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84 | BROADBAND COMMUNITIES | www.broadbandcommunities.com | MARCH/APRIL 2014 FIBER TESTING The Unique Test Challenges Of PON Deployment Part 1 of a two-part article details testing procedures at the time a passive optical network is installed. Part 2 will describe troubleshooting procedures. By Michael Scholten / AFL P roper testing is a critical part of installing, activating and maintaining a passive optical network (PON). Tough most components are tested during the manufacturing process, they are tested again after splicing and the installation of splitters and access terminals. Field testing is required to ensure no excess loss or refectance has been introduced through microbends in installed fber, poor splices, macrobends in splice closures or access terminals, or dirty, damaged or improperly seated connectors. If not detected and corrected, excess loss or refectance often results in poor network performance. Performance may initially seem acceptable, but over time, transmission errors may begin to increase long before the need for any maintenance activity would normally be expected. Tests commonly used to verify optical links include the following: • Connector inspection • Insertion loss test • Optical return loss test • Optical time domain refectometry. Connector inspection and cleaning during installation and maintenance is among the most efective methods for ensuring that an optical network will deliver expected performance. Connector inspection is typically performed using an optical microscope. To prevent accidental eye damage when inspecting fbers potentially carrying live trafc, a video microscope images the connector end face and displays the magnifed image on a handheld display. Dirt, debris or damage is easily detected. Images may be captured before and after cleaning, then compared for any variation. Connector contamination and damage are the most common causes of poor optical network performance, according to a recent study by NTT Advanced Technology. An insertion loss test measures the end- to-end loss of an installed link by injecting light with a known power level and wavelength at one end and measuring the received power level output from the other end. Te measured diference between the transmitted and received power levels indicates the optical loss through the network. Insertion loss is considered acceptable when the measured loss level is lower than the budgeted loss level. An optical return loss test injects light with known wavelength and power level into one end and measures the power level returned to that same end. Te diference between the injected power level and the measured return level is the return loss. Return loss is considered acceptable when it is higher than the budgeted return loss target. A low return loss value (below 35 dB) is often an indication of one or more sources of excess refection in the network under test, typically due to dirty or damaged connectors or a fber break. BBC_Mar14.indd 84 3/14/14 3:22 PM