A method to selectively enhance or inhibit optical nonlinearities in a chip-scale device has been developed by scientists, led by the University of Sydney. The researchers from the Centre for Ultrahigh bandwidth Devices for Optical Systems, (CUDOS) based at the University of Sydney published their results in today ("Enhancing and inhibiting stimulated Brillouin scattering in photonic integrated circuits"). 
from left: Professor Benjamin Eggleton, Thomas Büttner and Moritz Merklein, researchers from CUDOS at the University of Sydney with the chalcogenide photonic chip. “This breakthrough is a fundamental advance for research in photonic chips and optical communications,” said Moritz Merklein, lead author from the University’s School of Physics. “In optical communications systems optical nonlinearities are often regarded as a nuisance, which corrupts the flow of information. But at the same time there are many useful applications that harness these nonlinear effects. We showed that we can dramatically enhance the optical nonlinearity so that it can be made even more useful. On the other hand we showed that we can completely suppress the same nonlinear optical effects using the same principle. Importantly our experiments were performed in a photonic chip.” To achieve their result the scientists investigated a specific optical nonlinearity that deals with the interaction between light and sound on chip scale devices. “The effect we looked at (known as stimulated Brillouin scattering) occurs when two optical waves and an acoustic wave interact. If the optical wave travelling along a fibre is disrupted - scattered - by the acoustic wave, it produces a backward traveling wave, called the Stokes wave. This nonlinear scattering process can cause signal distortions in fibre communications and signal processing applications and is well known to limit the capacity of optical fiber communications networks. “While we want to avoid this disruption this effect has also some unique properties which can be harnessed for important applications in manipulating microwave signals and developing certain types of lasers. So we have shown that we can selectively enhance or inhibit this interaction, depending on the context or application. We think this approach can be generalized to many other optical nonlinearities.” To address this, the researchers introduced a grating structure on to the chip. The grating, which comprises a small modulation in the optical material properties, forms a bandgap for light, which strongly effects the propagation of light, in the same way that semiconductors control the flow of electrons. When the laser wavelength is tuned close to the edge of the bandgap, the speed of light is reduced. This will greatly enhance the optical nonlinearity. At a slightly different frequency, the bandgap will completely inhibit (or suppress) the optical nonlinearity. The grating can be tuned so that the optical nonlinearity can be turned on and off on-demand. “On-chip optical research is a thriving and competitive area because of its importance to manipulating classical or quantum signals in small devices, essential for future communications, computing and information processing applications,” said CUDOS director and co-author Ben Eggleton. “I am delighted our CUDOS team at the University of Sydney, in collaboration with our CUDOS colleagues at the Australian National University have achieved this fundamental important result.”
from left: Professor Benjamin Eggleton, Thomas Büttner and Moritz Merklein, researchers from CUDOS at the University of Sydney with the chalcogenide photonic chip. “This breakthrough is a fundamental advance for research in photonic chips and optical communications,” said Moritz Merklein, lead author from the University’s School of Physics. “In optical communications systems optical nonlinearities are often regarded as a nuisance, which corrupts the flow of information. But at the same time there are many useful applications that harness these nonlinear effects. We showed that we can dramatically enhance the optical nonlinearity so that it can be made even more useful. On the other hand we showed that we can completely suppress the same nonlinear optical effects using the same principle. Importantly our experiments were performed in a photonic chip.” To achieve their result the scientists investigated a specific optical nonlinearity that deals with the interaction between light and sound on chip scale devices. “The effect we looked at (known as stimulated Brillouin scattering) occurs when two optical waves and an acoustic wave interact. If the optical wave travelling along a fibre is disrupted - scattered - by the acoustic wave, it produces a backward traveling wave, called the Stokes wave. This nonlinear scattering process can cause signal distortions in fibre communications and signal processing applications and is well known to limit the capacity of optical fiber communications networks. “While we want to avoid this disruption this effect has also some unique properties which can be harnessed for important applications in manipulating microwave signals and developing certain types of lasers. So we have shown that we can selectively enhance or inhibit this interaction, depending on the context or application. We think this approach can be generalized to many other optical nonlinearities.” To address this, the researchers introduced a grating structure on to the chip. The grating, which comprises a small modulation in the optical material properties, forms a bandgap for light, which strongly effects the propagation of light, in the same way that semiconductors control the flow of electrons. When the laser wavelength is tuned close to the edge of the bandgap, the speed of light is reduced. This will greatly enhance the optical nonlinearity. At a slightly different frequency, the bandgap will completely inhibit (or suppress) the optical nonlinearity. The grating can be tuned so that the optical nonlinearity can be turned on and off on-demand. “On-chip optical research is a thriving and competitive area because of its importance to manipulating classical or quantum signals in small devices, essential for future communications, computing and information processing applications,” said CUDOS director and co-author Ben Eggleton. “I am delighted our CUDOS team at the University of Sydney, in collaboration with our CUDOS colleagues at the Australian National University have achieved this fundamental important result.”
a) 105°C in air b) 115°C in air, c) 125°C in air, d) 105°C in Nitrogen, e) 115°C in Nitrogen, and f) 125°C in Nitrogen. Grain sizes on perovskite films are larger when prepared in air between 105 to 125 degrees centigrade than in a nitrogen atmosphere. (click on image to enlarge) The type of material is called Perovskite. Since the discovery of its application in harvesting light for electricity in 2009, research on solar cell application has skyrocketed. Fabrication techniques are being developed around the world to improve their power conversion efficiencies. The OIST study gives perovskite solar cells another shot in the arm by making the materials easier to mass produce. Earlier studies had concluded that exposing perovskite films to ambient air was detrimental because moisture reacted with perovskite, which degraded over time. It was therefore believed the material had to be prepared using a heat treatment called annealing in a water-free environment. OIST researchers set out to investigate the effects of moisture on perovskite formation during 45 minutes of annealing, at temperatures between 105 and 125 degrees centigrade. They grew a type of perovskite that has been shown to work better for solar cells. Then, they compared the Perovskite film's formation in a nitrogen atmosphere with its formation in humid air and found that the films actually receive a growth improvement resulting in larger grain sizes than usual in the presence of moisture. The film grows slowly, so larger grains can form. 
Voltage curves of two perovskite solar cells annealed in air (red) and Nitrogen (black). The average power conversion efficiency for 6 solar cells annealed in air was 11.1%. In a nitrogen atmosphere it was 8.5%. "Larger grain sizes mean the crystals on the film is more continuous, and the electrons passing through the film face fewer interruptions," said Sonia Ruiz-Raga, the study’s first author. Larger grains make perovskite solar cells more efficient. The highest efficiency achieved by the study was 12.7 percent. While other teams have achieved higher efficiencies, the OIST result ensures that future industries need not invest in expensive climate control machinery to keep the moisture down to one part per million. Air annealing costs nothing. Overall, 12.7 percent efficiency is by no means the ceiling for this fabrication technique and it is possible to obtain even larger grain sizes. While global research and development to boost solar cell efficiencies continue, these results potentially provide a way to jumpstart industry.
A facile and efficient method has been developed to fabricate bright quantum-dot-sized single-chain conjugated polyelectrolyte probes for specific extracellular labeling and imaging. (© WILEY-VCH Verlag) The team’s method is elegant in its simplicity — it improves the optical properties of the probes by just varying the size and shape of the nanoparticles ("Bright Quantum-Dot-Sized Single-Chain Conjugated Polyelectrolyte Nanoparticles: Synthesis, Characterization and Application for Specific Extracellular Labeling and Imaging"). “This allows us to circumvent complicated molecular design and synthesis processes,” explains Liu. “It provides a facile but efficient method for developing highly far-red–near-infrared fluorescent probes.” The researchers produced the nanoparticles in water by two methods — stirring and ultrasonication (that is, ‘shaking’ at very high frequencies). Ultrasonication yielded nanoparticles with average sizes of 4 nanometers, which is considerably smaller than their stirred counterparts. These nanoparticles were also much brighter, having a quantum yield of 26 per cent in water — more than five times brighter than the nanoparticles produced by stirring. Liu explains that ultrasonication produces polymer chains that are closer together, resulting in “compact structures that can effectively prevent water invasion and thus suppress quenching, yielding enhanced fluorescence.” The researchers then tested the behavior of the nanoparticles produced by sonication in a biological setting to determine whether they would be effective probes for a specific biological target. They chose streptavidin, a protein that has a high affinity for epithelial cell adhesion molecule (EpCAM) — a common biomarker for various cancers. After conjugating streptavidin to the surfaces of the nanoparticles, the researchers investigated the nanoparticles’ effectiveness as an extracellular probe for EpCAM by employing MCF-7 breast cancer cells as a model cell line (see image). The nanoparticles exhibited an excellent photostability and a much higher fluorescence than a commercially available probe (Cy3-SA). Liu notes that by switching streptavidin with another protein the same nanoparticles could be used to target other biomarkers. “This will lead to a new generation of fluorescent probes for image-guided therapy,” she says.
High-performance solar cells can be produced using inexpensive materials by minimizing the copper-rich and interfacial insulating layers in the interface between the cupric oxide (CuO) and silicon (Si) layers. (Image: A*STAR Institute of Materials Research and Engineering) On paper, copper oxide and silicon are a perfect pair for producing high-performance solar cells. In practice, however, their performance has been disappointing because of the tendency of holes and electrons to recombine in them — a process known as charge recombination. This recombination limits the production of electricity in a solar cell since it reverses the generation of electrical charges from light. One cause of this problem is the poor quality of the interface between copper oxide and silicon as the result of silicon oxide on the silicon surface. Now, Goutam Dalapati from the A*STAR Institute of Materials Research and Engineering at Singapore and co-workers have used conventional procedures to produce high-performance solar cells that employ cupric oxide as the p-type material and silicon as the n-type material. They realized this by increasing the pressure during the deposition stage of fabrication, which they found enhances both the crystal and interface quality, thereby reducing the charge recombination rate. Using a sequence of analytical techniques — Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy — they showed that the interface quality was limited by the formation of a copper-rich oxide layer as well as by the production of a silicon oxide layer on silicon surface. Dalapati explains that the team were surprised by the formation of this copper-rich layer as the cupric oxide target contained an equal mix of copper and oxygen. But the scientists also discovered that they could minimize this layer by increasing the pressure during deposition and the annealing time. Using this tactic, the team successfully produced a high-quality solar cell that had a low charge recombination rate. Dalapati notes that “to develop cost-effective, environmentally friendly photovoltaic devices using Earth-abundant nontoxic cupric oxide, it is essential that we can increase the efficiency further.” This is possible, he adds, “by reducing, or even eliminating, the copper-rich interfacial layer and the silicon oxide insulating layer.”