The world's fastest nanoscale photonics switch

International team of researchers from Lomonosov Moscow State University and the Australian National University in Canberra created an ultrafast all-optical switch on silicon nanostructures.

This device may become a platform for future computers and permit to transfer data at an ultrahigh speed. The article with the description of the device was published in Nano Letters journal and highlighted in Nature Materials.

This work belongs to the field of photonics - an optics discipline which appeared in the 1960-s, simultaneously with the invention of lasers. Photonics has the same goals as electronics does, but uses photons--the quanta of light--instead of electrons. The biggest advantage of using photons is the absence of interactions between them. As a consequence, photons address the data transmission problem better than electrons. This property can primarily be used for in computing where IPS (instructions per second) is the main attribute to be maximized. The typical scale of eletronic transistors--the basis of contemporary electronic devices--is less than 100 nanometers, wheres the typical scale of photonic transistors stays on the scale of several micrometers.

Nanostructures that are able to compete with the electronic structures--for example, plasmonic nanoparticles--are characterized by low efficiency and significant losses. Therefore, coming up with a compact photonic switch was a very challenging task.

Three years ago several groups of researchers simultaneously discovered an important effect: they found out that silicon nanoparticles are exhibit strong resonances in the visible spectrum - the so-called magnetic dipole resonances. This type of resonance is characterized by strong localization of light waves on subwavelength scales, inside the nanoparticles. This effect turned out to be interesting to researches, but, according to Maxim Shcherbakov, the first author of the article published in Nano Letters, nobody thought that this discovery could create a basis for development of a compact and very rapid photonic switch.

Nanoparticles were fabricated in the Australian National University by e-beam lithography followed by plasma-phase etching. It was done by Alexander Shorokhov, who served an internship in the University as a part of Presidential scholarship for studying abroad. The samples were brought to Moscow, and all the experimental work was carried out at the Faculty of Physics of Lomonosov Moscow State University, in the Laboratory of Nanophotonics and Metamaterials.

"In our experimental research me and my colleague Polina Vabishchevich from the Faculty used a set of nonlinear optics methods that address femtosecond light-matter, -- explains Maxim Shcherbakov. -- We used our femtosecond laser complex acquired as part of the MSU development program".

Eventually, researches developed a "device": a disc 250 nm in diameter that is capable of switching optical pulses at femtosecond rates (femtosecond is a one millionth of one billionth of a second). Switching speeds that fast will allow to create data transmission and processing devices that will work at tens and hundreds terabits per second. This can make possible downloading thousands of HD-movies in less than a second.

The operation of the all-optical switch created by MSU researchers is based on the interaction between two femtosecond pulses. The interaction becomes possible due to the magnetic resonance of the silicon nanostructures. If the pulses arrive at the nanostructure simultaneously, one of them interacts with the other and dampers it due to the effect of two-photon absorption. If there is a 100-fs delay between the two pulses, the interaction does not occur, and the second pulse goes through the nanostructure without changing.

"We were able to develop a structure with the undesirable free-carrier effects are suppressed, -- says Maxim Shcherbakov. -- Free carriers (electrons and electron holes) place serious restrictions on the speed of signal conversion in the traditional integrated photonics. Our work represents an important step towards novel and efficient active photonic devices-- transistors, logic units, and others. Features of the technology implemented in our work will allow its use in silicon photonics. In the nearest future, we are going to test such nanoparticles in integrated circuits".

http://www.nanotechnologyworld.org/#!The-worlds-fastest-nanoscale-photonics-switch/c89r/565dba120cf2c000e929c875 

Lomonosov Moscow State University

Tracking slow nanolight in natural hyperbolic metamaterial slabs

Tracking slow nanolight in natural hyperbolic metamaterial slabs

Researchers at CIC nanoGUNE (Basque Country) in collaboration with colleagues at ICFO - The Institute of Photonic Sciences (Catalunya) have imaged how light moves inside an exotic class of matter known as hyperbolic materials. They observed, for the first time, ultraslow pulse propagation and backward propagating waves in deep subwavelength-scale thick slabs of boron nitride - a natural hyperbolic material for infrared light. This work has been funded by the EC Graphene Flagship and was recently reported in Nature Photonics.

Hyperbolic materials are very special because they behave like a metal in one direction, but like an insulator in the other. Until now, these materials have been used to fabricate complex nanostructures that permit subwavelength-scale imaging, as well as the focusing and controlling of light at the nanoscale. However, in order to fully exploit their potential, it is necessary to study and understand how light behaves inside them.

The work lays the foundations for studying the precise manner in which light travels through complex optical systems at the subwavelength scale in extremely high levels of detail. Such a capability will be vital for verifying that future nanophotonic devices, perhaps with biosensing or optical computing applications, are functioning as expected.

“The difficulty in performing the reported experiments is the extremely short wavelength of light when it is inside a hyperbolic material” explains Ikerbasque Professor Rainer Hillenbrand, leader of the nanooptics group at nanoGUNE. When light moves inside the material - in our case mid-infrared light in a 135 nm boron nitride slab - it travels in the form of what we call a polariton, where the light is actually coupled to the vibrations of the matter itself".

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Magnetic wormhole created for first time

Scientists in the Department of Physics at the Universitat Autònoma de Barcelona have designed and created in the laboratory the first experimental wormhole that can connect two regions of space magnetically. The device could have applications in medicine, opening up ways to make MRIs more comfortable for patients.

"Wormholes" are cosmic tunnels that can connect two distant regions of the universe, and have been popularised by the dissemination of theoretical physics and by works of science fiction like Stargate, Star Trek or, more recently, Interstellar. Using present-day technology it would be impossible to create a gravitational wormhole, as the field would have to be manipulated with huge amounts of gravitational energy, which no-one yet knows how to generate. In electromagnetism, however, advances in metamaterials and invisibility have allowed researchers to put forward several designs to achieve this.

Scientists in the Department of Physics at the Universitat Autònoma de Barcelona have designed and created in the laboratory the first experimental wormhole that can connect two regions of space magnetically. This consists of a tunnel that transfers the magnetic field from one point to the other while keeping it undetectable – invisible – all the way.

The researchers used metamaterials and metasurfaces to build the tunnel experimentally, so that the magnetic field from a source, such as a magnet or a an electromagnet, appears at the other end of the wormhole as an isolated magnetic monopole. This result is strange enough in itself, as magnetic monopoles – magnets with only one pole, whether north or south – do not exist in nature. The overall effect is that of a magnetic field that appears to travel from one point to another through a dimension that lies outside the conventional three dimensions.

The wormhole in this experiment is a sphere made of different layers: an external layer with a ferromagnetic surface, a second inner layer, made of superconducting material, and a ferromagnetic sheet rolled into a cylinder that crosses the sphere from one end to the other. The sphere is made in such a way as to be magnetically undetectable – invisible, in magnetic field terms – from the exterior.

The magnetic wormhole is an analogy of gravitational ones, as it "changes the topology of space, as if the inner region has been magnetically erased from space", explains Àlvar Sánchez, the lead researcher.

These same researchers had already built a magnetic fibre in 2014: a device capable of transporting the magnetic field from one end to the other. This fibre was, however, detectable magnetically. The wormhole developed now, though, is a completely three-dimensional device that is undetectable by any magnetic field.

This means a step forward towards possible applications in which magnetic fields are used: in medicine for example. This technology could, for example, increase patients' comfort by distancing them from the detectors when having MRI scans in hospital, or allow MRI images of different parts of the body to be obtained simultaneously.

Nanotechnology World Association

First phononic crystal that can be altered in real time

Author’s impression of an acoustic micro-cloak made
of an array of spherical particlesImage courtesy of Mihai Caleap,
University of Bristol, copyright © 2014

Using an acoustic metadevice that can influence the acoustic space and can control any of the ways in which waves travel, engineers have demonstrated, for the first time, that it is possible to dynamically alter the geometry of a three-dimensional colloidal crystal in real time.

The colloidal crystals designed in the study, called metamaterials, are artificially structured materials that extend the properties of existing naturally occurring materials and compounds. The research by academics from the University of Bristol’s Department of Mechanical Engineering is published online this week in PNAS (Proceedings of the National Academy of Sciences).

Dr Mihai Caleap, Research Associate in the Department of Mechanical Engineering, said: “We have been working on systems that are reconfigurable in real time with a view to creating genuinely active metamaterials.

“Such materials will allow researchers to gain unprecedented control over a range of optical and acoustic wave phenomena. To date, whilst numerous examples of metamaterials now exist, none are reconfigurable in three-dimensions.”

The researchers used acoustic assembly to trap a suspension of microspheres in patterns resembling crystal lattices. The study showed the experimental realisation of a three-dimensional colloidal crystal that is reconfigurable in real time and that has the ability to rapidly alter its acoustic filtering characteristics.

Dynamically reconfigurable metamaterials based devices with optical or acoustic wavelengths from ten microns to ten cm could have a wide range of applications. In optics it could lead to new beam deflectors or filters for terahertz imaging and in acoustics it might be possible to create acoustic barriers that can be optimised depending on the changing nature of the incident sound. Further applications in reconfigurable cloaks and lenses are also now conceivable.

Bruce Drinkwater, Professor of Ultrasonics in the Department of Mechanical Engineering and co-author, said: “Our reconfigurable acoustic assembly method is an important step as it has clear advantages over other possible approaches, for example optical trapping and self-assembly.

“In particular, acoustic assembly is scalable with wavelength from microns to metres. The method will work on a vast range of materials, such as nearly all solid-fluid combinations, it will also enable almost any geometry to be assembled and it is cheap and easy to integrate with other systems.”

Paper: Acoustically trapped colloidal crystals that are reconfigurable in real-time, Mihai Caleap and Bruce Drinkwater, PNAS, online early edition the week of March 31, 2014.

Source: http://www.bristol.ac.uk/news/2014/march/colloidal-crystal.html

How to Make a Better Invisibility Cloak—With Lasers

Images: Clockwise from top left: Karlsruhe Institute of Technology; Karlsruhe Institute of Technology/ Nature Materials; Karlsruhe Institute of Technology; Karlsruhe Institute of Technology/Applied Physics Letters

Made From Scratch: Lasers were used to draw the micrometer-scale structures in these metamaterials. Pictured clockwise from top left are a bichiral photonic crystal [top view], a photonic quasicrystal, a bichiral photonic crystal [oblique view], and a pentamode metamaterial.

Direct laser writing creates metamaterial structures small enough to manipulate visible light

For a century or more, nearly all technological advances have depended on our ability to produce and manipulate the vast variety of materials that nature has given us. Nowhere is that dependence more evident than in the field of electronics. From a smorgasbord of semiconductors, polymers, and metals, we’ve been able to create a dazzling array of circuitry that now underpins pretty much every aspect of modern life.

So now imagine what we could do if we weren’t limited to the materials found in nature. Researchers have long believed that it would someday be possible to produce artificial materials, or “metamaterials,” and that they would bring about some stunning, otherworldly technologies—the sort that have figured in science fiction tales for years. These innovations include invisibility cloaks that could mask the presence of objects or their electromagnetic signatures, “unfeelability cloaks” that could mechanically mask the tactile feel of an object, superlenses that could resolve features too small to be seen with ordinary microscope lenses, and power absorbers that could capture essentially all of the sunlight hitting a solar cell.

To achieve these advances we’ll need better metamaterials, and those are on the way. Metamaterials are made up of “meta-atoms”—small two- or three-dimensional structures made of polymer, dielectric material, or metal. When these structures are arranged in regular, repeating crystals, they can be used to manipulate electromagnetic radiation in new ways. Ultimately, the capabilities of a metamaterial are determined by the size, shape, and quality of these structures. And the technology to fabricate meta-atoms has recently turned a corner.

Over the past few years, research groups around the world have succeeded in developing a way to draw meta-atoms using lasers. The resulting structures can now take on nearly any shape and be stacked in three dimensions in dense, crystal-like arrangements. What’s more, they can be made small enough to exhibit unique mechanical and thermal properties and to alter the flow of light in a range of wavelengths—including the long-inaccessible visible chunk of the spectrum. Thanks to this microscopic fabrication technology, we can finally see a path beyond the materials nature has provided us into entirely new realms that are limited only by our imaginations.

Source: http://spectrum.ieee.org/semiconductors/materials/how-to-make-a-better-invisibility-cloakwith-lasers