planar components based on diffractive optics (e.g., gratings, Fresnel lenses) and thin-film optics (e.g., dielectric filters, Bragg reflectors) have been around for decades; however, their limited functionality and difficulty of integration have been key incentives to search for better alternatives. Owing to its potential for vertical integration and marked design flexibility, metasurface-based flat optics provides a rare opportunity to overcome these challenges. The building blocks (BBs) of metasurfaces are subwavelength-spaced scatterers. By suitably adjusting their shape, size, position, and orientation with high spatial resolution, one can control the basic properties of light (phase, amplitude, polarization) and thus engineer its wavefront at will. This possibility greatly expands the frontiers of optical design by enabling multifunctional components with attendant reduction of thickness, size, and complexity. ADVANCES Recent progress in fabrication techniques and in the theory and design of metasurfaces holds promise for this new optical platform (metaoptics) to replace or complement conventional components in many applications. One major advance has been the migration to all-dielectric metasurfaces. Here, we discuss the key advantages of using dielectric phase-shifting elements with low optical loss and strong light confinement in the visible and near-infrared regions as BBs of flat lenses (metalenses). High–numerical aperture metalenses that are free of spherical aberrations have been implemented to achieve diffraction-limited focusing with subwavelength resolution, without requiring the complex shapes of aspherical lenses. Achromatic metalenses at discrete wavelengths and over a bandwidth have been realized by dispersion engineering of the phase shifters. By suitably adjusting the geometrical parameters of the latter, one can impart polarization- and wavelength-dependent phases to realize multifunctional metalenses with only one ultrathin layer. For example, polarization-sensitive flat lenses for chiral imaging and circular dichroism spectroscopy with high resolution have been realized, and off-axis metalenses with large engineered angular dispersion have been used to demonstrate miniature spectrometers. The fabrication of metalenses is straightforward and often requires one-step lithography, which can be based on high-throughput techniques such as deep-ultraviolet and nanoimprint lithography. OUTLOOK In the near future, the ability to fabricate metalenses and other metaoptical components with a planar process using the same lithographic tools for manufacturing integrated circuits (ICs) will have far-reaching implications. We envision that camera modules widely employed in cell phones, laptops, and myriad applications will become thinner and easier to optically align and package, with metalenses and the complementary metal-oxide semiconductor–compatible sensor manufactured by the same foundries. The unprecedented design freedom of metalenses and other metasurface optical components will greatly expand the range of applications of micro-optics and integrated optics. We foresee a rapidly increasing density of nanoscale optical elements on metasurface-based chips, with attendant marked increases in performance and number of functionalities. Such digital optics will probably follow a Moore-like law, similar to that governing the scaling of ICs, leading to a wide range of high-volume applications.

http://science.sciencemag.org/content/sci/358/6367/eaam8100.full.pdf

Metalenses: Versatile multifunctional photonic components

Nanofabrication by electron beam lithography and its applications

We demonstrate a conceptually new mechanism for focusing at optical frequencies based upon the use of nano-hole quasi-periodic arrays in metal screens. Using coherent illumination at 660nm and scanning near-field optical microscopy, ~ 290nm "hot spots", were observed at a distance of ~ 12:5µm from the array. Even smaller hot-spots of about 200nm in waist were observed closer to the plane of the array.

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Focusing of light by a nanohole array

The bright and iridescent blue color from Morpho butterfly wings has attracted worldwide attentions to explore its mysterious nature for long time. Although the physics of structural color by the nanophotonic structures built on the wing scales has been well established, replications of the wing structure by standard top-down lithography still remains a challenge. This paper reports a technical breakthrough to mimic the blue color of Morpho butterfly wings, by developing a novel nanofabrication process, based on electron beam lithography combined with alternate PMMA/LOR development/dissolution, for photonic structures with aligned lamellae multilayers in colorless polymers. The relationship between the coloration and geometric dimensions as well as shapes is systematically analyzed by solving Maxwell's Equations with a finite domain time difference simulator. Careful characterization of the mimicked blue by spectral measurements under both normal and oblique angles are carried out. Structural color in blue reflected by the fabricated wing scales, is demonstrated and further extended to green as an application exercise of the new technique. The effects of the regularity in the replicas on coloration are analyzed. In principle, this approach establishes a starting point for mimicking structural colors beyond the blue in Morpho butterfly wings.

/pdf/nanofabrication-and-coloration-study-of-artificial-morpho-36e4ie5lwp.pdf

Nanofabrication and coloration study of artificial Morpho butterfly wings with aligned lamellae layers.

The fabrication of indented ('intaglio') or raised ('bas-relief') sub-wavelength metamaterial patterns on a metal surface provides a mechanism for changing and controlling the colour of the metal without employing any form of chemical surface modification, thin-film coating or diffraction effects. We show that a broad range of colours can be achieved by varying the structural parameters of metamaterial designs to tune absorption resonances. This novel approach to the 'structural colouring' of pure metals offers great versatility and scalability for both aesthetic (e.g. jewellery design) and functional (e.g. sensors, optical modulators) applications. We focus here on visible colour but the concept can equally be applied to the engineering of metallic spectral response in other electromagnetic domains.

Controlling the Colour of Metals: Intaglio and Bas-Relief Metamaterials

We present transmissive plasmonic structural colors from subwavelength nanohole arrays with bottom metal disks for scaled-up manufacturing by nanoimprint lithography (NIL). Comprehensive theoretical and experimental studies are carried out to understand the specific extraordinary optical transmission behavior of the structures with such bottom metal disks. Distinctive colors covering the entire visible spectrum can be generated by changing the structural dimensions of hole arrays in Ag covered by the metal disks. The plasmonic energy hybridization theory is applied to explain the unstable color output with shallow holes so that a large processing window during NIL could be achieved for mass production. A high-resolution of 127,000 dots per inch is demonstrated with potential applications, including color filters and displays, high-resolution color printing, CMOS color imaging, and anti-counterfeiting.

Yifang Chen

Papers

Nanofabrication by electron beam lithography and its applications

Focusing of light by a nanohole array

Nanofabrication and coloration study of artificial Morpho butterfly wings with aligned lamellae layers.

Controlling the Colour of Metals: Intaglio and Bas-Relief Metamaterials

High-resolution plasmonic structural colors from nanohole arrays with bottom metal disks.