Taking a cue from master engineer Mother Nature, researchers have figured out how a type of firefly gives off light (Opt. Express 21, 764) and used the results to raise the light-extraction efficiency of an existing LED by 55 percent (Opt. Express 21, A179).
Annick Bay, a doctoral student at the University of Namur (Belgium), and her colleagues studied the morphology of the segments of the luminescent abdomens of fireflies of the genus Photuris. They modeled the propagation of 560 nm light—close to the peak wavelength of the flies’ emission—within these structures, and they experimentally checked their calculations by measuring the radiance of light beamed through pieces of the insects’ abdomens.
The team found that Photuris has “misfit” chitin scales, with one edge of each scale protruding a few micrometers outward. The scales create a corrugated “factory roof” surface that improves light extraction from the abdomen over a flat surface with the same refractive index. They used this pattern to design an LED overlayer, which increased light extraction by 55 percent. The researchers speculate that, with achievable modifications to current manufacturing techniques, it should be possible to apply these novel, energy-saving design enhancements to current LED production within the next few years. —Patricia Daukantas
Coordinating random scattered photons.
Can something be both random and organized? Apparently so. Although light scattering is a random process, photons emitted in a complex and disordered structure can travel mutually coordinated paths, according to researchers at the Niels Bohr Institute at the University of Copenhagen (Denmark). The findings provide new ways of enhancing light-matter interaction for quantum electrodynamics and energy harvesting and may find applications in subwavelength diffuse-wave spectroscopy for biophotonics.
Researcher David Garcia and his team tracked photons emitted by a quantum dot embedded in a disordered photonic crystal (Phys. Rev. Lett. 109, 253902). Due to the wavelike nature of light, the photons took different paths but were interdependent in the sense that the chance of observing a photon at one outlet was increased if another photon is seen at the other.
The emitters probed the microscopic details of the medium and imprinted the near-field properties onto the far-field correlations.
Garcia explains: “The photons are scattered in all directions … But photons are not just light particles, they are also waves, and waves interact with each other. This creates a link between the photons, and we can now demonstrate in our experiments that the photons’ path through the material is not independent from the other photons.”
The method might someday be used to measure the spatial properties of complex disordered materials such as biological tissue. —Yvonne Carts-Powell
Mechanical Switching Inside Optical Fibers
Once drawn, optical fibers are usually mechanically rigid—in other words, frozen forever. But scientists in the United Kingdom have used tiny mechanical interior movements to switch light between the two cores of a single glass fiber (Opt. Express 20, 29386). The experiments could lead to “smart fibers” for many telecommunications and sensing applications.
Research associate Zhenggang Lian and his colleagues at the University of Southampton’s Optoelectronics Research Centre constructed the nanomechanical fiber out of lead silicate glass, with the two cores independently suspended and yet optically coupled. At one point along the fiber, the researchers etched away the cladding to provide the outside environment with access to one of the cores.
The altered section was passed through a nitrogen-filled pressure chamber, which the team used to apply selective pressure on one of the cores. The researchers beamed polarized diode-laser light at a standard telecom wavelength (1,550 nm) down the fiber. By varying the chamber pressure by a few hundred millibars, the team moved one core by as much as 8 nm and switched the light between the two cores.
In future applications, electrostatic actuators, which are now used in many micro-electro-mechanical systems, could perform the tiny mechanical movements more quickly than the external pressure changes. Such nanoscale devices within fibers could move some of the switching, buffering and routing functions of a network from optoelectronic chips to the fibers themselves. Sensors could benefit from the fibers’ ability to detect minuscule pressure changes or vibrations in the environment. —Patricia Daukantas
Beating the Quantum Limit in Optical Communications
Teasing meaningful information out of a weak signal—whether in a child’s game of “telephone” or an optical network—can be difficult or impossible due to intrinsic noise. Now, scientists at the Joint Quantum Institute (JQI; U.S.A.) have devised a method for lowering the error rate of a quantum system below the standard quantum limit, which could lead to more efficient communications (Nature Photon, doi: 10.1038/nphoton.2012.316).
An ideal, 100-percent-efficient receiver can distinguish nonorthogonal coherent states down to a certain minimum level of error probability known as the standard quantum limit, according to Francisco Elohim Becerra, a postdoctoral researcher at JQI. Scientists can squeeze more information into a signal by encoding the data into multiple phases of light, but the higher the number of states or phases, the more difficult it is to distinguish them at the receiver, especially with low-intensity signals.
To “beat” the standard limit, the JQI team devised an adaptive feedback system that makes multiple assessments of the phase of the incoming signal. The receiver uses the first measurement to adjust itself before making the next measurement. The researchers tracked the experimental error probability involved in distinguishing among four states in the format known as quadrature phase-shift keying. The experiment yielded error probability that is 6 dB below the standard quantum limit for an ideal receiver. —Patricia Daukantas
Focusing Light to a Nanoscale Point
Squeezing light down to the smallest possible space is crucial for integrating tiny devices onto a single photonic chip and performing biomedical imaging. Scientists in California have built a tiny plasmonic waveguide that “nanofocuses” near-infrared light to a point less than 100 nm wide (Nature Photon., doi: 10.1038/nphoton.2012.277).
The tapered structure, consisting of silicon dioxide sandwiched between two layers of gold, is less than 2 µm in overall length, says Hyuck Choo, assistant professor of electrical engineering at the California Institute of Technology in Pasadena. The waveguide compresses light in the two dimensions perpendicular to the propagation of the radiation.
Computer simulations revealed the optimal geometry for the taper to produce nanofocusing. The bottom of the device remains flat for ease of on-chip implementation, with the sides and top narrowing from front to back.
The team focused 830-nm light from a femtosecond laser into a spot 14 nm by 80 nm, with an intensity 400 times greater than the original beam. By the group’s calculations, the smallest possible pinpoint of light that the tapered waveguide could produce would be 2 nm wide and 5 nm long, although they have not yet achieved that experimentally. —Patricia Daukantas
113th Congressional Committee Guides
Between the 2012 U.S. elections, retirements and committee chairmanship term limits, the new Congress holds a lot of changes for House and Senate committee rosters. To keep track of who’s who and what’s in store for the upcoming term, the OSA public policy team has put together committee-by-committee guides for both chambers. You can find them online at www.osa.org/about_osa/public_policy/washington_updates/.
Something New on the EU Horizon
“Horizon 2020” is the new, integrated funding system that will cover all research and innovation funding currently provided through the Framework Programme for Research and Technical Development, the Competitiveness and Innovation Framework Programme and the European Institute of Innovation and Technology. It combines these funding mechanisms in a way that allows for more award flexibility.
Horizon 2020 is a seven-year program that will evolve to incorporate a broader economic and policy framework as it progresses, with the goal of delivering ideas, growth and jobs for the future. It also will be a key tool in implementing the Innovation Union flagship initiative, which is aimed at securing Europe’s global competitiveness.
The proposed support for research and innovation under Horizon 2020 will:
- strengthen the EU’s position in science
- bolster industrial leadership in innovation, including major investments in technology and small- and medium-sized enterprises; and
- address concerns shared by most Europeans, including climate change, affordable renewable energy, elder care and food safety.
For information on funding opportunities, visit www.osa-opn.org/home/#tab-randd.
Strong Component Growth Predicted through 2019
A report released by Wintergreen Research (Lexington, Mass., U.S.A.) estimates that the optical component market will grow from $3.6 billion in 2012 to $12.3 billion by 2019. Optical Components: Market Shares, Strategy, and Forecasts, Worldwide, 2013 to 2019, available for purchase at www.ResearchandMarkets.com, covers optical communication network elements and infrastructure, which are expected to surge along with the growth of smart phone use and Internet data transmission. —Valerie Coffey
OLED TVs Reach Consumer Market
LG Electronics (Korea) launched a commercially available organic LED (OLED) television at this year’s Consumer Electronics Show (CES). The 55” OLED screen TVs will go on sale for about KRW 11M (US $10,000).
OLED TV technology enables the elimination of a backlight, resulting in ultra-thin displays only 4 mm thick compared to the conventional flat-screen thickness of 15 mm. The weight of the set is thus reduced to 10 kg (22 lb). OLED TVs also use less power to produce brighter and sharper images compared to LCD and plasma displays.
Samsung introduced a 55” OLED TV prototype at CES 2013, but a commercial launch date had not yet been announced as of press time. —Valerie Coffey