Tag Archives: photonic

Fully experimental image of a nanoscaled and ultrafast optical rogue wave retrieved by Near-field Scanning Optical Microscope (NSOM). The flow lines visible in the image represent the direction of light energy. 
Credit: KAUST

Tsunami on demand: the power to harness catastrophic events

A new study published in Nature Physics features a nano-optical chip that makes possible generating and controlling nanoscale rogue waves. The innovative chip was developed by an international team of physicists, led by Andrea Fratalocchi from KAUST (Saudi Arabia), and is expected to have significant applications for energy research and environmental safety.

Can you imagine how much energy is in a tsunami wave, or in a tornado? Energy is all around us, but mainly contained in a quiet state. But there are moments in time when large amounts of energy build up spontaneously and create rare phenomena on a potentially disastrous scale. How these events occur, in many cases, is still a mystery.

To reveal the natural mechanisms behind such high-energy phenomena, Andrea Fratalocchi, assistant professor in the Computer, Electrical and Mathematical Science and Engineering Division of King Abdullah University of Science and Technology (KAUST), led a team of researchers from Saudi Arabia and three European universities and research centers to understand the dynamics of such destructive events and control their formation in new optical chips, which can open various technological applications. The results and implications of this study are published in the journal Nature Physics.

“I have always been fascinated by the unpredictability of nature,” Fratalocchi said. “And I believe that understanding this complexity is the next frontier that will open cutting edge pathways in science and offer novel applications in a variety of areas.”

Fratalocchi’s team began their research by developing new theoretical ideas to explain the formation of rare energetic natural events such as rogue waves — large surface waves that develop spontaneously in deep water and represent a potential risk for vessels and open-ocean oil platforms.”

“Our idea was something never tested before,” Fratalocchi continued. “We wanted to demonstrate that small perturbations of a chaotic sea of interacting waves could, contrary to intuition, control the formation of rare events of exceptional amplitude.”

Fully experimental image of a nanoscaled and ultrafast optical rogue wave retrieved by Near-field Scanning Optical Microscope (NSOM). The flow lines visible in the image represent the direction of light energy.  Credit: KAUST
Fully experimental image of a nanoscaled and ultrafast optical rogue wave retrieved by Near-field Scanning Optical Microscope (NSOM). The flow lines visible in the image represent the direction of light energy.
Credit: KAUST

A planar photonic crystal chip, fabricated at the University of St. Andrews and tested at the FOM institute AMOLF in the Amsterdam Science Park, was used to generate ultrafast (163 fs long) and subwavelength (203 nm wide) nanoscale rogue waves, proving that Fratalocchi’s theory was correct. The newly developed photonic chip offered an exceptional level of controllability over these rare events.

Thomas F. Krauss, head of the Photonics Group and Nanocentre Cleanroom at the University of York, UK, was involved in the development of the experiment and the analysis of the data. He shared, “By realizing a sea of interacting waves on a photonic chip, we were able study the formation of rare high energy events in a controlled environment. We noted that these events only happened when some sets of waves were missing, which is one of the key insights our study.”

Kobus Kuipers, head of nanophotonics at FOM institute AMOLF, NL, who was involved in the experimental visualization of the rogue waves, was fascinated by their dynamics: “We have developed a microscope that allows us to visualize optical behavior at the nanoscale. Unlike conventional wave behavior, it was remarkable to see the rogue waves suddenly appear, seemingly out of nowhere, and then disappear again…as if they had never been there.”

Andrea Di Falco, leader of the Synthetic Optics group at the University of St. Andrews said, “The advantage of using light confined in an optical chip is that we can control very carefully how the energy in a chaotic system is dissipated, giving rise to these rare and extreme events. It is as if we were able to produce a determined amount of waves of unusual height in a small lake, just by accurately landscaping its coasts and controlling the size and number of its emissaries.”

The outcomes of this project offer leading edge technological applications in energy research, high speed communication and in disaster preparedness.

Fratalocchi and the team believe their research represents a major milestone for KAUST and for the field. “This discovery can change once and for all the way we look at catastrophic events,” concludes Fratalocchi, “opening new perspectives in preventing their destructive appearance on large scales, or using their unique power for ideating new applications at the nanoscale.”The title of the Nature Physics paper is “Triggering extreme events at the nanoscale in photonic seas.” The paper is accessible on the Nature Photonics website: http://dx.doi.org/10.1038/nphys3263

Source : KAUST News

Illustration of superconducting detectors on arrayed waveguides on a photonic integrated circuit for detection of single photons.

Credit: F. Najafi/ MIT

Toward quantum chips

Packing single-photon detectors on an optical chip is a crucial step toward quantum-computational circuits.

By Larry Hardesty


CAMBRIDGE, Mass. – A team of researchers has built an array of light detectors sensitive enough to register the arrival of individual light particles, or photons, and mounted them on a silicon optical chip. Such arrays are crucial components of devices that use photons to perform quantum computations.

Single-photon detectors are notoriously temperamental: Of 100 deposited on a chip using standard manufacturing techniques, only a handful will generally work. In a paper appearing today in Nature Communications, the researchers at MIT and elsewhere describe a procedure for fabricating and testing the detectors separately and then transferring those that work to an optical chip built using standard manufacturing processes.

Illustration of superconducting detectors on arrayed waveguides on a photonic integrated circuit for detection of single photons. Credit: F. Najafi/ MIT
Illustration of superconducting detectors on arrayed waveguides on a photonic integrated circuit for detection of single photons.
Credit: F. Najafi/ MIT

In addition to yielding much denser and larger arrays, the approach also increases the detectors’ sensitivity. In experiments, the researchers found that their detectors were up to 100 times more likely to accurately register the arrival of a single photon than those found in earlier arrays.

“You make both parts — the detectors and the photonic chip — through their best fabrication process, which is dedicated, and then bring them together,” explains Faraz Najafi, a graduate student in electrical engineering and computer science at MIT and first author on the new paper.

Thinking small

According to quantum mechanics, tiny physical particles are, counterintuitively, able to inhabit mutually exclusive states at the same time. A computational element made from such a particle — known as a quantum bit, or qubit — could thus represent zero and one simultaneously. If multiple qubits are “entangled,” meaning that their quantum states depend on each other, then a single quantum computation is, in some sense, like performing many computations in parallel.

With most particles, entanglement is difficult to maintain, but it’s relatively easy with photons. For that reason, optical systems are a promising approach to quantum computation. But any quantum computer — say, one whose qubits are laser-trapped ions or nitrogen atoms embedded in diamond — would still benefit from using entangled photons to move quantum information around.

“Because ultimately one will want to make such optical processors with maybe tens or hundreds of photonic qubits, it becomes unwieldy to do this using traditional optical components,” says Dirk Englund, the Jamieson Career Development Assistant Professor in Electrical Engineering and Computer Science at MIT and corresponding author on the new paper. “It’s not only unwieldy but probably impossible, because if you tried to build it on a large optical table, simply the random motion of the table would cause noise on these optical states. So there’s been an effort to miniaturize these optical circuits onto photonic integrated circuits.”

The project was a collaboration between Englund’s group and the Quantum Nanostructures and Nanofabrication Group, which is led by Karl Berggren, an associate professor of electrical engineering and computer science, and of which Najafi is a member. The MIT researchers were also joined by colleagues at IBM and NASA’s Jet Propulsion Laboratory.

Relocation

The researchers’ process begins with a silicon optical chip made using conventional manufacturing techniques. On a separate silicon chip, they grow a thin, flexible film of silicon nitride, upon which they deposit the superconductor niobium nitride in a pattern useful for photon detection. At both ends of the resulting detector, they deposit gold electrodes.

Then, to one end of the silicon nitride film, they attach a small droplet of polydimethylsiloxane, a type of silicone. They then press a tungsten probe, typically used to measure voltages in experimental chips, against the silicone.

“It’s almost like Silly Putty,” Englund says. “You put it down, it spreads out and makes high surface-contact area, and when you pick it up quickly, it will maintain that large surface area. And then it relaxes back so that it comes back to one point. It’s like if you try to pick up a coin with your finger. You press on it and pick it up quickly, and shortly after, it will fall off.”

With the tungsten probe, the researchers peel the film off its substrate and attach it to the optical chip.

In previous arrays, the detectors registered only 0.2 percent of the single photons directed at them. Even on-chip detectors deposited individually have historically topped out at about 2 percent. But the detectors on the researchers’ new chip got as high as 20 percent. That’s still a long way from the 90 percent or more required for a practical quantum circuit, but it’s a big step in the right direction.

Source: MIT News Office