To accept the fiber installation for a GPON network before turn-up, at a minimum, the insertion loss (IL) needs to be tested at each endpoint. For each PON, this means testing at the optical line terminal (OLT) and at each optical network terminal (ONT). The IL at each endpoint needs to meet the vendor specifications for the GPON equipment being installed. Typically, this is between -28 dBm and -8 dBm at the OLT and between -27 dBm and -8 dBm at each ONT. These tests are normally conducted using an optical light source (OLS) and an optical power meter (OPM). From the OLT to each ONT, the tests should be conducted at 1490 nanometres (nm) and, additionally, at 1550 nm if an RF overlay is being deployed. From each ONT to the OLT, the test should be conducted at 1310 nm.
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Other tests also can be specified as part of a certification process. Optical return loss (ORL), for example, can be tested using an optical return loss test set (OLTS) or an optical time domain reflectometer (OTDR). If tested, the ORL should be greater than 32 dB. If there are intermediate test points available in the network, such as connectorized splitters or patch panels, individual segment IL and ORL can be tested and compared against the specified loss budget.
Requiring a recorded OTDR trace as part of the final acceptance criteria is also good practice because it not only characterizes the network in terms of distance, continuity and relative quality of splices and connectors, but it also provides a baseline reference for any future troubleshooting activities.
Many testing equipment vendors now manufacture combination test kits that are specifically designed for fiber to the home (FTTH) networks and integrate the functionality of an individual OLS, OPM, OLTS or OTDR. These kits can automate much of the acceptance testing, store the results and create professional test reports.
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