EXFO-OLTS vs OTDR - VIRZ Expertennetzwerk · OTDR settings (pulse, range, averaging duration) are...

1© 2016 EXFO Inc. All rights reserved.

OLTS vs OTDR

Christian Till, Application Engineer

2016/12/09

Tier-2 Expert; How far from Tier-1?


›Bandwidth grows like crazy… Global DC traffic 5ZB now, 10.4ZB 2019

›Hyperscale are going 100% SMF… planning 200-400G intra-DC!

›MMF OM5 standard has been adopted… SWDM4 transceivers rise

›10 GbE (SFP) is OK at top-of-the rack switch, 40G/100G+ Leaf-Spine

›2016: Year of 25 GbE (SFP) and 4x25G lane, 100G Serial duplex OR Parralel

›Mobile & Telco operators re-architecture their CO in Data Center (CORD)

›Existing infrastructure (LC/UPC patch panels) are more sensitive to back reflection…

›What is the value of testing?

Why this industry is exciting!


Standard Testing Requirements

Tier-1Certification Tests

Tier-2Extended Tests & Troubleshooting

Normative Measurements

� Polarity (VFL)

� Insertion Loss (IL)� Length

Informative Measurements

� Polarity (VFL)

� Insertion Loss� Length� Connector and Splice

Loss� Connector Reflectance

Recommended Method

� LS/PM

� OLTS/Certifier

Recommended Method

� OTDR/iOLM


IEEE Standards (published or under development)

IEEE 802.3bs �� 200/400G Fiber

� Includes MMF & SMF options

� SMF� Duplex Series up to

500m/2Km/10Km

� MMF � Parallel 16x25G.

Source: Commscope


What fiber & connector types to choose?

Serial Duplex – LC connectors Parralel Optics - Multi-Fiber MPO/MTP

� Ceramic ferrule (zirconia)

� One fiber per connector

� Typically used in duplex (transmit & receive)

� Common types include LC

� Polymer ferrule

� Multiple fibers in linear array (8, 12, 24)

� High-density connectivity in single connector.

� Common type is MPO or MTP®

MMF (OM4, OM5) UPC versus SMF (OS1) / APC or UPC


Construction (Tier-1 test)

Only OLTS (or LSPM) defined for Tier 1 testing


Troubleshooting (Tier-2 test)

Copper (CAT)

Fiber

FIPFIP

FIP FIP

FIP

FIP

Mapping faults along the fiber requires the use of an iOLM-OTDR

iOLM

Receive fiber

Serial – DuplexTransceiversSMF or MMF

Launch fiber

Leaf

Spine

iOLM-OTDR is the only

tool for:

• Detect Macrobends

• Measure and

validate proper

return loss of

connectors

• Detect excessive

connector loss due

to contamination,

damage

• Identify the position

of a fiber fault or

issue

MTP/MPO trunks


Move Add & Change (MAC) Transceivers

Leaf

Spine

Copper (CAT)

Fiber

FIPFIP

FIP FIP

FIP

FIP

Serial – DuplexTransceiversSMF or MMF

OLTS

OLTS

OLTS and Fiber Inspection probe, because it’s faster (3 sec.)!

1- Validate channel is

Pass with OLTS

2- Clean & inspect

connectors

3- Connect new

transceivers/ link

4- Validate the link

works properly

5- If not proper,

transceiver is likely to

be the issue.

MTP/MPO trunks


Can OTDR provides total fiber link attenuation/loss measurement as

accurately as OLTS provides, “in the field”?

1. Slight variations of fiber geometry along the fiber under test induce some errors

in the OTDR measurement when tested from a single direction.

2. When testing link attenuation, the local errors due to fiber geometry mismatch

are not cumulative. The link attenuation error only depends on launch vs

receive fiber geometry.

3. Averaging measurements performed from both ends remove these errors

(bidirectional averaging).

OTDR for Tier-1 testing..?


Why Encircled Flux (EF) is Important

OFL/Mandrel Wrap per TIA-426-14-A,

Encircled Flux (EFL) TIA-426-14-B, Annex A

Source: Belden (2011)

Optical loss testing in the field, not as simple as it seems

VCSELLED

Ideal/ EF

conditioned


Uncertainty contributor Source of errors Value Comment

Light source instability Test Equipment +/- 0.05 dB Typical instability of a light source as

per IEC 61282-14

Light source wavelength Test Equipment/

FUT (spectral

dependency)

Spectral loss dependence

for 300 m at 850 nm +/- 30

nm

Light source wavelength tolerance

specified as per ISO/IEC-14763-3

(2016)

MMF Launch condition Test Equipment +/- 10% x 1.6 dB (850 nm) For Encircled Flux compliant source

Mating reproducibility FUT +/- 0.1 dB As per IEC 61282-14

Reference connector

repeatability

FUT +/- 0.05 dB As per IEC 61282-14

LSPM: Main uncertainty contributors

MMF loss measurement using a 1-cord reference, at 850 nm for a link of 300 m, with a total loss of 1.6 dB

+/- 0.27 dB (850 nm) total uncertainty ref. IEC TR 61282-14 (2016)

(considers statistical addition of all contributors, weight dependent)


›OLTS measurement has been made in duplex (1-cord reference)

›Typical FUT:

MMF: OLTS reference set-up

EF compliant EF compliantREF-Grade (3m) REF-Grade (3m)


MMF: OLTS attenuation (850 nm)

+/- 0.27 dB

Uncertainty of light-source / power meter

measurement on a MMF link as per

IEC TR 61282-14 (2016)

Reproductibility of the OLTS measurement is consistent with the expected measurement

uncertainty (using three different OLTS).

Test conditions:

3OLTS, TJ-REF

Jumpers


Uncertainty

contributor

Comment

Launch and receive

test cord fiber

geometry

Fiber geometry (mainly the core size and the numerical aperture of the fiber) influence the amount of

backscatter signal that a fiber generates (source uncertainty in the measurement of individual connectors and

splices loss with an OTDR).

The uncertainty contribution due to fiber geometry mismatch is +/- 0.19 dB for SMF assuming a (fairly typical)

fiber core specification of 9.2 +/- 0.4 mm. Performing bidirectional OTDR measurement will remove this error.

Loss spectral

dependency of fiber

The fact that the LS and the iOLM can have slightly different nominal wavelengths will cause some deviation in

the measurements due to the spectral attenuation characteristics of the fiber (in general, connectors and splices

losses have low dependencies on nominal wavelength, but not the fiber)

OTDR trace noise OTDR is dependent on the right adjustment of OTDR test parameters (pulse length, distance range and

averaging time).

Trace recovery When a strong reflectance occurs close to the end of the link under test, it may cause some error on the

measurement of the backscatter level on the receive test cord

Proper measurement

of link loss

Minimum receive test cord length depends on worse case reflectance that is expected.

Trace analysis/event

detection robustness

In general, OTDR performances are highly dependent on the quality of the “raw” OTDR trace (clean trace, no

distortion or artefacts) as well as the robustness of the algorithms performing trace analysis (event detection

and characterization).

OTDR - Main uncertainty contributors


iOLM IL measurement

- In the iOLM application, specify the Launch and Receive lengths

- Launch an iOLM acquisition and read the span loss.

DUT iOLM

SPSB-EF SPSB-100m

PM

MMF: iOLM reference set-up


Consistent results

over multiple instruments.

Test conditions:

3OTDRs, Launch & Receive fibers

Reproductibility of the iOLM measurement exhibits very good consistency (using

three different iOLM) .

MMF: iOLM attenuation (850 nm)

EXFO is willing to share its procedure for

comparison.


MMF: OLTS vs iOLM attenuation (850 nm)

iOLM measures slightly lower

attenuation than OLTS

(average bias -0.25 dB)

Test conditions:

3OTDRs, Launch &

Receive fibers

OLTS, TJ-REF Jumpers

This bias is explained by the fundamental mechanism of backscattering which produces a

slightly underfilled equivalent measurement (even if the iOLM is conditioned for EF).


SMF: iOLM reference set-up (1310/ 1550 nm)

A reference measurement is required to validate accuracy of OTDR method. The reference is done using Light

Source (LS) and Power Meter (PM). The best possible conditions are set for the reference:

LS is using OTDR source in CW mode to ensure same wavelength as OTDR measurement

A Polarization scrambler is used to reduce PDL effects

A high-linearity, cooled detector, Laboratory PM is used

Ambient temperature is 23 C +/- 1C

Long warm-up are allowed (>30 minutes) before measurements

This setup can provide an attenuation reference with 0.01 dB uncertainty.

OTDR settings (pulse, range, averaging duration) are appropriate to ensure a low-noise measurement.

Launch and receive cords are of sufficient lengths.

Polarization Scrambler

Launch Fiber

Power Meter

OTDR1310/1550

1625

Polarization Scrambler

Launch Fiber

FUTReceive

FiberPower Meter

OTDR1310/1550

1625

P1

P2

AttenuationREF = P1-P2

Presented at TR-42.11 meeting, Philadelphia 2016.10.08


SMF: Single Direction OTDR Measurement

Launch & receive from same fiber type & manufacturer (to reduce uncertainty due to MFD mismatch)

+/- 0.15 dB

Test

conditions:

5OTDRs

Launch fibers

Receive fibers


SMF: Bi-directional OTDR Measurement

Bi-directional OTDR measurement: cancel out Backscatter characteristics between launch & receive fibers

+/- 0.1 dB

Test

conditions:

5OTDRs

Launch fibers

Receive fibers


� For SMF, only launch & tail cords backscatter characteristics are important for link attenuation.

� When launch & tail cords have the same backscatter characteristics, there is no error introduced in the link attenuation.

� For MMF, there is a slight bias between OTDR and LSPM due to the nature of the backscattering process.

� OTDR can provide extremely accurate fiber link attenuation measurements for SMF and fairly accurate for MMF.

� OTDR should be considered as a valid tool/method for Tier 1 characterization of SMF.

� For characterization of MMF, improvements are on the way.

Conclusions


Reflectance issues at the patch panel?

Source: EXFO Application Note 327 – Touching on Failure: Sources of Singlemode Fiber Issues in the Data Center, December 2016

10-12 dB average change (clean vs. oil)

Strict correlation (clean vs. oil)0.70.70.70.7

0.60.60.60.6

0.50.50.50.5

0.40.40.40.4

0.30.30.30.3

0.20.20.20.2

0.10.10.10.1

0000

70707070

60606060

50505050

40404040

30303030

20202020

10101010

0000

Thresholds (customers):

Standards (TIA-568.3-D (2016, b.3), IEC-11801 (2010): SMF 35dB, MMF 20dB

Direct modulation (CWDM4, PSM4, PAM4): -40 to -45dB CRC issues

Coherent-based: -30dB = EDFA APR mode issue

Finger oil


MTP/MPO based links (Tier-1 & Tier-2)

Pre-installation quality test

Migration to 100G/ 200G/ 400G

1 2 3

Parallel optics


Server to server communication inside a DC


Leaf – Spine topology: Redundant, scalable

• Efficient use of most

affordable components,

QSFP28, switches

• Each servers in the data

center is linked with all the

other servers with the

same number of hops.

• Can be configured in Layer

2 (switched) or Layer 3

(routed)


OM5 MMF Considerations (SWDM4)

Source: Commscope

Test parameter Test vendor advices

Attenuation Testing 850 nm worst case appears the best practice850 nm presents higher attenuation than 950 or 1300 nm

ORL / Reflectance VCSEL is more sensitive to ORL than LEDORL is wavelength independent, not light source independent

Dispersion (Chromatic and Modal)

Expect the smallest differential mode delay (DMD) specs possible for WBMMFUnless stated otherwise by the fiber manufacturer, CD (chromatic) and modal dispersion shall be considered OK by design

Source: EXFO


What are the main contributors of uncertainty?

Light Source / Power Meter (OLTS) OTDR

� Light Source (LS) instability (warming time)

� LS wavelength drift after referencing

� Reference test jumpers conditions

� Multimode reference test jumpers launch condition

� Mating reproducibility

� Reference connector repeatability

� LSPM vs OLTS (coupler PDL)

� Ideal LSPM vs OTDR (same for SM, slight difference for MM)

� OTDR loss linearity (vs loss uncertainty)

� Launch vs receive fiber geometry (different backscattering ratio)

� Noise on trace (vs pulse, vs averaging time)

� Trace recovery (vs reflectance, vs length of receive fiber)

� Echos

� Trace analysis/ event detection robustness

1- Equipment variation (repeatability)

2- Product variation (FUT variation)

Respect calibration period and change

your test jumpers…


UNCERTAINTY SPECIFICATIONS

• Specifications of FTB-730-iOLM testing of short span links (3m<Link<500m)

• Results valid at Results valid at 1310 and 1550 nm at 23±3°C

• Launch/ Receive (matched): 150m (for FUT <5 dB IL) or 500m (for FUT <12 dB IL)

• Reflectance specifications valid for L ≥15 m

OTDR - iOLMSpecification (dB)

Typical Notes

Link IL uncertainty 0.1 Link loss for 3m<L<500m or <12 dB.

Single connector IL uncertainty 0.1 15m≤ L <500m

Reflectance uncertainty 0.75 From -45 to -65 dB

Short link ORL uncertainty 1For L<15 m. Includes two connectors and fibre loss

uncertainties. Events may be merged.

• USING SUITABLE REFERENCE CABLES

Source & Power meter - OLTSSpecification (dB)

Typical Notes

Link IL uncertainty 0.1 (0.2) PM/LS: Loss <46 dB (OLTS: Loss <55 dB)

Single connector IL uncertainty N/AReflectance uncertainty N/A

Short link ORL uncertainty 0.5 (1) PM/LS: mandrel method (OLTS: Up to 55 dB ORL for APC)


Why Encircled Flux method is so important?

LED

VCSEL

IDEAL (EF)

EF ready, no external mode conditioner required

EF ready, external mode conditioner required

10G+ fiber-optic testing, requires EF metric,

launching condition to satisfy the required

REPEATABILITY, REPRODUCIBILITY and OPTIMAL

UNCERTAINTY


Is up to 30% uncertainty acceptable?

OFL/Mandrel Wrap per TIA-426-14-A,

Encircled Flux (EFL) TIA-426-14-B, Annex A

Source: Belden (2011)

Optical loss testing in the field, not as simple as it seems

TIA-568 C.3 : 3.5dB (OM1-OM4)

IEEE 802.3ae 10GBASE-LX4 : 2dB (OM2-OM4)

IEEE 802.3ba 40/100GBASE-SR4 : 1.5dB (OM4)


OLTS/ PM-LS / certification

LC-MTP⁄MTP-LC (1G/10G)TX RX

100 m OM4, 2km OS1

<3 seconds, 2 wavelengths Duplex, bi-directional, EF testingOLTS IL = 1.27 dB

TIA-568-C.3 – ISO/IEC-14763.3 = 3.5 dB

IEEE802.3.ba 40/100GBASE-SR4 (4x25) = 1.9 dB

Two evolutive tablet-inspired Platforms

Expert guidance, every step of the way

On-board multistandard Certification

Reduced cost of ownership

TX RX

MAX-940-QUAD


Is MMF dead? I think not: WBMMF (SWDM4)

Wideband Multimode Fiber (WBMMF)

Source: Commscope

2 fibers / 850 nm

880 nm910 nm940 nm

Test parameter Test vendor advices

Attenuation Testing 850 nm worst case appears the best practice850 nm presents higher attenuation than 950 or 1300 nm

ORL / Reflectance VCSEL is more sensitive to ORL than LEDORL is wavelength independent, not light source independent

Dispersion (Chromatic and Modal)

Expect the smallest differential mode delay (DMD) specs possible for WBMMFUnless stated otherwise by the fiber manufacturer, CD (chromatic) and modal dispersion shall be considered OK by design

Chromatic Dispersion

Modal Dispersion

Pulse spreading

Source: EXFO


Questions, checklist & test objectives

# Checklist Prerequisite Note

Important: Test instruments calibration

and reference test jumpers

Change test jumpers each 200-300 connections or

if they are scratched.

Measurement uncertainty depends on these

factors.

Input: Multimode or Singlemode fiber Keep in mind the 150 m reach limitation for MMF

(OM4/WBMMF).

Tighter budget for 40G & 100G over OM4

MMF / WBMMF, SMF more $

Input: What volume or counts of fiber

to test

What is the test task: fiber certification,

troubleshooting, warranty registration

Set your objectives carefully.

Decision: Test tools, testing time &

test procedures

OLTS helps screen suspect links (ORL)

OTDR maps fault and connectors RL

Test instruments alone do not solve

everything!

1 Contaminants on the connector

endfaces

Clean & inspect, first time right. Ultimate baseline for an effective and

efficient optical testing!

2 Mastering test repeatability,

uncertainty

Multimode fiber, Encircled Flux compliant

equipment & procedure.

Respect calibration and test jumpers quality!

3 Test data valorization Documentation system and processes Best practices to speed up future trouble

shooting.

4 Managing 10G to 100G+ migration:

connectors’ RL impact

RL can kill a network at 25 Gbps line rate… 25/50 Gbps more demanding than

10 Gbps…


OLTS vs iOLM-OTDR / RL, BR, ORL… Tier-1 & 2

Return loss (RL) is the loss of power in the signal returned/reflected by a discontinuity in a transmission line or optical fiber. This

discontinuity can be a mismatch with the terminating load or with a device inserted in the line (also called Reflectance or back

reflection ).

Optical Return Loss (ORL) is a measure taken from one end of the total energy reflected back to the source by all the interfaces

due to a variation of the index of refraction (IOR), breaks, voids, backscatter, etc., created inside a component or along a link.

LC LC

iOLM

LaunchReceive

End-to-end

iOLM - OTDR

OLTS FasTest Simplex


EXAMPLE


OLTS/ ORL: screening & link certification

MAX-945iCERT-QUAD

Targeted applications

• Move, Add and Changes (MACs) of pluggables optics

• Construction, certification of total loss budget (tier-1)

MAX-945iCERT-QUAD

500 ft.

(150 m)

1- OLTS

1- OLTS2- FIP3- iOLM

1- OLTS2- iOLM


iOLM – OTDR single fiber

100G-SWDM4

MDA

IDA

DCI WDM

ToR

OTDR-iOLM positions faults,

loss, reflectance and provide

link loss and ORL.

Threshold and standard

certification-based Pass/Fail.

LC Patch panel

LC patch panel

1.5 dB / 150 m (OM4)

Standard OM3

SPSB-EF-30m

Launch

30m Receive


iOLM – OTDR software interface

OTDR-iOLM positions faults,

loss, reflectance and provide

link loss and ORL.

Threshold and standard

certification-based Pass/Fail.


Testing MPO


MTP/MPO cable configurations (polarity, types)


Adapter

MPO Unpinned (Female)

MPO Pinned (Male)

MPO Guiding holes

MPO Guiding pins


Physical ContactThe Physical Contact area is the critical

joining point in the fiber network.

If no clean physical connection, the light

path is disrupted and the connection is

compromised.

Multiple connects-disconnects can create fiber

misalignments (loose pin/ hole or memory shape related

issues)


LC serial duplex – MTP/MPO trunk

catastrophic


FIP MTP/ MPO inspection auto-center / focus

Low mag view PIP (100X):

Allows to see which fiber is being

inspected in High magnification

High mag view (400X):

Highest Magnification on the market

Auto-center + Auto Focus

FIP controls:� AutoCenter

� AutoFocus

� Capture

� Analysis

MTP12 – MTP24 (MM/SM)


10G MTP/ MPO trunk test

Step 1: Pre-installation quality test Step 2: End to end LC-LC permanent link test

EXFO-OLTS vs OTDR - VIRZ Expertennetzwerk · OTDR settings (pulse, range, averaging duration) are...

Documents

Transcript of EXFO-OLTS vs OTDR - VIRZ Expertennetzwerk · OTDR settings (pulse, range, averaging duration) are...