IEC TS 62129-3:2014

Calibration of wavelength/optical frequency measurement instruments - Part 3: Optical frequency meters using optical frequency combs

IEC TS 62129-3:2014, which is a technical specification, describes the calibration of optical frequency meters. It is applicable to instruments measuring the optical frequency emitted from sources that are typical for the fibre-optic communications industry. It is assumed that the optical radiation will be coupled to the optical frequency meter by a single-mode optical fibre. Keywords: calibration of optical frequency meters, single-mode optical fibre

General Information

• Status: Replaced
• Publication Date: 11-Feb-2014
• ICS: 33.180.30 - Optic amplifiers
• Technical Committee: TC 86 - Fibre optics
• Drafting Committee: WG 4 - TC 86/WG 4
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 20-May-2019

Relations

• Revised: IEC 62129-3:2019 - Calibration of wavelength/optical frequency measurement instruments - Part 3:Optical frequency meters internally referenced to a frequency comb
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC TS 62129-3


®


Edition 1.0 2014-02



TECHNICAL



SPECIFICATION




colour
inside


Calibration of wavelength/optical frequency measurement instruments –
Part 3: Optical frequency meters using optical frequency combs



IEC TS 62129-3:2014-02(EN)

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IEC TS 62129-3



®



Edition 1.0 2014-02







TECHNICAL





SPECIFICATION











colour

inside










Calibration of wavelength/optical frequency measurement instruments –

Part 3: Optical frequency meters using optical frequency combs



























INTERNATIONAL

ELECTROTECHNICAL

COMMISSION

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R




ICS 33.180.30 ISBN 978-2-8322-1421-3



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® Registered trademark of the International Electrotechnical Commission

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– 2 – TS 62129-3 © IEC:2014(E)


CONTENTS


FOREWORD . 3

INTRODUCTION . 5


1 Scope . 6

2 Normative references . 6

3 Terms and definitions . 6

4 Calibration test requirements . 7

4.1 Preparation . 7

4.2 Reference test conditions . 8
4.3 Traceability . 8
4.3.1 General . 8
4.3.2 National standard . 8
4.3.3 Transfer standard . 9
4.3.4 Working standard . 9
5 Optical frequency calibration . 9
5.1 General . 9
5.2 Establishing the calibration conditions . 11
5.3 Calibration procedure. 11
5.3.1 General . 11
5.3.2 Measurement configuration . 11
5.3.3 Detailed procedure . 13
5.4 Calibration uncertainty . 13
5.5 Reporting the results . 13
Annex A (normative) Mathematical basis . 14
A.1 General . 14
A.2 Type A evaluation of uncertainty . 14
A.3 Type B evaluation of uncertainty . 15
A.4 Determining the combined standard uncertainty . 15
A.5 Reporting . 16
Annex B (informative) References of optical frequency comb source . 17
B.1 Method A (mode-locked fibre laser + carrier-envelope phase lock) . 17
B.2 Method B (stabilized laser + electro-optical modulator) . 17
B.3 Method C (stabilized laser + supercontinuum source) . 18

Annex C (informative) Frequency-dependence of uncertainty . 19
Bibliography . 20

Figure 1 – Traceability chain using optical frequency measurement scheme . 9
Figure 2 – Schematic configuration of optical frequency measurement technique that
uses optical comb . 10
Figure 3 – Optical spectra of lasers and optical frequency combs . 11
Figure 4 – Optical frequency meter measurement using a reference source . 12
Figure 5 – Optical frequency meter measurement using a reference optical frequency
meter . 12
Figure B.1 – Mode-locked laser + nonlinear optical effect . 17
Figure B.2 – Electro-optical modulator type comb source . 18
Figure B.3 – Supercontinuum source . 18

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TS 62129-3 © IEC:2014(E) – 3 –





INTERNATIONAL ELECTROTECHNICAL COMMISSION


____________



CALIBRATION OF WAVELENGTH/OPTICAL

FREQUENCY MEASUREMENT INSTRUMENTS –



Part 3: Optical frequency meters using optical frequency combs


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC/TS 62129-3, which is a technical specification, has been prepared by IEC technical
committee 86: Fibre optics.

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– 4 – TS 62129-3 © IEC:2014(E)


The text of this technical specification is based on the following documents:


Enquiry draft Report on voting


86/461/DTS 86/465/RVC



Full information on the voting for the approval of this technical specification 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.


A list of all parts in the IEC 62129 series, published under the general title Calibration of
wavelength/optical frequency measurement instruments, can be found on the IEC website.
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
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

A bilingual version of this publication may be issued at a later date.

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.

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TS 62129-3 © IEC:2014(E) – 5 –


INTRODUCTION


It is essential for realizing fibre optic systems that optical channels are defined in the optical

frequency domain, not the wavelength domain. One example, the anchor frequency of the

ITU-T grid is 193,1 THz, and the channel spacings of the ITU-T grid are 12,5 GHz, 25 GHz,

1
50 GHz, and 100 GHz [2] .


ITU-T has also discussed λ-interface systems such as “black link” [3]. “Black link” includes

WDM MUX/DEMUX and a transmission fibre, and provides λ-interfaces. Especially in DWDM

systems (channel spacing <100 GHz), the uncertainty in specifying optical frequency needs to

be minimized.

To implement future telecom systems, it is expected that optical frequency measurements will
need to be extremely precise. For example, to achieve the channel spacing of 25 GHz, signal
optical frequency uncertainty (Uf ) and required measurement uncertainty (Uf ) need to
sig meas
–5 –6 –6
be 2 GHz to 200 MHz (Uf / f = 10 to 10 ) and 200 MHz to 2 MHz (Uf / f = 10 to
sig meas
–8
10 ), respectively. Unfortunately, conventional wavelength meters have measurement
–6 –7
uncertainties of 10 to 10 . The solution is to use optical frequency measurements since
–15 –16
measurement uncertainties can be as small as 10 to 10 , which satisfies the above
–6 –8
telecom requirement (Uf / f = 10 to 10 ). Therefore, an optical frequency
meas
measurement scheme is necessary for the calibration of future telecom systems.
Optical frequency measurement technology is progressing rapidly. Many fundamental papers
have examined the use of equally-spaced “optical frequency comb” lines (spacing of up to
50 GHz) from an optical frequency comb as a “ruler” for optical frequency measurement [4-15].
For example, mode-locked lasers with carrier-envelope phase locked enable ultra-low
–15 –16
measurement uncertainties of 10 to 10 . Some examples of practical optical frequency
combs are shown in Annex B (mode-locked fibre laser + carrier-envelope phase lock,
stabilized laser + electro-optical modulator, and stabilized laser + supercontinuum source).
Frequency measurements provide more accurate values than interferometric wavelength
measurements in air by eliminating the effects of refractive indices. Furthermore, they allow
the measurement devices to be significantly smaller than wavelength meters.

___________
1
Numbers between square brackets refer to the Bibliography.

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CALIBRATION OF WAVELENGTH/OPTICAL

FREQUENCY MEASUREMENT INSTRUMENTS –



Part 3: Optical frequency meters using optical frequency combs








1 Scope


This part of IEC 62129, which is a technical specification, describes the calibration of optical
frequency meters. It is applicable to instruments measuring the optical frequency emitted from
sources that are typical for the fibre-optic communications industry. It is assumed that the
optical radiation will be coupled to the optical frequency meter by a single-mode optical fibre.
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/TR 61931, Fibre optic – Terminology
ISO/IEC 98-3, Uncertainty of measurement – Part 3: Guide to the expression of uncertainty in
measurement (GUM:1995)
ISO/IEC 17025:2005, General requirements for the competence of testing and calibration
laboratories
3 Terms and definitions

For the purposes of this document, the terms and definitions contained in IEC/TR 61931, as
well as the following terms and definitions, apply.
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
measurement standards
3.2
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

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TS 62129-3 © IEC:2014(E) – 7 –


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.


[SOURCE: ISO/IEC Guide 99:2007, 2.39, modified] [16]


3.3

national (measurement) standard

measurement standard recognized by a national decision to serve, in a country, as the basis
for assigning values to other measurement standards of the quantity concerned
[SOURCE: ISO/IEC Guide 99:2007, 5.3 modified]
3.4
national standards laboratory
laboratory which maintains the national measurement standard
3.5
reference standard
measurement standard, generally having the highest metrological quality available at a given
location or in a given organization, from which measurements made there are derived
[SOURCE: ISO/IEC Guide 99:2007, 5.6 modified]
3.6
traceability
property of the result of a measurement or the value of a measurement standard whereby it
can be related to stated references, usually national or international measurement standards,
through an unbroken chain of comparisons all having stated uncertainties
[SOURCE: ISO/IEC Guide 99:2007, 2.41 modified]
3.7
traceability chain
unbroken chain of comparison
[SOURCE: ISO/IEC Guide 99:2007, 2.42 modified]

3.8
working standard
measurement 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.
[SOURCE: ISO/IEC Guide 99:2007, 5.7 modified]
4 Calibration test requirements
4.1 Preparation
The following recommendations apply.
The calibration laboratory should satisfy requirements of ISO/IEC 17025.

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– 8 – TS 62129-3 © IEC:2014(E)


There should be a documented measurement procedure for each type of calibration

performed, giving step-by-step operating instructions and equipment to be used.


The environmental conditions shall be commensurate with the degree of uncertainty that is

required for calibration:


a) the environment shall be clean;

b) temperature monitoring and control is required;

c) all laser sources shall be safely operated (refer to IEC 60825-1).


Perform all tests at an ambient room temperature of 23 °C ± 3 °C with a relative humidity of

(50 ± 20) % unless otherwise specified. Give the test equipment a minimum of 2 h prior to
testing to reach equilibrium with its environment. Allow the optical frequency meter a warm-up
period in accordance with the manufacturer’s instructions.
4.2 Reference test conditions
The reference test conditions usually include the following parameters and, if necessary, their
tolerance bands: date, temperature, relative humidity, displayed power level, displayed optical
frequency, fibre, connector-adapter combination, (spectral) bandwidth and resolution
bandwidth (spectral resolution) set. Unless otherwise specified, use a single-mode optical
fibre input pigtail as prescribed by IEC 60793-2-50, having a length of at least 2 m.
Operate the optical frequency meter in accordance with the manufacturer’s specifications and
operating procedures. Where practical, select a range of test conditions and parameters
which emulate the actual field operating conditions of the optical frequency meter under test.
Choose these parameters so as to optimize the optical frequency meter’s uncertainties, as
specified by the manufacturer’s operating procedures.
Because of the potential for hazardous radiation, be sure to establish and maintain conditions
of laser safety. Refer to IEC 60825-1 and IEC 60825-2.
NOTE The calibration results only apply to the set of test conditions used in the calibration process.
4.3 Traceability
4.3.1 General
The requirements of ISO/IEC 17025 should be met.
Make sure that any test equipment which has a significant influence on the calibration results
is calibrated in an unbroken chain to the appropriate national standard or natural physical

constant. Upon request, specify this test equipment and its calibration chain(s). The
recalibration period(s) shall be defined and documented.
Figure 1 shows an example of a traceability chain using the frequency comb. It consists of a
national standard, transfer standard, and working standard. The traceability chain can provide
optical frequency standards suitable for the telecom region.
4.3.2 National standard
The national standard of optical frequency (or wavelength) can be realized by using the
combination of UTC(k) (universal time, coordinated) and an optical frequency comb, for
example, described in 5.1. The optical frequency comb generates an optical frequency comb
with fixed, uniform spacing.
By using the optical frequency measurement technique shown in 5.1, uncertainty can be held
–15
to the standard frequency limited by the time base (up to 10 ) throughout the whole span of
the comb.

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TS 62129-3 © IEC:2014(E) – 9 –


4.3.3 Transfer standard


A stabilized laser can be utilized as the transfer standard which is generally utilized between

an accredited calibration laboratory and a calibration laboratory of company.


4.3.4 Working standard

The working standard is composed of a stabilized laser, and an optical frequency comb in
each calibration laboratory. As the optical frequency comb, mode-locked lasers, electro-

optical modulators or supercontinuum sources shown in Annex B can be used as they offer

–9
low uncertainty down to 10 .


UTC (k) Optical frequency
National Standard
Time base comb
Stabilized Transfer Standard
laser
Stabilized
Optical frequency
Working Standard
laser
meter
Test meter Test meter
IEC  0578/14

Figure 1 – Traceability chain using optical frequency measurement scheme
5 Optical frequency calibration
5.1 General
For optical frequency measurement, equally-spaced “frequency comb” lines (spacing of up to
50 GHz) from an optical frequency comb are utilized as a “ruler” for optical frequency
measurement [4 – 15]. Optical frequency measurements provide more accurate calibration

than interferometric wavelength measurements in air by eliminating the effects of refractive
indices.
Some examples of practical optical frequency comb are shown in Clause 5.
Figure 2 is the schematic configuration of an optical frequency measurement technique that uses optical frequency
combs. f (comb spacing) comb spacing
f (beat) beat frequency
f (N) optical frequency of
f (CEO) carrier envelope offset frequency
Figure 3 shows the optical spectrum of the laser and the optical frequency comb. The optical frequency comb
generates an optical frequency comb with uniform spacing (f (comb spacing)) which is equal to the electrical clock
frequency driving the optical frequency comb. f(comb spacing) is also equal to the pulse repetition rate. Thus, the
uncertainty of comb spacing based on that of the electrical clock. The comb spacing generally lies between 100
MHz and 25 GHz. In this case, the stabilized laser (f(stabilized laser)) output is combined with the optical
frequency comb, and then these two lights are input to an optical-electrical (O/E) converter. The beat frequency (f
(beat)) between the two lights is taken as the output of the O/E converter. Optical frequency (f(stabilized laser)) of
the stabilized laser can be calculated by the following equation (see f (comb spacing) comb spacing

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– 10 – TS 62129-3 © IEC:2014(E)


f (beat) beat frequency

f (N) optical frequency of

f (CEO) carrier envelope offset frequency


Figure 3):


f(stabilized laser)= f(N)± f(beat) (1)


Here, f(N) is the optical frequency of the N-th mode of optical frequency comb, and is the

summation of f(comb spacing) and the carrier envelope offset frequency f(CEO), as shown in

the following equation

( ) ( ) ( ) (2)
f N = N× f comb spacing + f CEO
Here, N is the large integer, and can be obtained by wavelength meter. The sign before the
beat frequency (+ or –) can be deduced by changing f(stabilized laser) slightly. f(CEO) is
related to the pulse-to-pulse phase shift, ∆φ, between the peak of electrical field and the peak
of envelope [5].
f(CEO)=(∆φ 2π) f(comb spacing) (3)

Optical frequency
Electrical Optical
O/E Frequency
clock comb source
converter counter
Stabilized
laser
Optical frequency
IEC  0579/14

Figure 2 – Schematic configuration of optical frequency
measurement technique that uses optical comb

f (beat)
f (comb spacing)
f (CEO) f (stabilized laser)
0 1 2
N−2 N−1 N N+1 N+2
f
f (N)
IEC  0580/14

Key
f optical frequency
f (stabilized laser) stabilized laser frequency

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TS 62129-3 © IEC:2014(E) – 11 –


f (comb spacing) comb spacing

f (beat) beat frequency

f (N) optical frequency of

f (CEO) carrier envelope offset frequency

Figure 3 – Optical spectra of lasers and optical frequency combs


5.2 Establishing the calibration conditions


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 ± 3 °C. The temperature
may need to be monitored continuously to ensure that it remains within the prescribed
limits,
c) the ambient r
...