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Table of Contents
Introduction..................................................................................................................... 3
1. How much loss can a link have? How do I calculate a loss budget?....................................... 4
2. Will my application run on this link?............................................................................... 6
3. How do I read a test report?........................................................................................... 8
4. What do the colors mean?.............................................................................................11
5. Why are some of my loss results positive and some negative?........................................... 13
6. How do I set a one jumper reference?............................................................................ 14
7. What is the best way to clean a fiber?.............................................................................17
8. How do I locate a break or bend on my fiber?.................................................................. 19
Glossary......................................................................................................................... 22
Fiber test and troubleshooting instruments ....................................................................... 25
Resources....................................................................................................................... 26
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Introduction
We’ve been supporting
customers testing fiber for
over twenty-five years. Our
current technical support
team has nearly 200 years
of combined experience,
so they’ve answered a lot
of questions. Here are
some of the ones that
come up the most.
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How much loss can a link have?
How do I calculate a loss budget?
1.
When you put a signal into one end of a fiber, the signal
that comes out the other end is weaker. The difference
between the input and the output signals is called
insertion loss.
Loss is expressed in decibels or dB, where every halving
of the signal strength is represented by 3 dB. If the
output signal is half of the input, that’s 3 dB of loss, ¼ is
6 dB of loss, etc.
The TIA and ISO define a loss limit or budget based on the
length of the fiber and the number of connectors and splices. There are multiple versions
of these parameters for different types of connectors and fiber, so for this example,
we’ll use OM5 multimode fiber, which has the same limits in the TIA and ISO (Table 1). To
calculate the loss budget of a link, just perform a calculation as shown:
Multimode
OM5
Fiber loss 3.0 dB / km
Connector loss 0.75 dB
Splice loss 0.3 dB
Table 1.
Loss specifications for OM5
multimode fiber and standard
grade connectors based on TIA and
ISO standards.
Loss
budget = Fiber length
in km x 3.0 dB + Number of mated
connectors x 0.75 dB + Number of
splices x 0.3dB
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Figure 1.
With CertiFiber Pro,
just enter the number
of connectors and
splices and it will
automatically calculate
the limits for the type of
fiber being tested.
If the measured loss of your link is 4.35 dB or less, you’ve passed! Note that our
CertiFiber™ Pro will calculate the exact loss budget for you based on the number
of connectors and splices (see figure 1). You don’t even have to enter the length –
CertiFiber Pro measures it for you.
Be aware that passing this test does not guarantee that your application will run – how
about we cover that next?
4.35 dB = 0.25 km x 3.0 dB + 4 x 0.75 dB + 2 x 0.3dB
Loss
budget = Fiber length
in km x 3.0 dB + Number of mated
connectors x 0.75 dB + Number of
splices x 0.3dB
With a 250 m length, four connections and two splices, the budget would be:
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Will my application run on this link?
If your fiber was certified and documented with a CertiFiber Pro, answering this question
is trivial. Just look at the bottom left of the test report under “Compliant Network
Standards” and you’ll see which applications the fiber will support based on its loss and
length (look for the A in Figure 2 on the next page).
If you lost your report or didn’t certify the cable, it’s more complicated, but you can
figure it out. The amount of loss and the length of the fiber are what determines whether
or not an application will run on it. You can find the limits for most common applications
in our Versiv™ Limit Lines document (registration required) – just search for your
application, for example, “40GBASE-SR4”, and you’ll find a table like the one below.
Depending on which type of cable you’re
running, just measure the loss and
length of the fiber and compare it to the
appropriate limits for the type of cable
you’re running. For example, if your
OM4 measures 1.1 dB of loss at 850 nm
wavelength and 125 meters, your cable
will support 40GBASE-SR4.
2.
40GBASE-SR4
Cable Type 850 nm Fixed Loss dB Length m
OM3 1.9 100
OM4, OM5 1.5 150
Table 2.
Loss and length limits for 40GBASE-SR4 (IEEE)
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Figure 2.
CertiFiber™ Pro test report.
1
2
3
4
3
A
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How do I read a test report?
There are two basic things you should look for in a test report and three others that
experts will look for in addition – but anyone can check these key factors. Refer to figure
2 to find the corresponding part of the report.
1 Look at whether or not the test passed as indicated by the green check or red X in
the upper right corner.
2 Second, what limits were used in the test? Imagine your eight-year old came home
with a failed math test. You’d be upset, but maybe a lot less upset if you saw the test
covered advanced multivariable calculus. As noted above, you can test against TIA/
ISO standards or application standards. Make sure the right limits were used.
Now, let’s look for the things that the experts look for.
3 Check out the actual loss measurements. In the case of CertiFiber™ Pro OLTS, loss
results are most commonly reported in pairs. A negative number in the “Loss” row
for any wavelength indicates that the signal got stronger as it traveled through
the fiber – a physical impossibility and an indication that the tester was set up
incorrectly. Note that the CertiFiber Pro OLTS will flag this as an error, but not all
testers will.
3.
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4 Fourth is the reference setting. The 1-jumper method is recommended for most situations – if
something else shows here, you should understand why. You can go further here: look at the number
of adapters and splices at the top of this section. When testing to TIA or ISO limits as defined in
question 1, an unscrupulous operator can turn a FAIL into a PASS by simply adding more connectors to
the limit than are actually present in the link. If the number seems too high, ask for an explanation.
5
Figure 3.
LinkWare™ Live screen showing set of CertiFiber™ Pro test reports. The first two reports are for the test reference cords (TRC) used in all
subsequent measurements.
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5 This information is not on an individual test, but can be found easily if you have access to the
complete reports in the LinkWare™ reporting software. Before making any tests, the user needs to
set a reference and then test the cords used for all the subsequent tests. The first set of tests in a
LinkWare report are for these cords, and their performance is shown (Figure 3). Experts will click
on these to access the detailed reports (Figure 4) to make sure that the losses aren’t too large,
which indicates poor quality cords which can lead to all measurements made with these cords being
inaccurate. If these numbers are negative, it indicates that the reference was set incorrectly, and all
subsequent measurements are wrong.
Figure 4.
Example of a detailed TRC report.
5
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What do the colors mean?
The colors of fiber optic cables usually indicate their type. The TIA and ISO provide rules
that make it easy to tell what you are working with, making it much less likely you’ll
connect two incompatible fibers together. Here’s what the fiber jacket colors mean with
some caveats to be aware of afterwards:
4.
Single-mode (OS1a, OS2)
Multimode (OM1 or OM2). When first launched, OM2 was often
provided in the same orange color as OM1. However, OM1 fiber
with a 62.5 micron core and OM2 with a 50 micron core should
not be mixed in the same fiber link. To prevent this, nearly all
later versions of OM2 have a grey jacket.
Multimode (OM2)
Multimode (OM3 or OM4)
Multimode (OM4) – The official name of this color is “Erika Violet”
or “Heather Violet”, and it was created to make it easier to
differentiate between OM3 and OM4. While these can be mixed on
the same run, OM4 offers superior performance, so knowing the
difference can be important.
Multimode (OM5)
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Connector colors are also relevant:
There are instances where these are not followed, including special purpose fibers,
bundles (where colors are used to identify the different fibers) outdoor, and military
installations. When in doubt or troubleshooting, carefully examine the jacket of the fiber
for the printed indication of the fiber type.
Adapters come in different colors, too and play a critical role in testing.
Our team has found the blue adapters provide the best results for
UPC connections for both single-mode and multimode.
Use green adapters for APC connectors.
Single-mode UPC (ultra physical contact)
Single-mode APC (angled physical contact)
62.5 or 50 micron core multimode
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Why are some of my loss results positive and
some negative?
The most common cause of this is setting the reference wrong. Let’s use an example.
Say you want to weigh your pets. You get on the scale and weigh yourself – that’s your
“reference weight”. Then you pick up each pet and record the combined weight. Let’s say
you get these results:
Something is obviously wrong – a hamster can’t have a
negative weight. If you repeat your measurement of Harry
and keep coming up with a negative number, then obviously
the reference is wrong – and so is every other measurement.
Setting the reference wrong is also how you get a negative loss measurement, and it
means that all measurements – including the positive ones – are also wrong.
Be aware that there can be confusion over whether loss numbers should be positive or
negative. The reason for the confusion is if you use some power meters to measure the
loss, the reference will be set to 0 dB, and the resulting displayed measurement of the
signal at the far end will be less than that, or negative. Our power meters show the loss
correctly – positive – when used in this mode. That’s because standards declare that fiber
losses are expressed as positive numbers (a negative loss would be a gain – that’s math).
And any time you get mixed positive and negative loss results, that’s an indication of a
potentially serious error with them all.
5.
Subject Combined Weight Pet (Net) Weight
You (reference) 85 kg (187 lbs.)
You + Rover the retriever 105 kg (231 lbs.) 20 kg (44 lbs.)
You + Clara the cat 90 kg (198 lbs.) 5 kg (11 lbs.)
You + Harry the hamster 84 kg (185 lbs.) -1 kg (-2 lbs.)
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How do I set a one jumper reference?
Standards recommend using a one-jumper method to set the reference when
measuring fiber loss. Before getting started, make sure the light source and power
meter have stabilized as per the manufacturer’s specifications.
The first step is to set the reference using the jumper which should be a high-quality
test reference cord (TRC). (See figure 5, A.) For the most accuracy and repeatability
with multimode testing, you may need to use specific cords recommended by the
manufacturer. The figure shows Fluke Networks Encircled Flux compliant launch cords
which ensure the right amount of light is applied to the cord being tested. Before
plugging in any fiber cable, inspect it to make sure it’s clean – if not, clean and
inspect again to ensure it is. Plug the TRC into the source, then the other end into the
meter. Then you can press the “Set Reference” button on the meter and the display
should show “0 dB”.
6.
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Figure 5.
Setting the reference for multimode fiber loss testing.
A: Setting the reference
B: Verifying the TRC
C: Performing a measurement
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Next, unplug the jumper from the meter and connect it to a bulkhead
adapter. After inspecting (and cleaning, if necessary), plug one end of the
second TRC to the adapter, and the second to the power meter. (See figure
5, B.) For single-mode, you want a reading between 0.0 dB and 0.25 dB1
.
For multimode, the reading should be between 0.0 dB and 0.15 dB. If so,
you are ready to disconnect the TRC’s from the adapter and start testing.
While testing, you should not disconnect from the power source, as that
can change the alignment between the source and TRC, requiring you to
set a new reference.
If the reading for the TRC is greater than the limits noted in the paragraph
above, you should inspect and clean the connectors and repeat this step.
If that does not solve it, try a different TRC. If you get a negative1
reading,
start over at step one after inspecting and clean the first TRC. If you still
have a problem, replace that TRC.
This is, of course more complex in Optical Loss Test Sets, as they test
fibers in pairs, requiring you to perform reference setting in pairs. Luckily,
the CertiFiber™ Pro leads users through these steps and checks the
measurements to make sure they are done correctly.
1
Our loss testing equipment
displays loss as a positive
number, in compliance with the
standards. If your meter displays
losses as negative, then reverse
the polarity of the guidance here.
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What is the best way to clean a fiber?
If you’ve inspected a fiber endface and
find it’s dirty, there are two approaches to
cleaning. The first is called dry cleaning
and is done using a click cleaner. Insert
the fiber connector ferrule into the
adapter in the cleaner, press it once so it
clicks, then inspect to see if it’s clean. You
may have to repeat these steps a couple of
times if the contamination is stubborn.
Dry cleaning works most of the time, but
if it doesn’t, or it looks like there is some
sort of smeared or oily contamination
(figure 6), wet cleaning is recommended.
There are a number of tools for wet
7.
cleaning, but most work the same way.
First, put a small amount of fiber cleaning
solvent on part of the cleaning material.
(Don’t use alcohol – it can make things
worse.) Then, touch the endface of the
fiber to the wet part and drag it across the
material to the dry part. The “touch and
drag” part of the process can be repeated
a couple of times, remembering to use a
different part of the cleaning material.
After cleaning, inspect the fiber again.
If it’s still dirty, you may be dealing with
some sort of a scratch or pit and can try
cleaning again or consider replacing
the fiber.
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Figure 7.
“Wet to Dry”: cleaning methodology using our optic
cleaning card. The solvent drop is placed at "1", and
the end face moved across the cleaning material from
"1" to "4".
Figure 6.
Residue left over from cleaning with alcohol. A good
example of an endface needing wet cleaning with a
proper solvent.
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How do I locate a break or bend on my fiber?
8.
There are three tools that can help you
find the location of a break, bend, or other
sort of “event” on a fiber.
A visual fault locator (VFL), such as our
VisiFault™, illuminates a fiber with a visible
laser, which will “leak” at points where
connections are bad, or the fiber is bent
or broken. These work well if you can
visually inspect the entire fiber run – not
so great if it’s two kilometers long and
goes through a conduit underground. On
the other hand, it’s unlikely that the fiber
broke in the underground conduit – the
interconnection points and equipment
cords are much more likely culprits. VFLs
are especially helpful for identifying bad
splices when using splice-on pigtails
since they are near the end of the link.
However, the VFL won’t help you find a
dirty connector.
Figure 8.
A Visual Fault Locator can show broken
or cracked fibers or connectors.
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Optical fault finders such as our
Fiber QuickMap™ quickly and
efficiently measure length and
identify high loss events and
breaks on multimode up to 1,500
meters (4,921 feet). Very simple
to use, this single-ended optical
fault finder uses technology
similar to an OTDR, sending a laser
light pulse through the fiber and
measuring the power and timing
of light reflected from high loss
connections and splices, and from
the end of the fiber. They are ideal
for measuring high-loss splices,
connections and breaks in a fiber
link, as well as the overall length of
the link. The QuickMap also detects
live optical signals before testing.
Figure 9.
Fiber QuickMap Fault Locator
shows the distance to faults
While you may be able to pinpoint
a problem with a VFL or optical
fault finder, sometimes you simply
need to know more. An Optical
Time Domain Reflectometer (OTDR)
calculates signal loss based on
the amount of reflected light, or
backscatter, that it detects. Using
this technology, an OTDR can be
used for locating fiber breaks,
bends, splices and connectors
and for measuring the loss of
these specific events. Access to
this level of detail with an OTDR
arms you with a complete picture
of the fiber installation and the
overall quality of the workmanship.
OTDRs are more expensive than
VFLs, an LSPM/OLTS and optical
fault finders, and they require
some expertise, but because they
measure the location, loss and
characteristics of individual events,
they are considered the ultimate
troubleshooting tool.
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Figure 11.
The OptiFiber™ Pro EventMap™ displays the trace
data (from figure 10) in an easy to understand
mode while flagging the result as a PASS or FAIL.
Users can toggle between the views by touching
EventMap and TRACE tabs.
Figure 10.
An OTDR trace provides details on
a variety of events in a fiber link.
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Glossary
Certification testing The process of testing the transmission performance of an
installed cabling system to a specified standard; requires an
OLTS for “Tier 1” certification and an OLTS plus OTDR for “Tier 2”
certification.
Channel End to end transmission medium between a transmitter and
receiver.
dB logarithmic unit of measurement used to express magnitude of
power relative to a specific or implied reference level; usually
associated with loss.
dBm Power level expressed as the logarithm of the ratio relative to
one milliwatt.
EF Encircled Flux, a method of specifying power throughout the
multimode fiber core using multiple control radii providing a
tight tolerance on mode power distribution in the outer radii
enabling improved agreement between EF-compliant test
instruments.
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FiberInspector™ Fluke Networks’ popular line of handheld fiber end-face and
bulkhead port inspection instruments, ranging from tube to
video microscopes.
Gbps Gigabits per second.
Launch cord fiber Length of fiber placed between the link segment under test and
the OTDR to improve the OTDR’s ability to grade the near-end
connector and any abnormalities in the first connection.
LED Light Emitting Diode, a relatively low-intensity light source.
Link The physical cabling for a transmission. A channel is built of one
or more links connected together.
LSPM Light Source/Power Meter, basic fiber verification instrument
composed of a power meter and a source to measure loss over
a link.
Mbps Megabits per second.
MPO Multi-fiber push on connectors, or MPOs for short, are fiber
connectors comprised of multiple optical fibers. While defined as
an array connector having more than 2 fibers, MPOs are typically
available with 8, 12, or 24 fibers for common data center and LAN
applications.
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OLTS Optical Loss Test Set, a baseline “Tier 1” certification instrument
that measures the loss of a link over its length.
OTDR Optical Time Domain Reflectometer, powerful fiber optic tester
often used for troubleshooting. OTDRs are also used in addition
to OLTSs for "Tier 2" testing.
TRC Test Reference Cord, a high-quality fiber cord between 1 and
3 meters long with high performance connectors, and ideally
with end-faces with special scratch resistant hardened surfaces
that enable numerous insertions without degradation in loss
performance.
VCSEL Vertical Cavity Surface Emitting Laser, commonly used in
multimode light sources. VCSELs should not be used as a testing
source per the standards, only for network system verification.
Verification testing The process of testing the transmission performance of an
installed cabling system to ensure that it meets a minimum
threshold.
VFL Visual Fault Locator, optical source that transmits low-powered
laser light to locate breaks and sharp bends in fiber links.
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Fiber test and
troubleshooting
instruments
Inspection and Cleaning MPO Testing
Loss Testing
(Tier 1 Certification)
Plant Characterization and Troubleshooting
(Tier 2 Certification)
FI-500
FiberInspector™
Micro Fiber
Inspection
Scope
FI-7000
FiberInspector™
Pro Video
Microscope
FI-3000
FiberInspector™
Pro Micro Fiber
Inspection
Scope
and FI2-7300
FiberInspector™
Pro MPO kit
Fiber Optic
Cleaning Kits
MultiFiber™ Pro
MPO Tester
SimpliFiber™
Pro Power
Tester and Fiber
Test Kits
CertiFiber™ Pro
Optical Loss
Test Set
VisiFault™
Visual
Fault Locator
Fiber
QuickMap™
Fault Locator
OptiFiber™ Pro
OTDR
Check end-face contamination
or damage
Single Single, MPO1
Single, MPO Single1
, MPO1
Single1
, MPO1
End-face inspection grading Single Single, MPO Optional Optional
Port Illumination Optional Optional
Auto-focus Optional Optional
Clean contamination
Check connectivity
Check polarity
Verify loss over entire
link to ensure loss
budget not exceeded
Dual-fiber loss testing
Single-mode Tier 1 certification
Multimode Encircled Flux
Compliant Tier 1 Certification
EF compliant at
the bulkhead
with EF TRC’s
Locate faults
Tier 2 certification
Pass/fail results
Document test results
Fiber types supported
Multimode
Single-mode
Multimode
Single-mode,
MPO
Multimode
Single-mode,
MPO
Multimode
Single-mode,
MPO
MPO
(Multimode and
Single-mode)
Multimode
Single-mode
Multimode
Single-mode
Multimode
Single-mode
Multimode
Single-mode
Multimode
Single-mode
Source type LED, FP Laser LED, FP Laser LED, FP Laser Laser Laser LED, FP Laser
1
Optional
