Identify Fiber Optic Ghosts and Dead Zones with OptiFiber Pro

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Identify Fiber Optic Ghosts and Dead Zones with
OptiFiber Pro-Mark Mullins
www.flukenetworks.com 2006-2017 Fluke
Corporation
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Identify Fiber Optic Ghosts and Dead Zones with
OptiFiber Pro
Its that time of year again with a chill in the
air, falling leaves and all things spooky. In
the spirit of Halloween, we thought it apropos to
take a look at two of the most confusing (and
perhaps scariest) OTDR events--ghosts and dead
zones.
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Identify Fiber Optic Ghosts and Dead Zones with
OptiFiber Pro
When You See What Doesn't Exist
By now you should know that an OTDR calculates
signal loss based on the amount of reflected
light, or backscatter, that it detects.
Connection points along the fiber demonstrate a
large reflection, which is used to determine the
return loss of the connection. When there is a
poor connection, light can bounce multiple times
between events. Not only will light be reflected
back towards the OTDR, it will also reflect in
the opposite direction towards the far end, which
is then reflected back again. By now you should
know that an OTDR calculates signal loss based on
the amount of reflected light, or backscatter,
that it detects. Connection points along the
fiber demonstrate a large reflection, which is
used to determine the return loss of the
connection. When there is a poor connection,
light can bounce multiple times between events.
Not only will light be reflected back towards the
OTDR, it will also reflect in the opposite
direction towards the far end, which is then
reflected back again
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Identify Fiber Optic Ghosts and Dead Zones with
OptiFiber Pro
When You See What Doesn't Exist
If you're not a highly experienced OTDR user, it
can be difficult to identify a ghost from a real
event by looking at just the trace itself. Events
that exhibit no loss or show repetition an equal
distance down a trace are probably ghosts.
Thankfully there's no reason to be scared
since Fluke Networks' OptiFiber Pro identifies
cable and fiber ghost events and ghost
sources. But it you really want to be a
"Ghostbuster" this Halloween, make sure that all
your fiber connections are properly cleaned,
properly mated and are of a good quality before
testing.
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Identify Fiber Optic Ghosts and Dead Zones with
OptiFiber Pro
Don't Stay There Too Long
Just like it takes your eyes a minute to recover
from a bright light, OTDRs can also become
temporary blinded by a high reflective event. The
amount of time it takes the ODTR to recover is
the source of whats called the dead
zone--either an event dead zone or an
attenuation dead zone. An event dead zone is the
minimum distance after an event where the OTDR
can detect another event. If the length of fiber
between two events is not long enough for the
OTDR to recover, it can't properly measure the
loss of the second event. The attenuation dead
zone is the minimum distance required to make a
loss measurement for an event. Short dead zones
enable OTDRs to accurately detect consecutive and
closely spaced events in a link. Other than
avoiding the risk of being eaten by zombies,
shorter dead zones are preferred to make sure all
connections are
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Identify Fiber Optic Ghosts and Dead Zones with
OptiFiber Pro
Don't Stay There Too Long
Identified and calculated, which is especially
important when you consider the number or shorter
fiber jumpers used to make connections in today's
virtualized data centers. So when evaluating an
OTDR, it's important to know what reflectance is
used for dead zone specifications. The lower the
reflectance, the smaller the dead zone. So stick
with the OptiFiber Pro and its ultra-low
reflectance specifications and ultra-short dead
zones. And Happy Halloween from all of us at
Fluke Networks.
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