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As the optical communications industry continues to evolve, industry standards are being established to characterize the performance of optical components. One of these emerging standards is FOTP-203, which characterizes multimode fibers by encircled flux analysis.

Encircled flux, as the name implies, describes the flux encircled within a circular radius inside the fiber. It is often quantified as the radius from the center of the fiber required to encircle 25% and 75% of the light energy through the fiber. Experimental data from several leading industrial labs has shown that the power distribution of a fiber described by the encircled flux value is a crucial factor in ensuring the required data transmission rate in Gigabit Ethernet systems.

The encircled flux measurement, as specified in FOTP Standard 203, is performed in the following manner: The near field of the fiber is imaged with a microscope objective lens and a Photon BeamProfiler Model 2320 CCD camera. The reference center of the fiber is determined from the near-field for a fully launched LED source. Then the telecomm laser source, typically a VCSEL, is installed with an offset launch condition to excite higher order modes. The encircled flux analysis is then performed for this source using the LED centroid reference.

The Photon FO 8350 Encircled Flux Fiber Analyzer is an instrument and software package dedicated to encircled flux measurement of multimode fiber, as specified in FOTP-203.