| Full title | Fibre-optic communication subsystem test procedures. Part 4-2: Installed cabling plant. Single-mode attenuation and optical return loss measurements |
| Publisher | IEC, subcommittee SC 86C |
| Current edition | Edition 3.0, 2024-05. Replaces Edition 2.0 (2014) |
| UK and European version | BS EN IEC 61280-4-2:2024 |
| Status | Current |
| Related standards | IEC 61280-4-1, IEC 61300-3-35, IEC 61746-1, ISO/IEC 14763-3, ITU-T G.650.3 |
What it covers
IEC 61280-4-2 sets out how to measure attenuation and optical return loss (ORL) of installed single-mode 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 applies to all single-mode fibre types, including the Class B fibres of IEC 60793-2-50. Its principles can also be applied to cabling with splitters, and to WDM, CWDM and DWDM passive components at the relevant wavelengths. It does not apply to cabling with active devices such as fibre amplifiers.
ISO/IEC 14763-3:2014 listed this standard as a normative reference. The current edition, ISO/IEC 14763-3:2024, does not: for attenuation it references IEC 61280-4-1 (multimode) and IEC 61280-4-5 (MPO). ITU-T G.650.3 refers to its test methods for longer telecoms links.
What changed in Edition 3
- Equipment cord method added.
- Test limit adjustment for test cord grade added.
- Measurement uncertainty refined.
Attenuation test methods
Four light source and power meter (LSPM) methods and one OTDR method are normative. Each suits a cabling configuration, labelled A to D in the standard.
| Method | Annex | Typical 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 | Includes the user’s equipment cords |
| OTDR | E | A to D | Set by the launch and tail cords |
Informative Annex K describes spectral attenuation measurement with a broadband source and an optical spectrum analyser.
Optical return loss methods
ORL is the ratio of launched power to power reflected back from the whole cabling. Edition 3 gives three normative methods.
| Method | Annex | Principle |
|---|---|---|
| OTDR | E | ORL calculated from the OTDR trace. Annex E also covers the reflectance of individual events |
| Continuous wave, Method A | F | Source, branching device and power meters, with a low reflection termination |
| Continuous wave, Method B | G | Return loss test set characterised with a known reflectance termination |
Test cords, wavelengths and uncertainty
- Normative Annex H covers reference-grade test cords. Table H.2 gives the test limit adjustment when they are used, and Table H.3 gives the same for OTDR testing.
- Table 3 links test limit adjustment and uncertainty to the test cord connector grade.
- Clause 5 also covers mode field diameter variation between fibres, reflections, source stability and bi-directional measurement.
- Uncertainty tables are given at 1310 nm, 1550 nm and 1625 nm for LSPM testing, and at 1310 nm and 1550 nm for OTDR testing.
- End faces are inspected to IEC 61300-3-35 and cleaned using IEC TR 62627-01 before measurement.
- Annex J gives procedures for verifying test cord loss.
OTDR guidance
Informative Annex I covers OTDR set-up and analysis. It includes dynamic range, dynamic margin, pulse width, averaging, dead zone, group index, ghosts and bi-directional trace analysis. The standard lists measurement without a tail cord, and two-cursor measurement, as non-recommended practices. OTDRs are calibrated to IEC 61746-1.
Related standards
| Standard | Relationship |
|---|---|
| IEC 61280-4-1 | Companion standard for multimode attenuation |
| IEC 61300-3-35 | End face inspection, referenced normatively |
| IEC 61746-1 | OTDR calibration for single-mode fibre |
| IEC 61315 | Calibration of fibre-optic power meters |
| ISO/IEC 14763-3 | Testing of optical fibre cabling for ISO/IEC 11801-1 premises cabling |
| ITU-T G.650.3 | Testing of long-distance telecoms links, using these methods |
What it means in practice
- Check the test report names the reference method. The method sets which connections are counted in the loss.
- Check whether reference-grade cords were used and the limit adjusted to match.
- Test at each wavelength the application uses. Longer wavelengths show bend loss more clearly.
- Check whether the specification asks for ORL or reflectance results as well as loss.
- Bi-directional OTDR testing gives more reliable splice and connector loss values.
Related reading: Fibre insertion loss and return loss explained · Fibre optic loss budget: how to calculate insertion loss.