Cover story

Anyone who has ever visited a ski resort will be familiar with the concept of a 'snow blower' — a machine that takes snow from one location and blows it to another, sending it through the air in a long wide arc. An analogous effect is demonstrated in this issue in the field of optics, with micrometre-sized glass particles transported by curved optical Airy beams from one location to another. The research, described by Jörg Baumgartl, Michael Mazilu and Kishan Dholakia from the University of St Andrews, UK, as “optically mediated particle clearing”, is the first example of an application for Airy beams, which were observed in the optical domain for the first time last year. Adding to existing capabilities in optical micromanipulation, such as tweezing and sorting, the scheme may prove useful in biology and colloidal science. [Letter p675 ; News & Views p652 ; Interview p702 ]

Plasmon beam source

A convenient electronic source of surface plasmons would prove to be a highly useful part of the nanophotonics toolbox of the future. Now, Daniel Koller and co-workers from Karl-Franzens University and Graz University of Technology have used a red organic LED (OLED) to create an electrically switchable source of plasmons that are emitted in a freely propagating beam. The device could prove useful for the construction of integrated organic circuits that exploit plasmons, or lead to organic devices for sensing and photovoltaics with improved performance. The plasmons are able to propagate up to tens of micrometres outside the OLED along a gold layer, and the researchers say that potentially this distance could be improved by using silver instead of gold or by optimizing the wavelength of the OLED. [Letter p684 ]

Total control

The integration of light sources with three-dimensional photonic crystals (3D-PhCs) is important for gaining complete control over photons and creating new types of optical devices for applications such as quantum computing. In this issue, Kanna Aoki and co-workers from the University of Tokyo report a study of the coupling of light from quantum dots embedded inside such 3D-PhCs. The 3D-PhC structure was made by stacking planar plates of microstructured GaAs and inserting an InAsSb quantum dot emitting light at 1.5 μm in the centre of one such plate. The result was construction of the highest-quality-factor (Q = 2,300) 3D-PhC, so far. During the assembly process photoluminescence spectra were taken showing how the light from the quantum dot couples into the defect modes of the PhC. The experimental measurements agree well with theoretical predictions for 3D-PhC behaviour, suggesting that such coupled systems could indeed be useful building blocks in the future for controlling light at the quantum level. [ Article p688 ; News & Views p650 ]

Double-sided cells

Dye-sensitized solar cells (DSCs) have come a long way since the pioneering experiments in the 1990s, and today optimized devices are able to boast efficiencies of around 10–11%. In this issue, Seigo Ito and co-workers from the University of Hyogo in Japan and École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland report a bifacial design that is based on an ionic liquid electrolyte (non-flammable, non-toxic). The solar cell is suitable for outdoor deployment and has almost the same conversion efficiency of around 6% when illuminated from either the front or rear surface. Key to the cell's performance is the use of a transparent layer of SiO2 particles to help guide light from the rear surface to the active conversion region of TiO2 particles, and careful optimization of the thickness of the TiO2 layer. [Article p693 ; News & Views p648 ]

Silk in optics

By pouring silk solution on to a patterned substrate, optical elements such as this 50-μm-thick white-light hologram can be created.

Natural silk has been a popular fabric for many years and is known to have the attractive qualities of great strength and comfort. Now scientists are starting to realize that it may also have a valuable role to play in photonics. Fiorenzo Omenetto and David Kaplan from Tufts University, USA, describe how silk could be used for creating high-performance biocompatible optical devices, such as diffraction gratings and thin films that can be doped with biologically active substances. The research may ultimately lead to a new breed of biofriendly photonic devices, such as sensors, with the added benefit that silk is easy to process and biodegradable. [Commentary p641 ]

Ultrahigh-performance fibre

The ability to guide ultrashort (less than 100 fs) laser pulses over substantial lengths of optical fibre is potentially useful for many applications, including materials processing, two-photon microscopy and photodynamic therapy. Unfortunately, issues in normal designs of fibre, such as dispersion and nonlinearity, stretch and distort transmitted pulses. Now, Julia Skibina and her co-workers have demonstrated that a chirped photonic-crystal fibre can overcome these problems. Their silica fibre has a large hollow core surrounded by a network of microstructured cells arranged in a series of concentric rings. The important aspect of the design is that the cells are chirped in size, that is, the cell size increases with the distance from the core. The chirp serves to almost eliminate the fibre's dispersion, allowing pulses as short as 13 fs to travel along a metre of fibre and only broaden by a factor of two in duration. In other fibres such short pulses would be broadened to many hundreds of femtoseconds or picoseconds in duration. This performance does have a cost though — a higher attenuation compared with other fibre designs. [Letter p679 ; News & Views p647 ]