23360467-otdr-basics
TRANSCRIPT
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8/7/1998 Exsell Training Services 1
Fiber Optic Testing andTroubleshooting
Stan Kubota, Exsell Training Services
Updated 11/26/2001
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8/7/1998 Exsell Training Services 2
Agenda
Review of Tools in Use Today
Review of Measurements Required Today
Construction Testing
Maintenance Testing and Troubleshooting
Tips
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Review of Measurements
Required Today Fiber Attenuation Characteristics (dB/km)
Transmitted Power Level, Receive Power
Level (instantaneous and over time, watts,
dBm)
Insertion Loss, Attenuation, End to End
Loss Measurements (dB)
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Fiber Loss
uManufacturers specs include
fiber loss at specifiedwavelength expressed in dB/km
Corning
AT&T
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Link Loss
Transmitter FPPU Splice FPP Receiver
Patch Cable System Fiber Patch Cable
Loss of complete system from transmitter to receiver
including system interconnects.
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Review of Measurements
Required Today Fault Location, Distance related
Measurements
Optical Return Loss Measurement
Reflectance
Optical Spectrum
Polarization Mode Distortion (PMD)
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Pictorial View of ORL
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Optical Spectrum Analyzer
Typical Output
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Polarization Mode Distortion (PMD)
Theoretical fiber
Hi-Birefringent Fiber
PMD Delay
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Review of Tools in Use Today
Light Source
LED
Laser CW (Continuous
Wave)
Modulated (2kHz)
Powermeter
Wavelengths
Referencing Memory
Bi-directional Testing
2kHz Detection
Monitoring
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Review of Tools in Use Today
Optical Return Loss Meter
Visual Fault Locator (VFL)
OTDR
Optical Signal and Direction Detector
Fiber Optic Talk Set Variable Attenuator
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Review of Tools in Use Today
Optical Tap or Programmable Switch
Optical Spectrum Analyzer (OSA)
Polarization Mode Distortion Analyzer
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Construction Testing
Fiber on Reel
Verifying fiber cable integrity as received from
the factory
Verifying manufacturers specifications for the
fiber in the cable
OTDR, real time mode, use first fiber asreference trace to compare all other fibers to
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Construction Testing
Fiber Installed
Verifying fiber cable integrity after installation
Verifying end to end continuity of each fiber
OTDR, real time mode, use first fiber as
reference trace to compare all other fibers to
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Construction Testing
End to End Testing
powermeter, lightsource testing, both directions
optical return loss and PMD, as required
assures no transpositions, catches any bad patch
panel adapters or pigtail connectors
identifies problem fiber runs OTDR trace of one typical fiber, verify distance
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SourcePower Meter
ON
OFF
850nm
1300nm
ON
OFF
1300nm
1550nm
-20.0
850nm 1300nm
A B
FIBER NETWORK850nm
Typical Insertion Loss Measurement after Referencing
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FOT-920 Max Tester
A B
FIBER NETWORK
FasTest Insertion
Loss Measurement
1310 nm, 1550 nm to
the B side
1310 nm, 1550 nm to
the A side
I/O
FOT-920 Max Tester
I/O
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Construction Testing
Troubleshooting Problems Found in End to
End testing
finding where the high loss feature is
finding the disconnect
patch panel connector check
obtain correct optical distances to features use the VFL and OTDR
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Construction Testing
Cable Plant Acceptance
Report on End to End Loss Measurements
Report on Optical Distances to All Features
Notes, comments, reminders, cautions
What are your standards?
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Construction Testing
Documentation and Record Keeping
As built loss, distance, ORL, and PMD
Create and use a standard labeling system
Locate the documentation in a central location
Provide rapid access to information
Update as changes are made
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Maintenance Testing and
Troubleshooting Techniques What indicators are available?
Check the obvious
Use the records and documentation
Determine the most advantageous
location(s) for troubleshooting
Deploy resources, people and equipment
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Maintenance Testing and
Troubleshooting Techniques Locating the break or problem
VFL, Visual Fault Locator
useful on distances under 3km
670 nm red light leak shows where break or problem
might be
useful with jumpers to do quick assessment of
connector quality
check pigtail splices, close in transition splice
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Visual Fault Locator
Visual Light Source (670 nm)
Typical range is 5 km
Light emission due to bends
Connector End Face Quality
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Source used with Live Fiber
Detector
Light Source, CW or 2 kHz modulated Live Fiber Detector
Direction of light, level, and 2 kHz
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Maintenance Testing and
Troubleshooting Techniques Locating the break or problem
OTDR,Optical Time Domain Reflectometer
setup .what index of refraction, what pulse width,what averaging time, what total display distance, is
there a reference trace from previous recordings
shooting the fiber and diagnosis do I see a good
launch, do I see the end, should I adjust the setupand shoot again, what problems are there
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OTDR Basics
Connector Splice EOF
Laser Pulser
Amplifier Detector
OTDR
Coupler
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OTDR Dead Zone
Caused by the pulse being launched into the
fiber under test
The wider the pulse width is, the larger thedead zone
Every reflective event causes this dead zone
Rough calculation for length of dead zone is
DZ = PW x Speed of Light
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Event Dead Zone
The ability to DETECT an eventthat closely follows a reflective
event
There is one Event Dead Zone
for each reflective event
Bigger reflectance (saturated)
means larger Event Dead Zone
Measured on the trace at 1.5 dB
from the peak of the reflective
event
1.5 dB1.5 dB
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Resolving Features
Smaller pulse width launch pulse means
more resolution in defining features on fiber
Also means less power is being launchedinto fiber, resulting in less distance being
covered
Larger pulse width means less resolution,but longer distances
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Resolution
1000ns (1us) pulse covers
close in connections
30ns pulse begins to
discover close in
connections
With a 10ns pulse you
can measure every thing
including your first
connector!
However you cant govery far with a 10 ns
pulse
OTDROTDR CC SS5 m5 m 5 m5 m
SS
200 m200 m
PulsePulse
1 us1 us
PulsePulse
30 ns30 ns
PulsePulse
10 ns10 ns
Patch CordPatch Cord NetworkNetwork
C
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Sampling Resolution
Distance Range / number of acquisition points
Its a physical specification of the OTDR
It has nothing to do with accuracy!
Example: 80 km /16000pts = 5 meters (two events 3meters apart would not be seen by the OTDR).
5 m5 m
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Offset Acquisition for Added
Resolution In essence placing the OTDR acquisition
memory at a location where it is most
effectively used Minimum acquisition memory should be
16K data points
Offset should be in feet or meters from thefront connection of the OTDR
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Optical Distance vs. Physical
Cable Distance OTDR measures optical distance using an
internal timer, timing the pulse sent and the
time the event returns to the OTDR Fiber spirals in cable, fiber length is not
equal to sheath marking length
Maintenance coils, splice tray coils, etc. addto the discrepancy between physical
distance and optical distance
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patch panel
wall mounttransition splice
OSP cable
OSP splice
case
OSP splice case
OSP splice case
wall mounttransition splice
OSP cable
cable coil
patch panel
Physical Distance vs. Optical Distance
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Reflectance
An event at a specific point in an OTDR
trace, a Fresnel reflection, change in IOR
Indicated by an upward movement of the
OTDR trace, an increase in reflected power
Perfect reflector, a flat surface reflects 4%
of the incident power or about -14.7dB
OTDR end of fiber reflectance value gives
connector quality information
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OTDR Ghost
Apparent feature or event on OTDR trace
caused by the launched pulse reflecting off
features in the fiber with power levels highenough to be captured by the OTDR
Distance measurements to these features is
some multiple of real events Loss across these apparent features is zero
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Gainer Splice
Indicated by an apparent increase or gain inreturned power level at the splice location
Caused by a number of factors such as
mismatches in numerical aperture, corediameter, mode field diameter, or backscatter characteristics of the two fibersspliced
Viewed from the opposite direction willresult in a definite loss
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Pulse Suppressor
A known length (typically 1000 ft) of fiberplaced between the OTDR and the fiber
under test, acts as a long jumper
Originally used to suppress the dead zone Dead zone cannot be suppressed
Useful for allowing a measurement of loss
of the first mated pair at the patch panel Useful for measuring fiber loss (dB/km) on
short fiber runs
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Tips and Things to Watch For
All Manufacturers are not 100% defect free
(this is not to say that they produce poor
products) Fiber can have variations in core size, core
to cladding concentricity, micro-voids, etc.
that exist at random locations on the fiber,and tests okay at the factory
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Tips and Things to Watch For
Connectors, Jumpers, Pigtails while
manufactured in a clean environment and
with precision machines may also havedefects
film on connectors, trapped dust/dirt from
protective covers ferrule to fiber concentricity offsets
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Tips and Things to Watch For
Patch panels, adapters or feed-throughs
trapped debris in adapter
loose or faulty connector insertion
out of tolerance adapter sleeves
Transmitters
LED or Laser output varying over time
on board connector, adapter problems
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Tips and Things to Watch For
Receivers
detector input power margin variation
on board connector, adapter problems
Test Equipment
dirty connectors, bad jumpers
internal connectors and adapters worn
not properly referenced
not in calibration
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Tips and Things to Watch For
Real Time Fiber Monitoring
use single, representative, spare fiber in a cable,
from all cables to be monitored
use remotely controllable OTDR
use programmable optical switch (1 x N)
program to scan the fibers to be tested, to alarm
at discrepancies
active fibers can be monitored via WDM and
1625 nm wavelength OTDR
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What is a WDM?
A fiber coupling technique allowing two
wavelengths to be combined onto a single
fiber, or two wavelengths to be de-coupledfrom a single fiber onto multiple fibers
The coupling ratio between incoming and
outgoing wavelengths is rigorouslycontrolled, optimized for 1310,1550 or
1625nm
1310
1550
1550
1310
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Tips and Things to Watch For
Cleanliness Is Everything in Fiber Optics
splicing, testing, turning up equipment
clean clean clean
Safety Is Even More Important
glass and materials disposal
cover all open patch panel adapters not in use
know your LED and laser emission classes
know the limitations of your equipment
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Commercial Time
Exsell Sales Associates can supply all the
equipment referred to in this presentation
In addition we conduct formal training on
fiber optics technology
In addition we supply cable, patch panels,
jumpers, adapters, and all related fiber optic
components
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The End
Questions
Contacts
Stan Kubota, Exsell Sales Associates
800-873-1873
Paul Raine, Exsell Sales Associates
800-873-1873