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![7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us 5
Fiber Optics
Historical Perspective
• Colladon / Babinet 1840s - Principle of total internal reflection in water jets & bent glass rods.
• Hopkins / Kapany /Snitzer 1950s – Light propagation with cladded fibers for applications of
medicine, defense, even television.
• Charles Kao / Standard Telecommunications Lab Team 1960s – proposed a perfected SiO2 fiber
light pipe for low loss transmission capabilities.
• Keck / Maurer / Schultz at Corning 1970s – proved Kao’s vision through designing and drawing
preforms of chemical vapor deposition glass.
• Kao the 2009 co-winner of the Nobel prize in physics. [courtesy Royal Swedish Academy of
Sciences]](https://image.slidesharecdn.com/demystifyingotdreventanalysiscctapresentation070714-230129101522-1722efdf/85/Demystifying-OTDR-Event-Analysis-CCTA-Presentation-070714-pdf-5-320.jpg)
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Fiber Optic FUNdamentals
• Losses - Attenuation
– dB or –dB
– Loss vs Wavelength (Loss vs Freq)
See Table
– Rayleigh Scattering Loss ≈ 1.7(0.85/λ)4
– Fresnel Reflections ρ = [(n-1)/(n+1)]2
– ORL Optical Return Loss
– Insertion Losses
– Connectorization Alignment
– Micro/macrobends & Absorption
7/15/14 8
© 2014 TTI / Mike Mazzatti / teratec.us](https://image.slidesharecdn.com/demystifyingotdreventanalysiscctapresentation070714-230129101522-1722efdf/85/Demystifying-OTDR-Event-Analysis-CCTA-Presentation-070714-pdf-8-320.jpg)
Uploaded byMani Kandan K
Demystifying OTDR Event Analysis CCTA Presentation 070714.pdf
This training presentation introduces OTDR event analysis. It discusses how OTDRs work by launching light pulses into fiber and measuring backscatter. It covers OTDR fundamentals like pulse width, averaging, and signal-to-noise ratio. The presentation teaches how to analyze events like splices and reflections to determine distances, losses, and other issues. Both manual and automatic event analysis techniques are described. The goal is to help users of all experience levels understand OTDR results.
Demystifying OTDR Event Analysis CCTA Presentation 070714.pdf
- 1. Demystifying OTDR EventAnalysis TTI Technical Training Presentation for CCTA July 15, 2014
- 2. 2 Training Abstract An OpticalTime Domain Reflectometer (OTDR) is the ubiquitous tool for fiber optic network health, reflectance, loss and distance measurements. For a new user, and even seasoned users in modern systems, OTDR event analysis can be a complicated and somewhat confusing endeavor. We will explain the nuances of OTDR manual and automated discontinuity detection, and provide a clear path to understanding the OTDR results. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 3. 7/15/14 © 2014TTI / Mike Mazzatti / teratec.us 3 Training Objectives • Introduction Into Optical Time Domain Reflectometry • Review of Fiber Optic Fundamentals • Understanding OTDRs • Understanding FO Event Characteristics • Understanding OTDR Results • Applying Best Practices for Event Analysis
- 4. 4 Training Sections • FiberOptic Introduction • Fiber Optic Fundamentals • OTDR Introduction • OTDR Fundamentals • Event Analysis Fundamentals • Conclusions 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 5. 7/15/14 © 2014TTI / Mike Mazzatti / teratec.us 5 Fiber Optics Historical Perspective • Colladon / Babinet 1840s - Principle of total internal reflection in water jets & bent glass rods. • Hopkins / Kapany /Snitzer 1950s – Light propagation with cladded fibers for applications of medicine, defense, even television. • Charles Kao / Standard Telecommunications Lab Team 1960s – proposed a perfected SiO2 fiber light pipe for low loss transmission capabilities. • Keck / Maurer / Schultz at Corning 1970s – proved Kao’s vision through designing and drawing preforms of chemical vapor deposition glass. • Kao the 2009 co-winner of the Nobel prize in physics. [courtesy Royal Swedish Academy of Sciences]
- 6. 6 Fiber Optic Introduction •FO medium is made of hair thin SiO2 glass material with an inner core section, surrounded by outer cladding section having differing optical densities. • As the laser light enters into the FO core, differing densities of the core/cladding interface trap the light via a mechanism of total Internal reflection. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 7. 7 • IOR n=cvac/cmat •Snell’s Law n1Sinθi=n2Sinθt • Critical Angle sinθ = nclad/ncore – Multimode Step Index – Multimode Graded Index – SingleMode • Trapping Light From The Source – Numerical Aperture NA = sinθ = (n2 core-n2 clad)½ 7/15/14 7 © 2014 TTI / Mike Mazzatti / teratec.us Fiber Optic FUNdamentals
- 8. 8 Fiber Optic FUNdamentals •Losses - Attenuation – dB or –dB – Loss vs Wavelength (Loss vs Freq) See Table – Rayleigh Scattering Loss ≈ 1.7(0.85/λ)4 – Fresnel Reflections ρ = [(n-1)/(n+1)]2 – ORL Optical Return Loss – Insertion Losses – Connectorization Alignment – Micro/macrobends & Absorption 7/15/14 8 © 2014 TTI / Mike Mazzatti / teratec.us
- 9. 9 • Radiation travellingback towards the source has two predominate classifications, Rayleigh scattering and Fresnel reflections. • Rayleigh scattering is the main source of loss of signal in the fiber. Intrinsic material property caused by the lightwave of ~1um, traveling though the sub-micron SiO2 crystalline matrix causes an elastic scattering. • The received backscatter power P as a function of t : = 0.5 α exp − , where: S ≅ . • A Fresnel reflection is caused by light traveling through a glass density change, where reflected power is: % ! = 100 #$ – #'( #$ + #'( * 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Fiber Optic FUNdamentals
- 10. 10 • An OTDRis one-dimensional Fiber Optic (FO) radar. • OTDR development started in the 1970s with a simple analog laser pulser, detection circuit, oscilloscope. • Of FO test and measurement tools available, the OTDR is only tool that provides time (or distance) measurements. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Introduction Into OTDR Technology
- 11. 7/15/14 © 2014TTI / Mike Mazzatti / teratec.us 11 Introduction Into OTDR Technology • Fiber Optic Radar – Launch an ultra-short laser pulse monitor the reflected light in sequential time samples. • A small amount of light is scattered back to the source by fiber impurities and crystalline structure. • Splices or connections cause large reflections back to the source. • OTDR Measures Scattering – Rayleigh – loss mechanisms of the exponentially decaying signal – Fresnel Reflections – high level signals at discontinuities
- 12. 7/15/14 © 2014TTI / Mike Mazzatti / teratec.us 12 • Examines Events – Distances – IOR fiber calibration – use reflecting events – Splices - Slope Loss Analysis - 2pnt / splice / least square appr. – Connectors – insertion loss and ORL – Ends Reflections - Breaks • What Gets In The Way ? – Pulse Widths – Event Attenuation Dead Zone – Dynamic Range – Noise – Types Of Losses – Dirty Front End / High Level Reflection Introduction Into OTDR Technology
- 13. 13 OTDR Fundamentals • FOspeed of light, and distance traveled is based on optical density of the glass, or the index of refraction ‘n’. • The light velocity ‘v’, and distance ‘D’ to a discontinuity is: + = , = * The reflection intensity verses the travel time (distance). 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 14. 14 • The detectedRayleigh scattering takes the shape of an exponential signal. • After every couple of kilometers, the received power is reduced approximately in half. • To make use of this decaying signal the OTDR provides a log conversion, which basically contracts the strong top signals and expands the weak bottom. Distance (1km/div) Linear Power (arb units) 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us OTDR Fundamentals
- 15. 15 • Typical un-averagedFO trace shows backscattered radiation dropping across sections of fiber containing discontinuities. • It not only is difficult to discern the drops due to pressure points or fiber mismatches, also discontinuities or ‘events’ very close together will not be seen. Distance (250m/div) Loss ( Arb Units ) 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us OTDR Fundamentals
- 16. 16 • To ImproveSNR without reducing spatial resolution, co-addition is used to maintain event features and reduce the uncorrelated noise. • Co-addition develops a significant SNR improvement by reducing the noise as a square root of the number of averages. • The SNR 2 way improvement will take the mathematical form (/2 for OTDR 1 way): -'./(01 = 102$ -13 Loss ( Arb Units ) 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us OTDR Fundamentals Signal to Noise Ratio
- 17. 17 • The signalis typically buried deep in the noise, so increase the laser power to increase the signal reduce the bandwidth to eliminate noise. • Increasing pulse length increases optical power, but will reduce the spatial resolution of the signal and capability to distinguish close events. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us OTDR Fundamentals Pulse Width
- 18. 18 • Again toimprove SNR, one should increase the number of averages to eliminate noise. • Increasing the average time by a factor of four improves the visible noise, and the OTDR dynamic range increases by 1.5dB. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us OTDR Fundamentals Co-addition / Averaging
- 19. 19 OTDR Apparatus Pulsed LasedDriver Analog Delay Line 1st Preamplifier 2nd Preamplifier Synchronous ADC Programmable APD 2 Port BFT Coupler FUT Acquisition Engine Optics Control Accumulator TI DSP Keyboard Flash Drives USB Display Engine 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 20. 20 Event Analysis Fundamentals • Afterco-addition of many pulses, and log conversion of exponential decaying signal, further analysis is needed. • We use a second derivative for slope change detection and monitor reflective rises in the signal for saturation and multiple events. • Further averaging for splice loss or LSA methods is used. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 21. 21 ‘Tail’ from adirty connection at 20.7 meters causes long ‘dead’ zone hiding the next reflection. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Reflection Event Analysis With a clean connection set the cursor at the left hand side of the reflection for accurate distance.
- 22. 22 • Set cursorat left of reflection for distance to event. Make certain splice loss areas around cursors are on level backscatter. • Below the green lines of the Least Square Approximation (LSA) areas need to be adjusted properly for level and accurate results. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Reflection Event Analysis
- 23. 23 • Set cursorbefore backscatter droop for distance to event. Make certain splice loss areas around cursors are on level backscatter. • Use SPL LSA method in lower noise areas for best accuracy. Use SPL AVG for maximum noise reduction with good results. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Splice Event Analysis
- 24. 24 • Need toadjust the SPL areas further away before and after closely spaced multiple reflection areas. • With reduced pulse width and more averaging time, sufficient resolution can be accomplished to detect distance and ORL at each reflection. However, losses could be combined. • In multiple fusion splices, use pulse knowledge to understand where high losses could be occurring. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Multiple Event Analysis
- 25. 25 • Ghosts eventsare caused by saturated (dirty) connections and end reflections. • Gainers are caused by splicing on higher backscatter coefficient fiber, examining the other direction will show a high loss. • Use a bidirectional loss method to average out the backscatter coefficient problems (gainers). Use macro bend analysis to detect macrobend issues. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Event Analysis Oddities Ghost Reflections at Double Network Length Macrobend Losses at 1550nm in Black
- 26. 26 • Link Losscan be calculated using the 2 Point method. To analyze end connectors a launch and receive patchcord is required. • System ORL can be calculated using a CW Continuous Optical Return Loss method. • PONs – Passive Optical Networks are tricky to evaluate. Live networks require out-of-band laser OTDR analysis. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us Other Event Analysis
- 27. 27 Automatic Event Analysis •Set parameter variable for loss and reflection thresholds – Splice Loss – Reflection Level – Link Loss – End Of Fiber • Use proportional and differential analysis to detect and mark events. • Analyze events against threshold settings and smart parameters (macrobends, ghosts), generate schematic. • Examine events for best end detection algorithm: – End of Fiber Threshold? – Saturated Reflections? – Last Event? Calculate Past Slope Calculate Forward Slope Calculate ORL Calculate Standard Deviation Calculate Slope Differential Test For Reflection Test For Saturation Test For Splice Display Events Test For Completio n Mark Event Analyze Parameters YES YES YES YES NO NO NO NO 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 28. 28 Manual and Automatic Advantages/ Disadvantages • Manual Advantages / Disadvantages: – Evaluation is adjusted for each network condition. Encountering new conditions such as ghosts, multiple events, etc., improves user experience and adaptability. – Looking closely at event traces can uncover problems such as dirty connectors or slight micro/macrobend conditions, that would be unrecognizable to the machine. – Without proper training and experience results could be confusing, unrepeatable and inaccurate. • Automatic Advantages / Disadvantages: – Accurate evaluation against preset parameters. Can be very repeatable. – Quickest response and documentation process. – Unforgiving in complex situations, cannot learn from new experiences. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 29. 29 Summary • We introducedFO principles and discussed measurement of network losses and distance. • We introduced OTDR fundamentals and explored measurement techniques. • We analyzed FO network discontinuities and perturbations to distinguish and localize events. • We evaluated event detection mechanisms and determined methods to improve analysis performance and accuracy. 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us
- 30. 30 Conclusion Muchas Gracias! Merci!Dank U! Thank You! Tenk Yuh! To Learn More Visit: Terahertz Technologies Inc. teratec.us 1-888-US-OTDRS 315-736-3642 mmazzatti(at)teratec(dot)com 7/15/14 © 2014 TTI / Mike Mazzatti / teratec.us