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Fujitsu Laboratories Ltd.

Pathbreaking Fujitsu Technology Enables Simultaneous Amplification
of 1000 Wavelengths of 10Gbps Optical Signals

Tokyo, November 8, 2002 -- Fujitsu Laboratories Ltd. today announced the development of new technology that will enable the simultaneous amplification of one thousand wavelengths, each carrying a 10 gigabit-per-second optical signal, across a 201.8 nm bandwidth. Fujitsu has successfully tested the new technology over a distance of 120km.

Compared to previous amplifiers, Fujitsu's new amplifier technology uses a simpler repeater, has lower noise, higher gain, and lower cost, making it a promising candidate for future terabit-class multiplexed optical transmission networks.

Wavelength-division multiplexing (WDM) technology, which can transmit large volumes of data quickly over long distances, works by sending multiple wavelengths of light down a single optical fiber-the larger the number of wavelengths, the larger the amount of data that can be transmitted. The forthcoming generation of optical networks will use wavelength routing and optical cross-connects to switch light beams based on their wavelengths. To ensure a flexible network architecture, these systems will need to multiplex 1,000 separate wavelengths, creating a need for an optical amplifier that can simultaneously amplify the multiplexed optical signals.

Currently, single wavelengths carrying as much as 10 Gbps of data are widely used for data transmission over short-range access or metro networks as well as long-haul networks that span thousands of kilometers. A tightly multiplexed signal carrying many 10 Gbps signals effectively needs 0.2 nm wavelength spacing between WDM signals, requiring a 200 nm range for 1000 wavelengths.

Fujitsu has developed proprietary Raman amplifier (*1) technology with an allocation that interleaves the WDM signal wavelengths and pump wavelengths. Details of this technology were originally announced on May 1, 2002. The technology has since been further refined to handle the 200-nm range needed to accommodate 1,000 wavelength signals each carrying 10 Gbps.

About the Technology
Some of the key features of Fujitsu's new amplification technology are:
  1. The Raman amplifier, which interleaves the WDM signal wavelengths and pump wavelengths, covers a range from 1360 nm to 1571 nm with eight pump wavelengths.
  2. For the transmission line, a newly developed type of fiber with low hydroxide-absorption loss (*2) limits in losses to less than 1 dB/km for a 1382-nm excitation beam.
  3. The 1571-nm pump light, which is typically a multi-mode oscillating laser, was replaced with a single-mode oscillating laser with an extremely tight 0.3-nm spectrum width. In addition, by using an optical filter that constricts a spectrum of the pump light inside the WDM signal light's band, the WDM signal light's band is effectively increased.

These technologies made it possible to multiplex together 423-wavelength 10-Gbps signals and successfully transmit them over 120 km in the 1450-nm to 1661-nm range -- a total bandwidth of 201.8 nm, exceeding the previous limit of 136.6 nm. Compared to rare-earth-doped fiber amplifiers, including erbium-doped fiber amplifiers (*3), this resulted in a five- to six-fold increase in frequency range.

Fujitsu intends to expand the new technology's frequency range to 400 nm and add low noise technology across a wide spectrum, so as to make it more applicable for actual use in transmission systems.

*1. Raman amplifier
An optical amplifier that uses a 1450-nm beam of light to take advantage of the Raman scattering effect, a nonlinear effect in optical fibers. This amplifies 1550-nm signal lights. These have already been used in submarine repeater-less transmission systems and terrestrial transmission systems. The power and oscillating wavelength of the pump light can be tuned to achieve desired gain-wavelength characteristics.
*2. Hydroxide absorption loss
The presence of hydroxide (OH) ion impurities in the optical fiber creates absorption losses that are seen at 950, 1240, and 1380 nm.
*3. Rare-earth-doped fiber amplifiers
An optical amplifier that uses an optical fiber doped with rare earths, taking advantage of stimulated emissions from the rare-earth ions to create amplification. In addition to erbium-doped amplifiers around 1550 nm, the element thulium is used in thulium-doped amplifiers around 1460 nm.

About Fujitsu
Fujitsu is a leading provider of customer-focused IT and communications solutions for the global marketplace. Pace-setting technologies, high-reliability/performance computing and telecommunications platforms, and a worldwide corps of systems and services experts make Fujitsu uniquely positioned to unleash the infinite possibilities of the broadband Internet to help its customers succeed. Headquartered in Tokyo, Fujitsu Limited (TSE:6702) reported consolidated revenues of 5 trillion yen (about US$38 billion) for the fiscal year ended March 31, 2002. For more information, please see:

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 IT Core Systems, IT Media, Networks, Peripherals, Advanced Materials and Electronic Devices.

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