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IEC standard 61280-1-4 was also published in 2009 and describes the methodology for measuring the encircled flux. The MPX Modal Explorer, shown left, was designed to comply with this standard and provides accurate characterisation of patchcords, mode filters, OTDRs, VCSEL sources, etc. It also measures the Mode Power Distribution, according to IEC 61300-3-43. The MPX-1 measures at 850nm and the MPX-2 at 1300 & 1550nm. A screenshot of the MPX software is shown below. |
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Click for a larger view |
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Requirement: Development of modal analysis system for multimode fibre |
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This standard describes the measurement of the attenuation of installed multimode optical fibre cabling, typically in lengths of up to 2,000 m. This cabling can include multimode fibres, connectors, adapters and splices. In order to achieve reproducible attenuation results, the standard defines the exact launch conditions to be used when making measurements. These conditions are based on the 'Encircled Flux' in the launch fibre, which is the integrated power distribution, going from zero at the fibre centre to unity at the core/cladding boundary. There are four templates: two for each fibre size, 50um and 62.5um, and two for each wavelength, 850nm and 1300nm. |
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The following standard was published in 2009: 'IEC 61280-4-1 Ed. 2.0: Fibre-optic communication subsystem test procedures - Part 4-1: Installed cable plant - Multimode attenuation measurement.' |
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The figure right shows measured encircled flux, in blue, and a series of narrow windows at several radial control points. In order to pass the specification the encircled flux must pass through the windows. In the example shown here, the red markers indicate that the encircled flux has failed the template at the 20um and 22um control points, indicating that the modal distribution of the fibre is slightly overfilled. |
