Using Encircled Flux Compliant Light Sources For Testing Fibre Optic

October 12, 2016

International standards development organizations including ISO/IEC and ANSI/TIA are updating several key standards documents that affect field-testing of fibre optic cabling. In particular the
standards now describe the use of encircled flux compliant light sources.

Encircled flux refers to the distribution of light exiting the launch fibre of a light source used for testing. An ideal launch condition is one where light intensity is an even radial pattern across the face of the launch fibre. The purpose of the standards is to ensure that different test systems from any manufacturer report the same loss for a given cable under test.

Variation in LED and VCSEL launch patterns means that the optical power injected into the cable under test can result in variances in measured power loss values depending on connector alignment or the rotation of the launch cable. This is especially critical in multimode systems where the large fibre core will accept the uneven distribution from the light source and couple it into the cabling under test.

 

Figure 1 depicts the output from an LED into the launch fibre. While the light is distributed axially through the fibre, the intensity is much higher at the edge of the core (represented by a darker red colour) and a noticeable amount of power is present in the cladding (outer ring), creating an overfilled launch condition.

The results are artificially high loss readings when mandrels are not used on the launch cable or when there is mild misalignment between two connectors.

The reasons are that light in the cladding attenuates very quickly, and if this jumper were connected to the power meter during calibration, the light in the cladding will be detected, though it will dissipate in the cable under test and result in a high insertion loss measurement.

Additionally, when the core is overfilled, small misalignments between two connectors can result in abnormally high loss. Especially if the power distribution is weighted to the outside of the core as depicted in Figure 1.

 

 

Figure 2 depicts the output from a VCSEL, which is a low cost laser used in multimode systems to provide higher bandwidth at longer distances. A VCSEL typically has an elongated output that creates a “blade” of light in the fibre core that maintains its shape as it propagates down the cable.

VCSELs also produce spots of high intensity light that further reduce the even distribution of power. In this diagram the spots appear to be dirt, but are actually intense modes (beams) of light.

Rather than try and control the output pattern of LEDs and VSCELs, the solution to the problem is to use specialized launch cables (in the past called mode conditioning cables) that accept an uneven light pattern, scramble it and emit an even light pattern.

These cables can be used with virtually any LED light source and make it encircled flux compliant. While these specialty cables are expensive, they have the benefit of allowing installers to keep their existing multimode light sources and make them encircled flux compliant by simply replacing the launch cable.

 

Figure 3 depicts an encircled flux launch cord connected to a light source. This cord replaces the standard launch cord when testing the installed cabling. The output from the EF launch cord into the fibre under test has an even distribution pattern that does not extend into the cladding of the fibre. Because the distribution pattern depends on whether the fibre core is 50 or 62.5 micron, the EF cord used for testing must match the core size of the fibre under test.

 

 

 

Multimode fibre optic systems do have limitations when compared to single-mode, but their key advantage is the lower cost of the active equipment in the system. And as multimode systems support data rates of 100Gb/s and more, the loss budgets become increasingly stringent.

Therefore, installers need to utilize every tool and technology available to ensure they obtain accurate test data and give themselves the best probability of a problem-free testing experience.

While the encircled flux testing requirements will slowly make its way into contracts and testing requirements, installers should not delay in ensuring the test cords that accompany their power meters and light sources are made with reference grade connectors.

One last note; even the best connectors, launch cables and testers are useless if the end faces are not kept perfectly clean. It’s critical that technicians apply best practices and clean the ports of the test equipment and test cords every time they are used.

When combined, reference-grade connectors/cords, encircled flux compliant launches and clean connectors will provide the best possible testing experience resulting in fewer failed tests and less time spent troubleshooting.

This article was first published online by Ideal Networks: www.idealnetworks.net/US/EN/News/Using-Encircled-Flux-Compliant-Light-Sources-for-Testing-Fiber-Optic.aspx.

 

 

Related Articles


Changing Scene

  • LEDVANCE Expands Ontario Presence with New Specification Agent

    LEDVANCE Expands Ontario Presence with New Specification Agent

    LEDVANCE is pleased to announce the appointment of Sterling Architectural Products Ltd. (Sterling Lights) as their new specification agent in Ontario. This partnership strengthens LEDVANCE’s presence in the region and reinforces their commitment to serving the professional lighting design and specification community with innovative, reliable lighting solutions. With decades of experience and a service-driven mindset,… Read More…

  • May 29, 2025 - Eureka Wins Three 2025 Red Dot Awards for Product Design

    Eureka Wins Three 2025 Red Dot Awards for Product Design

    Eureka is pleased to announce that its Velia, Cirra, and Junction luminaires have each received a 2025 Red Dot Design Award for Product Design. It is the 11th consecutive year that Eureka products have been honored with this prestigious award, which is a testament to the company’s consistency and relentless drive to design exceptional luminaires.… Read More…


Design

  • 60-Watt vs 100-Watt Light Bulbs: Brightness & Wattage

    60-Watt vs 100-Watt Light Bulbs: Brightness & Wattage

    With the widespread use of LED light bulbs, the replacement and upgrade of different light bulbs have also made the concept of “equivalent wattage” more and more discussed. When comparing 60-watt vs 100-watt bulb, the wattage and brightness are the factors that need to be figured out first. Wattage is used to measure the energy consumption while many… Read More…

  • What is Human Centric Lighting: Benefits & Applications

    What is Human Centric Lighting: Benefits & Applications

    Human centric lighting (HCL) is a kind of illuminated way based on human physical and psychological needs. Its core goal is to imitate the changes in natural light to support the body’s circadian rhythm, improve visual comfort, and enhance mood. The key element of human centric lighting contains dynamic ​color temperature adjustment, adjustable brightness, spectrum… Read More…


New Products

  • LightForm: New Saule-L-01 Suspension Luminaire

    LightForm: New Saule-L-01 Suspension Luminaire

    LightForm is thrilled to introduce Saule, the newest lighting collection from Quebec atelier Larose Guyon, now exclusively available at LightForm. Inspired by the gentle grace of the willow tree, Saule is a sculptural light that feels alive. Cascading hand-formed brass leaves shimmer like foliage in the breeze, suspended from arched metal arms that echo the tree’s elegant… Read More…

  • Transform Outdoor Spaces with Lutron: Control, Elegance, & Performance

    Transform Outdoor Spaces with Lutron: Control, Elegance, & Performance

    Outdoor lighting is about more than just light—it’s an extension of the ambiance, design, and comfort of living spaces. With Lutron’s outdoor modules RR-15OUT-BL (for RadioRA 3 systems) and HQR-15OUT-BL (for HomeWorks QS systems), you can offer your clients powerful tools to transform their outdoor projects—whether gardens, patios, pools, or façades. Read More…