Fibre Testing FAQs

When setting up my fibre test equipment (LSPM*/OLTS**) which jumper reference method should I use?

*Light Source Power Meter

**Optical Loss Test Set

There are several ways to set the reference when using an LSPM/OLTS, and industry standards specify 1-jumper, 2-jumper and 3-jumper reference methods. The recommended 1-jumper method offers the best accuracy.

A 1-jumper reference references out the launch cord from the point where it connects to the light source to the point where it connects to the power meter. If you were to use a 2-jumper reference, the mated connection between the two jumpers would also need to be referenced out. And a 3-jumper reference would add yet another mated connection that would need to be referenced out.

The 1-jumper method is the only method that includes the loss of the connections at both ends, actually simulating the way the cable plant will be used and providing the lowest uncertainty of all measurement methods. However, it's important to remember that after the reference is set with the single launch cord, the tail cord should still be measured for proper loss -- a maximum of 0.1dB for multimode and 0.2dB for singlemode. And do not remove the launch reference cord once the reference is set or you'll have to start over and set it again.


What is encircled flux and why must my TRC adhere to this requirement?

EF is a multimode launch-condition metric that serves several purposes. Its first intention is to reduce link-loss variation when using different light sources so test results are similar, independent of the supplier. This variation has been limited to ± 10% for link loss higher than 1 dB. EF was developed to keep up with components used in high-speed networks, e.g. 10/40/100-Gbit Ethernet. It was not until high-speed transmission over multimode fiber became a reality that EF measurements became important.

Fluke Networks and other experts developing international standards recognized that a simple mode filter was inadequate, and responded with a qualification template based on mode power distribution (MPD). MPD was the metric used to describe launch conditions within the International Organization for Standardization and International Electrotechnical Commission’s standard ISO/IEC 14763-3 Information Technology – Implementation and Operation of Customer Premises Cabling – Testing of Optical Fibre Cabling. The metric is now superseded by EF because it was found that channel or link loss consistency using sources compliant with MPD are insufficient to meet the tight loss budgets for Gigabit Ethernet.

EF solves the problem by controlling the number of mode groups launched from the test cord. Consistency in launching repeatable mode groups is both an optical and geometric problem and is related to the launch wavelength, the initial launch condition (i.e., overfilled or OFL launch), the test cord’s fiber-core size, the fiber numerical aperture, the external mandrel, and other fiber properties.