EN 61744:2005

SLOVENSKI STANDARD
01-marec-2006
1DGRPHãþD
SIST EN 61744:2004
8PHUMDQMHSULERUD]DSUHVNXãDQMHNURPDWLþQHGLVSHU]LMH,(&
Calibration of fibre optic chromatic dispersion test sets
Kalibrierung von Prüfaufbauten zur Bestimmung der chromatischen Dispersion
Etalonnage des ensembles d'essai de la dispersion chromatique des fibres optiques
Ta slovenski standard je istoveten z: EN 61744:2005
ICS:
33.140 Posebna merilna oprema za Special measuring
uporabo v telekomunikacijah equipment for use in
telecommunications
33.180.01 6LVWHPL]RSWLþQLPLYODNQLQD Fibre optic systems in
VSORãQR general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 61744
NORME EUROPÉENNE
EUROPÄISCHE NORM December 2005

ICS 33.180.01 Supersedes EN 61744:2001

English version
Calibration of fibre optic chromatic dispersion test sets
(IEC 61744:2005)
Etalonnage des ensembles d'essai  Kalibrierung von Prüfaufbauten
de la dispersion chromatique zur Bestimmung der chromatischen
des fibres optiques Dispersion
(CEI 61744:2005) (IEC 61744:2005)

This European Standard was approved by CENELEC on 2005-09-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61744:2005 E
Foreword
The text of document 86/236/FDIS, future edition 2 of IEC 61744, prepared by IEC TC 86, Fibre
optics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61744 on 2005-09-01.
This European Standard supersedes EN 61744:2001.
The principal change is the addition of reference to wavelength in vacuum. This reference is critical for
accurate production, measurement and sale of products in the emerging market applications of fibre
optics such as dense wavelength division multiplexing (DWDM) systems.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2006-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2008-09-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61744:2005 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 61315 NOTE Harmonized as EN 61315:1997 (not modified).
IEC 61746 NOTE Harmonized as EN 61746:2005 (not modified).
IEC 60793-1-1 NOTE Harmonized as EN 60793-1-1:2003 (not modified).
ISO 9000 NOTE Harmonized in the EN ISO 9000 series (not modified).
ISO 10012 NOTE Harmonized as EN ISO 10012 (not modified).
__________
- 3 - EN 61744:2005
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
1)
IEC 60050-731 - International Electrotechnical Vocabulary - -
(IEV)
Chapter 731: Optical fibre communication

1) 2)
IEC 60825-1 - Safety of laser products EN 60825-1 1994
Part 1: Equipment classification, + corr. February 1995
requirements and user's guide
3)
IEC 62129 - Calibration of optical spectrum analyzers- -

ISO 9000 Series Quality management and quality EN ISO 9000 Series
assurance standards
BIPM/IEC/IFCC/ 1995 Guide to the Expression of Uncertainty in - -
ISO/IUPAC/ Measurement (GUM)
IUPAP/OIML
1) 2)
ISO/IEC 17025 - General requirements for the competence EN ISO/IEC 2005
of testing and calibration laboratories 17025

1)
Undated reference.
2)
Valid edition at date of issue.
3)
At draft stage.
NORME CEI
INTERNATIONALE
IEC
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2005-09
Etalonnage des ensembles d'essai
de la dispersion chromatique
des fibres optiques
Calibration of fibre optic chromatic
dispersion test sets
 IEC 2005 Droits de reproduction réservés  Copyright - all rights reserved
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électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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XA
PRICE CODE
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International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue

61744  IEC:2005 – 3 –
CONTENTS
FOREWORD.7

0 Introduction.11
0.1 Chromatic dispersion in optical fibres.11
0.2 Chromatic dispersion (CD) test sets .11
0.3 Overview of calibration procedures described in this standard .11
1 Scope .15
2 Normative references.15
3 Terms and definitions.17
4 Calibration .29
4.1 Rationale for calibration of CD test sets .29
4.2 Preparation for calibration.33
4.3 Calibration procedure.35
4.4 Calibration checking procedure .37
5 Wavelength calibration procedure .37
5.1 General .37
5.2 Discrete sources.39
5.3 Tunable sources .39
5.4 Uncertainties and reporting .45
6 Delay [dispersion] calibration procedure .45
6.1 General .45
6.2 Equipment and preparation .45
6.3 Calibration procedure.49
6.4 Uncertainties and reporting .51
7 Calibration checking procedure .51
7.1 General .51
7.2 Equipment and preparation .53
7.3 Procedure.53
7.4 Uncertainties and reporting .55
7.5 Generation of infant reference fibre.55
8 Documentation.57
8.1 Specifications, measurement data and uncertainties .57
8.2 Traceability information.59

Annex A (normative) Mathematical basis .61
Annex B (normative) Assessment of operational uncertainties .71
Annex C (informative) Chromatic dispersion .87
Annex D (informative) CD test set calibration compensation .95
Annex E (informative) Vacuum and air wavelength.101

Bibliography .107

61744  IEC:2005 – 5 –
Figure 1 – Typical calibration chain for CD test sets.19
Figure 2 – Typical optical delay line artefact for CD test set delay calibration .47
Figure 3 – Typical differential delay [dispersion] simulator for CD test set calibration.49
Figure 4 – Reference fibre comparison .55
Figure 5 – Generation of a reference fibre .55
Figure A.1 – Deviation and uncertainty type B, and how to replace both by an
appropriately larger uncertainty .65
Figure C.1 – Schematic diagram of a CD test set.89
Figure E.1 – Dispersion and air and vacuum wavelength.103

61744  IEC:2005 – 7 –
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 in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61744 has been prepared by IEC technical committee 86: Fibre
optics.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision. The principal change is the addition of reference to wavelength
in vacuum. This reference is critical for accurate production, measurement and sale of products
in the emerging market applications of fibre optics such as dense wavelength division
multiplexing (DWDM) systems.
The text of this standard is based on the following documents:
FDIS Report on voting
86/236/FDIS 86/240/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.

61744  IEC:2005 – 9 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until the
maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
61744  IEC:2005 – 11 –
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 C and
IEC 60793-1-1.
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 C 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. Thus, wavelength constitutes the ‘x-axis’ and delay or
dispersion the ‘y-axis’.
0.3 Overview of calibration procedures described in this standard
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 standard
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, measuring its response and
adjusting (correcting) the CD test set to achieve results that match the standards used. In this
way the CD test set results will be brought to close agreement with other CD test sets also
calibrated in the manner described in this standard.
Primarily the artefacts or standards used are as follows:
a) wavelength artefact(s) 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’) in
order that the correct delay or dispersion (the ‘y-axis’) be determined subsequently;
b) delay or dispersion artefact(s) used to calibrate the delay or dispersion response of the CD
test set (the ‘y-axis’).
Calibration can only be carried out using these artefacts. After a calibration has been
completed, a calibration period is defined over which the CD test set is deemed to remain
calibrated. At the end of this period, it would be necessary to establish if the CD test set
calibration requires updating (changing); this can be performed using the artefact described
above, or by use of a known standard fibre (reference fibre) whose chromatic dispersion is
known. This is referred to as calibration checking. The fibre forms a stable source of known
dispersion and may be used as a simple dispersion artefact.
If it is found that the calibration has not changed within the required uncertainty limits, then it is
possible to simply extend the calibration period again by a defined amount.

61744  IEC:2005 – 13 –
If, however, 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), then calibration using the
artefacts (if not already carried out at this time) should be carried out and the calibration
renewed.
The above rationale ensures that the CD test set calibration is only ever performed using
known standards (artefacts), but that if the CD test set is sufficiently stable over the calibration
period selected, then a simple check of calibration can suffice to ascertain this and to (justify)
allow the extension of the calibration period. The extension can be repeated indefinitely over
many calibration periods, provided the CD test set continues to remain within uncertainty limits
over the entire set of calibration periods.
In order to be considered calibrated and in conformance with this standard, a CD test set must
have its calibration adjusted based on comparison to artefacts for the primary parameters of
wavelength and delay [dispersion]. In all cases, this calibration of primary parameters is
necessary, but may or may not be sufficient, to ensure calibration of the CD test set to the
required uncertainty.
In addition, it may be necessary to also confirm or compensate the calibration state of a CD
test set using a calibrated reference fibre. The CD test set calibration compensation is
explained more fully in Annex D. It should be noted that use of a calibrated reference fibre
alone is not sufficient to ensure calibration of a CD test set.
It should also be noted that if a calibrated CD test set undergoes calibration compensation
using a calibrated reference fibre, the scope and extent of its calibration is limited to the
conditions used at the time of calibration compensation (i.e. wavelength, fibre type, loss
regime, etc.) Care should be exercised that test sets calibrated and compensated in this
manner are used only within the appropriate limits of their calibration extent. The adjustments
required to effect compensation on one set of wavelengths for one fibre type may increase the
uncertainty of measurement of other fibre types with different minimum dispersion wavelengths.
In this document, the reference medium for wavelength and the velocity of light is assumed to
be in normal air. However, since the velocity of light in air (or rather, the refractive index of air)
is dependent on barometric pressure, humidity and temperature, it is sometime advantageous
to reference the velocity of light in vacuum, and hence define the refractive index =1,0000000.
This leads to a slight shift in the wavelength scale of the order of 0,3 nm to 0,4 nm depending
on the wavelength value, between the so-called “wavelength in air” (as assumed in this
document) and the wavelength in vacuum, also called “vacuum wavelength”.
Vacuum wavelength is typically used where very accurate dispersion control is required such
as in long-haul or submarine fiber cable systems. CD test sets for measuring fibers used in
these applications are typically calibrated to vacuum wavelength, e.g. using a wavemeter, or by
mathematical correction of results obtained with an internal air wavelength calibration.
In order that the user be familiar with the conversion from air wavelength and the mathematical
corrections involved, an informative annex, Annex E, is provided.

61744  IEC:2005 – 15 –
CALIBRATION OF FIBRE OPTIC CHROMATIC DISPERSION
TEST SETS
1 Scope
This International Standard provides standard procedures for the calibration of optical fibre
chromatic dispersion (CD) test sets. It also provides procedures to perform calibration checking
on CD test sets whereby an extension to the test set calibration period may be obtained.
This standard is applicable to all types of CD test sets, with the exception that measurements
on multimode optical fibres are excluded.
The purpose of this standard 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 may be measured on many CD test sets, this standard will restrict discussion to single
mode fibre measurements only.
The purpose of the procedures outlined in this standard 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;
b) setting specifications of CD test sets;
c) extending the calibration period of an already calibrated CD test set.
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 referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 60050-731, International Electrotechnical Vocabulary (IEV) – Chapter 731: Optical fibre
communication
IEC 60825-1, Safety of laser products – Part 1: Equipment classification, requirements and
1)
user’s guide
___________
1)
A consolidated edition 1.2 exists (1998) that includes IEC 60825-1 (1993) and its Amendment 1 (1997) and
Amendment 2 (2001).
61744  IEC:2005 – 17 –
2)
IEC 62129, Calibration of optical spectrum analyzers
ISO 9000 (all parts), Quality management and quality assurance standards

BIPM/IEC/IFCC/ISO/IUPAC/IUPAP/OIML:1995, Guide to the Expression of Uncertainty in
Measurement (GUM)
ISO/IEC 17025, General requirements for the competence of testing and calibration
laboratories
3 Terms and definitions
For the purposes of this document, the terms and definitions contained in IEC 60050(731) and
the following definitions apply.
3.1
accredited calibration laboratory
calibration laboratory authorized by the appropriate national standards laboratory to issue
calibration certificates with a minimum specified uncertainty, which demonstrate traceability to
national standards
3.2
adjustment
modifying the hardware or firmware of a CD test set with the intention of making the
measurement result of the CD test set equal to that of a national standard or a similar
calibrated CD test set. This has the effect of correcting all subsequent measurements on that
CD test set
3.3
artefact
device, instrument or equipment used in the process of calibrating a CD test set, for both
wavelength and delay [dispersion]. The artefact is a means of transferring calibration of these
parameters to a CD test set
3.4
calibration
process by which the relationship between the values indicated by the infant CD test set and
known values of the calibration standard is established under specified conditions
NOTE The intention of calibration is to bring all CD test sets into substantial agreement with a suitable national
standards laboratory. This may be performed by first comparing the relevant parameter of a measurement artefact
with that produced by the CD test set, followed by transfer of that result, either by adjustment of the CD test set or
by documentation of a calibration factor(s) in a calibration certificate. The pertaining environmental conditions and
instrument state are usually recorded. Calibration includes estimation of all uncertainties. The use of reference
fibres is for calibration checking only.
3.5
calibration chain
unbroken chain of transfers from a primary standard to the CD test set via reference standards,
intermediate and/or working standards (see Figure 1)
___________
2)
To be published.
61744  IEC:2005 – 19 –
National wavelength
Uncertainty
and delay standard
Uncertainty of
reference
standard
Uncertainty of
Reference wavelength Transfer
transfer
and delay standard uncertainty
standard
Transfer
Uncertainty of
uncertainty
working
standard
Transfer wavelength
and delay standard
Transfer
Uncertainty of
uncertainty
CD test set at
reference
Working wavelength
condition
and delay standard
Total
Transfer
uncertainty of
uncertainty
CD test set
CD test set at
reference conditions
Operational
uncertainty
CD test set at normal
operating conditions
IEC  1329/05
Figure 1 – Typical calibration chain for CD test sets
3.6
calibration checking
process of establishing that a CD test set which has been previously calibrated, but is nearing
the end of its calibration period, remains within specified uncertainty limits. If the CD test set
has drifted outside these limits, then calibration is required. Otherwise, the calibration period
can be extended for a stated period, and calibration checking may be repeated indefinitely if
the CD test set remains stable over successive calibration periods
NOTE Calibration checking is performed using a reference fibre or working standard. Essentially calibration
checking is the first part of the process of calibration, but without the additional process of transfer or adjustment.
3.7
calibration period
interval of confirmation
time period over which a calibration performed in accordance with the procedures in this
standard is deemed to remain within the uncertainty limits set. (i.e. remain valid). The time
allotted will be governed by individual user requirements, CD test set characteristics, past
experience, environmental conditions, etc. and by monitored CD test set measurement result
experience in normal use (see also ISO 10012)

61744  IEC:2005 – 21 –
3.8
calibration standard
artefact that is calibrated against a reference standard and is used to calibrate CD test sets.
The artefact may be a delay [dispersion] or a wavelength standard artefact. Proper use of the
calibration standard ensures traceability. The term includes the national standard, reference
standard, the transfer standard and the working standard in descending order of metrological
uncertainty
3.9
central wavelength
power-weighted mean wavelength of a light source in air, in units of nanometers (nm)
For a continuous source spectrum, the central wavelength λ in air is defined by the following
c
integral, where the integration limits enclose the entire spectrum of the source:
λ = (1/ P ) × [ p(λ) × λ dλ]  (1)
c total
∫
where
P = p(λ) dλ is the total optical source power.
total
∫
For a spectrum consisting of i discrete lines, the centre wavelength in air λ is defined as:
c
 
λ = (1/ P ) ×  p λ   (2)
∑ i i
c total
 
 i 
where
p(λ) is the spectral power density of the source in W/nm;
λ is the central wavelength in air 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.
i
total ∑
i
3.10
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, typically the 1 310 nm and/or 1 550 nm
wavebands
3.11
combined standard uncertainty
combination of a number of individual standard uncertainties
NOTE The term “accuracy” should be avoided in this context.
All calibration reports and technical data sheets should report the combined standard
uncertainty of the CD test set as an overall expanded uncertainty, U, with the applicable
confidence level, for example 95,5 % or 99,7 %.

61744  IEC:2005 – 23 –
3.12
confidence level
estimation of the probability that the true value of a measured parameter lies in the given range
(the expanded uncertainty)
3.13
correction offset,
CO
number that is added to or subtracted from the measurement result of a CD test set to correct
for a known physical effect or systematic uncertainty
3.14
coverage factor,
k
used to calculate the expanded uncertainty, U, from the standard uncertainty σ (see 3.15)
3.15
expanded uncertainty,
U
(confidence interval)
range of values within which the measurement parameter, at the stated confidence level, can
be expected to lie. It is equal to the coverage factor k times the standard uncertainty σ :
U = k × σ (3)
NOTE When the distribution of uncertainties is assumed to be normal and a large number of measurements are
made, then confidence levels of 68,3 %, 95,5 % and 99,7 % correspond to values of k of 1, 2 and 3, respectively.
The measurement uncertainty of a CD test set should be specified in the form of expanded
uncertainty U.
3.16
infant reference fibre
fibre whose dispersion is measured against a parent reference fibre. The infant reference fibre
would then be intended for calibration checking of a CD test set
3.17
instrument state
complete description of the measurement conditions and state of the CD test set during the
calibration process
NOTE Typical parameters of the instrument state are the wavelength range in use, the data fit model (as
applicable), warm-up time and other instrument settings.
3.18
measurement result
displayed or electrical output of any CD test set, in dispersion D in units of
–1 –1
• ps × nm × km , lambda zero λ in units of nm, or zero dispersion slope S in units of
0 0
–2 –1
• ps × nm × km , after completing all actions suggested by the operating instructions, for
example warm-up.
61744  IEC:2005 – 25 –
3.19
national standard
standard whose measurement is traceable to fundamental properties, such as the speed of
light, which is recognized by an official national decision and used as the basis for fixing the
value, in a country, of all other standards of the quantity concerned
3.20
national standards laboratory
body or laboratory that maintains and operates the national standard
3.21
operating range
all conditions of, for example, the dispersion, temperature and other influencing quantities, over
which the CD test set is designed to perform within the stated expanded uncertainty
3.22
parent reference fibre
reference fibre which is used as the reference for generating an infant reference fibre. The
parent reference fibre may be used for calibration checking of a CD test set
3.23
reference standard
artefact calibrated against a national standard and used to calibrate CD test sets. The artefact
may be a delay [dispersion] or wavelength standard artefact. Proper use of the calibration
standard ensures traceability. The term includes the national standard, reference standard, the
transfer standard and the working standard in descending order of metrological uncertainty
NOTE In this standard, reference standard can also be taken to mean the fibre (infant or parent) which is used as
the reference for calibration checking of a CD test set.
3.24
scaling factor,
SF
ratio of known standard values for a standard artefact to the values indicated by the CD test set
when no correction offsets are applied. The factors can apply to wavelength, delay [dispersion]
calibration, as well as to recorded zero dispersion wavelength, slope and actual dispersion data
values when using a calibrated reference fibre (see Annex D).
3.25
spectral bandwidth
full-width half-maximum (FWHM) spectral width of the source
If the source exhibits a continuous spectrum, then the spectral bandwidth, B, shall be the full-
width-half-maximum (FWHM) of the spectrum.
If the source exhibits a spectrum consisting of i discrete line (for example, a laser diode with a
multiple-longitudinal mode spectrum), then the FWHM spectral bandwidth B shall be the r.m.s.
spectral bandwidth, multiplied by 2,35 (assuming the source has a Gaussian envelope):
2 2 ½
B = 2,35 × [{ ( 1/ P ) × ( p λ )} – λ ] (4)
i
total ∑ i c
i
61744  IEC:2005 – 27 –
where
λ is the central wavelength (see 3.9) of the laser diode, in nm;
c
P = p is the total power, in W;
i
total ∑
i
th
p is the power of i longitudinal mode, in W;
i
th
λ is the wavelength of i longitudinal mode, in nm.
i
3.26
standard uncertainty
standard deviation
uncertainty of a measurement result expressed as a standard deviation σ
NOTE 1 For further information, refer to Annex A, and the Guide to the Expression of Uncertainty in Measurement.
NOTE 2 In order to combine standard uncertainties from different sources (see Annex A) it is important that they
are all stated at the same confidence level, i.e. for normally distributed data, at a confidence level of 68,3 %. This
may be achieved by the use of each respective coverage factor k which is determined with reference to student’s
t-distribution for each individual uncertainty component.
3.27
traceability
ability to demonstrate, for a measurement result or a CD test set, an unbroken calibration chain
originating from a national standard
CD test sets calibrated by the procedures of this standard are traceable. In the sense of this
standard, direct traceability of the measurement result to either a national standards laboratory
or to an accredited calibration laboratory is demonstrated. Such traceability includes the
calibration schedules of all artefacts in the calibration chain and detailed calculations of all
(cumulative) transfer uncertainties in the calibration chain. The use of a reference fibre or
working standard alone to compare/monitor CD test set calibration will not establish or re-
establish traceability, but only extend the duration of the traceability certification (calibration
period) if no change is found.
3.28
transfer
part of the calibration process where, following comparison of the relevant parameter of a
calibrated artefact to that of a CD test set, the artefact result is applied to the CD test set
Transfer may be performed either by adjustment of the CD test set, or by documentation of a
calibration factor in a calibration certificate.
3.29
transfer standard
intermediary artefact, for example a delay [dispersion] or wavelength artefact used to calibrate
new working standards of a corresponding type
3.30
transfer uncertainty
estimate, characterizing the additional uncertainty of a CD test set caused by uncertainties in
the calibration process, at the given confidence level
NOTE These uncertainties may arise from the calibration standards or artefacts as well as from the CD test set.

61744  IEC:2005 – 29 –
3.31
uncertainty type A
type A uncertainty is obtained by statistical analysis of a series of observations, such as when
evaluating certain random effects of measurement
(see Guide to the Expression of Uncertainty in Measurement)
3.32
uncertainty type B
type B uncertainty is obtained by means other than a statistical analysis of a series of
observations, for example an estimation of probable sources of uncertainty, such as when
evaluating systematic effects of measurement
(see Guide to the Expression of Uncertainty in Measurement)
NOTE Other means may include previous measurement data, experience with or general knowledge of the
behavior and properties of relevant materials, artefacts and instruments, manufacturer’s specifications, data
provided in calibration and other certificates, and uncertainties assigned to reference data taken from handbooks.
3.33
uncertainty limits
limits of permissible error (of a measuring instrument)
bounds or extreme values of expanded uncertainty permitted by user requirements, manu-
facturer’s specification, regulatory documentation, etc.
(see ISO 10012)
3.34
working standard
standard which, usually calibrated against a reference standard or transfer standard, is used on
a routine basis to check CD test sets
4 Calibration
This clause summarizes the action of calibrating a chromatic dispersion (CD) test set and
details the recommendations for the environmental requirements of the calibration facility.
4.1 Rationale for calibration of CD test sets
4.1.1 (Full) calibration
There are two fundamental and common aspects of the various chromatic dispersion measure-
ment techniques (refer to Annex C):
a) the use of a series of known (i.e. fixed) or programmable (i.e. variable) source test
wavelengths, injected into the test fibre(s);
b) the electronic or optical measurement of the pulse delay, phase shift, differential phase shift
or interference fringe peak position (according to CD test set type) produced by the test
fibre(s). Fibre dispersion is obtained by appropriate calculations on the measured data.
In essence, all CD test sets operate with wavelength as a programmed (independent) variable,
usually the ordinate (x-axis) and dispersion or time delay as the abscissa (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

61744  IEC:2005 – 31 –
measured. This makes it impossible merely to transfer calibration from one CD test set to
another by exposing them to a single appropriate dispersion source, unless the use of the CD
test set is to be restricted in the range of fibre dispersion values measured (see introduction).
Rather, it is necessary to independently calibrate wavelength and delay [dispersion] response
to establish the minimum possible uncertainty in each.
The process of CD test set calibration shall therefore be broken down into two parts:
a) ensuring that the programmed wavelengths are calibrated;
b) exposing the CD test set, to known delays [dispersions] in order to calibrate the delay
[dispersion] response.
These two separate calibration stages are generally independent but ideally should always be
carried out as unified sequential operations. The detailed procedure is given in 4.3.
In each case, calibration is achieved by exposing the test set to independent transfer standards
or artefacts of wavelength and delay [dispersion]. These standards form the calibration chain
(Figure 1).
4.1.2 Calibration checking
The rationale of 4.1.1 describes (full) calibration. However, typical routine operational
calibration verification (such as may frequently be carried out on CD test sets in use) may be
sufficient to perform calibration checking of CD test sets using a reference fibre as a working
standard.
The distinction between calibration checking and calibration (i.e. adjustment of correction
offsets, etc.) shall be clearly made. While it is sufficient to establish stability of the CD test set
using the reference fibre, this is not a substitute for actual calibration (see introduction). The
use of this fibre is described in Clause 7.
It is not possible to use the reference fibre for full calibration for the following reasons:
a) To correctly evaluate the full wavelength range and fibre lengt
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