Page 332 - Optical Communications Essentials

Test and Measurement

322 Chapter Nineteen

Optical Mux Optical Optical
sources filters receivers
Demux
EDFA Fiber
• •
OADM
• OADM •
• Gain vs λ
• ASE noise
• Status • Insertion loss
• Channel width
• Power output • Insertion loss • Attenuation • Eye diagram
• Spectrum • Channel width • Modal dispersion • BER
• Peak λ • Chromatic dispersion • Jitter
• Pulse width • PMD • Response time
• Extinction ratio • Fault location • Responsivity
Figure 19.1. Some of the relevant test parameters and at what points in a WDM
link they are of importance.

here are measurements for WDM links. Figure 19.1 shows some of the relevant
test parameters and at what points in a WDM link they are of importance. The
chapter first addresses measurement standards in Sec. 19.1 and basic test equip-
ment for optical fiber communication links in Sec. 19.2. Next, Sec. 19.3 discusses
optical power and its measurement with optical power meters. Section 19.4
describes tunable laser sources, which are important support instruments for
wavelength-dependent tests. The optical spectrum analyzer (OSA) is a key
instrument since it measures optical power as a function of wavelength. This
instrument and some its applications are described in Sec. 19.5. The long-term
workhorse measurement system in fiber optic systems is the optical time-
domain reflectometer (OTDR). This instrument is mainly for field evaluations
of fibers, as Sec. 19.6 explains.

19.1. Measurement Standards

Before we examine measurement techniques, let us look at what standards exist
for fiber optics. As summarized in Table 19.1, there are three basic classes: pri-
mary standards, component testing standards, and system standards.
Primary standards refer to measuring and characterizing fundamental phys-
ical parameters such as attenuation, bandwidth, mode-field diameter for single-
mode fibers, and optical power. In the United States the main organization
involved in primary standards is the National Institute of Standards and
Technology (NIST). This organization carries out fiber optic and laser stand-
ardization work, and it sponsors an annual conference on optical fiber meas-
urements. Another goal is to support and accelerate the development of
emerging technologies. Other national organizations include the National
Physical Laboratory (NPL) in the United Kingdom and the Physikalisch-
Technische Bundesanstalt (PTB) in Germany.

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