Weaknesses of Fiber Optic Connector Assemblies

The weakest link in a fiber optic connector assembly is the area in the ferrule, which contains the ribbon transition point (where the buffer fiber is stripped into bare fiber), and is mostly filled with epoxy. In this discussion, I will focus on the banded transition point, while the epoxy discussion deserves a separate dedicated discussion.

The transition point is where the buffered fiber is stripped to expose the bare fiber. This is usually done mechanically, so there is a chance that the stripping tool will damage the bare fiber. Very small damage to the glass rib is very weak, greatly increasing the risk of fiber breakage under normal stress. This is observed during scribing, where the fiber is scored with a sharp scribing tool, which makes the fiber very susceptible to breakage under small side loads or tensile loads.

A fiber that is damaged during the stripping process may not break under normal operation during production assembly, but the defect remains in the finished product; a potential ticking time bomb that could break at any time after the customer receives it and has installed it product.

In order to ensure maximum long-term reliability of the final product, it is important that production sites consider such precautions to reduce the chance of fiber damage during stripping and measures to determine if such damage exists prior to connection. . . These measures may include:

Perform a bend test on each stripped fiber by holding the buffer just below the stripping point and bending it 45 degrees in each of the 4 directions. If the fiber is scratched during the stripping process, it will most likely break during this test. It is better to break the product now and have to re-bundle it than to have it break later in the process, or in the worst case, after the customer receives it.

When cleaning fibers with alcohol before splicing (and you should always do this), make sure the operator is cleaning the fiber with a squeaky sound - the vibration of the fiber that makes the squeaking noise can be enough to damage a fiber that has been damaged during the stripping process.

Put all stripping tools on a preventive maintenance schedule, inspect stripping blades for wear, and evaluate stripping effectiveness. A maintenance program can use the results of a failed bend test to trigger immediate blade replacement, or it can be used to determine an appropriate time-based or strip-based blade replacement schedule.

Always ensure the stripper blade is clean and free of debris before stripping each fiber

Before inserting the ferrule, make sure the stripped fiber does not come into contact with anything other than a lab wipe for cleaning. Even resting a stripped fiber on a production bench surface can cause damage to the bare fiber. If the operator needs to drop the bare fiber before inserting it into the ferrule, the bare fiber end should be suspended in the air and not allowed to touch and rise to the surface.

Even though the stripped fiber remains intact during stripping and handling before insertion into the ferrule, it can still break easily if it is not completely sealed in the ferrule. All end operators are familiar with the connector ribbon diagrams provided by fiber optic connector manufacturers. Such a strip chart should always show the target strip length along with the tolerance. The length of the buffer strip is critical, especially in booted (crimped) assemblies, to ensure that the transition point is deep enough in the connector to ensure it is fully sealed by the epoxy after insertion. The cured epoxy helps protect the transition area from any bending or pulling that may occur during the life of the product. For example, stress during installation, stress caused by environmental changes.

Ideally, the transition point will end up at the rear of the ceramic ferrule, ie just touching or behind it (less than 1mm). It is an excellent practice to periodically take samples from the production line and perform cross-sectional inspections to look inside the finished fiber optic connector to verify the length of the strip template and the fiber optic connector connection process to understand where the transition points are and whether they are adequately encapsulated in cured epoxy resin.