Page 340 - Optical Communications Essentials

Test and Measurement

330 Chapter Nineteen

Collimating
lens
Rotating
diffraction
grating
Collimated
beam
Fiber input
Photodiode

To signal processor
and display
Exit slit and
optical filter
Figure 19.5. Operation of a grating-based optical spec-
trum analyzer.

Figure 19.6. Example of portable universal test sets that can be
used for OTDR analysis, optical spectrum analysis, dispersion
analysis, and other test functions. (Model FTB-400, provided cour-
tesy of EXFO; www.exfo.com.)

19.6. Optical Time-Domain Reflectometer

The long-term workhorse instrument in fiber optic systems is the optical time-
domain reflectometer (OTDR). In addition to locating faults within an optical
link, this instrument measures parameters such as attenuation, length, con-
nector and splice losses, and reflectance levels. A typical OTDR consists of an
optical source and receiver, a data acquisition module, a central processing unit
(CPU), an information storage unit for retaining data either in the internal
memory or on an external disk, and a display. As an example of an OTDR
instrument, the portable unit shown in Fig. 19.6 can perform tests for outside
plant installation, maintenance, and troubleshooting.

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