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EETE JANUARY 2013

CONNECTORS & CABLING Readying copper cable technicians to install optical fibres By Andy Cole The rATe AT whiCh fibre-to-the-home and fibre-to-the-office But installation professionals with no special expertise in fibre are being installed is accelerating dramatically. Attracted by may be helped considerably by the test automation capabilities the opportunity to take a share of valuable media markets such of the latest instruments. as video-on-demand and video telephony, European telecoms network owners are extending the reach of their optical fibre What does an OTDR do? networks from the core to the access network in order to of- The modern Optical Time Domain Reflectometer (OTDR) fer homes and small businesses broadband connections of performs the majority of fibre optic measurements required 100Mb/s or faster. today. It is used in the commissioning process, to verify a new As optical fibre begins to reach the ‘last mile’ from exchange installation, and to identify and locate faults in existing installa- to premises, the existing cable installation workforce, trained tions. Indeed, a trace from a handheld installation tester such as and experienced in the installation of copper connections, faces the Access Master OTDR or the Network Master µOTDR from the challenge of mastering new technology and a new physi- Anritsu will form the basis of the commissioning report submit- cal medium. The skills, practices, habits and knowledge which ted to a network owner as proof that an installation has been have served telecoms installers well in the copper era need to completed correctly – a requirement for contractors to secure be replaced by new skills in the fibre optic age. payment for their work. So what are the main differences installers must take ac- The benefit of using a modern OTDR is that it will take count of when working with fibre for the first time? And how can measurements automatically, relieving the user of the burden of modern instruments make the transition easier? designing, configuring and implementing test routines. This is perfect when measurement results are required quickly, or when Optical fibre’s mechanical properties the user is not experienced in the use of an OTDR. Metal cables can be installed by pulling them into ducts and Indeed, an OTDR with automatic measurement capability conduits: the cable is physically robust enough to withstand can drastically reduce the need for time-consuming and costly the traction and torsion forces applied to it. Copper cable can training for copper cable installers who are making the transition also be bent around corners with a tight radius to present a neat to fibre installation. For more experienced OTDR users, these installation. So long as lengths of metallic cable are physically instruments will still provide full flexibility to set the parameters joined, continuity of the electrical path is maintained. Joints can and the display manually as required. be soldered, twisted, crimped, or fastened with a screw: as long With a single measurement (‘trace’), the OTDR provides as they are made to a reasonable standard, the electrical con- a complete picture of the fibre installation. It measures and nection should perform without trouble for many years. displays the length of the cable, the total loss over this length, Optical fibre, on the other hand, must be handled with great the loss across spliced joints, the insertion loss of connectors care. It will not withstand the same mechanical stresses as cop- and other components such as splitters used in Passive Optical per cable, and is more easily damaged. In addition, the optimal Networks (PONs), and the return loss. direction of travel of light is in a straight line: while bends of a limited radius are allowable, too tight a radius will dramatically reduce or even block the passage of light. Dirt and contaminants, which have very little effect on copper cable, can also seriously compromise the performance of optical fibre. Even a very small amount of dirt in a fibre joint can result in high losses, and seriously impair its ability to transmit light. This means that the pre-requisites of a successful fibre installation are: • The use of high-quality components •The use of high-quality tooling (such as a fibre optic splicer) • The implementation of good working practices • To verify whether an installation has in fact been Fig. 1: a simplified rendering of an OTDR trace showing the typical shape of successful, the installer needs to test the cable. Here reflective and non-reflective events. again, there are significant differences between the test practices required for copper and those required for fibre. The OTDR also identifies events, such as connector joints, spliced joints, and splitters used in PONs, in an easily read Andy Cole is Field Applications Engineer at Anritsu (UK) - table. This verifies that an installation is within its allowable www.anritsu.com limits for each parameter, and alerts the user to any events for 34 Electronic Engineering Times Europe January 2013 www.electronics-eetimes.com


EETE JANUARY 2013
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