SAN MATEO, Calif. Researchers at IBM Corp. claim they have achieved sustainable line rates of 56 Gbits/second using silicon from a production-level silicon-germanium process. The experiment shows that existing SiGe processes can build devices for upcoming OC-768 (40-Gbit/s) networks with plenty of speed to spare, said IBM researcher Modest Oprysko.
The results are being presented at the GaAs IC Symposium to be held in Baltimore next Tuesday (Oct. 22).
IBM built a 4:1 multiplexer and corresponding demultiplexer using its 0.18-micron 7HP process at a production fab in Burlington, Vt. Researchers then sent four 14-Gbit/s signals into the mux, which combined them into a 56-Gbit/s feed, as verified by oscilloscope traces. IBM then used that 56-Gbit/s feed to test the demux, as no commonly available laser source can reach that speed.
"The important thing is that we know we have the headroom and margin to design these [OC-768] circuits in silicon germanium," Oprysko said. The chips operated within reasonable parameters as well: a 3.3-volt power supply, consuming 360 milliamps of current, and operating at temperatures up to 100±Celsius.
At the symposium, IBM also will discuss the design of a SiGe electroabsorption modulator, demonstrating that despite its low breakdown voltage at high frequencies, SiGe could be suitable for OC-768 analog circuits.