ADC Optical Return
Loss (ORL) Testing
ADCP-90-387 • Issue 1 • 02/2009
Content
Page
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1
GENERAL INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2
OPTICAL RETURN LOSS (ORL) TESTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3
2.1
OTDR Near End, Testing and Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2
Specific OTDR Event Anaylis and Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.3
Miscellaneous Trace Views and Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
CUSTOMER INFORMATION AND ASSISTANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
INTRODUCTION
These instructions provide information for ORL testing of single mode and multimode fiber
cable assemblies.
Revision History
ISSUE
DATE
1
2/2009
REASON FOR CHANGE
Original.
List of Changes
PAGE
IDENTIFIER
All
–
DESCRIPTION OF CHANGE
New
Trademark Information
ADC is a registered trademark of ADC Telecommunications, Inc.,
Westover and OptiTip are trademarks of Westover Scientific
Admonishments
Important safety admonishments are used throughout this manual to warn of possible hazards to
persons or equipment. An admonishment identifies a possible hazard and then explains what
may happen if the hazard is not avoided. The admonishments — in the form of Dangers,
Warnings, and Cautions — must be followed at all times. These warnings are flagged by use of
the triangular alert icon (seen below), and are listed in descending order of severity of injury or
damage and likelihood of occurrence.
1454361 Rev A
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© 2009, ADC Telecommunications, Inc.
ADCP-90-387 • Issue 1 • 02/2009
Danger: Danger is used to indicate the presence of a hazard that will cause severe personal
injury, death, or substantial property damage if the hazard is not avoided.
Warning: Warning is used to indicate the presence of a hazard that can cause severe personal
injury, death, or substantial property damage if the hazard is not avoided.
Caution: Caution is used to indicate the presence of a hazard that will or can cause minor
personal injury or property damage if the hazard is not avoided.
General Safety Precautions
Caution: Fiber optic cables may be damaged if bent or curved to a radius that is less than the
recommended minimum bend radius. Always observe the recommended bend radius limit when
installing fiber optic cables and patch cords.
Danger: Exposure to laser radiation can seriously damage the retina of the eye. Do not look
into the ends of any optical fiber. Do not assume the laser power is turned-off or that the fiber is
disconnected at the other end.
Caution: Improper handling can damage fiber optic cables. Do not bend fiber optic cable more
sharply than the minimum recommended bend radius specified by the cable manufacturer. Do not
apply more pulling force to the cable than specified. Do not compress the fiber or allow it to kink.
Warning: Invisible infrared radiation can seriously damage the retina of your eye. Do not look
into the launching (output) end of an active fiber. A clean, protective cap or hood MUST be
immediately placed over any radiating bulkhead receptacle or optical connector to avoid
exposure to potentially dangerous amounts of radiation. This practice also helps to prevent
contamination of connectors and adapters.
1
GENERAL INFORMATION
This procedure will assist field personnel in testing and repair or replacement of fiber cable
assemblies.
2
OPTICAL RETURN LOSS (ORL) TESTING
Depending on whether you are testing singlemode or multimode fiber, you must determine the
appropriate wavelength before setting up the OTDR.You must also determine the correct launch
cable to connect to the OTDR.
Launch cables for OTDR test sets are typically 40 meters or longer in length. This allows the
OTDR to show events beyond the OTDR “dead zone”. Most OTDR test sets use SMSC or
SMFC connectors and some cable assemblies come with SMASC, SMST, MMSC, or other less
common connectors. You will need to locate a launch cable that will connect to the OTDR and
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© 2009, ADC Telecommunications, Inc.
ADCP-90-387 • Issue 1 • 02/2009
to the fiber cable assembly, with sufficient length to eliminate the OTDR “dead zone” from the
trace source.
Danger: Exposure to laser radiation can seriously damage the retina of the eye. Do not look
into the ends of any optical fiber. Do not assume the laser power is turned-off or that the fiber is
disconnected at the other end.
The following list gives an outline of the ORL test procedure. Familiarize yourself with the
process before proceeding with the testing and troubleshooting procedure.
•
•
•
•
•
•
•
•
2.1
Adjust OTDR settings to typical or to the end customer’s specifications
Clean all connectors and inspect for clean end-faces
Connect launch cable to OTDR and near end connector on fiber cable assembly
Initiate trace and zoom/format as necessary. If OTDR has cursors, set the A cursor at the
end of the launch cable on the screen.
Examine trace and look for unexpected or unusual events. The OTDR Near End, Testing
and Troubleshooting chart provides examples of typical and non-typical events for
reference purposes.
Position B cursor at the leading edge of the non-typical event and document the distance
between the A and B cursors. This should provide a good distance measurement to the
event causing the higher than expected loss.
If the high loss event is located in or near a mated connector, check connectors for end-face
damage and cleanliness. Clean all connector end-faces, test again and document results.
If the event is in the fiber, between connectors, the waveform should provide indications of
an open fiber or a micro/macro bend. If the individual fibers are visible you may be able to
verify an open fiber with a visible light source.
OTDR Near End, Testing and Troubleshooting
Required tools and supplies:
•
•
•
•
•
Optical Time Domain Reflectometer (OTDR)
Launch Cables
Fiber Optic Cleaning Kit
Spare Bulkhead Adapters
Fiber End-face Scope (200x magnification or better)
Optional Tools:
•
•
•
•
Return Loss Meter
Power Meter
Light Source
Patch Cords
Before proceeding with the test obtain a copy of the work order or a knowledge of the end
customer’s specifications or goals. You also need to fully understand the test methodology and
procedures. The OTDR Near End, Testing and Troubleshooting flow chart does not supersede
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ADCP-90-387 • Issue 1 • 02/2009
the test equipment manufacturer’s recommended test procedures. The flow chart is intended as a
troubleshooting guide not an acceptance test plan.
Note: Always clean all connectors including both ends of the patch cords and the “rear”
connector on the panel in question before starting any testing or troubleshooting.
Typical settings for Single Mode near-end connector and splice loss troubleshooting and testing
are:
•
•
•
•
•
•
•
1310 and 1550nm wavelengths
8km range
0.5m – 1m resolution
50ns pulse width
Medium averaging to attain trace times of 30sec – 3min
1.468 refractive index
–83dB backscatter coefficient for standard singlemode fiber (–80dB for NZ-DSF)
Some OTDRs have an automatic mode, for these tests it is better to operate in the manual mode.
Manual mode allows greater freedom to vary test modes, which is more important during
troubleshooting than during acceptance testing. If troubleshooting a quality issue use settings as
close as possible to the settings at which the customer or contractor discovered the issue.
Troubleshoot using the OTDR Near End Testing and Troubleshooting Chart and the information
provided on the next several pages.
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OTDR NEAR END TESTING AND TROUBLESHOOTING
PREPARATION WORK
Equipment Inventory
Work Order or Goals
Training and
Understanding
OTDR INITIATION AND VERIFICATION
Operate per Manufacturer’s Instructions
Adjust to Desired Settings
Verify Proper Operation
LAUNCH CORD VERIFICATION
Connectors are rated up to 500 matings
– manufacturer reconnectorization and
test acceptance is required beyond the
recommended matings.
Launch cord length must be of sufficient
length to show events beyond the OTDR
“dead zone”. Typically 1km or greater.
NO
Using OTDR features for measuring losses, record the insertion
loss (attenuation) of any events and the span cable length.
Also record the return loss (reflectance) of any event.
OTDR OPERATING PROPERLY
AND CALIBRATED
NO
YES
NO
Are results as expected
and within the end customer
specifications for acceptance?
YES
LAUNCH CABLE
OPERATING PROPERLY
AND CALIBRATED
YES
CONDUCT INITIAL TRACE
For typical troubleshooting the OTDR testing will be performed
in manual modes rather than automatic features.
Adjust settings to typical or to the end customer
specifications.
Clean ALL connectors and inspect for clean end-faces.
Connect launch cable to OTDR and to the near end connector.
Initiate trace and zoom/format as necessary.
Is trace appearance as
expected for the near end
connection and span?
See Figure 1.
End of procedure – ensure all reports,
notifications, and follow-up are completed.
YES
NO
Determine which specification has not been met.
See Section 2.2 to determine fault and corrective action.
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Typical trace appearance will indicate a reflective event for connections and may appear lossless
for splices. The end of the fiber is shown as a drop to the noise floor. See Figure 1.
Figure 1. Sample OTDR Trace
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ADCP-90-387 • Issue 1 • 02/2009
2.2
Specific OTDR Event Anaylis and Troubleshooting
Refer to Figure 2 to map the event then prceed to the appropriate section for further instructions.
Figure 2. Possible Events seen on OTDR Trace
• Event 1 Figure 2, shows an example of a reflective event. See Section 2.2.1 OTDR Testing
and Troubleshooting – Reflective Events.
• Event 2 is an example of a splice (non-reflective loss). See Section 2.2.2 OTDR Testing
and Troubleshooting – Splice Events.
• Event 3 is an example of span attenuation. See Section 2.2.3 OTDR Testing and
Troubleshooting – Span or Link Events.
• Event 4 is an indication of end of fiber. See Section 2.2.4 OTDR Testing and
Troubleshooting – End of Fiber Event.
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ADCP-90-387 • Issue 1 • 02/2009
2.2.1
OTDR Testing and Troubleshooting – Reflective Events
Excessive Insertion Loss across a connection (something typically
greater than 0.75dB) is an indication of a poor connection, poor
connector end-face, and/or improper bend radius in system.
Is the Insertion Loss
(point-to-point loss)
value within specification?
NO
YES
Always clean, inspect, and ensure proper seating of all connectors.
If improper bend or pinches are suspected – use a light source
through the path to help indentify light loss/leakage points.
An improper bend can be identified by comparing the 1550nm loss
at the event to the 1310nm loss at the same event. If the longer
1550nm has a greater loss than the 1310nm there is an improper
bend in the fiber path.
A glow of light may indicate a bend radius violation and can
usually be massaged out. A pinpoint of light may indicate a
fiber breakage or improper splice.
If the connection is in question, use a different fully certified launch
cable and different bulkhead.
Conduct trace test.
Is the Return Loss
value (reflectance)
within specification?
YES
NO
Excessive reflectance values (for example –35dB) or low return loss
values (for example 35dB) are very often caused by improper
connector end-face characteristics.
Examples of improper end-face characteristics include, excessive
air gap due to dirty connectors, larger air gap due to short ferrule lengths
(connector end-face polished too low), fiber core not centered, improper
curvature of ferrule end-face, or maybe residual cleaning material left
on the end-face connection.
Refer to list of events.
Most reflective issues are resolved through proper cleaning and
inspection of the “rear” connector and the launch cable connector.
Ensure that the launch cable connector is at peak performance.
Typical connectors are rated to 500 matings – that means for most
modern frame distribution systems, the launch cable will need to be
reconnectorized and/or repolished by a fiber vendor more than
once per frame.
Clean all connector end-faces and inspect with scope.
Increase pulse length one step.
If OTDR has features to attenuate signal – conduct
the OTDR procedure.
Conduct another trace test.
Conduct trace test and reevaluate the system.
Conduct the trace test with a different launch cable and
bulkhead adapter.
Some specific examples and troubleshooting can be found in the text.
If repeated traces, with new launch cables and bulkhead, still do not
yield acceptable readings – contact the appropriate vendor for
further assistance.
YES
Does the Return Loss
value (reflectance)
indicate “saturation”?
NO
• This type of occurrence will be measured at connections with air gaps or breaks in fiber.
Examples include connections through a bulkhead adapter, some mechanical splices, and
some passive optical components such as a splitter or WDM.
• Issues associated with this event include excessive reflection of light or more
appropriately, a low return loss value. Another problem may be a “saturated” return loss
value or trace indication.
High Insertion Loss is seen by a dB difference in the fiber readings taken before and after an
event. Some of these are explained in the following text and shown in Figure 3 and Figure 4.
Tailing – is a gradual slope seen after the reflective event and is an indication of a poor OTDR
recovery. Typically if the reflective event has this tailing effect rather than sharper angles the
connector may be dirty. A clean connector and clean connection will tend toward better
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recovery in the OTDR calculations and yield sharper transitions. Verify the launch cable
properties are still best quality.
Ghosting – is a harmonic event of a large reflective event. Ghost indications are not a true event,
rather an anomaly of the OTDR. Typically very high reflective events will cause ghosts at
multiples of the distance of OTDR to the event. Check the Launch Cable connection to the OTDR.
Ensure good clean connections and verify the launch cable properties are still best quality.
Saturation – is seen as a clipping effect of the trace at the reflective peak. Saturation is an
indication of system overload due to very high reflections, the value given is not an accurate
number for return loss evaluation and should not be used.
DIFFERENCE IS INSERTION
LOSS IN dB
Figure 3. Tailing Reflective Event
NOTE SATURATED PEAK
TAILING EFFECT IS SEEN
AS A SLOPE VS. SHARPER EDGES
Figure 4. Saturation Reflective Event
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ADCP-90-387 • Issue 1 • 02/2009
2.2.2
OTDR Testing and Troubleshooting – Splice Events
Is splicing equipment
operating properly and
indicating good splices?
NO
Refer to original splice equipment
manufacturer for technical assistance.
Note: ADC does not manufacture
fiber splice or test equipment.
YES
Does OTDR trace show
excessive loss, gain, or
reflectance at the splice
location resulting in values
out of specification?
NO
An excessive loss or gain may be an
indication of a splice of two different
fiber glass types. For example, a central
office singlemode fiber of type SMF-28
spliced to a OSP longhaul Corning LEAF
type fiber. The backscatter coefficients of
the fibers are different and show up on the
OTDR as a gain or loss event. The splice
should be measured in both directions
and averaged to yield the estimated
loss through the splice.
YES
A reflective event at a splice may be
due to different glass types, mechanical
splice, or a poor or broken fusion splice.
If any values are out of specification
for the splice event the splice should
be redone and evaluated.
Refer to list of events.
• Most splice technology today should only record very small loss values over that splice
and may be difficult to see on an OTDR trace.
• The indication in Event 2 could also increase on the dB scale. This is called a “gainer” and
is a function of the calculations of reflected light during changes of fiber type. A
pronounced “gainer” is typical for matched clad fiber to non-zero dispersion shifted fiber
due to different backscatter coefficients.
• The most common cause of concern at this event is an excessive loss value (typical values
are less than 0.2dB). Also, there may be indication of fiber break or end of fiber at the
distance the splice should be located.
Splice events (See Figure 5) for today's best splicers are almost unseen on a long haul trace.
Typical splices will reveal a slight insertion loss or attenuation of signal through the splice with
no return loss or reflection of light. The typical range of values seen for insertion loss will be
0.1dB – 0.5dB.
A “gainer” is an occurrence in which the splice appears to gain light level through the splice.
Obviously, there is no amplification through a simple fiber splice. The reason for a gain is found
in the OTDR's calculations and the methods of measuring the returning light. Most often a
gainer will be found when a regular singlemode fiber (matched clad) is spliced to a long haul
non-zero dispersion shifted fiber. The different backscatter coefficients of these fiber types, as
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well as the different cladding structure, will yield different backscattered light to the OTDR.
The OTDR is set for only one backscatter coefficient and when calculations are made will
display either a perceived light gain or a high light loss.
The contracting provider or representative agency determines the minimum acceptable splice loss.
EXAMPLE OF A GAINER
SPLICE EVENT WITH LOSS
MEASURED BY MARKING
dB DIFFERENCE.
Figure 5. Splice Events
2.2.3
OTDR Testing and Troubleshooting – Span or Link Events
Is the span loss more
than specified for the distance?
Review records and ensure there are
no splices or connections within
the span distance.
YES
Review the fiber cable assembly
specifications to ensure the loss
measured is out of manfacturers
specification.
NO
Is span distance
measured within estimation
of distance engineered?
NO
Recall that actual outer cable jacket
distance may differ from the distance
of the fiber glass contained within the
jacket. Fiber glass manufacturers will
place twists within the glass to
compensate for spooling and
environmental effects to the jacketing.
The additional loss due to greater
distance of actual fiber versus cable
assembly markings should be
insignificant to loss budget analysis.
YES
Refer to list of events.
• Span or Link attenuation can be measured by noting the decrease in decibel (dB) level
over the given distance.
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• The fiber manufacturer gives maximum span attenuation values and a maximum value of
1.0 dB/km for singlemode fiber is common.
The span or OSP cable attenuation is the measured slope of the OTDR trace. Since the OTDR
trace shows a line with decibel loss on the y axis and distance on the x axis the slope of this line
yields attenuation. See Figure 6. The attenuation in dB/km can be compared to the cable
manufacturer's specifications for acceptance.
Excessive cable attenuation is a function of the cable manufacture and not the end connectors or
splicing.
Maximum values for cable attenuation are given by the cable manufacturer and are typically the
following:
•
•
•
•
3.5dB/km Multimode at 850nm
1.5dB/km Multimode at 1300nm
1.0dB/km Singlemode at 1310nm
1.0dB/km Singlemode at 1550nm
THE SLOPE OF THE LINE IS THE FIBER CABLE
ATTENUATION IN dB/KM. NOTE THE GREATER
THE SLOPE THE GREATER THE ATTENUATION LOSS.
Figure 6. Span Event
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ADCP-90-387 • Issue 1 • 02/2009
2.2.4
OTDR Testing and Troubleshooting – End of Fiber Event
Is the “end of fiber”
event located at the
distance expected?
YES
Refer to list of events.
Check that all connectors are properly
plugged into the bulkhead adapters.
NO
Using visible light source mark if light is
sighted at the other end of span under test
or at the expected end of fiber. Note that
visible light can still pass through broken
fiber, but intensisty of light is a useful
indication. No light indicates full fiber
breakage or improper connection.
If end of fiber event is located at a splice
location the splice should be evaluated
for re-splicing.
If end of fiber event is at a connection
point ensure the proper jumpers or patch
cords are correctly terminated. Evaluate
the connector for re-connectorization.
• The reflective event followed by noise is an indication of the end of fiber. This also can be
an indication of a fiber break.
A drop to a noise floor will mark the end of the fiber run. See Figure 7. The same indication will
be present for broken fibers, unspliced fiber, and unterminated cross-connects.
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ADCP-90-387 • Issue 1 • 02/2009
REFLECTIVE EVENT DUE TO FIBER END NOT
TERMINATED AND THEN DROP TO NOISE FLOOR.
Figure 7. End of Fiber Event
2.3
Miscellaneous Trace Views and Descriptions
The following six figures show traces taken with an EXFO OTDR. They are provided for
reference only.
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ADCP-90-387 • Issue 1 • 02/2009
100_A
Trace showing 4-Point Splice Loss calculation. Splice loss is taken by subtracting loss levels
before and after an event. 4-Point method will remove loss due to cable length attenuation and
yield insertion loss for the event only.
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ADCP-90-387 • Issue 1 • 02/2009
100_B
Same trace showing the poor reflectance level for the first event (first mated pair connection
after the connection of launch cable to OTDR). The Optical Return Loss (ORL) would be given
as 31.64dB.
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ADCP-90-387 • Issue 1 • 02/2009
100_C
Same set-up as previous page with cleaned connectors, note the better insertion loss.
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ADCP-90-387 • Issue 1 • 02/2009
100_D
Same trace (and set-up) with cleaned connectors, note the improved reflectance value. ORL is
56.09 dB.
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ADCP-90-387 • Issue 1 • 02/2009
100_E
100 meter launch cord from the OTDR going to 10 meter cross-connect then spliced to OSP
going out to the long-haul.
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ADCP-90-387 • Issue 1 • 02/2009
100_F
Same set-up with 100 meter launch to 10 meter patch cord as cross-connect, except that there is
a bend radius violation in the 10 meter patch cord. Note that the bend radius violation induces a
2.4dB loss. The reflectance of the far connection (the second peak) is also reduced due to the
attenuation of that returned light to the near end OTDR.
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© 2009, ADC Telecommunications, Inc.
ADCP-90-387 • Issue 1 • 02/2009
3
CUSTOMER INFORMATION AND ASSISTANCE
PHONE:
U.S.A. or CANADA
Sales:
1-800-366-3891
Extension
73000
Technical Assistance: 1-800-366-3891
Connectivity Extension:
73475
Wireless Extension:
73476
EUROPE
Sales Administration: +32-2-712-65 00
Technical Assistance: +32-2-712-65 42
EUROPEAN TOLL FREE NUMBERS
Germany:
0180 2232923
UK:
0800 960236
Spain:
900 983291
France:
0800 914032
Italy:
0800 782374
ASIA/PACIFIC
Sales Administration: +65-6294-9948
Technical Assistance: +65-6393-0739
ELSEWHERE
Sales Administration: +1-952-917-3000
Technical Assistance: +1-952-917-3475
13944-Q
WRITE:
ADC Telecommunications (S’PORE) PTE, LTD;
100 Beach Road, #18-01, Shaw Towers.
Singapore 189702.
ADC Telecommunications, INC
PO Box 1101,
Minneapolis, MN 55440-1101, USA
ADC European Customer Service, INC
Belgicastraat 2,
1930 Zaventem, Belguim
PRODUCT INFORMATION AND TECHNICAL ASSISTANCE:
connectivity.tac@adc.com
wireless.tac@adc.com
euro.tac@adc.com
asiapacific.tac@adc.com
REPRINTS:
PDF copies of manuals are available
for downloading at the following link:
www.adc.com/manuals
ADCP Number:
90-387
Contents herein are current as of the date of publication. ADC reserves the right to change the contents
without prior notice. In no event shall ADC be liable for any damages resulting from loss of data,
loss of use, or loss of profits and ADC further disclaims any and all liability for indirect, incidental,
special, consequential or other similar damages. This disclaimer of liability applies to all products,
publications and services during and after the warranty period.
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© 2009, ADC Telecommunications, Inc.