IEC 61280-1-3:2021

Fibre optic communication subsystem test procedures - Part 1-3: General communication subsystems - Measurement of central wavelength, spectral width and additional spectral characteristics

IEC 61280-1-3:2021 provides definitions and measurement procedures for several wavelength and spectral width properties of an optical spectrum associated with a fibre optic communication subsystem, an optical transmitter, or other light sources used in the operation or test of communication subsystems. This document also provides definitions and measurement procedures for side-mode suppression ratio and signal-to-source spontaneous emission ratio. The measurement is done for the purpose of system construction and/or maintenance. In the case of communication subsystem signals, the optical transmitter is typically under modulation. NOTE Different properties can be appropriate to different spectral types, such as continuous spectra characteristics of light-emitting diodes (LEDs), as well as multilongitudinal-mode (MLM), multitransverse-mode (MTM) and single-longitudinal mode (SLM) spectra, which are characteristic of laser diodes (LDs). This third edition cancels and replaces the second edition published in 2010. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- addition of measurement of signal-to-source spontaneous emission ratio in 8.9;
- change of document title to reflect the additional measurement;
- additional information on the resolution bandwidth used in the measurement of the side-mode suppression ratio in 8.8;
- use of a calibrated optical wavelength meter for accurate wavelength measurements of single-longitudinal mode lasers.

Procédures d'essai des sous-systèmes de télécommunication fibroniques - Partie 1-3: Sous-systèmes généraux de télécommunication - Mesure de la longueur d'onde centrale, de la largeur spectrale et des caractéristiques spectrales supplémentaires

IEC 61280-1-3:2021 fournit des définitions et des procédures de mesure pour plusieurs propriétés de longueur d’onde et de largeur spectrale d’un spectre optique associées à un sous-système de télécommunication fibronique, un émetteur optique ou d’autres sources de lumière utilisées pour l’exploitation ou les essais des sous-systèmes de télécommunication. Le présent document fournit également des définitions et des procédures de mesure du rapport de suppression des modes latéraux et du taux d’émission spontanée entre signal et source. Le mesurage est effectué pour les besoins de la construction et/ou de la maintenance d'un système. Dans le cas des signaux dans les sous-systèmes de télécommunication, l’émetteur optique fonctionne généralement en modulation. NOTE Des propriétés différentes peuvent être appropriées pour des types de spectres différents, telles que les caractéristiques spectrales continues des diodes électroluminescentes (LED), les spectres de mode multilongitudinal (MLM), de mode multitransversal (MTM) et unimodal longitudinal (SLM), qui sont caractéristiques des diodes lasers (LD).
Cette troisième édition annule et remplace la deuxième édition parue en 2010. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- ajout du mesurage du taux d’émission spontanée entre signal et source en 8.9;
- modification du titre du document pour tenir compte du mesurage supplémentaire;
- information supplémentaire relative à la résolution spectrale utilisée pour le mesurage du rapport de suppression des modes latéraux en 8.8;
- utilisation d'un appareil optique de mesure de longueur d'onde étalonné pour des mesurages précis de longueur d'onde des lasers unimodaux longitudinaux.

General Information

• Status: Published
• Publication Date: 04-Jul-2021
• ICS: 33.180.01 - Fibre optic systems in general
• Technical Committee: SC 86C - Fibre optic systems, sensing and active devices
• Drafting Committee: WG 1 - TC 86/SC 86C/WG 1
• Current Stage: PPUB - Publication issued
• Start Date: 05-Jul-2021
• Completion Date: 29-Jul-2021

Relations

• Revises: IEC 61280-1-3:2010 - Fibre optic communication subsystem test procedures - Part 1-3: General communication subsystems - Central wavelength and spectral width measurement
• Effective Date: 05-Sep-2023

Overview

IEC 61280-1-3:2021 is part of the IEC 61280 series of fibre optic communication subsystem test procedures. This international standard defines terms and measurement procedures for central wavelength, spectral width and other spectral characteristics of optical spectra used in fibre optic communication subsystems. It covers measurements for transmitters and light sources used during system construction and maintenance, typically with the optical transmitter under modulation.

Key additions in the 2021 (3rd) edition include:

• Measurement of signal-to-source spontaneous emission ratio (SSER)
• Updated title reflecting the additional measurement
• Guidance on resolution bandwidth (RBW) for side-mode suppression ratio (SMSR) measurements
• Use of a calibrated optical wavelength meter (OWM) for accurate single-longitudinal-mode (SLM) laser wavelength measurements

Key topics and technical requirements

• Definitions: centre wavelength, peak wavelength, centroidal wavelength, half-power wavelength, and related spectral terms.
• Spectral width metrics: RMS spectral width, n-dB-down spectral width, full-width at half-maximum (FWHM) and other standardized ways to quantify spectral width.
• Additional spectral characteristics: Side-Mode Suppression Ratio (SMSR) and Signal-to-Source Spontaneous Emission Ratio (SSER).
• Measurement apparatus: calibrated Optical Spectrum Analyzer (OSA), calibrated Optical Wavelength Meter (OWM), power supplies, modulators/input signal sources, and test cords.
• Procedures: two main measurement procedures (Method A and Method B) with guidance on setup, spectrum analyzer control settings, and wavelength meter settings.
• Spectral types addressed: continuous spectra (e.g., LEDs), multilongitudinal-mode (MLM), multitransverse-mode (MTM) and single-longitudinal-mode (SLM) laser spectra.
• Normative references: safety and calibration standards such as IEC 60825-1, IEC 62129-1 and IEC 62129-2.

Practical applications and users

IEC 61280-1-3:2021 is applicable for:

• Fibre optic system engineers and designers performing transmitter characterization
• Test laboratories and quality assurance teams verifying central wavelength and spectral width for compliance
• Manufacturers of LEDs and laser diodes (LDs) preparing product datasheets and acceptance tests
• Field technicians and maintenance teams conducting system construction, installation verification and troubleshooting
• Calibration facilities using calibrated OSA/OWM for precision wavelength and spectral measurements

Practical outcomes include reliable specification of central wavelength and spectral width for link design, verification of transmitter behavior under modulation, and standardized reporting of SMSR and SSER for laser sources.

Related standards

• IEC 60825-1 - Safety of laser products
• IEC 62129-1 - Calibration of optical spectrum analyzers
• IEC 62129-2 - Calibration of Michelson interferometer wavelength meters

Keywords: IEC 61280-1-3, central wavelength, spectral width, SMSR, SSER, optical spectrum analyzer, optical wavelength meter, LED spectrum, SLM, MLM, fibre optic test procedures.

Standards Content (Sample)

IEC 61280-1-3 ®
Edition 3.0 2021-07
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures –
Part 1-3: General communication subsystems – Measurement of central
wavelength, spectral width and additional spectral characteristics
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
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copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
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About the IEC
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IEC 61280-1-3 ®
Edition 3.0 2021-07
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures –

Part 1-3: General communication subsystems – Measurement of central

wavelength, spectral width and additional spectral characteristics

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.01 ISBN 978-2-8322-9954-8

– 2 – IEC 61280-1-3:2021 © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviated terms . 6
3.1 Wavelength . 6
3.2 Spectral width . 7
3.3 Additional spectral characteristics . 7
3.4 Abbreviated terms . 8
4 Apparatus . 8
4.1 Calibrated optical spectrum analyzer (OSA) . 8
4.2 Calibrated optical wavelength meter (OWM) . 8
4.3 Power supplies . 9
4.4 Input signal source or modulator . 9
4.5 Test cord . 9
5 Test sample . 9
6 Procedure (method A) . 9
6.1 General . 9
6.2 Setup . 10
6.3 Adjustment of spectrum analyzer controls . 10
6.4 Setting of optical wavelength meter. 11
7 Procedure (method B) . 11
7.1 Setup . 11
7.2 Adjustment of spectrum analyzer controls . 11
7.3 Setting of optical wavelength meter. 11
7.4 Continuous LED and SLM spectra . 12
7.5 Discrete MLM spectra . 12
7.6 SLM spectra. 12
8 Calculation . 13
8.1 General . 13
8.2 Centre wavelength . 13
8.2.1 Continuous LED spectra . 13
8.2.2 Discrete MLM spectra . 13
8.3 Centroidal wavelength . 13
8.4 Peak wavelength . 14
8.4.1 Continuous LED and SLM spectra . 14
8.4.2 Discrete MLM spectra . 14
8.5 RMS spectral width (Δλ ) . 14
rms
8.6 n-dB-down spectral width (Δλ ) . 14
n-dB
8.7 Full-width at half-maximum spectral width (Δλ ) . 14
fwhm
8.7.1 Continuous LED spectra . 14
8.7.2 Discrete MLM spectra . 15
8.8 Side-mode suppression ratio (SMSR) . 15
8.9 Signal-to-source spontaneous emission ratio (SSER) . 15
9 Test results . 15
9.1 Required information . 15

9.2 Information to be available on request . 16
10 Examples of results . 16
Bibliography . 21

Figure 1 – Example of a LED optical spectrum . 16
Figure 2 – Typical spectrum analyzer output for MLM laser . 18
Figure 3 – Δλ spectral width measurement for MLM laser. 18
fwhm
Figure 4 – Δλ spectral width calculation for MLM laser . 19
fwhm
Figure 5 – Peak emission wavelength and Δλ measurement for SLM laser . 19
30-dB
Figure 6 – Resolution bandwidth (RBW) dependence of SMSR for SLM laser . 20
Figure 7 – Signal-to-source spontaneous emission ratio measurement for SLM laser . 20

Table 1 – Measurement points for LED spectrum from Figure 1 . 17
Table 2 – RMS spectral characterization . 17

– 4 – IEC 61280-1-3:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 1-3: General communication subsystems – Measurement of central
wavelength, spectral width and additional spectral characteristics

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.
IEC 61280-1-3 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is an International Standard.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of measurement of signal-to-source spontaneous emission ratio in 8.9;
b) change of document title to reflect the additional measurement;
c) additional information on the resolution bandwidth used in the measurement of the side-
mode suppression ratio in 8.8;
d) use of a calibrated optical wavelength meter for accurate wavelength measurements of
single-longitudinal mode lasers.

The text of this International Standard is based on the following documents:
Draft Report on voting
86C/1701/CDV 86C/1717/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 61280 series, published under the general title Fibre optic
communication subsystem test procedures, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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 document 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 61280-1-3:2021 © IEC 2021
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 1-3: General communication subsystems – Measurement of central
wavelength, spectral width and additional spectral characteristics

1 Scope
This part of IEC 61280 provides definitions and measurement procedures for several
wavelength and spectral width properties of an optical spectrum associated with a fibre optic
communication subsystem, an optical transmitter, or other light sources used in the operation
or test of communication subsystems. This document also provides definitions and
measurement procedures for side-mode suppression ratio and signal-to-source spontaneous
emission ratio.
The measurement is done for the purpose of system construction and/or maintenance. In the
case of communication subsystem signals, the optical transmitter is typically under
modulation.
NOTE Different properties can be appropriate to different spectral types, such as continuous spectra
characteristics of light-emitting diodes (LEDs), as well as multilongitudinal-mode (MLM), multitransverse-mode
(MTM) and single-longitudinal mode (SLM) spectra, which are characteristic of laser diodes (LDs).
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 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 62129-1, Calibration of wavelength/optical frequency measurement instruments – Part 1:
Optical spectrum analyzers
IEC 62129-2, Calibration of wavelength/optical frequency measurement instruments – Part 2:
Michelson interferometer single wavelength meters
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms, definitions and abbreviated terms
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 Wavelength
NOTE The following wavelength terms provide quantitative definitions for the description of the central
wavelength of a spectrum. In this document, "central wavelength" is a general category label for these terms.

3.1.1
centre wavelength
λ
mean of the closest spaced half-power wavelengths in an optical spectrum, one above and
one below the peak wavelength
Note 1 to entry: Centre wavelength is also called “half-power mid-point”.
3.1.2
half-power wavelength
λ
3dB
wavelength corresponding to a half-peak power value of the optical spectrum
3.1.3
peak wavelength
λ
p
wavelength corresponding to the maximum power value of the optical spectrum
3.1.4
centroidal wavelength
λ
c
mean or average wavelength of an optical spectrum
3.2 Spectral width
3.2.1
RMS spectral width
Δλ
rms
square root of the second moment of the power distribution about the centroidal wavelength
3.2.2
n-dB-down spectral width
Δλ
n-dB
positive difference of the closest spaced wavelengths, one above and one below the peak
wavelength λ , at which the spectral power density determined in a specified resolution
p
bandwidth is n dB down from its peak value
3.2.3
full-width at half-maximum
Δλ
fwhm
positive difference of the closest spaced wavelengths, one above and one below the peak
, at which the spectral power density determined in a specified resolution
wavelength λ
p
bandwidth is 3 dB down from its peak value
3.3 Additional spectral characteristics
3.3.1
side-mode suppression ratio
SMSR
ratio of the largest peak of the optical spectrum to the second largest peak under non-
modulated (continuous wave) operating condition, which is determined in a specified
wavelength resolution bandwidth (RBW), for a nominally single-longitudinal mode (SLM)
spectrum
Note 1 to entry: See 8.8.
– 8 – IEC 61280-1-3:2021 © IEC 2021
3.3.2
signal-to-source spontaneous emission ratio
SSER
ratio between the signal power and maximum source spontaneous emission (SSE) power
under the non-modulated (CW) condition which is determined in a specified bandwidth
3.4 Abbreviated terms
CW continuous wave
DFB distributed feedback
ESD electrostatic discharge
InGaAsP  indium gallium arsenide phosphide
LD  laser diode
LED light-emitting diode
MLM multi-longitudinal mode
MTM multi-transverse mode
OSA optical spectrum analyzer
OWM optical wavelength meter
RBW resolution bandwidth
RMS root-mean-square
SLM single-longitudinal mode
SMSR side-mode suppression ratio
SSE source spontaneous emission
SSER signal-to-source spontaneous emission ratio
TLA tuneable laser assembly
VCSEL vertical cavity surface emitting lasers
WDM wavelength-division multiplexing
4 Apparatus
4.1 Calibrated optical spectrum analyzer (OSA)
This special-purpose test equipment uses a dispersive spectrophotometric method to resolve
and record the optical spectral distribution. The required wavelength resolution bandwidth and
range depend on the type and variety of signals to be measured. Generally, LED sources
have wide spectra with little structure, so a range of at least 200 nm and resolution bandwidth
of 1 nm or narrower are recommended. Laser sources have much narrower spectra and can
be used in wavelength-division multiplexing (WDM) applications, where more accurate
determination of the wavelength is required. A resolution bandwidth of 0,1 nm or narrower is
recommended, and the actual requirement is determined by the application. In any case, the
sensitivity and wavelength range of the spectrum analyzer shall be sufficient to measure all of
the spectrum within at least −20 dB from the peak power. For measurement of SMSR, a larger
dynamic range is typically required.
OSA equipment shall be calibrated for vacuum wavelengths in order to be consistent with the
calibration processes and results of IEC 62129-1. The equipment used shall have a valid
calibration certificate, in accordance with the applicable quality system for the period over
which the testing is done.
4.2 Calibrated optical wavelength meter (OWM)
For central wavelength measurements of SLM lasers, such as distributed feedback (DFB)
lasers or tuneable laser assemblies (TLAs) for dense WDM applications, sufficient

measurement accuracy is required. In this case, an optical wavelength meter based on
interferometric spectroscopy can be used. The accuracy of the central wavelength
measurement is generally specified for non-modulated (CW) lasers. When the SLM laser is
modulated, the uncertainty of the central wavelength measurement increases with the
increasing modulation frequency or symbol rate.
OWM equipment shall be calibrated in accordance with IEC 62129-2. The equipment used
shall have a v
...

IEC 61280-1-3 ®
Edition 3.0 2021-07
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures –
Part 1-3: General communication subsystems – Central wavelength and spectral
width measurement Measurement of central wavelength, spectral width and
additional spectral characteristics

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.: [phone]
3, rue de Varembé [e-mail]
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 IEC online collection - oc.iec.ch
The advanced search enables to find IEC publications by a Discover our powerful search engine and read freely all the
variety of criteria (reference number, text, technical publications previews. With a subscription you will always
committee, …). It also gives information on projects, replaced have access to up to date content tailored to your needs.
and withdrawn publications.
Electropedia - www.electropedia.org
IEC Just Published - webstore.iec.ch/justpublished
The world's leading online dictionary on electrotechnology,
Stay up to date on all new IEC publications. Just Published
containing more than 22 000 terminological entries in English
details all new publications released. Available online and
and French, with equivalent terms in 18 additional languages.
once a month by email.
Also known as the International Electrotechnical Vocabulary

(IEV) online.
IEC Customer Service Centre - webstore.iec.ch/csc

If you wish to give us your feedback on this publication or
need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC 61280-1-3 ®
Edition 3.0 2021-07
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures –
Part 1-3: General communication subsystems – Central wavelength and spectral
width measurement Measurement of central wavelength, spectral width and
additional spectral characteristics
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.01 ISBN 978-2-8322-4937-6
– 2 – IEC 61280-1-3:2021 RLV © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviated terms . 6
3.1 Wavelength . 6
3.2 Spectral width . 7
3.3 Additional spectral characteristics . 7
3.4 Abbreviated terms . 8
4 Apparatus . 8
4.1 Calibrated optical spectrum analyzer (OSA) . 8
4.2 Calibrated optical wavelength meter (OWM) . 8
4.3 Power supplies . 9
4.4 Input signal source or modulator . 9
4.5 Test cord . 9
5 Test sample . 9
6 Procedure (method A) . 9
6.1 General . 9
6.2 Setup . 10
6.3 Adjustment of spectrum analyzer controls . 10
6.4 Setting of optical wavelength meter. 11
7 Procedure (method B) . 11
7.1 Setup . 11
7.2 Adjustment of spectrum analyzer controls . 11
7.3 Setting of optical wavelength meter. 12
7.4 Continuous LED and SLM spectra . 12
7.5 Discrete MLM spectra . 12
7.6 Continuous SLM spectra . 13
8 Calculation . 13
8.1 General . 13
8.2 Centre wavelength . 13
8.2.1 Continuous LED spectra . 13
8.2.2 Discrete MLM spectra . 13
8.3 Centroidal wavelength . 13
8.4 Peak wavelength . 14
8.4.1 Continuous LED and SLM spectra . 14
8.4.2 Discrete MLM spectra . 14
8.5 RMS spectral width (Δλ ) . 14
rms
8.6 n-dB-down spectral width (Δλ ) . 14
n-dB
8.7 Full-width at half-maximum spectral width (Δλ ) . 15
fwhm
8.7.1 Continuous LED spectra . 15
8.7.2 Discrete MLM spectra . 15
8.8 Side-mode suppression ratio (SMSR) . 15
8.9 Signal-to-source spontaneous emission ratio (SSER) . 15
9 Test results . 15
9.1 Required information . 15

9.2 Information to be available on request . 16
10 Examples of results . 16
Bibliography . 21

Figure 1 – Example of a LED optical spectrum . 16
Figure 2 – Typical spectrum analyzer output for MLM laser . 18
Figure 3 – Δλ spectral width measurement for MLM laser. 18
fwhm
Figure 4 – Δλ spectral width calculation for MLM laser . 19
fwhm
Figure 5 – Peak emission wavelength and Δλ measurement for SLM laser . 19
30-dB
Figure 6 – Resolution bandwidth (RBW) dependence of SMSR for SLM laser . 20
Figure 7 – Signal-to-source spontaneous emission ratio measurement for SLM laser . 20

Table 1 – Measurement points for LED spectrum from Figure 1 . 17
Table 2 – RMS spectral characterization . 17

– 4 – IEC 61280-1-3:2021 RLV © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 1-3: General communication subsystems – Central wavelength and
spectral width measurement Measurement of central wavelength, spectral
width and additional spectral characteristics

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.
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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 IEC 61280-1-3:2010. A vertical bar appears in the margin wherever a
change has been made. Additions are in green text, deletions are in strikethrough red text.

IEC 61280-1-3 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is an International Standard.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of measurement of signal-to-source spontaneous emission ratio in 8.9;
b) change of document title to reflect the additional measurement;
c) additional information on the resolution bandwidth used in the measurement of the side-
mode suppression ratio in 8.8;
d) use of a calibrated optical wavelength meter for accurate wavelength measurements of
single-longitudinal mode lasers.
The text of this International Standard is based on the following documents:
Draft Report on voting
86C/1701/CDV 86C/1717/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 61280 series, published under the general title Fibre optic
communication subsystem test procedures, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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 document 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 61280-1-3:2021 RLV © IEC 2021
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 1-3: General communication subsystems – Central wavelength and
spectral width measurement Measurement of central wavelength, spectral
width and additional spectral characteristics

1 Scope
This part of IEC 61280 provides definitions and measurement procedures for several
wavelength and spectral width properties of an optical spectrum associated with a fibre optic
communication subsystem, an optical transmitter, or other light sources used in the operation
or test of communication subsystems. This document also provides definitions and
measurement procedures for side-mode suppression ratio and signal-to-source spontaneous
emission ratio.
The measurement is done for the purpose of system construction and/or maintenance. In the
case of communication subsystem signals, the optical transmitter is typically under
modulation.
NOTE Different properties may can be appropriate to different spectral types, such as continuous spectra
characteristics of light-emitting diodes (LEDs), as well as multilongitudinal-mode (MLM), multitransverse-mode
(MTM) and single-longitudinal mode (SLM) spectra, which are characteristic of laser diodes (LDs).
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 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 62129-1, Calibration of wavelength/optical frequency measurement instruments – Part 1:
Optical spectrum analyzers
IEC 62129-2, Calibration of wavelength/optical frequency measurement instruments – Part 2:
Michelson interferometer single wavelength meters
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms, definitions and abbreviated terms
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 Wavelength
NOTE The following wavelength terms provide quantitative definitions for the description of the central
wavelength of a spectrum. In this document, "central wavelength" is a general category label for these terms.

3.1.1
centre wavelength
λ
mean of the closest spaced half-power wavelengths in an optical spectrum, one above and
one below the peak wavelength
Note 1 to entry: Centre wavelength is also called “half-power mid-point”.
3.1.2
half-power wavelength
λ
3dB
wavelength corresponding to a half-peak power value of the optical spectrum
3.1.3
peak wavelength
λ
p
wavelength corresponding to the maximum power value of the optical spectrum
3.1.4
centroidal wavelength
λ
c
mean or average wavelength of an optical spectrum
3.2 Spectral width
3.2.1
RMS spectral width
Δλ
rms
square root of the second moment of the power distribution about the centroidal wavelength
3.2.2
n-dB-down spectral width
Δλ
n-dB
positive difference of the closest spaced wavelengths, one above and one below the peak
wavelength λ , at which the spectral power density determined in a specified resolution
p
bandwidth is n dB down from its peak value
3.2.3
full-width at half-maximum
Δλ
fwhm
a special case of n-dB-down width with n = 3
positive difference of the closest spaced wavelengths, one above and one below the peak
wavelength λ , at which the spectral power density determined in a specified resolution
p
bandwidth is 3 dB down from its peak value
3.3 Additional spectral characteristics
3.3.1
side-mode suppression ratio
SMSR
ratio of the largest peak of the optical spectrum to the second largest peak under non-
modulated (continuous wave) operating condition, which is determined in a specified
wavelength resolution bandwidth (RBW), for a nominally single-longitudinal mode (SLM)
spectrum
Note 1 to entry: See 8.8.
– 8 – IEC 61280-1-3:2021 RLV © IEC 2021
3.3.2
signal-to-source spontaneous emission ratio
SSER
ratio between the signal power and maximum source spontaneous emission (SSE) power
under the non-modulated (CW) condition which is determined in a specified bandwidth
3.4 Abbreviated terms
CW continuous wave
DFB distributed feedback
ESD electrostatic discharge
InGaAsP  indium gallium arsenide phosphide
LD  laser diode
LED light-emitting diode
MLM multi-longitudinal mode
MTM multi-transverse mode
OSA optical spectrum analyzer
OWM optical wavelength meter
RBW resolution bandwidth
RMS root-mean-square
SLM single-longitudinal mode
SMSR side-mode suppression ratio
SSE source spontaneous emission
SSER signal-to-source spontaneous emission ratio
TLA tuneable laser assembly
VCSEL vertical cavity surface emitting lasers
WDM wavelength-division multiplexing
4 Apparatus
4.1 Calibrated optical spectrum analyzer (OSA)
This special-purpose test equipment uses a dispersive spectrophotometric method to resolve
and record the optical spectral distribution. The required wavelength resolution bandwidth and
range depend on the type and variety of signals to be measured. Generally, LED sources
have wide spectra with little structure, so a range of at least 200 nm and resolution bandwidth
of 1 nm or narrower are recommended. Laser sources have much narrower spectra and may
can be used in wavelength-domain division multiplexing (WDM) applications, where more
accurate determination of the wavelength is required. A wavelength resolution bandwidth of
0,1 nm or narrower is recommended, and the actual requirement is determined by the
application. In any case, the sensitivity and wavelength range of the spectrum analyzer shall
be sufficient to measure all of the spectrum within at least −20 dB from the peak power. For
measurement of SMSR, a larger dynamic range is typically required.
OSA equipment shall be calibrated for vacuum wavelengths in accordance order to be
consistent with the calibration processes and results of IEC 62129-1. The equipment used
shall have a valid calibration certificate, in accordance with the applicable quality system for
the period over which the testing is done.
4.2 Calibrated optical wavelength meter (OWM)
For central wavelength measurements of SLM lasers, such as distributed feedback (DFB)
lasers or tuneable laser assemblies (TLAs) for dense WDM applications, sufficient

measurement accuracy is required. In this case, an optical wavelength meter based on
interferometric spectroscopy can be used. The accuracy of the central wavelength
measurement is generally specified for non-modulated (CW) lasers. When the SLM laser is
modulated, the uncertainty of the central wavelength measurement increases with the
increasing modulation frequency or symbol rate.
OWM equipment shall be calibrated in accordance with IEC 62129-2. The equipment used
shall have a valid calibration certificate, in accordance with the applicable quality system for
the period over which the testing is done.
4.3 Power supplies
As required for the device under test.
4.4 Input signal source or modulator
The input signal source is a signal generator or modulator with the appropriate digital or
analogue signal of the system.
4.5 Test cord
Unless otherwise specified, the physical and optical properties of the test cords shall match
the cable plant with which the equipment is intended to operate. The cords shall be 2 m to
5 m long and shall contain fibres with coatings which remove cladding light. Appropriate
connectors shall be used. Single-mode cords shall be deployed with two 90 mm diameter
loops or otherwise assure rejection of cladding modes. If the equipment is intended for
multimode operation and the intended cable plant is unknown, the fibre size shall be
50/125 µm.
5 Test sample
The test sample shall be a specified fibre optic subsystem, transmitter, or light source. The
system inputs and outputs shall be those normally seen by the user. The spectral width
parameters are typically used for characterizing MLM and LED transmitters. The widths of
MTM and SLM lasers without modulation are normally too narrow to measure with the
dispersive spectral instruments used with this method. Modulated SLM transmitters have
broadened linewidths for high data rates (above about 2,5 Gb/s) caused by chirp that may can
be measurable by this method.
WARNING – Exercise care to avoid possible eye damage from looking into the end of an
energized fibre from any light source. Most importantly, avoid looking into any energized fibre
using any type of magnification device.
The requirements in IEC 60825-1 shall be followed.
Because of the potential for hazardous radiation, conditions of laser safety shall be
established and maintained. Refer to IEC 60825-1.
6 Procedure (method A)
6.1 General
Method A is designed for the use of typical commercial optical spectrum analyzer instruments
that allow quick measurement of spectra with 1 000 wavelength samples or more and allow
for the analysis of such spectra based on all of the samples, rather than selecting for example
only the samples at the peaks of mode wavelengths. The previous method using a smaller
number of discrete wavelength points is included in Clause 7 as method B, for compatibility
with the first edition of this document. Method A has the advantage of easier, simpler

– 10 – IEC 61280-1-3:2021 RLV © IEC 2021
automated analysis and better representation of complex but narrow spectra, such as multi-
transverse-mode vertical cavity surface emitting lasers (VCSELs). Due to its convenience and
prevalence in the industry, method A is considered the reference test method.
For measurements of the central wavelength of SLM lasers, a commercial optical wavelength
meter can also be used. These instruments typically allow the user to specify whether the
optical signal is a continuous wave (CW) signal or a modulated communication signal. An
appropriate mode should be selected according to the condition of the light signal under test.
In the case of modulated SLM lasers, the uncertainty of the central wavelength measurement
typically increases with increasing modulation frequency or symbol rate.
6.2 Setup
6.2.1 Use appropriate handling procedures to prevent damage from electrostatic discharge
(ESD), which can cause opto-electronic devices to fail.
6.2.2 With the exception of ambient temperature, standard ambient conditions shall be
used, unless otherwise specified. The ambient or reference point temperature shall be
23 °C ± 2 °C, unless otherwise specified.
6.2.3 Unless otherwise specified, apply a modulated input signal to the optical source.
Allow sufficient time (according to the manufacturer’s recommendation or as specified in the
detail specification) for the optical source/transmitter to reach a steady-state temperature.
6.2.4 Turn the optical spectrum analyzer measuring instruments, such as the OSA or the
OWM, on and allow the recommended warm-up and settling time to achieve the rated
measurement performance level.
6.2.5 Connect the optical output of the optical source under test to the optical input
connector of the optical spectrum analyzer measuring instrument. If the transmitter under test
does not include isolation from back-reflections, as often the case at 850 nm, these
reflections can cause the spectrum to be unstable and should be reduced with high return-
loss connections and possibly external isolation or attenuation at the transmitter output.
6.3 Adjustment of spectrum analyzer controls
6.3.1 Using the resolution bandwidth control, select an appropriate resolution bandwidth
(see 4.1). Typically, less than 1/10 of the spectral width to be measured or the finest available
resolution bandwidth (0,1 nm or narrower) should be used. Set the number of data points in
the acquired signal to be sure to adequately sample the detail of the optical spectrum.
Typically, this is set to at least four times the sample resolution times the total measured
width. For example, a 10 nm measurement span using 0,1 nm resolution bandwidth requires a
minimum of 400 points in the measurement, which is given by four times the total
measurement span divided by the resolution bandwidth.
6.3.2 Using the span control, select an appropriate span of wavelength range on the
display section of the spectrum analyzer. Initially, select a sufficiently wide span to determine
the appropriate position of the peak wavelength; then reduce and adjust the span again to fit
all of the source spectrum or at least all that is within at least 20 dB of the peak power. For
SLM lasers, the span may need to be changed, typically from 2 nm to 20 nm full scale, to
determine the spectral width and SMSR.
6.3.3 Using the gain or reference level control, select a gain or reference level so that the
amplitude of the peak output extends over the entire screen vertical scale.
6.3.4 If available, use the spectrum analyzer log-scale for amplitude measurement to
achieve the maximum dynamic range

6.3.5 For OSAs that are not capable of performing the subsequent calculations in Clause 8
internally, download the measured optical spectra data to a computer for further analysis in a
format that contains both the wavelength and amplitude of all points in the measurement.
6.4 Setting of optical wavelength meter
6.4.1 The optical wavelength meter is implemented with a longitudinal mode detecting
function. The appropriate parameters should be set, such as threshold from the peak and
excursion from the peak.
6.4.2 Generally, the optical wavelength meter is also implemented with a light signal
condition setting function. The appropriate condition should be set, such as continuous wave
(CW) or modulated signal.
7 Procedure (method B)
7.1 Setup
7.1.1 Use appropriate handling procedures to prevent damage from electrostatic discharge
(ESD), which can cause opto-electronic devices to fail.
7.1.2 With the exception of ambient temperature, standard ambient conditions shall be
used, unless otherwise specified. The ambient or reference point temperature shall be
23 °C ± 2 °C, unless otherwise specified.
7.1.3 Unless otherwise specified, apply a modulated input signal to the optical source.
Allow sufficient time (according to the manufacturer’s recommendation or as specified in the
detail specification) for the optical source/transmitter to reach a steady-state temperature.
7.1.4 Turn the optical spectrum analyzer measuring instruments, such as the OSA or the
OWM, on and allow the recommended warm-up and settling time to achieve the rated
measurement performance level.
7.1.5 Connect the optical output of the optical source under test to the optical input
connector of the optical spectrum analyzer measuring instrument. If the transmitter under test
does not include isolation from back-reflections, as is often the case at 850 nm, these
reflections can cause the spectrum to be unstable and should be reduced with high return-
loss connections and possibly external isolation or attenuation at the transmitter output.
7.2 Adjustment of spectrum analyzer controls
7.2.1 Using the resolution bandwidth control, select an appropriate resolution bandwidth
(see 4.1).
7.2.2 Using the span control, select an appropriate span of wavelength range on the
display section of the spectrum analyzer. Initially, select the maximum span to obtain the
appropriate position of the peak wavelength; then adjust the span again so that, at the
selected gain, the smallest detectable output power level occupies the extreme edges of the
screen horizontal scale. For SLM lasers, the span may need to be changed, typically from 2
nm to 20 nm full scale, to determine the spectral width and SMSR.
7.2.3 Using the gain or reference level control, select a gain or reference level so that the
amplitude of the peak output extends over the entire screen vertical scale. If available, use
the spectrum analyzer log-scale for amplitude measurement to achieve the maximum dynamic
range.
– 12 – IEC 61280-1-3:2021 RLV © IEC 2021
7.3 Setting of optical wavelength meter
7.3.1 The optical wavelength meter is implemented with a longitudinal mode detecting
function, and appropriate parameters should be set, such as threshold from the peak and
excursion from the peak.
7.3.2 Generally, the optical wavelength meter is also implemented with a light signal
condition setting function, and the appropriate conditions should be set, such as continuous
wave (CW) or modulated signal.
7.4 Continuous LED and SLM spectra
7.3.1 General
7.4.1 Refer to Figure 1 and Figure 5 for samples of LED and SLM-LD spectrum analyzer
outputs. At the end of several single measurement sweeps, ensure that the output spectrum is
stable (power variation at any wavelength is ≤ 10 % or ~0,5 dB between sweeps).
7.4.2 Determine the peak wavelength, λ . (Most optical spectrum analyzers have a peak-
p
search button that automatically performs this function.)
7.4.3 For LEDs, record the two half-power wavelengths on both sides of the peak
wavelength that are 3 dB down from the peak amplitude. Determine the number of points to
, and the amplitude p for each point i in the displayed
record (minimum 11), the wavelength λ
i i
spectrum as follows.
7.4.4 On both sides of the peak, find the wavelengths closest to the peak, corresponding to
the two points n dB down from the peak (see example in Figure 1), where n is typically 20.
7.4.5 To find 11 equally spaced points, subtract these two wavelengths and divide the
result by 10. This gives the spacing between points.
7.4.6 Starting with the minimum wavelength as the first point, add the wavelength spacing
th
to find the next point. Continue until 11 points are found (the 11 point should correspond to
the maximum wavelength from 7.4.4). Record the wavelengths in Table 2, column 2.
7.4.7 Find the output power (in dBm) corresponding to each wavelength point and record
in Table 2, column 3.
[0,1 P (dBm) +6]
7.4.8 Convert the power in dBm to nanowatts (nW) using P(nW) = 10 and
record in Table 2, column 4.
7.5 Discrete MLM spectra
7.5.1 At the end of a single measurement sweep, measure and record the wavelength and
the amplitude, for all the modes displayed, in Table 2. The display at the end of the
measurement sweep will determine the number of modes and the reference nominal
wavelength for each mode. Refer to Figure 2 for a sample spectrum analyzer output.
7.5.2 Measure and record the wavelength and the amplitude for each mode displayed for
each of the 10 single measurement sweeps. Include modes at least n dB below the peak
mode, where n is typically 20 to 25. For each mode at nominal wavelengths measured and
recorded in 7.5.1, calculate the average of the 10 measured wavelengths and the
corresponding average of the 10 amplitude readings. Record these average values in Table 2.
7.5.3 Compare the readings of 7.5.1 and 7.5.2 for each mode. For any mode, if the
difference in wavelength readings is more than 0,2 nm, or the difference in amplitude readings
is more than 10 %, this indicates mode instability, and the calculations may not be accurate.

7.6 Continuous SLM spectra
7.6.1 Measure and record the amplitude power (M ) at the peak wavelength and the
amplitude power (M ) of the strongest side-mode under the non-modulated (CW) condition.
7.6.2 Measure and record the two wavelengths on both sides of the peak wavelength that
are n dB down from the peak amplitude, where n is typically 20 or 30.
7.6.3 Measure and record the optical signal power (P ) and the maximum value (P ) of the
1 2
optical power level of source spontaneous emission (SSE) under non-modulated (CW)
operating condition. The SSE power level shall be determined over the entire wavelength
range where the laser (TLA) can oscillate, with the exclusion of typically ±1 nm around the
optical signal wavelength (see Figure 7). The resolution bandwidth of OSA is usually set to
0,1 nm. The actual resolution bandwidth (B ) should be calibrated.
r
8 Calculation
8.1 General
Many optical spectrum analyzers calculate some or all the following parameters internally.
Note that for method A, there will be N points corresponding to all the data points taken.
Before beginning calculations, it is recommended that any power data points that are more
than 20 dB (or another chosen and documented range) below the maximum power reading not
be used in the calculations. This will especially prevent the user from overestimating the RMS
spectral width. For method B, the total number of data points N will be the number of recorded
mode peaks.
8.2 Centre wavelength
8.2.1 Continuous LED spectra
This is the average of the half-power wavelengths determined from the result of 6.3.5 for
method A or 7.4.3 for method B.
8.2.2 Discrete MLM spectra
This is the average of the half-power wavelengths that can be determined as follows by
interpolation, since the laser may not have modes at these wavelengths.
Connect the tip of each mode to the tips of adjacent modes as shown in Figure 3; draw a
horizontal line 3 dB down from the peak power point. The two or more intersection points of
the horizontal line with the tip-connecting lines define the half-power wavelengths. The
average of the half-power wavelengths that are furthest separated is λ .
8.3 Centroidal wavelength
Using the wavelengths and corresponding linear power (nW) in Table 2 for method B or the
result of 6.3.5 for method A, calculate the centroidal wavelength as follows:
N

λλ= P (1)
 ∑
c ii
P
i =1
0
where
th
λ is the wavelength of the i point;
i
– 14 – IEC 61280-1-3:2021 RLV © IEC 2021
th
P is the power of the i point;
i
N
P is the total power summed for all points: PP=
0 0 ∑ i
i =1
N is the number of points.
Refer to Table 1 for a calculation example.
8.4 Peak wavelength
8.4.1 Continuous LED and SLM spectra
Use the value measured in 7.4.2 for method B or the wavelength of the maximum power in the
spectrum of 6.3.5 for method A as the peak wavelength.
8.4.2 Discrete MLM spectra
The peak wavelength can be obtained directly from the wavelength corresponding to
maximum power in the spectrum from 6.3.5 for method A or from Table 2 (log or linear scale),
representing the average of 10 readings, by reading the wavelength corresponding to the
peak power level for method B. If the maximum power occurs in more than one mode, take
the average of the wavelength of all modes with the maximum power. Use the average value
as the peak wavelength.
8.5 RMS spectral width (Δλ )
rms
Using the wavelengths and corresponding linear power (nW), in the spectrum from 6.3.5 for
method A or from Table 2 (single or average values) for method B, calculate the RMS spectral
width as:
N 2

(2)
λ P(λλ− )
rms ∑ ii c
P
i =1
0
Refer to Table 1 for a calculation example. Note that Δλ does not apply to SLM sources. As
rms
mentioned at the beginning of Clause 8, a documented method for limiting the range of the
data points should be used, such as a cutoff of 20 dB from the peak power.
8.6 n-dB-down spectral width (Δλ )
n-dB
The difference in wavelengths recorded in 7.5.2 for method B, or which are n dB below the
peak in the spectrum from 6.3.5 from method A, is Δλ (see Figure 5). This Δλ applies
n-dB n-dB
to SLM lasers but does not apply to MLM lasers or to LEDs.
n-dB-down spectral width depends on the resolution bandwidth of the OSA, because the main
mode of SLM lasers, such as DFB-LDs and TLAs, is substantially narrower than the resolution
bandwidth of an OSA. Therefore, information on the resolution bandwidth of the OSA that was
used to measure the signal spectrum should be noted together with n-dB-down spectral width
test result.
∆=
8.7 Full-width at half-maximum spectral width (Δλ )
fwhm
8.7.1 Continuous LED spectra
The difference of the half-power wavelengths recorded in 7.4.3 from method B or determined
from the spectra of 6.3.5 for method A is Δλ .
fwhm
8.7.2 Discrete MLM spectra
This is the difference of the half-power wavelengths that can be determined as follows by
interpolation, since the laser may not have modes at these wavelengths.
Connect the tip of each mode to the tips of adjacent modes, as shown in the examples of
Figure 3 and Figure 4, and draw a horizontal line 3 dB down from the peak power point. The
two or more intersection points between these lines define the half-power wavelengths. The
maximum difference in half-power wavelengths is Δλ .
fwhm
NOTE The procedure of 8.7.2 uses interpolation based on a segmented linear fit. In many cases, the spectrum
can also be well represented by a Gaussian fit. In this case, the FWHM spectral width can also be calculated on
the basis of the RMS spectral width. For a Gaussian distribution, ΔΔλλ2,355× .
fwhm rms
8.8 Side-mode suppression ratio (SMSR)
From the power of the highest signal peak of an SLM, M , and the power of the highest side-
mode, M , as determined in 7.6.1 from method B or from the spectrum of 6.3.5 from method A,
calculate the side-mode suppression ratio (R in dB) as:
SMS
M
R = 10 log
(3)

SMS 10
M
2
Typically, the side modes of non-modulated (CW) SLM lasers, such as DFB-LDs and TLAs,
exhibit a linewidth that is substantially narrower than the resolution bandwidth of an OSA.
However, due to the influence of spontaneous light emission and narrow mode spacing, the
power of the highest side mode, M , depends on the resolution bandwidth of the OSA that is
used when the spectra are measured. Therefore, the side-mode suppression ratios measured
with different resolution bandwidths can differ significantly (see Figure 6). Information on the
resolution bandwidth of the OSA, which was used to measure the signal spectrum, should be
noted together with SMSR test results.
8.9 Signal-to-source spontaneous emission ratio (SSER)
From the optical signal power of a non-modulated (CW) SLM laser, P , and the maximum
optical power level, P , of the spontaneous emission as determined in 7.6.3 from method B,
calculate the signal-to-source spontaneous emission ratio (R in dB/nm) as:
SSE

P B
2r
R = −10 log 
(4)
SMS 10

P

9 Test results
9.1 Required information
The required information shall include:
=
– 16 – IEC 61280-1-3:2021 RLV © IEC 2021
a) date, title of test, and procedures used;
b) identification of the fibre optic transmitter (terminal device) or the optical source to be
tested, together with applicable data;
c) reference point temperature;
d) results of the examination.
9.2 Information to be available on request
Information to be available on request is as follows:
a) test equipment used and latest date of calibration;
b) names of test personnel;
c) measurement uncertainty due to measurement inaccuracy and display resolution;
d) data rate and input signal characteristics, including modulation depth and pulse shape;
e) supply voltage(s) and/or current(s);
f) bias circuit configuration for discret
...

IEC 61280-1-3 ®
Edition 3.0 2021-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic communication subsystem test procedures –
Part 1-3: General communication subsystems – Measurement of central
wavelength, spectral width and additional spectral characteristics

Procédures d'essai des sous-systèmes de télécommunication fibroniques –
Partie 1-3: Sous-systèmes généraux de télécommunication – Mesure de la
longueur d'onde centrale, de la largeur spectrale et des caractéristiques
spectrales supplémentaires
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IEC 61280-1-3 ®
Edition 3.0 2021-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic communication subsystem test procedures –

Part 1-3: General communication subsystems – Measurement of central

wavelength, spectral width and additional spectral characteristics

Procédures d'essai des sous-systèmes de télécommunication fibroniques –

Partie 1-3: Sous-systèmes généraux de télécommunication – Mesure de la

longueur d'onde centrale, de la largeur spectrale et des caractéristiques

spectrales supplémentaires
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.01 ISBN 978-2-8322-1051-9

– 2 – IEC 61280-1-3:2021 © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviated terms . 6
3.1 Wavelength . 6
3.2 Spectral width . 7
3.3 Additional spectral characteristics . 7
3.4 Abbreviated terms . 8
4 Apparatus . 8
4.1 Calibrated optical spectrum analyzer (OSA) . 8
4.2 Calibrated optical wavelength meter (OWM) . 8
4.3 Power supplies . 9
4.4 Input signal source or modulator . 9
4.5 Test cord . 9
5 Test sample . 9
6 Procedure (method A) . 9
6.1 General . 9
6.2 Setup . 10
6.3 Adjustment of spectrum analyzer controls . 10
6.4 Setting of optical wavelength meter. 11
7 Procedure (method B) . 11
7.1 Setup . 11
7.2 Adjustment of spectrum analyzer controls . 11
7.3 Setting of optical wavelength meter. 11
7.4 Continuous LED and SLM spectra . 12
7.5 Discrete MLM spectra . 12
7.6 SLM spectra. 12
8 Calculation . 13
8.1 General . 13
8.2 Centre wavelength . 13
8.2.1 Continuous LED spectra . 13
8.2.2 Discrete MLM spectra . 13
8.3 Centroidal wavelength . 13
8.4 Peak wavelength . 14
8.4.1 Continuous LED and SLM spectra . 14
8.4.2 Discrete MLM spectra . 14
8.5 RMS spectral width (Δλ ) . 14
rms
8.6 n-dB-down spectral width (Δλ ) . 14
n-dB
8.7 Full-width at half-maximum spectral width (Δλ ) . 14
fwhm
8.7.1 Continuous LED spectra . 14
8.7.2 Discrete MLM spectra . 15
8.8 Side-mode suppression ratio (SMSR) . 15
8.9 Signal-to-source spontaneous emission ratio (SSER) . 15
9 Test results . 15
9.1 Required information . 15

9.2 Information to be available on request . 16
10 Examples of results . 16
Bibliography . 21

Figure 1 – Example of a LED optical spectrum . 16
Figure 2 – Typical spectrum analyzer output for MLM laser . 18
Figure 3 – Δλ spectral width measurement for MLM laser. 18
fwhm
Figure 4 – Δλ spectral width calculation for MLM laser . 19
fwhm
Figure 5 – Peak emission wavelength and Δλ measurement for SLM laser . 19
30-dB
Figure 6 – Resolution bandwidth (RBW) dependence of SMSR for SLM laser . 20
Figure 7 – Signal-to-source spontaneous emission ratio measurement for SLM laser . 20

Table 1 – Measurement points for LED spectrum from Figure 1 . 17
Table 2 – RMS spectral characterization . 17

– 4 – IEC 61280-1-3:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 1-3: General communication subsystems – Measurement of central
wavelength, spectral width and additional spectral characteristics

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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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
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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
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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.
IEC 61280-1-3 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is an International Standard.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) addition of measurement of signal-to-source spontaneous emission ratio in 8.9;
b) change of document title to reflect the additional measurement;
c) additional information on the resolution bandwidth used in the measurement of the side-
mode suppression ratio in 8.8;
d) use of a calibrated optical wavelength meter for accurate wavelength measurements of
single-longitudinal mode lasers.

The text of this International Standard is based on the following documents:
Draft Report on voting
86C/1701/CDV 86C/1717/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement,
available at www.iec.ch/members_experts/refdocs. The main document types developed by
IEC are described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 61280 series, published under the general title Fibre optic
communication subsystem test procedures, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under 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 document 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 61280-1-3:2021 © IEC 2021
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 1-3: General communication subsystems – Measurement of central
wavelength, spectral width and additional spectral characteristics

1 Scope
This part of IEC 61280 provides definitions and measurement procedures for several
wavelength and spectral width properties of an optical spectrum associated with a fibre optic
communication subsystem, an optical transmitter, or other light sources used in the operation
or test of communication subsystems. This document also provides definitions and
measurement procedures for side-mode suppression ratio and signal-to-source spontaneous
emission ratio.
The measurement is done for the purpose of system construction and/or maintenance. In the
case of communication subsystem signals, the optical transmitter is typically under
modulation.
NOTE Different properties can be appropriate to different spectral types, such as continuous spectra
characteristics of light-emitting diodes (LEDs), as well as multilongitudinal-mode (MLM), multitransverse-mode
(MTM) and single-longitudinal mode (SLM) spectra, which are characteristic of laser diodes (LDs).
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 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 62129-1, Calibration of wavelength/optical frequency measurement instruments – Part 1:
Optical spectrum analyzers
IEC 62129-2, Calibration of wavelength/optical frequency measurement instruments – Part 2:
Michelson interferometer single wavelength meters
3 Terms, definitions and abbreviated terms
For the purposes of this document, the following terms, definitions and abbreviated terms
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 Wavelength
NOTE The following wavelength terms provide quantitative definitions for the description of the central
wavelength of a spectrum. In this document, "central wavelength" is a general category label for these terms.

3.1.1
centre wavelength
λ
mean of the closest spaced half-power wavelengths in an optical spectrum, one above and
one below the peak wavelength
Note 1 to entry: Centre wavelength is also called “half-power mid-point”.
3.1.2
half-power wavelength
λ
3dB
wavelength corresponding to a half-peak power value of the optical spectrum
3.1.3
peak wavelength
λ
p
wavelength corresponding to the maximum power value of the optical spectrum
3.1.4
centroidal wavelength
λ
c
mean or average wavelength of an optical spectrum
3.2 Spectral width
3.2.1
RMS spectral width
Δλ
rms
square root of the second moment of the power distribution about the centroidal wavelength
3.2.2
n-dB-down spectral width
Δλ
n-dB
positive difference of the closest spaced wavelengths, one above and one below the peak
wavelength λ , at which the spectral power density determined in a specified resolution
p
bandwidth is n dB down from its peak value
3.2.3
full-width at half-maximum
Δλ
fwhm
positive difference of the closest spaced wavelengths, one above and one below the peak
, at which the spectral power density determined in a specified resolution
wavelength λ
p
bandwidth is 3 dB down from its peak value
3.3 Additional spectral characteristics
3.3.1
side-mode suppression ratio
SMSR
ratio of the largest peak of the optical spectrum to the second largest peak under non-
modulated (continuous wave) operating condition, which is determined in a specified
wavelength resolution bandwidth (RBW), for a nominally single-longitudinal mode (SLM)
spectrum
Note 1 to entry: See 8.8.
– 8 – IEC 61280-1-3:2021 © IEC 2021
3.3.2
signal-to-source spontaneous emission ratio
SSER
ratio between the signal power and maximum source spontaneous emission (SSE) power
under the non-modulated (CW) condition which is determined in a specified bandwidth
3.4 Abbreviated terms
CW continuous wave
DFB distributed feedback
ESD electrostatic discharge
InGaAsP  indium gallium arsenide phosphide
LD  laser diode
LED light-emitting diode
MLM multi-longitudinal mode
MTM multi-transverse mode
OSA optical spectrum analyzer
OWM optical wavelength meter
RBW resolution bandwidth
RMS root-mean-square
SLM single-longitudinal mode
SMSR side-mode suppression ratio
SSE source spontaneous emission
SSER signal-to-source spontaneous emission ratio
TLA tuneable laser assembly
VCSEL vertical cavity surface emitting lasers
WDM wavelength-division multiplexing
4 Apparatus
4.1 Calibrated optical spectrum analyzer (OSA)
This special-purpose test equipment uses a dispersive spectrophotometric method to resolve
and record the optical spectral distribution. The required wavelength resolution bandwidth and
range depend on the type and variety of signals to be measured. Generally, LED sources
have wide spectra with little structure, so a range of at least 200 nm and resolution bandwidth
of 1 nm or narrower are recommended. Laser sources have much narrower spectra and can
be used in wavelength-division multiplexing (WDM) applications, where more accurate
determination of the wavelength is required. A resolution bandwidth of 0,1 nm or narrower is
recommended, and the actual requirement is determined by the application. In any case, the
sensitivity and wavelength range of the spectrum analyzer shall be sufficient to measure all of
the spectrum within at least −20 dB from the peak power. For measurement of SMSR, a larger
dynamic range is typically required.
OSA equipment shall be calibrated for vacuum wavelengths in order to be consistent with the
calibration processes and results of IEC 62129-1. The equipment used shall have a valid
calibration certificate, in accordance with the applicable quality system for the period over
which the testing is done.
4.2 Calibrated optical wavelength meter (OWM)
For central wavelength measurements of SLM lasers, such as distributed feedback (DFB)
lasers or tuneable laser assemblies (TLAs) for dense WDM applications, sufficient

measurement accuracy is required. In this case, an optical wavelength meter based on
interferometric spectroscopy can be used. The accuracy of the central wavelength
measurement is generally specified for non-modulated (CW) lasers. When the SLM laser is
modulated, the uncertainty of the central wavelength measurement increases with the
increasing modulation frequency or symbol rate.
OWM equipment shall be calibrated in accordance with IEC 62129-2. The equipment used
shall have a valid calibration certificate, in accordance with the applicable quality system for
the period over which the testing is done.
4.3 Power supplies
As required for the device under test.
4.4 Input signal source or modulator
The input signal source is a signal generator or modulator with the appropriate digital or
analogue signal of the system.
4.5 Test cord
Unless otherwise specified, the physical and optical properties of the test cords shall match
the cable plant with which the equipment is intended to operate. The cords shall be 2 m to
5 m long and shall contain fibres with coatings which remove cladding light. Appropriate
connectors shall be used. Single-mode cords shall be deployed with two 90 mm diameter
loops or otherwise assure rejection of cladding modes. If the equipment is intended for
multimode operation and the intended cable plant is unknown, the fibre size shall be
50/125 µm.
5 Test sample
The test sample shall be a specified fibre optic subsystem, transmitter, or light source. The
system inputs and outputs shall be those normally seen by the user. The spectral width
parameters are typically used for characterizing MLM and LED transmitters. The widths of
MTM and SLM lasers without modulation are normally too narrow to measure with the
dispersive spectral instruments used with this method. Modulated SLM transmitters have
broadened linewidths for high data rates (above about 2,5 Gb/s) caused by chirp that can be
measurable by this method.
Because of the potential for hazardous radiation, conditions of laser safety shall be
established and maintained. Refer to IEC 60825-1.
6 Procedure (method A)
6.1 General
Method A is designed for the use of typical commercial optical spectrum analyzer instruments
that allow quick measurement of spectra with 1 000 wavelength samples or more and allow
for the analysis of such spectra based on all of the samples, rather than selecting for example
only the samples at the peaks of mode wavelengths. The previous method using a smaller
number of discrete wavelength points is included in Clause 7 as method B, for compatibility
with the first edition of this document. Method A has the advantage of easier, simpler
automated analysis and better representation of complex but narrow spectra, such as multi-
transverse-mode vertical cavity surface emitting lasers (VCSELs). Due to its convenience and
prevalence in the industry, method A is considered the reference test method.
For measurements of the central wavelength of SLM lasers, a commercial optical wavelength
meter can also be used. These instruments typically allow the user to specify whether the

– 10 – IEC 61280-1-3:2021 © IEC 2021
optical signal is a continuous wave (CW) signal or a modulated communication signal. An
appropriate mode should be selected according to the condition of the light signal under test.
In the case of modulated SLM lasers, the uncertainty of the central wavelength measurement
typically increases with increasing modulation frequency or symbol rate.
6.2 Setup
6.2.1 Use appropriate handling procedures to prevent damage from electrostatic discharge
(ESD), which can cause opto-electronic devices to fail.
6.2.2 With the exception of ambient temperature, standard ambient conditions shall be
used, unless otherwise specified. The ambient or reference point temperature shall be
23 °C ± 2 °C, unless otherwise specified.
6.2.3 Unless otherwise specified, apply a modulated input signal to the optical source.
Allow sufficient time (according to the manufacturer’s recommendation or as specified in the
detail specification) for the optical source/transmitter to reach a steady-state temperature.
6.2.4 Turn the optical spectrum measuring instruments, such as the OSA or the OWM, on
and allow the recommended warm-up and settling time to achieve the rated measurement
performance level.
6.2.5 Connect the optical output of the optical source under test to the optical input
connector of the optical spectrum measuring instrument. If the transmitter under test does not
include isolation from back-reflections, as often the case at 850 nm, these reflections can
cause the spectrum to be unstable and should be reduced with high return-loss connections
and possibly external isolation or attenuation at the transmitter output.
6.3 Adjustment of spectrum analyzer controls
6.3.1 Using the resolution bandwidth control, select an appropriate resolution bandwidth
(see 4.1). Typically, less than 1/10 of the spectral width to be measured or the finest available
resolution bandwidth (0,1 nm or narrower) should be used. Set the number of data points in
the acquired signal to be sure to adequately sample the detail of the optical spectrum.
Typically, this is set to at least four times the sample resolution times the total measured
width. For example, a 10 nm measurement span using 0,1 nm resolution bandwidth requires a
minimum of 400 points in the measurement, which is given by four times the total
measurement span divided by the resolution bandwidth.
6.3.2 Using the span control, select an appropriate span of wavelength range on the
display section of the spectrum analyzer. Initially, select a sufficiently wide span to determine
the appropriate position of the peak wavelength; then reduce and adjust the span again to fit
all of the source spectrum or at least all that is within at least 20 dB of the peak power. For
SLM lasers, the span may need to be changed, typically from 2 nm to 20 nm full scale, to
determine the spectral width and SMSR.
6.3.3 Using the gain or reference level control, select a gain or reference level so that the
amplitude of the peak output extends over the entire screen vertical scale.
6.3.4 If available, use the spectrum analyzer log-scale for amplitude measurement to
achieve the maximum dynamic range
6.3.5 For OSAs that are not capable of performing the subsequent calculations in Clause 8
internally, download the measured optical spectra data to a computer for further analysis in a
format that contains both the wavelength and amplitude of all points in the measurement.

6.4 Setting of optical wavelength meter
6.4.1 The optical wavelength meter is implemented with a longitudinal mode detecting
function. The appropriate parameters should be set, such as threshold from the peak and
excursion from the peak.
6.4.2 Generally, the optical wavelength meter is also implemented with a light signal
condition setting function. The appropriate condition should be set, such as continuous wave
(CW) or modulated signal.
7 Procedure (method B)
7.1 Setup
7.1.1 Use appropriate handling procedures to prevent damage from electrostatic discharge
(ESD), which can cause opto-electronic devices to fail.
7.1.2 With the exception of ambient temperature, standard ambient conditions shall be
used, unless otherwise specified. The ambient or reference point temperature shall be
23 °C ± 2 °C, unless otherwise specified.
7.1.3 Unless otherwise specified, apply a modulated input signal to the optical source.
Allow sufficient time (according to the manufacturer’s recommendation or as specified in the
detail specification) for the optical source/transmitter to reach a steady-state temperature.
7.1.4 Turn the optical spectrum measuring instruments, such as the OSA or the OWM, on
and allow the recommended warm-up and settling time to achieve the rated measurement
performance level.
7.1.5 Connect the optical output of the optical source under test to the optical input
connector of the optical spectrum measuring instrument. If the transmitter under test does not
include isolation from back-reflections, as is often the case at 850 nm, these reflections can
cause the spectrum to be unstable and should be reduced with high return-loss connections
and possibly external isolation or attenuation at the transmitter output.
7.2 Adjustment of spectrum analyzer controls
7.2.1 Using the resolution bandwidth control, select an appropriate resolution bandwidth
(see 4.1).
7.2.2 Using the span control, select an appropriate span of wavelength range on the
display section of the spectrum analyzer. Initially, select the maximum span to obtain the
appropriate position of the peak wavelength; then adjust the span again so that, at the
selected gain, the smallest detectable output power level occupies the extreme edges of the
screen horizontal scale. For SLM lasers, the span may need to be changed, typically from 2
nm to 20 nm full scale, to determine the spectral width and SMSR.
7.2.3 Using the gain or reference level control, select a gain or reference level so that the
amplitude of the peak output extends over the entire screen vertical scale. If available, use
the spectrum analyzer log-scale for amplitude measurement to achieve the maximum dynamic
range.
7.3 Setting of optical wavelength meter
7.3.1 The optical wavelength meter is implemented with a longitudinal mode detecting
function, and appropriate parameters should be set, such as threshold from the peak and
excursion from the peak.
– 12 – IEC 61280-1-3:2021 © IEC 2021
7.3.2 Generally, the optical wavelength meter is also implemented with a light signal
condition setting function, and the appropriate conditions should be set, such as continuous
wave (CW) or modulated signal.
7.4 Continuous LED and SLM spectra
7.4.1 Refer to Figure 1 and Figure 5 for samples of LED and SLM-LD spectrum analyzer
outputs. At the end of several single measurement sweeps, ensure that the output spectrum is
stable (power variation at any wavelength is ≤ 10 % or ~0,5 dB between sweeps).
. (Most optical spectrum analyzers have a peak-
7.4.2 Determine the peak wavelength, λ
p
search button that automatically performs this function.)
7.4.3 For LEDs, record the two half-power wavelengths on both sides of the peak
wavelength that are 3 dB down from the peak amplitude. Determine the number of points to
record (minimum 11), the wavelength λ , and the amplitude p for each point i in the displayed
i i
spectrum as follows.
7.4.4 On both sides of the peak, find the wavelengths closest to the peak, corresponding to
the two points n dB down from the peak (see example in Figure 1), where n is typically 20.
7.4.5 To find 11 equally spaced points, subtract these two wavelengths and divide the
result by 10. This gives the spacing between points.
7.4.6 Starting with the minimum wavelength as the first point, add the wavelength spacing
th
to find the next point. Continue until 11 points are found (the 11 point should correspond to
the maximum wavelength from 7.4.4). Record the wavelengths in Table 2, column 2.
7.4.7 Find the output power (in dBm) corresponding to each wavelength point and record
in Table 2, column 3.
[0,1 P (dBm) +6]
7.4.8 Convert the power in dBm to nanowatts (nW) using P(nW) = 10 and
record in Table 2, column 4.
7.5 Discrete MLM spectra
7.5.1 At the end of a single measurement sweep, measure and record the wavelength and
the amplitude, for all the modes displayed, in Table 2. The display at the end of the
measurement sweep will determine the number of modes and the reference nominal
wavelength for each mode. Refer to Figure 2 for a sample spectrum analyzer output.
7.5.2 Measure and record the wavelength and the amplitude for each mode displayed for
each of the 10 single measurement sweeps. Include modes at least n dB below the peak
mode, where n is typically 20 to 25. For each mode at nominal wavelengths measured and
recorded in 7.5.1, calculate the average of the 10 measured wavelengths and the
corresponding average of the 10 amplitude readings. Record these average values in Table 2.
7.5.3 Compare the readings of 7.5.1 and 7.5.2 for each mode. For any mode, if the
difference in wavelength readings is more than 0,2 nm, or the difference in amplitude readings
is more than 10 %, this indicates mode instability, and the calculations may not be accurate.
7.6 SLM spectra
7.6.1 Measure and record the power (M ) at the peak wavelength and the power (M ) of
1 2
the strongest side-mode under the non-modulated (CW) condition.

7.6.2 Measure and record the two wavelengths on both sides of the peak wavelength that
are n dB down from the peak amplitude, where n is typically 20 or 30.
7.6.3 Measure and record the optical signal power (P ) and the maximum value (P ) of the
1 2
optical power level of source spontaneous emission (SSE) under non-modulated (CW)
operating condition. The SSE power level shall be determined over the entire wavelength
range where the laser (TLA) can oscillate, with the exclusion of typically ±1 nm around the
optical signal wavelength (see Figure 7). The resolution bandwidth of OSA is usually set to
0,1 nm. The actual resolution bandwidth (B ) should be calibrated.
r
8 Calculation
8.1 General
Many optical spectrum analyzers calculate some or all the following parameters internally.
Note that for method A, there will be N points corresponding to all the data points taken.
Before beginning calculations, it is recommended that any power data points that are more
than 20 dB (or another chosen and documented range) below the maximum power reading not
be used in the calculations. This will especially prevent the user from overestimating the RMS
spectral width. For method B, the total number of data points N will be the number of recorded
mode peaks.
8.2 Centre wavelength
8.2.1 Continuous LED spectra
This is the average of the half-power wavelengths determined from the result of 6.3.5 for
method A or 7.4.3 for method B.
8.2.2 Discrete MLM spectra
This is the average of the half-power wavelengths that can be determined as follows by
interpolation, since the laser may not have modes at these wavelengths.
Connect the tip of each mode to the tips of adjacent modes as shown in Figure 3; draw a
horizontal line 3 dB down from the peak power point. The two or more intersection points of
the horizontal line with the tip-connecting lines define the half-power wavelengths. The
average of the half-power wavelengths that are furthest separated is λ .
8.3 Centroidal wavelength
Using the wavelengths and corresponding linear power (nW) in Table 2 for method B or the
result of 6.3.5 for method A, calculate the centroidal wavelength as follows:
N
1
λλ= P (1)

c ∑ ii
P
i=1
0
where
th
λ is the wavelength of the i point;
i
th
P is the power of the i point;
i
N
P is the total power summed for all points: PP=
0 0 ∑ i
i=1
– 14 – IEC 61280-1-3:2021 © IEC 2021
N is the number of points.
Refer to Table 1 for a calculation example.
8.4 Peak wavelength
8.4.1 Continuous LED and SLM spectra
Use the value measured in 7.4.2 for method B or the wavelength of the maximum power in the
spectrum of 6.3.5 for method A as the peak wavelength.
8.4.2 Discrete MLM spectra
The peak wavelength can be obtained directly from the wavelength corresponding to
maximum power in the spectrum from 6.3.5 for method A or from Table 2 (log or linear scale),
representing the average of 10 readings, by reading the wavelength corresponding to the
peak power level for method B. If the maximum power occurs in more than one mode, take
the average of the wavelength of all modes with the maximum power. Use the average value
as the peak wavelength.
8.5 RMS spectral width (Δλ )
rms
Using the wavelengths and corresponding linear power (nW), in the spectrum from 6.3.5 for
method A or from Table 2 (single or average values) for method B, calculate the RMS spectral
width as:
N 2

(2)
λ P(λλ− )
∑
rms ii c
P
i=1
0
Refer to Table 1 for a calculation example. Note that Δλ does not apply to SLM sources. As
rms
mentioned at the beginning of Clause 8, a documented method for limiting the range of the
data points should be used, such as a cutoff of 20 dB from the peak power.
8.6 n-dB-down spectral width (Δλ )
n-dB
The difference in wavelengths recorded in 7.5.2 for method B, or which are n dB below the
peak in the spectrum from 6.3.5 from method A, is Δλ (see Figure 5). This Δλ applies
n-dB n-dB
to SLM lasers but does not apply to MLM lasers or to LEDs.
n-dB-down spectral width depends on the resolution bandwidth of the OSA, because the main
mode of SLM lasers, such as DFB-LDs and TLAs, is substantially narrower than the resolution
bandwidth of an OSA. Therefore, information on the resolution bandwidth of the OSA that was
used to measure the signal spectrum should be noted together with n-dB-down spectral width
test result.
8.7 Full-width at half-maximum spectral width (Δλ )
fwhm
8.7.1 Continuous LED spectra
The difference of the half-power wavelengths recorded in 7.4.3 from method B or determined
from the spectra of 6.3.5 for method A is Δλ .
fwhm
∆=
8.7.2 Discrete MLM spectra
This is the difference of the half-power wavelengths that can be determined as follows by
interpolation, since the laser may not have modes at these wavelengths.
Connect the tip of each mode to the tips of adjacent modes, as shown in the examples of
Figure 3 and Figure 4, and draw a horizontal line 3 dB down from the peak power point. The
two or more intersection points between these lines define the half-power wavelengths. The
maximum difference in half-power wavelengths is Δλ .
fwhm
NOTE The procedure of 8.7.2 uses interpolation based on a segmented linear fit. In many cases, the spectrum
can also be well represented by a Gaussian fit. In this case, the FWHM spectral width can also be calculated on
the basis of the RMS spectral width. For a Gaussian distribution, ΔΔλλ2,355× .
fwhm rms
8.8 Side-mode suppression ratio (SMSR)
From the power of the highest signal
...