TABLE OF CONTENTS A major challenge in the operation of WDM networks is how to verify that the system is functioning properly. Thus there is a crucial need to monitor each wavelength intelligently in order to meet network reliability requirements and to guarantee a specific quality of service (QoS) to the end customer, as spelled out in a service-level agreement (SLA). The key performance parameters to monitor are wavelength, optical power, and optical signal-to-noise ratio (OSNR).
This chapter examines the parameters needed to evaluate the performance of a network. Section 14.1 discusses the concept of bit error rate (BER) for measuring the performance of digital systems, which encompass the predominant application of fiber optic links. Since the BER depends on the OSNR, Sec. 14.2 addresses that topic. Next, Sec. 14.3 discusses the performance of analog links, which is given in terms of a carrier-to-noise ratio. How to measure these parameters is the theme of Sec. 14.4. Chapter 18 gives more details on performance monitoring and control of optical communication links.
In the operation of a digital optical fiber link, first a light source launches a certain amount of optical power into a fiber. As the optical signal travels along the link, it becomes attenuated due to loss mechanisms in the fiber, at connectors, and in other components. There also may be signal degradation mechanisms due to factors such as chromatic dispersion, polarization mode dispersion, nonlinear effects in the fiber, and various electrical and optical noises. As described...
