OLTS vs OTDR Tier-2 Expert; How far from Tier-1?

OLTS vs OTDR Tier-2 Expert; How far from Tier-1? Christian Till, Application Engineer 2016/12/09 1

Why this industry is exciting! 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? 2

Standard Testing Requirements Tier-1 Certification Tests Normative Measurements Polarity (VFL) Insertion Loss (IL) Length Recommended Method LS/PM OLTS/Certifier Tier-2 Extended Tests & Troubleshooting Informative Measurements Polarity (VFL) Insertion Loss Length Connector and Splice Loss Connector Reflectance Recommended Method OTDR/iOLM 3

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 4

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 5

Construction (Tier-1 test) Only OLTS (or LSPM) defined for Tier 1 testing 6

Troubleshooting (Tier-2 test) Copper (CAT) Fiber Mapping faults along the fiber requires the use of an iolm-otdr iolm-otdr is the only tool for: FIP FIP FIP Leaf Detect Macrobends Measure and validate proper return loss of connectors Serial Duplex Transceivers SMF or MMF FIP MTP/MPO trunks FIP Receive fiber iolm FIP Spine Detect excessive connector loss due to contamination, damage Identify the position of a fiber fault or issue Launch fiber 7

Move Add & Change (MAC) Transceivers Copper (CAT) Fiber OLTS and Fiber Inspection probe, because it s faster (3 sec.)! 1-Validate channel is Pass with OLTS Leaf 2-Clean & inspect connectors Serial Duplex Transceivers SMF or MMF FIP FIP MTP/MPO trunks FIP FIP OLTS FIP FIP Spine 3-Connect new transceivers/ link 4-Validate the link works properly 5-If not proper, transceiver is likely to be the issue. OLTS 8

OTDR for Tier-1 testing..? 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). 9

Why Encircled Flux (EF) is Important LED VCSEL Ideal/ EF conditioned 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 10

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 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 mat 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 +/-0.27 db (850 nm) total uncertainty ref. IEC TR 61282-14 (2016) (considers statistical addition of all contributors, weight dependent) 11

MMF: OLTS reference set-up OLTS measurement has been made in duplex (1-cord reference) EF compliant REF-Grade (3m) REF-Grade (3m) EF compliant Typical FUT: 12

MMF: OLTS attenuation (850 nm) Uncertainty of light-source / power meter measurement on a MMF link as per IEC TR 61282-14 (2016) +/- 0.27 db Test conditions: 3 OLTS, TJ-REF Jumpers Reproductibility of the OLTS measurement is consistent with the expected measurement uncertainty (using three different OLTS). 13

OTDR - Main uncertainty contributors Uncertainty contributor Launch and receive test cord fiber geometry Comment 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 OTDR trace noise Trace recovery Proper measurement of link loss Trace analysis/event detection robustness 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 is dependent on the right adjustment of OTDR test parameters (pulse length, distance range and averaging time). 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 Minimum receive test cord length depends on worse case reflectance that is expected. 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). 14

MMF: iolm reference set-up iolm IL measurement - In the iolm application, specify the Launch and Receive lengths - Launch an iolm acquisition and read the span loss. iolm SPSB-EF DUT SPSB-100m PM 15

MMF: iolm attenuation (850 nm) Consistent results over multiple instruments. Test conditions: 3 OTDRs, Launch & Receive fibers Reproductibility of the iolm measurementexhibitsvery good consistency (using three different iolm). EXFO is willing to share its procedure for comparison. 16

MMF: OLTS vs iolm attenuation (850 nm) Test conditions: 3 OTDRs, 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). iolm measures slightly lower attenuation than OLTS (average bias -0.25 db) 17

SMF: iolm reference set-up (1310/ 1550 nm) Presented at TR-42.11 meeting, Philadelphia 2016.10.08 1625 OTDR 1310/1550 Polarization Scrambler Launch Fiber Power Meter P1 Attenuation REF = P1-P2 1625 OTDR 1310/1550 Polarization Scrambler Launch Fiber FUT Receive Fiber Power Meter P2 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. 18

SMF: Single Direction OTDR Measurement Test conditions: 5 +/- 0.15 db OTDRs Launch fibers Receive fibers Launch & receive from same fiber type & manufacturer (to reduce uncertainty due to MFD mismatch) 19

SMF: Bi-directional OTDR Measurement Test conditions: 5 +/- 0.1 db OTDRs Launch fibers Receive fibers Bi-directional OTDR measurement: cancel out Backscatter characteristics between launch & receive fibers 20

Conclusions 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. 21

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Reflectance issues at the patch panel? 0.7 0.6 0.5 0.4 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 Strict correlation (clean vs. oil) 70 60 50 40 Finger oil 0.3 0.2 0.1 0 30 20 10 0 10-12 db average change (clean vs. oil) Source: EXFO Application Note 327 Touching on Failure: Sources of Singlemode Fiber Issues in the Data Center, December 2016 23

MTP/MPO based links (Tier-1 & Tier-2) Parallel optics Pre-installation quality test Migration to 100G/ 200G/ 400G 1 2 3 24

Server to server communication inside a DC 25

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) 26

OM5 MMF Considerations (SWDM4) Source: Commscope Test parameter Attenuation ORL / Reflectance Dispersion (Chromatic and Modal) Test vendor advices Testing 850 nm worst case appears the best practice 850 nm presents higher attenuation than 950 or 1300 nm VCSEL is more sensitive to ORL than LED ORL is wavelength independent, not light source independent Expect the smallest differential mode delay (DMD) specs possible for WBMMF Unless stated otherwise by the fiber manufacturer, CD (chromatic) and modal dispersion shall be considered OK by design Source: EXFO 27

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 (samefor 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 Respect calibration period and change your test jumpers 1- Equipment variation (repeatability) 2- Product variation(fut variation) 28

UNCERTAINTY SPECIFICATIONS Source & Power meter-olts Specification (db) Typical Notes Link IL uncertainty 0.1 (0.2) PM/LS: Loss <46 db (OLTS: Loss <55 db) Single connector IL uncertainty N/A Reflectance uncertainty N/A Short link ORL uncertainty 0.5 (1) PM/LS: mandrel method (OLTS: Up to 55 db ORL for APC) USING SUITABLE REFERENCE CABLES OTDR -iolm Typical Specification (db) 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 ForL<15 m. Includes two connectors and fibre loss Short link ORL uncertainty 1 uncertainties. Events may be merged. 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 29

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 30

Is up to 30% uncertainty acceptable? 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) 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 31

OLTS/ PM-LS / certification TX RX LC-MTP MTP-LC (1G/10G) TX RX MAX-940-QUAD 100 m OM4, 2km OS1 <3 seconds, 2 wavelengths Duplex, bi-directional, EF testing OLTS 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 tabletinspired Platforms Expert guidance, every step of the way On-board multistandar d Certification Reduced cost of ownership 32

Is MMF dead? I think not: WBMMF (SWDM4) 2 fibers / 850 nm 880 nm 910 nm 940 nm Wideband Multimode Fiber (WBMMF) Source: Commscope Test parameter Test vendor advices Attenuation Testing 850 nm worst case appears the best practice 850 nm presents higher attenuation than 950 or 1300 nm ORL / Reflectance VCSEL is more sensitive to ORL than LED ORL is wavelength independent, not light source independent Chromatic Dispersion Dispersion (Chromatic and Modal) Expect the smallest differential mode delay (DMD) specs possible for WBMMF Unless stated otherwise by the fiber manufacturer, CD (chromatic) and modal dispersion shall be considered OK by design Modal Dispersion Pulse spreading Source: EXFO 33

Questions, checklist & test objectives # Checklist Prerequisite Note Important: Test instruments calibration and reference test jumpers Changetest 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). Input:What volume orcounts of fiber to test Decision:Test tools, testing time & test procedures 1 Contaminantson the connector endfaces 2 Masteringtest repeatability, uncertainty What is the test task:fiber certification, troubleshooting, warranty registration OLTS helps screen suspect links (ORL) OTDR maps fault and connectors RL Clean& inspect, first time right. Multimode fiber, EncircledFlux compliant equipment & procedure. Tighter budgetfor 40G& 100G over OM4 MMF/ WBMMF, SMF more $ Set your objectives carefully. Testinstruments alone do not solve everything! Ultimate baseline for an effectiveand efficient optical testing! Respect calibration and test jumpers quality! 3 Testdata valorization Documentation system and processes Bestpractices to speed up future trouble shooting. 4 Managing10G to 100G+ migration: connectors RL impact RL can kill a network at 25Gbps line rate 25/50 Gbps more demandingthan 10 Gbps 34

OLTS vs iolm-otdr / RL, BR, ORL Tier-1 & 2 Return loss(rl) is thelossof power in the signal returned/reflected by a discontinuityin 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. iolm iolm -OTDR Launch Receive LC LC End-to-end OLTS FasTest Simplex 35

EXAMPLE 36

OLTS/ ORL: screening & link certification MAX-945iCERT-QUAD MAX-945iCERT-QUAD 500 ft. (150 m) Targeted applications 1- OLTS 1- OLTS 2- FIP 3- iolm 1- OLTS 2- iolm Move, Add and Changes (MACs) of pluggables optics Construction, certification of total loss budget (tier-1) 37

iolm OTDR single fiber 100G-SWDM4 IDA LC patch panel SPSB-EF-30m Launch LC Patch panel Standard OM3 30m Receive ToR MDA 1.5 db / 150 m (OM4) DCI WDM OTDR-iOLM positions faults, loss, reflectance and provide link loss and ORL. Threshold and standard certification-based Pass/Fail. 38

iolm OTDR software interface OTDR-iOLM positions faults, loss, reflectance and provide link loss and ORL. Threshold and standard certification-based Pass/Fail. 39

Testing MPO 40

MTP/MPO cable configurations (polarity, types) 41

Adapter MPO Pinned (Male) MPO Unpinned (Female) MPO Guiding pins MPO Guiding holes 42

Physical Contact The 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-disconnectscan create fiber misalignments (loose pin/ hole or memory shape related issues) 43

LC serial duplex MTP/MPO trunk catastrophic 44

FIP MTP/ MPO inspection auto-center / focus MTP12 MTP24 (MM/SM) High mag view (400X): Highest Magnification on the market Auto-center + Auto Focus FIP controls: Low mag view PIP (100X): Allows to see which fiber is being inspected in High magnification AutoCenter AutoFocus Capture Analysis 45

10G MTP/ MPO trunk test Step 1: Pre-installation quality test Step 2: End to end LC-LC permanent link test 46

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