Fiber Characterization Training

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 Point

Buildings

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.

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

Attenuation,

Dispersion,

NOT FOR USE OUTSIDE VERIZON AND JDSU

4

Optical Transmission

5

© 2007 JDSU. All rights reserved.

Optical Fiber Types
2 types: – Singlemode – Multimode

6

© 2007 JDSU. All rights reserved.

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

7

© 2007 JDSU. All rights reserved.

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 OTDR Trace of a fiber link

8

© 2007 JDSU. All rights reserved.

(Received power)

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) 9

© 2007 JDSU. All rights reserved.

Optical Return Loss (ORL)
Amount of transmitted light reflected back to the source PPC

PAPC

Pelement

PAPC

PR Receiver (Rx)

Source (Tx)

PBS

PBS

PT: Output power of the light source

PT

ORL (dB) = 10.Log

PBS

(

PT >) 0 PR

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 is measured in dB and is a positive value.  The higher the number, the smaller the reflection - yielding the desired result. 10

© 2007 JDSU. All rights reserved.

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. 11

© 2007 JDSU. All rights reserved.

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

12

© 2007 JDSU. All rights reserved.

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]

d

0 Tx

Rx fiber span

13

DC modules © 2007 JDSU. All rights reserved.

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 ∆τ [ps/√km]

V1 > V2

DGD

v2 v1

Perfect SM Fiber span

14

© 2007 JDSU. All rights reserved.

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 2.5 Gbit/s (OC-48)

6,400 km

10 Gbit/s (OC-192)

400 km

40 Gbit/s (OC-768

25 km DGD

v2 v1

15

© 2007 JDSU. All rights reserved.

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 Sleeve

Alignment 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 cause significant back reflection, insertion loss and even equipment damage.

Light

Back Reflection

Core Cladding

DIRT

19

© 2007 JDSU. All rights reserved.

Insertion Loss

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. 20

© 2007 JDSU. All rights reserved.

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

© 2007 JDSU. All rights reserved.

Link & Network Characterization
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 bidirectional – Tests – Connector Inspection, IL, ORL, OTDR, PMD, CD, AP Point A

– 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 ROADM

Optical Amplifier

Router

DWD M Optica l Netwo rk

Point B Video Headend

Optical Amp. CWDM/DWDM Optical Network

23

© 2007 JDSU. All rights reserved.

☼

LASER ON/OFF

Testing the Fiber Plant

PREV

CW/ FMOD

LEVEL ADJUST

MENU ENTER

@ @


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

On Charge

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

25

© 2007 JDSU. All rights reserved.

Inspect, Clean, Inspect, and Go! Fiber inspection and cleaning are SIMPLE steps with immense benefits.

1

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.

2

3

Clean

■ If the fiber is dirty, use a simple cleaning tool to CLEAN the fiber surface.

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.

26

© 2007 JDSU. All rights reserved.

4

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.

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 Optical power meter

Calibrated Light Source M Ca e nc n el u

d W B d m B

d W B m d B

>2s Perm

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. 27

© 2007 JDSU. All rights reserved.

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

28

OTDR method

© 2007 JDSU. All rights reserved.

Optical Time Domain Reflectometer (OTDR) OTDR depends on two types of phenomena: - Rayleigh scattering - Fresnel reflections.

Light reflection phenomenon = Fresnel reflection

Rayleigh scattering and backscattering effect in a fiber

29

© 2007 JDSU. All rights reserved.

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 30

© 2007 JDSU. All rights reserved.

Optical Time Domain Reflectometer (OTDR)
Detect, locate, and measure events at any location on the fiber link

Fusion Splice

Connector or mechanical Splice

Gainer

Macrobend

Fiber end or break

• 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. 31

© 2007 JDSU. All rights reserved.

Contamination and Signal Performance 1

CLEAN CONNECTION

Fiber Contamination and Its Effect on Signal Performance

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 32

© 2007 JDSU. All rights reserved.

Measuring PMD <10 seconds PMD Light Source

PMD 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 33

© 2007 JDSU. All rights reserved.

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 34

© 2007 JDSU. All rights reserved.

Measuring CD CD Light Source

CD Receiver


There are different methods to measure the chromatic dispersion. IEC 607931-42 / 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 35

© 2007 JDSU. All rights reserved.

Measuring AP Broadband Light Source














36

Narrowband Receiver

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.

Water peak

C+L DWDM Band AP results

IEC 60793-1-1 Optical fibers – Part 1-1: Generic Specification – GeneralTest procedure ITU-T G.650.1

© 2007 JDSU. All rights reserved.

Fiber Characterization Results

37

© 2007 JDSU. All rights reserved.

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
Inspection & Cleaning
Power Meters
Ethernet Testers
BER Testers
Optical Spectrum Analyzers
Network Characterization (System Total Dispersion) 39

© 2007 JDSU. All rights reserved.

Q&A and Resources


Questions
Contacts Name - 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]

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/characterization There you’ll find… Technical Posters, White Papers, Quick Start Guides, FO Guidebooks, Product and Service Information, and more… 40

© 2007 JDSU. All rights reserved.