| Full title | Fibre-optic communication subsystem test procedures. Part 4-1: Installed cabling plant. Multimode attenuation measurement |
| Publisher | IEC, subcommittee SC 86C |
| Current edition | Edition 3.0 (2019-05) with Amendment 1 (2021-12). Consolidated as Edition 3.1. Corrigenda 2020 and 2022 |
| European version | EN IEC 61280-4-1:2019 and A1:2022 |
| Status | Current. Edition 3 replaced Edition 2 (2009) |
| Related standards | IEC 61280-4-2, IEC 61280-1-4, IEC 61300-3-35, ISO/IEC 14763-3, ANSI/TIA-526-14-C |
What it covers
IEC 61280-4-1 sets out how to measure the attenuation (loss) of installed multimode fibre cabling. The cabling can include fibre, connectors, adapters, splices and other passive devices. It applies to residential, commercial, industrial, data centre and outside plant installations.
It covers 50/125 µm OM2, OM3, OM4 and OM5 fibre and 62.5/125 µm OM1 fibre, as specified in IEC 60793-2-10. Edition 3 added bend-insensitive multimode fibre.
Test methods
The standard has five normative test methods. Four use a light source and power meter (LSPM). One uses an optical time domain reflectometer (OTDR). Each method suits a different cabling configuration, labelled A to D in the standard.
| Method | Annex | Configuration | End connections in result |
|---|---|---|---|
| One-cord reference | A | A | Both |
| Three-cord reference | B | B | Neither |
| Two-cord reference | C | C | One |
| Equipment cord | D | D (channel) | Includes the user’s equipment cords |
| OTDR | E | A, B, C and D | Set by the launch and tail cords |
Which method to use
- The one-cord method suits cabling with sockets or adapters at both ends. It has the lowest uncertainty of the LSPM methods and is the method most often recommended.
- The two-cord method suits cabling with plugs at one or both ends.
- The three-cord method suits cabling that connects directly to equipment, such as spliced pigtails, where neither end connection is part of the result.
- The equipment cord method measures a channel with the customer’s own cords in place. Edition 3 added this method. A new reference is needed for each channel.
In older TIA documents the one-cord, two-cord and three-cord methods were called Method B, Method A and Method C. The current names state how many cords are used to set the reference.
Launch condition: encircled flux
Multimode loss results depend on how light is launched into the fibre. An overfilled launch tends to overstate loss. An underfilled launch tends to understate it.
Annex F requires the source to meet encircled flux (EF) templates. EF describes how launched power is spread across the core. The templates apply at 850 nm and 1300 nm for 50 µm and 62.5 µm fibre. Edition 3 aligned Annex F with IEC TR 62614-2 but kept the EF limits unchanged. EF is measured to IEC 61280-1-4.
Test cords and uncertainty
- Test cords use reference-grade fibre and connectors, which have tightly controlled tolerances.
- Normative Annex I explains the bias this causes. Results measured with reference-grade cords read lower than the cabling would show with standard-grade mated connectors, and the annex gives worked examples of the effect on the test limit.
- Annex H gives procedures for verifying test cord loss.
- Clause 5 lists the main uncertainty sources, including the power meter and test cord connector grade. Edition 3 updated the uncertainty values.
- End faces are inspected and cleaned to IEC 61300-3-35 before each measurement.
OTDR testing
Annex E covers OTDR loss measurement with launch and tail cords. Informative Annex G covers OTDR set-up: dynamic range, pulse width, averaging time, dead zone and index of refraction. It also covers bi-directional measurement. The standard lists measurement without a tail cord, and simple cursor measurement, as non-recommended practices.
Related standards
| Standard | Relationship |
|---|---|
| IEC 61280-4-2 | Companion standard for single-mode attenuation and optical return loss |
| IEC 61280-1-4 | How to measure the encircled flux of a light source |
| IEC 61300-3-35 | End face inspection, referenced normatively |
| ISO/IEC 11801-1 | Cabling design standard. Defers multimode launch conditions to IEC 61280-4-1 |
| ANSI/TIA-526-14-C | North American adaptation of IEC 61280-4-1 |
What it means in practice
- Check the test report states the reference method used. A one-cord result includes both end connections. A three-cord result includes neither.
- Check the source meets encircled flux at the wavelengths tested.
- Check test cords are reference grade and the limit has been set for this.
- Record the test details that Clause 9 requires, including the reference method, wavelengths and test cords.
Related reading: Fibre optic loss budget: how to calculate insertion loss · Fibre insertion loss and return loss explained.