IEC 61280-4-1:2009

Fibre-optic communication subsystem test procedures - Part 4-1: Installed cable plant - Multimode attenuation measurement

IEC 61280-4-1:2009 is applicable to the measurement of attenuation of installed fibre-optic cabling using multimode fibre, typically in lengths of up to 2 000 m. This cabling can include multimode fibres, connectors, adapters and splices. In this standard, the fibre types that are addressed include category A1a (50/125 µm) and A1b (62,5/125 µm) multimode fibres, as specified in IEC 60793-2-10. The attenuation measurements of the other multimode categories can be made, using the approaches of this standard, but the source conditions for the other categories have not been defined. The main changes with respect to the previous edition are:
- An additional measurement method based on optical time domain reflectometry (OTDR) is documented, with guidance on best practice in using the OTDR and interpreting OTDR traces.
- The requirement for the sources used to measure multimode fibres is changed from one based on coupled power ratio (CPR) and mandrel requirement to one based on measurements of the near field at the output of the launching test cord.
- Highlighting the importance of, and giving guidance on, good measurement practices including cleaning and inspection of connector end faces.

Procédures d'essai des sous-systèmes de télécommunication à fibres optiques - Partie 4-1: Installations câblées - Mesure de l'affaiblissement en multimodal

La CEI 61280-4-1:2009 s'applique à la mesure de l'affaiblissement d'une installation de câblage en fibre optique utilisant des fibres multimodes, généralement sur des longueurs allant jusqu'à 2 000 m. Cette installation de câblage peut inclure des fibres multimodes, des connecteurs, des raccords et des épissures. Dans la présente norme, les types de fibres abordées comportent les fibres multimodes de catégorie A1a (50/125 µm) et A1b (62,5/125 µm) spécifiées dans la CEI 60793-2-10. Les mesures d'affaiblissement des autres catégories multimodales peuvent être effectuées en utilisant les approches de la présente norme, mais les conditions de source des autres catégories n'ont pas été définies. Les principales modifications portant sur cette précédente édition sont:
- Une méthode de mesure supplémentaire basée sur la réflectométrie optique dans le domaine temporel (OTDR) est rapportée, avec des indications sur les meilleures pratiques d'utilisation de l'OTDR et d'interprétation des tracés de l'OTDR.
- L'exigence concernant les sources utilisées pour mesurer les fibres multimodes passe d'une exigence basée sur le taux de puissance couplée (CPR) et l'exigence relative au mandrin à une exigence basée sur des mesures en champ proche à la sortie du cordon d'essai d'amorce.
- La mise en valeur de l'importance et la fourniture de directives sur de bonnes pratiques de mesure incluant le nettoyage et l'examen des faces d'extrémité des connecteurs.

General Information

• Status: Published
• Publication Date: 09-Jun-2009
• ICS: 33.180.01 - Fibre optic systems in general
• Technical Committee: SC 86C - Fibre optic systems, sensing and active devices
• Drafting Committee: WG 1 - TC 86/SC 86C/WG 1
• Current Stage: DELPUB - Deleted Publication
• Start Date: 22-May-2019
• Completion Date: 26-Oct-2025

Relations

• Revises: IEC 61280-4-1:2003 - Fibre-optic communication subsystem test procedures - Part 4-1: Cable plant and links - Multimode fibre-optic cable plant attenuation measurement
• Effective Date: 05-Sep-2023
• Revised: IEC 61280-4-1:2019 - Fibre-optic communication subsystem test procedures - Part 4-1: Installed cabling plant - Multimode attenuation measurement
• Effective Date: 05-Sep-2023

Overview

IEC 61280-4-1:2009 - Fibre‑optic communication subsystem test procedures - Part 4‑1: Installed cable plant – Multimode attenuation measurement - defines standardized procedures for measuring attenuation of installed multimode fibre cabling (typically up to 2 000 m). The standard covers multimode fibres, connectors, adapters and splices and specifically addresses category A1a (50/125 µm) and A1b (62.5/125 µm) multimode fibres as specified in IEC 60793‑2‑10. It provides both power‑based substitution methods and a newly documented OTDR (optical time domain reflectometry) measurement method, plus guidance on launch conditions, source requirements and good measurement practice.

Key topics and requirements

• Measurement scope: Attenuation of installed multimode cable plants (includes connectors, adapters, splices) for lengths typically up to 2 000 m.
• Fibre types: Explicitly for A1a (50/125 µm) and A1b (62.5/125 µm); other multimode types can be measured using the same approaches but source conditions for these are not defined.
• Measurement methods:
  • LSPM / substitution power‑meter methods (one‑cord, two‑cord, three‑cord reference methods - normative annexes A, B, C).
  • OTDR method (Annex D) - new in this edition with best‑practice guidance on OTDR configuration and interpreting traces.
• Source and launch requirements:
  • Transition from CPR/mandrel‑based requirements to a requirement based on near‑field measurements at the output of the launching test cord (encircled flux concepts are included in Annex E).
  • Test‑cord care, insertion‑loss verification and reference measurements are specified (Annex H).
• Measurement quality:
  • Guidance on measurement uncertainty (informative Annex F) and calibration requirements.
  • Emphasis on connector end‑face cleaning and inspection, and documented procedures for making, calculating and recording measurements.

Applications and users

• Who uses it:
  • Fibre‑optic installers and contractors validating installed multimode cable plants.
  • Test engineers, commissioning and acceptance teams in enterprise, campus and data‑centre environments.
  • Network designers, quality assurance and standards auditors requiring reproducible attenuation measurements.
• Practical uses:
  • Acceptance testing of multimode backbone and horizontal cabling.
  • Troubleshooting and locating high‑loss events using OTDR traces.
  • Verifying test equipment launch conditions and ensuring repeatable, standards‑compliant results.

Related standards

• IEC 60793‑2‑10 (multimode fibre category definitions - A1a, A1b).
• Other parts of the IEC 61280 series (general fibre‑optic subsystem test procedures) are relevant for complementary test methods and practices.

Keywords: IEC 61280‑4‑1:2009, multimode attenuation measurement, installed cable plant, OTDR, encircled flux, multimode fibre, test cords, connector cleaning, measurement uncertainty.

Standards Content (Sample)

IEC 61280-4-1 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
Fibre-optic communication subsystem test procedures –
Part 4-1: Installed cable plant – Multimode attenuation measurement

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form

or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,

please contact the address below or your local IEC member National Committee for further information.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: [e-mail]
Web: www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: [e-mail]
Tel.: [phone]
Fax: [phone]
IEC 61280-4-1 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
Fibre-optic communication subsystem test procedures –
Part 4-1: Installed cable plant – Multimode attenuation measurement

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 33.180.01 ISBN 978-2-88910-478-9
– 2 – 61280-4-1 © IEC:2009(E)
CONTENTS
FOREWORD.5

1 Scope.7

2 Normative references .7

3 Terms, definitions, graphical symbols and acronyms .8

3.1 Terms and definitions .8

3.2 Graphical symbols.9

3.3 Acronyms .11

4 Measurement methods .11
4.1 General .11
4.2 Cabling configurations and applicable test methods .12
4.3 Overview of uncertainties .12
4.3.1 General .12
4.3.2 Test cords .13
4.3.3 Launch conditions at the connection to the cabling under test .13
4.3.4 Optical source .13
4.3.5 Output power reference .13
4.3.6 Received power reference .14
5 Apparatus.14
5.1 General .14
5.2 Light source .14
5.2.1 Stability .14
5.2.2 Spectral characteristics .14
5.2.3 Launch cord .14
5.3 Receive or tail cord .15
5.4 Substitution/dummy cord .15
5.5 Power meter – LSPM methods only .15
5.6 OTDR apparatus .15
5.7 Connector end-face cleaning and inspection equipment .16
5.8 Adapters .16
6 Procedures.16
6.1 General .16
6.2 Common procedures .17

6.2.1 Care of the test cords .17
6.2.2 Make reference measurements (LSPM methods only) .17
6.2.3 Inspect and clean the ends of the fibres in the cabling.17
6.2.4 Make the measurements.17
6.2.5 Make the calculations .17
6.3 Calibration.17
6.4 Safety .17
7 Calculations .17
8 Documentation .18
8.1 Information for each test.18
8.2 Information to be available .18
Annex A (normative) One-cord reference method.19
Annex B (normative) Three-cord reference method .21

61280-4-1 © IEC:2009(E) – 3 –
Annex C (normative) Two-cord reference method .23

Annex D (normative) Optical time domain reflectometer.26

Annex E (normative) Requirements for the source characteristics for multimode

measurement.32

Annex F (informative) Measurement uncertainty examples.35

Annex G (informative) OTDR configuration information .44

Annex H (informative) Test cord insertion loss verification .53

Bibliography.61

Figure 1a – Socket and plug assembly.10
Figure 1b – Connector set (plug, adapter, plug) .10
Figure 1c – Light source .10
Figure 1d – Power meter.10
Figure 1 – Connector symbols .10
Figure 2 – Symbol for cabling under test.10
Figure 3 – OTDR schematic .16
Figure A.1 − Reference measurement.20
Figure A.2 − Test measurement .20
Figure B.1 − Reference measurement.22
Figure B.2 − Test measurement .22
Figure C.1 − Reference measurement.24
Figure C.2 − Test measurement.24
Figure C.3 – Test measurement for plug-socket style connectors.24
Figure D.1 − Test measurement for Method D.27
Figure D.2 − Location of the cabling under test ports .28
Figure D.3 − Graphic construction of F and F .29
1 2
Figure D.4 − Graphic construction of F , F , F and F .30
1 11 12 2
Figure E.1 – Encircled flux template example.33
Figure F.1 – Initial power measurement .37
Figure F.2 – Verification of reference grade connection .38
Figure F.3 – Two offset splices .38

Figure F.4 – Five offset splices .38
Figure F.5 – EF centred .40
Figure F.6 – EF underfilling.40
Figure F.7 – EF overfilling.41
Figure F.8 – L1 loss with mandrel .41
Figure F.9 – L1 loss with mandrel and mode conditioner.42
Figure F.10 – L2 loss (adjusted) with mandrel.42
Figure F.11 – L2 loss (adjusted) with mandrel and mode conditioning.42
Figure F.12 – L3 loss (adjusted) with mandrel.43
Figure F.13 – L3 loss (adjusted) with mandrel and mode conditioning.43
Figure G.1 − Splice and macro bend attenuation measurement.47
Figure G.2 − Attenuation measurement with high reflection connectors.48

– 4 – 61280-4-1 © IEC:2009(E)
Figure G.3 − Attenuation measurement of a short length cabling.49

Figure G.4 − OTDR trace with ghost .50

Figure G.5 − Cursors positioning.51

Figure H.1 − Obtaining reference power level P .54
Figure H.2 − Obtaining power level P .55
Figure H.3 − Obtaining reference power level P .56
Figure H.4 − Obtaining power level P .56

Figure H.5 − Obtaining reference power level P .57
Figure H.6 − Obtaining power level .57
Figure H.7 − Obtaining reference power level P .58
Figure H.8 − Obtaining power level P .58
Figure H.9 − Obtaining power level P .58
Figure H.10 − Obtaining reference power level P .59
Figure H.11 − Obtaining power level P .59
Table 1 – Cabling configurations.12
Table 2 – Test methods and configurations.12
Table 3 – Spectral requirements .14
Table E.1 – Threshold tolerance .33
Table E.2 – EF requirements for 50 μm core fibre cabling at 850 nm .34
Table E.3 – EF requirements for 50 μm core fibre cabling at 1 300 nm .34
Table E.4 – EF requirements for 62,5 μm core fibre cabling at 850 nm .34
Table E.5 – EF requirements for 62,5 μm core fibre cabling at 1 300 nm.34
Table F.1 – Expected loss for examples (note 1).35
Table G.1 – Default effective group index of refraction values.46

61280-4-1 © IEC:2009(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
FIBRE-OPTIC COMMUNICATION SUBSYSTEM

TEST PROCEDURES –
Part 4-1: Installed cable plant –

Multimode attenuation measurement

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61280-4-1 has been prepared by subcommittee 86C: Fibre optic
systems and active devices, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition, published in 2003, and constitutes
a technical revision.
The main changes with respect to the previous edition are listed below:
– An additional measurement method based on optical time domain reflectometry
(OTDR) is documented, with guidance on best practice in using the OTDR and
interpreting OTDR traces.
– The requirement for the sources used to measure multimode fibres is changed from
one based on coupled power ratio (CPR) and mandrel requirement to one based on
measurements of the near field at the output of the launching test cord.

– 6 – 61280-4-1 © IEC:2009(E)
– Highlighting the importance of, and giving guidance on, good measurement practices

including cleaning and inspection of connector end faces.

The text of this standard is based on the following documents:

FDIS Report on voting
86C/879/FDIS 86C/892/RVD
Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.

This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 61280 series, under the general title Fibre-optic
communication subsystem test procedure, can be found on the IEC website.
For the Part 4, the new subtitle will be Installed cable plant. Subtitles of existing standards in
this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

61280-4-1 © IEC:2009(E) – 7 –
FIBRE-OPTIC COMMUNICATION SUBSYSTEM

TEST PROCEDURES –
Part 4-1: Installed cable plant –

Multimode attenuation measurement

1 Scope
This part of IEC 61280-4 is applicable to the measurement of attenuation of installed fibre-
optic cabling using multimode fibre, typically in lengths of up to 2 000 m. This cabling can
include multimode fibres, connectors, adapters and splices.
Cabling design standards such as ISO/IEC 11801, ISO/IEC 24702 and ISO/IEC 24764 contain
specifications for this type of cabling. ISO/IEC 14763-3, which supports these design
standards, makes reference to the test methods of this standard.
In this standard, the fibre types that are addressed include category A1a (50/125 μm) and A1b
(62,5/125 μm) multimode fibres, as specified in IEC 60793-2-10. The attenuation
measurements of the other multimode categories can be made, using the approaches of this
standard, but the source conditions for the other categories have not been defined.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60825-2, Safety of laser products – Part 2: Safety of optical fibre communication systems
(OFCS)
IEC 61280-1-3, Fibre optic communication subsystem basic test procedures – Part 1-3: Test
procedures for general communication subsystems – Central wavelength and spectral width
measurement
IEC 61280-1-4, Fibre optic communication subsystem test procedures – Part 1-4: General
communication subsystems – Light source encircled flux measurement method

IEC 61300-3-35, Fibre optic interconnecting devices and passive components − Basic test
and measurement procedures − Part 3-35: Examinations and measurements − Fibre optic
cylindrical connector endface visual inspection
IEC 61315, Calibration of fibre-optic power meters
IEC 61745, End-face image analysis procedure for the calibration of optical fibre geometry
test sets
IEC 61746, Calibration of optical time-domain reflectometers (OTDRs)
—————————
A new edition is in preparation.

– 8 – 61280-4-1 © IEC:2009(E)
3 Terms, definitions, graphical symbols and acronyms

For the purposes of this document, the following terms, definitions, graphical symbols and

acronyms apply.
3.1 Terms and definitions
3.1.1
attenuation
reduction of optical power induced by transmission through a medium such as cabling, given

as L (dB)
L = 10 log (P /P )
10 in out
where P and P are the power, typically measured in mW, into and out of the cabling
in out
3.1.2
light source power meter
LSPM
test system consisting of a light source (LS), power meter (PM) and associated test cords
used to measure the attenuation of installed cable plant
3.1.3
optical time domain reflectometer
OTDR
test system consisting of an optical time-domain reflectometer and associated test cords used
to characterize and measure the attenuation of installed cable plant and specific elements
within that cable plant
3.1.4
test cord
terminated optical fibre cord used to connect the optical source or detector to the cabling, or
to provide suitable interfaces to the cabling under test
NOTE There are five types of test cords:
– launch cord: used to connect the light source to the cabling;
– receive cord: used to connect the cabling to the power meter (LSPM only);
– tail cord: attached to the far end of the cabling when an OTDR is used at the near end. This provides a means
of evaluating attenuation of the whole of the cabling including the far end connection;
– adapter cord: used to transition between sockets or other incompatible connectors in a required test
configuration;
– substitution cord: a test cord used within a reference measurement which is replaced during the measurement

of the loss of the cabling under test.
3.1.5
bidirectional measurement
two measurements of the same optical fibre, made by launching light into opposite ends of
that fibre
3.1.6
configuration
form or arrangements of parts or elements such as terminations, connections and splices
3.1.7
encircled flux
EF
fraction of cumulative near field power to total output power as a function of radial distance
from the optical centre of the core

61280-4-1 © IEC:2009(E) – 9 –
[from IEC 61280-1-4]
3.1.8
reference grade termination
connector (3.1.9) plug (3.1.10) with tightened tolerances terminated onto an optical fibre with

tightened tolerances such that the expected loss of a connection formed by mating two such

assemblies is less than or equal to 0,1 dB

EXAMPLE: as an example, the core diameter tolerance may need to be ±0,7 micron (ffs).
Other fibre tolerances are ffs.

NOTE 1 An adapter (3.1.11), required to assure this performance, may be considered to be part of the reference
grade termination where required by the test configuration (3.1.6)
NOTE 2 This definition remains as a point under study. When a more complete definition is available in another
document, this definition will be replaced by a reference.
3.1.9
connector
component normally attached to an optical cable or piece of apparatus, for the purpose of
providing frequent optical interconnection/disconnection of optical fibres or cables
{Definition 2.6.1 of IEC/TR 61931}
3.1.10
plug
male-type part of a connector
[Definition 2.6.2 of IEC/TR 61931]
3.1.11
adapter
female-part of a connector in which one or two plugs are inserted and aligned
[Definition 2.6.4 of IEC/TR 61931:1998]
3.1.12
socket-style connector
connector for which the adapter, including any alignment device, is integrated with, and
permanently attached to the connector plug on one side of the connection
NOTE Examples include the SG and many harsh environment connectors.
3.1.13
reference test method
RTM
test method used in the resolution of a dispute
3.2 Graphical symbols
The following graphic symbols for different connection options have been adapted from
IEC 61930.
– 10 – 61280-4-1 © IEC:2009(E)

a
c
d
IEC  924/09
b
IEC  923/09
Figure 1a – Socket and plug assembly Figure 1b – Connector set (plug, adapter, plug)
PM
P
LS
IEC  926/09
IEC  925/09
Figure 1c – Light source Figure 1d – Power meter
Key
a  socket d  plug inserted into plug-adapter assembly
b  plug LS light source
c plug-adapter assembly PM power meter
Figure 1 – Connector symbols
NOTE 1 In Figure 1b, and elsewhere in this standard, the plugs are shown with different sizes to indicate
directionality where the cabling has adapters pre-attached and the test cord does not, or vice versa. In Figure 1b,
the plug on the left has the adapter pre-attached.
NOTE 2 Reference grade terminations are shown shaded with grey.

IEC  927/09
Figure 2 – Symbol for cabling under test
In the figures that illustrate the measurement configurations in Annexes A through D, the
cabling under test is illustrated by a loop as shown in Figure 2. Although illustrated as just a
loop of fibre, it may contain additional splices and connectors in addition to the terminal
connectors. Note that for purposes of measuring the attenuation of this cabling, the losses
associated with the terminal connectors are considered separately from the cabling itself.

61280-4-1 © IEC:2009(E) – 11 –

NOTE 3 In Figure 2, the cabling is shown with adapters pre-attached and the plugs going into them are

associated with reference grade test cord plugs.

3.3 Acronyms
The following acronyms are used:

EF encircled flux
LSA least squares approximation

LSPM light source power meter
OTDR optical time domain reflectometer

RTM reference test method
4 Measurement methods
4.1 General
Four measurement methods are designated. The four measurement methods use test cords to
interface to the cable plant and are designated as follows:
• one-cord reference method;
• three-cord reference method;
• two-cord reference method;
• optical time domain reflectometer (OTDR) method.
The first three methods use an optical light source and power meter (LSPM) to measure input
and output power levels of the cabling under test to determine the attenuation. The main
functional difference between these methods is the way the input power level, known as the
reference power level, is measured and hence the inclusion or exclusion of the losses
associated with the connections to the cabling under test, and the associated uncertainties of
these connections. The process of measuring the input power level is commonly referred to
as ‘taking the reference power level,’ or ’normalization’.
The use of the term ‘reference’ in the description of the test methods refers to the process of
measuring the input power, not the status of the test.
The one-cord reference method includes the attenuation associated with connections at both
ends of the cabling under test. The three-cord reference method attempts to exclude the
attenuation of the connections of both ends of the cabling under test. The two-cord reference
method normally includes the attenuation associated with one of the connections of the
cabling under test.
NOTE The maximum allowed cabling attenuation specified (e.g. optical power budget or channel insertion loss)
for a transmission system normally excludes the connections made to the transmission equipment. It is therefore
appropriate to use the three cord reference method where the cabling under test is intended to be connected
directly to transmission equipment.
The OTDR method emits short light impulses into the cabling and measures the backscattered
power as a function of propagation time delay or length along the fibre. This also allows the
determination of individual cabling component attenuation values. It does not require a
separate reference measurement to be completed. Requirements for the launch cord and tail
cord are defined in Annex D.
Uncertainties in the specific methods are documented in respective annexes. An overview of
these uncertainties is given in 4.2.
General requirements for apparatus, procedures and calculations common to all methods are
given in the main text of this standard. Requirements that are specific to each particular

– 12 – 61280-4-1 © IEC:2009(E)

method are documented in Annexes A through D. The main text also includes related

procedures such as connector end face cleaning and inspection.

4.2 Cabling configurations and applicable test methods

This standard assumes that the installed cabling takes one of three forms shown in Table 1. If

the cabling is terminated with an adapter, the test cord shall be terminated with a plug and

vice versa.
Table 1 – Cabling configurations

Configuration Description
A Adapters attached to plugs or sockets attached to both ends of the cabling
B Plugs on both ends
C Mixed, where one end of the cabling is terminated with an adapter and the other end is
terminated with a plug
The variations in test method used to measure the cabling are dependent on the cabling
configuration. For example, a common cabling configuration is that of having adapters or
sockets on both ends of the cabling (e.g. within patch panels) awaiting connection to
electronic equipment with an equipment cord. This corresponds to configuration A. In this
case, the one-cord reference method is used to include the losses associated with both end
connectors of the cabling. Another example is a cabling configuration for which equipment
cords are installed on both ends of the cabling and are awaiting connection to electronic
equipment. This corresponds to configuration B. In this case, a three-cord reference method
is used to exclude the loss of the end plug connections.
The configuration A, B or C defines the test methods that should be applied as described in
Table 2. The reference test method offers the best measurement accuracy. Alternative test
methods may be called up in specific circumstances or by other standards but are subject to
reduced measurement accuracy compared with the reference test method. Reference grade
terminations on the test cords as described in 5.2.3, 5.3 and 5.4 shall be used for the
resolution of disputes, unless otherwise agreed.
Table 2 – Test methods and configurations
Configuration RTM Alternative method
a
A Annex A Annex B
B Annex B –
C Annex C Annex B
a
For situations where pinned/unpinned or plug/socket style connectors are
used such as MTRJ, SG or other harsh environment connector but the power
meter does not accept the unpinned or plug connector of the launch cord,
Figure C.3 may be used.
NOTE These configurations, RTMs and annexes are ordered according to the
frequency in which different configurations are typically encountered.

4.3 Overview of uncertainties
4.3.1 General
The uncertainties are affected by the type of fibre, the terminations of the cabling and the
measurement method used. See Annex F for some more detailed considerations.

61280-4-1 © IEC:2009(E) – 13 –

4.3.2 Test cords
A main source of uncertainty involves the connection of the terminated cabling to the test

equipment. The attenuation associated with the test cord connections may be different from

the attenuation present when the cabling is connected to other cords or transmission

equipment. The use of reference grade terminations on the test cords reduces this uncertainty
and improves reproducibility of the measurement, but the allocation of acceptable loss is

changed as listed in Table F.1.

4.3.3 Launch conditions at the connection to the cabling under test

For all methods, an additional source of uncertainty is related to the characteristic of the

optical source at the face of the launch cord. Different regions of the intensity vs. radial
position are attenuated differently, depending on how many connections are found in the
cabling and the radial offsets between fibre cores at these connection points. Usually, the
outer region is attenuated more than the inner region. This is known as differential mode
attenuation.
To obtain measurements that are relevant to the types of sources found in transmission
equipment, a restricted launch, not an overfilled launch, shall be used. The limits on this
restricted launch (see Annex E) are defined to yield attenuation variations of less than ±10 %
of the target attenuation for a number of defined conditions when the core diameter of the
launch cord fibre is equal to the specification mid-range (the nominal value for the fibre
types).
For the OTDR method, the differential mode attenuation occurs not only from the mode
coupling resulting from forward transmission through each connection, but also due to the
mode coupling resulting from the backscattered power through each connection in the reverse
direction. The limits on the near field of the launching cord provide some control on this, but it
is not as well quantified as it is for the LSPM methods. There can also be some additional
differential mode attenuation at the splitter within the OTDR on the path to the detector that is
not subject to an external test. bidirectional testing (see Clause G.6) may reduce this
uncertainty.
4.3.4 Optical source
The following sources of uncertainties are relevant to the attenuation measurements:
• Wavelength of the source – causes fibre attenuation variations between source
wavelength and cabling system transmitter wavelength.
• Spectral width – wider spectral widths cause fibre attenuation variations between the
source wavelength and the cabling system transmitter wavelength, narrower spectral
widths can introduce modal noise.

• Power meter nonlinearity – the linearity error of the power meter.
4.3.5 Output power reference
For methods using LSPM, one of the main sources of uncertainty is the variable coupling
efficiency of the light source to the launch cord due to mechanical tolerances. To minimize
this uncertainty, a reference power reading should be made whenever the connection is
disturbed by stress on the connector or disconnection.
For LSPM methods, a reference measurement shall be made to determine the output power of
the launch cord which will be coupled to the cable or cable plant under test. This
measurement should be made each time the launch cord is attached to the source, as this
coupling may be slightly different each time it is done.

– 14 – 61280-4-1 © IEC:2009(E)

4.3.6 Received power reference

If the power meter has a detector large enough to capture all the incident light then the

coupling of the receive cord to the power meter is minimal and shall be discounted. In other

circumstances (which may include the use of pigtailed detectors), the uncertainty introduced

shall be included in the overall measurement uncertainty.

5 Apparatus
5.1 General
Apparatus requirements that are specific to particular methods are found in Annexes A to D.
Some of the requirements common to the apparatus of LSPM methods are included in this
clause.
5.2 Light source
5.2.1 Stability
The light source is defined at the output of the launch cord. This is achieved by transmitting
the output of a suitable radiation source, such as laser or light emitting diode into the
launching cord. The source shall be stable in position, wavelength and power over the
duration of the entire measurement procedure.
5.2.2 Spectral characteristics
The spectral width of the light source shall meet the requirements of Table 3 when measured
in accordance with IEC 61280-1-3.
Table 3 – Spectral requirements
Centroidal wavelength Spectral width range, full width at
nm half maximum
nm
a
30 to 60
850 ± 30
a
1 280 – 1 350 100 to 140
a
The minimum of the spectral width range applies to LSPM methods only.

5.2.3 Launch cord
The optical fibre within the launch cord at the connection to the cabling under test shall be of

the same type, in terms of core diameter and numerical aperture, but not necessarily
bandwidth, as the optical fibre within the cabling under test. Except for the OTDR method, the
launch cord shall be 1 m to 5 m in length. See Annex D for the length of the OTDR launch
cord.
The requirements on the near field profile coming from the launch cord that are found in
Annex E shall be met. The required launch conditions can be achieved by including
appropriate equipment inside the light source, or by applying mode controlling or conditioning
devices on or in series with the launch cord.
The connector or adapter terminating the launch cord shall be compatible with the cabling and
should be of reference grade to minimize the uncertainty of measurement results.

61280-4-1 © IEC:2009(E) – 15 –

5.3 Receive or tail cord
The optical fibre within the receive or tail cord shall be of the same type, nominal core

diameter and nominal numerical aperture as the optical fibre within the cabling under test.

The connector or adapter terminating the launch cord shall be compatible with the cabling and

should be of reference grade to minimize the uncertainty of measurement results.

The termination of a receive cord at the connection to the power meter shall be compatible

with that of the power meter.
Where unidirectional testing is carried out, the remote end of the tail cord used for OTDR
testing has no requirement for a reference grade termination. Where bi-directional testing is
carried out, the tail cord becomes the launch cord (See Annex I) and shall comply with 5.2.3.
5.4 Substitution/dummy cord
The optical fibre within the substitution/dummy cord shall be of the same category, nominal
core diameter and nominal numerical aperture as the optical fibre within the cabling under
test.
The connector or adapter terminating the launch cord shall be compatible with the cabling and
should be of reference grade to minimize the uncertainty of measurement results.
5.5 Power meter – LSPM methods only
The power meter shall be capable of measuring the range of power normally associated with
the cabling, including considerations on the power launched into the cabling. The power meter
shall meet the calibration requirements of IEC 61315. The meter shall have a detecting
surface of sufficient size to capture all the power coming from the fibre that is put into it. If a
pigtail is used, the pigtail fibre shall be sufficiently large to capture all the power coming from
the test cord.
5.6 OTDR apparatus
Figure 3 is a schematic of the OTDR apparatus shown with a simple attachment point.
Annex D has some more detailed requirements for the length of the launch cord and other
aspects related to the OTDR measurement. The other requirements of 5.1 apply.
For high precision and repeatable measurements, it is recommended, but not mandatory, to
use, either before or after the splitter, a speckle scrambler functionally equivalent to the fibre
shaker described in 61280-1-4 in order to minimize the effects of coherence modal noise.

– 16 – 61280-4-1 © IEC:2009(E)

SPSP
PGPG LDLD
OSOS
SSSS
FCFC
CDCD
ACAC APDAPD
SSSS
IEC  928/09
Key
PG pulse generator
LD laser diode
OS optical splitter
SS speckle scrambler (optional)
FC front panel connector
APD avalanche photo diode
AC amplifier and converter
SP signal processor
CD control and display
Figure 3 – OTDR schematic
5.7 Connector end-face cleaning and inspection equipment
Cleaning equipment (including apparatus, materials, and substances) and the methods to be
used shall be suitable for the connectors to be cleaned. Connector suppliers’ instructions
shall be consulted where doubt exists as to the suitability of particular equipment and
cleaning methods.
A microscope compatible with IEC 61300-3-35, low resolution method, is required to verify
that the fibre and connector end faces of the test cords are clean and free of damage.
Microscopes with adapto
...

IEC 61280-4-1 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre-optic communication subsystem test procedures –
Part 4-1: Installed cable plant – Multimode attenuation measurement

Procédures d'essai des sous-systèmes de télécommunication
à fibres optiques –
Partie 4-1: Installations câblées – Mesure de l'affaiblissement en multimodal

All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by

any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or

IEC's member National Committee in the country of the requester.
If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication,
please contact the address below or your local IEC member National Committee for further information.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.

Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette

publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: [e-mail]
Web: www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: [e-mail]
Tel.: [phone]
Fax: [phone]
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: [e-mail]
Tél.: [phone]
Fax: [phone]
IEC 61280-4-1 ®
Edition 2.0 2009-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre-optic communication subsystem test procedures –
Part 4-1: Installed cable plant – Multimode attenuation measurement

Procédures d'essai des sous-systèmes de télécommunication
à fibres optiques –
Partie 4-1: Installations câblées – Mesure de l'affaiblissement en multimodal

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XB
CODE PRIX
ICS 33.180.01 ISBN 978-2-88912-046-8
– 2 – 61280-4-1 © IEC:2009
CONTENTS
FOREWORD.5

1 Scope.7

2 Normative references .7

3 Terms, definitions, graphical symbols and acronyms .8

3.1 Terms and definitions .8

3.2 Graphical symbols.9

3.3 Acronyms .11

4 Measurement methods .11
4.1 General .11
4.2 Cabling configurations and applicable test methods .12
4.3 Overview of uncertainties .12
4.3.1 General .12
4.3.2 Test cords .13
4.3.3 Launch conditions at the connection to the cabling under test .13
4.3.4 Optical source .13
4.3.5 Output power reference .13
4.3.6 Received power reference .14
5 Apparatus.14
5.1 General .14
5.2 Light source .14
5.2.1 Stability .14
5.2.2 Spectral characteristics .14
5.2.3 Launch cord .14
5.3 Receive or tail cord .15
5.4 Substitution/dummy cord .15
5.5 Power meter – LSPM methods only .15
5.6 OTDR apparatus .15
5.7 Connector end-face cleaning and inspection equipment .16
5.8 Adapters .16
6 Procedures.16
6.1 General .16
6.2 Common procedures .17

6.2.1 Care of the test cords .17
6.2.2 Make reference measurements (LSPM methods only) .17
6.2.3 Inspect and clean the ends of the fibres in the cabling.17
6.2.4 Make the measurements.17
6.2.5 Make the calculations .17
6.3 Calibration.17
6.4 Safety .17
7 Calculations .17
8 Documentation .18
8.1 Information for each test.18
8.2 Information to be available .18
Annex A (normative) One-cord reference method.19
Annex B (normative) Three-cord reference method .21

61280-4-1 © IEC:2009 – 3 –
Annex C (normative) Two-cord reference method .23

Annex D (normative) Optical time domain reflectometer.26

Annex E (normative) Requirements for the source characteristics for multimode

measurement .32

Annex F (informative) Measurement uncertainty examples.35

Annex G (informative) OTDR configuration information .44

Annex H (informative) Test cord insertion loss verification .53

Bibliography.61

Figure 1a – Socket and plug assembly.10
Figure 1b – Connector set (plug, adapter, plug) .10
Figure 1c – Light source .10
Figure 1d – Power meter.10
Figure 1 – Connector symbols .10
Figure 2 – Symbol for cabling under test.10
Figure 3 – OTDR schematic .16
Figure A.1 − Reference measurement.20
Figure A.2 − Test measurement .20
Figure B.1 − Reference measurement.22
Figure B.2 − Test measurement .22
Figure C.1 − Reference measurement.24
Figure C.2 − Test measurement.24
Figure C.3 – Test measurement for plug-socket style connectors.24
Figure D.1 − Test measurement for Method D.27
Figure D.2 − Location of the cabling under test ports .28
Figure D.3 − Graphic construction of F and F .29
1 2
Figure D.4 − Graphic construction of F , F , F and F .30
1 11 12 2
Figure E.1 – Encircled flux template example.33
Figure F.1 – Initial power measurement .37
Figure F.2 – Verification of reference grade connection .38
Figure F.3 – Two offset splices .38

Figure F.4 – Five offset splices .38
Figure F.5 – EF centred .40
Figure F.6 – EF underfilling.40
Figure F.7 – EF overfilling.41
Figure F.8 – L1 loss with mandrel .41
Figure F.9 – L1 loss with mandrel and mode conditioner.42
Figure F.10 – L2 loss (adjusted) with mandrel.42
Figure F.11 – L2 loss (adjusted) with mandrel and mode conditioning.42
Figure F.12 – L3 loss (adjusted) with mandrel.43
Figure F.13 – L3 loss (adjusted) with mandrel and mode conditioning.43
Figure G.1 − Splice and macro bend attenuation measurement.47
Figure G.2 − Attenuation measurement with high reflection connectors.48

– 4 – 61280-4-1 © IEC:2009
Figure G.3 − Attenuation measurement of a short length cabling.49

Figure G.4 − OTDR trace with ghost .50

Figure G.5 − Cursors positioning.51

Figure H.1 − Obtaining reference power level P .54
Figure H.2 − Obtaining power level P .55
Figure H.3 − Obtaining reference power level P .56
Figure H.4 − Obtaining power level P .56

Figure H.5 − Obtaining reference power level P .57
Figure H.6 − Obtaining power level .57
Figure H.7 − Obtaining reference power level P .58
Figure H.8 − Obtaining power level P .58
Figure H.9 − Obtaining power level P .58
Figure H.10 − Obtaining reference power level P .59
Figure H.11 − Obtaining power level P .59
Table 1 – Cabling configurations.12
Table 2 – Test methods and configurations.12
Table 3 – Spectral requirements .14
Table E.1 – Threshold tolerance .33
Table E.2 – EF requirements for 50 μm core fibre cabling at 850 nm .34
Table E.3 – EF requirements for 50 μm core fibre cabling at 1 300 nm .34
Table E.4 – EF requirements for 62,5 μm core fibre cabling at 850 nm .34
Table E.5 – EF requirements for 62,5 μm core fibre cabling at 1 300 nm.34
Table F.1 – Expected loss for examples (note 1).35
Table G.1 – Default effective group index of refraction values.46

61280-4-1 © IEC:2009 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
FIBRE-OPTIC COMMUNICATION SUBSYSTEM

TEST PROCEDURES –
Part 4-1: Installed cable plant –

Multimode attenuation measurement

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61280-4-1 has been prepared by subcommittee 86C: Fibre optic
systems and active devices, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition, published in 2003, and constitutes
a technical revision.
The main changes with respect to the previous edition are listed below:
– An additional measurement method based on optical time domain reflectometry
(OTDR) is documented, with guidance on best practice in using the OTDR and
interpreting OTDR traces.
– The requirement for the sources used to measure multimode fibres is changed from
one based on coupled power ratio (CPR) and mandrel requirement to one based on
measurements of the near field at the output of the launching test cord.

– 6 – 61280-4-1 © IEC:2009
– Highlighting the importance of, and giving guidance on, good measurement practices

including cleaning and inspection of connector end faces.

This bilingual version (2010-07) replaces the English version.

The text of this standard is based on the following documents:

FDIS Report on voting
86C/879/FDIS 86C/892/RVD
Full information on the voting for the approval of this standard can be found in the report on

voting indicated in the above table.
The French version of this standard has not been voted upon.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 61280 series, under the general title Fibre-optic
communication subsystem test procedure, can be found on the IEC website.
For the Part 4, the new subtitle will be Installed cable plant. Subtitles of existing standards in
this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
61280-4-1 © IEC:2009 – 7 –
FIBRE-OPTIC COMMUNICATION SUBSYSTEM

TEST PROCEDURES –
Part 4-1: Installed cable plant –

Multimode attenuation measurement

1 Scope
This part of IEC 61280-4 is applicable to the measurement of attenuation of installed fibre-
optic cabling using multimode fibre, typically in lengths of up to 2 000 m. This cabling can
include multimode fibres, connectors, adapters and splices.
Cabling design standards such as ISO/IEC 11801, ISO/IEC 24702 and ISO/IEC 24764 contain
specifications for this type of cabling. ISO/IEC 14763-3, which supports these design
standards, makes reference to the test methods of this standard.
In this standard, the fibre types that are addressed include category A1a (50/125 μm) and A1b
(62,5/125 μm) multimode fibres, as specified in IEC 60793-2-10. The attenuation
measurements of the other multimode categories can be made, using the approaches of this
standard, but the source conditions for the other categories have not been defined.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60825-2, Safety of laser products – Part 2: Safety of optical fibre communication systems
(OFCS)
IEC 61280-1-3, Fibre optic communication subsystem basic test procedures – Part 1-3: Test
procedures for general communication subsystems – Central wavelength and spectral width
measurement
IEC 61280-1-4, Fibre optic communication subsystem test procedures – Part 1-4: General
communication subsystems – Light source encircled flux measurement method

IEC 61300-3-35, Fibre optic interconnecting devices and passive components − Basic test
and measurement procedures − Part 3-35: Examinations and measurements − Fibre optic
cylindrical connector endface visual inspection
IEC 61315, Calibration of fibre-optic power meters
IEC 61745, End-face image analysis procedure for the calibration of optical fibre geometry
test sets
IEC 61746, Calibration of optical time-domain reflectometers (OTDRs)

– 8 – 61280-4-1 © IEC:2009
3 Terms, definitions, graphical symbols and acronyms

For the purposes of this document, the following terms, definitions, graphical symbols and

acronyms apply.
3.1 Terms and definitions
3.1.1
attenuation
reduction of optical power induced by transmission through a medium such as cabling, given

as L (dB)
L = 10 log (P /P )
10 in out
where P and P are the power, typically measured in mW, into and out of the cabling
in out
3.1.2
light source power meter
LSPM
test system consisting of a light source (LS), power meter (PM) and associated test cords
used to measure the attenuation of installed cable plant
3.1.3
optical time domain reflectometer
OTDR
test system consisting of an optical time-domain reflectometer and associated test cords used
to characterize and measure the attenuation of installed cable plant and specific elements
within that cable plant
3.1.4
test cord
terminated optical fibre cord used to connect the optical source or detector to the cabling, or
to provide suitable interfaces to the cabling under test
NOTE There are five types of test cords:
– launch cord: used to connect the light source to the cabling;
– receive cord: used to connect the cabling to the power meter (LSPM only);
– tail cord: attached to the far end of the cabling when an OTDR is used at the near end. This provides a means
of evaluating attenuation of the whole of the cabling including the far end connection;
– adapter cord: used to transition between sockets or other incompatible connectors in a required test
configuration;
– substitution cord: a test cord used within a reference measurement which is replaced during the measurement

of the loss of the cabling under test.
3.1.5
bidirectional measurement
two measurements of the same optical fibre, made by launching light into opposite ends of
that fibre
3.1.6
configuration
form or arrangements of parts or elements such as terminations, connections and splices
3.1.7
encircled flux
EF
fraction of cumulative near field power to total output power as a function of radial distance
from the optical centre of the core

61280-4-1 © IEC:2009 – 9 –
[from IEC 61280-1-4]
3.1.8
reference grade termination
connector (3.1.9) plug (3.1.10) with tightened tolerances terminated onto an optical fibre with

tightened tolerances such that the expected loss of a connection formed by mating two such

assemblies is less than or equal to 0,1 dB

EXAMPLE: as an example, the core diameter tolerance may need to be ±0,7 micron (ffs).
Other fibre tolerances are ffs.

NOTE 1 An adapter (3.1.11), required to assure this performance, may be considered to be part of the reference
grade termination where required by the test configuration (3.1.6)
NOTE 2 This definition remains as a point under study. When a more complete definition is available in another
document, this definition will be replaced by a reference.
3.1.9
connector
component normally attached to an optical cable or piece of apparatus, for the purpose of
providing frequent optical interconnection/disconnection of optical fibres or cables
[Definition 2.6.1 of IEC/TR 61931]
3.1.10
plug
male-type part of a connector
[Definition 2.6.2 of IEC/TR 61931]
3.1.11
adapter
female-part of a connector in which one or two plugs are inserted and aligned
[Definition 2.6.4 of IEC/TR 61931:1998]
3.1.12
socket-style connector
connector for which the adapter, including any alignment device, is integrated with, and
permanently attached to the connector plug on one side of the connection
NOTE Examples include the SG and many harsh environment connectors.
3.1.13
reference test method
RTM
test method used in the resolution of a dispute
3.2 Graphical symbols
The following graphic symbols for different connection options have been adapted from
IEC 61930.
– 10 – 61280-4-1 © IEC:2009
a
c
d
IEC  924/09
b
IEC  923/09
Figure 1a – Socket and plug assembly Figure 1b – Connector set (plug, adapter, plug)
PM
P
LS
IEC  926/09
IEC  925/09
Figure 1c – Light source Figure 1d – Power meter
Key
a  socket d  plug inserted into plug-adapter assembly
b  plug LS light source
c plug-adapter assembly PM power meter
Figure 1 – Connector symbols
NOTE 1 In Figure 1b, and elsewhere in this standard, the plugs are shown with different sizes to indicate
directionality where the cabling has adapters pre-attached and the test cord does not, or vice versa. In Figure 1b,
the plug on the left has the adapter pre-attached.
NOTE 2 Reference grade terminations are shown shaded with grey.

IEC  927/09
Figure 2 – Symbol for cabling under test
In the figures that illustrate the measurement configurations in Annexes A through D, the
cabling under test is illustrated by a loop as shown in Figure 2. Although illustrated as just a
loop of fibre, it may contain additional splices and connectors in addition to the terminal
connectors. Note that for purposes of measuring the attenuation of this cabling, the losses
associated with the terminal connectors are considered separately from the cabling itself.

61280-4-1 © IEC:2009 – 11 –
NOTE 3 In Figure 2, the cabling is shown with adapters pre-attached and the plugs going into them are

associated with reference grade test cord plugs.

3.3 Acronyms
The following acronyms are used:

EF encircled flux
LSA least squares approximation

LSPM light source power meter
OTDR optical time domain reflectometer

RTM reference test method
4 Measurement methods
4.1 General
Four measurement methods are designated. The four measurement methods use test cords to
interface to the cable plant and are designated as follows:
• one-cord reference method;
• three-cord reference method;
• two-cord reference method;
• optical time domain reflectometer (OTDR) method.
The first three methods use an optical light source and power meter (LSPM) to measure input
and output power levels of the cabling under test to determine the attenuation. The main
functional difference between these methods is the way the input power level, known as the
reference power level, is measured and hence the inclusion or exclusion of the losses
associated with the connections to the cabling under test, and the associated uncertainties of
these connections. The process of measuring the input power level is commonly referred to
as ‘taking the reference power level,’ or ’normalization’.
The use of the term ‘reference’ in the description of the test methods refers to the process of
measuring the input power, not the status of the test.
The one-cord reference method includes the attenuation associated with connections at both
ends of the cabling under test. The three-cord reference method attempts to exclude the
attenuation of the connections of both ends of the cabling under test. The two-cord reference
method normally includes the attenuation associated with one of the connections of the
cabling under test.
NOTE The maximum allowed cabling attenuation specified (e.g. optical power budget or channel insertion loss)
for a transmission system normally excludes the connections made to the transmission equipment. It is therefore
appropriate to use the three cord reference method where the cabling under test is intended to be connected
directly to transmission equipment.
The OTDR method emits short light impulses into the cabling and measures the backscattered
power as a function of propagation time delay or length along the fibre. This also allows the
determination of individual cabling component attenuation values. It does not require a
separate reference measurement to be completed. Requirements for the launch cord and tail
cord are defined in Annex D.
Uncertainties in the specific methods are documented in respective annexes. An overview of
these uncertainties is given in 4.2.
General requirements for apparatus, procedures and calculations common to all methods are
given in the main text of this standard. Requirements that are specific to each particular

– 12 – 61280-4-1 © IEC:2009
method are documented in Annexes A through D. The main text also includes related

procedures such as connector end face cleaning and inspection.

4.2 Cabling configurations and applicable test methods

This standard assumes that the installed cabling takes one of three forms shown in Table 1. If

the cabling is terminated with an adapter, the test cord shall be terminated with a plug and

vice versa.
Table 1 – Cabling configurations

Configuration Description
A Adapters attached to plugs or sockets attached to both ends of the cabling
B Plugs on both ends
C Mixed, where one end of the cabling is terminated with an adapter and the other end is
terminated with a plug
The variations in test method used to measure the cabling are dependent on the cabling
configuration. For example, a common cabling configuration is that of having adapters or
sockets on both ends of the cabling (e.g. within patch panels) awaiting connection to
electronic equipment with an equipment cord. This corresponds to configuration A. In this
case, the one-cord reference method is used to include the losses associated with both end
connectors of the cabling. Another example is a cabling configuration for which equipment
cords are installed on both ends of the cabling and are awaiting connection to electronic
equipment. This corresponds to configuration B. In this case, a three-cord reference method
is used to exclude the loss of the end plug connections.
The configuration A, B or C defines the test methods that should be applied as described in
Table 2. The reference test method offers the best measurement accuracy. Alternative test
methods may be called up in specific circumstances or by other standards but are subject to
reduced measurement accuracy compared with the reference test method. Reference grade
terminations on the test cords as described in 5.2.3, 5.3 and 5.4 shall be used for the
resolution of disputes, unless otherwise agreed.
Table 2 – Test methods and configurations
Configuration RTM Alternative method
a
A Annex A Annex B
B Annex B –
C Annex C Annex B
a
For situations where pinned/unpinned or plug/socket style connectors are
used such as MTRJ, SG or other harsh environment connector but the power
meter does not accept the unpinned or plug connector of the launch cord,
Figure C.3 may be used.
NOTE These configurations, RTMs and annexes are ordered according to the
frequency in which different configurations are typically encountered.

4.3 Overview of uncertainties
4.3.1 General
The uncertainties are affected by the type of fibre, the terminations of the cabling and the
measurement method used. See Annex F for some more detailed considerations.

61280-4-1 © IEC:2009 – 13 –
4.3.2 Test cords
A main source of uncertainty involves the connection of the terminated cabling to the test

equipment. The attenuation associated with the test cord connections may be different from

the attenuation present when the cabling is connected to other cords or transmission

equipment. The use of reference grade terminations on the test cords reduces this uncertainty
and improves reproducibility of the measurement, but the allocation of acceptable loss is

changed as listed in Table F.1.

4.3.3 Launch conditions at the connection to the cabling under test

For all methods, an additional source of uncertainty is related to the characteristic of the

optical source at the face of the launch cord. Different regions of the intensity vs. radial
position are attenuated differently, depending on how many connections are found in the
cabling and the radial offsets between fibre cores at these connection points. Usually, the
outer region is attenuated more than the inner region. This is known as differential mode
attenuation.
To obtain measurements that are relevant to the types of sources found in transmission
equipment, a restricted launch, not an overfilled launch, shall be used. The limits on this
restricted launch (see Annex E) are defined to yield attenuation variations of less than ±10 %
of the target attenuation for a number of defined conditions when the core diameter of the
launch cord fibre is equal to the specification mid-range (the nominal value for the fibre
types).
For the OTDR method, the differential mode attenuation occurs not only from the mode
coupling resulting from forward transmission through each connection, but also due to the
mode coupling resulting from the backscattered power through each connection in the reverse
direction. The limits on the near field of the launching cord provide some control on this, but it
is not as well quantified as it is for the LSPM methods. There can also be some additional
differential mode attenuation at the splitter within the OTDR on the path to the detector that is
not subject to an external test. bidirectional testing (see Clause G.6) may reduce this
uncertainty.
4.3.4 Optical source
The following sources of uncertainties are relevant to the attenuation measurements:
• Wavelength of the source – causes fibre attenuation variations between source
wavelength and cabling system transmitter wavelength.
• Spectral width – wider spectral widths cause fibre attenuation variations between the
source wavelength and the cabling system transmitter wavelength, narrower spectral
widths can introduce modal noise.

• Power meter nonlinearity – the linearity error of the power meter.
4.3.5 Output power reference
For methods using LSPM, one of the main sources of uncertainty is the variable coupling
efficiency of the light source to the launch cord due to mechanical tolerances. To minimize
this uncertainty, a reference power reading should be made whenever the connection is
disturbed by stress on the connector or disconnection.
For LSPM methods, a reference measurement shall be made to determine the output power of
the launch cord which will be coupled to the cable or cable plant under test. This
measurement should be made each time the launch cord is attached to the source, as this
coupling may be slightly different each time it is done.

– 14 – 61280-4-1 © IEC:2009
4.3.6 Received power reference

If the power meter has a detector large enough to capture all the incident light then the

coupling of the receive cord to the power meter is minimal and shall be discounted. In other

circumstances (which may include the use of pigtailed detectors), the uncertainty introduced

shall be included in the overall measurement uncertainty.

5 Apparatus
5.1 General
Apparatus requirements that are specific to particular methods are found in Annexes A to D.
Some of the requirements common to the apparatus of LSPM methods are included in this
clause.
5.2 Light source
5.2.1 Stability
The light source is defined at the output of the launch cord. This is achieved by transmitting
the output of a suitable radiation source, such as laser or light emitting diode into the
launching cord. The source shall be stable in position, wavelength and power over the
duration of the entire measurement procedure.
5.2.2 Spectral characteristics
The spectral width of the light source shall meet the requirements of Table 3 when measured
in accordance with IEC 61280-1-3.
Table 3 – Spectral requirements
Centroidal wavelength Spectral width range, full width at
nm half maximum
nm
a
30 to 60
850 ± 30
a
1 280 – 1 350 100 to 140
a
The minimum of the spectral width range applies to LSPM methods only.

5.2.3 Launch cord
The optical fibre within the launch cord at the connection to the cabling under test shall be of

the same type, in terms of core diameter and numerical aperture, but not necessarily
bandwidth, as the optical fibre within the cabling under test. Except for the OTDR method, the
launch cord shall be 1 m to 5 m in length. See Annex D, for the length of the OTDR launch
cord.
The requirements on the near field profile coming from the launch cord that are found in
Annex E shall be met. The required launch conditions can be achieved by including
appropriate equipment inside the light source, or by applying mode controlling or conditioning
devices on or in series with the launch cord.
The connector or adapter terminating the launch cord shall be compatible with the cabling and
should be of reference grade to minimize the uncertainty of measurement results.

61280-4-1 © IEC:2009 – 15 –
5.3 Receive or tail cord
The optical fibre within the receive or tail cord shall be of the same type, nominal core

diameter and nominal numerical aperture as the optical fibre within the cabling und
...