Multimode Test Standards Compliance

Kingfisher LED light sources & Loss Test Sets meet the requirements of the IEC international standard for Encircled Flux Compliance at 850 nm into 50 u core fiber, and Coupled Power Ratio Category 1 for 850 / 1300 nm, and 50 and 62.5u core fiber. This applies to all such equipment produced since 2007.

Background on Encircled Flux Compliance

Loss Testing of multimode fiber connectors and systems is critically affected by the beam geometry / modal distribution of the test source.

If various test sources with uncontrolled beam geometry are used to test the same multimode item, the measured results may vary widely, which can be a big problem when testing against requirements.

The traditional solution was to use 1 – 2 Km of multimode fiber after the light source, and the beam produced was assumed to have equilibrium modal distribution. This has been in broad use since around 1980. However, EMD was never properly defined, and in fact with modern multimode fiber, this method may fail since the fiber is so good that the beam coming out can have almost the same geometry as the beam going in.

A semi-successful attempt at defining multimode beam geometry was Coupled Power Ratio, however there was widespread industry confusion at the time, and a lack of equipment that met it. The standard could be fooled by sources with asymmetric fill, since they technically meet the standard, but then produced strange loss test results. CPR is easy to measure.

In 2007, Kingfisher introduced the industry’s first symmetric-filled CPR compliant LED source, and has fitted it as standard on all LED sources and loss test sets produced since this time.

The current Encircled Flux Compliance standard was introduced in xxxx with standard xxxxx. This is a hard-to-measure standard, however it does ensure symmetrical beam geometry. A symmetric-fill source that is CPR compliant, will also be approximately EF compliant.

The technical objective of EF compliance is to keep loss test variability due to source geometry variation, within 10% of the measured loss value.

The role of mandrel wraps

It is often wrongly assumed that a mandrel wrap can be used to create an EMD, CPR or EF modal condition. With modern multimode fiber, it does no such thing.

What a mandrel does do, is to strip off unstable edge modes, and so generally improve measurement consistency. So it's use is to recommended to further improve measurement consistency.

Kingfisher provides a pair of standards compliant mandrels with every LED source, for 50 u and 62.5 u core fiber.

What is the result?

If a collection of compliant sources are used to test multimode loss, good test variability can be achieved. In field use, we found that with Kingfisher EF compliant LED sources, multimode test uncertainty is typically limited by randomly changing the test leads. If mandrels are also used, variability can be further improved. Expected test uncertainty is explored in further detail in Application Note 21.