FNT Instructor Tip: October 2014

The Problems with Using Diamond Polishing Film on Connectors.

By: Jeff Dominique, Chief Instructor


We have all been there. I just spent the last 20 minutes polishing a connector only to find small scratches or a fracture when I look at it in my inspection scope. Another technician hands me a single sheet of diamond film and a few figure-8's later the connector endface looks flawless.

The problem is what we can't see when we look through that microscope. Fiber optic connectors use a zirconia ferrule, the reason is zirconia is harder than most material including the glass inserted into the center of a connector. This makes it easy to polish down the glass on a connector without reducing the ferrule itself. Diamond polishing film is one of only a few materials strong enough to sand down both the glass fiber and the zirconia ferrule. Why is this bad? Well, the end of a fiber connector is not flat, it's actually a dome shape. This allows only the center of the connector ferrule to contact a mated connector ferrule. When a ferrule is polished down too far with diamond film, an air gap is created between the mated pair causing a high dB loss. Diamond film also puts tiny scratches into the glass and endface invisible to the eye that can increase reflectance. This reflectance can restrict a network's performance from an optimal 40Gbps down to as little as 100 Mb.

FNT Instructors Recommend

That diamond film is used sparingly by technicians and only on multimode networks where the core alignment is not as critical.

Job can't wait? Contact FNT Training for a quote on getting certified on current telecom testing standards.

Call FNT for available Inspection Equipment, 1-866-818-8050 or Click the link below for on-line purchasing:

Click Here for Polishing Film selection

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