Tokyo, October 10, 2000 -- Fujitsu Laboratories, Ltd. has successfully tested, for the first time in the world, a newly-developed optical clock pulse recovery technology that is seen as a key technology for overcoming the limits of wavelength-division multiplexed (WDM) signals. The experiment marks a major step forward in the realization of optical level 3R regeneration (*1) technology, which is expected to be the ultimate technology for maximizing the potential of current fiber optic and future photonic networks.
The results of the experiment were presented at the European Conference on Optical Communication 2000, held in Munich, Germany in September.
[Development Background]
Along with the rapid spread of the Internet on a global scale, demand has been steadily increasing for longer distance, larger capacity fiber optic transmission. One of the technologies that meets this demand is WDM, which enables the transmission of multiple optical wavelengths over a single fiber.
Practical application of WDM transmission technology has been made possible by optical amplifier technology enabling simultaneous amplification of multiple wavelengths. Meeting the expanding communication needs of the future will require WDM transmission at a per channel speed of 40 Gb/s or higher, but under current technologies transmission distances at that speed are severely limited. This is because, over long-haul transmission, such factors as noise accumulating through repeated optical amplification, nonlinear optical effects within the optical fiber or a polarization-mode dispersion may result in waveform distortion of the optical signal or a timing jitter.
If, however, retiming technology to correct the timing for the optical signal and reshaping technology to correct distorted waveforms were developed and incorporated into optical repeaters, the limits on optical transmission distance could be eliminated.
[Technology Overview]
In this experiment, Fujitsu has succeeded in developing the world's first multi-channel recovery optical clock pulse technology. By employing the optical nonlinear effect known as supercontinuum (SC *2), simultaneous recovery of multiple WDM signals using optical clock pulse was made possible. Up to now, signals had to be recovered on a per channel basis.
Fujitsu's new recovery method is described below.
- (1) Optical clock pulse recovery
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One wavelength was extracted from a 20-channel, 20Gb/sec WDM signal with an optical filter. By using the extracted signal, a mode-locked laser (MLL) was oscillated to recover optical clock pulses at 20 GHz with a pulse width of 2 ps.
- (2) Generation of multiple optical clock pulses through widening of spectrum
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A 20 GHz optical pulse was amplified and input to a highly-nonlinear dispersion-shifted fiber (HNL-DSF), widening it to a nearly flat spectrum of 17 nm. Employing a multi-passband optical filter, 20-channel optical clock pulses were able to be regenerated simultaneously.
In the experiment, regenerated optical clock pulses and the original WDM signals were input to an optical gate together one channel at a time for a total of 20 channels. Successful recovery (3R regeneration) of each channel to nearly original quality was confirmed.
The most significant feature of this development is that single-channel clock recovery can also regenerate the clock pulses that have been dispersed over many channels through WDM. Fujitsu accomplished this by effectively employing the highly-nonlinear effects of the HNL-DSF technology it developed for optical signal processing. By further optimizing conditions in the future, simultaneous clock recovery of WDM signals covering the bandwidths currently used in optical transmission systems (C-band, L-band) will also be possible.
By enabling simultaneous recovery of WDM optical clock pulses rather than the channel by channel recovery required by existing technology, Fujitsu's new method is expected to lead to the development of a much smaller and simpler optical 3R regenerator, and to find wide application in optical add-drop multiplexing (OADM) in optical nodes of future photonic networks.
[Terminology]
- 1) Optical 3R regeneration:
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A technology that restores degraded signals to their former quality. It consists of reamplification, retiming and reshaping functions.
- 2) Supercontinuum:
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A light whose spectrum is coherently expanded ultra-widely by propagating a high-intensity optical pulse through a third-order optical nonlinear medium.
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- [About Fujitsu]
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Fujitsu Limited (TSE: 6702) is a leading provider of Internet-based information technology solutions for the global marketplace. Comprising over 500 group companies and affiliates worldwide -- including ICL, Amdahl and DMR Consulting -- it had consolidated revenues of 5.26 trillion yen ($49.6 billion) in the fiscal year ended March 31, 2000. Fujitsu's pace-setting technologies, world-class computing and telecommunications platforms, and global corps of over 60,000 systems and services experts make it uniquely positioned to unleash the infinite possibilities of the Internet to help its customers succeed. Altogether, the Fujitsu Group has 188,000 employees and operations in over 100 countries.
Internet: http://www.fujitsu.com/
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 five laboratories in Japan and one in the United States, 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.
- [Press contacts]
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Nick Hayashi, Bob Pomeroy, Scott Ikeda
Fujitsu Limited, Public Relations
Tel: +81-3-3215-5236 (Tokyo)
Fax: +81-3-3216-9365
E-mail: pr@hq.fujitsu.co.jp
- [Technical contact]
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Terumi Chikama
Fujitsu Laboratories Ltd., Network Systems Lab.
Tel: +81-44-754-2643
Fax: +81-44-754-2640
E-mail: chikama@flab.fujitsu.co.jp