21 November 2003 Munich, Germany Lightwave Europe -- Siemens researchers, in collaboration with British Telecom and the Technical University of Eindhoven in The Netherlands, have developed what they describe as a new, extremely fast switching system for optical communications. While conventional optical switches direct complete wavelengths, the time-domain optical add/drop multiplexer (TD-OADM) enables the creation of a flexible network in which diverse data elements can be transmitted in a single light wavelength and directed separately through the network.
In a field test carried out in the U.K., researchers have successfully tested the system under Siemens describes as "realistic conditions." It is expected that a shortening of the necessary light wavelength for the same transmission rate could significantly reduce the cost of future fiber-optic networks.
Over a two-year period, Siemens researchers collaborated with workers from the COBRA Institute of Eindhoven Technical University (Netherlands) and BTexact (British Telecom's research branch) in the EU-sponsored project Ultra Fast Switching in High-Speed OTDM Networks (FASHION). According to Dr. Gottfried Lehmann of Siemens Corporate Technology, the resulting TD-OADM offers an alternative to transmitting, for example, 16 wavelengths of 10-Gbit/sec traffic using conventional WDM. "We succeeded in bundling this amount of data on a single lightwave," says Dr. Lehmann. "In order to do so, we cascaded the data flows of 16 channels, one after the other. In the past, these data flows used to be transmitted in several parallel light wavelengths. We have now interwoven the data flows, thus enabling us to transmit them on a single wavelength."
To direct these data flows to different directions in the network, they must be separated at the nodal points. "Of the 160 billion bits which now hit the distribution point every second, each sixteenth belongs to the data flow which is due to be deflected," says Dr. Lehmann. This means that one bit has to be singled out every 100 psec. Access time for a single bit is therefore only 6.25 psec. This is too much of a strain on conventional electronic-mechanical switches. With the TD-OADM, FASHION now relies on an optical switch that filters out individual bits by means of laser control pulses. In the future, switches of this type in optical networks will direct the data elements to their destination.
A recent field test demonstrated the new switching system. BTexact made available four 70-km optical routes between the English towns of Ipswich and Newmarket. They carried the data error-free along the entire 280-km stretch. The TD-OADM succeeded in dropping and adding signals as required.
"The increase in data traffic creates the need for efficient and low-cost transmission of data through the net," says Lehmann summarizes. "This field test has demonstrated that the system we have developed in collaboration with our international partners is not only effective on a laboratory scale. It has fulfilled all requirements under real working conditions on an original BT link. The experience gained from these transmission experiments is now being fed into the final phase of the project. We have thus been able to demonstrate that fast optical switches are ready to be applied in the near future."