MECHANICAL FIBER POLISHINGTechniques for Achieving & Exceeding Connector Polishing Requirementswww.ultratecusa.comBackgroundWithin the communications field, high standards of connector performance are needed for telephonetransmission and even higher standards for CATVPolished connectors are quality tested to ensure they allow maximum light transmission with minimal interferenceIn this presentation we discuss the various important polishing performance criteria and suggest methods to ensure connectors are polished right first time, every timewww.ultratecusa.comEnsuring PerformanceThe key performance criteria for polished connectors are:z Backreflectionz Insertion Lossz Apex Offsetz Fiber Undercut / Protrusionz Visual Quality www.ultratecusa.comBackreflectionBackreflection (or “return loss”) refers to light reflected back through the fiber toward the source. It must be minimized (to less than 55dB) to insure speed and clarity of information transfer. Backreflection is tested as shown below:Backreflection can be improved (minimized) by control of the following factorswww.ultratecusa.comImproving BackreflectionPolishing Method Use of a mechanical polisher ensures an even polish of all sides of the connector endface This leads to reproducible finishes and connectors that mate perfectly improving backreflection Polishing Technique Recipes exist to improve clarity of the polish and so improve backreflectionCleaving A bad cleave before polishing will affect all subsequent polishing steps and overall performanceCleanliness This cannot be stressed enough. Thorough cleaning of connectors between each step, along with the use of rapid change polishing plates reduces the possibility for cross-contamination helps ensure backreflection resultswww.ultratecusa.comAsk ULTRA TEC for more detailsInsertion LossInsertion loss is the amount of optical power lost at the interface of two connectors. Poor insertion loss readings are generally a result of fiber misalignment, separation between connections and/or the quality of the finish on the end of the connector. www.ultratecusa.comImproving Insertion LossInsertion loss can be improved (minimized) byz CAREFUL SELECTION OF MACHINERY - A machine that produces poor end-face geometry will almost always generate unacceptable levels of loss. The currently stated standard for insertion loss is .3db, but the commonly expected level, has become .2db or less. In addition to the above performance characteristics, there is a specified product geometry-specified to assure reliability and ongoing proper connector performance under adverse conditions such as vibration and temperature cycling. These characteristics are are improved by the high level of control that a repeatable mechanical polisher provides.z POLISHING TECHNIQUE recipes exist to help you minimize loss. www.ultratecusa.comAsk ULTRA TEC for more detailsApex OffsetThe term Apex defines the highest point on the spherical surface at the end-face of the connector. Apex Offset is the measured distance between the center of the fiber and the actual high point of a polished connector. www.ultratecusa.comImproving Apex OffsetAlthough Apex Offset describes a physical condition of the polished fiber, rather than a performance parameter, it is considered an acceptance criterion in itself. An excessive Apex Offset contributes to a high Insertion Loss and high Backreflection reading. Key to optimizing (minimizing) apex offset is the use of a mechanical polisher that polishes all sides of the connector equally.www.ultratecusa.comAsk ULTRA TEC for more detailsRadius of CurvatureRadius of curvature is the measurement of a connectors end-face spherical condition. The radius generated on a connector end-face affects connector performance, and so is specified -the industry specification is 10-25mm. www.ultratecusa.comImproving Radius of CurvatureIn general, ferrules are pre-radiused. This radius is maintained during polishing by applying pressure between the connector and a resilient polishing surface, by applying weight or by setting a compression dimensionally. Although increasingly rare, the forming of a flat-ended ferrule into a PC end can be achieved through the same basic technique of applying pressure against a resilient surface. The harder the resilient polishing surface the larger will be the resultant connector radius (more flat). Conversely, the softer the polishing surface the smaller the connector radius. A proper radius, in conjunction with fiber undercut, allows for correct fiber-to-connector compression. www.ultratecusa.comAsk ULTRA TEC for more detailsFiber Undercut / ProtrusionWhen a fiber is recessed inside a connector ferrule the term used is Fiber Undercut. When a fiber protrudes above the ferrule it iscalled Fiber Protrusion. Measurement of this characteristic ismade on an interferometer observing the offset of the interference lines tha