On the Nature of Light

Fiber has been the long-haul transmission medium of choice for several years as well as for metropolitan area networks (MAN) in inner-city and inner-campus applications. Based on a demand by end customers for higher bandwidth, fiber penetration in the loop plant starts becoming noticeable as well. Synchronous optical network/synchronous digital hierarchy (SONET/SDH) technologies have paved the fiberway for ultrahigh bit rates and ultra bandwidths. Many thousands of kilometers of fiber are installed each year around the world. Advances in solid-state and photonic technology have transformed what once "could not be done" (Le., bit rates at 40 Gb/s over many kilometers of single-mode fiber) into a reality. In addition to traditional time division multiplexing (TDM) services (e.g., voice, low-speed data), new services (e.g., Internet, high-speed data, video, wireless, etc.) have triggered a voracious appetite for bandwidth that legacy communications networks have a hard time delivering. Currently, voice traffic is increasing at a rate of 10% per year. Data traffic increases at a rate of 80% per year. New communications systems have been designed and new standards have been recommended that promise prompt and reliable delivery of large volume of customer bits. However, although new systems are able to process a large quantity of data, the network must be able to transport and manage the increasing traffic, as well as the communication conduits that pass bits from one system to another. Therefore, a question arises: As the bandwidth keeps increasing, how do we assure that the transmission medium has a scalable bandwidth capacity? There are two approaches: