Revision to IEC 61280-4-1 Ed 2.0, Fibre-optic communication subsystem test procedure – Part 4-1: Installed cable plant – Multimode attenuation measurement
August 7, 2015 / Seymour Goldstein / General
This primary international standard provides guidance for measurement of attenuation using power meters, light sources and OTDRs on 50/125 µm and 62.5 µm multimode fiber cabling that may include connectors, adapters and splices. Various test methods and cabling configurations are described. This report gives important information regarding upcoming changes for anyone needing to specify testing. Architects, Consultants and Engineers may use this information to learn of changes in IEC, anticipate customer concerns and gain insight to cabling testing trends.
Scope: The scope of the standard will be more generic and similar to the single-mode version (IEC 61280-4-2) of the published test standard. It will describe where the cable plant may be installed. No change is recommended for the fiber types to be tested.
Encircled Flux: Proposals to relax the limits for all non 850 nm/50 µm cases has been discussed – the limits will not change. The published values are considered valid. The consensus was that extension of the uncertainties of measurement for 50 μm fibers at 1300 nm and for 62.5 μm fibers at 850 nm and 1300 nm does not warrant an increase of the encircled flux limits.
Bend insensitive fiber (BIF) testing: Testing is under study and best practices are undetermined. While BIF may be compatible with “traditional” fiber, the type of receive cord used is being investigated. In any case, an encircled flux launch is required.
Channel characterization: The channel test method used in ISO/IEC 14763-3 has been adapted as a channel characterization method. This will be a special configuration of the one-cord reference test method and will be “informative”. This cabling configuration includes customer equipment cords as part of the test.
Loss Uncertainty: The section on measurement uncertainty will be updated. A table of fiber lengths, attenuation and uncertainty for each of the three reference methods (e.g., 1-cord method) will be shown. Descriptions for sources of uncertainty are included.
Reference grade termination: The definition for a reference grade termination will be updated to specify ways to reduce connector attenuation such as controlling the core diameter, the numerical aperture and ferrule bore-hole size as a means to improve alignment. Reference grade terminations are quantified elsewhere in the standard but remain at less than or equal to 0.1 dB.
OTDR bi-directional testing: Bi-directional testing using an OTDR is expanded and the addition of a “smart loop” is described. The use of a loop back cord is a recent advancement that makes testing faster and prevents incorrect bi-directional measurements. While uni-directional testing may be desired, it is unlikely that launch and tail cords will have similar characteristics (backscatter coefficients) to warrant uni-directional testing.