On-Chip Photonics Advance
France’s III-V Lab said it has developed a tunable laser on silicon. The lab has been working on integrated photonic circuits which combine the active and passive functions of III-V- and silicon-based devices for telecommunications and data transfer.
The III-V lab, near Paris, is working towards fully integrated transceivers.
A joint lab of Alcatel-Lucent Bell Labs France, Thales Research and Technology, and CEA-Leti, the III-V lab said it has demonstrated single-wavelength tunable lasers with a 21mA threshold at 20°C, a 45nm tuning range and side mode suppression ratio larger than 40dB over the tuning range.
CEA-Leti and the III-V lab have been working to integrate on-chip devices, including a fully integrated transmitter working above 10Gb/s, as well as tunable single wavelength lasers. They represent key milestones towards fully integrated transceivers, said the III-V lab, which is located near Paris at two sites, Marcoussis and Palaiseau, and which includes about 100 permanent researchers and 25 PhD students.
ASTAR Simulates Nanotwinned Copper
Singapore’s A*STAR Institute for High Performance Computing has been simulating a form of copper known as nanotwinned copper, which may have semiconductor applications.
Using molecular dynamics simulations, the institute reported in a Science article that nanotwinned polycrystalline copper has been shown to possess “simultaneous ultra-high strength and ductility” with a maximum strength found at a small, finite twin spacing.
The simulations addressed questions arising from previous, unexplained experimental data which indicate that the crystal structure of nanotwinned copper exhibits many closely-spaced interruptions in an otherwise regular atomic array. “These interruptions, despite being termed ‘defects,’ actually increase the metal’s strength without reducing its ductility,” researcher Zhaoxuan Wu and co-workers reported.
Schematic illustrations of the (a) crystallographic orientation between nanotwins and (b) slip systems for nanotwinned grains. (Source: ASTAR)
In 2009, the researchers had observed that the strength of nanotwinned copper reached a maximum when the size of the defects in its crystal structure was about 15 nanometers. When the defects were made smaller or larger, the copper’s strength decreased. This contradicted the classical model, which predicted that the metal’s strength would increase continually as the defect size was reduced.
Wu and co-workers addressed this contradiction by using a very large-scale molecular dynamics simulation to calculate how a nanotwinned copper crystal consisting of more than 60 million atoms deforms under pressure.
Cornell Studies Iron-based Superconductors
Cornell researchers have confirmed some predictions about how iron-based high-temperature superconductors work. According to an article in the British publication, The Engineer, various research teams have discovered compounds of iron, arsenic and other elements which become superconductors at much higher temperatures. Early superconductor research focused on metals cooled to near absolute zero.
The Cornell University team studied electrons that have paired up with twins from adjacent atoms to form ‘Cooper pairs’ that move through the conductor without interference. “It is believed that Cooper pairs form when two electrons with opposite spins join up, analogous to two bar magnets snapping together with their north and south poles meeting,” the article in the U.K. publication said.
Anisotropic energy gaps of LiFeAs superconductors. (Source: Cornell University)
Studying crystals of a compound of lithium, iron and arsenic − LiFeAs − that becomes a superconductor at 15K, the Cornell researchers found three of the five possible electron bands.
‘There are two more pairing gaps that we should have been able to detect, and we don’t know yet why not,’ said team leader Séamus Davis of Cornell University. ‘But finding these three along with the directionality is enough to strongly support the theory, and the measurements give the theorists numbers to plug in to refine and extend their predictions.’
An article on the research appeared in Science magazine, saying that the lab’s measurements “will advance the quantitative theoretical analysis of the mechanism of Cooper pairing in iron-based superconductivity.”
