Page 273 - Optical Communications Essentials

Source: Optical Communications Essentials

Chapter
16

Optical Link Design

The preceding chapters have presented the fundamental characteristics of indi-
vidual building blocks of an optical fiber communication link and various con-
cepts, such as WDM, for implementing links. This chapter describes how these
individual parts can be put together to form complete optical fiber transmission
links. The main emphasis is on digital systems.
First Sec. 16.1 looks at the design criteria for a point-to-point link. This
includes examining the components that are available for a particular applica-
tion and seeing how they relate to the system performance criteria (such as bit
error rate and dispersion). Section 16.2 then shows that for a given set of com-
ponents and a specified set of system requirements, one can carry out a power
budget analysis to determine whether the designed fiber optic link meets the
allowed attenuation across the link or if amplifiers are needed periodically to
boost the power level. Next Sec. 16.3 describes how to perform a system rise-
time analysis to verify that the overall bandwidth requirements are met.
Section 16.4 addresses line-coding schemes that are suitable for digital data
transmission over optical fibers. These coding schemes are used to introduce
randomness and redundancy into the digital information stream to ensure effi-
cient timing recovery and to facilitate error monitoring at the receiver.
To increase the end-to-end fidelity of an optical transmission line, forward
error correction (FEC) can be used if the bit error rate is limited by optical noise
and dispersion. This is the topic of Sec. 16.5.
Owing to the complexity of modern optical fiber links, a variety of component,
link, and system modeling simulation tools have been developed. Section 16.6
describes the characteristics of some commercially available tools.

16.1. System Considerations
The design of a high-quality transmission link involves a series of tradeoffs
among the many interrelated performance variables of each component based
263
Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com)
Copyright © 2004 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.