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Scooped by Dr. Stefan Gruenwald!

Rayleigh scattering reveals light propagation in optical nanofibers

Rayleigh scattering reveals light propagation in optical nanofibers | Amazing Science |

Optical fibers are hair-like threads of glass used to guide light. Fibers of exceptional purity have proved an excellent way of sending information over long distances and are the foundation of modern telecommunication systems. Transmission relies on what's called total internal reflection, wherein the light propagates by effectively bouncing back and forth off of the fiber's internal surface. Though the word "total" implies light remains entirely trapped in the fiber, the laws of physics dictate that some of the light, in the form of what's called an evanescent field, also exists outside of the fiber. In telecommunications, the fiber core is more than ten times larger than the wavelength of light passing through. In this case, the evanescent fields are weak and vanish rapidly away from the fiber. Nanofibers have a diameter smaller than the wavelength of the guided light. Here, all of the light field cannot fit inside of the nanofiber, yielding a significant enhancement in the evanescent fields outside of the core. This allows the light to trap atoms (or other particles) near the surface of a nanofiber.

JQI researchers in collaboration with scientists from the Naval Research Laboratory have developed a new technique for visualizing light propagation through an optical nanofiber, detailed in a recent Optica paper. The result is a non-invasive measurement of the fiber size and shape and a real-time view of how light fields evolve along the nanofiber. Direct measurement of the fields in and around an optical nanofiber offers insight into how light propagates in these systems and paves the way for engineering customized evanescent atom traps.

In this work, researchers use a sensitive camera to collect light from what's known as Rayleigh scattering, demonstrating the first in-situ measurements of light moving through an optical nanofiber. Rayleigh scattering happens when light bounces, or scatters, off of particles much smaller than the wavelength of the light. In fibers, these particles can be impurities or density fluctuations in the glass, and the light scattered from them is ejected from the fiber. This allows one to view the propagating light from the side, in much the same way as one can see a beam of sunlight through fog. Importantly, the amount of light ejected depends on the polarization, or the orientation of oscillation of the light, and intensity of the field at each point, which means that capturing this light is a way to view the field.

The researchers here are interested in understanding the propagation of the field when the light waves are comprised from what are known as higher-order modes. Instead of having a uniform spatial profile, like that of a laser pointer, these modes can look like a doughnut, cloverleaf, or another more complicated pattern. Higher-order modes offer some advantages over the lowest order or "fundamental" mode. Due to their complexity, the evanescent field can have comparatively more light intensity in the region of interest—locally just outside the fiber. These higher order modes can also be used to make different types of optical patterns. Nanofibers aren't yet standardized and thus careful and complete characterization of both the fiber and the light passing through them is a necessary step towards making them a more practical and adaptable tool for research applications.

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Optical fibers made out of chalcogenide glass demonstrate brain-like computing is possible

Optical fibers made out of chalcogenide glass demonstrate brain-like computing is possible | Amazing Science |

UK and Singapore researchers have simulated neural networks and synapses in the brain using optical pulses as information carriers over fibers made from light-sensitive chalcogenide glass. The research, published in Advanced Optical Materials, has the potential to allow faster and smarter optical neuromorphic (brain-like) computers capable of learning, the researchers say.

Compared to biological systems, today’s computers are “up to a billion times less efficient — simulating 5 seconds of brain activity takes 500 seconds and needs 1.4 MW of power,” they note. The researchers, from the Optoelectronics Research Centre (ORC) at the University of Southampton, UK, and Centre for Disruptive Photonic Technologies (CDPT) at Nanyang Technological University (NTU), Singapore, developed a proof-of-concept system that demonstrated optical equivalents of brain functions. These include holding a neural resting state and simulating the changes in electrical activity in a nerve cell as it is stimulated.

The changing properties of the glass act as the varying electrical activity in a nerve cell, and light provides the stimulus to change these properties. This enables switching a light signal, the equivalent to a nerve cell firing.

The research paves the way for scalable brain-like computing systems that enable “photonic neurons” with ultrafast signal transmission speeds, higher bandwidth, and lower power consumption than their biological and electronic counterparts, including “non-Boolean computing and decision-making paradigms that mimic brain functionalities,” the researchers say.

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World record in color: Photonic crystal fiber generates light from the ultraviolet to the mid-infrared region

World record in color: Photonic crystal fiber generates light from the ultraviolet to the mid-infrared region | Amazing Science |

The light generated by researchers from the Max Planck Institute for the Science of Light in Erlangen is more colorful than a rainbow. The scientists couple a low-energy, infrared laser pulse into a photonic crystal fibre (PCF) which is tailor-made so that the spectrum of the pulse broadens significantly to become white light: the generated spectrum spans from the deep-ultraviolet region to the mid-infrared region – a world record at such low input energy. The researchers from MPL in Erlangen are the first to produce microstructured glass fibers from a material that is particularly resistant to ultraviolet light, unlike conventional quartz glass. This material (ZBLAN) is actually extremely difficult to draw fibers from, and up until now it was regarded as impossible to draw photonic crystal fibers from it. In such fibers, a 2D periodic structure of hollow channels surrounds the fibre core, and runs along the entire length the fibre. The light produced with the world-record spectrum, could facilitate many investigations in biomedical research, in physics and chemistry, or even make new ones possible in the first place.

Light is one of the most important scientific tools nowadays. If researchers want to study biochemical processes in cancer cells, for example, they irradiate the cell with light of different colours and search for ways to stop tumours with the aid of fluorescent proteins. Chemical reactions can be observed or even controlled with the aid of light. And nothing much happens in physics without light, as for example with spectroscopic methods it coaxes out of atoms, molecules and crystals a great deal of information about their structure and properties. A lamp with a very broad spectrum should therefore find many applications, especially if it can provide light source qualities (e.g. spatial coherence, high brightness…) similar as those presented by a team of researchers in Erlangen, headed by Philip Russell, Director at the Max Planck Institute for the Science of Light.

White light, which contains all wavelengths, i.e. colours of visible light, can be generated in many ways. However, in Russell’s team, scientists do it in a special way. They launch very short, infrared pulses with relatively low energy through a photonic crystal fibre, from which white light with record properties is generated: “What excites me most is the fact that our light covers such a large part of the ultraviolet range in the spectrum,” says Philip Russell. “There have not yet been comparable light sources, especially in this wavelength range.”

“In addition, the light generated from the PCF is very bright, and it retains more or less the same brightness over the whole spectrum,” says Russell. “This is particularly important for applications.” For example, biological/chemical scientists need light sources with a broad span of colours for many experiments. Normally they scan their experimental objects with different wavelengths. To do this, they filter the broadband light source with narrow bandwidth optical filters. The filtered light loses much of its brightness due to this process; in order to keep enough intensity, it is better to have a light source with reasonable brightness from the beginning.

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Laser may replace copper in computer chips for high-speed, low-energy data transmission

Laser may replace copper in computer chips for high-speed, low-energy data transmission | Amazing Science |

An international team of scientists has constructed the first germanium-tin* semiconductor laser for CMOS silicon chips. By replacing copper wires with optical transmission, the new device promises higher-speed data transmission on computer chips at a fraction of the energy.

The results by scientists from Forschungszentrum Jülich and the Paul Scherrer Institute in Switzerland in cooperation with international partners were published in the journal Nature Photonics.

Transferring data between multiple cores and between logic elements and memory cells is a key bottleneck in fast-developing computer technology. “Signal transmission via copper wires limits the development of larger and faster computers due to the thermal load and the limited bandwidth of copper wires,” explains Prof. Detlev Grützmacher, Director at the Forschungszentrum Jülich Peter Grünberg Institute. “The clock signal alone uses up to 30% of the energy, which can be saved through optical transmission.”

The more than 10% tin content is what enables the new germanium-tin semiconductor optical properties, according to the scientists. The laser is currently limited to low temperatures of up to minus 183 degrees Celsius in the test system. The next big step will be generating laser light with electricity, and without the need for cooling, if possible. The aim is to create an electrically pumped laser that functions at room temperature.

*The basis of chip manufacturing is silicon, an element of main group IV of the periodic table. Typical semiconductor lasers for telecommunication systems, made of gallium arsenide for example, however, are costly and consist of elements from main groups III or V. This has profound consequences on the crystal properties. Such laser components cannot therefore be applied directly onto silicon. They have to be produced externally at great effort and subsequently glued to the silicon wafer. However, the lifetime of this kind of component is greatly reduced due to the fact that the thermal expansion coefficients of these elements are significantly different from that of silicon. In contrast, semiconductors of main group IV — to which both silicon and germanium belong — can be integrated into the manufacturing process without any major difficulties. Neither element by itself is very efficient as a light source, however. They are classed among the indirect semiconductors. In contrast to direct semiconductors, they emit mostly heat and only a little light when excited.

The scientists at Jülich’s Peter Grünberg Institute have now for the first time succeeded in creating a “real” direct main group IV semiconductor laser by combining germanium and tin, which is also classed in main group IV.

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Physicists Create “Air Laser” In Laboratory

Physicists Create “Air Laser” In Laboratory | Amazing Science |

Laser light is generated by pumping energy into atoms or other objects. A chain reaction can occur in which energized atoms all stimulate each other to give off laser light. One way laser light differs from normal light is that all the light waves in a laser beam are the same frequency — that is, color. Another difference is that all the light waves in a laser beam are coherent — the peaks and troughs of these light waves overlap exactly. These properties help laser beams focus on tight spots and stay narrow for long distances. The material that gets stimulated to generate laser light can be exotic in nature, such as ruby or sapphire. However, in principle, even air can serve as a laser — a normal laser fired into the atmosphere, dubbed a pump laser, could potentially stimulate air it passed through enough to make that very air act like a laser in return.

However, despite years of research, scientists had not discovered a way to generate air lasers intense enough for practical use. Previous attempts mostly tried using pump lasers to excite air enough to generate filaments of plasma — electrically charged gases — that in turn would serve as lasers. However, these air lasers are rather weak, requiring highly sensitive detectors to spot their light. "Remote air lasing has been discussed for at least 10 years," said physicist Günter Steinmeyer at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy in Berlin, who did not take part in this research. “Several people claimed to have demonstrated it before, but these demonstrations were never fully convincing.” Now Polynkin and his colleagues have developed a new technique that could allow practical air lasers. This strategy is up to 200 times more efficient than previous methods when it comes to creating air lasers from atmospheric components such as nitrogen.

The new strategy involves two lasers of different colors. First, an infrared laser pulse breaks apart the nitrogen and oxygen molecules in the air into their constituent atoms. Next, an ultraviolet laser pulse can excite either the nitrogen or oxygen atoms, depending on which frequency of ultraviolet light is chosen, making the atoms give off near-infrared light like a laser. "The air laser is in the form of a single beam which traces the path of the original laser, but goes backwards, towards the observer," Polynkin said

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Study Unveils New Half-Light Half-Matter Quantum Particles

Study Unveils New Half-Light Half-Matter Quantum Particles | Amazing Science |

Prospects of developing computing and communication technologies based on quantum properties of light and matter may have taken a major step forward thanks to research by City College of New York physicists led by Dr. Vinod Menon.

In a pioneering study, Professor Menon and his team were able to discover half-light, half-matter particles in atomically thin semiconductors (thickness ~ a millionth of a single sheet of paper) consisting of two-dimensional (2D) layer of molybdenum and sulfur atoms arranged similar to graphene. They sandwiched this 2D material in a light trapping structure to realize these composite quantum particles.

“Besides being a fundamental breakthrough, this opens up the possibility of making devices which take the benefits of both light and matter,” said Professor Menon.  

For example one can start envisioning logic gates and signal processors that take on best of light and matter. The discovery is also expected to contribute to developing practical platforms for quantum computing. 

Dr. Dirk Englund, a professor at MIT whose research focuses on quantum technologies based on semiconductor and optical systems, hailed the City College study.

“What is so remarkable and exciting in the work by Vinod and his team is how readily this strong coupling regime could actually be achieved. They have shown convincingly that by coupling a rather standard dielectric cavity to exciton–polaritons in a monolayer of molybdenum disulphide, they could actually reach this strong coupling regime with a very large binding strength,” he said. 

Professor Menon’s research team included City College PhD students, Xiaoze Liu, Tal Galfsky and Zheng Sun, and scientists from Yale University, National Tsing Hua University (Taiwan) and Ecole Polytechnic -Montreal (Canada).

The study appears in the January issue of the journal “Nature Photonics.” It was funded by the U.S. Army Research Laboratory's Army Research Office and the National Science Foundation through the Materials Research Science and Engineering Center – Center for Photonic and Multiscale Nanomaterials. 

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Spiral laser beam used to create a whirlpool of hybrid light-matter particles called polaritons

Spiral laser beam used to create a whirlpool of hybrid light-matter particles called polaritons | Amazing Science |

Physicists at Australian National University have engineered a spiral laser beam and used it to create a whirlpool of hybrid light-matter particles called polaritons.  "Creating circulating currents of polaritons – vortices – and controlling them has been a long-standing challenge," said leader of the team, theoretician Dr Elena Ostrovskaya, from the Research School of Physics and Engineering. "We can now create a circulating flow of these hybrid particles and sustain it for hours."

Polaritons are hybrid particles that have properties of both matter and light. The ability to control polariton flows in this way could aid the development of completely novel technology to link conventional electronics with new laser and fibre-based technologies.

Polaritons form in semiconductors when laser light interacts with electrons and holes (positively charged vacancies) so strongly that it is no longer possible to distinguish light from matter.

The team created the spiral beam by putting their laser through a piece of brass with a spiral pattern of holes in it. This was directed into a semiconductor microcavity, a tiny wafer of aluminium gallium arsenide, a material used in LEDs, sandwiched between two reflectors. "The vortices have previously only appeared randomly, and always in pairs that swirl in opposite directions," said Dr Robert Dall, who led the experimental part of the project. "However, by using a spiral mask to structure our laser, we create a chiral system that prefers one flow direction. Therefore we can create a single, stable vortex at will."

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Turning loss into gain: Cutting power could dramatically boost laser output

Turning loss into gain: Cutting power could dramatically boost laser output | Amazing Science |
Lasers – devices that deliver beams of highly organized light – are so deeply integrated into modern technology that their basic operations would seem well understood. CD players, medical diagnostics and military surveillance all depend on lasers.

Re-examining longstanding beliefs about the physics of these devices, Princeton engineers have now shown that carefully restricting the delivery of power to certain areas within a laser could boost its output by many orders of magnitude. The finding, published Oct. 26 in the journal Nature Photonics, could allow far more sensitive and energy-efficient lasers, as well as potentially more control over the frequencies and spatial pattern of light emission.

"It's as though you are using loss to your advantage," said graduate student Omer Malik, an author of the study along with Li Ge, now an assistant professor at the City University of New York, and Hakan Tureci, assistant professor of electrical engineering at Princeton. The researchers said that restricting the delivery of power causes much of the physical space within a laser to absorb rather than produce light. In exchange, however, the optimally efficient portion of the laser is freed from competition with less efficient portions and shines forth far more brightly than previous estimates had suggested.

The results, based on mathematical calculations and computer simulations, still need to be verified in experiments with actual lasers, but the researchers said it represents a new understanding of the fundamental processes that govern how lasers produce light.

"Distributing gain and loss within the material is a higher level of design – a new tool – that had not been used very systematically until now," Tureci said.

The heart of a laser is a material that emits light when energy is supplied to it. When a low level of energy is added, the light is "incoherent," essentially meaning that it contains a mix of wavelengths (or colors). As more energy is added, the material suddenly reaches a "lasing" threshold when it emits coherent light of a particular wavelength.

The entire surface of the material does not emit laser light; rather, if the material is arranged as a disc, for example, the light might come from a ring close to the edge. As even more energy is added, more patterns emerge – for example a ring closer to the center might reach the laser threshold. These patterns – called modes – begin to interact and sap energy from each other. Because of this competition, subsequent modes requiring higher energy may never reach their lasing thresholds. However, Tureci's research group found that some of these higher threshold modes were potentially far more efficient than the earlier ones if they could just be allowed to function without competition.

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Beyond LEDs: Brighter, new energy-saving flat panel lights based on carbon nanotubes

Beyond LEDs: Brighter, new energy-saving flat panel lights based on carbon nanotubes | Amazing Science |
Even as the 2014 Nobel Prize in Physics has enshrined light emitting diodes (LEDs) as the single most significant and disruptive energy-efficient lighting solution of today, scientists around the world continue unabated to search for the even-better-bulbs of tomorrow.

Enter carbon electronics. Electronics based on carbon, especially carbon nanotubes (CNTs), are emerging as successors to silicon for making semiconductor materials. And they may enable a new generation of brighter, low-power, low-cost lighting devices that could challenge the dominance of light-emitting diodes (LEDs) in the future and help meet society's ever-escalating demand for greener bulbs.

Scientists from Tohoku University in Japan have developed a new type of energy-efficient flat light source based on carbon nanotubes with very low power consumption of around 0.1 Watt for every hour's operation—about a hundred times lower than that of an LED.

In the journal Review of Scientific Instruments, from AIP publishing, the researchers detail the fabrication and optimization of the device, which is based on a phosphor screen and single-walled carbon nanotubes as electrodes in a diode structure. You can think of it as a field of tungsten filaments shrunk to microscopic proportions.

They assembled the device from a mixture liquid containing highly crystalline single-walled carbon nanotubes dispersed in an organic solvent mixed with a soap-like chemical known as a surfactant. Then, they "painted" the mixture onto the positive electrode or cathode, and scratched the surface with sandpaper to form a light panel capable of producing a large, stable and homogenous emission current with low energy consumption.

"Our simple 'diode' panel could obtain high brightness efficiency of 60 Lumen per Watt, which holds excellent potential for a lighting device with low power consumption," said Norihiro Shimoi, the lead researcher and an associate professor of environmental studies at the Tohoku University.

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Superabsorbing ring could make light work of snaps, be the ultimate camera pixel

Superabsorbing ring could make light work of snaps, be the ultimate camera pixel | Amazing Science |
A quantum effect in which excited atoms team up to emit an enhanced pulse of light can be turned on its head to create 'superabsorbing' systems that could make the 'ultimate camera pixel'.

'Superradiance', a phenomenon where a group of atoms charged up with energy act collectively to release a far more intense pulse of light than they would individually, is well-known to physicists. In theory the effect can be reversed to create a device that draws in light ultra-efficiently. This could be revolutionary for devices ranging from digital cameras to solar cells. But there's a problem: the advantage of this quantum effect is strongest when the atoms are already 50% charged -- and then the system would rather release its energy back as light than absorb more.

Now a team led by Oxford University theorists believes it has found the solution to this seemingly fundamental problem. Part of the answer came from biology. 'I was inspired to study ring molecules, because they are what plants use in photosynthesis to extract energy from the Sun,' said Kieran Higgins of Oxford University's Department of Materials, who led the work. 'What we then discovered is that we should be able to go beyond nature's achievement and create a 'quantum superabsorber'.'

A report of the research is published in Nature Communications.

At the core of the new design is a molecular ring, which is charged to 50% by a laser pulse in order to reach the ideal superabsorbing state. 'Now we need to keep it in that condition' notes Kieran. For this the team propose exploiting a key property of the ring structure: each time it absorbs a photon, it becomes receptive to photons of a slightly higher energy. Charging the device is like climbing a ladder whose rungs are increasingly widely spaced.

'Let's say it starts by absorbing red light from the laser,' said Kieran, 'once it is charged to 50% it now has an appetite for yellow photons, which are higher energy. And we'd like it to absorb new yellow photons, but NOT to emit the stored red photons.' This can be achieved by embedding the device into a special crystal that suppresses red light: it makes it harder for the ring to release its existing energy, so trapping it in the 50% charged state.

The final ingredient of the design is a molecular 'wire' that draws off the energy of newly absorbed photons. 'If you built a system with a capacity of 100 energy units the idea would be to 'half-charge' it to 50 units, and the wire would then 'harvest' every unit over 50,' said Kieran. 'It's like an overflow pipe in plumbing -- it is engineered to take the energy level down to 50, but no lower.' This means that the device can handle the absorption of many photons in quick succession when it is exposed to a bright source, but in the dark it will simply sit in the superabsorbing state and efficiently grab any rare passing photon.

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Physicists teleport the quantum state of a photon to a crystal over 25 kilometers of optical fiber

Physicists teleport the quantum state of a photon to a crystal over 25 kilometers of optical fiber | Amazing Science |

Physicists at the University of Geneva have succeeded in teleporting the quantum state of a photon to a crystal over 25 kilometers of optical fiber. The experiment, carried out in the laboratory of Professor Nicolas Gisin, constitutes a first, and simply pulverises the previous record of 6 kilometres achieved ten years ago by the same UNIGE team. Passing from light into matter, using teleportation of a photon to a crystal, shows that, in quantum physics, it is not the composition of a particle which is important, but rather its state, since this can exist and persist outside such extreme differences as those which distinguish light from matter. The results obtained by Félix Bussières and his colleagues are reported in the latest edition of Nature Photonics.

Quantum physics, and with it the UNIGE, is again being talked about around the world with the Marcel Benoist Prize for 2014 being awarded to Professor Nicolas Gisin, and the publication of experiments in Nature Photonics. The latest experiments have enabled verifying that the quantum state of a photon can be maintained whilst transporting it into a crystal without the two coming directly into contact. One needs to imagine the crystal as a memory bank for storing the photon's information; the latter is transferred over these distances using the teleportation effect.

The experiment not only represents a significant technological achievement but also a spectacular advance in the continually surprising possibilities afforded by the quantum dimension. By taking the distance to 25 kilometres of optical fibre, the UNIGE physicists have significantly surpassed their own record of 6 kilometres, the distance achieved during the first long-distance teleportation achieved by Professor Gisin and his team in 2003.

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Atomically thin molybendum disulfide opens door to high-speed integrated nanophotonic circuits

Atomically thin molybendum disulfide opens door to high-speed integrated nanophotonic circuits | Amazing Science |

Scientists at the University of Rochester and Swiss Federal Institute of Technology in Zurich have devised an experimental circuit consisting of a silver nanowire and a single-layer atomically thin flake of molybendum disulfide (MoS2) — a step toward building computer chips capable of transporting digital information at light speed.

The researchers used a laser to excite electromagnetic waves called plasmons (vibrating electron clouds) at the surface of the wire, causing an MoS2 flake at the far end of the wire to generate strong light emission. MoS2 excitons can also decay into nanowire plasmons, they found.

This interaction an be exploited for creating nanophotonic integrated circuits, said Nick Vamivakas, assistant professor of quantum optics and quantum physics at the University of Rochester and senior author of the paper in the journal Optica.

Photonic devices can be much faster than electronic ones, but they are bulkier and cannot be miniaturized nearly as well as electronic circuits. The new results hold promise for guiding the transmission of light and maintaining the intensity of the signal in very small dimensions.

In bulk MoS2, electrons and photons interact as they would in traditional semiconductors like silicon and gallium arsenide. But when MoS2 is trimmed down to an atomically thin layer, the transfer of energy between electrons and photons becomes highly efficient.*

Combining electronics and photonics on the same integrated circuits could drastically improve the performance and efficiency of mobile technology. The researchers say the next step is to create a near-field detector based on MoS2 and an MoS2 light-emitting diode coupled to on-chip nanoplasmonic circuitry.

* The key to MoS2′s desirable photonic properties is in the structure of its energy band gap. As the material’s layer count decreases, it transitions from an indirect to direct band gap, which allows electrons to easily move between energy bands by releasing photons. Graphene is inefficient at light emission because it has no band gap.

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The World’s First Photonic Router

The World’s First Photonic Router | Amazing Science |
Weizmann Institute scientists have demonstrated for the first time a photonic router – a quantum device based on a single atom that enables routing of single photons by single photons. This achievement, as reported in Science magazine, is another step toward overcoming the difficulties in building quantum computers.

At the core of the device is an atom that can switch between two states. The state is set just by sending a single particle of light – or photon – from the right or the left via an optical fiber. The atom, in response, then reflects or transmits the next incoming photon, accordingly. For example, in one state, a photon coming from the right continues on its path to the left, whereas a photon coming from the left is reflected backwards, causing the atomic state to flip. In this reversed state, the atom lets photons coming from the left continue in the same direction, while any photon coming from the right is reflected backwards, flipping the atomic state back again. This atom-based switch is solely operated by single photons – no additional external fields are required.

“In a sense, the device acts as the photonic equivalent to electronic transistors, which switch electric currents in response to other electric currents,” says Dr. Barak Dayan, head of the Weizmann Institute’s Quantum Optics group, including Itay Shomroni, Serge Rosenblum, Yulia Lovsky, Orel Bechler and Gabriel Guendleman of the Chemical Physics Department in the Faculty of Chemistry. The photons are not only the units comprising the flow of information, but also the ones that control the device. 

This achievement was made possible by the combination of two state-of-the-art technologies. One is the laser cooling and trapping of atoms. The other is the fabrication of chip-based, ultra-high quality miniature optical resonators that couple directly to the optical fibers. Dayan’s lab at the Weizmann Institute is one of a handful worldwide that has mastered both these technologies.

Dayan: “The road to building quantum computers is still very long, but the device we constructed demonstrates a simple and robust system, which should be applicable to any future architecture of such computers. In the current demonstration a single atom functions as a transistor – or a two-way switch – for photons, but in our future experiments, we hope to expand the kinds of devices that work solely on photons, for example new kinds of quantum memory or logic gates.”
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Researchers cross a critical threshold in optical communications

Researchers cross a critical threshold in optical communications | Amazing Science |
Researchers from Lehigh University, Japan and Canada have advanced a step closer to the dream of all-optical data transmission by building and demonstrating what they call the 'world's first fully functioning single crystal waveguide in glass.'

In an article published in Scientific Reports, a Nature publication, the group said it had employed ultrafast femtosecond lasers to produce a three-dimensional single crystal capable of guiding light waves through glass with little loss of light. The article, published May 19, is titled "Direct laser-writing of ferroelectric single-crystal waveguide architectures in glass for 3D integrated optics."

The article's lead author, Adam Stone, received his Ph.D. in materials science and engineering from Lehigh in 2014. The coauthors are Himanshu Jain, professor of materials science and engineering, and Volkmar Dierolf, professor of physics, both at Lehigh, and researchers from Kyoto University in Japan and Polytechnique Montreal in Canada.

The group says its achievement will boost ongoing efforts to develop photonic integrated circuits (PICs) that are smaller, cheaper, more energy-efficient and more reliable than current networks that use discrete optoelectronic components—waveguides, splitters, modulators, filters, amplifiers—to transport optical signals.

"A major trend in optics," the researchers write, "has been a drive toward...replacing systems of large discrete components that provide individual functions with compact and multifunctional PICs, in much the same way that integration of electronics has driven the impressive advances of modern computer systems."

To make this transition, however, improved methods of fabricating 3D PICs are needed, the researchers say. "The methods currently employed for fabricating PICs are photolithographic and other processes suitable for planar geometries," the researchers write. "3D PIC fabrication techniques would enable a much higher density of components and much more compact devices, while at the same time creating opportunities for new technologies such as high density 3D optical memory."

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Photonics: Largest-scale, lowest-energy-loss switch reported to date

Photonics: Largest-scale, lowest-energy-loss switch reported to date | Amazing Science |

Today's explosion of video and Internet data is driving unprecedented traffic demand within datacenters. With data transfer rates exceeding 100 gigabits-per-second (Gb/s), communication between servers requires optical switches with faster switching time (micro-to nano-second level), broader band operation, larger capacity for switching elements and lower energy consumption.
Researchers at the University of California, Berkeley have developed a novel silicon photonic switch, which is the largest-scale and the lowest-energy loss switch reported to date. It features a switching time of sub-micro seconds and a broad bandwidth of hundreds of nanometers.
The researchers will present their photonic switching innovation on 23 March 2015 during the Optical Fiber Communication Conference and Exposition (OFC) in Los Angeles, California, USA. A step forward towards achieving large-scale silicon photonic switches for high-traffic datacenter networks, the new device will boost other technologies that rely on manipulating multi-channel optical signals, such as secure communications and quantum computing.
"Our photonic switch has 50 input and 50 output channels, for a total of 2,500 switching elements located on the cross points of these channels, which is the largest-scale silicon photonic switch ever reported," said Tae Joon Seok, a postdoctoral researcher at the Integrated Photonics Laboratory at the university. "The switch can be compactly integrated on a silicon chip smaller than 1 cm x 1 cm."
Seok said that the largest-scale silicon photonic switch previously reported by other groups has 8 input and 8 output channels. "Generally, the light energy loss, or technically called optical insertion loss, is quickly added up as the scale of the switch increases," Seok said. "To compensate for the loss, optical amplification is required, which increases power consumption used by the switch. This, in turn, increases the overall price per switch."
To address this problem, Seok and his co-workers designed a new switch architecture that enables scalability. Rather than connecting smaller optical switches in succession to form a switching network, the new architecture is a single-stage switch with a MEMS switching mechanism, which completely eliminated the problem of cumulative loss.
According to Seok, he and his colleagues first patterned a bottom silicon layer to create the east-to-west input and north-to-south output channels. Then, with the aid of a sacrificial spacer layer, a top silicon layer was built on and patterned to form a specific type of switching element, called an adiabatic coupler. An adiabatic coupler is a gradually tapered waveguide, which transfers light from one channel to another channel without wavelength dependency.
When the switch is in the "on" mode, adiabatic couplers on the top layer are pulled down to bottom channels, transferring light and making 90 degree turns from the input channel to the output channel. When the switch is in the "off" mode, the light stays in the input channel and is not affected by the switching elements due to the distance between the top and bottom layers.
"In this architecture, light from each input port would only pass one switching element in their light paths rather than passing multiple ones like in conventional silicon switch, which greatly reduces the energy losses," Seok explained.

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Perfect colors, captured with one ultra-thin nanotech lens

Perfect colors, captured with one ultra-thin nanotech lens | Amazing Science |

 Most lenses are, by definition, curved. After all, they are named for their resemblance to lentils, and a glass lens made flat is just a window with no special powers. But a new type of lens created at the Harvard School of Engineering and Applied Sciences(SEAS) turns conventional optics on its head.

A major leap forward from a prototype device demonstrated in 2012, it is an ultra-thin, completely flat optical component made of a glass substrate and tiny, light-concentrating silicon antennas. Light shining on it bends instantaneously, rather than gradually, while passing through. The bending effects can be designed in advance, by an algorithm, and fine-tuned to fit almost any purpose.

With this new invention described today in Science, the Harvard research team has overcome an inherent drawback of a wafer-thin lens: light at different wavelengths (i.e., colors) responds to the surface very differently. Until now, this phenomenon has prevented planar optics from being used with broadband light. Now, instead of treating all wavelengths equally, the researchers have devised a flat lens with antennas that compensate for the wavelength differences and produce a consistent effect—for example, deflecting three beams of different colors by the same angle, or focusing those colors on a single spot.

“What this now means is that complicated effects like color correction, which in a conventional optical system would require light to pass through several thick lenses in sequence, can be achieved in one extremely thin, miniaturized device,” said principal investigator Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at Harvard SEAS.

Donald Schwartz's curator insight, February 20, 2015 11:19 AM

Less glass is good. I'm so excited, I just can't hide it. 

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First-of-its-kind tube laser created for on-chip optical communications

First-of-its-kind tube laser created for on-chip optical communications | Amazing Science |

Nanophotonics, which takes advantage of the much faster speed of light compared with electrons, could potentially lead to future optical computers that transmit large amounts of data at very high speeds. Working toward this goal, researchers in a new study have developed a tiny laser 100 micrometers long and 5 micrometers in diameter—right at the limit of what the unaided human eye can see. As the first rolled-up semiconductor tube laser that is electrically powered, it can fit on an optical chip and serve as the light source for future optical communications technology.

A team of engineers, M. H. T. Dastjerdi, et al., at McGill University in Montreal have reported their development of the tiny laser in a recent issue of Applied Physics LettersFuture optical chips will require many vital components, such as modulators (which convert electrical signals into optical ones), photodetectors (which do the reverse), and waveguides (which control the path of light). Another essential requirement is, of course, the light itself, which may come from a micro- or nano-scale laser that can be integrated with the other components onto a silicon (Si) platform.

Although many different types of micro-sized lasers have been studied over the past several years, one promising candidate is a laser made from rolled-up semiconductor tubes. These lasers are fabricated by straining 2D nanomembranes on a substrate, and then selectively releasing parts of the nanomembranes so that they roll up into tiny tubes that act as optical cavities. The rolled-up tube lasers have an advantage over most other types of small lasers in that their optical emission characteristics can be precisely tailored using standard photolithography processes. They can also be easily transferred onto a Si platform, allowing for seamless integration with other chip components.

"In contrast to electrically injected devices, optically pumped devices require additional light sources (lasers, LEDs) to operate that take additional space on the chip and add a significant level of complexity," Zetian Mi, Associate Professor at McGill University, told "Therefore, optically pumped light sources are not practical for integrated chip-level optical communication systems."

As the researchers explain, fabricating electrically powered rolled-up tube lasers is difficult because the very thin nanomembranes make the process of injecting charge carriers into the laser very inefficient. To overcome this problem, the researchers designed the laser to lie horizontally on top of two supporting pieces connected to the electrodes in a U-shaped mesa design. In this formation, charge carriers are injected into the laser cavity from the sides. By circumventing the thin membrane walls, this lateral carrier injection scheme emits light from the center of the tube laser, significantly increasing injection efficiency.

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New optical beam-forming device makes 'twisted light' a reality

New optical beam-forming device makes 'twisted light' a reality | Amazing Science |
A team of engineers has developed a new acousto-optic device that can shape and steer beams of light at speeds never before achieved. The new technology will enable better optical devices to be made, such as holographs that can move rapidly in real time.

The research led by Bruce Drinkwater, Professor of Ultrasonics at the University of Bristol and Dr Mike MacDonald at the University of Dundee is published in the journal, Optics ExpressThe array consists of 64 tiny piezo-electric elements which act as high frequency loudspeakers. The complex sound field generated deflects and sculpts any light passing through the new device. As the sound field changes, so does the shape of the light beam.

Professor Drinkwater from the Department of Mechanical Engineering said: "This reconfigurability can happen extremely fast, limited only by the speed of the sound waves. The key advantage of this method is that it potentially offers very high refresh rates - millions of refreshes per second is now possible. This means that in the future laser beam-based devices will be able to be reconfigured much faster than is currently possible. Previously, the fastest achieved is a few thousand refreshes per second."

The advancement will enable reconfigurable lenses that can automatically compensate for aberrations allowing for improved microscopy and a new generation of optical tweezers that will make them more rapidly reconfigurable and so allow better shaped traps to be produced.

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A time cloak that conceals events rather than objects

A time cloak that conceals events rather than objects | Amazing Science |

A "time cloak" that conceals events rather than objects can hide secret messages through a trick of light, making information invisible to all but the intended recipient. Like an invisibility cloak that makes something disappear in plain sight, a time cloak makes an event disappear in time. It works by manipulating light traveling along an optical fiber.

Imagine a row of cars speeding along a road slowing down in concert to create brief paths for pedestrians to safely cross. When the cars that let the pedestrians cross ahead of them speed up and re-join the rest of the traffic, no one can tell there was ever a gap in the flow – the pedestrians' presence has been cloaked. In the same way, photons' paths can be tweaked to create brief gaps where information can safely hide.

Last year, a team at Purdue University in Indiana built a cloak that could transfer hidden data at 1.5 gigabits a second, fast enough to make it theoretically useful for real communication. The only thing was, the message was hidden so well that no one could actually read it. That problem has now been solved.

"With this new device, we don't just limit ourselves to thinking about cloaks as a way of preventing somebody from getting information, but also as a way to enable communication," says Joseph Lukens, an electrical engineer at Purdue. "One guy sees nothing, the other guy sees everything."

Lukens and his colleagues created two different communications channels using lasers tuned to two different frequencies. One is a regular frequency and the other is a time-cloaked channel that remains hidden unless you know it's there. Photons from each laser traveled along the same fibre, but the intended recipient just needs to tune in to the right channel to reveal the secret information.

Not only could the cloak deliver the messages, it also successfully fended off outside attempts to scramble the information. A similar device could one day improve current communication systems, says Moti Fridman at Bar-Ilan University in Israel.

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World's first photonic pressure sensor outshines traditional mercury standard

World's first photonic pressure sensor outshines traditional mercury standard | Amazing Science |

For almost 400 years, mercury gauges have prevailed as the most accurate way to measure pressure. Now, within weeks of seeing "first light," a novel pressure-sensing device has surpassed the performance of the best mercury-based techniques in resolution, speed, and range at a fraction of the size. The new instrument, called a fixed-length optical cavity (FLOC), works by detecting subtle changes in the wavelength of light passing through a cavity filled with nitrogen gas.

The FLOC system is poised to depose traditional mercury pressure sensors – also called manometers – as the standard used to calibrate commercial equipment, says the interdisciplinary team of NIST researchers who developed the system and will continue to refine it over the next few years. The new design is also a promising candidate for a factory-floor pressure instrument that could be used by a range of industries, including those associated with semiconductor, glass, and aerospace manufacturing.

"We've exceeded the expectations we had three years ago," says Thermodynamic Metrology Group Leader Gregory Strouse. "This device is not only a photonic sensor, it's also a primary standard. It's the first photonic-based primary pressure standard. And it works."

About the size of a travel mug, the FLOC has a resolution of 0.1 mPa (millipascal or thousandths of a pascal), 36 times better than NIST'S official U.S. pressure standard, which is a 3-meter-tall (about 10-foot) column of liquid mercury that extends through the ceiling of the calibration room.

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255 Terabits/s: Researchers demonstrate record data transmission over new type of fiber

255 Terabits/s: Researchers demonstrate record data transmission over new type of fiber | Amazing Science |

Researchers at Eindhoven University of Technology (TU/e) in the Netherlands and the University of Central Florida (CREOL), report in the journal Nature Photonics the successful transmission of a record high 255 Terabits/s over a new type of fiber allowing 21 times more bandwidth than currently available in communication networks. This new type of fiber could be an answer to mitigating the impending optical transmission capacity crunch caused by the increasing bandwidth demand.

Due to the popularity of Internet services and emerging network of capacity-hungry datacentres, demand for telecommunication bandwidth is expected to continue at an exponential rate. To transmit more information through current optical glass fibers, an option is to increase the power of the signals to overcome the losses inherent in the glass from which the fibre is manufactured. However, this produces unwanted photonic nonlinear effects, which limit the amount of information that can be recovered after transmission over the standard fiber.

The team at TU/e and CREOL, led by dr. Chigo Okonkwo, an assistant professor in the Electro-Optical Communications (ECO) research group at TU/e and dr. Rodrigo Amezcua Correa, a research assistant professor in Micro-structured fibers at CREOL, demonstrate the potential of a new class of fiber to increase transmission capacity and mitigate the impending 'capacity crunch' in their article that appeared yesterday in the online edition of the journal Nature Photonics.

The new fiber has seven different cores through which the light can travel, instead of one in current state-of-the-art fibers. This compares to going from a one-way road to a seven-lane highway. Also, they introduce two additional orthogonal dimensions for data transportation – as if three cars can drive on top of each other in the same lane. Combining those two methods, they achieve a gross transmission throughput of 255 Terabits/s over the fiber link. This is more than 20 times the current standard of 4-8 Terabits/s.

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Physicists design record-breaking laser that accelerates the interaction between light and matter by ten times

Physicists design record-breaking laser that accelerates the interaction between light and matter by ten times | Amazing Science |

Reporting in the journal Nature Physics, physicists from Imperial College London and the Friedrich-Schiller-Universität Jena, in Germany, used semiconductor nanowires made of zinc oxide and placed them on a silver surface to create ultra-fast lasers. 

By using silver rather than a conventional glass surface, the scientists were able to shrink their nanowire lasers down to just 120 nanometres in diameter - around a thousandth the diameter of human hair.

The physicists were able to shrink the laser by using surface plasmons, which are wave-like motions of excited electrons found at the surface of metals. When light binds to these oscillations it can be focused much more tightly than usual. 

By using surface plasmons they were able to squeeze the light into a much smaller space inside the laser, which allowed the light to interact much more strongly with the zinc oxide. 

This stronger interaction accelerated the rate at which the laser could be turned on and off to ten times that of a nanowire laser using a glass surface. These are the fastest lasers recorded to date, in terms of the speed at which they can turn on and off.

Senior author Dr Rupert Oulton from the Department of Physics at Imperial College London said: “This work is so exciting because we are engineering the interaction of light and matter to drive light generation in materials much faster than it occurs naturally. When we first started working on this, I would have been happy to speed up switching speeds to a picosecond, which is one trillionth of a second. But we’ve managed to go even faster, to the point where the properties of the material itself set a speed limit.” 

PhD student Robert Röder, from Friedrich-Schiller Universität Jenasaid: “This is not only ‘world record’ regarding the switching speed. Most likely we also achieved the maximum possible speed at which such a semiconductor laser can be operated.” 

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New nanoscale structure leads to better and cheaper LEDs for phones and lighting

New nanoscale structure leads to better and cheaper LEDs for phones and lighting | Amazing Science |
Princeton University researchers have developed a new method to increase the brightness, efficiency and clarity of LEDs, which are widely used on smartphones and portable electronics as well as becoming increasingly common in lighting.

Using a new nanoscale structure, the researchers, led by electrical engineering professor Stephen Chou, increased the brightness and efficiency of LEDs made of organic materials (flexible carbon-based sheets) by 58 percent. The researchers also report their method should yield similar improvements in LEDs made in inorganic (silicon-based) materials used most commonly today.

The method also improves the picture clarity of LED displays by 400 percent, compared with conventional approaches. In an article published online August 19 in the journal Advanced Functional Materials, the researchers describe how they accomplished this by inventing a technique that manipulates light on a scale smaller than a single wavelength.

"New nanotechnology can change the rules of the ways we manipulate light," said Chou, who has been working in the field for 30 years. "We can use this to make devices with unprecedented performance."

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Fastest Ever Built Photon Switch of 500 GHz in an Engineered Fiber

Fastest Ever Built Photon Switch of 500 GHz in an Engineered Fiber | Amazing Science |

Researchers at the University of California, San Diego have built the first 500 Gigahertz (GHz) photon switch. “Our switch is more than an order of magnitude faster than any previously published result to date,” said UC San Diego electrical and computer engineering professor Stojan Radic. “That exceeds the speed of the fastest lightwave information channels in use today.” The work took nearly four years to complete and it opens a fundamentally new direction in photonics – with far-reaching potential consequences for the control of photons in optical fiber channels.

According to an article in the journal Science*, switching photons at such high speeds was made possible by advances in the control of a strong optical beam using only a few photons, and by the scientists’ ability to engineer the optical fiber itself with accuracy down to the molecular level.

In the research paper, Radic and his colleagues in the UC San Diego Jacobs School of Engineering argue that ultrafast optical control is critical to applications that must manipulate light beyond the conventional electronic limits. In addition to very fast beam control and fast switching, the latest work opens the way to a new class of sensitive receivers (also capable of operating at very high rates), faster photon sensors, and optical processing devices.

To build the new switch, the UC San Diego team developed a new measurement technique capable of resolving sub-nanometer fluctuations in the fiber core. This was critical because local fiber dispersion varies substantially, even with small core fluctuations, and until recently, control of such small variations was not considered feasible, particularly over long device lengths.

In the experiment, a three-photon input was used to manipulate a Watt-scale beam at a speed exceeding 500 Gigahertz.

In their research, the engineers in the Photonic Systems Laboratory of UC San Diego’s Qualcomm Institute demonstrated that fast control becomes possible in fiber made of silica glass. “Silica fiber represents a nearly ideal physical platform because of very low optical loss, exceptional transparency and kilometer-scale interaction lengths,” noted Radic. “We showed that a silica fiber core can be controlled with sub-nanometer precision and be used for fast, few-photon control.”

Until recently, control of small variations was not considered feasible – particularly over long scales. But once they were able to profile the fluctuation of the actual fiber, it became clear that the silica fiber core could be controlled with sub-nanometer precision – and be used for fast, few-photon control.

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Super efficient LEDs could be made from ‘wonder material’ perovskite

Super efficient LEDs could be made from ‘wonder material’ perovskite | Amazing Science |

A hybrid form of perovskite - the same type of material which has recently been found to make highly efficient solar cells that could one day replace silicon - has been used to make low-cost, easily manufactured LEDs, potentially opening up a wide range of commercial applications in future, such as flexible color displays.

This particular class of semiconducting perovskites have generated excitement in the solar cell field over the past several years, after Professor Henry Snaith’s group at Oxford University found them to be remarkably efficient at converting light to electricity. In just two short years, perovskite-based solar cells have reached efficiencies of nearly 20%, a level which took conventional silicon-based solar cells 20 years.

Now, researchers from the University of Cambridge, University of Oxford and the Ludwig-Maximilians-Universität in Munich have demonstrated a new application for perovskite materials, using them to make high-brightness LEDs. The results are published in the journal Nature Nanotechnology.

Perovskite is a general term used to describe a group of materials that have a distinctive crystal structure of cuboid and diamond shapes. They have long been of interest for their superconducting and ferroelectric properties. But in the past several years, their efficiency at converting light into electrical energy has opened up a wide range of potential applications.

The perovskites that were used to make the LEDs are known as organometal halide perovskites, and contain a mixture of lead, carbon-based ions and halogen ions known as halides. These materials dissolve well in common solvents, and assemble to form perovskite crystals when dried, making them cheap and simple to make.

“These organometal halide perovskites are remarkable semiconductors,” said Zhi-Kuang Tan, a PhD student at the University of Cambridge’s Cavendish Laboratory and the paper’s lead author. “We have designed the diode structure to confine electrical charges into a very thin layer of the perovskite, which sets up conditions for the electron-hole capture process to produce light emission.”

The perovskite LEDs are made using a simple and scalable process in which a perovskite solution is prepared and spin-coated onto the substrate. This process does not require high temperature heating steps or a high vacuum, and is therefore cheap to manufacture in a large scale. In contrast, conventional methods for manufacturing LEDs make the cost prohibitive for many large-area display applications.

“The big surprise to the semiconductor community is to find that such simple process methods still produce very clean semiconductor properties, without the need for the complex purification procedures required for traditional semiconductors such as silicon,” said Professor Sir Richard Friend of the Cavendish Laboratory, who has led this programme in Cambridge.

“It’s remarkable that this material can be easily tuned to emit light in a variety of colours, which makes it extremely useful for colour displays, lighting and optical communication applications,” said Tan. “This technology could provide a lot of value to the ever growing flat-panel display industry.”

The team is now looking to increase the efficiency of the LEDs and to use them for diode lasers, which are used in a range of scientific, medical and industrial applications, such as materials processing and medical equipment. The first commercially-available LED based on perovskite could be available within five years.

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