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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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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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Light Source

LED

Laser CW (Continuous

Wave)

Modulated (2kHz)

Powermeter

Wavelengths

Referencing Memory

Bi-directional Testing

2kHz Detection

Monitoring

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Optical Return Loss Meter

Visual Fault Locator (VFL)

OTDR

Optical Signal and Direction Detector

Fiber Optic Talk Set Variable Attenuator

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Optical Tap or Programmable Switch

Optical Spectrum Analyzer (OSA)

Polarization Mode Distortion Analyzer

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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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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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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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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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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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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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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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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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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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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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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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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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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

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