The need for Encircled Flux, real or imaginary?

Version 1.7 The need for Encircled Flux, real or imaginary? Harley Lang, RCDD Fluke Networks 14 March, 2013

Presentation agenda What s the issue Mandrels are they needed? Review of standards Coupled Power Ratio Test methods Mode controllers

Reducing multimode uncertainty Encircled Flux (EF) is the final piece in the puzzle to reducing measurement uncertainty in the field

The issue Launch control Even today folks are not using mandrels to control the launch No mandrel, reading may be pessimistic Power Meter 1 Multimode Source 1 Power Meter 1 Multimode Source 1

The issue Launch control 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

The issue Launch control 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 Do not use Bend Insensitive Fiber Test Reference Cords Power Meter 1 Multimode Source 1

The issue Launch control 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 Do not use Bend Insensitive Fiber Test Reference Cords Power Meter 1 Multimode Source 2

Launch at source is different Diagrams shown to visualize the issue as best as possible Source 1 Over filled Source 2 Under filled

Traceable calibration Only the power meter is calibrated to traceable standards The optical source has no traceable calibration Traceable calibration No traceable calibration That s why there is a standard to specify the source output, Encircled Flux

ANSI/TIA-526-14-A (2003) Attempted to limit variation Specified something called Coupled Power Ratio For Multimode measurements, a Category 1 light source was required (850 nm example here) Let s look at how that was determined

Coupled Power Ratio 1. If testing a 50/125 µm fiber optical link, you would connect the source and meter together using a 50/125 µm cord Power Meter Multimode Source 2. After allowing the source to stabilize, record the received power in dbm

Coupled Power Ratio 3. Insert a singlemode cord and record the received power again 30 mm loop acts as a mode filter 4. The difference in power received defines the category of light source (850 nm example below) TIA requirement for multimode

CPR assessment shortfall CPR compares power in center to total power. It can t provide assessment of mode power distribution in the outer radii which is critical to obtain good agreement with different test instruments. Source 1 Over filled Source 2 Under filled

EF assessment improvement EF specifies power throughout core using multiple control radii. EF provides tight tolerance on mode power distribution in the outer radii enabling improved agreement between EF-compliant test instruments. Source 1 Over filled Source 2 Under filled

VCSEL alert Some believe the source should be a VCSEL Reasoning Use the same source type as the active equipment Problem The optical loss limits i 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 Using the CPR method shown previously as found in ANSI/TIA- 526-14-A A VCSEL is somewhere between Category 3 & 4 Don t use a VCSEL unless you are specifically told to do so Some vendors will not warrant a cabling system if a VCSEL source is used to test

ANSI/TIA-526-14-A 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 1 edition 2, titled: Fibre-Optic Communications Subsystem Test Procedure Part 4-1: Installed cable plant- Multimode attenuation measurement

ANSI/TIA-526-14-A 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 g 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-568-C.0-2 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) 40GBASE-SR4 (150 m, 1.5 db over OM4) 100GBASE-SR10 (100 m, 1.9 db over OM3) 100GBASE-SR10 (150 m, 1.5 db over OM4) Limits are getting tighter, CPR and MPD no longer good enough

What is done today Sadly, most folks are setting a reference this way? db Issues You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

What is done today So you end up with this y db x db z db Measurement = x + y + z -? Issues You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

What is done today Let s take an example 0.75 db Issues You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

What is done today Let s take an example 0.1 db 0.3 db 0.3 db Issues Measurement = 0.3 + 0.1 + 0.3 0.75 = -0.05 db You have no idea what the loss is in the adapter Whatever it is, it s subtracted from your measurement The uncertainty is horrendous negative loss

What is done today ANSI/TIA describes this as Method A? db Not for enterprise cabling systems Used in long haul measurements Uncertainty of one connector not considered critical?

What is done today For testing an installed fiber optical link, should always use the 1 Jumper Reference Method Does require the test equipment to have interchangeable adapters on the INPUT ports

Removed from INPUT port only It s ok to remove the fiber from the input ports You cannot remove the fiber from the output port, doing You cannot remove the fiber from the output port, doing so will invalidate the reference you just made

Connect known good cord To the INPUT ports

Connect known good cord To the INPUT ports

Connect known good cord How do I know if those cords are good?

Verifying the cords Connect them together using a singlemode adapter and measure the loss * ISO/IEC 14763-3 0.1 db for Multimode 0.2 db for Singlemode ANSI/TIA-568-C.0 0.75 db? * This can be up to 0.15 db for LC Cabling Vendors 0.50 db? Why not save this as proof of good test reference cords?

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 t reference cord values ( 075dB?) 0.75 You are expected to specify this? Require documentation of TRCs

Disconnect

Connect to the fiber optic link ANSI/TIA-568-C.0 0.75 db 0.75 db First and last connections 0.75 db All other connections 075dB 0.75

Connect to the fiber optic link ISO/IEC 11801:2010 & ISO/IEC 14763-3 0.30 db 0.30 db First and last connections 0.30 db All other connections 075dB 0.75

Impact of test reference cords In ISO/IEC 14763-3 (2006), cords were recognized as a source of great uncertainty This standard reduced uncertainty by defining the performance of the test cord connector Reference grade connectors were required Multimode 0.10 010dB Singlemode 0.20 db 0.10 db 0.75 db 0.20 db 0.75 db 0.30 db 0.50 db

Measurement uncertainty ISO/IEC 14763-3 group working on this The figure of 0.09 db assumes 1 Jumper Reference method with a test reference cord using a reference grade connector of 0.10 db Excludes Encircled Flux uncertainty

LC to SC fiber links Myth: cannot use 1 Jumper Reference

LC to SC fiber links Myth: cannot use 1 Jumper Reference

LC to SC fiber links Myth: cannot use 1 Jumper Reference

LC to SC fiber links Myth: cannot use 1 Jumper Reference

LC to SC fiber links Myth: cannot use 1 Jumper Reference

Look out for TIA-TSB-4979 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 Helps users understand Encircled Flux and the options for implementing it

Practical implementation of EF Option 1 Ignore it

Practical implementation of EF Option 2 Use an external mode controller Replaces the mandrels

Practical Considerations of Encircled Flux Compliance Today s solution When that LC connector breaks or wears out, it cannot be re-terminated in the field Re terminations need to be Re-terminations need to be verified for EF compliance

Practical Considerations of Encircled Flux Compliance 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

Practical Considerations of Encircled Flux Compliance Can I add a sacrificial cord to protect that LC? Sacrificial cord Adapter concentricity may not be good enough Fiber core would have to be ±0.5 µm diameter for the sacrificial cord No practical way to verify in the field

Verifying EF compliance in the field Similar to the CPR method, ANSI/TIA-526-14-B describes a 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 a field 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 measure near field radiation

Biggest myth on EF It is claimed that different labs show different results when verifying 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 except for one (defect in camera)

Summary At a minimum, verify your Test Reference Cords and use a mandrel This does not yield the controlled launch condition the industry desires that is Encircled Flux, but it reduces uncertainty. Save the results and make it part of your documentation Don t use a VCSEL source -Too much variability Consider investing in fiber optic test equipment that allows a 1 Jumper Reference reduced uncertainty If Encircled Flux is a contractual requirement, use mode controllers or stay tuned for matched solution Per TIA TSB 4979