Yokogawa Electric Corporation and Fujitsu Limited today announced the joint development of the world's first practical 40 Gbps optical transmission technologies using differential quadrature phase shift keying (DQPSK). The two companies are respectively planning to incorporate the technologies in various new products for 40 Gbps 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 Ltd. Sample products were on display at the Optical Fiber Communication Conference and Exposition (OFC) and the National Fiber Optic Engineers Conference (NFOEC) 2007, to be held in Anaheim, California from March 27 - 29, 2007.

Background of Development

The dissemination of optical access networks that directly connect households via optical fibers and the construction of next generation networks have led to a increasing demand for greater capacity in inter-city optical transmission networks. In order to meet this demand, increasing the maximum transmission speed from 10 Gbps used in current optical transmission systems to 40 Gbps is being considered.

Overview of Development Challenge

Typically, when transmission speed is increased, distortion caused by polarization mode dispersion (PMD) becomes pronounced, limiting transmission reach. For example, in the case of transmission of a 40 Gbps signal using a standard binary modulation in an optic fiber that meets the PMD specification (0.2 ps /√km) recommended by the ITU-T, transmission reach is limited to a maximum of 100 km. Thus, inter-city transmission, which requires long-distance transmission of more than several hundred kilometers, has not been possible.

Seeking to overcome this obstacle, advances are being made in investigating DQPSK-type transmission, which is tolerant to waveform distortion due to PMD, and its high performance has been confirmed in the laboratory experiments. However, the configuration of a DQPSK format is complex, and thus large size and high power consumption of the optical transceivers have proved to be challenges.