Interpretation Of Reflectometry Measurements (Otdr) And Link Compliance - Cailabs Aroona Star Instruction Manual

B. Interpretation of reflectometry measurements (OTDR) and link compliance
The measurements must then be analyzed by the operator to
identify events:
• Optical splices
• Connectors along the link (to be replaced by optical splices
during installation)
• Local losses (mechanical constraints)
• Reflective events
The table below identifies the type of event and indicates
whether the link is validated (OK) or not (NOK). The loss
levels indicated in the analysis table are valid at 1310 nm,
by averaging the losses obtained in both directions of
measurement.
Event
Low loss, < 0.3 dB
non-reflective
Highly > 0.5 dB
reflective
Loss, > 2 dB
reflective
Reflective < 2 dB
Loss, non- > 0.3 dB
reflective
High slope > 1.5 dB/km
• In pre-installation, the analysis mainly allows to determine
the length of the links and to locate intermediate connectors
to be replaced by fusion splices.
• NOK events require action to make them
• For a post-installation "loss, reflective" event type at the
position of an AROONA-STAR: if the various prescribed
actions have not made it possible to reduce to an acceptable
level, redo the splicing of the AROONA-STAR on multi-
mode fiber to upgrade.
• "Warning" type events do not necessarily require action to
make them "OK".
14
L o ss Refl ect io n
< -55 dB •
•
•
≈ -20 dB
(+/-5 dB)
•
> -55 dB •
(+/-5 dB)
> -55 dB •
(+/-5 dB)
•
•
< -55 dB •
•
/ •
OK (see table).
Note: Given the low loss values measured for each event, it is
not necessary to go back to the linear values to perform the
averaging; approximation of an average directly with dB values
is allowed.
Caus e O K / N O K
proper splicing • OK
artifact (RAS) • OK
•
very dirty or poorly NOK
clipped connectors
broken fiber • NOK
dirty connectors • NOK
at the start/end
of line
MMF connectors • NOK
present
start/end of line • OK
•
ghost peak (RAS) OK
poor splicing • warning
local stress • warning
distributed stress/ • warning
strain
• An AROONA-STAR makes it possible to transition from
an SMF fiber to an MMF fiber, its insertion loss into the
OTDR can therefore only be correctly measured by means
of the two directions of measurement. This loss will always
be overestimated in the direction SMF to MMF and always
underestimated by measuring in the direction MMF to SMF.
• Ghost peaks may appear with long pulses (> 10 ns), a
comparison of the measurements in both directions should
make it possible to identify them. They can also appear
even with short pulses if there is a highly reflective event
(therefore NOK) on the OTDR trace. Eliminating this highly
reflective event should make them disappear.
Ac ti on r eq ui r ed
•
check that the SMF and MMF
connectors are clean
properly clipped; if this does not
solve the issue, try changing
the SMF patch cables
replacing the MMF connector
with a SMF connector
• repair the fiber
• check that the SMF and MMF
connectors are clean
properly clipped; if this does not
solve the issue, try changing
the SMF patch cables
replacing the MMF connector
with a SMF connector
• Replace the intermediate
connectors by fusion splicing
• redo the splicing
(if loss > 1.5 dB)
• repair the fiber if accessible
• no possible action for reducing
linear loss
and
or
and
or