Optical amplifiers - Test methods - Part 4-1: Gain transient parameters - Two-wavelength method

IEC 61290-4-1:2016 applies to optical amplifiers (OAs) using active fibres (optical fibre amplifiers (OFAs)) containing rare-earth dopants including erbium-doped fibre amplifiers (EDFAs) and optically amplified elementary sub-systems. These amplifiers are commercially available and widely deployed in service provider networks. The object of document is to provide the general background for OFA transients and related parameters, and to describe a standard test method for accurate and reliable measurement of the following transient parameters: - channel addition or removal transient gain overshoot and transient net gain overshoot; - channel addition or removal transient gain undershoot and transient net gain undershoot; - channel addition or removal gain offset; - channel addition or removal transient gain response time constant (settling time). This second edition cancels and replaces the first edition published in 2011. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: - extended the applicability from only EDFAs to all OFAs; - updated definitions for consistency with other documents in the IEC 61290-4 series. Keywords: optical amplifiers (OAs), optical fibre amplifiers (OFAs), rare-earth dopants, erbium-doped fibre amplifiers

Lichtwellenleiter-Verstärker - Prüfverfahren - Teil 4-1: Transiente Verstärkerparameter - Zwei-Wellenlängen-Verfahren

Amplificateurs optiques - Méthodes d’essai - Partie 4-1: Paramètres de gain transitoire - Méthode à deux longueurs d'onde

L'IEC 61290-4-1:2016 s'applique aux amplificateurs optiques (OA) utilisant des fibres actives (amplificateurs à fibres optiques (OFA)), dopées aux terres rares. Elle concerne également les amplificateurs à fibre dopée à l'erbium (EDFA) et les sous-systèmes élémentaires à amplification optique. Ces amplificateurs sont disponibles sur le marché et sont largement déployés dans les réseaux de prestataires de service. La présente partie de l'IEC 61290-4 a pour objet de fournir le contexte général pour les transitoires d'OFA et les paramètres associés, et de décrire une méthode d'essai normalisée de mesure exacte et fiable des paramètres transitoires suivants: - dépassement positif du gain transitoire lors de l'ajout ou de la suppression de canaux et dépassement positif du gain net transitoire; - dépassement négatif du gain transitoire lors de l'ajout ou de la suppression de canaux et dépassement négatif du gain net transitoire; - décalage de gain lors de l'ajout ou de la suppression de canaux; - constante de temps de réponse du gain transitoire lors de l'ajout ou de la suppression de canaux (temps de stabilisation). Cette deuxième édition annule et remplace la première édition parue en 2011. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: - extension de l'application des seuls EDFA à l'ensemble des OFA; - mise à jour des définitions dans un objectif de cohérence avec les autres documents de la série IEC 61290-4. Mots clés: amplificateurs optiques (OA), amplificateurs à fibres optiques (OFA), dopées aux terres rares, des amplificateurs à fibre dopée à l'erbium

Optični ojačevalniki - Preskusne metode - 4-1. del: Prehodni parametri ojačenja - Dvovalovna metoda (IEC 61290-4-1:2016)

Ta del standarda IEC 61290-4 se uporablja za optične ojačevalnike (OA), ki uporabljajo aktivna vlakna (ojačevalniki z optičnimi vlakni (OFA)) z redkimi zemeljskimi dopanti, vključno z ojačevalniki z vlakni, dopiranimi z erbijem (EDFA), in optično ojačanimi osnovnimi podsistemi. Ti ojačevalniki so komercialno dostopni in splošno razširjeni v omrežjih ponudnikov storitev.
Namen tega dokumenta je podati splošno ozadje za ojačenje ojačevalnikov z optičnimi vlakni in z njimi povezanih parametrov ter opisati standardno preskusno metodo za natančne in zanesljive meritve naslednjih parametrov ojačenja:
a) dodajanje ali odstranjevanje presežnega prehodnega ojačenja in presežnega prehodnega neto ojačenja kanala;
b) dodajanje ali odstranjevanje nedoseženega prehodnega ojačenja in nedoseženega prehodnega neto ojačenja kanala;
c) dodajanje ali odstranjevanje prehodne izravnave kanala;
d) dodajanje ali odstranjevanje konstante odzivnega časa prehodnega ojačenja kanala (odzivni čas).

General Information

Status
Published
Publication Date
22-Dec-2016
Current Stage
6060 - Document made available
Due Date
10-Jul-2017

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SLOVENSKI STANDARD
SIST EN 61290-4-1:2017
01-februar-2017
1DGRPHãþD
SIST EN 61290-4-1:2011

2SWLþQLRMDþHYDOQLNL3UHVNXVQHPHWRGHGHO3UHKRGQLSDUDPHWULRMDþHQMD

'YRYDORYQDPHWRGD ,(&

Optical amplifiers - Test methods - Part 4-1: Gain transient parameters - Two-wavelength

method (IEC 61290-4-1:2016)

Lichtwellenleiter-Verstärker - Prüfverfahren - Teil 4-1: Transiente Verstärkerparameter -

Zwei-Wellenlängen Verfahren

Amplificateurs optiques - Méthodes d'essai - Partie 4-1 : paramètres de gain transitoire -

Méthode à deux longueurs d'onde
Ta slovenski standard je istoveten z: EN 61290-4-1:2016
ICS:
33.180.30 2SWLþQLRMDþHYDOQLNL Optic amplifiers
SIST EN 61290-4-1:2017 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 61290-4-1:2017
---------------------- Page: 2 ----------------------
SIST EN 61290-4-1:2017
EUROPEAN STANDARD EN 61290-4-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
December 2016
ICS 33.180.30 Supersedes EN 61290-4-1:2011
English Version
Optical amplifiers - Test methods -
Part 4-1: Gain transient parameters - Two-wavelength method
(IEC 61290-4-1:2016)

Amplificateurs optiques - Méthodes d'essai - Lichtwellenleiter-Verstärker - Prüfverfahren -

Partie 4-1: Paramètres de gain transitoire - Méthode à deux Teil 4-1: Transiente Verstärkerparameter - Zwei-

longueurs d'onde Wellenlängen-Verfahren
(IEC 61290-4-1:2016) (IEC 61290-4-1:2016)

This European Standard was approved by CENELEC on 2016-10-31. CENELEC members are bound to comply with the CEN/CENELEC

Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC

Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by translation

under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,

Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels

© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN 61290-4-1:2016 E
---------------------- Page: 3 ----------------------
SIST EN 61290-4-1:2017
EN 61290-4-1:2016
European foreword

The text of document 86C/1347/CDV, future edition 2 of IEC 61290-4-1, prepared by SC 86C "Fibre

optic systems and active devices" of IEC/TC 86 "Fibre optics" was submitted to the IEC-CENELEC

parallel vote and approved by CENELEC as EN 61290-4-1:2016.
The following dates are fixed:
(dop) 2017-07-31
• latest date by which the document has to be
implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2019-10-31
standards conflicting with the
document have to be withdrawn
This document supersedes EN 61290-4-1:2011.

EN 61290-4-1:2016 includes the following significant technical changes with respect to

EN 61290-4-1:2011:
a) Extended the applicability from only EDFAs to all OFAs;

b) Updated definitions for consistency with other documents in the EN 61290-4 Series.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such

patent rights.
Endorsement notice

The text of the International Standard IEC 61290-4-1:2016 was approved by CENELEC as a

European Standard without any modification.

In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 61290-1 Series NOTE Harmonized as EN 61290-1 Series.
IEC 61290-3-1 NOTE Harmonized as EN 61290-3-1.
IEC 61290-3-2 NOTE Harmonized as EN 61290-3-2.
IEC 61290-4-2 NOTE Harmonized as EN 61290-4-2.
---------------------- Page: 4 ----------------------
SIST EN 61290-4-1:2017
EN 61290-4-1:2016
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

NOTE 1 When an International Publication has been modified by common modifications, indicated by (mod), the relevant

EN/HD applies.

NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available here:

www.cenelec.eu
Publication Year Title EN/HD Year
IEC 61291-1 - Optical amplifiers - EN 61291-1 -
Part 1: Generic specification
---------------------- Page: 5 ----------------------
SIST EN 61290-4-1:2017
---------------------- Page: 6 ----------------------
SIST EN 61290-4-1:2017
IEC 61290-4-1
Edition 2.0 2016-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical amplifiers – Test methods –
Part 4-1: Gain transient parameters – Two-wavelength method
Amplificateurs optiques – Méthodes d’essai –
Partie 4-1: Paramètres de gain transitoire – Méthode à deux longueurs d'onde
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.30 ISBN 978-2-8322-3659-8

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
SIST EN 61290-4-1:2017
– 2 – IEC 61290-4-1:2016 © IEC 2016
CONTENTS

FOREWORD ......................................................................................................................... 3

INTRODUCTION ................................................................................................................... 5

1 Scope ............................................................................................................................ 6

2 Normative references..................................................................................................... 6

3 Terms, definitions and abbreviated terms ....................................................................... 6

3.1 Terms and definitions ............................................................................................ 6

3.2 Abbreviated terms ................................................................................................. 8

4 Measurement apparatus ................................................................................................ 8

5 Test specimen ............................................................................................................. 11

6 Procedure ................................................................................................................... 11

7 Calculations ................................................................................................................ 12

8 Test results ................................................................................................................. 12

Annex A (informative) Background on transient phenomenon in optical amplifiers ............... 13

Annex B (informative) Slew rate effect on transient gain response ...................................... 16

B.1 The importance of rise time and fall time of input power ....................................... 16

B.2 Measured data and explanation ........................................................................... 16

Bibliography ....................................................................................................................... 19

Figure 1 – Definitions of rise and fall times ............................................................................ 9

Figure 2 – OFA transient gain response .............................................................................. 10

Figure 3 – Generic transient control measurement setup...................................................... 11

Figure A.1 – OFA pump control for a chain of 5 OFAs and 4-fibre spans .............................. 14

Figure A.2 – EDFA spectral hole depth for different gain compression .................................. 15

Figure A.3 – EDFA spectral hole depth for different wavelengths ......................................... 15

Figure B.1 – Transient gain response at various slew rates .................................................. 17

Figure B.2 – 16 dB add and drop (rise and fall time = 10 µs) ................................................ 18

Figure B.3 – 16 dB add and drop (rise and fall time = 1 000 µs) ........................................... 18

Table 1 – Examples of add and drop scenarios for transient control measurement .............. 12

Table 2 – Typical results of transient control measurement .................................................. 12

Table B.1 – Transient gain response for various rise times and fall times (16 dB add or

drop) .................................................................................................................................. 17

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SIST EN 61290-4-1:2017
IEC 61290-4-1:2016 © IEC 2016 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL AMPLIFIERS –
TEST METHODS –
Part 4-1: Gain transient parameters –
Two-wavelength method
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 61290-4-1 has been prepared by subcommittee 86C: Fibre optic

systems and active devices, of IEC technical committee 86: Fibre optics.

This second edition cancels and replaces the first edition published in 2011. This edition

constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous

edition:
a) extended the applicability from only EDFAs to all OFAs;

b) updated definitions for consistency with other documents in the IEC 61290-4 series.

---------------------- Page: 9 ----------------------
SIST EN 61290-4-1:2017
– 4 – IEC 61290-4-1:2016 © IEC 2016
The text of this standard is based on the following documents:
CDV Report on voting
86C/1347/CDV 86C/1397/RVC

Full information on the voting for the approval of this International Standard can be found in

the report on voting indicated in the above table.

This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

A list of all parts of the IEC 61290 series, published under the general title Optical amplifiers –

Test methods can be found on the IEC website.

The committee has decided that the contents of this publication will remain unchanged until

the stability date indicated on the IEC website under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
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SIST EN 61290-4-1:2017
IEC 61290-4-1:2016 © IEC 2016 – 5 –
INTRODUCTION

This part of IEC 61290-4 is devoted to optical amplifiers (OAs). The technology of OAs is

quite new and still emerging; hence amendments and new editions to this document can be

expected.

Background information on the transient phenomenon in erbium-doped fibre amplifiers and

the consequences on fibre optic systems is provided in Annex A and on slew rate effects in

Annex B.
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SIST EN 61290-4-1:2017
– 6 – IEC 61290-4-1:2016 © IEC 2016
OPTICAL AMPLIFIERS –
TEST METHODS –
Part 4-1: Gain transient parameters –
Two-wavelength method
1 Scope

This part of IEC 61290-4 applies to optical amplifiers (OAs) using active fibres (optical fibre

amplifiers (OFAs)) containing rare-earth dopants including erbium-doped fibre amplifiers

(EDFAs) and optically amplified elementary sub-systems. These amplifiers are commercially

available and widely deployed in service provider networks.

The object of document is to provide the general background for OFA transients and related

parameters, and to describe a standard test method for accurate and reliable measurement of

the following transient parameters:

a) channel addition or removal transient gain overshoot and transient net gain overshoot;

b) channel addition or removal transient gain undershoot and transient net gain undershoot;

c) channel addition or removal gain offset;

d) channel addition or removal transient gain response time constant (settling time).

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 61291-1, Optical amplifiers – Part 1: Generic specification
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in IEC 61291-1 and the

following apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
surviving channel
optical signal that remains after a drop event
3.1.2
rise time

time it takes for the input optical signal to rise from 10 % to 90 % of the total difference

between the initial and final signal levels during an add event
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SIST EN 61290-4-1:2017
IEC 61290-4-1:2016 © IEC 2016 – 7 –
Note 1 to entry: See Figure 1(a).
3.1.3
initial gain
gain of the surviving or pre-existing channel before a drop or add event
3.1.4
final gain

steady-state gain of the surviving or pre-existing channel after a long period of time (i.e. once

the gain has stabilized) after a drop or add event
3.1.5
gain offset
change of the gain between initial and final state
Note 1 to entry: Gain offset is expressed in dB.
Note 2 to entry: Gain offset = final gain (in dB) ‒ initial gain (in dB).

Note 3 to entry: Gain offset may be positive or negative for both channel addition and removal events.

3.1.6
gain stability

specified peak-to-peak gain fluctuations of the OFA under steady state conditions (i.e. not in

response to a transient event)
3.1.7
transient gain response time constant
settling time

amount of time required to bring the gain of the surviving or pre-existing channel to the final

gain

Note 1 to entry: This parameter is the measured time from the beginning of the drop or add event that created the

transient gain response to the time at which the surviving or pre-existing channel gain first enters within the gain

stability band centred on the final gain.
Note 2 to entry: Hereon, this will also be referred to as "settling time".
3.1.8
transient gain overshoot

difference between the maximum surviving or pre-existing channel gain reached during the

OFA transient response to a drop or add event, and the lowest of either the initial gain and

final gain
Note 1 to entry: Transient gain overshoot is expressed in dB.
Note 2 to entry: Hereon, this will also be referred to as "gain overshoot".
3.1.9
transient net gain overshoot

difference between the maximum surviving or pre-existing channel gain reached during the

OFA transient response to a drop or add event, and the highest of either the initial gain and

final gain
Note 1 to entry: The transient net gain overshoot is expressed in dB.

Note 2 to entry: The transient net gain overshoot is the transient gain overshoot minus the gain offset, and

represents the actual transient response not related to the shift of the amplifier from the initial steady state

condition to the final steady state condition.
Note 3 to entry: Hereon, this will also be referred to as "net gain overshoot".
---------------------- Page: 13 ----------------------
SIST EN 61290-4-1:2017
– 8 – IEC 61290-4-1:2016 © IEC 2016
3.1.10
transient gain undershoot

difference between the minimum surviving or pre-existing channel gain reached during the

OFA transient response to a drop or add event, and the highest of either the initial gain and

final gain
Note 1 to entry: The transient gain undershoot is expressed in dB.
Note 2 to entry: Hereon, this will also be referred to as "gain undershoot".
3.1.11
transient net gain undershoot

difference between the minimum surviving or pre-existing channel gain reached during the

OFA transient response to a drop or add event and the lowest of either the initial gain and

final gain
Note 1 to entry: The transient net gain undershoot is expressed in dB.

Note 2 to entry: The transient net gain undershoot is the transient gain undershoot minus the gain offset and

represents the actual transient response not related to the shift of the amplifier from the initial steady state

condition to the final steady state condition.
Note 3 to entry: Hereon this will also be referred to as "net gain undershoot".
3.2 Abbreviated terms
AGC automatic gain control
AOM acousto-optic modulator
BER bit error rate
DFB distributed feedback
DWDM dense wavelength division multiplexing
EDFA erbium-doped fibre amplifier
FWHM full-width half-maximum
NEM network equipment manufacturer
NSP network service provider
O/E optical-to-electronic
OA optical amplifier
OFA optical fibre amplifier
OSNR optical signal-to-noise ratio
SHB spectral-hole-burning
VOA variable optical attenuator
WDM wavelength division multiplexing
4 Measurement apparatus

When the input power to an OFA operating in saturation changes sharply, the gain of the

amplifier will typically exhibit a transient response before settling back into the required gain.

This response is dictated both by the optical characteristics of the active fibre within the OFA

as well as the performance of the automatic gain control (AGC) mechanism.

Since a change in input power typically occurs when part of the dense wavelength division

multiplexing (DWDM) channels within the specified transmission band are dropped or added,

definitions are provided that describe a dynamic event leading to transient response. Rise and

fall time definitions are shown in Figure 1.
---------------------- Page: 14 ----------------------
SIST EN 61290-4-1:2017
IEC 61290-4-1:2016 © IEC 2016 – 9 –
Rise time
Time
Channel
Channel
addition start
addition end
IEC
(a) Definitions of rise and fall times in the case of a channel addition event
Fall time
Time
Channel
Channel
removal start
removal end
IEC
(b) Definitions of rise and fall times in the case of a channel removal event
Figure 1 – Definitions of rise and fall times

The parameters generally used to characterize the transient gain behaviour of a gain

controlled OFA for the case of channel removal are defined in Figure 2(a). The figure

specifically represents the time dependence of the gain of one of the surviving channels when

channels are removed. Likewise, the transient gain behaviour for the case when channels are

added is shown in Figure 2(b). The main transient parameters are: transient gain response

time constant (settling time), gain offset, transient net gain overshoot, and transient gain net

undershoot. The transient gain overshoot and undershoot are particularly critical to carriers

Input power to EDFA
Input power to EDFA
(linear a.u.)
(linear a.u.)
10 % of change
100 % of change
10 % of change
90 % of change
90 % of change
100 % of change
---------------------- Page: 15 ----------------------
Transient gain response time
constant (settling time)
SIST EN 61290-4-1:2017
– 10 – IEC 61290-4-1:2016 © IEC 2016

and network equipment manufacturers (NEMs) given that the speed and amplitude of gain

fluctuations compound through the network as the optical signal passes through an increasing

number of cascaded amplifiers. Properly designed optical amplifiers have very small values

for these transient parameters.
Final gain
Initial
Gain offset
gain
Net gain
undershoot
Time
IEC
(a) OFA transient gain response for a channel removal event
Net gain
Gain overshoot
Overshoot
Gain offset
Initial
gain
Final gain
Transient gain response time
constant (settling time)
Time
IEC
(b) OFA transient gain response for a channel addition event
Figure 2 – OFA transient gain response

Figure 3 shows a typical setup to characterize the transient response properties of OFAs.

Gain
stability
Gain (dB)
Gain (dB)
Gain overshoot
Gain undershoot
Net gain
overshoot
Gain stability
Gain
undershoot
Net gain undershoot
---------------------- Page: 16 ----------------------
SIST EN 61290-4-1:2017
IEC 61290-4-1:2016 © IEC 2016 – 11 –
DDFFBB Las Laserer
VOVOA1A1
Optical OOOFFFAAA Pass
Optical Pass
under
coupler underunder filter
coupler filter
test
tteestst
Pol. Optical
DDFFBB Las Laserer
Pol. Optical
VOVOA2A2
modulator
scrambler modulator
DetDecettecor tor
TTrriiggergger
Pulse generator OOsciscillllooscoscoppee
Pulse generator
IEC
Figure 3 – Generic transient control measurement setup
5 Test specimen

The OFA shall operate at nominal operating conditions. If the OFA is likely to cause laser

oscillations due to unwanted reflections, optical isolators should be used to bracket the OFA

under test. This will minimize signal instability and measurement inaccuracy.
6 Procedure

In the setup shown in Figure 3, the input signal power into the amplifier being tested is the

combination of two distributed feedback (DFB) lasers with wavelengths approximately 1 nm

apart. One of the wavelengths represents add or drop channels while the other represents

pre-existing or surviving channels. Each wavelength channel is subsequently adjusted with a

variable optical attenuator (VOA) to the desired optical input power levels. One optical

modulator driven by a function generator acts as an on/off switch, to simulate add and drop

events. The two optical channels are subsequently combined onto the same fibre before the

signal is directed to the amplifier being tested. A tuneable filter, an optical-to-electronic (O/E)

converter and an oscilloscope are placed in tandem at the output of the amplifier. The pre-

existing or surviving channel is selected with the tuneable filter and its transient response is

monitored with the O/E converter and oscilloscope. A waveform similar to the one shown in

Figure 2 is displayed on the oscilloscope’s screen.

To simulate a drop event at the input of the amplifier being tested, the two lasers are set so

that their total input power is equal to the amplifier’s typical input power (e.g. 1 dBm).

Therefore, the two lasers at –2 dBm each represent 20 optical channels having –15 dBm

power per channel. When the function generator turns the modulator into the “off” position,

the second laser is completely suppressed, changing the system’s channel loading. For

instance, when one laser is switched off, it simulates a 3 dB "drop" or a change in the

system’s channel loading from 40 channels to 20 channels. Similarly, when the modulator is

changed into an "on" state, the addition of a second laser simulates a 3 dB add in optical

power, or a change in the system’s channel loading from 20 channels to 40 channels. For

other transient control measurements, the VOAs can be adjusted accordingly so that the input

power levels will differ by an appropriate value.

Several transient control measurements can be performed, according to the operating

conditions and specifications that are provided. Measurements may also be taken for various

add and drop scenarios as shown in Table 1. These measurements are typically performed

over a broad range of input power levels.
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SIST EN 61290-4-1:2017
– 12 – IEC 61290-4-1:2016 © IEC 2016
Table 1 – Examples of add and drop scenarios
for transient control measurement
Pre-existing or Channels added or
Scenario Total channels
surviving channels dropped
20 dB add or drop 100 1 99
16 dB add or drop 40 1 39
13 dB add or drop 40 2 38
10 dB add or drop 40 4 36
6 dB add or drop 40 10 30
3 dB add or drop 40 20 20
7 Calculations
The results of the transient measurement are the following parameters:

• Channel addition or removal transient gain overshoot and transient net gain overshoot

• Channel addition or removal transient gain undershoot and transient net gain undershoot

• Channel addition or removal gain offset

• Channel addition or removal transient gain response time constant (settling time)

These parameters can be extracted from the oscilloscope display, as described in Figure 2.

8 Test results

Table 2 shows typical measurement conditions and transient control measurement results of

C-band OFAs. The measurement conditions include gain, surviving channel wavelength, input

power, transie
...

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