All-raman Amplification Enables Cost-Effective Unrepeatered Applications Using “Non-ideal” Fiber
During the recent SubOptic 2007 conference, held in Baltimore, Maryland, a joint paper between Cable and Wireless and Xtera Communications provided insights into the considerations for using non-ideal fiber for deployments of unrepeatered submarine systems. As indicated in the paper, “Raman Opens Up Bandwidth on Non-Ideal Fibres for Unrepeatered Systems,” service providers deploying the latest advancements in all-Raman amplification are now well-equipped to overcome the impairments of nonideal fiber and improve their return on investments. This improvement results from lowering the cost of deploying new services, delivering significantly more services and gaining a time-to-market advantage by using existing fiber assets. There is a growing demand for a cost-effective solution to providing bandwidth-intensive applications to offshore communities. These communities continue to seek improved communications to the rest of the world and the potential economic benefits of making these services available to resident, business, and government offices. Service providers continue to seek innovative methods to cost-effectively and quickly respond to these requirements. Non-ideal fibers
By Daryl Chaires
To understand the opportunities for deployment of non-ideal fiber, we must decipher the term non-ideal and understand the challenges of using the fiber to offer higher quantities of bandwidth-intensive services. The paper presented at SubOptic 2007, characterized non-ideal fiber as “not optimal in
design or characteristics for the purposes in which they intend to be used; this could be due to their loss, their chromatic and polarization mode dispersion or their susceptibility to non-linear effects.” From a practical standpoint this could be: (1) A section of fiber optic cable which was designed or “intended for use” on one system, but used on another. In this case, excess cable is re-directed for use on a new unrepeatered submarine link. (2) A section of fiber optic cable, which was both designed and deployed on a repeatered submarine network. In this case, the cable may have been deployed, decommissioned, and recovered for use on a new unrepeatered link. In each of the two scenarios given above, the fiber optic cable was designed for a repeatered submarine network. A cable that is designed for a repeatered application is not generally wellsuited for deployment on an unrepeatered route. Dispersion shifted fiber, for example, was often used, a in submarine cables to transmit a single 2.5 Gb/s service over a long distance. The low loss of the cable (0.2 dB/km) along with transmitting on a wavelength near “the carefully screened zerodispersion wavelength prevented pulse broadening,” as noted in the SubOptic 2007 paper, and helped to maximize the length of transmission. “DSF also made the implementation of these systems fairly cost-effective by eliminating the need for expensive dispersion compensation units.”
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