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Reducing Measurement Uncertainty in Multimode Optical Fiber

Encircled flux (EF) is the final piece in the puzzle of reducing measurement uncertainty in multimode optical fiber cable loss measurements. It is potentially the biggest contributor to variations in loss measurements.

What is a launch condition?

A light source’s launch condition determines how and where the light is distributed within the fiber.

1. Over-filled launch - example LED

 white light path led

2. Under-filled launch - example laser

white light path laser

3. Encircled flux compliant launch - example any light source with “ModCon” attached

white light path controlled


An overfilled launch puts too much power into the higher order modes. This power gets removed at the first connection. The result can be unrealistically high loss values.

led offset

An underfilled launch puts too little power in the higher order modes. Very little power is removed at the connections. The result can be unrealistically low loss values.

laser offset

An encircled flux compliant launch puts the right amount of light into the higher order modes so that you will see increased loss values when there is a problem with the cable, connectors or installation.

controlled offset

Just as important is that because you are using “standard” conditions, you will obtain results which can be compared with other measurements such as those provided by the cable manufacturer.

'ModCon' mode controllers

Fortunately, there is a really easy way to achieve this EF compliance – use the “ModCon” from Arden Photonics.


The ModCon will take the output from any source and convert it into a “EF compliant” launch.

Each ModCon is thoroughly tested using Arden’s MPX-1 Encircled Flux meter.

MPX Software

EF Extender cords

The “ModCon” replaces your reference test cord, but

  • the output connector will eventually become worn out, or
  • you may need to test a system with a different input connector.

So increase the lifetime and the applicability of the ModCon by using EF Extender cords. The fiber used in our EF Extender cords is carefully matched to that used in the ModCon, so it is not possible to use other reference test cords for this purpose. 

For more information on the products Arden Photonics can offer, visit


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