Ppt

Fiber Characterization
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

Local Convergence Buildings
Point

Network Access
Points

CO/Headend/M
TSO

Multi-home Units

Residential

2 © 2007 JDSU. All rights reserved.

Fiber Review
Singlemode Optical Fiber

Light propagation is a function of Attenuation, dispersion and
non-linearities.

∂A i 1 ∂2A 2
i + αA − β 2 +γ A A= 0
∂z 2 2 dT 2

Attenuation, Dispersion,
NOT FOR USE OUTSIDE VERIZON 4
AND JDSU

Optical Transmission


Optical Fiber Types

 2 types:
– Singlemode
– Multimode


Industry Standards

Industry Standards for Fiber (ITU)
For Multimode & Single Mode


Elements of Loss

Fiber Attenuation
 Caused by scattering & absorption of light as it travels through the fiber
 Measured as function of wavelength (dB/km)

Pin
(Emitted
Power)
Power variation

Pout
(Received
power)
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
 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
PR

Source Receiver
(Tx) (Rx)

PBS PBS PBS

PT PT: Output power of the light source
PAPC: Back-reflected power of APC connector
PT
ORL (dB) = 10.Log ( )
>0 PPC: Back-reflected power of PC connector
PR
PBS: Backscattered power of fiber
PR: Total amount of back-reflected power

 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
 Higher incidence of transmitter damage
SC - PC SC - APC

 The angle reduces the back-reflection
of the connection.

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.

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
delay [ps]

0 d

Tx Rx

fiber span
DC modules


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 [ps], expressed by the PMD delay coefficient ∆τc [ps/√km]

V1 > V2
an
fiber sp
SM
dard
Stan
DGD
v2

v1

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

6,400 km ed)
ntrat
2.5 Gbit/s (OC-48)
2.5 Gbit/s (OC-48)
e
ly conc
10 Gbit/s (OC-192)
10 Gbit/s (OC-192) 400 km ndom
(ra
ections
ent s
40 Gbit/s (OC-768
40 Gbit/s (OC-768
25 km
ing
Birefr
DGD
v2
!
ss !
v1 l stre
erna
Ext

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

Focused On the Connection

Bulkhead Adapter

Ferrule
Fiber
Fiber Connector

Physical
Contact
Alignment Alignment
Sleeve Sleeve

Fiber connectors are widely known as the WEAKEST AND MOST
PROBLEMATIC points in the fiber network.

17 © 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL & PROPRIETARY INFORMATION

What Makes a GOOD Fiber Connection?

The 3 basic principles that are critical to achieving an efficient fiber optic
connection are “The 3 P’s”:

Light Transmitted
 Perfect Core Alignment
 Physical Contact
Core
 Pristine Connector Cladding

Interface
CLEAN

Today’s connector design and production techniques have eliminated most of
the challenges to achieving Core Alignment and Physical Contact.

18 © 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL & PROPRIETARY INFORMATION

What Makes a BAD Fiber Connection?

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.

 A single particle mated into
the core of a fiber can Light Back Reflection Insertion Loss
cause significant
back reflection, insertion
loss and even equipment Core
damage. Cladding

DIRT


Illustration of Particle Migration

15.1µ

10.3µ

11.8µ
Core

Cladding

Actual fiber end face images 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.


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

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  Network Characterization
– It provides the network baseline
– It measures the fiber measurements before turning the
performance and the quality of transmission system up.
any interconnections – Network Characterization includes
– The suite of tests mostly depend measurements through the optical
amplifiers, dispersion compensators,
on the user’s methods and and any elements in line.
procedures – It is a limited suite of tests as
– It could be uni-directional or bi- compared to Link Characterization
directional ROADM

– Tests – Connector Inspection, IL, Router
Optical Amplifier

ORL, OTDR, PMD, CD, AP DWD
M
Optica
l
Netwo
Point A Point B rk

Video Optical Amp.
Headend
CWDM/DWDM
Optical
Network


LASER
☼

Testing the Fiber Plant
ON/OFF

CW/ LEVEL
FMOD ADJUST
MENU
PREV ENTER

@ On
@ Charge

 Connector inspection
 Insertion Loss
 OTDR
 Optical Return Loss
 Polarization Mode Dispersion (PMD)
 Chromatic dispersion (CD)
 Attenuation profile (AP)

Inspect Before You Connectsm

Follow this simple “INSPECT BEFORE YOU CONNECT” process to ensure fiber
end faces are clean prior to mating connectors.


Inspect, Clean, Inspect, and Go!

Fiber inspection and cleaning are SIMPLE steps with immense benefits.

1 Inspect 2 Clean 3 Inspect 4 Connect

■ Use a probe ■ If the fiber is dirty, use ■ Use a probe ■ If the fiber is clean,
microscope to a simple cleaning tool microscope to CONNECT the
INSPECT the fiber. to CLEAN the fiber RE-INSPECT (confirm connector.
surface. fiber is clean).
– If the fiber is dirty, go NOTE: Be sure to inspect
to step 2, cleaning. – If the fiber is still dirty, both sides (patch cord
go back to step 2, “male” and bulkhead
– If the fiber is clean, go
cleaning. “female”) of the fiber
to step 4, connect.
interconnect.
– 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
Perm
>2s

m
B
d
B
d

W

W

m
B
B
d
d
lu
ce
an
C
n
e
M

Pt Pr

It is the difference between the transmitted power and the received power at
the each end of the link

This measurement is the most important test to be performed, as
each combination of transmitter/receiver has a power range limit.


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)

OCWR method OTDR method


Optical Time Domain Reflectometer (OTDR)

OTDR depends on two types of phenomena:
- Rayleigh scattering
- Fresnel reflections.

Rayleigh scattering and Light reflection phenomenon = Fresnel
backscattering effect in a fiber 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

Fiber under test

Distance


Optical Time Domain Reflectometer (OTDR)

 Detect, locate, and measure events at any location on
the fiber link

Fusion Splice Connector or Gainer Macrobend Fiber end or break
mechanical
Splice
• 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.


Contamination and Signal Performance

Fiber Contamination and Its Effect on Signal Performance
1 CLEAN CONNECTION

Back Reflection = -67.5 dB
Total Loss = 0.250 dB

3 DIRTY CONNECTION

Clean Connection vs. Dirty Connection
This OTDR trace illustrates a significant decrease in signal
performance when dirty connectors are mated.

Back Reflection = -32.5 dB
Total Loss = 4.87 dB


Measuring PMD
<10 seconds
PMD
Light PMD
Source Receiver

 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
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.

ps

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


Measuring CD
CD
Light CD
Source Receiver

 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

Measuring AP
Broadband
Light Narrowband
Source Receiver

 Every fiber presents varying levels of attenuation
across the transmission spectrum. The purpose of
Water peak
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. C+L DWDM Band AP results
 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 IEC 60793-1-1 Optical fibers – Part 1-1: Generic
transmission system: C-band or C+L band. Specification – GeneralTest procedure
ITU-T G.650.1


Fiber Characterization Results


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
 Inspection & Cleaning
 Power Meters
 Ethernet Testers
BER Testers
 Optical Spectrum Analyzers
 Network Characterization (System
Total Dispersion)

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/characterization
There you’ll find…
Technical Posters, White Papers, Quick Start Guides, FO Guidebooks,
Product and Service Information, and more…


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Editor's Notes