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  1. 1. Fiber CharacterizationAssessing the fiber’s capacityTim YountMarket Manager - Fiber Optic Test SolutionsJDSU Fiber Optic Division
  2. 2. 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 Buildings Point Network Access Points CO/Headend/M TSO Multi-home Units Residential2 © 2007 JDSU. All rights reserved.
  3. 3. Fiber ReviewSinglemode Optical Fiber
  4. 4. Light propagation is a function of Attenuation, dispersion andnon-linearities. ∂A i 1 ∂2A 2 i + αA − β 2 +γ A A= 0 ∂z 2 2 dT 2 Attenuation, Dispersion, NOT FOR USE OUTSIDE VERIZON 4 AND JDSU
  5. 5. Optical Transmission5 © 2007 JDSU. All rights reserved.
  6. 6. Optical Fiber Types  2 types: – Singlemode – Multimode6 © 2007 JDSU. All rights reserved.
  7. 7. Industry Standards Industry Standards for Fiber (ITU) For Multimode & Single Mode7 © 2007 JDSU. All rights reserved.
  8. 8. 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 (Received power) OTDR Trace of a fiber link8 © 2007 JDSU. All rights reserved.
  9. 9. 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.
  10. 10. Optical Return Loss (ORL)  Amount of transmitted light reflected back to the source PAPC PPC Pelement PAPC PR Source Receiver (Tx) (Rx) PBS PBS PBS PT PT: Output power of the light source PAPC: Back-reflected power of APC connector PT ORL (dB) = 10.Log ( ) >0 PPC: Back-reflected power of PC connector PR 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.
  11. 11. 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.
  12. 12. 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 Spreading12 © 2007 JDSU. All rights reserved.
  13. 13. 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] 0 d Tx Rx fiber span DC modules13 © 2007 JDSU. All rights reserved.
  14. 14. 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 [ps/√km] V1 > V2 an fiber sp SM dard Stan DGD v2 v1 Perfect SM Fiber span14 © 2007 JDSU. All rights reserved.
  15. 15. 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 6,400 km ed) ntrat 2.5 Gbit/s (OC-48) 2.5 Gbit/s (OC-48) e ly conc 10 Gbit/s (OC-192) 10 Gbit/s (OC-192) 400 km ndom (ra ections ent s 40 Gbit/s (OC-768 40 Gbit/s (OC-768 25 km ing Birefr DGD v2 ! ss ! v1 l stre erna Ext15 © 2007 JDSU. All rights reserved.
  16. 16. Connector ContaminationUnderstanding Contamination on Fiber OpticConnectors and Its Effect on SignalPerformance
  17. 17. Focused On the Connection Bulkhead Adapter Ferrule Fiber Fiber Connector Physical Contact Alignment Alignment Sleeve 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
  18. 18. 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
  19. 19. 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 Light Back Reflection Insertion Loss cause significant back reflection, insertion loss and even equipment Core damage. Cladding DIRT19 © 2007 JDSU. All rights reserved.
  20. 20. 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.
  21. 21. Characterizing the Fiber PlantUnderstanding Fiber Link and NetworkCharacterization
  22. 22. 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 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/nm22 © 2007 JDSU. All rights reserved.
  23. 23. Link & Network Characterization  Link Characterization  Network Characterization – It provides the network baseline – It measures the fiber measurements before turning the performance and the quality of transmission system up. any interconnections – Network Characterization includes – The suite of tests mostly depend measurements through the optical amplifiers, dispersion compensators, on the user’s methods and and any elements in line. procedures – It is a limited suite of tests as – It could be uni-directional or bi- compared to Link Characterization directional ROADM – Tests – Connector Inspection, IL, Router Optical Amplifier ORL, OTDR, PMD, CD, AP DWD M Optica l Netwo Point A Point B rk Video Optical Amp. Headend CWDM/DWDM Optical Network23 © 2007 JDSU. All rights reserved.
  24. 24. LASER ☼Testing the Fiber Plant ON/OFF CW/ LEVEL FMOD ADJUST MENU PREV ENTER @ On @ Charge Connector inspection Insertion Loss OTDR Optical Return Loss Polarization Mode Dispersion (PMD) Chromatic dispersion (CD) Attenuation profile (AP)
  25. 25. 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.
  26. 26. Inspect, Clean, Inspect, and Go! Fiber inspection and cleaning are SIMPLE steps with immense benefits. 1 Inspect 2 Clean 3 Inspect 4 Connect ■ Use a probe ■ If the fiber is dirty, use ■ Use a probe ■ If the fiber is clean, microscope to a simple cleaning tool microscope to CONNECT the INSPECT the fiber. to CLEAN the fiber RE-INSPECT (confirm connector. surface. fiber is clean). – If the fiber is dirty, go NOTE: Be sure to inspect to step 2, cleaning. – If the fiber is still dirty, both sides (patch cord go back to step 2, “male” and bulkhead – If the fiber is clean, go cleaning. “female”) of the fiber to step 4, connect. interconnect. – If the fiber is clean, go to step 4, connect.26 © 2007 JDSU. All rights reserved.
  27. 27. 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 Calibrated Light Source Optical power meter Perm >2s m B d B d W W m B B d d lu ce an C n e M 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.
  28. 28. 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 OTDR method28 © 2007 JDSU. All rights reserved.
  29. 29. Optical Time Domain Reflectometer (OTDR) OTDR depends on two types of phenomena: - Rayleigh scattering - Fresnel reflections. Rayleigh scattering and Light reflection phenomenon = Fresnel backscattering effect in a fiber reflection29 © 2007 JDSU. All rights reserved.
  30. 30. 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 Distance30 © 2007 JDSU. All rights reserved.
  31. 31. Optical Time Domain Reflectometer (OTDR)  Detect, locate, and measure events at any location on the fiber link Fusion Splice Connector or Gainer Macrobend Fiber end or break mechanical Splice • 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.
  32. 32. Contamination and Signal Performance Fiber Contamination and Its Effect on Signal Performance 1 CLEAN CONNECTION 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 dB32 © 2007 JDSU. All rights reserved.
  33. 33. Measuring PMD <10 seconds PMD Light PMD Source 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. ps33 © 2007 JDSU. All rights reserved.
  34. 34. 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 measured34 © 2007 JDSU. All rights reserved.
  35. 35. Measuring CD CD Light CD Source Receiver  There are different methods to measure the chromatic dispersion. IEC 60793- 1-42 / 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 slope35 © 2007 JDSU. All rights reserved.
  36. 36. Measuring AP Broadband Light Narrowband Source Receiver Every fiber presents varying levels of attenuation across the transmission spectrum. The purpose of Water peak 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. C+L DWDM Band AP results 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 IEC 60793-1-1 Optical fibers – Part 1-1: Generic transmission system: C-band or C+L band. Specification – GeneralTest procedure ITU-T G.650.136 © 2007 JDSU. All rights reserved.
  37. 37. Fiber Characterization Results37 © 2007 JDSU. All rights reserved.
  38. 38. Wrap Up
  39. 39. 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.
  40. 40. Q&A and Resources  Questions  Contacts Name - Company (Title) Phone E-mail Fred Ingerson – 4th Wave (JDSU Mfg Rep) (315) 436-0895 fred@4th-wave.com Mark Leupold – JDSU (MSO Acct Mgr) (540) 226-6284 mark.leupold@jdsu.com John Swienton – JDSU (FO App Specialist) (413)231-2077 john.swienton@jdsu.com Greg Lietaert – JDSU (FO Prod Line Mgr) (240) 404 2517 gregory.lietaert@jdsu.com Tim Yount – JDSU (FO Test Mkt Mgr) (207)329-3342 tim.yount@jdsu.com 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.