462 Chapter 15
Testing fiber optic continuity is important for system
function checks. This test for continuity is simple and
doesn’t require elaborate equipment. A technician on
one end shines a flashlight into the fiber, and the techni-
cian on the other end looks to see if any light emerges.
That quick test can be checked by measuring cable
attenuation. Sites of discontinuities can be located with
optical time domain reflectometers (OTDRs), as well as
attenuation measurements of the cable.
The OTDR contains a high-power laser source and a
sensitive photodetector coupled to a signal amplifier
that has a wide dynamic range. The output signal is
displayed on an integral oscilloscope. OTDRs use the
fundamental reflection or backscatter properties of
optical fibers by launching a well-defined optical pulse
shape into the fiber and measuring and displaying the
return level. However, OTDRs are more elaborate and
expensive. The alternative for the audio engineer might
be an optical fault finder like the one by Tektronix®
(Model TOP300) in Fig. 15-17. The TOP300 is a hand-
held unit which weighs about one pound and incorpo-
rates easy to read LEDs. No experience is necessary for
the user, just push the buttons and read the LEDs. The
strong laser light shows where the fault is located. There
are other test instruments for fiber optics which is
beyond the scope of this chapter.
15.4.3.4 Advancements in OTDR TestingThe optical time domain reflectometer (OTDR) is
designed to troubleshoot fiber breaks and fiber losses.
In the past the OTDR was very elaborate and extremely
expensive. Fiber optic manufacturers finally have made
the OTDR’s measurement less complicated. An exam-
ple of one such device is the OptiFiber® Advanced
OTDR by Fluke Networks, Fig. 15-18.The OptiFiber Advanced OTDR Package will test
the fiber link/span, certify it, diagnose it, and document
it. This is one of the first certifying OTDRs designed for
network owners and installers.
The use of fiber optics in audio and broadcast
networks is continually growing, and so are the require-
ments for testing and certifying. To insure the perfor-
mance of these optical networks/LANs, network owners
are demanding more information that gives them a
complete picture of the fiber links. Using this type of
OTDR provides a more complete picture.
The OptiFiber is the first test instrument specifically
designed to keep network owners and installers on top
of the latest requirements for testing and certifying fiber
networks. OptiFiber integrates insertion loss and fiber
length measurement, OTDR analysis, and fiber
Figure 15-17. An optical fault finder. Courtesy Tektronix®. connector end face imaging to provide a higher standard
Figure 15-18. OptiFiber Advanced Certifying OTDR.
Courtesy of Fluke Networks.