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www.sea-technology.com July 2014 / st 37 Important fber propagation effects include attenuation, chromatic and polarization mode dispersion, and f- ber nonlinearities including stimulated Brillouin scattering and others. Characterization of datacom trans- ceivers through laboratory experimen- tation is often required. It is extremely important to make sure that a suff- cient and statistically representative population of the transceiver devices is tested. This will reduce the amount of performance margin that needs to be reserved to account for such un- certainties. An excess in reserved per- formance margin can simplistically translate into additional and perhaps unnecessary repeaters. The design process continues with wet system performance simulation, detailed amplifer design, repeater manufacture, testing and integration. Although not always necessary due to the advances in simulation tools available to undersea telecom suppli- ers, further confdence can be gained through a transmission testbed valida- tion of the undersea system. While not typically conducted for undersea tele- com systems, cabled ocean observato- ry projects may also include an end-to- end integrated factory demonstration of the undersea transmission system. Close coordination with the undersea cable factory and integration facility is essential. Undersea Telecom Powering Elements Ocean observatories need electri- cal power for data transmission, ob- servatory control and sensor functions. While batteries are an acceptable tech- nology in many sensor applications, these need to be maintained, charged or replaced, necessitating down-time at the expense of regular at-sea opera- tions. Cabled ocean observatories use permanently powered, fber-optic un- dersea cables and can take advantage of a remote source of electrical power. If undersea repeaters are required, they may be powered from either the same power source as the nodes or a com- plementary power source. The under- sea telecom industry has off-the-shelf components available and qualifed for deepwater applications that can be combined to support scientifc ap- plications with unique powering and transmission requirements, including functions demanding higher power than basic, low-data-rate sensor func- tions. Single-conductor, fber-optic cable is designed and constructed for stan- dard transoceanic undersea cable sys- tems, usually with a loose tube central unit fber structure (UFS). Its single copper conductor is designed for series powering of repeaters, branching units and other undersea equipment. A dual-conductor cable can be used to power repeaters and obser- vatories over separate, independent conductors. TE SubCom's SL dual- conductor cable (DCC) is built on the concept of a coaxial cable structure, which has been utilized in undersea systems for many decades. A fully in- dependent electrical powering path is provided by the second conductor that, in combination with compatible repeaters, branching units, couplings and joints, may be used to power branches and undersea devices from diverse power sources. The DCC uti- lizes the feld-proven loose tube and composite steel wire/copper tube ca- ble structure as its foundation, with the same polyethylene insulation material for electrical insulation. A longitudinal copper conducting tape is wrapped over the frst layer of insulation to form an outer second power conductor. The DCC lightweight (LW) cable is fnished with a second layer of polyethylene insulating jacket material. Both of the conductors are capable of supporting 12.5-kilovolt maximum DC voltage, with a maximum voltage differential between the inner and outer conduc- tors of 15 kilovolts. A high-current repeater has been developed for the ocean observatory community based on TE SubCom's standard undersea repeater design, but differs by providing a capability to bypass excess current. Internal power conditioning circuits provide power to the amplifers within the repeater and divert excess current via a bypass cir- cuit. This design enables a scientifc customer, who has the necessary un- dersea power conversion devices, to provide a single power source capable of powering the in-line repeaters as well as the observatory. The high-cur- rent repeater is used to deliver line cur- rent of approximately 1 ampere to the repeaters, and to bypass approximately 9 amperes of current from the same power source for use by the observa- tory. Additional powering fexibility is available if needed, since repeaters can be provided in either unipolar or bipolar designs.