ICT Today

ICT Today March/April 19

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54 I ICT TODAY Before making any connection, it is critical to inspect first for cleanliness. Even when a connector has an end cap, do not assume it is clean. Connectors are divided in different zones (i.e., core, cladding, adhesive and contact) with different tolerance levels in terms of number of scratches and the number of defects it can tolerate, as defined in the standards and shown in Figure 6. By measuring the number and the size of those defects per region, the ICT technician can validate if a connector is good (clean) or bad (dirty or damaged). Connector inspection is done with analytical software that will identify and measure those defects against industry standards to ensure result uniformity for all users. CONNECTOR CLEANING Always inspect first, before cleaning. If the connector is clean, do not touch it, since doing so may introduce dirt or scratches. When there is a failed connector, it needs to be cleaned. Once it is clean, it needs to be reinspected to make sure that it is really clean. Repeat those steps until the connector is clean or, if after repeated attempts it still does not pass inspection, the connector must be replaced. There are three methods used for cleaning connectors: • The dry method • A click-on cleaning pen • A wet method that uses swabs pre-saturated with isopropyl alcohol to dissolve contaminants Some people use a hybrid method; dry cleaning is performed after wet cleaning to eliminate any residue on the connector. Zones Scratches Defects A. Core None None B. Cladding No limit ≤3 μm None >3 μm C: Adhesive No limit No limit D: Contact No limit No limit ≥10 μm No limit <2 μm None >5 μm 5 from 2–5 μm FIGURE 6: Illustration of connector zones and tolerance levels. Core 0-25 µm Cladding 25-120 µm Adhesive 120-130 µm Contact 130-250 µm Non-critical zone 250+ µm FIBER CHARACTERIZATION Just like any fiber optic system, a POL must be tested to ensure that transmission system requirements are met, which means that the system operates within the specified loss budget. In a POL, the overall channel loss of the network is determined by the end-to-end path between the OLT and the ONT. Insertion loss, link length and optical return loss are measured with OLTS equipment, which consists of a master and remote unit and combines both a light source and power meter. One remote and one master unit are used to do bidirectional testing. This process consists of emitting from the source and measuring at the other end with the power meter (first from A to B and then from B to A). When designing a POL, the engineers predict the loss of every component of the network (e.g., fiber loss, attenuation, splitting ratio, number of splices, number of connectors, tolerated loss). The predicted loss is validated and certified with field measurements using an OLTS. If the loss is not within the boundaries of the expected budget, then tools such as an OTDR or iOLM can be used to identify the source of the excess loss. TROUBLESHOOTING OTDRs and iOLM (a software tool) are the preferred methods/tools to locate and fix issues. Short distances, high loss and multiple network components require a combination of multiple OTDR pulse widths that can be manually adjusted on the OTDR or automatically with the iOLM software. A simple click of a button will

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