Optical fibres - Part 1-49: Measurement methods and test procedures - Differential mode delay

IEC 60793-49:2018 applies only to multimode, graded-index glass-core (category A1) fibres. The test method is commonly used in production and research facilities, but is not easily accomplished in the field. This document describes a method for characterizing the modal structure of a graded-index multimode fibre. This information is useful for assessing the bandwidth performance of a fibre especially when the fibre is intended to support a range of launch conditions, for example, those produced by standardized laser transmitters. This third edition cancels and replaces the second edition published in 2006. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) better alignment with original intent by filling some omissions and therefore improving measurement rigor;
b) the measurement of fibres with smaller differential mode delay (and higher modal bandwidth) such as type A1a.3 fibres of IEC 60793-2-10 that are used in constructing OM4 performance category cables; new requirements on specifying detector amplitude and temporal response, specimen deployment conditions, four-quadrant scanning, and uniformity of radial locations for calculating bandwidth.
Keywords: modal structure of a graded-index multimode fibre, bandwidth performance

Fibres optiques - Partie 1-49: Méthodes de mesure et procédures d'essai - Retard différentiel de mode

IEC 60793-1-49:2018 s'applique uniquement aux fibres multimodales à cœur en verre à gradient d'indice (catégorie A1). Cette méthode d'essai, qui est généralement utilisée dans les installations de production et de recherche, n'est pas facilement réalisée sur le terrain. Le présent document décrit une méthode de caractérisation de la structure modale d'une fibre multimodale à gradient d'indice. Cette information est utile pour évaluer les performances de largeur de bande d'une fibre, en particulier lorsque la fibre est destinée à supporter une plage de conditions d'injection, par exemple celles produites par les émetteurs lasers normalisés. Cette troisième édition annule et remplace la deuxième édition parue en 2006 dont elle constitue une révision technique. La présente édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) un meilleur alignement sur l'objectif initial en remédiant à certaines omissions pour améliorer la rigueur des mesures;
b) la mesure des fibres avec un plus petit retard différentiel de mode (et une plus grande largeur de bande modale) telles que des fibres de type A1a.3 de l'IEC 60793-2-10 utilisées pour construire des câbles de catégorie de performance OM4, de nouvelles exigences sur la spécification de l'amplitude du détecteur et de la réponse temporelle, les conditions de déploiement des spécimens, le balayage des quatre quadrants et l'uniformité des emplacements radiaux pour calculer la largeur de bande.
Mots clés: structure modale d'une fibre multimodale à gradient d'indice, performances de largeur de bande

General Information

Status
Published
Publication Date
14-Aug-2018
Technical Committee
Current Stage
PPUB - Publication issued
Completion Date
15-Aug-2018
Ref Project

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IEC 60793-1-49
Edition 3.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Optical fibres –
Part 1-49: Measurement methods and test procedures – Differential mode delay
Fibres optiques –
Partie 1-49: Méthodes de mesure et procédures d'essai – Retard différentiel de
mode
IEC 60793-1-49:2018-08(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 60793-1-49
Edition 3.0 2018-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Optical fibres –
Part 1-49: Measurement methods and test procedures – Differential mode delay
Fibres optiques –
Partie 1-49: Méthodes de mesure et procédures d'essai – Retard différentiel de
mode
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.10 ISBN 978-2-8322-5954-2

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 60793-1-49:2018 © IEC 2018
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 6

3 Terms and definitions ...................................................................................................... 7

4 Apparatus ........................................................................................................................ 8

4.1 Overview................................................................................................................. 8

4.2 Optical source ......................................................................................................... 9

4.3 Probe fibre ............................................................................................................ 10

4.4 Scanning stage ..................................................................................................... 10

4.5 Probe to test sample coupling ............................................................................... 10

4.6 Cladding mode stripper ......................................................................................... 10

4.7 Detection system .................................................................................................. 10

4.8 Sampler and digitizer ............................................................................................ 11

4.9 Computational equipment ..................................................................................... 11

4.10 System performance ............................................................................................. 11

4.10.1 General ......................................................................................................... 11

4.10.2 Pulse temporal stability .................................................................................. 12

4.10.3 System stability frequency limit (SSFL) ........................................................... 12

5 Sampling and specimens ............................................................................................... 13

5.1 Test sample .......................................................................................................... 13

5.2 Specimen end-faces ............................................................................................. 13

5.3 Specimen length ................................................................................................... 13

5.4 Specimen deployment ........................................................................................... 13

5.5 Specimen positioning ............................................................................................ 13

6 Procedure ...................................................................................................................... 13

6.1 Fibre coupling and system setup ........................................................................... 13

6.2 Determination of centre ......................................................................................... 14

6.3 Measurement of the test sample ........................................................................... 14

6.3.1 Selection of radii and quadrant ...................................................................... 14

6.3.2 Collection of scan data .................................................................................. 14

6.4 Determination of ∆T and ∆T ................................................................. 14

PULSE REF

6.5 Reference test method .......................................................................................... 14

7 Calculations and interpretation of results ....................................................................... 15

7.1 General ................................................................................................................. 15

7.2 Differential mode delay (DMD) .............................................................................. 15

7.2.1 General ......................................................................................................... 15

7.2.2 Deconvolution ................................................................................................ 15

7.2.3 Pulse folding .................................................................................................. 15

7.2.4 Determination of DMD ................................................................................... 16

7.3 Minimum calculated effective modal bandwidth ..................................................... 17

7.3.1 General ......................................................................................................... 17

7.3.2 Time domain pulse computation .................................................................... 17

7.3.3 Calculate the transfer function ....................................................................... 18

7.3.4 Compute the power spectrum ........................................................................ 18

7.3.5 Compute EMB and minEMB ........................................................................ 18

c c

7.4 Length normalization ............................................................................................. 18

---------------------- Page: 4 ----------------------
IEC 60793-1-49:2018 © IEC 2018 – 3 –

8 Documentation .............................................................................................................. 18

8.1 Information to be reported ..................................................................................... 18

8.2 Information available upon request ....................................................................... 19

9 Specification information ............................................................................................... 19

Annex A (normative) Source spectral width limitation ........................................................... 20

A.1 Limiting the effect of chromatic dispersion (CD) on the value of DMD ................... 20

A.1.1 General ......................................................................................................... 20

A.1.2 Limit CD contribution to DMD to be measured ............................................... 20

A.1.3 Limit CD contribution to reference width ........................................................ 20

A.1.4 Adjust ∆T to account for CD contribution ................................................. 21

REF

A.1.5 High-performance DMD fibres and spectral requirements .............................. 21

A.2 Chromatic dispersion in multimode fibres .............................................................. 22

Annex B (informative) Determination of fibre optical centre .................................................. 23

B.1 General ................................................................................................................. 23

B.2 Method ................................................................................................................. 23

Annex C (normative) Detection system modal measurement ................................................ 26

C.1 General ................................................................................................................. 26

C.2 Determination of coupling function ........................................................................ 26

C.2.1 Overview ....................................................................................................... 26

C.2.2 Fibre sample and coupling ............................................................................. 26

C.2.3 Detector response ......................................................................................... 26

C.2.4 Reference response ...................................................................................... 27

C.2.5 Coupling function determination ..................................................................... 28

Annex D (informative) Discussion of measurement details ................................................... 29

D.1 DMD ..................................................................................................................... 29

D.2 EMB calculation ................................................................................................... 30

Annex E (informative) Determining DMD weights for EMB calculation ................................. 33

E.1 Selecting a set of weightings ................................................................................. 33

E.2 Procedure for generating DMD weightings given encircled flux data ...................... 33

Annex F (informative) EMB calculation information ............................................................. 35

F.1 Default DMD weightings for transmitters conforming to IEC 60793-2-10 ................ 35

F.2 Example method to determine if an adjusted bandwidth (BW) metric is

adequate............................................................................................................... 36

Bibliography .......................................................................................................................... 38

Figure 1 – Example apparatus ................................................................................................ 9

Figure B.1 – Typical area data from centring waveforms ....................................................... 24

Figure D.1 – Idealized DMD data .......................................................................................... 29

Table A.1 – Worst-case chromatic dispersion........................................................................ 22

Table C.1 – Theoretical normalized coupling efficiency ......................................................... 27

Table F.1 – DMD weightings ................................................................................................. 35

Table F.2 – DMD weightings ................................................................................................. 36

---------------------- Page: 5 ----------------------
– 4 – IEC 60793-1-49:2018 © IEC 2018
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL FIBRES –
Part 1-49: Measurement methods and test procedures –
Differential mode delay
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

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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

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misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

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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

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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 60793-1-49 has been prepared by subcommittee 86A: Fibres and

cables, of IEC technical committee 86: Fibre optics.

This third edition cancels and replaces the second edition published in 2006. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:

a) better alignment with original intent by filling some omissions and therefore improving

measurement rigor;
---------------------- Page: 6 ----------------------
IEC 60793-1-49:2018 © IEC 2018 – 5 –

b) the measurement of fibres with smaller differential mode delay (and higher modal

bandwidth) such as type A1a.3 fibres of IEC 60793-2-10 [1] that are used in constructing

OM4 performance category cables; new requirements on specifying detector amplitude

and temporal response, specimen deployment conditions, four-quadrant scanning, and

uniformity of radial locations for calculating bandwidth.
The text of this International Standard is based on the following documents:
CDV Report on voting
86A/1812/CDV 86A/1860/RVC

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

This International Standard is to be used in conjunction with IEC 60793-1-1:2017.

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 document will remain unchanged until the

stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to

the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
___________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 7 ----------------------
– 6 – IEC 60793-1-49:2018 © IEC 2018
OPTICAL FIBRES –
Part 1-49: Measurement methods and test procedures –
Differential mode delay
1 Scope

This part of IEC 60793 applies only to multimode, graded-index glass-core (category A1)

fibres. The test method is commonly used in production and research facilities, but is not

easily accomplished in the field.

This document describes a method for characterizing the modal structure of a graded-index

multimode fibre. This information is useful for assessing the bandwidth performance of a fibre

especially when the fibre is intended to support a range of launch conditions, for example,

those produced by standardized laser transmitters.

With this method, the output from a probe fibre that is single-moded at the test wavelength

excites the multimode fibre under test. The probe spot is scanned across the end-face of the

fibre under test at specified radial positions, and a set of response pulses are acquired at

these positions.
Three specifiable parameters can be derived from the collected set of data.

• The first parameter, differential modal delay (DMD), is the difference in optical pulse delay

time between the fastest and slowest mode groups of the fibre under test. DMD

specifications place limits on modal delay over a specified range of probe fibre radial

offset positions. DMD specifications are determined by modeling and experimentation to

correspond to a minimum effective modal bandwidth (EMB) for the expected range of

transmitters used in a link at a given performance level.

• The second specifiable parameter is derived by combining the pulses using sets of

specific radial weights to determine an approximation of a set of pulses from typical

transmitters. Using Fourier transforms, the calculated effective modal bandwidth (EMB ) is

values (minEMB ) is the
determined for each weight set. The minimum of these EMB
c c
specifiable parameter.

• The third specifiable parameter, the computed overfilled launch bandwidth, OMB , is

determined in a manner similar to EMB , but by applying just one weight set to the set of

pulses; this weight set corresponds to the overfilling condition, where all mode groups are

equally excited.

The test's intent is to quantify the effects of interactions of the fibre modal structure and the

source modal characteristics excluding the source's spectral interaction with fibre chromatic

dispersion. Adding the effects of fibre chromatic dispersion and the source spectral

characteristics will reduce the overall transmission bandwidth, but this is a separate

calculation in most transmission models. In this test, the contribution of chromatic dispersion

is controlled by limiting the spectral width of usable test sources. Practical test sources will

have non-zero spectral width and will thus slightly distort the DMD, minEMB and OMB

c c
values. These chromatic dispersion effects are considered in Annex A.

NOTE Comparison between IEC 60793-1-49 and ITU recommendations: ITU-T Recommendation G.650.1 [2]

contains no information on how to measure the DMD of a graded-index multimode fibre.

2 Normative references

The following documents are referred to in the text in such a way that some or all of their

content constitutes requirements of this document. For dated references, only the edition

---------------------- Page: 8 ----------------------
IEC 60793-1-49:2018 © IEC 2018 – 7 –

cited applies. For undated references, the latest edition of the referenced document (including

any amendments) applies.

IEC 60793-1-1:2017, Optical fibres – Part 1-1: Measurement methods and test procedures −

General and guidance

IEC 60793-1-22, Optical fibres – Part 1-22: Measurement methods and test procedures –

Length measurement

IEC 60793-1-41, Optical fibres – Part 1-41: Measurement methods and test procedures –

Bandwidth

IEC 60793-1-45, Optical fibres – Part 1-45: Measurement methods and test procedures –

Mode field diameter

IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements

IEC 60825-2, Safety of laser products – Part 2: Safety of optical fibre communication systems

(OFCS)

IEC 61280-1-4, Fibre optic communication subsystem test procedures – Part 1-4: General

communication subsystems – Light source encircled flux measurement method
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
maximum DMD

maximum DMD occurring between the outer (R ) and inner (R ) limits of radial offset

OUTER INNER
position over which the probe spot is scanned for one or more sets of R and R
OUTER INNER
3.2
minimum EMB
minEMB
minimum EMB among the EMB values calculated from a sequence of DMD weightings
c c

Note 1 to entry: The user of this document may also specify the calculated overfilled modal bandwidth (OMB ).

3.3
differential mode delay
DMD

estimated difference in optical pulse delay time between the fastest and slowest modes

excited for all radial offset positions between and including R and R
INNER OUTER
Note 1 to entry: This note applies to the French language only.
---------------------- Page: 9 ----------------------
– 8 – IEC 60793-1-49:2018 © IEC 2018
3.4
effective modal bandwidth
EMB

bandwidth associated with the transfer function, H(f), of a particular laser/fibre combination

Note 1 to entry: This note applies to the French language only.
3.5
calculated overfilled modal bandwidth
OMB

bandwidth associated with the transfer function, H(f), when the fibre is overfilled

3.6
quadrant

radial section at one of four possible azimuthal angles over which a radial set of pulse data

can be collected

Note 1 to entry: For example, a radial section may be taken from one of the sets x-positive, x-negative, y-positive

or y-negative.
3.7
mode field diameter
MFD

diameter of the mode emanating from the end-face of a single-mode fibre, as determined by

IEC 60793-1-45
Note 1 to entry: This note applies to the French language only.
3.8
reference test method
RTM

test method in which a given characteristic of a specified class of optical fibres or optical

cables (and associated components) is measured strictly according to the definition of this

characteristic, and which gives results that are accurate, reproducible and relatable to

practical use
Note 1 to entry: This note applies to the French language only.
3.9
full width quarter maximum
FWQM
full width at 25 % of maximum amplitude of an optical pulse
Note 1 to entry: This note applies to the French language only.
4 Apparatus
4.1 Overview

The apparatus shall provide a means to inject and detect short-duration pulses of light of a

small spot size launched into known locations of the core of the multimode fibre to be

measured. An example is diagrammed in Figure 1.
---------------------- Page: 10 ----------------------
IEC 60793-1-49:2018 © IEC 2018 – 9 –
Sampler
dig
...

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