Fiber Characterization Training

Fiber CharacterizationAssessing 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.

01 2

2

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NOT FOR USE OUTSIDE VERIZON

AND JDSU

4

Attenuation, Dispersion,

02

1

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∂∂∂∂AA

dT

AA

i

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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)

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


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)

Optical Return Loss (ORL)

� Amount of transmitted light reflected back to the source

PAPCPPC Pelement PAPC

PBS PBS PBS

Source

(Tx)

Receiver

(Rx)

PR


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


– 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.


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


– DC fiber modules correct for chromatic dispersion in the link

Tx Rx

DC modulesfiber 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]


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


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 ConnectorFiber

Ferrule

© 2009 JDSU. All rights reserved. JDSU CONFIDENTIAL & PROPRIETARY INFORMATION17

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 INFORMATION18

� 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.


� 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 LossLight

Illustration of Particle Migration

11.8µ

15.1µ

10.3µ

Core

Cladding


� 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


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


– It could be uni-directional or bi-directional

– Tests – Connector Inspection, IL, ORL, OTDR, PMD, CD, AP

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

LASER

ON/OFF

PREV

LEVEL

ADJUSTMENUENTER

CW/

FMOD

☼LASER

ON/OFF

PREV

LEVEL

ADJUSTMENUENTER

CW/

FMOD

☼☼

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.

44 Connect22 Clean11 Inspect 33 Inspect


■ 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


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

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)


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.


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


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


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 PerformanceCLEAN CONNECTION

Back Reflection = -67.5 dB

Total Loss = 0.250 dB

11



DIRTY CONNECTION

Back Reflection = -32.5 dB


33

Clean Connection vs. Dirty Connection

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

<10 secondsPMD

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


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…)


– 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


� 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


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

Fiber Characterization Results


Wrap Up

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


Network / Transport

� Inspection & Cleaning

� Power Meters

� Ethernet Testers

�BER Testers

� Optical Spectrum Analyzers

� Network Characterization (System Total Dispersion)

Q&A and Resources

� Questions

� ContactsName - Company (Title) Phone E-mail

Fred Ingerson – 4th Wave (JDSU Mfg Rep) (315) 436-0895 [email protected]

Mark Leupold – JDSU (MSO Acct Mgr) (540) 226-6284 [email protected]


Mark Leupold – JDSU (MSO Acct Mgr) (540) 226-6284 [email protected]

John Swienton – JDSU (FO App Specialist) (413)231-2077 [email protected]

Greg Lietaert – JDSU (FO Prod Line Mgr) (240) 404 2517 [email protected]

Tim Yount – JDSU (FO Test Mkt Mgr) (207)329-3342 [email protected]

For more on Fiber Characterization visit: www.jdsu.com/characterizationThere you’ll find…

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Fiber Characterization Training

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