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Fiber Characterization Assessing the fiber’s capacity
Tim YountMarket Manager - Fiber Optic Test SolutionsJDSU Fiber Optic Division
© 2007 JDSU. All rights reserved. 2
Optical Communication Networks
There are a large variety of network topologies possible according to
distance reach, environments, bandwidth and transmission speeds.
Buildings
Multi-home Units
Residential
CO/Headend/
MTSO
Local Convergence Point
Network Access Points
High Speed DWDM network Access/FTTx network- HFC, RFoG, Docsis PON
Fiber Review
Singlemode Optical Fiber
NOT FOR USE OUTSIDE VERIZON AND JDSU
4
Light propagation is a function of Attenuation, dispersion and non-linearities.
Attenuation, Dispersion,
02
1
2
2
2
2
2
AAdT
AA
i
z
Ai
© 2007 JDSU. All rights reserved. 5
Optical Transmission
© 2007 JDSU. All rights reserved. 6
Optical Fiber Types
2 types:– Singlemode– Multimode
© 2007 JDSU. All rights reserved. 7
Industry Standards
Industry Standards for Fiber (ITU)
For Multimode & Single Mode
© 2007 JDSU. All rights reserved. 8
Elements of Loss
Pin (Emitted Power)
Pout
(Received power)
Power variation
Fiber Attenuation
Caused by scattering & absorption of light as it travels through the fiber
Measured as function of wavelength (dB/km)
OTDR Trace of a fiber link
© 2007 JDSU. All rights reserved. 9
Bending Losses
Microbending – Microbending losses are due to
microscopic fiber deformations in the core-cladding interface caused by induced pressure on the glass
Macrobending – Macrobending losses are due to
physical bends in the fiber that are large in relation to fiber diameterAttenuation due to macrobending increases with wavelength (e.g. greater at 1550nm than at 1310nm)
© 2007 JDSU. All rights reserved. 10
Optical Return Loss (ORL)
Amount of transmitted light reflected back to the source
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
PAPCPPC Pelement PAPC
PT
PBS PBS PBS
Source(Tx)
Receiver(Rx)
PR
ORL is measured in dB and is a positive value. The higher the number, the smaller the reflection - yielding the desired result.
© 2007 JDSU. All rights reserved. 11
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
Higher incidence of transmitter damage
The angle reduces the back-reflection of the connection.
SC - PC SC - APC
© 2007 JDSU. All rights reserved. 12
Pulse Spreading
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.
© 2007 JDSU. All rights reserved. 13
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
Tx Rx
DC modulesfiber span
delay [ps]
0 d
© 2007 JDSU. All rights reserved. 14
Standard SM fiber span
DGD
v1
v2
V1 > V2
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 [ps], expressed by the PMD delay coefficient c [ps/km]
Perfect SM Fiber span
© 2007 JDSU. All rights reserved. 15
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
10 Gbit/s (OC-192)10 Gbit/s (OC-192)
40 Gbit/s (OC-76840 Gbit/s (OC-768
2.5 Gbit/s (OC-48)2.5 Gbit/s (OC-48) 6,400 km6,400 km
400 km400 km
25 km25 km
Max Distance @ 0.5ps√km
Birefringent sections (randomly concentrated)
DGD
v1
v2
External stress !!
Connector Contamination
Understanding Contamination on Fiber Optic Connectors and Its Effect on Signal Performance
© 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL & PROPRIETARY INFORMATION17
Focused On the Connection
Fiber connectors are widely known as the WEAKEST AND MOST
PROBLEMATIC points in the fiber network.
Bulkhead Adapter
Fiber Connector
Alignment Sleeve
Alignment Sleeve
Physical Contact
FiberFerrule
© 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL & PROPRIETARY INFORMATION18
What Makes a GOOD Fiber Connection?
Perfect Core Alignment
Physical Contact
Pristine Connector Interface
The 3 basic principles that are critical to achieving an efficient fiber optic
connection are “The 3 P’s”:
Core
Cladding
CLEAN
Light Transmitted
Today’s connector design and production techniques have eliminated most of the challenges to achieving Core Alignment and Physical Contact.
© 2007 JDSU. All rights reserved. 19
What Makes a BAD Fiber Connection?
A single particle mated into the core of a fiber can cause significant back reflection, insertion loss and even equipment damage.
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.
DIRT
Core
Cladding
Back Reflection Insertion LossLight
© 2007 JDSU. All rights reserved. 20
Illustration of Particle Migration
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.
11.8µ
15.1µ
10.3µ
Actual fiber end face images of particle migration
Core
Cladding
Characterizing the Fiber Plant
Understanding Fiber Link and Network Characterization
© 2007 JDSU. All rights reserved. 22
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
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
© 2007 JDSU. All rights reserved. 23
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-directional
– Tests – Connector Inspection, IL, ORL, OTDR, PMD, CD, AP
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
Point BPoint A
CWDM/DWDM Optical Network
Optical Amp.Video Headend
DWDM
Optical
Network
ROADM
Optical AmplifierRouter
Testing the Fiber Plant Connector inspection Insertion Loss OTDR Optical Return Loss Polarization Mode Dispersion (PMD) Chromatic dispersion (CD) Attenuation profile (AP)
@ On@ Charge
LASERON/OFF
PREV
LEVELADJUST
MENUENTER
CW/FMOD
☼LASERON/OFF
PREV
LEVELADJUST
MENUENTER
CW/FMOD
☼☼
© 2007 JDSU. All rights reserved. 25
Inspect Before You Connectsm
Follow this simple “INSPECT BEFORE YOU CONNECT” process to ensure fiber
end faces are clean prior to mating connectors.
© 2007 JDSU. All rights reserved. 26
Inspect, Clean, Inspect, and Go!
Fiber inspection and cleaning are SIMPLE steps with immense benefits.
44 Connect
■ 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.
22 Clean
■ If the fiber is dirty, use a simple cleaning tool to CLEAN the fiber surface.
11 Inspect
■ 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.
33 Inspect
■ 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.
© 2007 JDSU. All rights reserved. 27
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
dBm WMenu Ca
nc
el
dB
>2s
Perm
Optical power meter
d B mW 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
© 2007 JDSU. All rights reserved. 28
OCWR method
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)• The OTDR is able to measure not only the total ORL of the link but
also section ORL (cursor A – B)
OTDR method
© 2007 JDSU. All rights reserved. 29
Optical Time Domain Reflectometer (OTDR)
OTDR depends on two types of phenomena:- Rayleigh scattering - Fresnel reflections.
Rayleigh scattering and backscattering effect in a fiber
Light reflection phenomenon = Fresnel reflection
© 2007 JDSU. All rights reserved. 30
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
Distance
Fiber under test
© 2007 JDSU. All rights reserved. 31
Optical Time Domain Reflectometer (OTDR)
Detect, locate, and measure events at any location on the fiber link
Fusion Splice Connector ormechanical 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
© 2007 JDSU. All rights reserved. 32
Contamination and Signal Performance
Fiber Contamination and Its Effect on Signal PerformanceCLEAN CONNECTION
Back Reflection = -67.5 dBTotal Loss = 0.250 dB
11
DIRTY CONNECTION
Back Reflection = -32.5 dBTotal Loss = 4.87 dB
33
Clean Connection vs. Dirty Connection
This OTDR trace illustrates a significant decrease in signal performance when dirty connectors are mated.
© 2007 JDSU. All rights reserved. 33
ps
<10 secondsPMDLight
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
PMDReceiver
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.
© 2007 JDSU. All rights reserved. 34
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…)– 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
© 2007 JDSU. All rights reserved. 35
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 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
CDLight
Source
CDReceiver
© 2007 JDSU. All rights reserved. 36
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 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 procedureITU-T G.650.1
C+L DWDM Band AP results
Water peak
BroadbandLight
Source
NarrowbandReceiver
© 2007 JDSU. All rights reserved. 37
Fiber Characterization Results
Wrap Up
© 2007 JDSU. All rights reserved. 39
The Tools for Installing & Maintaining NetworksFiber Links
Inspection & Cleaning
Loss/ ORL Test sets
OTDR
Dispersion testers (PMD and CD)
Attenuation Profile testers
Network / Transport
Inspection & Cleaning
Power Meters
Ethernet Testers
BER Testers
Optical Spectrum Analyzers
Network Characterization (System Total Dispersion)
© 2007 JDSU. All rights reserved. 40
Q&A 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
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/characterizationThere you’ll find…Technical Posters, White Papers, Quick Start Guides, FO Guidebooks, Product and Service Information, and more…
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