Chips are up

As the demand for faster broadband internet grows, so does the need for technology that can handle ever-increasing amounts of data quickly and cheaply.

To meet this need a collaboration between Siemens Communications and microprocessor specialist Infineon has developed a chip which, the companies claim, can handle 107Gb – the equivalent of two DVDs – every second, more than twice the current maximum rate.

Internet traffic is generally transmitted as light pulses along optical fibre, and therefore has to be converted back into an electrical signal for computers to do anything with it. But the amount of data that can be carried on an optical fibre is so great that before it can be converted, it has to be split into several signals at a lower rate.

These signals are converted individually and simultaneously by photodiodes. Moreover, the system needs a clock function which can detect the rate of the data transfer. All of these functions are performed by individual components, making the entire system extremely complex and expensive.

Siemens and Infineon have managed to devise a chip which contains all the necessary components, and is made entirely from silicon. ‘Currently, chips like this are made from materials like silicon-germanium, but pure silicon is much faster,’ said Infineon’s Reiner Schönrock.

Measuring 1.7mm x 2.5mm, the chip incorporates extremely small components, which necessitated careful and precise design and fabrication. ‘If the circuit is wrongly dimensioned, you get defective signals,’ explained Rainer Derksen, project co-ordinator at Siemens Corporate Technology in Munich. Wrongly-proportioned circuits can reflect signals within the chip rather than transmitting them, which causes the signal to oscillate and leads to transmission errors.

‘To check the viability of this integrated receiver we carried out a transmission test over a 480km fibre-optic cable route together with the Heinrich Hertz institute in Berlin,’ said Derksen. the device received and transmitted all signals sent to it error-free. ‘This is the first time that the feasibility of a purely electrical 107Gb/sec receiver for optical transmission has been proven in practice,’ he said.

Because the chip is made from a single material, it can be mass-produced relatively cheaply, and is likely to be used at switching centres for large network operators. Here, they will handle the signals arriving at large cities, transforming optical information into electrical signals that can be sent into a copper cable network. Theoretically, the chip could process signals from 100,000 broadband users simultaneously.

The chip will be also be suitable for use in proposed 100Gb/sec ethernet transmission systems, an extremely flexible data transfer technique in which telecommunications companies are interested to move data around large networks.

Unlike existing transmission systems, ethernet does not use fixed routes, but can move data by a variety of routes to avoid sections with heavy traffic.

‘The ability to reach such high frequencies, coupled with the compactness, means that the design of future integrated systems will be much easier,’ said Schönrock.