Replacing Electricity With Light: First Physical 'Metatronic' Circuit Created

Replacing Electricity With Light: First Physical 'Metatronic' Circuit Created

  8:15:00 PM    Science Lover

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The technological world of the 21^st century owes a tremendous amount to advances in electrical engineering, specifically, the ability to finely control the flow of electrical charges using increasingly small and complicated circuits. And while those electrical advances continue to race ahead, researchers at the University of Pennsylvania are pushing circuitry forward in a different way, by replacing electricity with light.

Figure A. When the plane of the electric field is
in line with the nanorods the circuit is wired in
parallel. Figure B. When the plane of the electric
field crosses both the nanorods and the gaps the
circuit is wired in series. (Credit: Image courtesy
of University of Pennsylvania)

"Looking at the success of electronics over the last century, I have always wondered why we should be limited to electric current in making circuits," said Nader Engheta, professor in the electrical and systems engineering department of Penn's School of Engineering and Applied Science. "If we moved to shorter wavelengths in the electromagnetic spectrum -- like light -- we could make things smaller, faster and more efficient."

Different arrangements and combinations of electronic circuits have different functions, ranging from simple light switches to complex supercomputers. These circuits are in turn built of different arrangements of circuit elements, like resistors, inductors and capacitors, which manipulate the flow of electrons in a circuit in mathematically precise ways. And because both electric circuits and optics follow Maxwell's equations -- the fundamental formulas that describe the behavior of electromagnetic fields -- Engheta's dream of building circuits with light wasn't just the stuff of imagination. In 2005, he and his students published a theoretical paper outlining how optical circuit elements could work.

Now, he and his group at Penn have made this dream a reality, creating the first physical demonstration of "lumped" optical circuit elements. This represents a milestone in a nascent field of science and engineering Engheta has dubbed "metatronics."

Engheta's research, which was conducted with members of his group in the electrical and systems engineering department, Yong Sun, Brian Edwards and Andrea Alù, was published in the journal Nature Materials.

In electronics, the "lumped" designation refers to elements that can be treated as a black box, something that turns a given input to a perfectly predictable output without an engineer having to worry about what exactly is going on inside the element every time he or she is designing a circuit.

"Optics has always had its own analogs of elements, things like lenses, waveguides and gratings," Engheta said, "but they were never lumped. Those elements are all much larger than the wavelength of light because that's all that could be easily built in the old days. For electronics, the lumped circuit elements were always much smaller than the wavelength of operation, which is in the radio or microwave frequency range."

Nanotechnology has now opened that possibility for lumped optical circuit elements, allowing construction of structures that have dimensions measured in nanometers. In this experiment's case, the structure was comb-like arrays of rectangular nanorods made of silicon nitrite.

The "meta" in "metatronics" refers to metamaterials, the relatively new field of research where nanoscale patterns and structures embedded in materials allow them to manipulate waves in ways that were previously impossible. Here, the cross-sections of the nanorods and the gaps between them form a pattern that replicates the function of resistors, inductors and capacitors, three of the most basic circuit elements, but in optical wavelengths.

"If we have the optical version of those lumped elements in our repertoire, we can actually make designs similar to what we do in electronics but now for operation with light," Engheta said. "We can build a circuit with light."

In their experiment, the researchers illuminated the nanorods with an optical signal, a wave of light in the mid-infrared range. They then used spectroscopy to measure the wave as it passed through the comb. Repeating the experiment using nanorods with nine different combinations of widths and heights, the researchers showed that the optical "current" and optical "voltage" were altered by the optical resistors, inductors and capacitors with parameters corresponding to those differences in size.

"A section of the nanorod acts as both an inductor and resistor, and the air gap acts as a capacitor," Engheta said.

Beyond changing the dimensions and the material the nanorods are made of, the function of these optical circuits can be altered by changing the orientation of the light, giving metatronic circuits access to configurations that would be impossible in traditional electronics.

This is because a light wave has polarizations; the electric field that oscillates in the wave has a definable orientation in space. In metatronics, it is that electric field that interacts and is changed by elements, so changing the field's orientation can be like rewiring an electric circuit.

When the plane of the field is in line with the nanorods, as in Figure A, the circuit is wired in parallel and the current passes through the elements simultaneously. When the plane of the electric field crosses both the nanorods and the gaps, as in Figure B, the circuit is wired in series and the current passes through the elements sequentially.

"The orientation gives us two different circuits, which is why we call this 'stereo-circuitry,'" Engheta said. "We could even have the wave hit the rods obliquely and get something we don't have in regular electronics: a circuit that's neither in series or in parallel but a mixture of the two."

This principle could be taken to an even higher level of complexity by building nanorod arrays in three dimensions. An optical signal hitting such a structure's top would encounter a different circuit than a signal hitting its side. Building off their success with basic optical elements, Engheta and his group are laying the foundation for this kind of complex metatronics.

"Another reason for success in electronics has to do with its modularity," he said. "We can make an infinite number of circuits depending on how we arrange different circuit elements, just like we can arrange the alphabet into different words, sentences and paragraphs.

"We're now working on designs for more complicated optical elements," Engheta said. "We're on a quest to build these new letters one by one."

This work was supported in part by the U.S. Air Force Office of Scientific Research.

Andrea Alù is now an assistant professor at the University of Texas at Austin.

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Artificial light-harvesting method achieves 100% energy transfer efficiency

Artificial light-harvesting method achieves 100% energy transfer efficiency

  5:52:00 PM    Science Lover

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In an attempt to mimic the photosynthetic systems found in plants and some bacteria, scientists have taken a step toward developing an artificial light-harvesting system (LHS) that meets one of the crucial requirements for such systems: an approximately 100% energy transfer efficiency. Although high energy transfer efficiency is just one component of the development of a useful artificial LHS, the achievement could lead to clean solar-fuel technology that turns sunlight into chemical fuel.

By arranging porphyrin dye molecules on a clay surface using the “Size-Matching Effect,” researchers have demonstrated an energy transfer efficiency of approximately 100%, which is an important requirement for designing efficient artificial light-harvesting systems. Image credit: Ishida, et al. ©2011 American Chemical Society

The researchers, led by Shinsuke Takagi from the Tokyo Metropolitan University and PRESTO of the Japan Science and Technology Agency, have published their study on their work toward an artificial LHS in a recent issue of the Journal of the American Chemical Society.

“In order to realize an artificial light-harvesting system, almost 100% efficiency is necessary,” Takagi told PhysOrg.com. “Since light-harvesting systems consist of many steps of energy transfer, the total energy transfer efficiency becomes low if the energy transfer efficiency of each step is 90%. For example, if there are five energy transfer steps, the total energy transfer is 0.9 x 0.9 x 0.9 x 0.9 x 0.9 = 0.59. In this way, an efficient energy transfer reaction plays an important role in realizing efficient sunlight collection for an artificial light-harvesting system.”

As the researchers explain in their study, a natural LHS (like those in purple bacteria or plant leaves) is composed of regularly arranged molecules that efficiently collect sunlight and carry the excitation energy to the system’s reaction center. An artificial LHS (or “artificial leaf”) attempts to do the same thing by using functional dye molecules.

Building on the results of previous research, the scientists chose to use two types of porphyrin dye molecules for this purpose, which they arranged on a clay surface. The molecules’ tendency to aggregate or segregate on the clay surface made it challenging for the researchers to arrange the molecules in a regular pattern like their natural counterparts.

“A molecular arrangement with an appropriate intermolecular distance is important to achieve nearly 100% energy transfer efficiency,” Takagi said. “If the intermolecular distance is too near, other reactions such as electron transfer and/or photochemical reactions would occur. If the intermolecular distance is too far, deactivation of excited dye surpasses the energy transfer reaction.”




In order to achieve the appropriate intermolecular distance, the scientists developed a novel preparation technique based on matching the distances between the charged sites in the porphyrin molecules and the distances between negatively charged (anionic) sites on the clay surface. This effect, which the researchers call the “Size-Matching Rule,” helped to suppress the major factors that contributed to the porphyrin molecules’ tendency to aggregate or segregate, and fixed the molecules in an appropriate uniform intermolecular distance. As Takagi explained, this strategy is significantly different than other attempts at achieving molecular patterns.

“The methodology is unique,” he said. “In the case of usual self-assembly systems, the arrangement is realized by guest-guest interactions. In our system, host-guest interactions play a crucial role for realizing the special arrangement of dyes. Thus, by changing the host material, it is possible to control the molecular arrangement of dyes on the clay surface.”

As the researchers demonstrated, the regular arrangement of the molecules leads to an excited energy transfer efficiency of up to 100%. The results indicate that porphyrin dye molecules and clay host materials look like promising candidates for an artificial LHS.

“At the present, our system includes only two dyes,” Takagi said. “As the next step, the combination of several dyes to adsorb all sunlight is necessary. One of the characteristic points of our system is that it is easy to use several dyes at once. Thus, our system is a promising candidate for a real light-harvesting system that can use all sunlight. We believe that even photochemical reaction parts can be combined on the same clay surface. If this system is realized and is combined with a photochemical reaction center, this system can be called an ‘inorganic leaf.’”

More information: Yohei Ishida, et al. “Efficient Excited Energy Transfer Reaction in Clay/Porphyrin Complex toward an Artificial Light-Harvesting System.” Journal of the American Chemical Society

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From a Flat Mirror, Designer Light: Bizarre Optical Phenomena Defies Laws of Reflection and Refraction

From a Flat Mirror, Designer Light: Bizarre Optical Phenomena Defies Laws of Reflection and Refraction

  4:34:00 PM    Science Lover

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Exploiting a novel technique called phase discontinuity, researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have induced light rays to behave in a way that defies the centuries-old laws of reflection and refraction.

Top, clockwise from left: Patrice Genevet, Nanfang Yu, Federico Capasso, Zeno Gaburro, and Mikhail A. Kats. Bottom: A simulation of the image that would appear in a large mirror patterned with the team's new phase mirror technology. (Credit: Photos by Eliza Grinnell and Nanfang Yu)

The discovery, published this week in Science, has led to a reformulation of the mathematical laws that predict the path of a ray of light bouncing off a surface or traveling from one medium into another -- for example, from air into glass.

"Using designer surfaces, we've created the effects of a fun-house mirror on a flat plane," says co-principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. "Our discovery carries optics into new territory and opens the door to exciting developments in photonics technology."

It has been recognized since ancient times that light travels at different speeds through different media. Reflection and refraction occur whenever light encounters a material at an angle, because one side of the beam is able to race ahead of the other. As a result, the wavefront changes direction.

The conventional laws, taught in physics classrooms worldwide, predict the angles of reflection and refraction based only on the incident (incoming) angle and the properties of the two media.

While studying the behavior of light impinging on surfaces patterned with metallic nanostructures, the researchers realized that the usual equations were insufficient to describe the bizarre phenomena observed in the lab.

The new generalized laws, derived and experimentally demonstrated at Harvard, take into account the Capasso group's discovery that the boundary between two media, if specially patterned, can itself behave like a third medium.

"Ordinarily, a surface like the surface of a pond is simply a geometric boundary between two media, air and water," explains lead author Nanfang Yu (Ph.D. '09), a research associate in Capasso's lab at SEAS. "But now, in this special case, the boundary becomes an active interface that can bend the light by itself."

The key component is an array of tiny gold antennas etched into the surface of the silicon used in Capasso's lab. The array is structured on a scale much thinner than the wavelength of the light hitting it. This means that, unlike in a conventional optical system, the engineered boundary between the air and the silicon imparts an abrupt phase shift (dubbed "phase discontinuity") to the crests of the light wave crossing it.

Each antenna in the array is a tiny resonator that can trap the light, holding its energy for a given amount of time before releasing it. A gradient of different types of nanoscale resonators across the surface of the silicon can effectively bend the light before it even begins to propagate through the new medium.



The resulting phenomenon breaks the old rules, creating beams of light that reflect and refract in arbitrary ways, depending on the surface pattern.

In order to generalize the textbook laws of reflection and refraction, the Harvard researchers added a new term to the equations, representing the gradient of phase shifts imparted at the boundary. Importantly, in the absence of a surface gradient, the new laws reduce to the well-known ones.

"By incorporating a gradient of phase discontinuities across the interface, the laws of reflection and refraction become designer laws, and a panoply of new phenomena appear," says Zeno Gaburro, a visiting scholar in Capasso's group who was co-principal investigator for this work. "The reflected beam can bounce backward instead of forward. You can create negative refraction. There is a new angle of total internal reflection."

Moreover, the frequency (color), amplitude (brightness), and polarization of the light can also be controlled, meaning that the output is in essence a designer beam.

The researchers have already succeeded at producing a vortex beam (a helical, corkscrew-shaped stream of light) from a flat surface. They also envision flat lenses that could focus an image without aberrations.

Yu, Capasso, and Gaburro's co-authors included Patrice Genevet, Mikhail A. Kats, Francesco Aieta, and Jean-Philippe Tetienne.

Story Source: The above story is reprinted (with editorial adaptations) from materials provided by Harvard University, via EurekAlert!, a service of AAAS.

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New Invisibility Cloak Hides Objects from Human View

New Invisibility Cloak Hides Objects from Human View

  2:26:00 PM    Science Lover

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For the first time, scientists have devised an invisibility cloak material that hides objects from detection using light that is visible to humans. The new device is a leap forward in cloaking materials, according to a report in the ACS journal Nano Letters.

A real-life invisibility cloak, shown in this cross- sectional 
illustration, can hide objects from human view. (Credit: ACS)

Xiang Zhang and colleagues note that invisibility cloaks, which route electromagnetic waves around an object to make it undetectable, "are still in their infancy." Most cloaks are made of materials that can only hide things using microwave or infrared waves, which are just below the threshold of human vision. To remedy this, the researchers built a reflective "carpet cloak" out of layers of silicon oxide and silicon nitride etched in a special pattern. The carpet cloak works by concealing an object under the layers, and bending light waves away from the bump that the object makes, so that the cloak appears flat and smooth like a normal mirror.

Although the study cloaked a microscopic object roughly the diameter of a red blood cell, the device demonstrates that it may be "capable of cloaking any object underneath a reflective carpet layer. In contrast to the previous demonstrations that were limited to infrared light, this work makes actual invisibility for the light seen by the human eye possible," the scientists write.



The authors acknowledge funding from the U.S. Army Research Office, the Natural Sciences and Engineering Research Council of Canada, and the NSF Graduate Research Fellowship Program.

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Squeezed light from single atoms

Squeezed light from single atoms

  9:11:00 PM    Science Lover

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Max Planck Institute of Quantum Optics scientists generate amplitude-squeezed light fields using single atoms trapped inside optical cavities.

A single rubidium atom in a cavity squeezes the quantum
fluctuations of a weak laser beam, decreasing the fluctuations
of the amplitude at the expense of the phase.
The effect is exaggerated for clarity.

In classical optics light is usually described as a wave, but at the most fundamental quantum level this wave consists of discrete particles called photons. Over the time, physicists developed many tools to manipulate both the wave-like and the particle-like quantum properties of the light. For instance, they created single photon sources with single atoms, using their ability to absorb and emit photons one by one. A team around Professor Gerhard Rempe, Director at the Max Planck Institute of Quantum Optics (Garching near Munich) and head of the Quantum Dynamics Division, has now observed that the light emitted by a single atom may exhibit much richer dynamics (Nature 474, 623, June 30, 2011). Strongly interacting with light inside a cavity, the atom modifies the wave-like properties of the light field, reducing its amplitude or phase fluctuations below the level allowed for classical electromagnetic radiation. This is the very first observation of “squeezed” light produced by a single atom.

The “graininess” of the photons in a light wave causes small fluctuations of the wave’s amplitude and phase. For classical beams, the minimal amount of amplitude and phase fluctuations is equal. However, by creating interactions between the photons, one can “squeeze” the fluctuations of the amplitude below this so-called “shot noise” level at the expense of increasing the fluctuations of the phase, and vice-versa. Unfortunately, the photonic interactions inside standard optical media are very weak, and require bright light beams to be observed. Single atoms are promising candidates to enable such interactions at a few-photon level. Their ability to generate squeezed light has been predicted 30 years ago, but the amount of light they emit is very tiny and so far all attempts to set this idea into realization have failed. In the Quantum Dynamics Division at MPQ sophisticated methods for cooling, isolating and manipulating single atoms have been developed over many years, and made this observation possible.



A single rubidium atom is trapped inside a cavity made of two very reflective mirrors in a distance of about a tenth of a millimetre from each other. When weak laser light is injected into this cavity, the atom can interact with one photon many times, and forms a kind of artificial molecule with the photons of the light field. As a consequence, two photons can enter the system at the same time and become correlated. “According to the model of Bohr, a single atom emits exactly one single energy quantum, i.e., one photon. That means that the number of photons is exactly known, but the phase of the light is not defined”, Professor Gerhard Rempe explains. “But the two photons that are emitted by this strongly coupled atom are indistinguishable and oscillate together. Therefore this time the wave-like properties of the propagating light field are modified.”

When the physicists use a laser beam which is resonant with the excitation frequency of the atom, the measurements show a suppression of the phase fluctuations. If the laser light is resonant with the cavity, they observe a squeezing of the amplitude instead.

The latter situation is illustrated in the figure: The atom in the cavity turns a laser beam into light which has less amplitude and more phase fluctuations than the shot-noise limit. “Our experiment shows that the light emitted by single atoms is much more complex than in the simple view of Albert Einstein concerning photo-emission”, Dr. Karim Murr emphasizes. “The squeezing that we observe is due to the coherent interaction between the two photons emitted from the system. Our measurement is in excellent agreement with the predictions of quantum electrodynamics in the strong-coupling regime.” And Dr. Alexei Ourjoumtsev, who has been working on the experiment as a post doc, adds: “Usually single quantum objects are used to manipulate the particle-like properties of light. It is interesting to see that they can also modify its wave-like properties, and create observable squeezing with excitations beams containing only two photons on average”.

So far squeezed light has only been generated with systems containing many atoms, such as crystals, using very high intensity beams, i.e. many photons. For the first time now physicists have succeeded in generating this kind of non-classical radiation with single atoms and extremely weak light fields. The ability of a single atom to induce strong coherent interactions between propagating photons opens up new perspectives for photonic quantum logic with single emitters.

More information: A. Ourjoumtsev, A. Kubanek, M. Koch, C. Sames, P. W. H. Pinkse, G. Rempe, & K. Murr

Observation of squeezed light from one atom excited with two photons , Nature 474, 623, 30 June 2011. Provided by Max-Planck-Gesellschaft

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Tiny Ring Laser Accurately Detects and Counts Nanoparticles

Tiny Ring Laser Accurately Detects and Counts Nanoparticles

  8:05:00 PM    Science Lover

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A tiny doughnut-shaped laser is the latest marvel of silicon microminiaturization, but instead of manipulating bits it detects very small particles. Small particles play a big -- and largely unnoticed -- role in our everyday lives. Virus particles make us sick, salt particles trigger cloud formation, and soot particles sift deep into our lungs and make it harder to breathe.

Whispering-gallery microlasers can count 
and measure nano-scale synthetic or biological 
particles. As this conceptual illustration shows, 
a particle disturbs the lasing "mode" to split 
into two frequencies (shown here as two different 
colors) and the frequency split acts a ruler that 
allows the particle to be measured. The inset 
at the top right shows a particle landing on the 
microlaser (a torus supported by a pedestal). 
Lina He, a graduate student in electrical and 
systems engineering at Washington University 
in St. Louis, and her co-workers demonstrated 
that the microlasers can detect particles 10 
nanometers in radius. Their resolution limit is 
about one nanometer. (Credit: J. Zhu, L. He, 
S. K. Ozdemir, and L. Yang/WUSTL)

The sensor belongs to a category called whispering gallery resonators, which work like the famous whispering gallery in St. Paul's Cathedral in London, where someone on the one side of the dome can hear a message spoken to the wall by someone on the other side. Unlike the dome, which has resonances or sweet spots in the audible range, the sensor resonates at light frequencies.

Light traveling round the micro-laser is disturbed by a particle that lands on the ring, changing the light's frequency. The ring can count the touch-down of as many as 800 nanoparticles before the signals begin to be lost in the noise. By exciting more than one mode in the ring, scientists can double-check the accuracy of the count. And by changing the "gain medium," they can adapt the sensor for water rather than air.

Lan Yang, PhD, assistant professor of electrical and systems engineering at Washington University in St. Louis who leads the team that fabricated the new sensor, says that there is already lively interest in its commercialization in fields ranging from biology to aerosol science. The sensor is described and characterized in the June 26 online edition of Nature Nanotechnology.

Whispering gallery resonator becomes microlaser

A whispering gallery resonator supports "frequency degenerate modes" (modes, or patterns of excitation in the ring, with the same frequency, one traveling clockwise and the other counterclockwise around the ring.

The mode fields have "evanescent tails" that penetrate the surface of the ring and probe the surrounding medium. When a particle lands on one of the "hot spots" it scatters energy from one of the modes into the other, and the modes adopt slightly different resonance frequencies. This is referred to as mode splitting.

In an earlier work, Yang team used mode splitting in a simple glass ring that functioned as a waveguide for light coupled into it from outside. Because the ring was passive, the external-laser had to be an expensive tunable laser so that it could scan a frequency range looking for the ring's resonances to measure mode splitting. (For more information on this sensor see "Tiny sensor takes measure of nanoparticles.")

The new sensor differs from earlier whispering gallery resonators in that it is itself a miniature laser rather than the resonating cavity of an external laser.

The new sensor is also glass but glass laced with atoms of the rare earth elements that serve as a "gain medium." The glass is doped with rare-earth atoms and when an external light source boosts enough of them into an excited state, the ring begins to lase at its own preferred frequency.

When a particle lands on the microlaser, a single lasing line splits into two slightly different frequencies.

A simple way of measuring the frequency splitting is to mix the split laser modes in a photodetector, which produces a "beat frequency" that corresponds to the frequency difference.

"The tiny sensors are mass produced by sol-gel method on silicon wafer, and it is easy to switch the gain medium" says Lina He, a graduate student and first author of the paper. "The resonators are made by mixing the rare-earth ions of choice into a solution of tetraethoxysilane, water and hydrochloric acid. The solution is heated until it becomes viscous and then spin-coated on a silicon wafer and annealed to remove solvents and complete the transition to amorphous glass. The thin film of glass is then etched to create silica disks supported underneath by silicon pillars. As a final step, the rough silica disks are reflowed into smooth toroids by laser annealing."

Active sensor outperforms passive one



"The light used for sensing is generated inside the resonator itself, and so it is purer than the light in the passive sensor," says Yang "When the light is not that pure, you might not be able to see small frequency changes. But the active sensor hits one frequency -- it has a really narrow linewidth -- and so it is much more sensitive."

The microlaser is orders of magnitude more sensitive than the passive resonator, she says. Its effective resolution limit is about one nanometer. One nanometer is to a meter, what a marble is to Earth.

Moreover, because the laser is now in the ring rather than coupled to it, the entire system is simpler and more self contained. "Now you just need a light source to excite the optical medium," says Yang, "and you can use a cheap laser diode for that instead of an expensive tunable laser."

Detecting many particles

The effect of a particle on a lasing mode depends on the particle's "polarizability," which is a function of its size and refractive index. To cover the possibilities, the Washington University team tested the micro-laser's performance with nanoparticles of various sizes made of various materials, including polystyrene (packing peanuts), virions (virus particles) and gold.

As particles enter the "mode volume" of the micro-laser one by one, the scientists can see a discrete upward or downward jump in the beat frequency. Each discrete jump signals the binding of a particle on the ring, and the number of the jumps reflects the number of particles.

Because the "resonator field" traps the particles on the resonator, once landed, they rarely drop off. But the team found they were able to count many particles before the losses induced by the particles made the laser linewidths so broad they couldn't detect changes in frequency splitting due to the latest arrival.

For example, they were able to detect and count as many as 816 gold nanoparticles using the same laser mode.

"When the line broadening is comparable to the change in splitting, then you're done," says Yang. "However, the whole resonator is fabricated on the chip, so you could just move on to the next resonator if necessary."

Doubling up for accuracy

The micro-laser can support more than one laser mode at a time. "By controlling the overlap of the pump light with the gain medium, you can excite more than one laser line," says Sahin Kaya Ozdemir, PhD, a research associate and co-author. "Then when a particle lands on the ring, each laser line will split into two, and generate a beat frequency. So you will have two beat frequencies instead of one."

That's an advantage, he explains, because the beat frequency depends in part on where the particle lands on the ring. If there is only one laser line and the particle falls between "hot spots" it might not be detected. The second beat frequency prevents these "false negatives," ensuring that every particle produces a detectable beat frequency.

Detecting particles in water

The microlasers intended to sense particles in air had been doped with erbium, a rare-earth element whose optical properties are well matched with those of air. In a final experiment designed to see whether this technique could be used to sense particles in water or blood, the team fabricated sensors that were doped with ytterbium rather than erbium.Ytterbium lases at wavelengths with low absorption of light by water

Yang's team has already begun working to make use of the enhanced sensitivity provided by the microlaser for studying various problems. In terms of applications, "the near-term use will be the monitoring of dynamic behaviors of particles in response to environmental and chemical changes at single particle resolution," says Yang.

The next step, the team see is to engineer the surface of these tiny microlasers to detect DNA and individual biological molecules. If the DNA is tagged with engineered nanoparticles, the micro-laser sensor can count individual DNA molecules or fragments of molecules.

Listening to Yang it is hard to escape the impression that you're hearing for the first time about an astonishing device that will one day be as ubiquitous -- and probably as underappreciated -- as the logic gates in our microwaves, cellphones and cars.

The Washington University in St. Louis team behind these results includes: L. He, W. Kim and J. Zhu, graduate students; S. K. Ozdemir, PhD, a research associate, and L. Yang, PhD, assistant professor in electrical and systems engineering.

This work is supported by National Science Foundation.

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Model finds optimal fiber optic network connections 10,000 times more quickly

Model finds optimal fiber optic network connections 10,000 times more quickly

  11:29:00 PM    Science Lover

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Designing fiber optic networks involves finding the most efficient way to connect phones and computers that are in different places – a costly and time-consuming process. Now researchers from North Carolina State University have developed a model that can find optimal connections 10,000 times more quickly, using less computing power to solve the problem.

"Problems that used to take days to solve can now be solved in just a few seconds," says Dr. George Rouskas, computer science professor at NC State and author of a paper describing the new method. The model could solve problems more than 10,000 times faster when data is routed through larger "rings," in the network, Rouskas says.

Every time you make a phone call or visit a website, you send and receive data in the form of wavelengths of light through a network of fiber optic cables. These data are often routed through rings that ensure the information gets where it needs to go. These ring networks are faced with the constant challenge of ensuring that their system design can meet user requirements efficiently. As a result, ring network designers try to determine the best fiber optic cable route for transmitting user data between two points, as well as which wavelength of light to use. Most commercial fiber optics handle approximately 100 different wavelengths of light.

Solving these design challenges is difficult and time-consuming. Using existing techniques, finding the optimal solution for a ring can take days, even for smaller rings. And a ring's connections are modified on an ongoing basis, to respond to changing use patterns and constantly increasing traffic demands.



But the new model developed by Rouskas and his team should speed things up considerably. Specifically, the researchers have designed a mathematical model that identifies the exact optimal routes and wavelengths for ring network designers. The model creates a large graph of all the paths in a ring, and where those paths overlap. The model then breaks that graph into smaller units, with each unit consisting of the paths in a ring that do not overlap. Because these paths do not overlap, they can use the same wavelengths of light. Paths that overlap cannot use the same wavelengths of light – because two things cannot occupy the same space at the same time.

By breaking all of the potential paths down into these smaller groups, the model is able to identify the optimal path and wavelength between two points much more efficiently than previous techniques.

"This will significantly shorten the cycle of feedback and re-design for existing rings," Rouskas says. "It also means that the ring design work can be done using fewer computer resources, which makes it less expensive. This should allow network providers to be more responsive to user demands than ever before."

More information: The paper, "Fast Exact ILP Decompositions for Ring RWA," is published in the July issue of the Journal of Optical Communications and Networking.

Provided by North Carolina State University

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Bringing a Whole New Meaning to 'High-Speed Internet'

Bringing a Whole New Meaning to 'High-Speed Internet'

  8:11:00 PM    Science Lover

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Researchers push a staggering 100 terabits of data per second through an optical fiber.

Faster broadband needed (Image: Ray Tang/Rex Features)

Talk about fast. Researchers have recently reported sending over 100 terabits of information per second through an optical fiber, New Scientist recently reported. That's a staggering amount of data--it would take three months' worth of HD video footage to use so much space.

The findings were revealed at the Optical Fiber Communications Conference, held in Los Angeles recently. First, an NEC Laboratories researcher (in Princeton, NJ) named Dayou Qian shared how he managed to push 101.7 terabits of data per second along 103 miles of fiber. The trick involved using pulses from 370 different lasers to multiply the amount of information that could be encoded at once. The light pulses were further varied to encode more information by using different polarities, phases, and amplitudes of light waves, according to reports.

Breakthroughs often occur in pairs (otherwise we wouldn't have so many patent disputes). Not to be outdone, a researcher at the Japanese National Institute of Information and Communications Technology, Jan Sakaguchi, had an even more impressive figure to share. Sakaguchi managed to squeeze 109 terabits per second through a fiber. His technique was different, and a little more intuitive--he simply used seven light-guiding cores in his fiber, rather than the more traditional single core. "We introduced a new dimension, spatial multiplication, to increasing transmission capacity," as he put it to New Scientist.



Does this mean your page-loading woes are forever dissipated? According to the report, the finding has little immediate bearing on your day-to-day Internet usage. The numbers involved here are so large, that they matter less to the individual consumer than they do to major data centers like those fueling giants like Google and Facebook (though presumably, any time saved there might ultimately benefit you in one way or another). Even looking on an infrastructural level, the numbers involved simply dwarf current commercial need. 100 terabits per second? One of today's most heavily trafficked broadband channels, that between New York and DC, only needs to send over a handful of terabits per second--not anywhere near 100 of them. Still, the rise of video-streaming and other data intensive projects means it can't hurt to have this tech in our back pocket, by any means. "Traffic has been growing about 50% per year for the last few years," Tim Strong of Telegeography Research told New Scientist.

As more and more cities come online in serious, data-guzzling ways--as we enter what's been termed the Terabit Age--it certainly won't hurt to have hit what one NEC researcher dubbed this "critical milestone in fiber capacity."

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Optical Microscope Without Lenses Produces High-Resolution 3-D Images on a Chip

Optical Microscope Without Lenses Produces High-Resolution 3-D Images on a Chip

  8:43:00 AM    Science Lover

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UCLA researchers have redefined the concept of a microscope by removing the lens to create a system that is small enough to fit in the palm of a hand but powerful enough to create three-dimensional tomographic images of miniscule samples.

Lens-free tomographic imaging: Schematic diagram 
of the lens-free tomography setup showing the angles of 
rotation for the light source to illuminate a sample. 
(Credit: Image courtesy of UCLA)

The advance, featured in the early online edition of the journal Proceedings of the National Academy of Sciences, represents the first demonstration of lens-free optical tomographic imaging on a chip, a technique capable of producing high-resolution 3-D images of large volumes of microscopic objects.

"This research clearly shows the potential of lens-free computational microscopy," said Aydogan Ozcan, senior author of the research and an associate professor of electrical engineering at UCLA's Henry Samueli School of Engineering and Applied Science. "Wonderful progress has been made in recent years to miniaturize life-sciences tools with microfluidic and lab-on-a-chip technologies, but until now optical microscopy has not kept pace with the miniaturization trend."

An optical imaging system small enough to fit onto an opto-electronic chip provides a variety of benefits. Because of the automation involved in on-chip systems, scientific work could be sped up significantly, which might have a great impact in the fields of cell and developmental biology. In addition, the small size not only has great potential for miniaturizing systems but also leads to cost savings on equipment.

The optical microscope, invented more than 400 years ago, has tended to grow larger and more complex as it has been modified to image ever-smaller objects with better resolution. To address this lack of progress in miniaturization, Ozcan's research group -- with graduate student Serhan Isikman and postdoctoral scholar Waheb Bishara as lead researchers -- developed the new tomographic microscopy platform through the next evolution of a lens-free imaging technology the group created and has been improving for years.

Ozcan, a researcher at the California NanoSystems Institute at UCLA, makes the analogy that a traditional optical microscope is like a huge set of pipes delivering content, in the form of images, to the user. Over years of development, bottlenecks occur that impede further improvement. Even if one part of the system -- that is, one bottleneck -- is improved, other bottlenecks keep that improvement from being fully realized. Not so with the lens-free system, according to Ozcan.

"Lens-free imaging removes the pipes altogether by utilizing an entirely new design," he said.

The system takes advantage of the fact that organic structures, such as cells, are partially transparent. So by shining a light on a sample of cells, the shadows created reveal not only the cells' outlines but details about their sub-cellular structures as well.

"These details can be captured and analyzed if the shadow is directed onto a digital sensor array," Isikman said. "The end result of this process is an image taken without using a lens."

Ozcan envisions this lens-free imaging system as one component in a lab-on-a-chip platform. It could potentially fit beneath a microfluidic chip, a tool for the precise control and manipulation of sub-millimeter biological samples and fluids, and the two tools would operate in tandem, with the microfluidic chip depositing and subsequently removing a sample from the lens-free imager in an automated, or high-throughput, process.

The platform's 3-D images are created by rotating the light source to illuminate the samples from multiple angles. These multiple angles also allow the system to utilize tomography, a powerful imaging technique. Through the use of tomography, the system is able to produce 3-D images without sacrificing resolution.

"The field of view of lens-based microscopes is limited because the lens focuses on a narrow area of a sample," Bishara said. "A lens-free microscope has both a much larger field of view and depth of field because the imaging is done by the digital sensor array and is not constrained by a lens."

The research was funded by grants from the National Science Foundation, the U.S. Office of Naval Research and the National Institutes of Health and was also supported by the Gates Foundation and the Vodafone Americas Foundation.

For more information on the Ozcan research group, visit http://innovate.ee.ucla.edu/.

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Holograms in True Color

Holograms in True Color

  9:46:00 PM    Science Lover

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Researchers have developed a new way to create true-color holograms that can be viewed from any angle using ordinary white light. The advance could lead to a new generation of electronic devices, such as cell phones or miniature televisions that display three-dimensional (3D) images.

In living color. This three-dimensional, true-color
image of an apple was generated using a new
technique of making holograms (inset) that allows
the image to be viewed using ordinary white light.

Credit: Science/AAAS

True 3D images can be created in several ways. In the 1960s, researchers generated the first holograms by firing a laser at an object and then using a photosensitive material to record the pattern of interference between light waves reflected off the object and those striking the material directly from the laser. This hologram, if later illuminated with the same wavelength of laser light, reproduced a 3D (but monochromatic) image of the object. One well-known hologram of that era captured in red laser light a chessboard on which pieces could be viewed from various angles as a viewer shifted position.

The so-called rainbow holograms now common on credit cards are generated differently, using white light reflected off a silvery backing through a plastic film that contains several images, each stored in a different color in its own layer. As the hologram is viewed from different angles, the shifting view of those colored layers with respect to one another provide a 3D perspective. In many cases, the image produced by these rainbow holograms isn’t a true-color representation of the object depicted.

Now, researchers report today in Science that they can create true-color holograms that can be viewed using only white light. Like the first holograms, the new technique uses lasers to generate an interference pattern, says Satoshi Kawata, a photonics physicist at Osaka University in Japan. To capture colors, Kawata and his colleagues illuminate the original object with three different lasers: red, blue, and green, the three primary colors of projected light. They store the hologram in a light-sensitive material coated with a thin layer of metal such as gold or silver, a veneer that contains free electrons that are easily excited when struck by radiation such as light waves.



To reproduce a 3D image, the researchers bathe the metal-sheathed material in ordinary white light, which contains all wavelengths of visible light (including red, blue, and green). That white light excites the free electrons; their resulting movements and oscillations (so-called surface plasmons) in turn give off light that regenerates the image—an image that combines the red, blue, and green versions of the hologram to generate a true-color representation of the original object. In their lab tests, Kawata and his colleagues created realistically hued holograms of an apple, a flower, a Japanese origami crane, and several other objects. For now, Kawata says, the new technique can produce only static holograms—no pint-sized Princess Leia pleading for help from Obi-Wan Kenobi just yet.

“It’s quite a scientific achievement,” says physicist Pierre-Alexandre Blanche of the University of Arizona in Tucson. The technique may be able to generate brighter images that can be seen through a broader range of viewing angles than holograms produced using other methods, adds media technologist V. Michael Bove Jr. of the Massachusetts Institute of Technology in Cambridge. The problem, he says, may be figuring out how to mass-produce images more cheaply than other techniques can.

Yet another issue may be scaling up the holograms to large size, says photonics physicist Nasser Peyghambarian of the University of Arizona. So far, the researchers apparently have created holograms only about the size of an index card. The prisms used to illuminate the holograms, which in the current scheme are mounted beneath or behind the metal-coated material, could easily become cumbersome in much larger displays, he contends.

Nevertheless, the notion of watching the Super Bowl on a coffee table with an embedded holographic display—complete with little linemen, wee wide receivers, even a tiny blimp floating a few feet above the potato chips and beer coasters—may someday become a reality to sports fans everywhere.

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New Light-Sensing Mechanism Found in Neurons

New Light-Sensing Mechanism Found in Neurons

  1:06:00 AM    Science Lover

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A UC Irvine research team led by Todd C. Holmes has discovered a second form of phototransduction light sensing in cells that is derived from vitamin B2. This discovery may reveal new information about cellular processes controlled by light.

This image shows blue-light sensing arousal neurons. (Credit: UCI)

For more than 100 years, it had been believed that the phototransduction process was solely based on a chemical derived from vitamin A called retinal. Phototransduction is the conversion of light signals into electrical signals in photoreceptive neurons and underlies both image-forming and non-image-forming light sensing.
In discovering this new light-sensing phototransduction mechanism, the UCI scientists found that phototransduction can also be mediated by a protein called cryptochrome, which uses a B2 vitamin chemical derivative for light sensing. Cryptochromes are blue-light photoreceptors found in circadian and arousal neurons that regulate slow biochemical processes, but this is the first time they have been linked to rapid phototransduction.

Their work appears March 3 on online Express site for the journal Science.

"This is totally novel mechanism that does not depend on retinal," said Holmes, a professor of physiology & biophysics. "This discovery opens whole new technology opportunities for adapting light-sensing proteins to drive medically relevant cellular activities."

This basic science breakthrough -- "which literally and figuratively came 'out of the blue,'" Holmes said -- has implications in the fast-growing field of optogenetics. Optogenetics combines optical and genetic research techniques to probe neural circuits at the high speeds needed to understand brain information processing. In one area, it is being used to understand how treatments such as deep brain massage can aid people with neurodegenerative diseases.

Holmes' team found that cryptochrome mediates phototransduction directly in fruit fly circadian and arousal neurons in response to blue-light wavelengths. The researchers also found that they could genetically express cryptochrome in neurons that are not ordinarily electrically responsive to light to make them light responsive.

Keri Fogel, Kelly Parson and Nicole Dahm of UCI contributed to the study, which received National Institutes of Health support.

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Researchers Create 'Quantum Cats' Made of Light

Researchers Create 'Quantum Cats' Made of Light

  9:18:00 PM    Science Lover

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Researchers at the National Institute of Standards and Technology (NIST) have created "quantum cats" made of photons (particles of light), boosting prospects for manipulating light in new ways to enhance precision measurements as well as computing and communications based on quantum physics.

These colorized plots of electric field values indicate how closely the NIST "quantum cats" (left) compare with theoretical predictions for a cat state (right). The purple spots and alternating blue contrast regions in the center of the images indicate the light is in the appropriate quantum state. (Credit: Gerrits/NIST)

The NIST experiments, described in a forthcoming paper, repeatedly produced light pulses that each possessed two exactly opposite properties -- specifically, opposite phases, as if the peaks of the light waves were superimposed on the troughs. Physicists call this an optical Schrödinger's cat. NIST's quantum cat is the first to be made by detecting three photons at once and is one of the largest and most well-defined cat states ever made from light. (Larger cat states have been created in different systems by other research groups, including one at NIST.)

A "cat state" is a curiosity of the quantum world, where particles can exist in "superpositions" of two opposite properties simultaneously. Cat state is a reference to German physicist Erwin Schrödinger's famed 1935 theoretical notion of a cat that is both alive and dead simultaneously.

"This is a new state of light, predicted in quantum optics for a long time," says NIST research associate Thomas Gerrits, lead author of the paper. "The technologies that enable us to get these really good results are ultrafast lasers, knowledge of the type of light needed to create the cat state, and photon detectors that can actually count individual photons."

The NIST team created their optical cat state by using an ultrafast laser pulse to excite special crystals to create a form of light known as a squeezed vacuum, which contains only even numbers of photons. A specific number of photons were subtracted from the squeezed vacuum using a device called a beam splitter. The photons were identified with a NIST sensor that efficiently detects and counts individual photons. Depending on the number of subtracted photons, the remaining light is in a state that is a good approximation of a quantum cat says Gerrits -- the best that can be achieved because nobody has been able to create a "real" one, by, for instance, the quantum equivalent to superimposing two weak laser beams with opposite phases.

NIST conducts research on novel states of light because they may enhance measurement techniques such as interferometry, used to measure distance based on the interference of two light beams. The research also may contribute to quantum computing -- which may someday solve some problems that are intractable today -- and quantum communications, the most secure method known for protecting the privacy of a communications channel. Larger quantum cats of light are needed for accurate information processing.

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Tiny Logo Demonstrates Advanced Display Technology Using Nano-Thin Metal Sheets

Tiny Logo Demonstrates Advanced Display Technology Using Nano-Thin Metal Sheets

  5:22:00 PM    Science Lover

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In a step toward more efficient, smaller and higher-definition display screens, a University of Michigan professor has developed a new type of color filter made of nano-thin sheets of metal with precisely spaced gratings.

An optical microscopy image of a 12-by-9-micron U-M logo 
produced with this new color filter process. (Credit: Jay Guo)

The gratings, sliced into metal-dielectric-metal stacks, act as resonators. They trap and transmit light of a particular color, or wavelength, said Jay Guo, an associate professor in the Department of Electrical Engineering and Computer Science. A dielectric is a material that does not conduct electricity.

"Simply by changing the space between the slits, we can generate different colors," Guo said. "Through nanostructuring, we can render white light any color."

A paper on the research is published Aug. 24 in Nature Communications.

His team used this technique to make what they believes is the smallest color U-M logo. At about 12-by-9 microns, it's about 1/6 the width of a human hair.

Conventional LCDs, or liquid crystal displays, are inefficient and manufacturing-intensive to produce. Only about 5 percent of their back-light travels through them and reaches our eyes, Guo said. They contain two layers of polarizers, a color filter sheet, and two layers of electrode-laced glass in addition to the liquid crystal layer. Chemical colorants for red, green and blue pixel components must be patterned in different regions on the screen in separate steps.

Guo's color filter acts as a polarizer simultaneously, eliminating the need for additional polarizer layers. In Guo's displays, reflected light could be recycled to save much of the light that would otherwise be wasted.

Because these new displays contain fewer layers, they would be simpler to manufacture, Guo said. The new color filters contain just three layers: two metal sheets sandwiching a dielectric. Red, green and blue pixel components could be made in one step by cutting arrays of slits in the stack. This structure is also more robust and can endure higher- powered light.

Red light emanates from slits set around 360 nanometers apart; green from those about 270 nanometers apart and blue from those approximately 225 nanometers apart. The differently spaced gratings essentially catch different wavelengths of light and resonantly transmit through the stacks.

"Amazingly, we found that even a few slits can already produce well-defined color, which shows its potential for extremely high-resolution display and spectral imaging," Guo said.

The pixels in Guo's displays are about an order of magnitude smaller than those on a typical computer screen. They're about eight times smaller than the pixels on the iPhone 4, which are about 78 microns. He envisions that this pixel size could make this technology useful in projection displays, as well as wearable, bendable or extremely compact displays.

The paper is called "Plasmonic nano-resonators for high resolution color filtering and spectral imaging."

Guo is also an associate professor in the Department of Macromolecular Science and Engineering. This research is supported in part by the Air Force Office of Scientific Research and the Defense Advanced Research Projects Agency. The university is pursuing patent protection for the intellectual property and is seeking commercialization partners to help bring the technology to market.

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