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  6. Technology enabling optical wavelength division multiplexed communication

Fujitsu successfully demonstrates technology enabling optical wavelength division multiplexed communication over 7400km at 2.4 terabits/second

Fujitsu

Tokyo, October 24, 2001

Fujitsu Laboratories Ltd today announced a ground-breaking research achievement in multi-terabit wavelength division multiplexing (WDM) technology for the broadband Internet of the future. Fujitsu has successfully demonstrated transmission of WDM signals at 2.4 terabits/sec over a distance of 7400km using a single band between 1536nm and 1610nm. This new research accomplishment would enable transatlantic (about 6500km) data transmission at 2.4 terabits/sec over a single fibre by multiplexing a 10-gigabits/sec signal into 240 channels.

Moreover, because Fujitsu's newly developed Raman amplifier technology enables amplification of WDM signals with a continuously single bandwidth of 74nm, significant advances are expected to be made in simplifying repeater configuration, reducing optical noise, increasing output power and reducing costs.

Fujitsu announced the development at the recent 27th European Conference on Optical Communication (ECOC'2001), which took place in Amsterdam.

Background

Data communications volume is set to increase explosively as broadband Internet becomes more widespread, driving demand for the development of dramatically higher-capacity, long-distance data transmission systems. WDM technology, which enables the transmission of multiple optical wavelengths over a single fibre, can achieve high-capacity data transmission in parallel with increases in the number of wavelengths.

There are two key methods of increasing transmission capacity: increasing the number of optical signal wavelengths transmitted within a fixed bandwidth (the high density approach), and broadening the bandwidth to accommodate an increased number of wavelengths. However, at high densities, neighbouring signals cause a strong non-linear effect(1) along the fibre over which they are transmitted, and the resulting waveform distortion makes long-distance transmission difficult. And with conventional transmission methods using erbium-doped fibre amplifiers(2) , there are limits to expanding bandwidth, since it is constrained by the gain wavelength characteristics.

Up to now, these problems have been addressed by employing a method of dividing the bandwidth among multiple amplifiers and then combining the optical amplifiers handling the various divided bandwidths for transmission. However, this has the disadvantage of requiring optical amplifiers for each of the signal band as well as multiplexers and de-multiplexers, which increases the size of the equipment as well as costs.

Accordingly, there has arisen a need for development of a technology whereby equipment could be simplified and long-distance transmission facilitated by amplification in single WDM band.

Fujitsu's new technology

Fujitsu has developed a Raman amplifier(3) for amplifying WDM signals that have been attenuated as they are transmitted over an optical fibre as well as a hybrid transmission line employing two types of optical fibres suitable for Raman amplifier. Using only the new Raman amplifier as an optical repeater and combining it with the hybrid transmission line, Fujitsu has achieved continuous expansion of the wavelength bandwidth up to 74nm and improvement of the signal-to-noise ratio (optical S/N ratio).

Two important features of the technology are detailed below:

1. Broadband optical amplifier

Optimising the pump wavelength and optical power for the Raman amplifier produces consistent gain wavelength characteristics. At wavelength bandwidth between 1536nm to 1610nm (74nm) with a wavelength spacing of about 0.3nm, Fujitsu was able to simultaneously amplify a 240-channel WDM signal using only the Raman amplifier.

2. Broadband transmission fibre suitable for Raman amplifier

Fujitsu used optical fibres with two different characteristics to have a broadband transmission performance. That is, a hybrid transmission line consisted of a large core diameter, low-loss optical fibre at the front end of the repeater span and, at the opposite end, an optical fibre that can compensate for a chromatic dispersion causing a waveform distortion in the first optical fibre. This has produced broad bandwidth and low optical noise while decreasing waveform distortion.

Fujitsu Limited already has a commercially available terabit-class optical undersea cable system with 105-channel 10-gigabits/sec WDM signals. Fujitsu Laboratories' newly developed technology offers the prospect of further increasing system capacity, reducing the complexity of the optical amplifier repeaters, reducing optical noise, increasing output power and reducing costs. Fujitsu will now engage in detailed research into the practical application of the new technology, which it expects to incorporate into products around 2005.

Terms and explanations


  • [1] non-linear effect

    When an optical signal enters an optical fibre, the amplitude of the incident optical signal power varies the refractive index, which means the light speeds of it and other wavelengths are modulated. Especially in the case of long-distance transmission of up to 10,000 kilometers or 100 or more multiplexed wavelength signals, the accumulation of this effect becomes serious. Accordingly, crosstalk occurs among the WDM signals during the transmission and the waveforms are gradually distorted. The degree of distortion caused by the occurrence of non-linear effects is closely related to the chromatic dispersion in the fibre, so highly accurate dispersion management in the transmission line is required. With the pump light, the signal light is amplified by scattering due to the molecule vibration in the substance of which the fibre is composed. This is a non-linear effect called the stimulated Raman scattering.

  • [2] erbium-doped fibre amplifiers

    An amplifier that amplifies an optical signal in the 1.5mm band, employing pump light at 0.98mm or 1.48mm in an optical fibre doped with the element erbium. It has found wide practical application in WDM transmission systems.

  • [3] Raman amplifier

    An amplifier that employs pump light in the 1.4mm band and amplifies an optical signal in the 1.5mm band, applying the stimulated Raman scattering effect. It has already been applied for repeater-less transmission systems. Adjusting the pump wavelengths and optical power allows engineers to freely design advantageous gain wavelength characteristics.

  • [4] Note:

    all company/product names mentioned may be trademarks or registered trademarks of their respective holders and are used for identification purpose only.

About Fujitsu Laboratories Ltd

Founded in 1968 as a wholly owned subsidiary of Fujitsu Limited, Fujitsu Laboratories Limited is one of the premier research centres in the world. With a global network of laboratories in Japan, China, the United States and Europe, the organisation 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 Limited

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.
For more information, please see: www.fujitsu.com

Gillian Lamrock

Phone: Phone: (02) 9776 4799
E-mail: E-mail: gillian.lamrock@fujitsu.com.au
Company:Fujitsu Australia Limited

Shuna Boyd

Phone: Phone: (02) 9418 8100
E-mail: E-mail: shuna@boydpr.com.au
Company:BoydPR

Date: 24 October, 2001
City: Tokyo
Company: Fujitsu Limited