101483423-Fiber-Characterization-Training.pdf

Fiber Characterization
Assessing the fiber’s capacity`
Assessing the fiber’s capacity`
Tim Yount
Market Manager - Fiber Optic Test Solutions
JDSU Fiber Optic Division

Optical Communication Networks
There are a large variety of network topologies possible according to
distance reach, environments, bandwidth and transmission speeds.
High Speed DWDM network Access/FTTx network
- HFC, RFoG, Docsis PON
© 2007 JDSU. All rights reserved.
2
Buildings
Multi-home Units
Residential
CO/Headend/M
TSO
Local Convergence
Point
Network Access
Points

Fiber Review
Singlemode Optical Fiber

Light propagation is a function of Attenuation, dispersion and
non-linearities.
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NOT FOR USE OUTSIDE VERIZON
AND JDSU
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Attenuation, Dispersion,
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Optical Transmission
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Optical Fiber Types
2 types:
– Singlemode
– Multimode
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Industry Standards
Industry Standards for Fiber (ITU)
For Multimode Single Mode
7

Elements of Loss
Fiber Attenuation
Caused by scattering absorption of light as it travels through the fiber
Measured as function of wavelength (dB/km)
8
Pin
(Emitted
Power)
Pout
(Received
power)
Power variation
OTDR Trace of a fiber link

Bending Losses
Microbending
– Microbending losses are due to
microscopic fiber deformations in
the core-cladding interface
caused by induced pressure on
the glass
9
the glass
Macrobending
– Macrobending losses are due to
physical bends in the fiber that
are large in relation to fiber
diameter
Attenuation due to macrobending increases with wavelength
(e.g. greater at 1550nm than at 1310nm)

Optical Return Loss (ORL)
Amount of transmitted light reflected back to the source
PAPC
PPC Pelement PAPC
PBS PBS PBS
Source
(Tx)
Receiver
(Rx)
PR
10
PT: Output power of the light source
PAPC: Back-reflected power of APC connector
PPC: Back-reflected power of PC connector
PBS: Backscattered power of fiber
PR: Total amount of back-reflected power
ORL (dB) = 10.Log 0
)
(
R
T
P
P
PT
ORL is measured in dB and is a positive value.
The higher the number, the smaller the reflection - yielding the desired
result.

Effects of High ORL (Low values)
Increase in transmitter noise
– Reducing the OSNR in analog video transmission
– Increasing the BER in digital transmission systems
Increase in light source interference
– Changes central wavelength and output power
11
– Changes central wavelength and output power
Higher incidence of transmitter damage
The angle reduces the back-reflection
of the connection.
SC - PC SC - APC

Chromatic Dispersion
Chromatic Dispersion (CD) is the effect that different
wavelengths (colors or spectral components of light) travel at
different speed in a media (Fiber for ex.)
The more variation in the velocity, the more the individual pulses
spread which leads to overlapping.
12
Pulse
Spreading

Dispersion Compensation
The Good News: CD is stable, predictable, and
controllable
– Dispersion zero point and slope obtained from manufacturer
– Dispersion compensating fiber (“DC fiber”) has large negative
dispersion
– DC fiber modules correct for chromatic dispersion in the link
13
– DC fiber modules correct for chromatic dispersion in the link
Tx Rx
DC modules
fiber span
delay [ps]
0 d

V V
Polarization Mode Dispersion
Different polarization modes travel at different velocities presenting a different
propagation time between the two modes (PSPs).
The resulting difference in propagation time between polarization modes is called
Differential Group Delay (DGD).
PMD is the average value of the Differential Group Delay (mean DGD), so called PMD
delay ∆τ
∆τ
∆τ
∆τ [ps], expressed by the PMD delay coefficient ∆τ
∆τ
∆τ
∆τc [ps/√km]
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DGD
v1
v2
V1 V2
Perfect SM Fiber span

What are my PMD limitations ?
According to the theoretical limits or equipment manufacturers specs,
determine the PMD delay [ps] margin.
– PMD varies randomly so abs. value to be used with care.
– Consider margin knowing “typical” variation (from the data) occur in a 10-20%
magnitude.
What are my distance limitations due to PMD?
– PMD coefficient [ps/√km ] calculated
Max Distance @ 0.5ps√km
15
10 Gbit/s (OC-192)
40 Gbit/s (OC-768
2.5 Gbit/s (OC-48) 6,400 km
400 km
25 km
DGD
v1
v2

Connector Contamination
Understanding Contamination on Fiber Optic
Connectors and Its Effect on Signal
Performance

Focused On the Connection
Bulkhead Adapter
Fiber Connector
Fiber
Ferrule
© 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL PROPRIETARY INFORMATION
17
Fiber connectors are widely known as the WEAKEST AND MOST
PROBLEMATIC points in the fiber network.
Alignment
Sleeve
Alignment
Sleeve
Physical
Contact

What Makes a GOOD Fiber Connection?
Perfect Core Alignment
Physical Contact
The 3 basic principles that are critical to achieving an efficient fiber optic
connection are “The 3 P’s”:
Light Transmitted
© 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL PROPRIETARY INFORMATION
18
Physical Contact
Pristine Connector
Interface
Core
Cladding
CLEAN
Today’s connector design and production techniques have eliminated most of
the challenges to achieving Core Alignment and Physical Contact.

What Makes a BAD Fiber Connection?
A single particle mated into
Today’s connector design and production techniques have eliminated most of
the challenges to achieving CORE ALIGNMENT and PHYSICAL CONTACT.
What remains challenging is maintaining a PRISTINE END FACE. As a result,
CONTAMINATION is the #1 source of troubleshooting in optical networks.
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A single particle mated into
the core of a fiber can
cause significant
back reflection, insertion
loss and even equipment
damage.
DIRT
Core
Cladding
Back Reflection Insertion Loss
Light

Illustration of Particle Migration
11.8µ
15.1µ
10.3µ
Core
Cladding
20
Each time the connectors are mated, particles around the core are displaced, causing them to
migrate and spread across the fiber surface.
Particles larger than 5µ usually explode and multiply upon mating.
Large particles can create barriers (“air gaps”) that prevent physical contact.
Particles less than 5µ tend to embed into the fiber surface, creating pits and chips.
Actual fiber end face images of particle migration

Characterizing the Fiber Plant
Understanding Fiber Link and Network
Characterization

What is Fiber Characterization?
Fiber Characterization is simply the process of testing optical
fibers to ensure that they are suitable for the type of transmission
(ie, WDM, SONET, Ethernet) for which they will be used.
The type of transmission will dictate the measurement standards
used
22
Trans type Speed PMD Max CD Max
SONET 10 Gbs 10 ps 1176ps/nm
Ethernet 10 Gbs 5 ps 738 ps/nm
SONET 40 Gbs 2.5 ps 64 ps/nm

Link Network Characterization
Link Characterization
– It measures the fiber
performance and the quality of
any interconnections
– The suite of tests mostly depend
on the user’s methods and
procedures
– It could be uni-directional or bi-
Network Characterization
– It provides the network baseline
measurements before turning the
transmission system up.
– Network Characterization includes
measurements through the optical
amplifiers, dispersion compensators,
and any elements in line.
– It is a limited suite of tests as
compared to Link Characterization
23
– It could be uni-directional or bi-
directional
– Tests – Connector Inspection, IL,
ORL, OTDR, PMD, CD, AP
compared to Link Characterization
Point B
Point A
CWDM/DWDM
Optical
Network
Optical Amp.
Video
Headend
DWD
M
Optica
l
Netwo
rk
ROADM
Optical Amplifier
Router

Testing the Fiber Plant
Connector inspection
Insertion Loss
OTDR
Optical Return Loss
Polarization Mode Dispersion (PMD)
Chromatic dispersion (CD)
Attenuation profile (AP)
@ On
@ Charge
LASER
ON/OFF
PREV
LEVEL
ADJUST
MENU
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CW/
FMOD
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LASER
ON/OFF
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LEVEL
ADJUST
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CW/
FMOD
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Inspect Before You Connectsm
Follow this simple “INSPECT BEFORE YOU CONNECT” process to ensure fiber
end faces are clean prior to mating connectors.
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Inspect, Clean, Inspect, and Go!
Fiber inspection and cleaning are SIMPLE steps with immense benefits.
4
4 Connect
2
2 Clean
1
1 Inspect 3
3 Inspect
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■ If the fiber is clean,
CONNECT the
connector.
NOTE: Be sure to
inspect both sides
(patch cord “male” and
bulkhead “female”) of the
fiber interconnect.
■ If the fiber is dirty, use
a simple cleaning tool
to CLEAN the fiber
surface.
■ Use a probe
microscope to
INSPECT the fiber.
– If the fiber is dirty, go
to step 2, cleaning.
– If the fiber is clean, go
to step 4, connect.
■ Use a probe
microscope to
RE-INSPECT (confirm
fiber is clean).
– If the fiber is still dirty,
go back to step 2,
cleaning.
– If the fiber is clean, go
to step 4, connect.

Measuring Insertion Loss
The insertion loss measurement over a complete link requires a
calibrated source and a power meter.
This is a unidirectional measurement, however could be
performed bi-directionally for operation purposes
Calibrated Light Source Optical power meter
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Calibrated Light Source
d
B
m
W
M
e
n
u
Ca
nc
el
d
B
2s
Perm
Optical power meter
d
B
m
W
d
B
Pt Pr
This measurement is the most important test to be performed, as
each combination of transmitter/receiver has a power range limit.
It is the difference between the transmitted power and the received power at
the each end of the link

Measuring Optical Return Loss
Different methods available
The 2 predominant test methods:
– Optical Continuous Wave Reflectometry (OCWR)
• A laser source and a power meter, using the same test port, are
connected to the fiber under test.
– Optical Time Domain Reflectometry (OTDR)
28
OCWR method
– Optical Time Domain Reflectometry (OTDR)
• The OTDR is able to measure not only the total ORL of the link but also
section ORL (cursor A – B)
OTDR method

Optical Time Domain Reflectometer (OTDR)
OTDR depends on two types of phenomena:
- Rayleigh scattering
- Fresnel reflections.
29
Rayleigh scattering and
backscattering effect in a fiber
Light reflection phenomenon =
Fresnel reflection

How does OTDR work ?
An Optical Time Domain Reflectometer (OTDR) operates as one-dimensional
radar allowing for complete scan of the fiber from only one end.
The OTDR injects a short pulse of light into one end of the fiber and analyzes
the backscatter and reflected signal coming back
The received signal is then plotted into a backscatter X/Y display in dB vs.
distance
Event analysis is then performed in order to populate the table of results.
OTDR Block Diagram Example of an OTDR trace
30
OTDR Block Diagram Example of an OTDR trace
Distance
Fiber under test

Optical Time Domain Reflectometer (OTDR)
Detect, locate, and measure events at any location on
the fiber link
31
Fusion Splice Connector or
mechanical
Splice
Gainer
• OTDR tests are often performed in both directions and the results are
averaged, resulting in bi-directional event loss analysis.
• OTDRs most commonly operate at 1310, 1550 and 1625 nm
singlemode wavelengths.
Macrobend Fiber end or break

Contamination and Signal Performance
Fiber Contamination and Its Effect on Signal Performance
CLEAN CONNECTION
Back Reflection = -67.5 dB
Total Loss = 0.250 dB
1
1
32
DIRTY CONNECTION
Back Reflection = -32.5 dB
3
3
Clean Connection vs. Dirty Connection
This OTDR trace illustrates a significant decrease in signal
performance when dirty connectors are mated.

10 seconds
PMD
Light
Source
Measuring PMD
Different PMD standards describing test methods
• IEC 60793-1-48/ ITU-T G.650.2/ EIA/TIA Standard FOTP-XXX
The broadband source sends a polarized light which is analyzed
by a spectrum analyzer after passing through a polarizer
PMD
Receiver
33
ps
by a spectrum analyzer after passing through a polarizer
The PMD measurement range should be compatible
the transmission bit rate. In order to cover a broad
range of field applications, it should be able to
measure between 0.1 ps and 60 ps.
PMD measurement is typically performed
unidirectional. When PMD results are too close to
the system limits, it may be required to perform a
long term measurement analysis in order to get a
better picture of the variation over the time.

Dealing with PMD
PMD constraints increase with:
– Channel Bit rate
– Fiber length (number of sections)
– Number of channels (increase missing channel possibility)
PMD decreases with:
– Better fiber manufacturing control (fiber geometry…)
34
– Better fiber manufacturing control (fiber geometry…)
– PMD compensation modules.
PMD is more an issue for old G652 fibers (1996) than newer
fibers
At any given signal wavelength the PMD is an
unstable phenomenon, unpredictable. So has
to be measured

Measuring CD
There are different methods to measure the chromatic dispersion. IEC 60793-
1-42 / ITU-T G650.1; EIA/TIA-455- FOTP-175B
The Phase Shift method is the most versatile one. It requires a source
(broadband or narrow band) and a receiver (phase meter) to be connected to
each end of the link
The Chromatic dispersion measurement will be performed over a given
CD
Light
Source
CD
Receiver
35
The Chromatic dispersion measurement will be performed over a given
wavelength range and results will be correlated to the transmission system
limits according to the bit rate being implemented.
Parameters to be controlled in such
way to correlate to the equipment
specifications:
– Total link dispersion.
– Dispersion slope
– Zero dispersion wavelength and
associated slope

Measuring AP
Every fiber presents varying levels of attenuation
across the transmission spectrum. The purpose of
the AP measurement is to represent the attenuation
as a function of the wavelength.
A reference measurement of the source and fiber
jumpers is required prior to performing the
Water peak
Broadband
Light
Source
Narrowband
Receiver
36
jumpers is required prior to performing the
measurements.
The receiver records the attenuation per wavelength
of the source used for transmission.
This could be used to determine amplifier locations
and specifications, and could have an impact on
channel equalization (macro or micro-bends).
Spectral attenuation measurements are typically
performed unidirectional. The wavelength
measurement range should be at least equivalent to
transmission system: C-band or C+L band.
IEC 60793-1-1 Optical fibers – Part 1-1: Generic
Specification – GeneralTest procedure
ITU-T G.650.1
C+L DWDM Band AP results

Fiber Characterization Results
37

The Tools for Installing Maintaining Networks
Fiber Links
Inspection Cleaning
Loss/ ORL Test sets
OTDR
Dispersion testers (PMD and CD)
Attenuation Profile testers
Network / Transport
39
Network / Transport
Inspection Cleaning
Power Meters
Ethernet Testers
BER Testers
Optical Spectrum Analyzers
Network Characterization (System Total
Dispersion)

QA and Resources
Questions
Contacts
Name - Company (Title) Phone E-mail
Fred Ingerson – 4th Wave (JDSU Mfg Rep) (315) 436-0895 fred@4th-wave.com
Mark Leupold – JDSU (MSO Acct Mgr) (540) 226-6284 mark.leupold@jdsu.com
40
Mark Leupold – JDSU (MSO Acct Mgr) (540) 226-6284 mark.leupold@jdsu.com
John Swienton – JDSU (FO App Specialist) (413)231-2077 john.swienton@jdsu.com
Greg Lietaert – JDSU (FO Prod Line Mgr) (240) 404 2517 gregory.lietaert@jdsu.com
Tim Yount – JDSU (FO Test Mkt Mgr) (207)329-3342 tim.yount@jdsu.com
For more on Fiber Characterization visit: www.jdsu.com/characterization
There you’ll find…
Technical Posters, White Papers, Quick Start Guides, FO Guidebooks,
Product and Service Information, and more…

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