IEC 60793-1-43:2015

Optical fibres - Part 1-43: Measurement methods and test procedures - Numerical aperture measurement

IEC 60793-1-43:2015 establishes uniform requirements for measuring the numerical aperture of optical fibre, thereby assisting in the inspection of fibres and cables for commercial purposes. The numerical aperture (NA) of categories A1, A2, A3 and A4 multimode fibre is an important parameter that describes a fibre's light-gathering ability. It is used to predict launching efficiency, joint loss at splices, and micro/macrobending performance. The numerical aperture is defined by measuring the far-field pattern (NAff). In some cases the theoretical numerical aperture (NAth) is used in the literature, which can be determined from measuring the difference in refractive indexes between the core and cladding. Ideally these two methods should produce the same value. This second edition of IEC 60793-1-43, together with other standards in the IEC 60793-4X series, cancels and replaces the first edition of IEC 60793-1-43, published in 2001, and constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- expansion of the scope to include A1, A2, A3 and A4 multimode fibre categories;
- addition of measurement parameters of sample length and threshold values, product specific to the variables that are now found in the product specifications;
- a new Annex B entitled "Product specific default values for NA measurement";
- addition of a new Technique 4 for measuring NA of A4d fibres;
- a new Annex A entitled "Mapping NA measurement to alternative lengths" that gives a mapping function to correlate shorter sample length measurements to the length suggested in the reference test method Naff. Keywords: numerical aperture of optical fibre, inspection of fibres and cables
This publication is to be read in conjunction with IEC 60793-1-1:2008, IEC 60793-1-21:2001  and IEC 60793-1-22:2001.

Fibres optiques - Partie 1-43: Méthodes de mesure et procédures d'essai - Mesure de l'ouverture numérique

IEC 60793-1-43:2015 établit des exigences uniformes pour mesurer l'ouverture numérique d'une fibre optique, contribuant ainsi au contrôle des fibres et câbles dans des relations commerciales. L'ouverture numérique (NA, numerical aperture) d'une fibre multimodale des catégories A1, A2, A3 et A4 est un paramètre important qui décrit la capacité de la fibre à capter le rayonnement lumineux. Il est utilisé pour prévoir l'efficacité de l'injection, les pertes aux épissures et la tenue aux microcourbures et aux macrocourbures. L'ouverture numérique est définie en mesurant le diagramme en champ lointain (NAff). Dans certains cas, l'ouverture numérique théorique (NAth) est utilisée dans la documentation. Elle peut être déterminée en mesurant la différence entre l'indice de réfraction du cœur et celui de la gaine. Idéalement, il convient que ces deux méthodes donnent la même valeur. Cette deuxième édition annule et remplace la première édition parue en 2001, dont elle constitue une révision technique. La présente édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
– élargissement du domaine d'application pour inclure les catégories A1, A2, A3 et A4 de fibres multimodales;
– ajout de paramètres de mesure de la longueur des échantillons et de valeurs seuils spécifiques aux produits, aux variables actuelles des spécifications de produit;
– une nouvelle Annexe B, "Valeurs par défaut spécifiques à un produit pour la mesure de l'ouverture numérique";
– ajout d'une nouvelle Technique 4, destinée à la mesure de l'ouverture numérique des fibres A4d;
– une nouvelle Annexe A, "Mise en correspondance de mesures d'ouvertures numériques avec des longueurs différentes" qui présente une fonction de mise en correspondance destinée à établir une relation entre des mesures sur des échantillons plus courts et la longueur proposée pour obtenir Naff par la méthode d'essai de référence.
Mots clés: l'ouverture numérique d'une fibre optique, contrôle des fibres et câbles

General Information

• Status: Published
• Publication Date: 26-Mar-2015
• ICS: 33.180.10 - Fibres and cables
• Technical Committee: SC 86A - Fibres and cables
• Drafting Committee: WG 1 - TC 86/SC 86A/WG 1
• Current Stage: PPUB - Publication issued
• Start Date: 27-Mar-2015
• Completion Date: 30-Jun-2015

Relations

• Revises: IEC 60793-1-43:2001 - Optical fibres - Part 1-43: Measurement methods and test procedures - Numerical aperture
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60793-1-43 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
colour
inside
Optical fibres –
Part 1–43: Measurement methods and test procedures– Numerical aperture
measurement
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
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IEC 60793-1-43 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
colour
inside
Optical fibres –
Part 1–43: Measurement methods and test procedures– Numerical aperture

measurement
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.10 ISBN 978-2-8322-2545-5

– 2 – IEC 60793-1-43:2015 © IEC 2015
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Overview of method . 6
4 Reference test method . 7
5 Apparatus . 8
5.1 Input system . 8
5.1.1 Light source . 8
5.1.2 Input optics . 8
5.1.3 Fibre input end support and alignment . 8
5.1.4 Cladding mode stripper . 8
5.2 Output system and detection . 8
5.2.1 General . 8
5.2.2 Technique 1 – Angular scan (see Figure 2) . 9
5.2.3 Technique 2 – Angular scan (see Figure 3) . 10
5.2.4 Technique 3 – Scan of the spatial field pattern (see Figure 4) . 10
5.2.5 Technique 4 – Inverse far-field measurement (see Figure 5, applicable
to subcategory A4d fibres). 12
6 Sampling and specimens . 13
6.1 Specimen length . 13
6.2 Specimen endface . 13
7 Procedure . 13
8 Calculations . 13
8.1 Far-field versus maximum theoretical value . 13
8.2 Threshold intensity angle, θ . 14
k
8.3 Numerical aperture, NA . 14
ff
8.4 Calculating far-field intensity pattern when using Technique 3 . 15
8.5 Calculating NA when using Technique 4 . 15
9 Results . 15
9.1 Information available with each measurement . 15
9.2 Information available upon request . 16
10 Specification information . 16
Annex A (informative) Mapping NA measurement to alternative lengths . 17
A.1 Introductory remark . 17
A.2 Mapping long length NA measurement to short length NA measurement . 17
ff ff
Annex B (normative) Product specific default values for NA measurement . 18
B.1 Introductory remark . 18
B.2 Table of default values used in NA measurement for multimode products . 18

Figure 1 – Representative refractive index profile for a graded index multimode fibre . 7
Figure 2 – Technique 1 – Angular scan . 9
Figure 3 –Technique 2 – Angular scan . 10
Figure 4 – Technique 3 – Scan of the spatial field pattern . 11

Figure 5 – Technique 4 – Inverse far-field method . 13
Figure 6 – Example of a far-field NA measurement . 14
Figure 7 – Sample output of an A4d fibre measured using Technique 4 . 15

Table B.1 – Default values for parameters used in the far-field NA measurement of
multimode fibres . 18

– 4 – IEC 60793-1-43:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1–43: Measurement methods and test procedures–
Numerical aperture 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 60793-1-43 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This second edition cancels and replaces the first edition published in 2001, and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– expansion of the scope to include A1, A2, A3 and A4 multimode fibre categories;
– addition of measurement parameters of sample length and threshold values, product
specific to the variables that are now found in the product specifications;
– a new Annex B entitled "Product specific default values for NA measurement";
– addition of a new Technique 4 for measuring NA of A4d fibres;

– a new Annex A entitled "Mapping NA measurement to alternative lengths" that gives a
mapping function to correlate shorter sample length measurements to the length
suggested in the reference test method Na .
ff
This International Standard is to be used in conjunction with IEC 60793-1-1, IEC 60793-1-21
and IEC 60793-1-22.
The text of this standard is based on the following documents:
CDV Report on voting
86A/1566/CDV 86A/1622/RVC
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 parts in the IEC 60793 series, published under the general title Optical fibres, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.

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.
– 6 – IEC 60793-1-43:2015 © IEC 2015
OPTICAL FIBRES –
Part 1–43: Measurement methods and test procedures–
Numerical aperture measurement

1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the numerical
aperture of optical fibre, thereby assisting in the inspection of fibres and cables for
commercial purposes.
The numerical aperture (NA) of categories A1, A2, A3 and A4 multimode fibre is an important
parameter that describes a fibre's light-gathering ability. It is used to predict launching
efficiency, joint loss at splices, and micro/macrobending performance.
The numerical aperture is defined by measuring the far-field pattern (NA ). In some cases the
ff
theoretical numerical aperture (NA ) is used in the literature, which can be determined from
th
measuring the difference in refractive indexes between the core and cladding. Ideally these
two methods should produce the same value.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60793-1-1, Optical fibres – Part 1-1: Measurement methods and test procedures –
General and guidance
IEC 60793-1-21, Optical fibres – Part 1-21: Measurement methods and test procedures –
Coating geometry
IEC 60793-1-22, Optical fibres – Part 1-22: Measurement methods and test procedures –
Length measurement
IEC 60793-2-10, Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 60793-2-20, Optical fibres – Part 2-20: Product specifications – Sectional specification for
category A2 multimode fibres
IEC 60793-2-30, Optical fibres – Part 2-30: Product specifications – Sectional specification for
category A3 multimode fibres
IEC 60793-2-40, Optical fibres – Part 2-40: Product specifications – Sectional specification for
category A4 multimode fibres
3 Overview of method
This test procedure describes a method for measuring the angular radiant intensity (far-field)
distribution from an optical fibre. The numerical aperture of multimode optical fibre can be

calculated from the results of this measurement using Equation (10) for NA in the far-field,
NA , as described in 8.3.
ff
As background the maximum theoretical NA of a multimode fibre is defined as follows:
NA = sin θ (1)
th m
where
NA is the maximum theoretical numerical aperture;
th
θ is the largest incident meridional ray angle that will be guided by the fibre.
m
In terms of the fibre index profile:
2 2
NA = (2)
n − n
th
1 2
where n is the maximum refractive index of the core, and n is the average refractive index of
1 2
the cladding far from the core region. Figure 1 below shows a refractive index profile of a
graded index multimode fibre and indicates n and n .
1 2
n
n
Light guiding core
Cladding Cladding
IEC
Figure 1 – Representative refractive index
profile for a graded index multimode fibre
NA can be determined from a far-field radiation pattern measurement on a short length of
ff
fibre or from a measurement of a fibre's refractive index profile. Using the far-field method,
the intensity pattern, I(θ), of a fibre is acquired, and the NA (numerical aperture in the far-
ff
field) is defined as the sine of the half-angle where the intensity has decreased to a threshold
percentage (k %) of its maximum value. The threshold used depends on the type of
NA
multimode fibre being measured and are given in the detailed product specification for the
fibre being measured.
4 Reference test method
The reference test method (RTM) for measuring numerical aperture is the far-field
measurement defined in this standard.
NOTE The core and cladding indexes can be empirically determined by Method A (refractive near-field
measurement) of IEC 60793-1-20 to approximate the theoretical NA (NA ).
th
– 8 – IEC 60793-1-43:2015 © IEC 2015
5 Apparatus
5.1 Input system
5.1.1 Light source
Use an incoherent light source capable of producing an area of substantially constant
radiance (variations of less than 10 % in intensity) on the endface of the specimen. It shall be
stable in intensity and position over a time interval sufficient to perform the measurement.
Class A fibres' core geometry shall be determined by employing an illuminator at the
op
...

IEC 60793-1-43 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical fibres –
Part 1-43: Measurement methods and test procedures – Numerical aperture
Measurement
Fibres optiques –
Partie 1-43: Méthodes de mesure et procédures d'essai – Mesure de l'ouverture
numérique
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IEC 60793-1-43 ®
Edition 2.0 2015-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical fibres –
Part 1-43: Measurement methods and test procedures – Numerical aperture

Measurement
Fibres optiques –
Partie 1-43: Méthodes de mesure et procédures d'essai – Mesure de l'ouverture

numérique
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.10 ISBN 978-2-8322-7387-6

– 2 – IEC 60793-1-43:2015 © IEC 2015
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Overview of method . 6
4 Reference test method . 7
5 Apparatus . 8
5.1 Input system . 8
5.1.1 Light source . 8
5.1.2 Input optics . 8
5.1.3 Fibre input end support and alignment . 8
5.1.4 Cladding mode stripper . 8
5.2 Output system and detection . 8
5.2.1 General . 8
5.2.2 Technique 1 – Angular scan (see Figure 2) . 9
5.2.3 Technique 2 – Angular scan (see Figure 3) . 10
5.2.4 Technique 3 – Scan of the spatial field pattern (see Figure 4) . 10
5.2.5 Technique 4 – Inverse far-field measurement (see Figure 5, applicable
to subcategory A4d fibres) . 12
6 Sampling and specimens . 13
6.1 Specimen length . 13
6.2 Specimen endface . 13
7 Procedure . 13
8 Calculations . 13
8.1 Far-field versus maximum theoretical value . 13
8.2 Threshold intensity angle, θ . 14
k
8.3 Numerical aperture, NA . 14
ff
8.4 Calculating far-field intensity pattern when using Technique 3 . 15
8.5 Calculating NA when using Technique 4 . 15
9 Results . 15
9.1 Information available with each measurement . 15
9.2 Information available upon request . 16
10 Specification information . 16
Annex A (informative) Mapping NA measurement to alternative lengths . 17
A.1 Introductory remark . 17
A.2 Mapping long length NA measurement to short length NA measurement . 17
ff ff
Annex B (normative) Product specific default values for NA measurement . 18
B.1 Introductory remark . 18
B.2 Table of default values used in NA measurement for multimode products . 18

Figure 1 – Representative refractive index profile for a graded index multimode fibre . 7
Figure 2 – Technique 1 – Angular scan . 9
Figure 3 –Technique 2 – Angular scan . 10
Figure 4 – Technique 3 – Scan of the spatial field pattern . 11

Figure 5 – Technique 4 – Inverse far-field method . 13
Figure 6 – Example of a far-field NA measurement . 14
Figure 7 – Sample output of an A4d fibre measured using Technique 4 . 15

Table B.1 – Default values for parameters used in the far-field NA measurement of
multimode fibres . 18

– 4 – IEC 60793-1-43:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-43: Measurement methods and test procedures–
Numerical aperture 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 60793-1-43 has been prepared by subcommittee 86A: Fibres and
cables, of IEC technical committee 86: Fibre optics.
This bilingual version (2019-09) corresponds to the monolingual English version, published in
2015-03.
This second edition cancels and replaces the first edition published in 2001, and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– expansion of the scope to include A1, A2, A3 and A4 multimode fibre categories;
– addition of measurement parameters of sample length and threshold values, product
specific to the variables that are now found in the product specifications;

– a new Annex B entitled "Product specific default values for NA measurement";
– addition of a new Technique 4 for measuring NA of A4d fibres;
– a new Annex A entitled "Mapping NA measurement to alternative lengths" that gives a
mapping function to correlate shorter sample length measurements to the length
suggested in the reference test method Na .
ff
This International Standard is to be used in conjunction with IEC 60793-1-1, IEC 60793-1-21
and IEC 60793-1-22.
The text of this standard is based on the following documents:
CDV Report on voting
86A/1566/CDV 86A/1622/RVC
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 parts in the IEC 60793 series, published under the general title Optical fibres, can
be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.
– 6 – IEC 60793-1-43:2015 © IEC 2015
OPTICAL FIBRES –
Part 1-43: Measurement methods and test procedures–
Numerical aperture measurement

1 Scope
This part of IEC 60793 establishes uniform requirements for measuring the numerical
aperture of optical fibre, thereby assisting in the inspection of fibres and cables for
commercial purposes.
The numerical aperture (NA) of categories A1, A2, A3 and A4 multimode fibre is an important
parameter that describes a fibre's light-gathering ability. It is used to predict launching
efficiency, joint loss at splices, and micro/macrobending performance.
The numerical aperture is defined by measuring the far-field pattern (NA ). In some cases the
ff
theoretical numerical aperture (NA ) is used in the literature, which can be determined from
th
measuring the difference in refractive indexes between the core and cladding. Ideally these
two methods should produce the same value.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60793-1-1, Optical fibres – Part 1-1: Measurement methods and test procedures –
General and guidance
IEC 60793-1-21, Optical fibres – Part 1-21: Measurement methods and test procedures –
Coating geometry
IEC 60793-1-22, Optical fibres – Part 1-22: Measurement methods and test procedures –
Length measurement
IEC 60793-2-10, Optical fibres – Part 2-10: Product specifications – Sectional specification for
category A1 multimode fibres
IEC 60793-2-20, Optical fibres – Part 2-20: Product specifications – Sectional specification for
category A2 multimode fibres
IEC 60793-2-30, Optical fibres – Part 2-30: Product specifications – Sectional specification for
category A3 multimode fibres
IEC 60793-2-40, Optical fibres – Part 2-40: Product specifications – Sectional specification for
category A4 multimode fibres
3 Overview of method
This test procedure describes a method for measuring the angular radiant intensity (far-field)
distribution from an optical fibre. The numerical aperture of multimode optical fibre can be

calculated from the results of this measurement using Equation (10) for NA in the far-field,
NA , as described in 8.3.
ff
As background the maximum theoretical NA of a multimode fibre is defined as follows:
NA = sin θ (1)
th m
where
NA is the maximum theoretical numerical aperture;
th
θ is the largest incident meridional ray angle that will be guided by the fibre.
m
In terms of the fibre index profile:
2 2
NA = (2)
n − n
th
1 2
where n is the maximum refractive index of the core, and n is the average refractive index of
1 2
the cladding far from the core region. Figure 1 below shows a refractive index profile of a
graded index multimode fibre and indicates n and n .
1 2
n
n
Light guiding core
Cladding Cladding
IEC
Figure 1 – Representative refractive index
profile for a graded index multimode fibre
NA can be determined from a far-field radiation pattern measurement on a short length of
ff
fibre or from a measurement of a fibre's refractive index profile. Using the far-field method,
the intensity pattern, I(θ), of a fibre is acquired, and the NA (numerical aperture in the far-
ff
field) is defined as the sine of the half-angle where the intensity has decreased to a threshold
percentage (k %) of its maximum value. The threshold used depends on the type of
NA
multimode fibre being measured and are given in the detailed product specification for the
fibre being measured.
4 Reference test method
The reference test method (RTM) for measuring numerical aperture is the far-field
measurement defined in this standard.
NOTE The core and cladding indexes can be empirically determined by Method A (refractive near-field
measurement) of IEC 60793-1-20 to approximate the theoretical NA (NA ).
th
– 8 – IEC 60793-1-43:2015 © IEC 2015
5 Apparatus
5.1 Input system
5.1.1 Light source
Use an incoherent light source capable of producing an area of substantially constant
radiance (variations of less than 10 % in intensity) on the endface of the specimen. It shall be
stable in intensity and position over a time interval sufficient to perform the measurement.
Class A fibres' core geometry shall be determined by employing an illuminator at the
operating wavelength of the fibre that satisfies the following spatial and angular requirements.
The power per unit area in the focal plane of the fibre under test shall not vary more
than ±10 % across the core area.
The power per unit solid angle shall not vary more than ±10 % across the core's acceptance
cone.
5.1.2 Input optics
Use a system of optical components to create a substantially constant radiance spot larger in
diameter than the endface of the specimen and with a numerical aperture greater than that of
the specimen. The light source shall be incoherent but with a spectral width < 100 nm, full-
width half-maximum.
The NA is impacted by the measurement wavelength. For this reason, the centre wavelength
ff
is given as part of the detailed product specifications including IEC 60793-2-10,
IEC 60793-2-20, IEC 60793-2-30 and IEC 60793-2-40. Default values for the centre
wavelength are also listed in Annex B. Provide a means of verifying the alignment of the
endface. Optical filters may be used to limit the spectral width of the source.
5.1.3 Fibre input end support and alignment
Provide a means of supporting the input end of the specimen to allow stable and repeatable
positioning without introducing significant fibre deformation. Provide suitable means to align
the input endface with respect to the launch radiation.
5.1.4 Cladding mode stripper
Provide means to remove cladding light from the specimen. Often the fibre coating is
sufficient to perform this function. Otherwise, it will be necessary to use cladding mode
strippers near both ends of the test specimen. Note that some detailed product specifications
require longer specimen lengths to help remove cladding modes as well.
5.2 Output system and detection
5.2.1 General
Four equivalent techniques may be used to detect the angular radiant intensity (far-field)
distribution from the specimen. Techniques 1 and 2 are angular scans of the far-field pattern.
Technique 3 is a scan of the spatial transform of the angular intensity pattern. (A small or
large area scanning detector may be used.) Technique 4 uses an inverse far-field
measurement.
5.2.2 Technique 1 – Angular scan (see Figure 2)
5.2.2.1 Fibre output end support and alignment
Use a means of supporting and aligning the output end of the specimen that allows alignment
of the endface coincident with the axis of rotation of the optical detector and coincident with
the plane of rotation of the optical detector.
For example, a vacuum chuck mounted on X-Y-Z micropositioners, with a microscope fixture
for aligning the fibre end would be suitable. Examples include a goniometer or stepper-motor
driven rotational stage.
Top view
Zero
Clamp Detector
Side view
Specimen
Finished output end
Zero
Pivot
Movable arm
Base
IEC
Figure 2 – Technique 1 – Angular scan
5.2.2.2 Detection system mechanics
Use a suitable means for rotation of the optical detector that allows the detector to scan an
arc sufficient to cover essentially the full radiation cone from the specimen (for example, a
calibrated goniometer). The axis of rotation of the mechanism shall intercept the endface of
the specimen and shall be perpendicular to the specimen axis, and the rotation plane of this
mechanism shall be coincident with specimen axis. Provide means for recording the relative
angular position of the detector with respect to the specimen output axis.
Use a detector that is linear within 5 % over the range of intensity encountered. A pinhole
aperture may be used to restrict the effective size of the detector in order to achieve
increased resolution. The detector or aperture size can be determined according to the
angular resolution that is desired for the apparatus according to Equation (3):
D = 4 R sin(δ) (3)
where
D is the detector aperture diameter, in mm;
δ is the desired angular resolution, in degrees (°);
R is the distance from the specimen output endface to the detector or aperture, in mm;
A is the resolution of ± 0,5° that is typically used. R shall also meet the far-field requirement:

– 10 – IEC 60793-1-43:2015 © IEC 2015
d
R ≥ (4)
λ
where
R is the distance from the sample output endface to the detector or aperture, in mm;
d is the diameter of the emitting region of the specimen, in µm;
λ is the centre wavelength of the optical source, in nm.
5.2.2.3 Recording
The detection angle is recorded directly using this technique.
5.2.3 Technique 2 – Angular scan (see Figure 3)
Use a means of supporting the specimen such that the output endface is coincident with the
axis of rotation of the specimen. This mechanism (e.g. a goniometer or precision rotating
stage) shall rotate sufficiently to allow the full radiation cone in the plane of rotation to sweep
past the fixed detector. That is, the rotation shall be greater than the total angle of the
specimen output radiation.
The detector requirements are the same as Technique 1 and like Technique 1 the angle is
recorded as a direct result of this method. Provide means to record the included angle formed
by the specimen axis and the imaginary line between the detector and the specimen endface.
Top view
Zero
Detector
Clamp
Side view
Specimen
Finished output end
Zero
Pivot
Movable arm
Base
IEC
Figure 3 –Technique 2 – Angular scan
5.2.4 Technique 3 – Scan of the spatial field pattern (see Figure 4)
5.2.4.1 Fibre output end support apparatus
Provide a means of supporting and aligning the specimen output end that allows stable and
repeatable positioning.
Far-field
f
f
θ
Zero
Zero
Lens L
(transform)
Clamp
Detector
scanner
Specimen
(typical)
IEC
Figure 4 – Technique 3 – Scan of the spatial field pattern
5.2.4.2 Far-field transformation and projection
Create a spatial representation of the far-field of the specimen by suitable means (for
example, by using a microscope objective or other well corrected lens to obtain the Fourier
transform of the fibre output near-field pattern).
Scan this pattern or its image using a pinhole aperture so as to enable the far-field intensity to
be recorded. The size of the pinhole aperture shall be less than, or equal to, one-half the
diffraction limit of the system:
1,22 M λ f
d ≤ (5)
2D
where
d is the diameter of the pinhole, in µm;
M is the magnification from the back focal plane of the transforming lens to the scanning
plane;
λ is the spectral wavelength emitted from the fibre, in nm;
f is the focal length of the transform lens, in mm;
D is the fibre core diameter, in mm.
The numerical aperture of the lens, L , should be large enough so as not to limit the
numerical aperture of the fibre specimen.
5.2.4.3 Scanning system
Provide a method of scanning the far-field pattern with respect to the pinhole aperture and
detector.
5.2.4.4 System calibration
Perform a calibration to measure the distance of movement of the scanning system in the
back focal plane of the far-field transforming lens to the emission angle, θ, with respect to the
specimen output end axis as shown in Equation (6). Inputting a set of known angles and
recording the output positions can be used for this purpose.
y
– 12 – IEC 60793-1-43:2015 © IEC 2015
y = f sin θ (6)
where
y is the distance from the central axis to the spatial plane;
f is the focal length of the transform lens, L ;
θ is the angle with respect to the optical axis.
5.2.4.5 Recording system
Provide means to record E(y), the detected intensity as a function of the scan position, y, and
to correct the detected intensity as follows:
I(θ) = E(y) cos θ (7)
where
I(θ) is the angular intensity distribution as detected by angular scan lens;
E(y) is the radiance at distance y from the axis of the spatial pattern;
y is the distance from the axis of the spatial field pattern;
θ is the angle with respect to the axis of the specimen output.
5.2.4.6 Optical detector
For Technique 3, Equation (8) describes the detector aperture and Equation (5) gives the
appropriate detector size:
D = 2 f sin(δ) (8)
where
D is the detector aperture diameter, in µm;
f is the focal length of the transform lens, in mm;
δ is the desired angular resolution, in degrees (°).
5.2.5 Technique 4 – Inverse far-field measurement (see Figure 5, applicable to
subcategory A4d fibres)
Provide suitable means to align the centre of the input endface of the specimen to the incident
spot of collimated light. Scan the angle of the incident light to the specimen, and measure the
output power at each angle. The light source shall be in accordance with that described in
5.1.1 and 5.1.2. The spot size of the light shall be small enough, for example less than or
equal to one-tenth of the specimen in diameter. Maximum launch angle, θ in Figure 5, shall
L
be greater than the estimated maximum propagation angle of the specimen.

Optical powermeter
Rotation stage
Light source
θ
Specimen
θ
L
IEC
Figure 5 – Technique 4 – Inverse far-field method
6 Sampling and specimens
6.1 Specimen length
The NA can be impacted by the specimen length. For this reason, the specimen length is
ff
given as part of the detailed product specifications including IEC 60793-2-10,
IEC 60793-2-20, IEC 60793-2-30 and IEC 60793-2-40. Default values are also listed in
Annex B. Longer specimen lengths than what are practical to measure on a regular basis may
be required for some products. In these cases a mapping function may be used as described
in informative Annex A.
6.2 Specimen endface
Prepare a flat endface, orthogonal to the fibre axis, at the input and output ends of each
specimen. The accuracy of these measurements is affected by a non-perpendicular endface.
End angles less than 2° are recommended.
7 Procedure
The following procedure shall be followed:
• Place the specimen ends in the support devices. The input end shall be approximately at
the centre of the input place of the focused image of the constant radiance spot.
• Set the optical source to the desired wavelength and spectral width.
• Scan the far-field radiation pattern along a diameter and record intensity versus angular
position.
8 Calculations
8.1 Far-field versus maximum theoretical value
The relationship between the far-field numerical aperture and the maximum theoretical
numerical aperture as described in Equation (2) is dependent upon the measurement
wavelength of the far-field and profile measurements. Most far-field measurements are made
at 850 nm, whereas profile measurements are commonly made at 540 nm or 633 nm. For
these wavelengths, the relationship between NA and NA is given by
ff th
NA = β NA (9)
ff th
– 14 – IEC 60793-1-43:2015 © IEC 2015
where
NA is the NA in the far-field;
ff
β = 0,95 when the profile measurement is made at 540 nm, and β = 0,96 when the
measurement is made at 633 nm;
NA is the maximum theoretical NA.
th
Report NA at 850 nm as the fibre numerical aperture. This value may be obtained directly
ff
from a far-field measurement at 850 nm or, using Equation (12), indirectly from a profile
measurement.
8.2 Threshold intensity angle, θ
k
Normalize the scanned pattern to the peak intensity. For measurement Techniques 1, 2 and 3,
note the points on the pattern at which the intensity is k % of the maximum. The value of
NA
k is product specific. For this reason, they are given as part of the detailed product
NA
specifications including IEC 60793-2-10, IEC 60793-2-20, IEC 60793-2-30 and
IEC 60793-2-40. Default values are also listed in Annex B. Record half the angle between
these points as θ .
k
Technique 4, inverse far-field measurement, does not use a specific threshold; instead, a
local minimum in the far-field intensity pattern is used to define the NA.
8.3 Numerical aperture, NA
ff
When the NA measurement is conducted using Techniques 1 and 2, calculate the far-field
numerical aperture using the following equation:
NA = sin θ
ff k (10)
where
NA is the far-field numerical aperture.
ff
Figure 6 gives an example of a far-field scan of an A1a.2 multimode fibre with an NA = 0,20.
ff
The data is normalized so the maximum value of one is in the centre of the scan and the
= 5 % level is shown as a dashed line.
k
NA
Typical far-field data (A1a.2 fibre)
850 nm 100 metres
0,75
0,50
0,25
K = 5 %
–0,3 –0,2 –0,1 0 0,1 0,2 0,3
NA (sin θ)
IEC
Figure 6 – Example of a far-field NA measurement
Arbitrary unit
8.4 Calculating far-field intensity pattern when using Technique 3
When using Technique 3 the distance, y, shall be transformed into the angle θ. This is done
using the following approach:
Find the central y position y in the scan by typical centring techniques (the average of the
50 % points, first moments analysis, etc.). Subtract y from the recorded y positions, yielding
a corrected set of positions, y’. Now calculate the set of θ’s using Equation (11):
θ = arcsin(y’/f) (11)
Finally, compute the far-field intensity pattern using Equation (10).
8.5 Calculating NA when using Technique 4
When using Technique 4, a local minimum in the far-field intensity pattern is used to
determine the numerical aperture. Figure 7 shows a representative data from this
measurement.
Inverse FFP
θ θ
1 2
–40 –30 –20 –10 0 10 20 30 40
Angle (degree)
IEC
Figure 7 – Sample output of an A4d fibre measured using Technique 4
θ and θ are determined by finding the local minimums as shown in Figure 7.
The two angles,
1 2
The NA is then determined using Equation (12) below:
 
θ + θ
1 2
 
NA = sin (12)
ff
 
 
9 Results
9.1 Information available with each measurement
Report the following information with each measurement:
– date and title of measurement;
Intensity (arbritary unit)
– 16 – IEC 60793-1-43:2015 © IEC 2015
– identification of specimen;
– optical source wavelength;
– measurement results obtained from Clause 8.
9.2 Information available upon request
The following information shall be available upon request:
– centre wavelength and spectral width of interference filters, if used;
– detection system technique used in 5.2;
– detection system calibration and angular resolution;
– size and numerical aperture of launch spot;
– technique used to strip cladding modes.
– specimen length(s)
10 Specification information
The detail specification shall specify the following information:
– type of fibre to be measured;
– failure or acceptance criteria;
– formation to be reported;
– any deviations to the procedure that apply;
– specimen length;
– source wavelength;
– threshold (k).
Annex A
(informative)
Mapping NA measurement to alternative lengths
A.1 Introductory remark
The far-field NA can have length dependence. Annex A presents a mapping function that can
be used to relate the reference test method to an alternative test using a different specimen
length.
A.2 Mapping long length NA measurement to short length NA measurement
ff ff
The specimen length specified in the detailed product specification may not be practical for a
production measurement. If a manufacturer can show that the length dependence of the far-
field is reproducible and predictable for a given design they can develop a mapping function
for a short length production measurement to the NA obtained using the
that relates the NA
ff ff
reference test method. A relationship that has been shown to work for some designs is given
in Equations (13) and (14). The NA is measured with a specimen length other than what is
ff,alt
recommended in the detailed product using Equation (13).
NA = sinθ (13)
ff,alt k, NA,alt
Then the alternative NA is mapped to the NA with Equation (14):
NA = NA + f(NA ) (14)
ff ff,alt ff,alt
As an example the NA is measured on a 2 m specimen using k = 5 % using
ff NA,alt
Equation (13). Then using f(NA ) = –0,01 and Equation (14) one can predict the NA for the
ff,alt ff
reference test method.
– 18 – IEC 60793-1-43:2015 © IEC 2015
Annex B
(normative)
Product specific default values for NA measurement
B.1 Introductory remark
Several values from the product specification are needed to complete the far-field numerical
aperture measurement. They include the measurement wavelength (λ ), the threshold value
NA
(k ) and the specimen length (L). These product specifications are all currently being revised
NA
to include this information. Since we cannot be sure that all of the product specifications will
be completed with this essential information this appendix lists default values for these
variables as a function of product type. This is done to allow time for the respective product
specification documents to be revised to incorporate these parameters. Once published in the
product specification the default values in this annex will become informative.
B.2 Table of default values used in NA measurement for multimode products
Table B.1 gives the default values for parameters used in the far-field NA measurement of
multimode fibres.
Table B.1 – Default values for parameters used in the far-field
NA measurement of multimode fibres
Product Detailed product Specimen length Threshold value Measurement
specification  wavelength
L k
λ
NA NA %
NA
Model A1a.1a multimode fibres IEC 60793-2-10 2,0 ± 0,2 m 5 850 ± 10 nm
Model A1a.1b multimode fibres
IEC 60793-2-10 100 m ± 10 5 850 ± 10 nm
(bend insensitive version)
Model A1a.2a multimode fibres IEC 60793-2-10 2,0 m ± 0,2 5 850 ± 10 nm
Model A1a.2b multimode fibres
IEC 60793-2-10 100 ± 10m 5 850 ± 10 nm
(bend insensitive version)
Model A1a.3a multimode fibres IEC 60793-2-10 2,0 m ± 0,2 5 850 ± 10 nm
Model A1a.3b multimode fibres
IEC 60793-2-10 100 ± 10m 5 850 ± 10 nm
(bend insensitive version)
Subcategory A1b multimode fibres
IEC 60793-2-10 2,0 m ± 0,3 5 850 ± 10 nm
Subcategory A1d multimode fibres IEC 60793-2-10 2,0 m ± 0,3 5 850 ± 10 nm
Category A2 multimode fibres IEC 60793-2-20 2,0 m ± 0,2 50 850 ± 10 nm
Category A3 multimode fibres IEC 60793-2-30 50
2,0 m ± 0,2 850 ± 10 nm
Subcategory A4a multimode fibres
IEC 60793-2-40 2,0 m ± 0,2 50 650 ± 10 nm
Subcategory A4b multimode fibres IEC 60793-2-40 2,0 m ± 0,2 50 650 ± 10 nm
Subcategory A4c multimode fibres IEC 60793-2-40 50
2,0 m ± 0,2 650 ± 10 nm
Subcategory A4d multimode fibres
IEC 60793-2-40 2,0 m ± 0,2 50 650 ± 10 nm
Subcategory A4e multimode fibres IEC 60793-2-40 2,0 m ± 0,2 50 650 ± 10 nm
Subcategory A4f multimode fibres IEC 60793-2-40 6,0 m ± 0,6 5 850 ± 10 nm
Subcategory A4g multimode fibres
IEC 60793-2-40 6,0 m ± 0,6 5 850 ± 10 nm
Subcategory A4h multimode fibres IEC 60793-2-40 6,0 m ± 0,6 5 850 ± 10 nm

_____________
– 20 – IEC 60793-1-43:2015 © IEC 2015
SOMMAIRE
SOMMAIRE . 20
AVANT-PROPOS . 22
1 Domaine d'application . 24
2 Références normatives . 24
3 Présentation de la méthode . 24
4 Méthode d'essai de référence . 25
5 Appareillage . 25
Système d'entrée . 25
5.1.1 Source de rayonnement lumineux . 25
5.1.2 Optique d'entrée . 26
5.1.3 Soutien et alignement de l'extrémité d'entrée de la fibre . 26
5.1.4 Extracteur de modes de gaine . 26
Système de sortie et détection . 26
5.2.1 Généralités . 26
5.2.2 Technique 1 – Balayage angulaire (voir Figure 2) . 26
5.2.3 Technique 2 – Balayage angulaire (voir Figure 3) . 28
5.2.4 Technique 3 – Balayage du diagramme en champ spatial (voir Figure 4) . 28
5.2.5 Technique 4 – Mesure en champ lointain inverse (voir Figure 5, applicable
aux fibres de la sous-catégorie A4d) . 30
6 Echantillonnage et spécimens . 31
Longueur des spécimens . 31
Face d'extrémité de spécimen . 31
7 Procédure . 31
8 Calculs . 31
Relation entre valeur théorique maximal
...