Encircled Flux still a hot topic in the standards
November 8, 2011 / General
Fluke Network's fiber optic technologist Seymour Goldstein just returned from Melbourn Australia where he attended IEC SC86C/WG1, and ISO/IEC JTC 1 SC25/WG3 meetings. I caught up with him this week and got a download from his trip.
Seymour indicated that Encircled Flux was prevalent in many of the discussions in Melbourne. This is interesting, because Encircled Flux was selected as the multimode fiber launch condition by both the international standard IEC 61280-4-1 Ed. 2.0 and adopted as TIA 526-14-B in North America quite a while ago.
Encircled Flux is a new method to define and measure the output of optical sources used for testing. It obsoletes the use of VCSEL lasers (lots of variability) for optical testing, and eliminates uncertainty from ambiguous launch condition specifications. In use, it ensures consistent, repeatable and accurate loss testing.
While there have been some concerns over the practicality of complying with the new standards, and there have been a few outspoken individuals who have been unable to technically substantiate thier criticism of Encircled Flux. But Encircled flux is recognized by the vast majority of the industry's experts as the most precise method to certify components and systems.
Nonetheless, a call to re-energize the "Multimode Launch Condition Correspondence Group" has been requested. The purpose is to make sure that fiber core diameter measurement is accurate enough to ensure tolerances necessary to adequately implement encircled flux. It is also significant that SC86B/WG4 has taken the position that encircled flux should only be required at 850 nm for 50 um fiber cabling. This notion has also been discussed by other groups since the original intent of encircled flux was to characterize the worst case launch condition of an 850 nm VCSEL. This topic will remain an important one to keep an eye on for some time.