Speeding up optical networks

Yokogawa Electric Corporation and Fujitsu have jointly developed the world’s first practical 40Gbps optical transmission technologies for long-distance communication.

The two companies are respectively planning to incorporate the technologies, which use differential quadrature phase shift keying (DQPSK), in various new products for 40Gbps ultra high-speed optical transmission networks.

The new technologies were developed under the strategic partnership established between Yokogawa and Fujitsu in March of 2006 to jointly develop core system technologies and key components for ultra high-speed optical transmission systems, and with the cooperation of Fujitsu Laboratories. The new technology would quadruple the maximum transmission speed of 10Gbps used in current optical transmission systems.

Typically, when transmission speed is increased, distortion caused by polarisation mode dispersion (PMD) becomes pronounced, limiting transmission reach. For example, in the case of transmission of a 40Gbps signal using a standard binary modulation in an optic fibre, transmission reach is limited to a maximum of 100km. This means inter-city transmission, which requires long-distance transmission of more than several hundred kilometres, has not been possible.

Advances are being made in investigating DQPSK-type transmission, which is tolerant to waveform distortion due to PMD to overcome this obstacle, and its high performance has been confirmed in the laboratory experiments.