Yokogawa and Fujitsu develop 40-Gbit/sec DQPSK optical transmission technology

April 5, 2007
APRIL 5, 2007 -- The companies say their 40-Gbit/sec DQPSK transceivers support transmission distances that are eight times longer than distances achieved by transceivers using standard binary modulation.

APRIL 5, 2007 -- Yokogawa Electric Corp. (search for Yokogawa Electric) and Fujitsu Ltd (search for Fujitsu) today announced the joint development of what they claim are the world's first practical 40-Gbit/sec optical transmission technologies using differential quadrature phase shift keying (search for DQPSK). The two companies say they are planning to incorporate the technologies in various new products for 40-Gbit/sec ultra high-speed optical transmission networks.

The proliferation 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, carriers are considering an increase in maximum transmission speed from the 10 Gbits/sec of today's optical transmission networks to 40 Gbits/sec.

Typically, when transmission speed is increased, distortion caused by polarization mode dispersion (search for PMD) becomes pronounced, limiting transmission reach. For example, transmission reach is limited to a maximum of 100 km when transmitting a 40-Gbit/sec signal using a standard binary modulation in an optical fiber that meets the PMD specification (0.2 psec per square-root-kilometer) recommended by the ITU-T. 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.

Yokogawa Electric and Fujitsu Limited, in cooperation with Fujitsu Laboratories Ltd, have successfully developed what they claim are the world's first practical 40-Gbit/sec DQPSK optical transmission technologies, including:

  • DQPSK LN optical modulator
    The LN optical modulator for DQPSK modulation, which was developed by Fujitsu and operates with the world's lowest drive voltage, enables a compact optical transmission component design and lower power consumption.

  • Dedicated ICs and devices that enable DQPSK:
    Compact, low power consumption, dedicated ICs and other devices that enable DQPSK, including a driver device optimized for the DQPSK LN optical modulator; optical/electrical conversion devices that operate stably despite PMD waveform distortion; and clock and data recovery devices were developed with Yokogawa Electric's InP Hetero-Junction Bipolar Transistor (InP HBT) technology.

  • Compact optical transmission module:
    Control technology was developed that allows the newly developed key devices to operate in a stable manner. The companies also developed a mounting technology that enables a compact size, making possible a compact 110- x 320- x 40-mm package equipped with all functions necessary for 40-Gbit/sec DQPSK in the transmission equipment and a low-power consumption of 35 W (with case temperature of 72 ° Celsius).

    According to the companies, 100 units of 40-Gbit/sec DQPSK optical transceivers were manufactured, and transmission performance and stable operation--despite environmental changes such as temperature fluctuations and variations in supply voltages--were confirmed. Furthermore, the transmission reach as limited by PMD was found to be approximately eight times better than that of standard binary modulation, say the companies.

    The resulting technology is expected to significantly reduce the time it will take to implement major inter-city high-capacity optical networks.

    The new technologies were developed under a 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 with the cooperation of Fujitsu Laboratories Ltd. Sample products were on display at last week's OFC/NFOEC Conference in Anaheim, CA.

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