Terms: Macro- Or Micro-Bending?
Two of the more confusing terms used in fiber optics are macrobending and microbending. Most of the technical definitions we have read in researching this topic don't make a clear distinction between the two. The best explanation I found was in a Corning paper by John Jay where we found this graph:
Corning makes the distinction here at about 2mm bend radius, but it's more subtle than that.
Here is what OFS says in a paper about bend-insensitive fibers: "What’s the difference between macrobending and microbending? Bends fall into two categories: macrobends are bends that are large enough to be seen by the human eye, and microbends are microscopic deviations along the fiber axis. An example of a macrobend is the routing of a jumper in a patch panel; a microbend could be caused if the fiber coating squeezes a fiber as it contracts at very low temperatures. Both types of bends can result in increased attenuation that can degrade system performance."
Macrobend loss refers to losses induced in bends around mandrels (or corners in installations), generally more at the cable level or for fibers, the bends necessary to fit fibers inside splice closures or patch panels. To illustrate this, macrobending testing is done by wrapping the fiber or cable around a mandrel of a specified diameter.
Microbend loss refers to small scale "bends" in the fiber, often from pressure exerted on the fiber itself as when it is cabled and the other elements in the cable press on it. There is no real "test" for microbending. There have been attempts, for example sandwiching fibers between sandpaper or wire mesh or kinking it over a small pin, but the results have not been adequately reproducible, so no standard test exists for microbending.
Where does bend-insensitive fiber fit in this discussion? It was intended to reduce macrobending loss so cables could be run around corners better and fibers would not have as much loss when stuffed into small spaces. But microbending loss, according to technical papers we read, is helped also by careful attention to the fiber primary coating (or coatings, if applied in several layers) which protects the fiber from being bent in the first place.
It's easy to see why these two terms are so confusing! Both are similar and the differences are not so easily defined.
Many modern fibers, and most multimode fibers, are designed to be "bend insensitive" fibers.
FOA thanks three major manufacturers of optical fiber for their contributions to this page.
Table of Contents: The FOA Reference Guide To Fiber Optics