IEC 61315:2019
(Main)Calibration of fibre-optic power meters
Calibration of fibre-optic power meters
IEC 61315:2019 is applicable to instruments measuring radiant power emitted from sources that are typical for the fibre-optic communications industry. These sources include laser diodes, light emitting diodes (LEDs) and fibre-type sources. Both divergent and collimated radiations are covered. This document defines the calibration of power meters to be performed by calibration laboratories or by power meter manufacturers. This third edition cancels and replaces the second edition published in 2005. It constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
a) update of terms and definitions;
b) update of 5.1, including Table 1 (new type of source);
c) update of Annex A;
d) addition of Annex B on dB conversion.
Keywords: Fibre-optic power meters
Etalonnage de wattmètres pour dispositifs à fibres optiques
L'IEC 61315:2019 s'applique aux appareils qui mesurent la puissance rayonnante émise par des sources typiques pour l'industrie des communications par fibres optiques. Ces sources comprennent les diodes laser, les diodes émettant de la lumière (LED) et les sources fibrées. Le rayonnement divergent ainsi que le rayonnement collimaté sont couverts par le présent document. Ce dernier définit l'étalonnage des wattmètres à effectuer par des laboratoires d'étalonnage ou par des fabricants de wattmètres. Cette troisième édition annule et remplace la deuxième édition parue en 2005. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a) mise à jour des termes et définitions;
b) mise à jour du 5.1, y compris le Tableau 1 (nouveau type de source);
c) mise à jour de l'Annexe A;
d) ajout d'une Annexe B sur la conversion en dB.
Mots-clés : wattmètres pour dispositifs à fibres optiques
General Information
Relations
Standards Content (Sample)
IEC 61315 ®
Edition 3.0 2019-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Calibration of fibre-optic power meters
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.
IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.
IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary
(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and 67 000 electrotechnical terminology entries in English and
once a month by email. French extracted from the Terms and Definitions clause of
IEC publications issued since 2002. Some entries have been
IEC Customer Service Centre - webstore.iec.ch/csc collected from earlier publications of IEC TC 37, 77, 86 and
If you wish to give us your feedback on this publication or CISPR.
need further assistance, please contact the Customer Service
Centre: sales@iec.ch.
IEC 61315 ®
Edition 3.0 2019-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Calibration of fibre-optic power meters
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.140; 33.180.10 ISBN 978-2-8322-6732-5
– 2 – IEC 61315:2019 RLV © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions. 7
4 Preparation for calibration . 16
4.1 Organization. 16
4.2 Traceability . 17
4.3 Advice for measurements and calibrations . 17
4.4 Recommendations to customers users . 18
5 Absolute power calibration . 18
5.1 Calibration methods . 18
5.2 Establishing the calibration conditions . 19
5.3 Calibration procedure . 20
5.4 Calibration uncertainty . 21
5.4.1 General . 21
5.4.2 Uncertainty due to the setup . 22
5.4.3 Uncertainty of the reference meter . 22
5.4.4 Correction factors and uncertainty caused by the change of conditions . 23
5.4.5 Uncertainty due to the test meter spectral bandwidths . 27
5.5 Reporting the results . 28
6 Measurement uncertainty of a calibrated power meter . 28
6.1 Overview . 28
6.2 Uncertainty at reference conditions . 28
6.3 Uncertainty at operating conditions . 29
6.3.1 General . 29
6.3.2 Determination of dependences on conditions . 30
6.3.3 Ageing . 30
6.3.4 Dependence on temperature . 31
6.3.5 Dependence on the power level (nonlinearity). 31
6.3.6 Dependence on the type of fibre or on the beam geometry . 31
6.3.7 Dependence on the connector-adapter combination . 33
6.3.8 Dependence on wavelength . 33
6.3.9 Dependence on spectral bandwidth . 34
6.3.10 Dependence on polarization . 35
6.3.11 Other dependences . 35
7 Nonlinearity calibration . 35
7.1 General . 35
7.2 Nonlinearity calibration based on superposition . 36
7.2.1 General . 36
7.2.2 Procedure . 37
7.2.3 Uncertainties. 38
7.3 Nonlinearity calibration based on comparison with a calibrated power meter . 39
7.3.1 General . 39
7.3.2 Procedure . 39
7.3.3 Uncertainties. 39
7.4 Nonlinearity calibration based on comparison with an attenuator . 40
7.5 Calibration of power meter for high power measurement . 40
Annex A (normative) Mathematical basis for measurement uncertainty calculations . 41
A.1 General . 41
A.2 Type A evaluation of uncertainty . 41
A.3 Type B evaluation of uncertainty . 42
A.4 Determining the combined standard uncertainty . 42
A.5 Reporting . 43
Annex B (informative) Linear to dB scale conversion of uncertainties . 44
B.1 Definition of decibel . 44
B.2 Conversion of relative uncertainties . 44
Bibliography . 45
Figure 1 – Typical spectral responsivity of photoelectric detectors . 14
Figure 2 – Example of a traceability chain . 16
Figure 3 – Measurement setup for sequential, fibre-based calibration . 19
Figure 4 – Change of conditions and uncertainty . 24
Figure 5 – Determining and recording an extension uncertainty . 30
Figure 6 – Possible subdivision of the optical reference plane into 10 × 10 squares, for
the measurement of the spatial response . 31
Figure 7 – Wavelength dependence of response due to Fabry-Perot type interference . 34
Figure 8 – Measurement setup of polarization dependent response . 35
Figure 9 – Nonlinearity calibration based on superposition . 36
Figure 10 – Measurement setup for nonlinearity calibration by comparison . 39
Table 1 – Calibration methods and correspondent typical power . 19
Table 2 – Nonlinearity . 38
– 4 – IEC 61315:2019 RLV © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CALIBRATION OF FIBRE-OPTIC POWER METERS
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.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition. A vertical bar appears in the margin wherever a change
has been made. Additions are in green text, deletions are in strikethrough red text.
International Standard IEC 61315 has been prepared by IEC technical committee 86: Fibre
optics.
This third edition cancels and replaces the second edition published in 2005. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) update of terms and definitions;
b) update of 5.1, including Table 1 (new type of source);
c) update of Annex A;
d) addition of Annex B on dB conversion.
The text of this International Standard is based on the following documents:
CDV Report on voting
86/533/CDV 86/540A/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.
In this document, the following print types are used:
– terms defined in the document: in italic type.
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.
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 61315:2019 RLV © IEC 2019
INTRODUCTION
Fibre-optic power meters are designed to measure optical power from fibre-optic sources as
accurately as possible. This capability depends largely on the quality of the calibration process.
In contrast to other types of measuring equipment, the measurement results of fibre-optic
power meters usually depend on many conditions of measurement. The conditions of
measurement during the calibration process are called calibration conditions. Their precise
description must is therefore be an integral part of the calibration.
This document defines all of the steps involved in the calibration process: establishing the
calibration conditions, carrying out the calibration, calculating the uncertainty, and reporting the
uncertainty, the calibration conditions and the traceability.
The absolute power calibration describes how to determine the ratio between the value of the
input power and the power meter's result. This ratio is called correction factor. The
measurement uncertainty of the correction factor is combined following Annex A from
uncertainty contributions from the reference meter, the test meter, the setup and the
procedure.
The calculations go through detailed characterizations of individual uncertainties. It is important
to know that
a) estimations of the individual uncertainties are acceptable some uncertainties are type B
estimations, experience-based,
b) a detailed uncertainty analysis is usually only necessary done once for each power meter
type under test, and all subsequent calibrations can be are usually based on this one-time
analysis, using the appropriate type A measurement contributions evaluated at the time of
the calibration, and
c) some of the individual uncertainties can are simply be considered to be part of a checklist,
with an actual value which can be neglected.
Calibration according to Clause 5 defines absolute power calibration, which is mandatory for
calibration reports referring to this document.
Clause 6 describes the evaluation of the measurement uncertainty of a calibrated power meter
operated within reference conditions or within operating conditions. It depends on the
calibration uncertainty of the power meter as calculated in 5.4, the conditions and its
dependence on the conditions. It is usually performed by manufacturers in order to establish
specifications and is not mandatory for reports referring to this document. One of these
dependences, the nonlinearity, is determined in a separate calibration (Clause 7).
NOTE Fibre-optic power meters measure and indicate the optical power in the air, at the end of an optical fibre. It
is about 3,6 % lower than in the fibre due to Fresnel reflection at the glass-air boundary (with N = 1,47). This should
be kept in mind when the power in the fibre has to be known.
CALIBRATION OF FIBRE-OPTIC POWER METERS
1 Scope
This document is applicable to instruments measuring radiant power emitted from sources that
are typical for the fibre-optic communications industry. These sources include laser diodes,
light emitting diodes (LEDs) and fibre-type sources. The radiation may be divergent or
collimated. Both divergent and collimated radiations are covered. This document describes
defines the calibration of power meters to be performed by calibration laboratories or by power
meter manufacturers.
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 60050-300, International Electrotechnical Vocabulary – Electrical and electronic
measurements and measuring instruments – Part 311: General terms relating to measurements
– Part 312: General terms relating to electrical measurements – Part 313: Types of electrical
measuring instruments – Part 314: Specific terms according to the type of instrument
IEC 60359, Electrical and electronic measurement equipment – Expression of performance
IEC 60793-2, Optical fibres – Part 2: Product specifications – General
IEC 61300-3-12, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-12: Examinations and measurements – Polarization
dependence of attenuation of a single-mode fibre optic component: Matrix calculation method
IEC 61930, Fibre optic graphical symbology
IEC TR 61931:1998, Fibre optic – Terminology
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
ISO/IEC 17025, General requirements for the competence of testing and calibration
laboratories
BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, and OIML:1993, International vocabulary of basic terms
in metrology (VIM)
BIPM, IEC, IFCC, ISO, IUPAC, IUPAP, and OIML:1995, Guide to the expression of uncertainty
in measurement (GUM)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TR 61931 and the
following apply.
– 8 – IEC 61315:2019 RLV © IEC 2019
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
accredited calibration laboratory
calibration laboratory authorized by the appropriate national organization to issue calibration
certificates with a minimum specified uncertainty, which demonstrate traceability to national
standards (3.14)
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
Note 1 to entry: When the instrument is made to give a null indication corresponding to a null value of the
measurand, the set of operations is called zero adjustment.
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 3.11.
[SOURCE: IEC 60050-311:2001, 311-03-16, modified – The words "of a measuring instrument"
have been deleted from the term, and Note 2 to entry has been added. see also VIM 4.30]
3.3
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.
[VIM, 6.11, modified]
3.4
calibration conditions
conditions of measurement in which the calibration is performed
3.5
centre centroidal wavelength
λ
centre
power-weighted mean wavelength of a light source in vacuum
Note 1 to entry: For a continuous spectrum, the centre centroidal wavelength is defined as:
λ = p(λ) × λ × dλ
centre
∫
P
total
and the total power is:
P = p(λ) × dλ
total
∫
where p(λ) is the power spectral density of the source, for example in W/nm.
For a spectrum consisting of discrete lines, the centre wavelength is defined as:
P × λ
∑ i i
λ =
centre
P
i
∑
where
th
P is the power of the i discrete line, for example in W, and
i
th
λ is the vacuum wavelength of the i discrete line.
i
p λ λdλ
( )
∫
λ =
(1)
c
P
total
For a spectrum consisting of discrete lines, the centroidal wavelength is defined as:
Pλ
∑ ii
i
λ = (2)
c
P
i
∑
i
where
p(λ) is the power spectral density of the source, for example, in W/nm;
th
λ is the vacuum wavelength of the i discrete line;
i
th
P is the power of the i discrete line, for example, in W;
i
P is the total power, for example, in W.
total
Note 2 to entry: The above integrals and summations theoretically extend over the entire spectrum of the light
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 than 0,1 % of the maximum spectral density p(λ) or power P .
i i
3.6
correction factor
CF
numerical factor by which the uncorrected result of a measurement is multiplied to compensate
for systematic error
Note 1 to entry: This note applies to the French language only.
[VIM, 3.16]
3.7
decibel
dB
submultiple of the bel (1 dB = 0,1 B), unit used to express values of power level on a
logarithmic scale. The power level is always relative to a reference power P :
P
L = 10 × log (dB)
P / P 10
P
where P and P are expressed in the same linear units.
The reference power must always be reported, for example, the power level of 200 µW relative
to 1 mW can be noted L = –7 dB or L (re 1 mW) = –7 dB.
P/1 mW P
– 10 – IEC 61315:2019 RLV © IEC 2019
The linear ratio, R , of two radiant powers, P and P , can alternatively be expressed as a
lin 1 2
power level difference in decibels (dB):
∆L = 10 log (R ) = 10 log (P /P ) = 10 log (P ) – 10 log (P ).
P 10 lin 10 1 2 10 1 10 2
Similarly, relative uncertainties, U , or relative deviations, can be alternatively expressed in
lin
decibels:
U = U ≅ 4,34 × U (dB)
dB lin lin
ln10
NOTE ISO 31-2 and IEC 60027-3 should be consulted for further details. The rules of IEC 60027-3 do not permit
attachments to unit symbols. However, the unit symbol dBm is widely used to indicate power levels relative to 1 mW
and often displayed by fibre-optic power meters.
3.7
detector
element of the power meter that transduces the radiant optical power into a measurable,
usually electrical, quantity
Note 1 to entry: In this document, the detector is assumed to be connected with the optical input port by an optical
path.
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 3.9.
[see IEC 61931 and VIM, 4.15]
3.8
deviation
D
for the purpose of this standard, the relative difference between the power measured by the
test meter (3.32) P and the reference power P :
DUT ref
PP−
DUT ref
D = (3)
P
ref
Note 1 to entry: This note applies to the French language only.
3.9
excitation
description of the distribution of optical power between the modes in the fibre
Note 1 to entry: In context with multimode fibres, the fibre excitation is described by
a) the spot diameter (3.31) on the surface of the fibre end, and
b) the numerical aperture (3.17) of the radiation emitted from the fibre.
Full excitation means radiation characterized by a spot diameter which is approximately equal
to the fibre's core diameter, and by a numerical aperture which is approximately equal to the
fibre's numerical aperture.
Single-mode fibres are generally assumed to be excited by only one mode (the fundamental mode).
3.10
instrument state
set of parameters that can be chosen on an instrument
Note 1 to entry: Typical parameters of the instrument state are the optical power range, the wavelength setting,
the display measurement unit and the output from which the measurement result is obtained (for example, display,
interface bus, analogue output).
3.11
irradiance
quotient of the incremental radiant power ∂P incident on an element of the reference plane by
the incremental area ∂A of that element:
∂P
E = W/m (4)
( )
∂A
Note 1 to entry: For more information, see IEC TR 61931:1998, 2.1.15.
3.12
measurement result
y
(displayed or electrical) output of a power meter (or standard), after completing all actions
suggested by the operating instructions, for example warm-up, zeroing zero adjustment and
wavelength-correction
Note 1 to entry: Measurement result is expressed in watts (W). For the purposes of uncertainty analysis,
measurement results in other units, for example volts, should be converted to watts. Measurement results in
decibels (dB) should also be converted to watts, because the entire uncertainty accumulation is based on
measurement results expressed in watts. See Annex B.
3.13
measuring range
set of values of measurands for which the error of a measuring instrument is intended to lie
within specified limits
Note 1 to entry: In this document, the measuring range is the range of radiant power (part of the operating range),
for which the uncertainty at operating conditions is specified. The term "dynamic range" should be avoided in this
context.
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 4.7.
[VIM, 5.4]
3.14
national measurement standard
national standard
standard recognized by a national decision to serve in a country as the basis for assigning
values to other standards of the quantity concerned
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 5.3.
[VIM, 6.3]
3.15
national standards laboratory
laboratory which maintains the national standard (3.14)
3.16
nonlinearity
NL
relative difference between the response (3.28) at a given power P and the response at a
reference power P :
rP
( )
nl −1 (5)
P/P
rP
( )
=
– 12 – IEC 61315:2019 RLV © IEC 2019
If expressed in decibels, the nonlinearity is:
rP
( )
NL 10×log (dB) (6)
P/P 10
rP
( )
Note 1 to entry: The nonlinearity is equal to zero at the reference power.
Note 2 to entry: The term "local nonlinearity" is used for the relative difference between the responses at two
different power levels (separated by 3,01 dB) obtained during the nonlinearity calibration. The term "global
nonlinearity" is used for the result of summing up the local nonlinearities (in dB); it is identical to the nonlinearity
defined here.
3.17
numerical aperture
description of the beam divergence of an optical source
Note 1 to entry: In this document, the numerical aperture is the sine of the (linear) half-angle at which the
irradiance is 5 % of the maximum irradiance.
Note 2 to entry: Adapted from the definition of the numerical aperture of multimode graded-index fibres in
IEC 60793-1-43:2015, Clause 3; in this document, the definition is used to describe the divergence of all divergent
beams.
3.18
operating conditions
appropriate set of specified ranges of values of influence quantities usually wider than the
reference conditions for which the uncertainties of a measuring instrument are specified (see
VIM, 5.5)
Note 1 to entry: The operating conditions and uncertainty at operating conditions are usually specified by the
manufacturer for the convenience of the user.
3.19
operating range
specified range of values of one of a set of operating conditions (3.18)
3.20
optical input port
physical input of the power meter (or standard) to which the radiant power is to be applied or to
which the optical fibre end is to be connected
Note 1 to entry: An optical path (path of rays with or without optical elements, such as lenses, diaphragms, light
guides, etc.) is assumed to connect the optical input port with the power meter's detector.
3.21
optical reference plane
plane on or near the optical input port (3.20) which is used to define the beam's spot diameter
(3.31)
Note 1 to entry: The optical reference plane is usually assumed to be perpendicular to the beam propagation, and
it should be described by appropriate mechanical dimensions relative to the power meter's optical input port.
3.22
polarization dependent response
PDR
variation in response of a power meter with respect to all possible polarization states of the
input light:
r
max
PDR 10×log (dB) (7)
r
min
=
=
where
r and r are the maximum and minimum response (3.28) taken over all polarization
max min
states
Note 1 to entry: Polarization dependent response is expressed in decibels.
Note 2 to entry: This note applies to the French language only.
3.23
fibre-optic power meter (fibre-optic)
instrument capable of measuring radiant power from fibre-coupled sources such as lasers and
LEDs, which are typical for the fibre-optic communications industry. These sources include
laser diodes, LEDs and fibres.
Note 1 to entry: The radiation may be divergent or collimated. The radiation is assumed to be incident on the
optical reference plane within the specified conditions.
Note 2 to entry: A power meter may consist of either a single instrument or a main instrument and a separate
sensing head. In the case of a separate sensing head, the head may be calibrated without the main instrument.
However, if any analogue electronics are used in the main instrument, the sensing head shall be calibrated together
with the main instrument.
NOTE The measurement result may be influenced by the main instrument, particularly if any analog electronics is
used in the main instrument. In such cases, the sensing head must be calibrated together with the main instrument.
Note 3 to entry: A fibre-optic power meter is usually capable of measuring the time-average of modulated optical
power. An increased uncertainty may be observed, which depends on the duty cycle and the peak power of
modulated optical power.
NOTE All of the standards in this standard are power meters.
3.24
radiant power
P
power emitted, transferred, or received in the form of optical radiation [1]
Note 1 to entry: Radiant power is expressed in watts.
3.25
reference conditions
conditions of use prescribed for testing the performance of a measuring instrument or for
intercomparison of results of measurements
Note 1 to entry: The reference conditions generally include reference values or reference ranges for the influence
quantities affecting the measuring instrument.
[VIM, 5.7]
3.26
reference meter
standard which is used as the reference for the calibration (3.3) of a test meter (3.32)
3.27
reference standard
standard, generally having the highest metrological quality available at a given location or in a
given organization, from which measurements made therein are derived
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 5.6.
[VIM, 6.6]
___________
Numbers in square brackets refer to the Bibliography.
– 14 – IEC 61315:2019 RLV © IEC 2019
3.28
response
r
measurement result of a power meter, y, divided by the radiant power on the power meter's
optical reference plane, P, at a given condition of measurement:
y
r = (W/W, dimensionless) (8)
P
Note 1 to entry: An ideal power meter exhibits a response of 1 for all operating conditions.
3.29
spectral responsivity
responsivity
R
quotient of the detector output current I by the incident monochromatic optical power P:
I
R = (A/W) (9)
P
Note 1 to entry: The responsivity depends on the conditions (wavelength, temperature, etc.). See Figure 1.
Note 2 to entry: This note applies to the French language only.
Key
Si silicon
Ge germanium
InGaAs indium gallium arsenide
Figure 1 – Typical spectral responsivity of photoelectric detectors
3.30
spectral bandwidth
B
full-width at half-maximum (FWHM) of the source spectrum
If the spectrum is non-continuous, for example as in the case of a laser diode with a multi-
longitudinal line spectrum, then the spectral bandwidth is defined with the help of the root-
mean-square spectral bandwidth, B :
rms
2 2
P × λ P(λ − λ )
∑ i i ∑ i i centre
i i
B = M × B = M − λ = M
rms centre
P P
i i
∑ ∑
i i
where
M = 2 2ln 2 ≅ 2,35 (calculated using a spectrum with a Gaussian envelope);
th
P is the power of the i discrete line, for example in W;
i
th
λ is the vacuum wavelength of the i discrete line;
i
λ is the centre wavelength.
centre
Note 1 to entry: If the source is a laser diode with a multiple-longitudinal mode spectrum, then the FWHM spectral
bandwidth B is the RMS spectral bandwidth, multiplied by 2,35 (assuming the source has a Gaussian envelope):
1 2
BP2,35 λλ− (10)
( )
∑ ici
P
total
i
P = P (11)
total ∑ i
i
where
λ is the centroidal wavelength (3.5) of the laser diode, in nm;
c
P is the total power, in W;
total
th
P is the power of i longitudinal mode, in W;
i
th
λ is the vacuum wavelength of i longitudinal mode, in nm.
i
Note 2 to entry: If the source emits at one wavelength only (single-line spectrum), it may be sufficient to specify
an upper limit, for example spectral bandwidth < 1 nm.
Note 3 to entry: It is usually sufficient to perform the integral or summation over the spectrum where the power is
higher than 0,1 % of the maximum power.
Note 4 to entry: This note applies to the French language only.
3.31
spot diameter
diameter of the irradiated area on the optical reference plane, defined by the (best-
approximation) circle at which the irradiance (3.11) has dropped to 5 % of the peak irradiance
Note 1 to entry: The ratio of 5 % was adopted for reasons of compatibility with the definition of the numerical
aperture. Other ratios are often used to describe laser beams, for example 1/e or 1/e. In that case, the ratio shall
be stated with the spot diameter value.
NOTE 2 The diameter of the optical reference plane must be larger than the spot diameter in order to measure the
whole optical power.
3.32
test meter
fibre-optic power meter (3.23) (or standard) to be calibrated by comparison with the reference
meter (3.26)
3.33
traceability
property of the result of a measurement or the value of a standard whereby it can be related to
stated references, usually national or international standards, through an unbroken chain of
comparisons all having stated uncertainties
=
– 16 – IEC 61315:2019 RLV © IEC 2019
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 2.41.
[VIM, 6.10]
3.34
traceability chain
unbroken chain of comparison (See Figure 2)
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 2.42.
Figure 2 – Example of a traceability chain
[VIM 6.10]
3.35
working standard
standard that is used routinely to calibrate or check measuring instruments
Note 1 to entry: A working standard is usually calibrated against a reference standard (3.27).
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 5.7.
[VIM, 6.7]
3.36
zero error
measurement result of a power meter without irradiation of the optical input port
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 4.28.
(VIM, 5.23)
4 Preparation for calibration
4.1 Organization
The calibration laboratory should satisfy requirements of ISO/IEC 17025.
The calibration laboratory should ensure that suitable requirements for calibration are followed.
NOTE Guidance about good practices for calibration can be found in ISO/IEC 17025 [18].
There should be a documented measurement procedure for each type of calibration performed,
giving step-by-step operating instructions and equipment to be used.
4.2 Traceability
The requirements of ISO/IEC 17025 should be met.
The calibration laboratory should ensure that suitable requirements are followed.
NOTE Guidance about good practices for calibration can be found in ISO/IEC 17025 [18].
All standards used in the calibration process shall be calibrated according to a documented
program with traceability to national standards laboratories or to accredited calibration
laboratories. It is advisable to maintain more than one standard on each hierarchical level, so
that the performance of the standard can be verified by comparisons on the same level. Make
sure that any other test equipment which has a significant influence on the calibration results is
calibrated. Upon request, specify this test equipment and its traceability chain(s). The
re-calibration period(s) shall be defined and documented.
4.3 Advice for measurements and calibrations
4.3 gives general advice for all measurements and calibrations of optical and fibre-optic power
meters.
The calibration should be made in a temperature-controlled room if non-temperature-controlled
detectors are used. The recommended temperature is 23 °C. Humidity control may be
necessary if humidity-sensitive optical detectors are used, or if there is the possibility of
condensation on the components. A change of the laboratory's humidity may change the
absorption of air and thereby change the power. This effect is relatively strong between
1 360 nm and 1 410 nm, especially when a sequential-type, open-beam calibration is used and
the humidity changes between the steps. In parallel-type calibrations with open-beam paths of
approximately the same lengths, the measurement results of both the reference meter and the
test meter will change at approximately the same time, with negligible effect on the calibration
result.
The laboratory should be kept clean. Connectors and optical input ports should always be
cleaned before measurement. The quality and cleanness of the connector in front of the
detector should be checked. All fibres should be moved as little as possible during the
measurements; they can be fixed to the workbench if necessary. Sensors should be moved to
the fibre rather than the fibre to the sensor.
The optical source that is used for the excitation of the power meter should be characterized
for centre centroidal wavelength and spectral bandwidth. The spectral bandwidth should be
narrow enough to avoid averaging over a wide range of wavelengths. Means to ensure the
stability of the source, for example with the help of independent power monitoring, may be
advisable.
Laser diodes are sensitive to back reflections. To improve the stability, it is advisable to use an
optical attenuator or an optical isolator between the laser diode and the test meter. Because of
their narrow spectral bandwidths, the combination of laser diode and multimode fibre is also
capable of producing speckle patterns on the optical reference plane, resulting in an increased
measurement uncertainty.
Fibre connectors and connector adapters are likely to produce errors in the measurement
result [2] because of multiple reflections between the optical input port (or detector) and the
connector-adapter combination (as part of the source). Therefore, connectors and adapters
– 18 – IEC 61315:2019 RLV © IEC 2019
with low reflectivity are recommended for the calibration. Otherwise, a correction factor and an
increased uncertainty may have to be taken into account.
It is advisable to use reference meters with detector diameters of ≥ 3 mm, because they can
easily be irradiated with an open beam, and they are less susceptible to contamination (dirt and
dust). The reference meter's surface reflections should be as small as possible. If the
...
IEC 61315 ®
Edition 3.0 2019-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Calibration of fibre-optic power meters
Étalonnage de wattmètres pour dispositifs à fibres optiques
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.
Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite ni
utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et
les microfilms, sans l'accord écrit de l'IEC ou du Comité national de l'IEC du pays du demandeur. Si vous avez des
questions sur le copyright de l'IEC ou si vous désirez obtenir des droits supplémentaires sur cette publication, utilisez
les coordonnées ci-après ou contactez le Comité national de l'IEC de votre pays de résidence.
IEC Central Office Tel.: +41 22 919 02 11
3, rue de Varembé info@iec.ch
CH-1211 Geneva 20 www.iec.ch
Switzerland
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.
IEC publications search - webstore.iec.ch/advsearchform Electropedia - www.electropedia.org
The advanced search enables to find IEC publications by a The world's leading online dictionary on electrotechnology,
variety of criteria (reference number, text, technical containing more than 22 000 terminological entries in English
committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary
(IEV) online.
IEC Just Published - webstore.iec.ch/justpublished
Stay up to date on all new IEC publications. Just Published IEC Glossary - std.iec.ch/glossary
details all new publications released. Available online and once 67 000 electrotechnical terminology entries in English and
a month by email. French extracted from the Terms and Definitions clause of IEC
publications issued since 2002. Some entries have been
IEC Customer Service Centre - webstore.iec.ch/csc collected from earlier publications of IEC TC 37, 77, 86 and
If you wish to give us your feedback on this publication or need CISPR.
further assistance, please contact the Customer Service
Centre: sales@iec.ch.
A propos de l'IEC
La Commission Electrotechnique Internationale (IEC) est la première organisation mondiale qui élabore et publie des
Normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.
A propos des publications IEC
Le contenu technique des publications IEC est constamment revu. Veuillez vous assurer que vous possédez l’édition la
plus récente, un corrigendum ou amendement peut avoir été publié.
Recherche de publications IEC - Le premier dictionnaire d'électrotechnologie en ligne au monde,
webstore.iec.ch/advsearchform avec plus de 22 000 articles terminologiques en anglais et en
La recherche avancée permet de trouver des publications IEC français, ainsi que les termes équivalents dans 16 langues
en utilisant différents critères (numéro de référence, texte, additionnelles. Egalement appelé Vocabulaire
comité d’études,…). Elle donne aussi des informations sur les Electrotechnique International (IEV) en ligne.
projets et les publications remplacées ou retirées.
Glossaire IEC - std.iec.ch/glossary
IEC Just Published - webstore.iec.ch/justpublished 67 000 entrées terminologiques électrotechniques, en anglais
Restez informé sur les nouvelles publications IEC. Just et en français, extraites des articles Termes et Définitions des
Published détaille les nouvelles publications parues. publications IEC parues depuis 2002. Plus certaines entrées
Disponible en ligne et une fois par mois par email. antérieures extraites des publications des CE 37, 77, 86 et
CISPR de l'IEC.
Service Clients - webstore.iec.ch/csc
Si vous désirez nous donner des commentaires sur cette
publication ou si vous avez des questions contactez-nous:
sales@iec.ch.
Electropedia - www.electropedia.org
IEC 61315 ®
Edition 3.0 2019-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Calibration of fibre-optic power meters
Étalonnage de wattmètres pour dispositifs à fibres optiques
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.140; 33.180.10 ISBN 978-2-8322-6640-3
– 2 – IEC 61315:2019 © IEC 2019
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions. 7
4 Preparation for calibration . 15
4.1 Organization. 15
4.2 Traceability . 15
4.3 Advice for measurements and calibrations . 15
4.4 Recommendations to users . 16
5 Absolute power calibration . 16
5.1 Calibration methods . 16
5.2 Establishing the calibration conditions . 17
5.3 Calibration procedure . 18
5.4 Calibration uncertainty . 19
5.4.1 General . 19
5.4.2 Uncertainty due to the setup . 19
5.4.3 Uncertainty of the reference meter . 20
5.4.4 Correction factors and uncertainty caused by the change of conditions . 21
5.4.5 Uncertainty due to the spectral bandwidths . 24
5.5 Reporting the results . 25
6 Measurement uncertainty of a calibrated power meter . 26
6.1 Overview . 26
6.2 Uncertainty at reference conditions . 26
6.3 Uncertainty at operating conditions . 26
6.3.1 General . 26
6.3.2 Determination of dependences on conditions . 27
6.3.3 Ageing . 28
6.3.4 Dependence on temperature . 28
6.3.5 Dependence on the power level (nonlinearity). 28
6.3.6 Dependence on the type of fibre or on the beam geometry . 29
6.3.7 Dependence on the connector-adapter combination . 30
6.3.8 Dependence on wavelength . 31
6.3.9 Dependence on spectral bandwidth . 32
6.3.10 Dependence on polarization . 32
6.3.11 Other dependences . 33
7 Nonlinearity calibration . 33
7.1 General . 33
7.2 Nonlinearity calibration based on superposition . 33
7.2.1 General . 33
7.2.2 Procedure . 34
7.2.3 Uncertainties. 35
7.3 Nonlinearity calibration based on comparison with a calibrated power meter . 36
7.3.1 General . 36
7.3.2 Procedure . 36
7.3.3 Uncertainties. 37
7.4 Nonlinearity calibration based on comparison with an attenuator . 37
7.5 Calibration of power meter for high power measurement . 37
Annex A (normative) Mathematical basis for measurement uncertainty calculations . 38
A.1 General . 38
A.2 Type A evaluation of uncertainty . 38
A.3 Type B evaluation of uncertainty . 39
A.4 Determining the combined standard uncertainty . 39
A.5 Reporting . 40
Annex B (informative) Linear to dB scale conversion of uncertainties . 41
B.1 Definition of decibel . 41
B.2 Conversion of relative uncertainties . 41
Bibliography . 42
Figure 1 – Typical spectral responsivity of photoelectric detectors . 13
Figure 2 – Example of a traceability chain . 14
Figure 3 – Measurement setup for sequential, fibre-based calibration . 17
Figure 4 – Change of conditions and uncertainty . 22
Figure 5 – Determining and recording an extension uncertainty . 27
Figure 6 – Possible subdivision of the optical reference plane into 10 × 10 squares, for
the measurement of the spatial response . 29
Figure 7 – Wavelength dependence of response due to Fabry-Perot type interference . 32
Figure 8 – Measurement setup of polarization dependent response . 32
Figure 9 – Nonlinearity calibration based on superposition . 34
Figure 10 – Measurement setup for nonlinearity calibration by comparison . 36
Table 1 – Calibration methods and correspondent typical power . 16
Table 2 – Nonlinearity . 35
– 4 – IEC 61315:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CALIBRATION OF FIBRE-OPTIC POWER METERS
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 61315 has been prepared by IEC technical committee 86: Fibre
optics.
This third edition cancels and replaces the second edition published in 2005. It constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) update of terms and definitions;
b) update of 5.1, including Table 1 (new type of source);
c) update of Annex A;
d) addition of Annex B on dB conversion.
The text of this International Standard is based on the following documents:
CDV Report on voting
86/533/CDV 86/540A/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.
In this document, the following print types are used:
– terms defined in the document: in italic type.
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.
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 61315:2019 © IEC 2019
INTRODUCTION
Fibre-optic power meters are designed to measure optical power from fibre-optic sources as
accurately as possible. This capability depends largely on the quality of the calibration process.
In contrast to other types of measuring equipment, the measurement results of fibre-optic
power meters usually depend on many conditions of measurement. The conditions of
measurement during the calibration process are called calibration conditions. Their precise
description is therefore an integral part of the calibration.
This document defines all of the steps involved in the calibration process: establishing the
calibration conditions, carrying out the calibration, calculating the uncertainty, and reporting the
uncertainty, the calibration conditions and the traceability.
The absolute power calibration describes how to determine the ratio between the value of the
input power and the power meter's result. This ratio is called correction factor. The
measurement uncertainty of the correction factor is combined following Annex A from
uncertainty contributions from the reference meter, the test meter, the setup and the
procedure.
The calculations go through detailed characterizations of individual uncertainties. It is important
to know that
a) some uncertainties are type B estimations, experience-based,
b) a detailed uncertainty analysis is usually only done once for each power meter type under
test, and all subsequent calibrations are usually based on this one-time analysis, using the
appropriate type A measurement contributions evaluated at the time of the calibration, and
c) some of the individual uncertainties are simply considered to be part of a checklist, with an
actual value which can be neglected.
Clause 5 defines absolute power calibration, which is mandatory for calibration reports
referring to this document.
Clause 6 describes the evaluation of the measurement uncertainty of a calibrated power meter
operated within reference conditions or within operating conditions. It depends on the
calibration uncertainty of the power meter as calculated in 5.4, the conditions and its
dependence on the conditions. It is usually performed by manufacturers in order to establish
specifications and is not mandatory for reports referring to this document. One of these
dependences, the nonlinearity, is determined in a separate calibration (Clause 7).
CALIBRATION OF FIBRE-OPTIC POWER METERS
1 Scope
This document is applicable to instruments measuring radiant power emitted from sources that
are typical for the fibre-optic communications industry. These sources include laser diodes,
light emitting diodes (LEDs) and fibre-type sources. Both divergent and collimated radiations
are covered. This document defines the calibration of power meters to be performed by
calibration laboratories or by power meter manufacturers.
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 60793-2, Optical fibres – Part 2: Product specifications – General
IEC TR 61931:1998, Fibre optic – Terminology
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC TR 61931 and the
following 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
accredited calibration laboratory
calibration laboratory authorized by the appropriate national organization to issue calibration
certificates with a minimum specified uncertainty, which demonstrate traceability to national
standards (3.14)
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
Note 1 to entry: When the instrument is made to give a null indication corresponding to a null value of the
measurand, the set of operations is called zero adjustment.
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 3.11.
[SOURCE: IEC 60050-311:2001, 311-03-16, modified – The words "of a measuring instrument"
have been deleted from the term, and Note 2 to entry has been added.]
– 8 – IEC 61315:2019 © IEC 2019
3.3
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.
3.4
calibration conditions
conditions of measurement in which the calibration is performed
3.5
centroidal wavelength
λ
c
power-weighted mean wavelength of a light source in vacuum
Note 1 to entry: For a continuous spectrum, the centroidal wavelength is defined as:
p λ λdλ
( )
∫
λ = (1)
c
P
total
For a spectrum consisting of discrete lines, the centroidal wavelength is defined as:
Pλ
ii
∑
i
λ = (2)
c
P
∑ i
i
where
p(λ) is the power spectral density of the source, for example, in W/nm;
th
λ is the vacuum wavelength of the i discrete line;
i
th
P is the power of the i discrete line, for example, in W;
i
P is the total power, for example, in W.
total
Note 2 to entry: The above integrals and summations theoretically extend over the entire spectrum of the light
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 than 0,1 % of the maximum spectral density p(λ) or power P .
i i
3.6
correction factor
CF
numerical factor by which the uncorrected result of a measurement is multiplied to compensate
for systematic error
Note 1 to entry: This note applies to the French language only.
3.7
detector
element of the power meter that transduces the radiant optical power into a measurable,
usually electrical, quantity
Note 1 to entry: In this document, the detector is assumed to be connected with the optical input port by an optical
path.
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 3.9.
3.8
deviation
D
relative difference between the power measured by the test meter (3.32) P and the
DUT
reference power P :
ref
PP−
DUT ref
D= (3)
P
ref
Note 1 to entry: This note applies to the French language only.
3.9
excitation
description of the distribution of optical power between the modes in the fibre
Note 1 to entry: In context with multimode fibres, the fibre excitation is described by
a) the spot diameter (3.31) on the surface of the fibre end, and
b) the numerical aperture (3.17) of the radiation emitted from the fibre.
Single-mode fibres are generally assumed to be excited by only one mode (the fundamental mode).
3.10
instrument state
set of parameters that can be chosen on an instrument
Note 1 to entry: Typical parameters of the instrument state are the optical power range, the wavelength setting,
the display measurement unit and the output from which the measurement result is obtained (for example, display,
interface bus, analogue output).
3.11
irradiance
quotient of the incremental radiant power ∂P incident on an element of the reference plane by
the incremental area ∂A of that element:
∂P
E= W/m (4)
( )
∂A
[Note 1 to entry: For more information, see IEC TR 61931:1998, 2.1.15.
3.12
measurement result
y
(displayed or electrical) output of a power meter (or standard), after completing all actions
suggested by the operating instructions, for example warm-up, zero adjustment and
wavelength-correction
Note 1 to entry: Measurement result is expressed in watts (W). For the purposes of uncertainty, measurement
results in other units, for example volts, should be converted to watts. Measurement results in decibels (dB) should
– 10 – IEC 61315:2019 © IEC 2019
also be converted to watts, because the entire uncertainty accumulation is based on measurement results
expressed in watts. See Annex B.
3.13
measuring range
set of values of measurands for which the error of a measuring instrument is intended to lie
within specified limits
Note 1 to entry: In this document, the measuring range is the range of radiant power (part of the operating range),
for which the uncertainty at operating conditions is specified. The term "dynamic range" should be avoided in this
context.
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 4.7.
3.14
national measurement standard
national standard
standard recognized by a national decision to serve in a country as the basis for assigning
values to other standards of the quantity concerned
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 5.3.
3.15
national standards laboratory
laboratory which maintains the national standard (3.14)
3.16
nonlinearity
NL
relative difference between the response (3.28) at a given power P and the response at a
reference power P :
rP
( )
nl −1 (5)
P/P
rP
( )
If expressed in decibels, the nonlinearity is:
rP
( )
NL 10×log (dB) (6)
P/P 10
rP
( )
Note 1 to entry: The nonlinearity is equal to zero at the reference power.
Note 2 to entry: The term "local nonlinearity" is used for the relative difference between the responses at two
different power levels (separated by 3,01 dB) obtained during the nonlinearity calibration. The term "global
nonlinearity" is used for the result of summing the local nonlinearities (in dB); it is identical to the nonlinearity
defined here.
3.17
numerical aperture
description of the beam divergence of an optical source
Note 1 to entry: In this document, the numerical aperture is the sine of the (linear) half-angle at which the
irradiance is 5 % of the maximum irradiance.
Note 2 to entry: Adapted from the definition of the numerical aperture of multimode graded-index fibres in
IEC 60793-1-43:2015, Clause 3; in this document, the definition is used to describe the divergence of all divergent
beams.
=
=
3.18
operating conditions
appropriate set of specified ranges of values of influence quantities usually wider than the
reference conditions for which the uncertainties of a measuring instrument are specified
Note 1 to entry: The operating conditions and uncertainty at operating conditions are usually specified by the
manufacturer for the convenience of the user.
3.19
operating range
specified range of values of one of a set of operating conditions (3.18)
3.20
optical input port
physical input of the power meter (or standard) to which the radiant power is to be applied or to
which the optical fibre end is to be connected
Note 1 to entry: An optical path (path of rays with or without optical elements, such as lenses, diaphragms, light
guides, etc.) is assumed to connect the optical input port with the power meter's detector.
3.21
optical reference plane
plane on or near the optical input port (3.20) which is used to define the beam's spot diameter
(3.31)
Note 1 to entry: The optical reference plane is usually assumed to be perpendicular to the beam propagation, and
it should be described by appropriate mechanical dimensions relative to the power meter's optical input port.
3.22
polarization dependent response
PDR
variation in response of a power meter with respect to all possible polarization states of the
input light:
r
max
PDR 10×log (dB) (7)
r
min
where
r and r are the maximum and minimum response (3.28) taken over all polarization
max min
states
Note 1 to entry: Polarization dependent response is expressed in decibels.
Note 2 to entry: This note applies to the French language only.
3.23
fibre-optic power meter
instrument capable of measuring radiant power from fibre-coupled sources such as lasers and
LEDs, which are typical for the fibre-optic communications industry
Note 1 to entry: The radiation may be divergent or collimated. The radiation is assumed to be incident on the
optical reference plane within the specified conditions.
Note 2 to entry: A power meter may consist of either a single instrument or a main instrument and a separate
sensing head. In the case of a separate sensing head, the head may be calibrated without the main instrument.
However, if any analogue electronics are used in the main instrument, the sensing head shall be calibrated together
with the main instrument.
Note 3 to entry: A fibre-optic power meter is usually capable of measuring the time-average of modulated optical
power. An increased uncertainty may be observed, which depends on the duty cycle and the peak power of
modulated optical power.
=
– 12 – IEC 61315:2019 © IEC 2019
3.24
radiant power
P
power emitted, transferred, or received in the form of optical radiation [1]
Note 1 to entry: Radiant power is expressed in watts.
3.25
reference conditions
conditions of use prescribed for testing the performance of a measuring instrument or for
intercomparison of results of measurements
Note 1 to entry: The reference conditions generally include reference values or reference ranges for the influence
quantities affecting the measuring instrument.
3.26
reference meter
standard which is used as the reference for the calibration (3.3) of a test meter (3.32)
3.27
reference standard
standard, generally having the highest metrological quality available at a given location or in a
given organization, from which measurements made therein are derived
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 5.6.
3.28
response
r
measurement result of a power meter, y, divided by the radiant power on the power meter's
optical reference plane, P, at a given condition of measurement:
y
r= (W/W, dimensionless) (8)
P
Note 1 to entry: An ideal power meter exhibits a response of 1 for all operating conditions.
3.29
spectral responsivity
responsivity
R
quotient of the detector output current I by the incident monochromatic optical power P:
I
R= (A/W) (9)
P
Note 1 to entry: The responsivity depends on the conditions (wavelength, temperature, etc.). See Figure 1.
Note 2 to entry: This note applies to the French language only.
___________
Numbers in square brackets refer to the Bibliography.
Key
Si silicon
Ge germanium
InGaAs indium gallium arsenide
Figure 1 – Typical spectral responsivity of photoelectric detectors
3.30
spectral bandwidth
B
full-width at half-maximum (FWHM) of the source spectrum
Note 1 to entry: If the source is a laser diode with a multiple-longitudinal mode spectrum, then the FWHM spectral
bandwidth B is the RMS spectral bandwidth, multiplied by 2,35 (assuming the source has a Gaussian envelope):
1 2
BP2,35 λλ− (10)
( )
∑ ici
P
total
i
P = P (11)
total ∑ i
i
where
λ is the centroidal wavelength (3.5) of the laser diode, in nm;
c
P is the total power, in W;
total
th
P is the power of i longitudinal mode, in W;
i
th
λ is the vacuum wavelength of i longitudinal mode, in nm.
i
Note 2 to entry: If the source emits at one wavelength only (single-line spectrum), it may be sufficient to specify
an upper limit, for example spectral bandwidth < 1 nm.
Note 3 to entry: It is usually sufficient to perform the integral or summation over the spectrum where the power is
higher than 0,1 % of the maximum power.
Note 4 to entry: This note applies to the French language only.
3.31
spot diameter
diameter of the irradiated area on the optical reference plane, defined by the (best-
approximation) circle at which the irradiance (3.11) has dropped to 5 % of the peak irradiance
Note 1 to entry: The ratio of 5 % was adopted for reasons of compatibility with the definition of the numerical
aperture. Other ratios are often used to describe laser beams, for example 1/e or 1/e. In that case, the ratio shall
be stated with the spot diameter value.
=
– 14 – IEC 61315:2019 © IEC 2019
3.32
test meter
fibre-optic power meter (3.23) (or standard) to be calibrated by comparison with the reference
meter (3.26)
3.33
traceability
property of the result of a measurement or the value of a standard whereby it can be related to
stated references, usually national or international standards, through an unbroken chain of
comparisons all having stated uncertainties
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 2.41.
3.34
traceability chain
unbroken chain of comparison (see Figure 2)
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 2.42.
Figure 2 – Example of a traceability chain
3.35
working standard
standard that is used routinely to calibrate or check measuring instruments
Note 1 to entry: A working standard is usually calibrated against a reference standard (3.27).
Note 2 to entry: For more information, see ISO/IEC Guide 99:2007, 5.7.
3.36
zero error
measurement result of a power meter without irradiation of the optical input port
Note 1 to entry: For more information, see ISO/IEC Guide 99:2007, 4.28.
4 Preparation for calibration
4.1 Organization
The calibration laboratory should ensure that suitable requirements for calibration are followed.
NOTE Guidance about good practices for calibration can be found in ISO/IEC 17025 [18].
There should be a documented measurement procedure for each type of calibration performed,
giving step-by-step operating instructions and equipment to be used.
4.2 Traceability
The calibration laboratory should ensure that suitable requirements are followed.
NOTE Guidance about good practices for calibration can be found in ISO/IEC 17025 [18].
All standards used in the calibration process shall be calibrated according to a documented
program with traceability to national standards laboratories or to accredited calibration
laboratories. It is advisable to maintain more than one standard on each hierarchical level, so
that the performance of the standard can be verified by comparisons on the same level. Make
sure that any other test equipment which has a significant influence on the calibration results is
calibrated. Upon request, specify this test equipment and its traceability chain(s). The
re-calibration period(s) shall be defined and documented.
4.3 Advice for measurements and calibrations
4.3 gives general advice for all measurements and calibrations of optical and fibre-optic power
meters.
The calibration should be made in a temperature-controlled room if non-temperature-controlled
detectors are used. The recommended temperature is 23 °C. Humidity control may be
necessary if humidity-sensitive optical detectors are used, or if there is the possibility of
condensation on the components. A change of the laboratory's humidity may change the
absorption of air and thereby change the power. This effect is relatively strong between
1 360 nm and 1 410 nm, especially when a sequential-type, open-beam calibration is used and
the humidity changes between the steps. In parallel-type calibrations with open-beam paths of
approximately the same lengths, the measurement results of both the reference meter and the
test meter will change at approximately the same time, with negligible effect on the calibration
result.
The laboratory should be kept clean. Connectors and optical input ports should always be
cleaned before measurement. The quality and cleanness of the connector in front of the
detector should be checked. All fibres should be moved as little as possible during the
measurements; they can be fixed to the workbench if necessary. Sensors should be moved to
the fibre rather than the fibre to the sensor.
The optical source that is used for the excitation of the power meter should be characterized
for centroidal wavelength and spectral bandwidth. The spectral bandwidth should be narrow
enough to avoid averaging over a wide range of wavelengths. Means to ensure the stability of
the source, for example with the help of independent power monitoring, may be advisable.
Laser diodes are sensitive to back reflections. To improve the stability, it is advisable to use an
optical attenuator or an optical isolator between the laser diode and the test meter. Because of
their narrow spectral bandwidths, the combination of laser diode and multimode fibre is also
capable of producing speckle patterns on the optical reference plane, resulting in an increased
measurement uncertainty.
– 16 – IEC 61315:2019 © IEC 2019
Fibre connectors and connector adapters are likely to produce errors in the measurement
result [2] because of multiple reflections between the optical input port (or detector) and the
connector-adapter combination (as part of the source). Therefore, connectors and adapters
with low reflectivity are recommended for the calibration. Otherwise, a correction factor and an
increased uncertainty may have to be taken into account.
It is advisable to use reference meters with detector diameters of ≥ 3 mm, because they can
easily be irradiated with an open beam, and they are less susceptible to contamination (dirt and
dust). The reference meter's surface reflections should be as small as possible. If the source
emits a divergent beam, then a reference meter with an integrating sphere may be advisable. It
is also acceptable to use meters with "flat" detectors and mathematical correction, based on
multiplying the emitted far-field distribution with the measured angle-dependence of the
detector of the reference meter, and integrating over the range of far-field angles.
Temperature control of the detectors should be considered for highly accurate calibrations,
because detectors exhibit strong temperature dependence over some wavelength ranges.
4.4 Recommendations to users
It is recommended that the user of the power meter maintain at least one reference power
meter, which allows comparison of the meters for confidence. These comparisons are
particularly important before and after the meter is sent to recalibration, because they will allow
the user to determine whether or not their scale has changed – for example due to transport –
after the meter returns. Scale changes due to adjustment (3.2) (see IEC 60050-311:2001, 311-
03-16 and ISO/IEC Guide 99:2007, 4.30) will be reported on the calibration certificate.
A regular comparison of the correction factors (3.6), or of the deviations (3.8), will allow the
user to screen out excessive ageing, and possibly to adjust the recalibration intervals.
5 Absolute power calibration
5.1 Calibration methods
The calibration of a power meter is usually achieved by exposing both the meter under test and
a calibrated power meter with known uncertainty (the reference meter) to an optical radiation,
and by transferring the reference meter's (3.26) measurement result to the test meter (3.32).
The allowable spectral bandwidth (3.30) depends on the test meter's spectral responsivity
(3.29); the stronger its wavelength dependence, the narrower the spectral bandwidth. Usual
bandwidths are ≤ 10 nm, which excludes the possibility of calibrating with wider-bandwidth
LEDs. Therefore, one of the following is used in fibre-optic power meter calibrations:
combinations of "white-light" sources and narrow-bandwidth filters (for example
monochromators), laser diodes, or combinations of supercontinuum lasers with tuneable
bandpass filters.
Depending on the type of source and the exciting beam geometry, six most frequent calibration
methods can be distinguished, as depicted in Table 1:
Table 1 – Calibration methods and correspondent typical power
Radiation source Open-beam calibration Fibre beam calibration
"White-light" with filter
P ≈ 10 µW P ≈ 10 nW to 0,3 µW (MMF)
P ≈ 2 nW (SMF)
Laser diode
P ≈ 10 µW to a few mW
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...