EN 61315:2006

SLOVENSKI SIST EN 61315:2006
STANDARD
julij 2006
Umerjanje optovlakenskih števcev električne energije (IEC 61315:2005)
Calibration of fibre-optic power meters (IEC 61315:2005)
ICS 33.140; 33.180.01 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD
EN 61315
NORME EUROPÉENNE
January 2006
EUROPÄISCHE NORM
ICS 33.140;33.180.10 Supersedes EN 61315:1997

English version
Calibration of fibre-optic power meters
(IEC 61315:2005)
Etalonnage de wattmètres pour dispositifs Kalibrierung von Lichtwellenleiter-
à fibres optiques Leistungsmessern
(CEI 61315:2005) (IEC 61315:2005)

This European Standard was approved by CENELEC on 2005-11-01. 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

© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61315:2006 E
Foreword
The text of document 86/239/FDIS, future edition 2 of IEC 61315, prepared by IEC TC 86, Fibre
optics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61315 on 2005-11-01.
This European Standard supersedes EN 61315:1997.
Changes from EN 61315:1997 consist of adapting the uncertainty calculations to the approach taken
by the GUM, and adapting the terminology and graphical symbology to international standards VIM,
IEC 61931 and IEC 61930.
The importance of the nonlinearity calibration is emphasized by giving more detail and is now in a
separate clause.
Requirements concerning organization and traceability have been taken out of this standard since
they are general requirements concerning calibration laboratories and are given in EN ISO/IEC 17025.
The goal to standardize the type of power meter specifications has been removed since it does not
belong in a standard on calibration. Specifications should, however, still be based on calibrations
made following this standard and EN 60359.
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) 2006-08-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2008-11-01
__________
Endorsement notice
The text of the International Standard IEC 61315:2005 was approved by CENELEC as a European
Standard without any modification.
__________
NORME CEI
INTERNATIONALE
IEC
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2005-10
Etalonnage de wattmètres
pour dispositifs à fibres optiques

Calibration of fibre-optic
power meters
 IEC 2005 Droits de reproduction réservés  Copyright - all rights reserved
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61315  IEC:2005 – 3 –
CONTENTS
FOREWORD.5
INTRODUCTION.9

1 Scope.11
2 Normative references.11
3 Terms and definitions .13
4 Preparation for calibration.27
4.1 Organization .27
4.2 Traceability.27
4.3 Advice for measurements and calibrations .29
4.4 Recommendations to customers .31
5 Absolute power calibration .31
5.1 Establishing the calibration conditions.33
5.2 Calibration procedure .35
5.3 Calibration uncertainty .37
5.4 Reporting the results .51
6 Measurement uncertainty of a calibrated power meter .51
6.1 Uncertainty at reference conditions .51
6.2 Uncertainty at operating conditions .53
7 Nonlinearity calibration.67
7.1 Nonlinearity calibration based on superposition .69
7.2 Nonlinearity calibration based on comparison with a calibrated power meter.73
7.3 Nonlinearity calibration based on comparison with an attenuator .75
7.4 Calibration of power meter for high power measurement .75

Annex A (normative) Mathematical basis .79

Bibliography .85

Figure 1 – Typical spectral responsivity of photoelectric detectors.23
Figure 2 – Example of a traceability chain.27
Figure 3 – Measurement setup for sequential, fibre-based calibration .33
Figure 4 – Change of conditions and uncertainty.43
Figure 5 – Determining and recording an extension uncertainty.55
Figure 6 – Possible subdivision of the optical reference plane into 10 x 10 squares, for
the measurement of the spatial response .57
Figure 7 − Wavelength dependence of response due to Fabry-Perot type interference .65
Figure 8 – Measurement setup of polarization dependent response .65
Figure 9 – Nonlinearity calibration based on superposition .69
Figure 10 – Measurement setup for nonlinearity calibration by comparison.73

Table 1 – Typical calibration methods and correspondent power .31
Table 2 – Nonlinearity .71

61315  IEC:2005 – 5 –
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 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 61315 has been prepared by IEC technical committee 86: Fibre
optics.
This second edition cancels and replaces the first edition published in 1995. It constitutes a
technical revision.
Changes from the previous edition of this International Standard consist of adapting the
uncertainty calculations to the approach taken by the GUM, and adapting the terminology and
graphical symbology to international standards VIM, IEC 61931 and IEC 61930.
The importance of the nonlinearity calibration is emphasized by giving more detail and is now in
a separate clause.
61315  IEC:2005 – 7 –
Requirements concerning organization and traceability have been taken out of this standard
since they are general requirements concerning calibration laboratories and are given in
IEC/ISO 17025.
The goal to standardize the type of power meter specifications has been removed since it does
not belong in a standard on calibration. Specifications should, however, still be based on
calibrations made following this standard and IEC 60359.
The text of this standard is based on the following documents:
FDIS Report on voting
86/239/FDIS 86/248/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.
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.
61315  IEC:2005 – 9 –
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 therefore be an integral part of the calibration.
This International Standard 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;
b) a detailed uncertainty analysis is only necessary once for each power meter type under
test, and all subsequent calibrations can be based on this one-time analysis, using the
appropriate type A measurement contributions evaluated at the time of the calibration;
c) some of the individual uncertainties can simply be considered to be part of a checklist, with
an actual value which can be neglected.
Calibration according to Clause 5 is mandatory for reports referring to this standard.
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 5.3, 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 standard. 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.

61315  IEC:2005 – 11 –
CALIBRATION OF FIBRE-OPTIC
POWER METERS
1 Scope
This international standard is applicable to instruments measuring radiant power emitted from
sources which 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. The standard describes the calibration of power meters to be
performed by calibration laboratories or by power meter manufacturers.
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 60050-300, 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 61931, Fibre optic – Terminology
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)
61315  IEC:2005 – 13 –
3 Terms and definitions
For the purposes of this International Standard, the definitions contained in IEC 61931 and the
following definitions apply.
3.1
accredited calibration laboratory
a calibration laboratory authorized by the appropriate national organization to issue calibration
certificates with a minimum specified uncertainty, which demonstrate traceability to national
standards
3.2
adjustment
set of operations carried out on an instrument in order that it provides given indications
corresponding to given values of the measurand
[IEV 311-03-16; see also VIM 4.30]
NOTE 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
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
standards
[VIM, 6.11, modified]
NOTE 1 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 A calibration may also determine other metrological properties such as the effect of influence quantities.
NOTE 3 The result of a calibration may be recorded in a document, sometimes called a calibration certificate or
a calibration report.
3.4
calibration conditions
conditions of measurement in which the calibration is performed
3.5
centre wavelength
λ
centre
the power-weighted mean wavelength of a light source in vacuum.
For a continuous spectrum the centre 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.

61315  IEC:2005 – 15 –
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
NOTE 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
[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
0  
P
 0
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
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):
ΔL = 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.
3.8
detector
the element of the power meter that transduces the radiant optical power into a measurable,
usually electrical, quantity. In this standard, the detector is assumed to be connected with the
optical input port by an optical path
[see IEC 61931 and VIM, 4.15]
61315  IEC:2005 – 17 –
3.9
deviation
D
for the purpose of this standard, the relative difference between the power measured by the
test meter P and the reference power P
DUT ref
P − P
DUT ref
D =
P
ref
3.10
excitation (fibre)
a description of the distribution of optical power between the modes in the fibre. In context with
multimode fibres, the fibre excitation is described by:
a) the spot diameter on the surface of the fibre end, and
b) the numerical aperture 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)
3.11
instrument state
set of parameters that can be chosen on an instrument
NOTE 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).
3.12
irradiance
the 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/m²)
∂A
[IEC 61931, definition 2.1.15, modified]
3.13
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 and wavelength-
correction, expressed in watts (W). For the purpose 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.
3.14
measuring range
set of values of measurands for which the error of a measuring instrument is intended to lie
within specified limits
[VIM, 5.4]
61315  IEC:2005 – 19 –
NOTE In this standard, 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.
3.15
national (measurement) 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
[VIM, 6.3]
3.16
national standards laboratory
laboratory which maintains the national standard
3.17
nonlinearity
NL
relative difference between the response at a given power P and the response at a reference
power P :
r(P)
nl = − 1
P/P
r(P )
If expressed in decibels, the nonlinearity is:
r(P)
NL = 10 × log (dB)
P/P 10
r(P )
NOTE 1 The nonlinearity is equal to zero at the reference power.
NOTE 2 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; it is identical to the nonlinearity defined here.
3.18
numerical aperture
description of the beam divergence of an optical source. In this standard, the numerical
aperture is the sine of the (linear) half-angle at which the irradiance is 5 % of the maximum
irradiance.
NOTE This definition was adopted from the definition of the numerical aperture of multimode graded-index fibres
in IEC 60793-1-43. In this standard, the definition is used to describe the divergence of all divergent beams.
3.19
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 The operating conditions and uncertainty at operating conditions are usually specified by manufacturer for
the convenience of the user.
3.20
operating range
specified range of values of one of a set of operating conditions

61315  IEC:2005 – 21 –
3.21
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. An optical path (path of rays with or without
optical elements like lenses, diaphragms, light guides, etc.) is assumed to connect the optical
input port with the power meter's detector.
3.22
optical reference plane
plane on or near the optical input port which is used to define the beam's spot diameter
NOTE 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.
3.23
polarization dependent response
PDR
variation in response of a power meter with respect to all possible polarization states of the
input light, expressed in decibels:
 r 
max
 
PDR = 10 × log (dB)
 
r
min
 
where r and r are the maximum and minimum response taken over all polarization
max min
states.
3.24
power meter (fibre-optic)
in this standard, instrument capable of measuring radiant power from sources which are typical
for the fibre-optic communications industry. These sources include laser diodes, LEDs and
fibres. The radiation may be divergent or collimated. The radiation is assumed to be incident on
the optical reference plane within the specified conditions. A power meter may consist either of
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.
NOTE 1 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 2 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 3 All of the standards in this standard are power meters.
3.25
radiant power
P
1)
power emitted, transferred, or received in the form of optical radiation [1] . Unit: W.
3.26
reference conditions
conditions of use prescribed for testing the performance of a measuring instrument or for
intercomparison of results of measurements
[VIM, 5.7]
___________
1)
Figures in square brackets refer to the Bibliography.

61315  IEC:2005 – 23 –
NOTE The reference conditions generally include reference values or reference ranges for the influence
quantities affecting the measuring instrument.
3.27
reference meter
standard which is used as the reference for the calibration of a test meter
3.28
reference standard
standard, generally having the highest metrological quality available at a given location or in a
given organization, from which measurements made there are derived
[VIM, 6.6]
3.29
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)
P
NOTE An ideal power meter exhibits a response of 1 for all operating conditions.
3.30
(spectral) responsivity
R
quotient of the detector output current I by the incident monochromatic optical power P:
I
R = (A/W)
P
NOTE The responsivity depends on the conditions (wavelength, temperature, etc.).
1,2
InGaAs
1,0
0,8
Ge
0,6
Si
0,4
0,2
0,0
400 500 600 700 800 900 1 000 1 100 1 200 1 300 1 400 1 500 1 600 1 700
Wavelength  nm
IEC  1826/05
Key
Si: silicon
Ge: germanium
InGaAs: indium gallium arsenide
Figure 1 – Typical spectral responsivity of photoelectric detectors

Responsivity  A/W
61315  IEC:2005 – 25 –
3.31
spectral bandwidth
B
for the purpose of this standard, full-width at half-maximum (FWHM) of the 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 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 2 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.
3.32
spot diameter
in this standard, diameter of the irradiated area on the optical reference plane, defined by the
(best-approximation) circle at which the irradiance has dropped to 5 % of the peak irradiance
NOTE 1 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 it 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.
3.33
test meter
power meter (or standard) to be calibrated by comparison with the reference meter
3.34
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
[VIM, 6.10]
3.35
traceability chain
unbroken chain of comparison
[VIM 6.10]
61315  IEC:2005 – 27 –
National
standard
National standards laboratory
Working
standard
Accredited calibration laboratory
Transfer
standard
Calibration laboratory of company
Working
standard
Test Meter
IEC  1827/05
Figure 2 – Example of a traceability chain
3.36
working standard
standard that is used routinely to calibrate or check measuring instruments
[VIM, 6.7]
NOTE A working standard is usually calibrated against a reference standard.
3.37
zero error
measurement result of a power meter without irradiation of the optical input port
(VIM, 5.23)
4 Preparation for calibration
4.1 Organization
The calibration laboratory should satisfy requirements of ISO/IEC 17025.
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.
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.

61315  IEC:2005 – 29 –
4.3 Advice for measurements and calibrations
This subclause 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 work bench if necessary. Sensors should be moved to
the fibre rather than the fibre to the sensor.
The optical source which is used for the excitation of the power meter should be characterized
for centre 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, with the result of 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
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.

61315  IEC:2005 – 31 –
4.4 Recommendations to customers
It is recommended that the customer (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 re-calibration, because they will
allow the user to determine whether or not his scale has changed – for example due to
transport – after the meter returns. Scale changes due to adjustment (see IEV 311-03-16 and
VIM 4.30) will be reported on the calibration certificate.
A regular comparison of the correction factors, or of the deviations, will allow the user to
screen out excessive ageing, and to possibly adjust the recalibration intervals.
5 Absolute power calibration
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 measurement result to the test meter.
The allowable spectral bandwidth depends on the test meter's spectral responsivity; the
stronger its wavelength dependence, the narrower the spectral bandwidth. Usual bandwidths
are <15 nm, which excludes the possibility of calibrating with wider-bandwidth LEDs. Therefore,
either laser diodes or combinations of "white" sources and narrow-bandwidth filters (for
example monochromators) are typically used in optical power meter calibrations.
Depending on the type of source and the exciting beam geometry, four most frequent
calibration methods can be distinguished:
Table 1 – Typical calibration methods and correspondent power
Radiation source Open-beam calibration Fibre beam calibration
"White" with filter
P ≈ 10 µW P ≈ 10 nW to 0,3 µW (MM)
P ≈ 2 nW (SM)
Laser diode
P ≈ 10 µW to 1 mW P ≈ 10 µW to 1 mW (SM and MM)
MM: multimode fibre (usually graded-index fibre)
SM: single-mode fibre
One can distinguish between the sequential and the parallel measurement method. When
reference meter and test meter are sequentially exposed to the source, then the radiated
power should be kept as constant as possible, for example by appropriate stabilization. For the
parallel-type calibration, a beam splitter or a branching device is used to generate two beams
which excite both the reference meter and the test meter simultaneously. In this case, the
beam splitter or branching device ratio should be determined as accurately as possible, and its
stability should be investigated.
As an example, a measurement setup for sequential, fibre-based calibration is illustrated in
Figure 3. A launching device, for removal of the cladding modes and creation of an appropriate
modal excitation, is included in the setup.

61315  IEC:2005 – 33 –
Reference
power meter
dB
S
Cladding
Source Attenuator
Power meter
mode
(optional)
under test
stripper
IEC  1828/05
Figure 3 – Measurement setup for sequential, fibre-based calibration
5.1 Establishing the calibration conditions
The calibration conditions are the measurement conditions during the calibration process.
Establishing and maintaining the calibration conditions is an important part of the calibration,
because any change of these conditions is capable of producing erroneous measurement
results. The calibration conditions should be a close approximation to the intended operating
conditions. This ensures that the (additional) uncertainty in the operating environment is as
small as possible. The calibration conditions should be specified in the form of nominal values
with uncertainties when applicable. In order to meet the requirements of this standard, the
calibration conditions shall at least consist of:
a) the date of calibration;
b) the ambient temperature with uncertainty, for example 23 °C ± 1 °C;
c) the ambient relative humidity, if it has an influence, otherwise a relative humidity below the
condensation point is assumed;
d) the nominal radiant power on the optical reference plane;
e) the beam geometry:
1) an open (for example collimated) beam, described by the spot diameter on the optical
reference plane, the beam's numerical aperture and the irradiance distribution in the
beam. Typical irradiance distributions are: uniform, Gaussian or even irregular
(speckled);
2) the type of fibre and, if applicable, its degree of excitation (for example fully excited);
f) the connector-adapter combination: the connector type, polishing and adapter as part of the
exciting source (if applicable);
g) the centre wavelength of the exciting source with its uncertainty;
h) the spectral bandwidth of the exciting source with its uncertainty;
i) the state of polarization: "unpolarized light" or "polarized light, undefinite state". If the latter
is chosen, the uncertainty due to polarization dependent response shall be taken into
account in 5.3.2 and 5.3.4.
The above conditions may not be exhaustive. There may be other parameters which have a
significant influence on the calibration uncertainty and therefore shall be reported, too.
In the calibration with an open-beam, the power meter's optical reference plane should be
centrally irradiated with a beam diameter smaller than the active area of the optical reference
plane.
61315  IEC:2005 – 35 –
In the calibration with a fibre, a single-mode fibre or a multimode fibre may be used. A single-
mode fibre may be advantageous because of its re
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