IEC 61744:2023

IEC 61744
®

Edition 3.0 2023-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Calibration of fibre optic chromatic dispersion test sets

Étalonnage des ensembles d’essai de la dispersion chromatique fibronique

IEC 61744:2023-04(en-fr)

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IEC 61744

®


Edition 3.0 2023-04




INTERNATIONAL



STANDARD




NORME


INTERNATIONALE











Calibration of fibre optic chromatic dispersion test sets



Étalonnage des ensembles d’essai de la dispersion chromatique fibronique


















INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 33.180.01 ISBN 978-2-8322-6734-9




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

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– 2 – IEC 61744:2023 © IEC 2023
CONTENTS
FOREWORD . 4
0 Introduction . 6
0.1 Chromatic dispersion in optical fibres . 6
0.2 Chromatic dispersion (CD) test sets . 6
0.3 Overview of calibration procedures described in this document . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Calibration . 11
4.1 General . 11
4.2 Preparation for calibration . 12
4.2.1 General advice and organization. 12
4.2.2 Environmental conditions requirements . 12
4.2.3 Measurement equipment requirements . 12
4.2.4 Traceability . 12
4.3 Calibration procedure . 13
5 Wavelength and delay calibration procedure . 13
5.1 Wavelength calibration procedure . 13
5.1.1 General . 13
5.1.2 Discrete sources . 13
5.1.3 Tuneable sources . 14
5.1.4 Uncertainties and reporting . 16
5.2 Delay (dispersion) calibration procedure . 17
5.2.1 General . 17
5.2.2 Equipment and preparation . 17
5.2.3 Calibration procedure . 18
5.2.4 Uncertainties and reporting . 19
6 Calibration using a reference fibre . 19
6.1 General . 19
6.2 Equipment and preparation . 20
6.3 Procedure . 20
6.4 Uncertainties and reporting . 21
7 Documentation . 21
7.1 General . 21
7.2 Calibration certificate contents . 21
Annex A (normative) Mathematical basis for measurement uncertainty calculations . 22
A.1 General . 22
A.2 Deviations . 22
A.3 Uncertainties type A . 22
A.4 Uncertainties type B . 23
A.5 Determining the combined standard uncertainty . 24
A.6 Reporting . 25
Annex B (normative) Calibration uncertainty . 26
B.1 General . 26
B.2 Wavelength and delay calibration uncertainties . 26
B.2.1 Wavelength uncertainties . 26

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IEC 61744:2023 © IEC 2023 – 3 –
B.2.2 Optical delay calibration uncertainty . 26
B.2.3 Effect of dispersion modelling . 26
B.3 Uncertainty of a calibration using a reference fibre . 27
Annex C (informative) Uncertainty at operating conditions . 28
C.1 General . 28
C.2 Fibre related uncertainties . 28
C.2.1 Axial fibre strain. 28
C.2.2 Fibre temperature . 28
C.2.3 Second order modes . 29
–
C.2.4 OH absorption . 29
C.2.5 Total fibre loss . 29
C.2.6 Optical reflections . 29
Annex D (informative) Chromatic dispersion . 30
D.1 Chromatic dispersion in fibres . 30
D.2 Description of chromatic dispersion test sets . 30
D.3 Measurement techniques . 31
D.3.1 General . 31
D.3.2 Pulse delay method . 31
D.3.3 Phase shift method . 32
D.3.4 Differential phase shift method . 32
D.4 Fibre chromatic dispersion specifications . 32
Bibliography . 33

Figure 1 – Example of a traceability chain . 9
Figure 2 – Typical optical delay line artefact for CD test set delay calibration . 17
Figure 3 – Typical differential delay (dispersion) simulator for CD test set calibration . 18
Figure 4 – Reference fibre comparison . 20
Figure A.1 – Deviation and uncertainty type B and how to replace both by an
appropriately larger uncertainty . 23
Figure D.1 – Schematic diagram of a CD test set . 31

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– 4 – IEC 61744:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

CALIBRATION OF FIBRE OPTIC CHROMATIC
DISPERSION TEST SETS

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
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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
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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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
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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.
IEC 61744 has been prepared by IEC technical committee 86: Fibre optics. It is an International
Standard.
This third edition cancels and replaces the second edition published in 2005. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) updated terms and definitions;
b) the use of a reference fibre standard for calibration is now allowed and at the same level as
the other calibration method;
c) Annex B was split into a new Annex B (on calibration uncertainty, still normative) and a new
Annex C (on uncertainty at operating conditions, informative);
d) removed former C.3.4 on interferometric method since this method is no longer supported
in IEC 60793-1-42;
e) removed Annex D and other references in text to calibration compensation to align with
other calibration documents;

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IEC 61744:2023 © IEC 2023 – 5 –
f) removed Annex E and other references in text to use of air wavelength since it is not used
in the fibre domain.
The text of this International Standard is based on the following documents:
Draft Report on voting
86/615/FDIS 86/617/RVD

Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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.

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– 6 – IEC 61744:2023 © IEC 2023
0 Introduction
0.1 Chromatic dispersion in optical fibres
Chromatic dispersion is the variation with optical light wavelength of the light propagation delay
time in a length of fibre. This variation can cause bandwidth limitation in the fibre when used to
transmit communication signals. For a more detailed explanation, refer to Annex D and
IEC 60793-1-42.
0.2 Chromatic dispersion (CD) test sets
CD test sets are used to measure the chromatic dispersion properties of optical fibres and
typically comprise an optical source of known wavelength(s), a fibre light input coupling and
output coupling means, optical detection means, and electronic or optical means of determining
the optical delay or dispersion at the source wavelength. There are several variants each
requiring slightly different calibration techniques. Refer to Annex D for further details.
In general, all CD test sets produce an output of fibre delay or dispersion versus the light
wavelength, typically in graphical form.
In essence, all CD test sets operate with wavelength as a programmed (independent) variable,
usually the abscissa (x-axis) and dispersion or time delay as the ordinate (y-axis) as a measured
(dependent) variable. By their nature, fibre chromatic dispersion measurements require multiple
wavelengths to be programmed. Even in the case of a single dispersion point obtained using
the differential phase shift method, two separate wavelength values are used. It is also typical
to expect a wide range of dispersion values over a range of wavelengths to be measured.
0.3 Overview of calibration procedures described in this document
The requirement to calibrate the CD test set, traceable to known standards, is essential for
quality control in fibre optic production, fibre research and similar activities. This document
describes the detailed procedures used to establish calibration of a CD test set.
Calibration of a CD test set is established by applying known artefacts or standards (themselves
calibrated to reference standards) to the CD test set and measuring its response.
Primarily, the artefacts or standards used are as follows.
a) Wavelength artefact(s) or traceable wavelength measuring instruments used to calibrate the
light source wavelength(s) used by the CD test set. This is to establish the correct excitation
wavelength for the system (the "x-axis").
b) Delay or dispersion artefact(s) used to calibrate the delay or dispersion response of the CD
test set (the "y-axis").
c) Traceable chromatic dispersion reference fibre used to calibrate the CD test set. This
method allows a simultaneous calibration of the whole CD test set, including the
measurement of the delay or dispersion response of the CD test set as a function of
wavelength and also the internal data processing part. A proper selection of the type of
reference fibre is important, especially for an accurate calibration of the zero dipersion
wavelength.
Calibration can only be carried out using these artefacts; the use of a known standard fibre
(reference fibre described in c)) whose chromatic dispersion is known is recommended as the
fibre forms a stable source of known dispersion and may be used as a simple dispersion
artefact.
If it is found that the CD test set measurement results have changed significantly compared to
the user requirements (i.e. the test set has drifted by more than the repeatability), then
adjustment may be carried out depending on the need.
In this document, the reference medium for wavelength and the velocity of light is assumed to
be in vacuum, and hence define the refractive index = 1,000 000 0.

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IEC 61744:2023 © IEC 2023 – 7 –
CALIBRATION OF FIBRE OPTIC CHROMATIC
DISPERSION TEST SETS



1 Scope
This document provides standard procedures for the calibration of optical fibre chromatic
dispersion (CD) test sets.
This document is applicable to all types of CD test sets, with the exception that measurements
on multimode optical fibres are excluded.
The purpose of this document is to define a standard procedure for calibrating optical fibre
chromatic dispersion (CD) test sets. The detailed calibration steps used vary according to the
measurement technique used in the CD test set.
Whilst it is acknowledged that chromatic dispersion also occurs in multimode fibre and this fibre
can be measured on many CD test sets, this document will restrict discussion to single mode
fibre measurements applications only.
The purpose of the procedures outlined in this document is to focus manufacturers and users
of CD test sets toward the reduction of measurement uncertainty in chromatic dispersion
determination in optical fibres under all applicable conditions. The procedures apply to
calibration laboratories and to the manufacturers or users of CD test sets for the purpose of
a) calibrating CD test sets, and
b) evaluating the level of performance of the instrument.
Use of the procedures also allows correct evaluation of CD test set uncertainty, relative and
traceable to appropriate (for example, national) standards.
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 cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050-731, International Electrotechnical Vocabulary (IEV) – Chapter 731: Optical fibre
communication, available at www.electropedia.org
IEC 62129-1, Calibration of wavelength/optical frequency measurement instruments – Part 1:
Optical spectrum analyzers
IEC 62129-2, Calibration of wavelength/optical frequency measurement instruments – Part 2:
Michelson interferometer single wavelength meters
ISO/IEC Guide 98-3, Uncertainty of measurement – Guide to the expression of uncertainty in
measurement (GUM:1995)

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– 8 – IEC 61744:2023 © IEC 2023
3 Terms and definitions
For the purposes of this document, the terms and definitions contained in IEC 60050-731 and
the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
accredited calibration laboratory
calibration laboratory authorized by the appropriate national standards laboratory to issue
calibration certificates with a minimum specified uncertainty that demonstrate traceability to
national standards
3.2
adjustment
set of operations carried out on an instrument in order that it provides given indications
corresponding to given values of the measurand
3.3
artefact
device, instrument, or equipment used in the process of calibrating a CD test set for wavelength,
delay, or chromatic dispersion
3.4
calibration
set of operations that establish, under specified conditions, the relationship between the values
of quantities indicated by a measuring instrument and the corresponding values realized by
measurement standards
Note 1 to entry: The result of a calibration permits either the assignment of values of measurands to the indications
or the determination of corrections with respect to indications.
Note 2 to entry: A calibration may also determine other metrological properties such as the effect of influence
quantities.
Note 3 to entry: The result of a calibration may be recorded in a document, sometimes called a calibration certificate
or a calibration report.
Note 4 to entry: See also ISO/IEC Guide 99:2007, 2.39.
3.5
traceability chain
unbroken chain of comparison using standards
Note 1 to entry: See Figure 1.

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IEC 61744:2023 © IEC 2023 – 9 –

Figure 1 – Example of a traceability chain
3.6
centroidal wavelength
power-weighted mean wavelength of a light source in vacuum
Note 1 to entry: For a continuous source spectrum, the centroidal wavelength λ in vacuum is defined by the
c
following integral, where the integration limits enclose the entire spectrum of the source. However, it is usually
sufficient to perform the integral or summation over the spectrum where the spectral density p(λ) or power P is higher
i
than 0,1 % of the maximum spectral density p(λ) or power P :
i
λ = (1/ P ) × [ p(λ) × λ dλ]
(1)
c total
∫

where
P = p(λ) d is the total optical source power.
total
∫
For a spectrum consisting of i discrete lines, the centroidal wavelength in vacuum λ is defined as:
c

λ = (1/ P ) × pλ
(2)
c total ∑ i i

i

where
p(λ) is the spectral power spectral density of the source in W/nm;
λ is the centroidal wavelength in vacuum in nanometers;
c
th
λ is the i discrete line in nm;
i
p is the power levels at λ in W;
i i
=
P p is the total power in W.
total ∑ i
i

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– 10 – IEC 61744:2023 © IEC 2023
3.7
chromatic dispersion (CD) test sets
instrument capable of measuring the chromatic dispersion of a single mode fibre at various
wavelengths in the transmission windows of interest
Note 1 to entry: Windows o
...