As you can see below (next article) MPO connectors have a large area that can get dirty. They also depend on the polishing process leaving fibers protruding from the ferrule surface to ensure physical contact for low loss and reflectance. A typical MM MPO looks like this on an interferometer:

Polishing the connector so that all fibers protrude equally is not easy, but is mandatory to get consistent loss on all the fibers. You might remember an article in this newsletter that quoted a study about the MPO claiming that the outer fibers had higher loss. That article prompted feedback from a cable manufacturer who said it appeared to be an artifact of the polishing process and that another brand of polishing machine gave results where the inner fibers had higher loss. Puzzling!

Another option is the termination process developed by Arrayed Fiberoptics Corp. that polishes the MPO ferrule so that the fibers are undercut slightly, then the ferrule is coated with an anti-reflection coating like the coatings used on photographic lenses. The Arrayed MPO looks like this:

You can see the fibers do not protrude but are just slightly below the surface of the ferrule (just microns below). Generally this would cause high reflectance (~ -20dB) if there were an air gap between the fibers, but the ferrule ends are coated as you can see in this photo:

The ferrule on the right has an antireflection (AR) coating that reduces loss even with non-contact fibers. The manufacturer claims that this provides more repeatable loss on the line of fibers and reduces potential damage to the fibers. Although not one of their claims, AR coatings are often harder than glass and certainly the glass-filled plastic ferrule, so this should be a much more durable MPO.[1]

[1] The FOA Staff, The FOA. [Online]. Available: visit The FOA. [Accessed: 23-Oct- 2016]