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Fujitsu Develops World's Fastest 90 Gbps Optical Communications Circuit
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Fujitsu Laboratories Ltd.

Fujitsu Develops World's Fastest 90 Gbps Optical
Communications Circuit

Tokyo, February 7, 2002-- Fujitsu Laboratories Ltd. today announced the development of a two-to-one 90 Gbps multiplexer integrated circuit for optical communication systems that provides world's fastest transmission speeds. By achieving a performance margin greater than 80 Gbps - more than double the current state-of-the-art 40 Gbps -- the new circuit is expected to enable higher quality signal processing. This technology was presented in greater detail this month at ISSCC2002 (the 2002 IEEE International Solid-State Circuits Conference).

The explosive growth of the Internet has sparked research and development worldwide in high-speed, high-capacity communications systems operating at terabit-grade speeds, such as wavelength division multiplexing and dense wavelength division multiplexing*1. The bandwidth of the light wavelengths now in use, however, is reaching its limit. In order to achieve higher rates and ultra high capacity transmission systems, improvements in transmission speeds per wavelength are essential. There has been, therefore, a pressing need for new technologies and ICs capable of multiplexing at greater speeds.

The signal processing in conventional multiplexer circuits has generally used the full-rate method*2, whereby the signal processing runs in synchronization with the clock speed. Under this method, transistors require four or five times as high a cut-off frequency than the clock frequency. This means that, when using this approach, a circuit with performance of 80Gbps or greater would not be possible, since transistors with a cut-off frequency of 300-400 GHz would be required.

About the Technology
The new 2:1 multiplexer IC for 90 Gbps optic communications applies a half-rate approach*3 in which the circuit runs a clock at half the transfer rate as well as employs 0.13 µm inP-HEMT*4 technology with a cut-off frequency of 180 GHz. This high-speed circuit adopts impedance-matching technology to maintain the high quality of the waveform as it passes through the circuit, and AC coupling to minimize loss. Main features include:
  1. High quality waveform transmission with impedance matching technique Impedance-matching between the transistors that handle clock signal processing and those that handle data-signal processing ensures that waveforms maintain good fidelity as they pass through the circuit.
  2. Low loss and high gain
    The clock-buffer amplifier output unit and AC coupling eliminates the DC-level regulator circuit, a source of signal degradation, thereby resulting in low loss and high gain.
  3. Ultra-fast with low power consumption
    Running the signal processing at half the clock speed-the half-rate architecture-makes for ultra high speeds with lower power demands. This technology makes it possible to multiplex together two 45-Gbps signals into one 90 Gbps signal, bringing the potential of optical communications at speeds exceeding 40 Gbps closer to realization.

*1: Wavelength Division Multiplexing, Dense Wavelength Division Multiplexing
This is a multiplexing technique that allows multiple optic signals to be carried over one fiber-optic cable by changing the wavelength of the carrier waves. Using light beams with good properties-i.e., wavelengths that don't interfere with one another-permits many such beams to be multiplexed together and vastly more data to be carried over the fiber-optic cable. The number of waves that can be multiplexed together this way has recently reached 40; this is known as dense wave-division multiplexing.
*2: Full-rate
Running the circuit using a clock signal frequency equivalent to the data bit rate. For example, if the data rate were 43 Gbps, the circuit would be driven by a 43 GHz clock. Since the full-rate architecture can synch off of either the leading or trailing edge of the clock pulse, but not both, it is a way to achieve quality signal processing.
*3: Half-rate
Using a clock running at half the full-rate frequency. This architecture can synch off of both the clock's leading and trailing edge, and it uses fewer circuit elements than the full-rate architecture and requires less power.
*4: High Electron-Mobility Transistor (HEMT)
HEMTs are field-effect transistors that take advantage of the fact that electrons created from the hetero-interface of different kinds of semiconductor material (such as GaAs and AlGaAs) can be operated at higher speeds than those within conventional silicon (Si) semiconductors. Fujitsu pioneered the development of these devices in 1980, and today they are used in nearly all satellite transceivers.

Trademark notice
All product names and proper names mentioned in this document are trademarks or registered trademarks of their respective firms.

About Fujitsu Laboratories Ltd.
Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited is one of the premier research centers in the world. With a global network of laboratories in Japan, China, the United States and Europe, the organization conducts a wide range of basic and applied research in the areas of Multimedia, Personal Systems, Networks, Peripherals, Advanced Materials and Electronic Devices.

About Fujitsu
Fujitsu is a leading provider of Internet-focused information technology solutions for the global marketplace. Its pace-setting technologies, best-in-class computing and telecommunications platforms, and worldwide corps of systems and services experts make it uniquely positioned to unleash the infinite possibilities of the Internet to help its customers succeed. Headquartered in Tokyo, Fujitsu Limited (TSE:6702) reported consolidated revenues of 5.48 trillion yen for the fiscal year ended March 31, 2001.
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[Press Contacts]
Minoru Sekiguchi, Nancy Ikehara
Fujitsu Limited, Public Relations
Tel: +81-3-3215-5259 (Tokyo)
Fax: +81-3-3216-9365
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Fujitsu Laboratories
High-Speed Devices Division, G-Project
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