Page 274 - Optical Communications Essentials

Optical Link Design

264 Chapter Sixteen

on the system operating requirements. Thus the actual link design analyses
may require several iterations before they are completed satisfactorily. Since
performance and cost constraints are very important factors in a transmission
link, the designer must choose the components carefully to ensure that the link
meets the operational specifications over the expected system lifetime without
overstating the component requirements.

16.1.1. System requirements
The following key system requirements are needed in analyzing a link:
■ The transmission distance
■ The data rate or channel bandwidth
■ The bit error rate (BER)
■ The number of WDM channels
■ The link margin
■ Acceptable power penalties

To fulfill these requirements, the designer has a choice of many components
with various levels of associated characteristics, such as those listed in Table 16.1.

TABLE 16.1. Types and Characteristics of Components Used for Optical Link Design

Component Type Characteristics
Optical fibers Single-mode or multimode Attenuation, dispersion, CWDM or
DWDM use
Light source LED, DFB laser, VCSEL, or other Modulation rate, output power,
wavelength, spectral width, cost
Photodetector pin or APD Sensitivity, responsivity
Connectors Single- or multiple-channel Loss, size, mounting type
Wavelength multiplexers AWG, TFF, grating-based Cost, channel width
Optical amplifiers EDFA, Raman, SOA Complex long-haul, lower-cost metro,
gain, wavelength range
Passive components Optical filters, OADM, dispersion Peak wavelength, spectral range,
compensators, optical isolators, loss, size, cost, reliability
couplers
Active components VOA, dynamic gain equalizers, Tuning speed, peak wavelength, spectral
tunable optical filters, optical add/ range, loss, size, cost, reliability
drop multiplexers
Monitoring devices BER tester, spectrum analyzer, power Optical power, wavelength, OSNR
meter

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.