IEC 62522:2014

Calibration of tuneable laser sources

IEC 62522:2014 provides a stable and reproducible procedure to calibrate the wavelength and power output of a tuneable laser against reference instrumentation such as optical power meters and optical wavelength meters (including optical frequency meters) that have been previously traceably calibrated. Keywords: calibrate the wavelength and power output of a tuneable laser

Étalonnage des sources laser accordables

L'IEC 62522:2014 fournit une procédure stable et reproductible pour étalonner la longueur d'onde et la puissance de sortie d'un laser accordable en fonction des instruments de référence tels que des appareils de mesure de la puissance optique et des appareils de mesure de longueur d'onde optique (y compris des fréquencemètres optiques) dont la traçabilité a été préalablement étalonnée. Mots clés: étalonner la longueur d'onde et la puissance de sortie d'un laser accordable

General Information

• Status: Published
• Publication Date: 13-Feb-2014
• ICS: 31.260 - Optoelectronics. Laser equipment
• ICS: 33.180.01 - Fibre optic systems in general
• Technical Committee: TC 86 - Fibre optics
• Drafting Committee: WG 4 - TC 86/WG 4
• Current Stage: DELPUB - Deleted Publication
• Start Date: 20-Jun-2024
• Completion Date: 29-Apr-2022

Relations

• Revised: IEC 62522:2024 - Calibration of tuneable laser sources
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 62522 ®
Edition 1.0 2014-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Calibration of tuneable laser sources

Étalonnage des sources laser accordables

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IEC 62522 ®
Edition 1.0 2014-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Calibration of tuneable laser sources

Étalonnage des sources laser accordables

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 31.260; 33.180.01 ISBN 978-2-8322-1411-4

– 2 – IEC 62522:2014 © IEC 2014
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviations . 7
3.1 Terms and definitions . 7
3.2 Abbreviations . 10
4 Preparation for calibration . 10
4.1 Organization. 10
4.2 Traceability . 10
4.3 Preparation . 10
4.4 Reference calibration conditions . 11
5 Wavelength calibration . 11
5.1 Overview . 11
5.2 Wavelength calibration at reference conditions . 11
5.2.1 Set-up . 11
5.2.2 Calibration equipment . 11
5.2.3 Procedure for wavelength calibration . 12
5.2.4 Dependence on conditions . 12
5.2.5 Uncertainty at reference conditions . 14
5.3 Wavelength calibration at operating conditions . 15
5.3.1 General . 15
5.3.2 Optical power dependence . 15
5.3.3 Uncertainty at operating conditions . 16
6 Optical power calibration . 16
6.1 Overview . 16
6.2 Optical power calibration at reference conditions . 17
6.2.1 Set-up . 17
6.2.2 Calibration equipment . 17
6.2.3 Procedure for power calibration at reference conditions . 17
6.2.4 Dependence on conditions . 18
6.2.5 Uncertainty at reference conditions . 21
6.3 Optical power calibration at operating conditions . 22
6.3.1 General . 22
6.3.2 Wavelength dependence . 22
6.3.3 Uncertainty at operating conditions . 23
7 Documentation . 23
7.1 Calibration data and uncertainty . 23
7.2 Calibration conditions . 23
Annex A (normative) Mathematical basis . 25
A.1 General . 25
A.2 Type A evaluation of uncertainty . 25
A.3 Type B evaluation of uncertainty . 26
A.4 Determining the combined standard uncertainty . 26
A.5 Reporting . 27
Annex B (informative) Averaged wavelength (or power) deviation over a certain range . 28

Annex C (informative) Other testing . 30
C.1 General . 30
C.2 Wavelength resolution . 30
C.2.1 Set-up . 30
C.2.2 Testing equipment . 30
C.2.3 Testing procedure for determining wavelength resolution . 30
C.3 Optical power resolution . 31
C.3.1 Set-up . 31
C.3.2 Testing equipment . 31
C.3.3 Testing procedure for optical power resolution . 31
C.4 Signal to source spontaneous emission ratio . 32
C.4.1 Set-up . 32
C.4.2 Testing equipment . 32
C.4.3 Testing procedure for determining signal to source spontaneous
emission ratio . 32
C.5 Side mode suppression ratio . 33
C.5.1 General . 33
C.5.2 Set-up . 33
C.5.3 Testing equipment . 34
C.5.4 Testing procedure . 34
Bibliography . 37

Figure 1 – Measurement set-up for wavelength calibration . 11
Figure 2 – Measurement set-up for temperature dependence . 13
Figure 3 – Measurement set-up for wavelength stability . 14
Figure 4 – Measurement set-up for optical power dependence . 15
Figure 5 – Measurement set-up for intrinsic optical power calibration . 17
Figure 6 – Measurement set-up for temperature dependence . 18
Figure 7 – Measurement set-up for optical power stability . 20
Figure 8 – Measurement set-up for connection repeatability/reproducibility . 21
Figure 9 – Measurement set-up for wavelength dependence . 22
Figure C.1 – Measurement set-up for wavelength resolution . 30
Figure C.2 – Measurement set-up for optical power resolution setting test . 31
Figure C.3 – Measurement set-up for signal to total source spontaneous emission ratio . 32
Figure C.4 – Measurement of the signal to spontaneous emission ratio . 33
Figure C.5 – Measurement set-up for the side mode suppression ratio test . 33
Figure C.6 – Optical spectrum of tuneable laser source . 35
Figure C.7 – Measurement set-up for SMSR . 35

– 4 – IEC 62522:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
CALIBRATION OF TUNEABLE LASER SOURCES

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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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 62522 has been prepared by IEC technical committee 86: Fibre
optics.
The text of this standard is based on the following documents:
CDV Report on voting
86/443/CDV 86/459/RVC
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
stability 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.
– 6 – IEC 62522:2014 © IEC 2014
INTRODUCTION
Wavelength-division multiplexing (WDM) transmission systems have been deployed in optical
trunk lines. ITU-T Recommendations in the G.694 series describe the frequency and
wavelength grids for WDM applications. For example, the frequency grid of G.694.1 supports a
variety of channel spacing ranging from 12,5 GHz to 100 GHz and wider. WDM devices, such
as arrayed waveguide grating (AWG), thin film filter or grating based multiplexers (MUX) and
demultiplexers (DMUX) with narrow channel spacing are incorporated in the WDM transmission
systems. When measuring the characteristics of such devices, wavelength tuneable laser
sources are commonly used and are required to have well-calibrated performances;
wavelength uncertainty, wavelength tuning repeatability, wavelength stability and output optical
power stability are important parameters.
The tuneable laser source (TLS) is generally equipped with the following features:
a) the output wavelength is continuously tuneable in a wavelength range starting at 1 260 nm
or higher and ending at less than 1 675 nm (the output should excite only the fundamental
LP01 fibre mode);
b) an output port for optical fibre connectors.
The envelope of the spectrum is a single longitudinal mode with a FWHM of at most 0,1 nm.
Any adjacent modes are at least 20 dB lower than the main spectral mode (for example, a
distributed feedback laser diode (DFB-LD), external cavity laser, etc.)

CALIBRATION OF TUNEABLE LASER SOURCES

1 Scope
This International Standard provides a stable and reproducible procedure to calibrate the
wavelength and power output of a tuneable laser against reference instrumentation such as
optical power meters and optical wavelength meters (including optical frequency meters) that
have been previously traceably calibrated.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
IEC 60793-2-50, Optical fibres – Part 2-50: Product specifications – Sectional specification for
class B single-mode fibres
IEC 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 60825-2, Safety of laser products – Part 2: Safety of optical fibre communication systems
(OFCS)
IEC 62129-2, Calibration of wavelength/optical frequency measurement instruments – Part 2:
Michelson interferometer single wavelength meters
ISO/IEC 17025, General requirements for the competence of testing and calibration
laboratories
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
ISO/IEC Guide 99:2007, International vocabulary of metrology – Basic and general concepts
and associated terms (VIM)
3 Terms, definitions and abbreviations
For the purposes of this document, the following terms, definitions and abbreviations apply.
3.1 Terms and definitions
3.1.1
accredited calibration laboratory
calibration laboratory authorized by an appropriate national organization to issue calibration
certificates that demonstrates traceability to national standards
3.1.2
adjustment
set of operations carried out on an instrument in order that it provides given indications
corresponding to given values of the measurand

– 8 – IEC 62522:2014 © IEC 2014
[SOURCE: IEC 60050-300:2001, 311-03-16, modified – minor editorial change, omission of the
NOTE]
[See also ISO/IEC Guide 99:2007, 3.11, modified – 3 NOTES omitted].
3.1.3
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
Note 1 to entry: The results of a calibration permit either the assignment of measurand values to the indications or
the determination of corrections with respect to the indications.
Note 2 to entry: A calibration may also determine other metrological properties such as the effects of influence
quantities.
Note 3 to entry: The result of a calibration may be recorded in a document, called a calibration certificate or a
calibration report.
[SOURCE: ISO/IEC Guide 99:2007, 2.39, modified – shortened; the two NOTES replaced by 3
new NOTES].
3.1.4
calibration conditions
conditions of measurement in which the calibration is performed
3.1.5
calibration at reference conditions
calibration which includes the evaluation of the uncertainty at reference conditions of the light
source under calibration
3.1.6
calibration at operating conditions
calibration which includes the evaluation of the uncertainty at operating conditions of the light
source under calibration
3.1.7
level of confidence
estimated probability that the true value of a measured parameter lies in the given range
3.1.8
coverage factor
k
used to calculate the expanded uncertainty U from the standard uncertainty, u
3.1.9
decibels
dB, dBm
sub-multiple of the Bel, B, unit used to express values of optical power on a logarithmic scale
Note 1 to entry: The power level is always relative to a reference power P
 
P
L = 10× log  
P / P 10
0  
P
 0 
where P and P are expressed in the same linear units.
The unit symbol dBm is used to indicate power level relative to 1 mW:

 P 
 
L = 10× log
P /1mW 10
 
1mW
 
The linear ratio, R , of two radiant powers, P and P , can alternatively be expressed as an power level difference
lin 1 2
in decibels (dB):
 
P
ΔL = 10×log (R )= 10×log   = 10×log (P )−10×log (P )
P 10 lin 10 10 1 10 2
 
P
 2 
Similarly, relative uncertainties, U , or relative deviations, can be alternatively expressed in decibels:
lin
U = 10× log (1− U )
dB 10 lin
Note 2 to entry: For mathematical treatment all measurement results should be expressed in linear units (e.g.
watts) and all uncertainties should be expressed in linear form. This is recommended because the accumulation of
uncertainties in logarithmic units is mathematically difficult. The final statement of an uncertainty may be either in
the linear or in the dB form.
Note 3 to entry: ISO 80000-3 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 accepted in this standard because it is
widely used and accepted by users of fibre optic instrumentation.
3.1.10
optical power deviation
D
P
, and the
difference between the set power of the light source under calibration, P
TLS
corresponding reference power P , measured by the reference power meter
meas
P − P
TLS meas
D =
P
P
meas
3.1.11
operating conditions
appropriate set of specified ranges of values with influence quantities usually wider than the
reference conditions for which the uncertainties of a measuring instrument are specified
Note 1 to entry: Operating conditions and the uncertainty at operating conditions are usually specified by the
manufacturer for the convenience of the user.
3.1.12
reference conditions
conditions used for testing the performance of a measuring instrument or for the
intercomparison of the measurement results
Note 1 to entry: Reference conditions generally include reference values or reference ranges for the quantities
influencing and affecting the measuring instrument.
3.1.13
side-mode suppression ratio
SMSR
peak power ratio between the main mode spectrum and the largest side mode spectrum in a
single-mode laser diode such as a DFB-LD
Note 1 to entry: Side-mode suppression ratio is usually expressed in dB.
3.1.14
wavelength
wavelength (in a vacuum) of a light source

– 10 – IEC 62522:2014 © IEC 2014
3.1.15
wavelength deviation
D
λ
difference between the target wavelength, set on the light source under calibration, λ , and
TLS
the measured wavelength, λ , in nm or μm
meas
D = λ – λ
λ TLS meas
3.2 Abbreviations
APC Angled physical contact
DFB-LD Distributed feedback laser diode
FWHM Full-width/half-maximum
OSA Optical spectrum analyser
SMSR Side-mode suppression ration
TLS Tuneable laser source
WDM Wavelength-division multiplexing
4 Preparation for calibration
4.1 Organization
The calibration laboratory should satisfy requirements of ISO/IEC 17025.
There shall 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 calibration equipment which have a significant influence on the calibration results are
calibrated.
4.3 Preparation
The environmental conditions shall be commensurate with the level of uncertainty that is
required for calibration:
a) calibrations shall be carried out in a clean environment;
b) temperature monitoring and control is required;
c) all laser sources shall be safely operated (refer to IEC 60825-1 and IEC 60825-2);
d) the output of the tuneable laser source should be examined with an optical spectrum
analyser (OSA) to check for single mode operation.
The recommended temperature is 23 °C (for example, 23 °C ± 2 °C). Give the calibration
equipment a minimum of 2 h prior to testing to reach equilibrium within its environment. Allow
the tuneable laser source a warm-up period in accordance to the manufacturer’s instructions.

4.4 Reference calibration conditions
The reference calibration conditions usually include the following parameters and, if necessary,
their tolerance bands: date, temperature, relative humidity, atmospheric pressure, displayed
optical power, displayed wavelength, fibre, connector-adapter combination, (spectral)
bandwidth and resolution bandwidth (spectral resolution) set. Unless otherwise specified, use a
single-mode optical fibre category B1.1 or B1.3 pigtail as prescribed by IEC 60793-2-50, having
a length of at least 2 m. It is desirable to perform all the calibration in a situation where back-
reflections are negligible. Thus, angled connectors and isolators should be used wherever the
situation permits.
Operate the tuneable laser source in accordance with the manufacturer’s specifications and
operating procedures. Where practical, select a range of calibration conditions and parameters
that emulate the actual field operating conditions of the tuneable laser source under calibration.
Choose these parameters so as to optimize the tuneable laser source’s accuracy, as specified
by the manufacturer’s operating procedures.
Document the conditions as specified in Clause 7.
NOTE The calibration results only apply to the set of calibration conditions used in the calibration process.
5 Wavelength calibration
5.1 Overview
The factors making up the uncertainty in the wavelength of the light source under calibration
consist of
a) the intrinsic uncertainty of the light source under calibration as found in the calibration at
reference conditions including temperature and time dependences for these tight conditions,
and
b) the uncertainties due to dependences on optical power, temperature and time as found in
the calibrations at broader operating conditions.
The wavelength calibration at reference conditions, for discrete wavelengths, as described in
5.2 is mandatory. The calibration at operating conditions, described in 5.3, is optional.
5.2 Wavelength calibration at reference conditions
5.2.1 Set-up
Figure 1 shows a system for wavelength calibration. The calibration is performed under the
given reference conditions.
Optical fibre
Light source Wavelength meter
IEC  0620/14
Figure 1 – Measurement set-up for wavelength calibration
5.2.2 Calibration equipment
A wavelength meter shall be used for the calibration. The wavelength meter should be
calibrated using IEC 62129-2.
– 12 – IEC 62522:2014 © IEC 2014
5.2.3 Procedure for wavelength calibration
The calibration procedure is as follows:
a) Regarding the calibration system shown in Figure 1, the set wavelength of the light source
is given by λ and the measured values are given by λ .The uncertainty of the
TLS j meas i,j
wavelength measurement takes into account the tuning repeatability and hysteresis of the
tuneable laser source (TLS). Hysteresis is defined as the deviation resulting from tuning the
desired wavelength from both the shorter and the longer wavelengths.
b) Repeat the wavelength measurement λ at least 10 times. Ensure that the TLS is
meas i,j
tuned to λ prior to each measurement. The target wavelength (j) should be
TLS j
approached in such a way that tuning occurs from both longer and shorter wavelengths.
c) Calculate the average measured wavelength: λ
meas j
m
(1)
λ = λ
meas, j ∑ meas i,j
m
i=1
where m is the number of measurements performed. Each λ is suggested to be an
meas i,j
averaged value from the wavelength meter. Calculate the wavelength deviation:
D
λ
j
(2)
D = λ −λ
λ TLS j meas j
j
whereλ is the tuned wavelength of the TLS.
TLS j
d) Calculate the standard deviation for λ from the (m) wavelength measurement results:
j
λ
meas i,j
(3)
m
  2
s =  (λ −λ ) 
λ meas i,j meas j
∑
j
m−1
 
 i=1 
e) Calculate the wavelength tuning repeatability: S
rep,λ
j
(4)
S = 2× s
rep,λ λ
j j
This calibration procedure shall be performed for each calibration wavelength. A minimum of
10 discrete wavelengths or every 10 nm, including the first, the central and the last wavelength
of the range shall be measured.
5.2.4 Dependence on conditions
5.2.4.1 Temperature dependence (optional if known)
5.2.4.1.1 Set-up
Figure 2 shows a calibration system for temperature dependence. This calibration is performed
under the reference calibration conditions with the exception of temperature.

Optical fibre
Light source
Wavelength meter
Temperature-controlled chamber

IEC  0621/14
Figure 2 – Measurement set-up for temperature dependence
5.2.4.1.2 Calibration equipment
The calibration equipment is as follows:
a) A wavelength meter capable of detecting wavelength fluctuations at least ten times smaller
than the wavelength stability of the TLS.
b) Temperature-controlled chamber: make sure that the measurement results are immune to
the inner temperature distribution.
5.2.4.1.3 Calibration procedure for determining temperature dependence
The calibration procedure is as follows:
a) Regarding the calibration system of Figure 2, measure the nominal wavelength (j) of the
TLS at optical power P at reference conditions: λ . The wavelength used should
TLSj j,ref
possess the maximum response to temperature variations. Otherwise characterization of
several output wavelengths should be performed.
b) Measure the wavelength of the TLS at temperature (i): λ . Wavelength readings
j,Θ
i
corresponding to each temperature setting should be averaged to determine λ .
j,Θ
i
c) Calculate the relative wavelength deviation:
D = λ −λ (5)
λ j,Θ j,ref
j,Θ i
i
d) Repeat steps 2 and 3 with (m) different temperature settings Θ ensuring that the
i
instrument is allowed the necessary time to eliminate sufficiently any thermal gradients.
i=m i=m
e) Calculate the maximum ( ) and minimum ( ) wavelength
max D min D
λ λ
j,Θ j,Θ
i i
i=1 i=1
deviations.
f) The standard uncertainty for wavelength temperature dependence u at the calibration
λ
j,ΔΘ
wavelength (j) using a rectangular distribution model is
i=m i=m
1  
u = max(D ) − min(D ) (6)
λ  λ λ 
j,ΔΘ j,Θ j,Θ
i i
i=1 i=1
2 3
 
where ΔΘ is the temperature variation.
It is recommended that a wavelength acquisition be performed with the optical wavelength
meter for the duration of this calibration.

– 14 – IEC 62522:2014 © IEC 2014
5.2.4.2 Wavelength stability
5.2.4.2.1 Set-up
Figure 3 shows a calibration system for wavelength stability. This calibration is performed
under the reference calibration conditions with the exception of time.
Optical fibre
Light source Wavelength meter
IEC  0622/14
Figure 3 – Measurement set-up for wavelength stability
5.2.4.2.2 Calibration equipment
It is recommended to use a wavelength meter capable of detecting wavelength fluctuations at
least ten times smaller than the wavelength stability of the TLS.
5.2.4.2.3 Calibration procedure for wavelength stability
The calibration procedure is as follows:
a) Regarding the calibration system in Figure 3, the measurement is performed after the light
source is switched on and has been warmed up for some time in accordance with the
manufacturer’s instructions.
b) A specific time period (Δt), for example 10 min, must be chosen that is long enough to
permit at least 10 wavelength measurements with the reference wavelength meter (in the
case of the example, a stability over 10 min will be measured).
c) A continuous wavelength acquisition shall be performed with wavelength data and time
stamp saved to a computer compatible format.
d) Ensure to correlate (m) measurements per time period where (m > 10) and conforms
exactly to the desired time period (Δt).
e) Calculate the standard deviation of the (m) wavelength measurements corresponding to
time period (Δt)
m m
  2
1 1
u =  (λ − λ )  (7)
λ ,Δt ∑ j,t ∑ j,t
j i i
m−1 m
 
 i=1 i=1 
f) A minimum of 1 time period is required to evaluate the wavelength stability of the TLS
source. In this case the wavelength stability uncertainty becomes
S = 2× u (8)
stab,λ ,Δt λ ,Δt
j j
The wavelength of the light source should be measured more than 10 times (m times)
consecutively; at least a few measurements per minute is recommended. The time interval
between the repeated measurements should be longer than the response time of the light
source. It is preferred to calculate several time periods from the acquisition data using a sliding
window and report the maximum value.
5.2.5 Uncertainty at reference conditions
The uncertainty for the calibration wavelength (j) at reference conditions is given by

  2
s
λ
 j 
2 2 2 2
u = + u + u + u + u (9)
λ λ ,ΔΘ λ ,Δt λ ,res WM
 
j,ref j j j λ
j
m
 
 
where and are evaluated for the reference conditions as defined in 5.2.4,
u u u
λ ,ΔΘ λ ,Δt λ ,res
j j j
is the uncertainty of wavelength resolution defined by is wavelength
u = dλ / 2 3 (dλ
λ ,res j j
j
resolution of the wavelength meter) and u is the uncertainty of the wavelength meter at
WM
λ
j
wavelength (j) as described in its certification.
The expanded uncertainty for the calibration wavelength (j) at reference conditions: U with
λ
j,ref
a coverage factor k is expressed as follows:
U = ±ku (10)
λ λ
j,ref j,ref
where k corresponds to an appropriate level of confidence as described in Clause A.5.
If the wavelength has to be corrected based on the results of the calibration results, the
corrections are normally implemented by making software corrections to the instrument,
mathematical corrections to the results or hardware adjustments on the instrument. Once the
adjustments are made, it is advisable to repeat the calibrations to verify that the corrections are
correct.
5.3 Wavelength calibration at operating conditions
5.3.1 General
Perform the calibration procedure when the light source is used beyond the reference
conditions.
The individual factors in wavelength uncertainty at operating conditions consist of following:
a) optical power dependence;
b) temperature dependence;
c) wavelength stability.
5.3.2 Optical power dependence
5.3.2.1 General
Figure 4 shows a calibration system for optical power dependence. This calibration should be
performed under the reference calibration conditions with the exception of the optical power. It
shall be performed after the optical power calibration (6.2.3).
Optical fibre
Wavelength meter
Light source
IEC  0623/14
Figure 4 – Measurement set-up for optical power dependence

– 16 – IEC 62522:2014 © IEC 2014
5.3.2.2 Calibration equipment
The calibration equipment is as follows:
– A wavelength meter capable of detecting wavelength fluctuations at least ten times smaller
than the wavelength stability of the TLS.
5.3.2.3 Calibration procedures for determining power dependence
The calibration procedures are as follows:
a) The wavelength (j) is measured at m optical powers (more than 5) of the light source,
P including the upper and lower limits of the specified power range. The interval
TLS i, j
between these neighbouring levels should be smaller than 10 dB.
b) Regarding the calibration system of Figure 4, the set wavelength of the light source is given
by λ , and the instrument reading of the wavelength meter is given by λ .
TLS i, j P
i , j
c) Record the measured wavelengthλ for all (m) output power settings P used.
P
TLS i, j
i, j
d) Calculate the standard uncertainty of wavelength (j) due to TLS output optical power
according to
m m
 
1 1
u =  (λ − λ )  (11)
λ ∑ P ∑ P
j,P i, j i, j
m − 1 m
 
 i=1 i=1 
5.3.3 Uncertainty at operating conditions
The uncertainty for the calibration wavelength (j) for any operating conditions is given by
 2 2 2 2 2 2 2
u = s + u + u + u + u + u (12)
 
λ λ λ ,P λ ,ΔΘ λ ,Δt λ ,res WM
j,op j j j j j λ
j
 
where u , u and u are evaluated for the operating conditions, u is the
λ ,P λ ,ΔΘ λ ,Δt λ ,res
j j j j
uncertainty of wavelength resolution defined by u = dλ / 2 3 (dλ is wavelength resolution
λ ,res j j
j
of the wavelength meter) and u is the uncertainty of the wavelength meter at wavelength
WM
λ
j
(j) as described in its certification.
The expanded uncertainty for the calibration wavelength (j) under all operating conditions:
U with a coverage factor k is expressed as follows:
λ
j ,op
U = ±ku (13)
λ λ
j,op j,op
where k corresponds to an appropriate level of confidence as described in Clause A.5.
6 Optical power calibration
6.1 Overview
The factors making up the uncertainty in the set optical power of the light source under
calibration consists of
a) the intrinsic uncertainty of the light source under calibration as found in the calibration at
reference conditions including temperature, time and connection repeatability/
reproducibility dependences for these tight conditions, and
b) the uncertainties due to dependences on wavelength, temperature, time and connection
repeatability/reproducibility, as found in the calibrations at broader operating conditions.
The optical power calibration at reference conditions as described in 6.2 is mandatory. The
calibration at operating conditions, described in 6.3, is optional.
6.2 Optical power calibration at reference conditions
6.2.1 Set-up
Figure 5 shows a system for the calibration of the optical power. The calibration is performed
under the given reference cond
...