IS ENCIRCLED FLUX?
Encircled Flux (EF) is the ratio of the total optical power within a multimode fiber core to the amount of optical power exiting the fiber at a particular radius, measured at several different radii to determine how the optical power is distributed within the multimode fiber core, and to set limits based on where the fiber overfills and where it underfills.
In other words, EF is a method that defines whether or not the launch condition of the transmitter is acceptable (neither overfilling nor underfilling the fiber).
From the perspective of technicians who test and certify fiber cables, the above definition is merely academic because EF is not what is being measured here.
IF ENCIRCLED FLUX IS NOT A FIELD MEASUREMENT, WHAT IS IT
The goal of any measurement is to minimize the amount of uncertainty, or error, in the measurement. By minimizing measurement error, accuracy is increased.
Where EF is concerned, uncertainty is minimized by where the upper and lower fill limits are set. So, if a technician is required to test a link according to EF standards, technicians must ensure that EF-compliant test methods are followed.
Unfortunately, due to variance between different multimode test sources and reference cables, EF compliance cannot be fully ensured by current reference methods, such as mandrel-wrapping.
HOW IS "ENCIRCLED FLUX COMPLIANCE" ENSURED?
Thus, an EF-compliant test method must have a way to control the launch condition itself so that the output launch exiting the multimode reference cable is consistent regardless of what test source and/or reference cables are used.
Currently, EF compliance can be achieved a couple of different ways.
The first method requires two matched parts to ensure EF compliance: a specially designed light source partially controls modal output, and a special matching cable that completes the EF compliance. The problem with this method is that neither the source nor the cable can ensure EF compliance on their own, and they cannot be matched to other sources and cables.
(Arden Photonics ModCon Mode Controller shown here)
While Mode Controller cables are relatively expensive, they are a viable option to make any OWL multimode test kit EF compliant.
Call OWL at 262-473-0643 for more information about purchasing a Mode Controller cable for your OWL multimode fiber test kit.