![9 Dublin Workshop event 9
[All measurements taken at 1310nm Wavelength]
The Pulse Width of the
OTDR will determine
how much fibre can be
measured before
running into Noise.
OTDR Terminology
Dynamic Range Examples](https://image.slidesharecdn.com/otdrtheoryworkshop-221118230720-2a1c072a/85/otdr_theory_workshop-pdf-9-320.jpg)
otdr_theory_workshop.pdf
- 1. Anritsu Confidential Information OTDR Theory Training Workshop Event Nov 2010 edition
- 2. 2 Dublin Workshop event 2 Notice ANRITSU has prepared this material for use by Anritsu personnel and customers. The material contained herein is the property of ANRITSU ,and any unauthorised use or disclosure of this material is prohibited. The material also may not be reproduced, copied, or used in whole or in part, as the basis for manufacture, sale, or training without the prior written consent of ANRITSU. © Anritsu 2010 Anritsu shall not be liable for any errors contained herein.
- 3. 3 Dublin Workshop event 3 Agenda • OTDR Terminology • OTDR Basics » Distance Measurements » Loss Measurements » Reflectance Measurements » ORL Measurements • OTDR Setups » IOR » Backscatter coefficient » Wavelength » Range » Resolution » Pulse width » Number of averages • Anritsu MT9083x Access Master OTDR
- 4. 4 Dublin Workshop event 4 Launch Reflective Event Non-Reflective Event End/Fault Noise Distance Return Signal Level OTDR Terminology Trace Basics
- 5. 5 Dublin Workshop event 5 After light leaves fibre end, only internal electronic noise shows up on OTDR screen. End of fibre causes reflection of light. OTDR Terminology Locating the end of the fibre
- 6. 6 Dublin Workshop event 6 • Measured in dB. Typical range is 20-50dB • Describes how much loss an OTDR can measure in a fibre, which in turn describes how long of a fibre can be measured • Directly related to Pulse Width: larger pulse widths provide larger dynamic range • Increase by using longer PW and by decreasing noise thru averaging OTDR Terminology Dynamic Range
- 7. 7 Dublin Workshop event 7 • Converting Dynamic Range into Distance » Can only be done on a straight piece of glass (no events) » Need to know the dB/Km loss for each wavelength to be tested. » Need to know the dynamic range at each wavelength. » Distance = Dynamic Range dB/Km OTDR Terminology Dynamic Range
- 8. 8 Dublin Workshop event 8 Dynamic Range “98% noise level” (Bellcore standard) “SNR = 1” “RMS noise level” OTDR Terminology Dynamic Range
- 9. 9 Dublin Workshop event 9 [All measurements taken at 1310nm Wavelength] The Pulse Width of the OTDR will determine how much fibre can be measured before running into Noise. OTDR Terminology Dynamic Range Examples
- 10. 10 Dublin Workshop event 10 • Specified as a DISTANCE • Determines how CLOSE to OTDR you can detect and measure a splice loss • Determines how CLOSE TOGETHER two events (splices) can be measured • Directly related to PULSE WIDTH: larger pulse widths produce larger dead zones OTDR Terminology Dead zones
- 11. 11 Dublin Workshop event 11 The distance from the start of a reflective event until you can detect another reflective event. Measured at 1.5dB below the peak of the initial reflection. EDZ OTDR Terminology Reflective or Event Dead Zone
- 12. 12 Dublin Workshop event 12 The distance from the start of a reflective event until you can measure the loss of another event. Measured at 0.5dB up from the backscatter level after the reflection. 0.5dB up ADZ 2nd event (splice) OTDR Terminology Non-Reflective or Attenuation Dead Zone
- 13. 13 Dublin Workshop event 13 Distance measurements Locate End Locate Splice Loss measurements Measure splice losses Measure end to end Reflectance measurements Measure Reflectance Measure ORL OTDR Basics Measurements
- 14. 14 Dublin Workshop event 14 d = distance t = elapsed time c = speed of light in a vacuum n = Index of Refraction Test pulse fired Test pulse returned “d” d d = = t C t C 2 n 2 n If “n” is incorrect, then the distance measured will also be wrong!! Must divide by two to get one way elapsed time. OTDR Basics Distance Measurements
- 15. 15 Dublin Workshop event 15 • Measuring distance » To calculate the speed of light, the OTDR must know the Index of Refraction (IOR). » The IOR is a ratio between the speed of light in a vacuum and the speed of light in a fibre. » The IOR is obtained from the fibre manufacturer, entered into the OTDR by the user and must be accurate. OTDR Basics Distance Measurements
- 16. 16 Dublin Workshop event 16 • OTDRs measure backscatter OTDRs calculate loss OTDR calculates loss by comparing backscatter levels to determine loss between points in fibre OTDR Basics Distance Measurements OTDR Basics Loss Measurements
- 17. 17 Dublin Workshop event 17 Backscatter is directly related to the power of the test pulse. As the test pulse power decreases, so does the backscatter power. The difference in strength between two points of backscatter is directly proportional to the difference in strength between the test pulse at the same two points. A B Test pulse Backscatter OTDR Basics Loss Measurements
- 18. 18 Dublin Workshop event 18 • Different test wavelengths exhibit different loss characteristics. » 850nm - extremely susceptible to Rayleigh scattering loss » 1244nm - very susceptible to hydrogen absorption and Rayleigh scattering loss » 1300nm - very susceptible to Rayleigh scattering loss » 1310nm - susceptible to Rayleigh scattering loss » 1550nm - very susceptible to macrobending loss » 1625nm - extremely susceptible to macrobending loss OTDR Basics Loss Measurements
- 19. 19 Dublin Workshop event 19 1310nm 1625nm Different wavelengths respond very differently to various losses. OTDR Basics Loss Measurements
- 20. 20 Dublin Workshop event 20 Misaligned cores cause loss of light at splice point Splice Loss Splice Loss For proper splice loss measurement, the linear backscatter after the event must be extrapolated to the beginning of the event to account for the width of the test pulse. This is accomplished with LSA cursors. LSA cursor OTDR Basics Loss Measurements
- 21. 21 Dublin Workshop event 21 The most accurate method of OTDR splice loss measurement entails bi-directional OTDR traces. The fibre is shot from both ends and individual event splice losses are averaged together to account for gainers. OTDR Basics Bi-directional Loss Measurements
- 22. 22 Dublin Workshop event 22 • OTDRs calculate event reflectance by comparing the backscatter level just before an event to the backscatter level during an event. Reflectance (calculated from formula) Some events cause reflections, or “spikes” of returned light at the splice point or fibre end OTDR Basics Reflectance Measurements
- 23. 23 Dublin Workshop event 23 Optical Return Loss (ORL) is measured in +dB and represents the sum of all individual reflectances within a fibre span. ORL Backreflections from Rayleigh Scattering Fresnel Reflections Transmitted Light OTDR Basics ORL Measurements
- 24. 24 Dublin Workshop event 24 ORL is calculated as the total amount of light returning from the area between the cursors below the trace line to the noise level. It includes total Backscatter and all Reflections. A B OTDR Basics ORL Measurements
- 25. 25 Dublin Workshop event 25 • Pulsed Light vs. Continuous wave » OTDR affected by Noise, distance and Pulse width » Deadzones prevent OTDR from measuring small reflections that often follow large reflective events. • OTDR = evaluated ORL Measurement • CMA50 = True ORL Measurement • Accuracy » CMA50 ± 0.5dB » OTDR ± 4dB » CMA5000 SMART ORL ± 1dB OTDR Basics ORL Measurements
- 26. 26 Dublin Workshop event 26 OTDR Setups » IOR » Backscatter coefficient » Wavelength » Range » Resolution » Pulsewidth » Number of averages
- 27. 27 Dublin Workshop event 27 Setting Up The OTDR Fibre Details • IOR » obtain from fibre manufacturer, dial in on OTDR • Backscatter coefficient » obtain from fibre manufacturer, dial in on OTDR
- 28. 28 Dublin Workshop event 28 If the OTDR stops measuring here... …this data won’t be acquired! Setting Up the OTDR Range • Must be at least 25% greater than the fibre under test. • There is valuable information in the noise floor which must be measured.
- 29. 29 Dublin Workshop event 29 Typically begin with the lowest resolution (highest number) possible. Pros - much faster acquisition time, smaller trace file size Cons - minimal degradation in accuracy of measurements Setting Up the OTDR Resolution
- 30. 30 Dublin Workshop event 30 10m (33’) Actual Splice Location Measured Splice Location Actual End Location Measured End Location Low Density (long DPS) Setting Up the OTDR Resolution
- 31. 31 Dublin Workshop event 31 3m (10’) Actual Splice Location Measured Splice Location Actual End Location Measured End Location High Density (short DPS) Setting Up the OTDR Resolution
- 32. 32 Dublin Workshop event 32 Controls Dynamic Range and Dead Zone 10ns = 1 meter = 3 feet 100ns = 10 meters = 33 feet 10,000ns = 1,000 meters = 3,281 feet 10,000ns = 1,000 meters = 3,281 feet A light pulse from the OTDR travels along inside the fibre like water through a pipe. Setting Up the OTDR Pulse Width
- 33. 33 Dublin Workshop event 33 • The single most important parameter • Use the shortest pulse width which still provides sufficient dynamic range Too short (short deadzones but insufficient DR) Too long (good DR but large deadzones) Just right (good DR, short deadzones) Setting Up the OTDR Pulse Width
- 34. 34 Dublin Workshop event 34 Noise shows up as variations in the trace line. Longer averaging times reduce the noise level. Slow Scan Slow Scan Fast Scan Fast Scan Setting Up the OTDR Averaging
- 35. 35 Dublin Workshop event 35 • Number of Averages » The number of averages will contribute to the amount of noise present on a trace. » Use the least number of averages which still produces clean, useable traces. Too few (noisy trace) Too much (wasted time) Just right Setting Up the OTDR Averaging
- 36. 36 Dublin Workshop event 36 Thank You Questions?