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is opening up new LED applications in general illumination, in projection and in the industrial sector.
Researchers Raise the Bar for Tetrahertz Switching with GaAs Nanodevices
The scientists have identified a way in which GaAs emitters and detectors functioning at terahertz speeds can be used in optical switching for use in optical communication and eventually quantum computing.
Physicists in the United States and Germany have discovered a way to use a gallium arsenide (GaAs) nanodevice as a signal processor at “terahertz” speeds, the first time it’s been used for this purpose and an important step forward in the new world of optical communication and computing.
The record efficiency for an LED of 119 lm/W at an operating current of 350 mA (136 lm/W at 70mA) has been achieved by the latest generation of a red 1 mm² thin-film chip (InGaAlP). The chip is accommodated in a Golden Dragon Plus package and emits at a wavelength of 615 nm (λ dominant). At present, Osram claim that there is no LED with higher efficiency at this wavelength. Its efficiency has been measured at 44% (49% at 70mA), and even exceeds 50% for a wavelength of 642 nm.
Higher efficiency means greater output for the same current and lower power consumption in the relevant applications. There are also new design options because fewer chips will be needed and therefore less space to produce the same brightness. In addition, almost 50% less waste heat needs to be removed, which in turn considerably reduces the need for cooling. As brightness increases, the light sources can be made smaller and smaller.
The improved performance of the LEDs greatly expands the possible applications for this innovative light source. For example, exceptionally high efficiency means that warm white LED solutions can be produced with better quality of light and a better energy balance through color mixing than through the usual conversion of blue light.
“This will benefit all applications that use high- efficiency red, particularly projection applications. We expect to start equipping LED products with the new thin-film chips in about a year’s time,” said Wolfgang Schmid, who is responsible for developing this chip technology at Osram.
Existing communications and computer architecture are increasingly being limited by the pedestrian speed of electrons moving through wires, and the future of high-speed communication and computing is in optics, experts say. The Holy Grail of results would be “wireless interconnecting,” which operates at speeds 100 to 1,000 times faster than current technology.
The new discovery, made by researchers at Oregon State University, the University of Iowa and Philipps University in Germany, has identified a way in which nanoscale devices based on gallium arsenide can respond to strong terahertz pulses for an extremely short period, controlling the electrical signal in a semiconductor. The research builds on previous findings for which OSU holds an issued patent.
“Optical communication uses the extraordinary speed of light as the signal, but right now it’s still controlled and limited by electrical signaling at the end,” said Yun-shik Lee, an associate professor in the OSU Department of Physics. “Electrons and wires are too slow, they’re a bottleneck. The future is in optical switching, in which wires are replaced by emitters and detectors that can function at terahertz speeds.”
The gallium arsenide devices used in this research can do that, the scientists discovered.
“This could be very important,” Lee said. “We were able to manipulate and observe the quantum system, basically create a strong response and the first building block of optical signal processing.”
The first applications of this type of technology, Lee August/September 2010
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