Why is it crucial to use the correct polishing film grit sequence when terminating fiber optic connectors?

Using the correct polishing film grit sequence when terminating fiber optic connectors is crucial for achieving the desired end-face geometry and surface finish, which directly impacts the connector's optical performance. Polishing film grit refers to the size of the abrasive particles on the polishing film, with lower numbers indicating coarser films and higher numbers indicating finer films. The polishing process is typically performed in multiple stages, starting with a coarser grit film to remove excess epoxy and initial imperfections, and then progressing through successively finer grit films to create a smooth, scratch-free surface. If the grit sequence is incorrect, several problems can arise. Starting with a film that is too fine may not effectively remove the epoxy and fiber stubble, resulting in a rough or uneven surface. This can lead to high insertion loss and return loss due to poor physical contact between the fibers. Conversely, using a film that is too coarse for too long can create excessive scratches and pits on the end-face, which also degrade optical performance. The correct grit sequence ensures that material is removed gradually and uniformly, creating the desired end-face shape (e.g., physical contact, ultra physical contact, or angled physical contact) and surface finish. For example, a typical polishing sequence for a UPC connector might start with a 9-micron film to remove the bulk of the epoxy, followed by a 3-micron film to refine the surface, and then a 0.5-micron film to achieve the final polish. Deviating from this sequence could result in a connector that does not meet the required performance specifications. Therefore, following the manufacturer's recommended polishing procedure and using the correct grit sequence is essential for producing high-quality fiber optic terminations.