The industry's recognized authority for design, engineering and application of equipment and services in the global ocean community
Issue link: http://sea-technology.epubxp.com/i/344822
36 st / July 2014 www.sea-technology.com dersea-qualifed optical components. The optical design of the repeater can be tailored to accommodate a wide range of system applications through erbium-doped fber design, selection of the pump drive power level and appropriate specifcation of other passive optical components. Each amp-pair can be independently customized to optimize the performance for its particular fber paths. The amp-pairs are clear channel, meaning that they boost the signal independent of transmis- sion data rate or format. The amplifer design offers broad bandwidth, a low-noise fgure, gain fatness over the band and bit-rate independence. Designs are available with both single and dual stages of amplifer gain. A key TE SubCom repeater feature is a modular design that can accommodate up to 16 amplifers, making it pos- sible to facilitate customized system design needs on a qualifed undersea-proven hardware platform. Repeater designs can include multiple amplifer designs within the same repeater housing that support different capacity re- quirements for varying fber- pair functions. For example, a system architecture may need one fber pair for high- capacity telecom use, while another fber pair could sup- port a relatively low data rate for scientifc needs. EDFA Customization The EDFA can be tailored to support applications with a wide variety of data rates and modulation formats. While high-performance coherent transceivers with strong forward error correction (FEC) may be required for transoceanic telecom carrier applications, less costly datacom transceivers may be suffcient for re- peatered cabled ocean observatory applications. Typically, the manufacturers of ocean observatory undersea transmis- sion elements design their transmission systems with these lower-cost transceivers and house them for use in undersea observatory nodes. Subsea expertise in telecom transmission design, simula- tion and modeling can be leveraged to optimize the ampli- fer design and transmission performance for each specifc ocean observatory need. Undersea amplifers have been designed to support a number of scientifc applications that are outside the requirements of modern telecom carriers, ranging from low-capacity, single OC-1 (SONET) and giga- bit Ethernet channels to OADM (optical add-drop multiplex- ing) scenarios with 10-megabit-per-second and 10-gigabit- per-second channels. The amplifer design process requires an understanding of both the transceivers and fber-propagation effects. Im- portant transceiver characteristics include BER (bit error ra- tio) performance in the presence of optical noise, variation of the BER performance over the population of transceiv- ers, wavelength stability and operating system bandwidth. Data Transmission Despite the signifcant difference between available telecom capacity and the more modest needs of scientifc observatories, the same fundamental amplifer product can be used in both applications. Standard undersea telecom systems provide tremendous amounts of capacity. DWDM systems presently in production can transmit hundreds of channels (wavelengths) of 100 gigabits per second data rates. For example, TE SubCom (Eatontown, New Jersey) recently demonstrated transmission of 49.3 terabytes per second (81 x 162-gigabits-per-second channels and 201 x 180-gigabits-per-second channels) over 9,100 kilometers on a single-fber core incorporating state-of-the-art bandwidth utilization techniques. Such extremely high capacities are not needed for the operation of cabled ocean observatories, even those in their earliest planning stages, but the repeaters used for commercial telecom systems can, and have been, adapted for use with the lower capacities and data rates of cabled ocean observatories. Undersea Repeaters The basic repeater architecture consists of pairs of am- plifers (amp-pairs) that boost the signal on transmission paths (fbers) in opposite directions along the cable. These erbium-doped fber amplifers (EDFAs) are driven by shared 980-nanometer pump lasers and are implemented with un- (Top) High-current repeater enables repeater and obser- vatory powering over a sin- gle conductor. (Bottom) Hy- brid system with commercial traffc and multiple amplifer designs supporting scientifc functions. (Repeater Photo Credit: TE SubCom)