NEC Creates Signal-Reshaping LSI for 40 Gbps Optical Fiber Transmission

3/3/2006 - NEC Corporation today announced that it has succeeded in the development of a signal-reshaping large-scale integrated-circuit (LSI) that facilitates a 40 gigabit per second (Gbps) optical fiber transmission system. The new LSI significantly enhances the quality and length of 40 Gbps-based wavelength division multiplexing (WDM*) long-haul transmission as compared with conventional systems, due to its ability to compensate for signal distortion resulting from optical fiber impairments.

In its research, NEC has verified the capability of the LSI to compensate for signal distortion, proving that the maximum length of error-free transmission with a data rate of 40 Gbps can be at least doubled without replacing the existing fiber infrastructure, bringing 40 Gbps transmission systems closer to economic feasibility. The new LSI can compensate for signal distortion caused by polarization mode dispersion (PMD***), which is a kind of signal distortion evident in transmissions of 40 Gbps or higher in optical fiber communication. PMD tends to be more critical in older generation fiber, and as a result this new LSI enables the commercialization of 40 Gbps transmission systems on existing 10 Gbs based networks. The novel LSI is also expected to contribute to a size reduction in WDM system hardware.

The features of this LSI include:

  1. A fast signal processing speed responding to a data rate as high as 40 Gbps, based on indium phosphide (InP**) compound semiconductor technology.
  2. A signal reshaping capability designed to cope with complex signal distortion caused by PMD, with state-of-the-art performance as indicated by the differential group delay (DGD, note 4*) of 22 pico seconds (ps).
  3. An advanced function that responds to static signal distortion, as well as instantaneous and random events, which are characteristics of PMD.

Recently, with the rapid spread of the Internet worldwide, there is increasingly high demand for telecommunication networks with higher data transmission capacity. Amid this environment, the transmission capacity of backbone optical fiber network systems has been drastically increased using WDM technology. While multiplexing of 10 Gbps signal channels is common in conventional systems, 40 Gbps-based WDM systems will soon be in commercial use to meet the strong demand for even higher data rates per wavelength. However, in order to achieve this goal it was necessary to realize error-free long distance transmission, which is exceedingly difficult to achieve, because 40 Gbps signals are significantly more susceptible to distortion by PMD, than lower line rates are. Although PMD can be alleviated to some extent by using state-of-the-art optical fiber, from a practical and economical point of view, it is important to realize 40 Gbps transmission systems using optical fiber networks that are already in use for 10 Gbps systems.

While reshaping signals that are distorted during long distance transmission is common in optical fiber transmission systems, coping with PMD-related distortion is challenging as the resultant waveform is often too complex to reshape and partly because the PMD distortion is an instantaneous and random event in nature and can always occur due to mechanical vibration of the fibers. In addition, even if an optical device that can cope with PMD issues were to become available, it would increase both the cost and size of the WDM system.

NEC has accomplished this development through a new signal processing technique and its implementation in an electronic integrated circuit based on the latest high-speed semiconductor technology.

The results of this research will be presented on March 8 at the Optical-communication Fiber Conference (OFC) 2006, being held in Anaheim, CA, USA, from March 5 to 10, 2006.

NEC is continuing to develop this research toward commercialization of a next-generation 40 Gbps-based WDM system that leverages the newly developed LSI.


* Wavelength Division Multiplexing (WDM):
A technology that uses multiple lasers and transmits several wavelengths of light (lambdas) simultaneously over a single optical fiber. Each signal travels within its unique color band, which is modulated by the data (text, voice, video, etc.). WDM has dramatically increased the carrying capacity of the fiber infrastructure of the telecommunication carriers. The most advanced WDM systems can support hundreds of wavelengths, each carrying 10 Gbps or 40 Gbps. That means terabits of data per second can travel over one optical strand, thinner than a human hair.

** Indium phosphide (InP):
Is a semiconductor composed of indium and phosphorus. It is used in very high frequency electronics because of its superior electron velocity with respect to the more common semiconductors such as silicon or gallium arsenide.

*** Polarization Mode Dispersion (PMD):
Dispersion refers to broadening of the waveforms over long distances by the time they reach the receiving end, which makes them difficult to interpret. PMD is the type of dispersion that occurs in singlemode fiber due to a lack of perfect symmetry in the fiber and from external pressures on the cable. Light travels over singlemode fiber in two polarization states. Over long distances, PMD causes each one to arrive at the receiving end at a different time.

**** Differential Group Delay (DGD):
DGD is the time separation or delay between two polarization states of the transmission links at the receiver. DGD is often used as an indicator of the degree of signal distortion caused by PMD.

About NEC Corporation
NEC Corporation (TSE: 6701)(NASDAQ: NIPNY)(UK: NEC.IL) is one of the world's leading providers of Internet, broadband network, and enterprise business solutions dedicated to meeting the specialized needs of its diverse and global base of customers. Ranked as one of the world's top patent-producing companies, NEC delivers tailored solutions in the key fields of computers, networking, and electron devices by integrating its technical strengths in IT and networks and by providing advanced semiconductor solutions through NEC Electronics Corporation. The NEC Group employs more than 140,000 people worldwide and had net sales of 4,855 billion yen (approx. $45.4 billion) in the fiscal year that ended in March 2005.

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