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The Importance of Optical Time Domain Reflectometers (OTDRs) in Telecommunication Networks Speaker / Author: M. Nel Co-author: A. van Brakel. Content. Introduction Why Fibre? Proudly South African Use of OTDRs in the field Basics of OTDRs Selecting an OTDR Traceability
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The Importance of Optical Time Domain Reflectometers (OTDRs) in Telecommunication NetworksSpeaker / Author: M. NelCo-author: A. van Brakel
Content • Introduction • Why Fibre? • Proudly South African • Use of OTDRs in the field • Basics of OTDRs • Selecting an OTDR • Traceability • NMISA measurement capability
Introduction • Rapid growth of the ICT industry led to a global change in how business is done • Fibre optic communication networks • Ensure fast and efficient communication in Southern Africa and with the rest of the world • Business sector: • Fast access to information leads to wide range of new business opportunities
Tourism sector: Prospective tourists: travel destinations and information Websites, telephonic enquiries or e-mail Using the Voice-over-Internet Protocol (VoIP) via client programs such as Skype™ Introduction WWW.
Why Fibre? • Fibre optic networks transfer information across networks • Enormous potential for bandwidth and bit rate • Media types transmitted over fibre optic networks includes: voice, data, image and video • More secure • No electromagnetic interference • Data can travel long distances • Provide high-speed broadband access via • fixed-line networks, • mast-to-mast e.g. cellular phone
Very proud South Africa • 2.7 million spectators watching all 64 matches • 2.8 billion people watching the final • Information sent via Fibre optic networks • 22 750 hours of feed produced by HBS • Soccer being broadcast from South Africa http://www.fifa.com/worldcup/news/newsid=1223134/index.html www.telkom.co.za
OTDR • OTDRs mainly measure optical distance • provide a benchmark for installation • trouble-shooting of fibre optic networks • Creates a visual representation of the fibre under test • Manufacturers application notes available
Use of OTDRs in the field • Telecommunications industry • troubleshooting, verification and documentation • More OTDRs sold, at lower prices • Rugged and usually hand-held • Optical fibres installed • roadside, power lines, manufacturing plants, inside buildings • Technicians • Need training to interpret and identify • Advantage: access needed only to one end of the fibre
Front end connector Pulse generator Directional coupler Laser diode Avalanche photo diode A / D converter Amplifier Signal processing and trace analysis Basic OTDR block diagram
OTDR Basics • OTDR trace contains ‘events’ • Splices • connections • breaks etc. • Signal processing is performed within the OTDR to analyse each event • Properties and location of the event, can be determined
Typical OTDR trace Dead zone Splice End of fibre Connector Bend Lead in fibre Poor connection Noise
Selecting an OTDR • Different OTDRs on the market • Size, accuracy, operating ranges etc. • OTDR specifications are fairly complex and most of them are trade-offs • Some to look out for: • dead zone specification, dynamic range, resolution and distance range • Buyers: need solid understanding of these parameters to make best applications-based decision
Dynamic range • Dynamic range determines the maximum optical loss • bigger dynamic range means longer distances • Losses in the fibre link would also limit the measured length
Dead-zones • Types of ‘dead-zones’: • attenuation dead zone • event dead-zone • Detector is temporarily saturated • Time translates into distance • the longer the detector takes to recover, the longer the dead-zone • short dead-zone important for detecting closely spaced events • Patch cord can be introduced at the start to move out of the initial dead-zone
Guidance when using an OTDR • Select the • pulse width, distance range and sampling points according to application requirements • Resolution: between 4 cm to a few metres • Pulse width • Long pulse width gives better SNR • Shorter pulse detect closer spaced events • Using a large number of sampling points, to maintain a good resolution • few sample points: event may not appear on the trace
Future trends of OTDR usage • OTDR manufacturers • Improve measurement resolution and dead zones • Increased dynamic range • OTDR operating wavelengths • 850 nm and 1300 nm (MM) • 1310 nm and 1550 nm (SM) • Most wavelengths: CWDM and DWDM
Calibration of OTDRs • How do you know that your OTDR is in fact giving the correct length measurement? • Cost implication to customer and installer • Are your OTDR capable of measuring fibre links to achieve specification? • Losses tested against system specifications • OTDRs need to be calibrated and verified • Ensure accurate length and attenuation results • Calibration involves • Comparison with standards traceable to the SI units • Methods available e.g. IEC 61746:2009
Caesium clock South African National Time Standard Fibre attenuation standard from NPL Time interval counter OTDR loss scale calibration Fibre optic cable, calibrated for time-of-flight OTDR distance scale and location offset Traceability
NMISA measurement capability Distance scale deviation and location offset Calibrate fibre delay lines for time-of-flight at 850 nm, 1310nm, 1550 nm and 1625 nm Loss scale Loss measurements at 1310 nm and 1550 nm Reflectance Calibration of this parameter is still under investigation
Conclusion • 2010 FIFA World Cup™ presented a unique opportunity for South Africa’s ICT industry to • showcase technological achievements • world-class telecommunications infrastructure • Important role of OTDR in fibre optic network analysis • Importance of calibrating OTDRs • NMISA Measurement capabilities