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IBM hits new record for data density and optical signal latency

Contrary to pessimistic forecasts that optical technologies will not be integrated into semiconductor integrated circuits anytime soon, IBM today announces that it has reached new records in the size of speed, density and bandwidth of photonic devices. Last year, scientists at the IBM Research Center named after. Thomas J. Watson have already reported on the creation of miniature arrays of ring optical fibers, which make it possible to “slow down” light pulses (see. article Yu. Vlasova with comrades). Scientists have made progress this year in miniaturizing these nanoscopic devices, rivaling the level of integration of CMOS electronic ICs.

IBM ring resonators are only 6 microns in size, which allows the delay line to be placed on a silicon substrate in an area of ​​0.03 sq. mm. The previous record was held by Alcatel-Lucent Bell Laboratories, and their delay line was several millimeters long.

Optical delay lines are made on a 200-mm silicon substrate using SOI (silicon-on-insulator) technology. The thickness of the silicon layer is 226 nm, of the oxide – 2 microns. The resulting waveguides have a cross section of 510×226 nm and transmit well single-mode radiation at a wavelength of 1.55 μm – the loss is 1.7 dB / cm.

The resulting CMOS chips provide nanosecond latency times that can be used in commercial fiber-optic switches to queue up concurrent packets. Now, to unload fiber-optic switches in such a situation, optical signals have to be converted into electrical ones and stored in DRAM – with their subsequent forwarding by the transceiver as it becomes available.

An important problem that IBM researchers have been able to solve and have not been resolved at Bell Labs (as well as Hewlett-Packard, Cornell University, the University of Rochester, and the University of California, Santa Barbara) is to increase latency without sacrificing bandwidth. So, in delay lines with an area of ​​0.03 sq. mm, it is possible to simultaneously hold 10 bits of data, and not one, as in previous experiments of Bell’s lab, which is explained by the large number of 6-μm microcavities in one delay line.

Now IBM is working on increasing the density of optical data from 10 bits to hundreds and thousands, which will allow storing a signal that came with long delays or from a long distance without conversion into electricity in such lines, as well as on further reducing the size of microcavities.

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