For high-speed data transmission, optical fiber is a good vehicle but only when the light transmission is efficient across connector assemblies. This translates to the requirement of fiber polishing pad connector end faces to optimize performance. Increasingly, automation of the polishing process is becoming a necessity with the adoption of newer fiber configurations, as well as ever-tightening specifications.
Early physical contact connectors required the spherical forming of their flat end faces as part of the polishing procedure. A four-step process is included under traditional techniques: epoxy removal, ferrule forming, and preliminary and final polishing. For epoxy removal and ferrule forming these steps used aggressive materials that are generally accomplished with diamond polishing films.
Now, the polishing process has developed into a sequence of epoxy removal, followed by rough, intermediate, and final polishing cycles as almost all connectors are manufactured with a pre-radiused end face. One main goal is to avoid excessive disruption of the spherical surface, while still producing a good mating surface. Polished fiber optic connectors then need to conform to a range of performance and geometry-based acceptance criteria.
In two categories the polishing specifications for fiber polishing film connectors are included and they are related to performance and end-face geometry. Back reflection and insertion loss specifications are perhaps the most critical measures of polished end functionality. The latter is the amount of optical power that is lost at the interface between the connectors that usually occur by fiber misalignment, the separation between connections (the air gap), and the finish quality of each connector end. The current standard loss specification is less than 0.5 dB, but less than 0.3 dB is increasingly specified.
Regardless of the connector type, most polishing sequences have now started with aggressive materials, including silicon carbide that removes epoxy and diamond lapping films for beginning and intermediate polishing. These then at the same rate remove both surrounding material and fiber. The last polishing step, however, needs a less aggressive material, such as silicon dioxide, to attack only the fiber. For final fiber polishing liquid using a material that is too aggressive could lead to excessive undercut. The wrong final-polish material can lead to excessive protrusion, then to fiber chipping and cracking during the connector mating process.
