Unrepeatered Upgrades Are Available for Challenging Systems at a Fraction of the Cost of a New System
Fortunately, using the latest all-Raman technology, service providers are able to obtain the capacity of a new system through the upgrade of an existing one. Moreover, the upgrade is not limited to systems with prestine fiber, but can be accomplished on a wide range of existing systems, including those with the challenges of existing “in-line” technology or single channel unrepeatered systems using fibers that were not initially designed for high-capacity dense wavelength division multiplexing (DWDM) systems. Because upgrades can be accomplished without deploying new cable, they can be accomplished at one-tenth the cost of a new deployment. In addition, upgrades can be accomplished in a fraction of the time, which accelerates time to revenue and significantly shortens the payback period. Thus, with allRaman technology, it is difficult to imagine a scenario where a new parallel system would be justified. All-Raman based upgrades provide at least the capacity of new erbium-doped fiber amplifier (EDFA) based systems. In some cases, the upgrade provides more capacity than can be accomplished with a new deployment of an unrepeatered EDFA based solution. A brief review of all-Raman amplification will help us uncover the characteristics that make it so attractive for upgrades of unrepeatered sub-sea systems.
If you are a service provider with an existing unrepeatered sub-sea network and are considering deploying a new parallel system, this article is for you. This is especially true if you have been told that your existing system uses technology or a fiber type that makes upgrades too complex and costly. This is often the case for (1) Systems with previously deployed remote optically pumped amplifiers (ROPAs), (2) Short repeatered systems with regenerators or repeaters, (3) Older systems with aged, high-loss cables, and/ or
By Daryl Chaires
(4) Cables equipped with dispersion shifted fiber (DSF) or old (15 years or more) sub-sea fibers, which were not designed to carry multiple highcapacity wavelengths. Service providers with systems characterized by one or more of the challenges listed above have often been directed to deploy new parallel systems to respond to the recent increase in demand for bandwidth-intensive applications. Even if existing systems do not face those types of challenges, it is sometimes difficult to obtain the capacity of a new system through an upgrade.
Maximize the Benefits of Upgrades with All-Raman Technology Raman amplification is currently being used by most DWDM equipment manufacturers to enhance their EDFA based systems. Raman amplifiers are added to increase the distance of transmission on new unrepeatered deployments. These systems use a combination of erbium-doped fiber and Raman amplification. However, the maximum benefit for long unrepeatered links is obtained when EDFAs are totally eliminated, and amplification is obtained using allRaman technology. While all-Raman amplification provides the benefits of longer distance and higher capacity for new unrepeatered deployments, the same characteristics are also applicable to upgrades of existing unrepeatered sub-sea links. A single amplifier can provide gain over the entire low-loss region of the fiber (about 100 nm). As shown, in 24