The Fiber Connection

The Bend Insensitive Fiber Debate - Tuesday, September 27, 2011

There is a lot of buzz around the issue of bend insensitive fiber – is it compatible with other MM fiber and how do you properly test it? We even heard some talk at the BICSI Fall Conference last week. We thought a post on the subject would be of interest to our customers, so we started talking to people and digging around.

It is interesting that in January, 2011 both Corning and Panduit published articles about this subject. Corning’s was called “The facts about bend-insensitive multimode fibers” and concluded, “In summary, a well-designed BIMMF complies with all relevant industry standards and adheres to the following: …BIMMF OM2, OM3 and OM4 multimode fibers are fully compliant and fully backward-compatible with all relevant industry standards…”

Now, Panduit’s article was titled, “Compatibility issues with bend-insensitive and standard multimode optical fiber” – can you see where they might be going with this? In the end, they summarized it like this: “In conclusion, inconclusive”. Yes, that is the title of the summary section. Now what? Keep digging.

Less than a year ago, CommScope published a couple of white papers on the subject – one that ended with this statement: “At this time, there simply don’t seem to be enough benefits to risk installing a non-standard product that may limit you to a specific vendor, may become obsolete once standards are developed, or may have incompatibility issues with legacy and other systems.” Well – we know where they stand – for now.

OFS has weighed in as well, with their publication – 5 Things You Should Know about Bend Insensitive Fiber. They support more evaluation and express particular concern over possible bandwidth issues and overall system performance questions. They, like all the others, don’t question the improvement in bend performance

In April, 2011 Draka announced that it will begin shipping bend insensitive MM fiber in place of standard OM3 and OM4 fibers in their UC branded cabling solutions. They billed this as “…effectively a free bend-insensitive upgrade for our customers.” Based on some of the industry buzz and the questions many key players in the cable and connectivity markets still have, is this something everyone wants? Well, Draka must think so - and we know Corning made their ClearCurve® 50µm BIMMF a standard product in 2009.

In Corning’s May, 2011 publication called “The Truth About Bending” the issue of measurement is addressed and Corning defines 2 methods for testing BIMMF. The last line on this subject is this -

“Corning is working within standards bodies to ensure that a 4 mm mandrel is incorporated into existing testing standards.” So, a test method has been recommended by a leading fiber manufacturer, but has not yet been adopted in an industry standard.

After seeing so much information on both sides of this issue, I turned to one of my favorite sites - The FOA. This led me to their Feb., 2011 newsletter talking about…. Wait for it… the 2 BIMMF articles that I referenced here. As I read through the newsletter, I noticed several notes in italics and with asterisks. The tone was leaning toward the idea that compatibility issues were solved with newer versions of BI fiber – and then I reached the note associated with those * sections.

“*…. After this article was first published, we received comments that indicate that not everyone in the industry feels a solution is that close, leading to the new text. How long will it take for there to be compatibility between new BI fibers and legacy fibers - or how long will it take for different manufacturers' fibers to be compatible? What are the implications of BI fiber designs beyond mating loss - like bandwidth which was raised as an issue at the TIA meeting discussed below? Stay tuned for more on this topic…“

I guess “inconclusive” may be the best we can do for now, relative to testing in particular. There is still some question about backward compatibility in some applications and no standard published yet for test methods. We do notice that no one seems to be saying that bend insensitive fiber is not working or not able to handle the bends as claimed. Is the issue of a testing standard a big enough question to prevent someone who needs a tight bend radius from using it? Some of the advantages, like smaller hardware and higher density, are a big advantage for some applications – so there is definitely a need and no major reason to not install BIMMF in many applications.

So, we don’t have all the answers yet. We do promise to stay on top of this and keep you posted though. Until the next time, here are links to the information referenced here:

FOA News – February, 2011

Draka BendBright technology is now a standard …

Compatibility issues with bend-insensitive and standard multimode optical fiber - Panduit

The facts about bend-insensitive multimode fibers - Corning

The Truth About Bending - Corning

CommScope white paper

OFS – 5 Things You Should Know

Bend insensitive fiber, BIMMF, bend tolerant fiber, multimode fiber