IEC TR 61292-12:2022

Optical amplifiers - Part 12: Fibre amplifiers for space division multiplexing transmission

IEC TR 61292-12:2022 which is a Technical Report, provides general information on optical fibre amplifiers for space division multiplexed transmission systems using multi-core, few-mode, and multi-core and few-mode optical fibres. This document describes the classification, concepts, configurations, and implementations of these amplifiers as well as state-of-the-art development technologies, specific features and measurement methods.

General Information

• Status: Published
• Publication Date: 27-Sep-2022
• ICS: 33.180.10 - Fibres and cables
• ICS: 33.180.30 - Optic amplifiers
• Technical Committee: SC 86C - Fibre optic systems and active devices
• Current Stage: PPUB - Publication issued
• Start Date: 01-Nov-2022
• Completion Date: 28-Sep-2022

Standards Content (Sample)

IEC TR 61292-12
®

Edition 1.0 2022-09
TECHNICAL
REPORT

colour
inside


Optical amplifiers –
Part 12: Fibre amplifiers for space division multiplexing transmission

IEC TR 61292-12:2022-09(en)

---------------------- Page: 1 ----------------------
THIS PUBLICATION IS COPYRIGHT PROTECTED
Copyright © 2022 IEC, Geneva, Switzerland

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 Secretariat 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 Products & Services Portal - products.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 have
committee, …). It also gives information on projects, replaced 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 22 300 terminological entries in English
details all new publications released. Available online and once
and French, with equivalent terms in 19 additional languages.
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].

---------------------- Page: 2 ----------------------
IEC TR 61292-12

®


Edition 1.0 2022-09




TECHNICAL



REPORT








colour

inside










Optical amplifiers –

Part 12: Fibre amplifiers for space division multiplexing transmission


























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 33.180.30, 33.180.10 ISBN 978-2-8322-5755-5




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


® Registered trademark of the International Electrotechnical Commission

---------------------- Page: 3 ----------------------
– 2 – IEC TR 61292-12:2022  IEC 2022
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Abbreviated terms . 8
4 Classification of SDM OFAs . 9
5 Multi-core OFA technology . 10
5.1 Outline of multi-core EDFAs . 10
5.2 State-of-the-art multi-core EDFA development technology . 12
5.2.1 Core pumped multi-core EDFA . 12
5.2.2 Cladding pumped multi-core EDFA . 16
5.2.3 Core and cladding hybrid pumped MC-EDFA . 18
5.3 State-of-the-art remotely pumped MC-EDFA and MC-FRA technologies. 18
5.4 Specific features and measurements. 19
6 Few-mode OFA technology . 21
6.1 Outline of few-mode EDFA . 21
6.2 State-of-the-art few-mode EDFA development technology. 22
6.2.1 Few-LP mode EDFA . 22
6.2.2 OAM mode EDFA and Coupled-core mode EDFA . 25
6.3 State-of-the-art FM-FRA development technology . 26
6.4 Specific feature and measurement . 27
7 Combined MC and FM-OFA technology . 28
Bibliography . 30

Figure 1 – Classification of SDM OFAs . 10
Figure 2 – Concept of an MC-EDFA . 11
Figure 3 – Amplification media and pump methods for MC-EDFAs . 11
Figure 4 – Configurations of core-pumped MC-EDFAs . 13
Figure 5 – Configuration and amplification characteristics of a core-pumped MC-EDFA
with 7-core MC-EDF and conventional WDM couplers . 14
Figure 6 – Configuration and amplification characteristics of a core-pumped MC-EDFA
with 19-core MC-EDF and MC WDM coupler . 15
Figure 7 – Configuration of a cladding-pumped MC-EDFA . 16
Figure 8 – Pump light combiner . 17
Figure 9 – Configuration and amplification characteristics of an EDFA with 32-core
cladding pumped MC-EDF . 17
Figure 10 – Configuration of core and cladding hybrid-pumped MC-EDFA . 18
Figure 11 – Configuration and performance of remotely pumped MC-EDFA and
MC-FRA . 19
Figure 12 – Multi-core EDFA evaluation setup for basic optical characteristics . 20
Figure 13 – XT evaluation methods with different wavelengths . 20
Figure 14 – Image of each mode propagating through the core . 22
Figure 15 – Configuration of an FM-EDFA. 22

---------------------- Page: 4 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 3 –
Figure 16 – Example of gain and NF of a 2-LP FM-EDFA (large core, step core index
and step erbium doping profile structured as in a conventional EDF) . 23
Figure 17 – Configuration and amplification characteristics of a 2-LP mode EDFA

prototype consisting of a ring-core FM-EDF, FM WDM coupler, and two FM isolators . 24
Figure 18 – Configuration and amplification characteristics of a 3-mode EDFA
prototype using 2-LP signal modes employing a ring-core FM-EDF . 25
Figure 19 – Configuration and amplification characteristics of a 2-OAM mode EDFA . 26
Figure 20 – 2-LP-mode FM-FRA experiment . 27
Figure 21 – FM-EDFA evaluation setup for basic optical characteristics . 28
Figure 22 – MC-EDFA with FM cores . 29

---------------------- Page: 5 ----------------------
– 4 – IEC TR 61292-12:2022  IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

OPTICAL AMPLIFIERS –

Part 12: Fibre amplifiers for space
division multiplexing transmission

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 TR 61292-12 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is a Technical Report.
1
External document OITDA/TP 33/AM [1] has served as a basis for the elaboration of this
document.
___________
1
 Numbers in square brackets refer to the Bibliography.

---------------------- Page: 6 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 5 –
The text of this Technical Report is based on the following documents:
Draft Report on voting
86C/1807/DTR 86C/1819/RVDTR

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 Technical Report 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 61292 series, published under the general title Optical amplifiers,
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.

---------------------- Page: 7 ----------------------
– 6 – IEC TR 61292-12:2022  IEC 2022
INTRODUCTION
Optical amplifiers (OAs) are essential components for designing long-haul optical transmission
systems, for which many standards have been published. Recently, research has been
conducted to develop higher data rate fibre optic transmission systems using space division
multiplexing (SDM) with multi-core and few-mode optical fibres. A development effort is also
underway to fabricate optical fibre amplifiers (OFAs) for SDM, which are necessary for
extending the transmission distance. The OFAs varieties include multi-core optical fibre
amplifiers, few-mode optical fibre amplifiers, and multi-core and few-mode optical fibre
amplifiers. This document provides a better understanding of OFAs for SDM fibre transmission
systems.
NOTE Few-mode fibres are special types of multimode fibres.

---------------------- Page: 8 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 7 –
OPTICAL AMPLIFIERS –

Part 12: Fibre amplifiers for space
division multiplexing transmission



1 Scope
This part of IEC 61292, which is a Technical Report, provides general information on optical
fibre amplifiers for space division multiplexed transmission systems using multi-core, few-mode,
and multi-core and few-mode optical fibres. This document describes the classification,
concepts, configurations, and implementations of these amplifiers as well as state-of-the-art
development technologies, specific features and measurement methods.
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 60050-731, International Electrotechnical Vocabulary (IEV) – Part 731: Optical fibre
communication
IEC 61291-1, Optical amplifiers – Part 1: Generic specification
IEC TR 61931, Fibre optic – Terminology
3 Terms, definitions, and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-731,
IEC 61291-1, IEC TR 61931, 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
erbium doped fibre amplifier
EDFA
amplifier with rare earth-doped fibre of which core is doped with erbium ions
[SOURCE: IEC TR 61292-3:2020, 3.1.1]
3.1.2
space division multiplexing optical fibre amplifier
SDM OFA
optical fibre amplifier that is used for SDM (space division multiplexing) fibre transmission
systems

---------------------- Page: 9 ----------------------
– 8 – IEC TR 61292-12:2022  IEC 2022
3.1.3
multi-core optical fibre amplifier
multi-core OFA
optical fibre amplifier for multi-core fibre transmission
3.1.4
multi-core erbium doped fibre amplifier
multi-core EDFA
erbium-doped fibre amplifier for multi-core fibre transmission
3.1.5
multi-core fibre Raman amplifier
multi-core FRA
fibre Raman amplifier for multi-core fibre transmission
3.1.6
few-mode optical fibre amplifier
few-mode OFA
optical fibre amplifier for few-mode fibre transmission
3.1.7
few-mode erbium doped optical fibre amplifier
few-mode EDFA
erbium-doped fibre amplifier for few-mode fibre transmission
3.1.8
few-mode fibre Raman amplifier
few-mode FRA
fibre Raman amplifier for few-mode fibre transmission
3.1.9
multi-core and few-mode optical fibre amplifier
multi-core and few-mode OFA
optical fibre amplifier for multi-core and few-mode fibre transmission
3.1.10
multi-core and few-mode erbium doped optical fibre amplifier
multi-core and few-mode EDFA
erbium-doped fibre amplifier for multi-core and few-mode fibre transmission
3.1.11
multi-core and few-mode fibre Raman amplifier
multi-core and few-mode FRA
fibre Raman amplifier for multi-core and few-mode fibre transmission
3.2 Abbreviated terms
EDF erbium-doped fibre
EDFA erbium-doped fibre amplifier
FM few-mode
FMF few-mode fibre
FRA fibre Raman amplifier
GFF gain flattening filter
LD laser diode
LP linearly polarized
MC multi-core

---------------------- Page: 10 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 9 –
MCF multi-core fibre
MC&FMF multi-core fibre with few-mode cores
MDG mode-dependent gain
MDL mode-dependent loss
MDM mode-division multiplexing
MIMO multi-input multi-output
NF noise figure
OA optical amplifier
OAM orbital-angular-momentum
OFA optical fibre amplifier
OSNR optical signal-to-noise ratio
ROPA remote optically pumped amplifier
SDM space division multiplexing
SNR signal-to-noise ratio
VOA variable optical attenuator
WDM wavelength division multiplexing
XT crosstalk
4 Classification of SDM OFAs
Fibre optic transmission systems using space division multiplexing (SDM) utilize multi-core fibre
(MCF) transmission, few-mode fibre (FMF) transmission, or multi-core few-mode fibre
(MC&FMF) transmission. These techniques are employed to overcome the capacity limits of
conventional fibre transmission and can potentially achieve ultra-high transmission capacity per
fibre (i.e., exabit/s). Long-haul transmission systems usually employ optical fibre amplifiers
(OFAs) to maintain sufficiently high optical signal power along the fibre optic transmission line.
SDM transmission systems typically use multi-core EDFAs (MC-EDFAs), few-mode EDFAs
(FM-EDFAs), or multi-core few mode EDFAs (MC&FM-EDFAs). In contrast to conventional
EDFAs, the input and output fibres of MC-EDFAs, FM-EDFAs and MC&FM-EDFAs are MCF,
FMF and MC&FMF, respectively. Amplification media used for the above are multi-core erbium-
doped fibres (MC-EDF), few-mode EDF (FM-EDF) and multi-core few-mode EDFs
(MC&FM-EDF) [2] to [45]. Furthermore, MCFs, FMFs and MC-FMFs are used as Raman
amplification media for multi-core fibre Raman amplifiers (MC-FRAs), few-mode fibre Raman
amplifiers (FM-FRAs), and multi-core few-mode fibre Raman amplifiers (MC&FM-FRAs).
Figure 1 shows the classification scheme for SDM OFAs, which consists of MC-OFAs and
FM-OFAs, as described in IEC TR 61292-3 [6]. MC-OFAs comprise MC-EDFAs and MC-FRAs,
whereas FM-OFAs include FM-EDFAs and FM-FRAs. Furthermore, as various mode
multiplexing techniques are under consideration for FMF transmission, FM-OFAs can have
multiple mode types for amplification, such as linearly polarized (LP) modes, orbital-angular-
momentum (OAM) modes, and coupled-core modes. MC&FM-OFAs can be made by combining
MC and FM-OFA techniques.

---------------------- Page: 11 ----------------------
– 10 – IEC TR 61292-12:2022  IEC 2022

Figure 1 – Classification of SDM OFAs
5 Multi-core OFA technology
5.1 Outline of multi-core EDFAs
Figure 2 shows the concept of an MC-EDFA. In this case, the EDFA consists of an array of
several conventional EDFAs (i.e., conventional gain blocks) with fan-out and fan-in elements
for connecting the MC-EDFA to the output and input MCFs. Newer versions of MC-EDFAs are
under development at the time of writing with the goal to improve performance through the
integration of optical components (see IEC TR 61292-1 [7]) and EDF cores, without degradation
in amplification properties and amplification efficiency. The amplification properties can be
degraded, for example, by crosstalk (XT) between the optical signals propagating through the
various amplifier cores.
Crosstalk characteristics are particularly important for MC-EDFAs, because several cores of
EDFs need to be integrated with high density. Furthermore, it is important to achieve the same
amplification characteristics for each core. It is expected that highly integrated MC-EDFA will
lead to smaller amplifier systems, lower complexity/cost, and lower power consumption,
compared with arrayed EDFAs.

---------------------- Page: 12 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 11 –

Figure 2 – Concept of an MC-EDFA
Figure 3 shows several amplification media and pump methods for MC-EDFAs. Multi-core EDFs
(MC-EDFs) are now actively under development [4], [5]. MC-EDFAs have the advantage that
multi-core fibre fabrication techniques can be applied, so that complexity and size can be
reduced through manufacturing. One of the challenges is to achieve uniform amplification
characteristics in each core of the MC-EDFA. There are two types of MC-EDF. One type is
designed for a single discrete pump laser; and the other type, which has a double cladding
structure, is designed for cladding pumping. For the first type, the pump methods and optical
components used for conventional EDFAs can be adapted. Additionally, this type has a highly
efficient pumping capacity and high-speed controlling ability. The second type is targeted to
have lower power consumption, and it can be downsized by decreasing the number of pump
laser diodes (LDs) used. It has also been reported that bundled EDFs and multi-element EDFs
can be used as amplification media for MC-EDFAs.

Source: TuS1-2, Photonics West 2014 [4], Figure 1, reproduced with the permission of SPIE.
Figure 3 – Amplification media and pump methods for MC-EDFAs

---------------------- Page: 13 ----------------------
– 12 – IEC TR 61292-12:2022  IEC 2022
5.2 State-of-the-art multi-core EDFA development technology
5.2.1 Core pumped multi-core EDFA
Figure 4 a) shows a typical configuration of a core-pumped MC-EDFA with MC-EDF and
conventional WDM couplers, and Figure 4 b) shows a configuration with MC EDF and a
multi-core WDM coupler. Other optical components used for MC-EDFAs include an MC tap
coupler, which monitors the signal intensity in each core, an MC isolator, and other optional
components such as MC ASE rejection filters, MC pump rejection filters, MC variable optical
attenuators (MC VOA), and MC gain flattening filters (MC GFF). These optional components
can be placed in different locations.
The most important component in Figure 4 a) and Figure 4 b) is the MC-EDF, which can be
equipped with up to 19 cores, all having practical amplification characteristics, by using modified
MCF fabrication techniques, according to previous reports [4], [5], [8] to [10]. One of the
important characteristics of MC-EDFs is optical crosstalk between the various cores. Crosstalk
is caused by mode coupling between cores. In general, the level of crosstalk depends on the
spatial separation between the cores and on the EDF length. Since the length of the MC-EDF
is much shorter than that of the MC transmission fibre, crosstalk in MC EDFs can be set to a
larger value compared with other MCFs. In MC EDFs, acceptable levels of crosstalk can
generally be achieved with a core pitch of 30 μm or larger.
Several prototypes have already been demonstrated, such as those equipped with a
core-pumped MC-EDFA with MC EDF and conventional WDM couplers, and those with MC EDF
and newly developed MC WDM couplers. Figure 5 shows an example of the configuration and
amplification characteristics of a core-pumped MC-EDFA with a 7-core EDF and conventional
WDM couplers [4], and Figure 6 shows the configuration and amplification characteristics of a
core-pumped MC-EDFA with 19-core MC-EDF and MC WDM coupler [8].
Other prototypes that have been demonstrated include core-pumped MC-EDFAs with a bundled
EDF and a multi-element EDF. For the purpose of developing a practical core-pumped
MC-EDFA, uniform amplification characteristics are required for the various EDF cores.
Moreover, multi-core optical components, such as MC tap couplers and MC GFFs, are
indispensable, because these components have better performance and reliability as well as
lower complexity/cost than arrays of conventional tap couplers and GFFs.

---------------------- Page: 14 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 13 –

a) Using conventional WDM couplers

b) Using MC WDM couplers

Figure 4 – Configurations of core-pumped MC-EDFAs

---------------------- Page: 15 ----------------------
– 14 – IEC TR 61292-12:2022  IEC 2022

a) Configuration

b) Amplification characteristics

Source: TuS1-2, Figure 3, Photonics West 2014 [4], reproduced with the permission of SPIE.
Figure 5 – Configuration and amplification characteristics of a core-pumped MC-EDFA
with 7-core MC-EDF and conventional WDM couplers

---------------------- Page: 16 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 15 –

a) Configuration

b) Amplification characteristics

Source: Optics Express 22, p. 90 (2014) [8], Figure 3 and Figure 4, reproduced with the permission of Optica
Publishing Group. © The Optical Society.
Figure 6 – Configuration and amplification characteristics of a core-pumped MC-EDFA
with 19-core MC-EDF and MC WDM coupler

---------------------- Page: 17 ----------------------
– 16 – IEC TR 61292-12:2022  IEC 2022
5.2.2 Cladding pumped multi-core EDFA
Figure 7 shows a typical configuration of a cladding-pumped MC-EDFA. In addition to the optical
components shown for the core-pumped MC-EDFA, this amplifier requires an MC-EDF designed
for cladding pumping as well as a special pump light combiner.

Figure 7 – Configuration of a cladding-pumped MC-EDFA
The cladding pump technique is used to increase the output power of optical amplifiers, as
described in IEC TR 61292-8 [11]. It is believed that cladding pumping can reduce the
complexity and power consumption of an MC-EDFA because the various EDF cores can be
pumped collectively.
An MC-EDF designed for cladding pumping has a double cladding structure that comprises the
cores, an inner cladding, and outer claddings. It has been reported that an MC-EDF with
cladding pumping can have up to 32-cores [4], [5], [9], [10], [13], [14].
To accomplish cladding pumping, the pump light is coupled to an inner cladding of the MC-EDF
with the help of a specially designed pump light combiner. Since the inner cladding area is much
larger than the core area, a high-power multimode LD can be used to inject the pump light into
the inner cladding. The pump light combiner is known from other cladding pumping techniques
and can be either a fused bundled fibre pump combiner, a lens system combiner, or a tapered
fibre side-coupled combiner, as shown in Figure 8 a), Figure 8 b) and Figure 8 c). Several
prototypes of the cladding-pumped MC-EDFAs have been reported [3], [4], [6] to [9]. Figure 9
shows an example of the configuration and amplification characteristics of an EDFA with a
32-core cladding-pumped MC-EDF [13].
A practical cladding-pumped MC-EDFA ideally has uniform amplification characteristics in the
various EDF cores, and its optical components have good performance and reliability.

---------------------- Page: 18 ----------------------
IEC TR 61292-12:2022  IEC 2022 – 17 –

a) Fused bundled fibre pump combiner b) Lens system combiner

c) Tapered fibre side-c
...