EncircledFlux FOLS Webinar

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The need for Encircled Flux,

real or imaginary?

AdrianYoung

Fluke NetworksDecember 13th, 2012

Version 1.7


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Fiber Optics LAN Section

Overview:

Part of the Telecommunications IndustryAssociation (www.tiaonline.org)

Formed 198 years ago

Mission: to educate users about the benefits of

deploying fiber in customer-owned networks

FOLS provides vendor-neutral information


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Current Members 3M

AFL/Noyes FiberSystems

Berk-Tek, a NexansCompany

Corning

CommScope Draka Communications

Fluke Networks General Cable

Leviton

OFS

Ortronics/legrand

Sumitomo ElectricLightwave

Superior Essex

TE Connectivity


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Recent Webinars Available on Demand

Preventing Network Failures by thoroughly Cleaning &

Testing FO Connectors

Tier 1 and Tier 2 Testing: Trouble Shooting &

Documentation

Visit www.fols.orgor our channel on BrightTalk

Webinars are eligible for CEC credit for up to two

years after they are first broadcast.


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Whats the issue

Mandrels are they needed?

Review of standards

Coupled Power Ratio

Test methods

Mode controllers

In this webinar


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Encircled Flux (EF) is the final piece in the puzzle toreducing measurement uncertainty in the field

Reducing multimode uncertainty


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Even today folks are not using mandrels to control the launch

The issue Launch control

Multimode Source 1Power Meter 1

Multimode Source 1Power Meter 1

No mandrel, reading may be pessimistic


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Mandrels

Mode is from the Latin for path/way

So Multimode is Multiple Paths/Ways

Higher and lower order modes found in sources

Higher modes are less stable

Lower modes are more stable

Need to remove those higher order modes

And that is what the mandrel does

Helps reduce measurement differences between different

sources



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Make an optical loss measurement

Using reference grade connectors

Better than 0.10 dB on the test reference cords

With a mandrel at the source


Multimode

Source 1

Power Meter 1

Do not use Bend

Insensitive Fiber TestReference Cords


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Make another optical loss measurement

Using the same reference grade connectors

Better than 0.10 dB on the test reference cords

With the same mandrel at the source

But using a different source


Multimode

Source 2

Power Meter 1

Do not use Bend

Insensitive Fiber TestReference Cords


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Diagrams shown to visualize the issue as best as possible

Launch at source is different

Source 1Over filled

Source 2Under filled


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Only the power meter is calibrated to traceable standards

The optical source has no traceable calibration

Thats why there is a standard to specify the sourceoutput, Encircled Flux

Traceable calibration

Traceablecalibration

No traceablecalibration


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Attempted to limit variation

Specified something called

Coupled Power Ratio

For Multimode measurements, a Category 1 light sourcewas required (850 nm example here)

Lets look at how that was determined

ANSI/TIA-526-14-A (2003)


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Coupled Power Ratio

1.

If testing a 50/125 !m fiber optical link, you would connectthe source and meter together using a 50/125 !m cord

2. After allowing the source to stabilize, record the receivedpower in dBm

Multimode SourcePower Meter


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Coupled Power Ratio

3.

Insert a singlemode cord and record the received poweragain

4. The difference in power received defines the category of

light source (850 nm example below)

30 mm loop actsas a mode filter

TIA requirement for multimode


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CPR assessment shortfall

Source 1Over filled


CPR compares power in center to total power.

It cant provide assessment of mode power distribution in the outer radiiwhich is critical to obtain good agreement with different test instruments.


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EF assessment improvement

Source 1Over filled


EF specifies power throughout core using multiple control radii.

EF provides tight tolerance on mode power distribution in the outer radiienabling improved agreement between EF-compliant test instruments.


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Some believe the source should be a VCSEL

Reasoning

Use the same source type as the active equipment

Problem

The optical loss limits in IEEE 802.3 are based on test equipment

using LEDs, same for ANSI/TIA and ISO/IEC

VCSELs are under filled results in optimistic readings

Launch condition varies greatly from source to source

What Category is a VCSEL source?

VCSEL alert


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Using the CPR method shown previously as found in ANSI/TIA-526-14-A

A VCSEL is somewhere between Category 3 & 4

Dont use a VCSEL unless you are specifically told to do so

Some vendors will not warrant a cabling system if a VCSELsource is used to test

VCSEL alert


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Replaced with ANSI/TIA-526-14-B (Oct 2010)

Also known as IEC 61280-4-1 edition 2,

Replaces Coupled Power Ratio with Encircled Flux

ANSI/TIA-526-14-B titled:

Optical Power Loss Measurements of Installed Multimode Fiber

Cable Plant

IEC 61280-4-1 edition 2, titled:

Fibre-Optic Communications Subsystem Test Procedure

Part 4-1: Installed cable plant- Multimode attenuation measurement

ANSI/TIA-526-14-A


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Was considered adequate for the time (2003)

Test limits getting tighter

1000BASE-SX (2.6 dB over OM1)

10GBASE-SR (2.6 dB over OM3)

Consultants tightening loss budgets

Manufacturers tightening loss budgets

ISO/IEC 14763-3 (2006) changed to MPD

Modal Power Distribution

Tighter than CPR

Now also adopting Encircled Flux to replace MPD

ANSI/TIA-526-14-A


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Titled:

Generic Telecommunications Cabling for Customer Premises

Addendum 2, General Updates

Published August 2012

New application limits

40GBASE-SR4 (100 m, 1.9 dB over OM3)




Limits are getting tighter, CPR and MPD no longer goodenough

ANSI/TIA-568-C.0-2


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Sadly, most folks are setting a reference this way

Issues

You have no idea what the loss is in the adapter

Whatever it is, its subtracted from your measurement

The uncertainty is horrendous negative loss

What is done today

? dB


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So you end up with this

Issues




What is done today

x dB z dB

y dB

Measurement = x + y + z - ?


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Lets take an example

Issues




What is done today

0.75 dB


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Lets take an example

Issues




What is done today

0.3 dB 0.3 dB

0.1 dB

Measurement = 0.3 + 0.1 + 0.3 0.75

= -0.05 dB


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ANSI/TIA describes this as Method A

Not for enterprise cabling systems

Used in long haul measurements

Uncertainty of one connector not considered critical?

What is done today

? dB


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For testing an installed fiber optical link, should always usethe 1 Jumper Reference Method

Does require the test equipment to have interchangeable

adapters on the INPUT ports

What is done today


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Removed from INPUT port only

Its ok to remove the fiber from the input ports

You cannot remove the fiber from the output port, doingso will invalidate the reference you just made


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To the INPUT ports

Connect known good cord


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To the INPUT ports



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How do I know if those cords are good?



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Connect them together using a singlemode adapter andmeasure the loss

Verifying the cords

ISO/IEC 14763-3 "0.1 dB for Multimode

"0.2 dB for Singlemode

ANSI/TIA-568-C.0 "0.75 dB?

Cabling Vendors "0.50 dB?

Why not save this as proof of good test reference cords?

*

* This can be up to 0.15 dB for LC


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Test Reference Cord Values

ISO/IEC 14763-3

1 Jumper method (0.1 dB for Multimode and 0.2 dB for Singlemode)

ANSI/TIA-568-C.0

Does not call out test reference cord values ("0.75 dB?)

You are expected to specify this

Require documentation of TRCs

?


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Disconnect


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ANSI/TIA-568-C.0

First and last connections "0.75 dB

All other connections "0.75 dB

Connect to the fiber optic link

!0.75 dB !0.75 dB


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ISO/IEC 11801:2010 & ISO/IEC 14763-3

First and last connections "0.30 dB

All other connections "0.75 dB

Connect to the fiber optic link

!0.30 dB !0.30 dB


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In ISO/IEC 14763-3 (2006), cords were recognized as asource of great uncertainty

This standard reduced uncertainty by defining theperformance of the test cord connector

Reference grade connectors were required

Multimode "0.10 dB

Singlemode "0.20 dB

Impact of test reference cords

0.75 dB0.10 dB

!0.30 dB

0.75 dB0.20 dB

!0.50 dB


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ISO/IEC 14763-3 group working on this

The figure of 0.09 dB assumes 1 Jumper Referencemethod with a test reference cord using a reference grade

connector of 0.10 dB

Excludes Encircled Flux uncertainty

Measurement uncertainty


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Myth: cannot use 1 Jumper Reference

LC to SC fiber links


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Titled:

Practical Considerations for Implementation of Multimode Launch

Conditions in the Field

Currently in draft

TSB = Telecommunications System Bulletin

Not an official standard

An advisory document

Chances are will end up in ANSI/TIA-568-D.3

Helps users understand Encircled Flux and the options for

implementing it

Look out for TIA-TSB-4979


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Option 1

Ignore it

Practical implementation of EF


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Option 2

Use an external mode controller

Replaces the mandrels

Practical implementation of EF


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Practical Considerations

of Encircled Flux Compliance

Todays solution

When that LC connector breaks or

wears out, it cannot be re-terminatedin the field

Re-terminations need to beverified for EF compliance


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So why not just make the source EF compliant?

EF compliance is at the end of the test cord



EF Compliance is met at the end of the Test Reference Cord

A Test Reference Cord will alter the EF template


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Can I add a sacrificial cord to protect that LC?

Adapter concentricity may not be good enough

Fiber core would have to be 0.5 !m

diameter for the sacrificial cord

No practical way to verify in the field



Sacrificial cord


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Similar to the CPR method, ANSI/TIA-526-14-B describesa field artifact, with multiple concatenated offset splices

The idea is to characterize the loss through the artifact

with an EF compliant launch and compare this loss with afield light source

While this artifact has been qualified in test labs, none

exist commercially

At this time, the only way to measure for EF compliance is

in a lab with bench top equipment designed to measurenear field radiation

Verifying EF compliance in the field


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It is claimed that different labs show different results whenverifying EF compliance

TIA initiated a round robin test

19 months and 14 vendors later, the results were

presented to TR 42.11

There was good agreement amongst all vendors exceptfor one (defect in camera)

Biggest myth on EF


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At a minimum, use a mandrel

This does not yield the controlled launch condition the industry

desires that is Encircled Flux

Dont use a VCSEL source

Too much variability

Consider investing in fiber optic test equipment that allows

a 1 Jumper Reference reduced uncertainty

Verify your Test Reference Cords

Save the results and make it part of your documentation

If Encircled Flux is a contractual requirement, use mode

controllers for now

Summary


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