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news digest ♦ Lasers it won’t perform at all.


“These holes are almost perfectly round with smooth interior walls and are very important to the laser’s function. They act like a hall of mirrors to reflect photons back toward the centre of the laser,” said Vuckovic.


Here, in the heart of the wafer, the photons are concentrated and amplified into a tiny ball of light, a laser which can be modulated up to 100 billion times per second, 10 times the best data transmitters now in use. Thus the light becomes binary data – light on, 1; light off, 0.


At one end of a semiconductor circuit is a laser transmitter beaming out 1s and 0s as blasts of light. At the other end is a receiver that turns those blasts of light back into electrical impulses. All that is needed is a way to connect the two.


To do this, the researchers heat and stretch a thin fibreoptic filament, hundreds of times thinner than a human hair. The light from the laser travels along the fibre to the next junction in the circuit.


All this happens in a layer so thin hundreds of these nanophotonic transmitters could be arranged on a single layer, and many layers could then be stacked into a single chip.


Before Vuckovic’s laser interconnect becomes commonplace, however, certain questions will need to be resolved. The new laser operates at relatively cold temperatures, 150 degrees Kelvin and below – about 190 degrees below zero Fahrenheit – but Vuckovic is confident and pressing forward.


“With improvements in processing,” she said, “we can produce a laser that operates at room temperature while maintaining energy efficiency at about 1,000 times less than today’s commercial technologies. We can see a light on the horizon.”


Kovic’s engineering research was made possible by funding from Stanford Graduate Fellowships, the Interconnect Focus Centre and the Air Force Office of Scientific Research.


Further details of this work have been published in the paper “Ultralow-threshold electrically pumped quantum-dot photonic-crystal nanocavity laser” by Bryan Ellis et al, in Nature Photonics 5, 297– 300,


144 www.compoundsemiconductor.net October 2011


Darwin Serkland measures the wavelength of the VCSEL. The image on the monitor (left) shows a bright circle of light emitted from a 894 nm VCSEL needed to drive the atomic clock. The objects that look like black baseball bats are tiny wire needles carrying milliampere currents. The round white plastic containers on Serkland’s workbench each contain about 5,000


(2011). doi:10.1038/nphoton.2011.51


VCSEL slashes power consumption in atomic clock


The GaAs based VCSEL operating at a wavelength of 894 nm operates at only 2 mW, and consumes over a thousand times less power than the conventional light source used in atomic clocks, a rubidium-based atomic vapour lamp.


A matchbook-sized atomic clock 100 times smaller than its commercial predecessors has been created by a team of researchers at Symmetricom Inc. Draper Laboratory and Sandia National Laboratories.


The portable Chip Scale Atomic Clock (CSAC), only about 1.5 inches on a side and less than a half-inch in depth, also requires 100 times less power than its predecessors; instead of 10 W, it uses only 100 mW.


“It’s the difference between lugging around a device powered by a car battery and one powered by two AA batteries,” said Sandia lead investigator Darwin Serkland.


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