Yorktown Heights, NY--A silicon-based nanophotonic avalanche photodetector capable of receiving optical signals at a record rate of 40 Gbit/s was unveiled last week by IBM scientists at the T. J. Watson Research Center. The device, which is detailed in the March issue of the journal Nature, is the fastest of its kind and could enable breakthroughs in energy-efficient computing that can have significant implications for the future of electronics. A germanium photodetector that can be monolithically integrated with silicon transistor technology is seen as a key element of on-chip interconnects. Such a device must detect very-low-power optical signals at very high speed. Although germanium avalanche photodetectors (APDs) can achieve high gain and thus detect low-power optical signals, they also exhibit high amplification noise. High gain with low excess noise has been demonstrated using a germanium layer only for detection of light signals, with amplification taking place in a separate silicon layer, but the relatively thick semiconductor layers required in such structures limit APD speeds to about 10 GHz, and require excessively high bias voltages of around 25 V. The IBM device uses a very thin layer of germanium to speed up operation. The avalanche multiplication takes place within just a few tens of nanometers and it happens very fast. The tiny size also means that multiplication noise is suppressed by 50% - 70% with respect to conventional APDs. Moreover, the device requires a low bias voltage of just 1.5 V. And of course, a major attraction of a silicon/germanium device is that both materials already are widely used in production of microprocessor chips, which means the APD can be fabricated alongside other chips using standard CMOS processes. “This dramatic improvement in performance is the result of manipulating the optical and electrical properties at the scale of just a few tens of atoms to achieve performance well beyond accepted boundaries,” said Dr. Assefa, the lead author on the Nature paper. “These tiny devices are capable of detecting very weak pulses of light and amplifying them with unprecedented bandwidth and minimal addition of unwanted noise.” According to IBM Research, this APD is the last piece of the puzzle that completes development of the “nanophotonics toolbox” of devices necessary to build on-chip interconnects. In December 2006, IBM demonstrated a silicon nanophotonic delay line--a requirement for building optical buffers for on-chip optical communications. In December 2007, IBM announced development of an ultra-compact silicon-based electro-optic modulator--a prerequisite for enabling on-chip optical communications. Then in March 2008 IBM scientists announced the world’s tiniest nanophotonic switch for on-chip optical communications, ensuring that optical messages can be efficiently routed.“This invention brings the vision of on-chip optical interconnections much closer to reality,” said Dr. T.C. Chen, vice president, Science and Technology, IBM Research. “With optical communications embedded into the processor chips, the prospect of building power-efficient computer systems with performance at the Exaflop level might not be a very distant future.”
Further more information visit http://www.research.ibm.com/photonicsPosted by Steve Andersonwww.laserfocusworld.com
Further more information visit http://www.research.ibm.com/photonicsPosted by Steve Andersonwww.laserfocusworld.com
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