Wavelength division multiplexing in long-haul transoceanic transmission systems

Wavelength division multiplexing (WDM) technology used in long-haul transmission systems has steadily progressed over the past few years. Newly installed state-of-the-art transoceanic systems now have terabit per second maximum capacity, while being flexible enough to have an initial deployed capacity at a fraction of the maximum. The steady capacity growth of these long-haul fiber-optic cable systems has resulted from many improvements in WDM transmission techniques and an increased understanding of WDM optical propagation. Important strides have been made in areas of dispersion management, gain equalization, modulation formats, and error-correcting codes that have made possible the demonstration of capacities approaching 4 Tb/s over transoceanic distances in laboratory experiments.

I. Introduction

In TODAY'S Internet age, information flows across continents just as easy as it flows across the office [1]. With so many “point-and-click” virtual connections, it is easy to forget that the world's communications needs are made possible by real systems, based on fiber-optic cables [2]. This, of course, comes as no surprise to those of us in the telecommunications community; however, many others underestimate the importance of undersea fiber-optic cables for intercontinental telecommunications. Anyone who makes international phone calls, sends international faxes, or simply surfs the web at sites on other continents uses undersea fiber-optic cables. This global connectivity is evident from the world map displayed in Fig. 1, which shows the majority of installed undersea cables. Fig. 1. World map showing the major undersea-cable systems that are in operation today. The thickness of the cable paths indicates the “Lit” capacity on each route. Source: TeleGeography Research, a division of PriMetrica, Inc.