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Power Meter
Test personnel also use an optical power meter and stabilized light source to measure
fiber attenuation and transmission loss in the field. Optical power meter measurements are
recommended when the length of an installed optical fiber cable or cable plant is less
than 50 meters. A test jumper is used to couple light from the stabilized source to one
end of the optical fiber (or cable plant) under test. An additional test jumper is also
used to connect the other end of the optical fiber (or cable plant) under test to the
power meter. Optical power meter measurements may be conducted using an optical
loss test set (OLTS). An OLTS combines the power meter and source functions into
one physical unit. When making measurements, it does not matter whether the stabilized
source and power meter are in one physical unit or two.
Power meter measurements are conducted on individual optical fiber cables installed on
board ship. The installed optical fiber cable must have connectors or terminations on both
ends to make the measurement. If the installed optical fiber cable does not have
connectors or terminations on both ends, an OTDR should be used to evaluate the cable. If
the cable is too short for evaluation with an OTDR, cable continuity can be verified using
a flashlight.
Power meter measurements for cable assembly link loss require that test personnel clean
all optical connections at test jumper interfaces before performing any measurement. Test
personnel should use cotton wipes dampened with alcohol to clean connectors and blow dry
before making connections. End users should also ensure that test equipment calibration is
current.
Power meter measurements connecting a test reference cable between the light source and
power meter. The test reference cable has the same nominal fiber characteristics as the
cable under test. The optical power present at the power meter is the reference power (P1).
Disconnect the test reference cable and connect the optical fiber cable under test between
the light source and power meter using test jumpers. If possible, the test reference cable
should be used as the input jumper cable for the test cable measurement. The test jumper
fiber properties, such as core diameter and NA, should be nominally equal to the fiber
properties of the cable being tested. The optical power present at the power meter is test
power (P2).
Test personnel use P1 and P2 to calculate the cable assembly link
loss. The cable assembly link loss (BCA) of optical fiber installed
with connectors or terminations on both ends is
The cable assembly link loss should always be less than the specified link loss for
that particular link.
Besides measuring individual cables, test personnel measure the transmission loss of
installed fiber optic cable plants. The transmission loss of fiber optic cable plants is
measured using EIA/TIA-526-14 method B (multimode fiber) or EIA/TIA-526-7 (single mode
fiber). The procedure measures the internal loss of the cable plant between points A and
B, plus two connection losses. Figure 5-18 (A) illustrates the method described in
EIA/TIA-526-14 method B for measuring the reference power (P1). Figure 5-18 (B)
shows the final test configuration for measuring the cable plant test power (P2).
Figure 5-18. - EIA/TIA-526-14 methods for measuring the reference power (P1).
The procedure is exactly the same as described for measuring the link loss of an
individual cable assembly. The total optical loss between any two termination points,
including the end terminations, of the optical fiber cable plant link is measured. The
measured cable plant link loss should always be less than the specified cable plant link
loss.
Test personnel should conduct cable assembly link loss, and cable plant transmission
loss measurements in both directions and at each system operational wavelength. By
performing these measurements in each direction, test personnel can better characterize
cable and link losses. Unlike optical time-domain reflectometry, bidirectional readings
are always possible when performing power meter measurements. In power meter measurements,
by definition, end users have access to both ends of the cable or cable plant.
Q.37 When is an optical power meter measurement recommended for conducting field
measurements on installed optical fiber cables or cable plants?
Q.38 If an installed optical fiber cable does not have connectors or terminations on both
ends, how should the cable be tested?
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