JDS Uniphase BACKREFLECTION METER RM3750 User Manual page 36

Loss Before the DUT
When a DUT is connected to the RM meter, the loss from connectors before the DUT affects
the backreflection reading. Because the light is going out from the RM meter and then
returning, it goes through the connectors twice, so the effect of the loss is doubled. If the loss
is close to 0.15 dB, its effect is compensated automatically by the meter. If the loss differs
substantially from 0.15 dB, follow the measurement procedures described at the end of the
Measuring Backreflection section.
Reflections Before the DUT
When a device is connected to the RM meter, the reflections from the connectors affect the
backreflection reading. The front panel FC/PC connections must have backreflection levels
lower than -45 dB for single mode (-25 dB for multi mode), and FC/APC connections must
have backreflection levels lower than -60 dB for single mode (-40 dB for multi mode). To
ensure that the RM meter automatically compensates for this backreflection, follow the setup
procedure described in the Setting Up the Meter for Backreflection Measurements section,
and ensure that the backreflections do not change from the time of the setup.
Reflections After the DUT
When making a backreflection measurement, the fiber after the DUT must be terminated to
eliminate the reflections from the end of the fiber (see the Termination Techniques section).
For greatest accuracy when making very low backreflection measurements, terminate near the
DUT to eliminate reflections from the fiber itself.
Front Panel Connectors
Follow the maintenance procedure described in the Maintaining the Meter section, to ensure
that the internal pigtail connectors are clean and properly connected to the front panel mating
sleeve.
Connector Loss and Backreflection
Ensure that the loss and backreflection of all the connectors are low and stable, complying
with the connector specifications.
Internal Backreflection (for single mode model only, except 980 nm model)
To confirm proper operation of the RM meter, terminate the internal cable while using the
factory-set BR value (BR
0
-65 dB.
Long Cables (for single mode model only, except 980 nm model)
Terminate the cables near the devices or connectors being tested in order to eliminate
backreflections from the fiber.
10112341 Rev 002
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key lamp is off). The backreflection reading must be less than
0
RM3 SERIES BACKREFLECTION METER
USER'S MANUAL
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