TP（技術資料）

空間分割多重伝送用光ファイバ増幅器（Optical fibre amplifier for space division multiplexing transmission）

OITDA/TP 33/AM：2022
第2版

公表

2022 年 4 月

取纏委員会
光増幅器及びダイナミックモジュール標準化部会

発行：一般財団法人光産業技術振興協会
Optoelectronics Industry and Technology Development Association（JAPAN）（1）

Intentionally Blank

目

次
ページ

まえがき ........................................................................................................................................................................ 3
INTRODUCTION .......................................................................................................................................................... 1
1

Scope ...................................................................................................................................................................... 1

2

Normative references ............................................................................................................................................. 1

3

Terms, definitions and abbreviated terms ............................................................................................................... 2
3.1

Terms and definitions ..................................................................................................................................... 2

3.2

Abbreviated terms .......................................................................................................................................... 3

4

Classification of SDM OFA ................................................................................................................................... 4

5

Multi-core OFA technology .................................................................................................................................... 4

6

7

5.1

Outline of multi-core EDFA ........................................................................................................................... 4

5.2

State-of-the-art multi-core EDFA development technology ........................................................................... 5

5.2.1

Core pumped multi-core EDFA .................................................................................................................. 5

5.2.2

Cladding-pumped multi-core EDFA........................................................................................................... 9

5.2.3

Core and cladding hybrid-pumped MC-EDFA ......................................................................................... 10

5.3

State-of-the-art remotely-pumped MC-EDFA and MC-FRA development technology ............................... 11

5.4

Specific features and measurement .............................................................................................................. 12

Few-mode OFA technology .................................................................................................................................. 13
6.1

Outline of few-mode EDFA ......................................................................................................................... 13

6.2

State-of-the-art few-mode EDFA development technology ......................................................................... 15

6.2.1

Few-LP mode EDFA ................................................................................................................................ 15

6.2.2

OAM mode EDFA and Coupled-core mode EDFA .................................................................................. 17

6.3

State-of-the-art FM FRA development technology ...................................................................................... 18

6.4

Specific features and measurement .............................................................................................................. 19

MC and FM-OFA technology ............................................................................................................................... 20

Bibliography ................................................................................................................................................................. 21（1）

TP 33/AM: 2022

（2）

TP 33/AM: 2022

まえがき
シングルモードファイバ(SMF) を用いた従来の光ファイバ通信システムでは，時分割多重，波長多重，
デジタルコヒーレント技術を用いることで伝送容量の拡大が図られてきた。しかし，通信トラフィックの増加に伴い，更なる光ファイバ通信システムの伝送容量の更なる増加が必要となっている。
近年、通信容量の飛躍的な増加を目的に，マルチコアファイバやマルチモードファイバを伝送路として用いる空間分割多重(SDM) の研究・開発が進められている。
この技術資料は，長距離の SDM 光ファイバ通信システムを構築する際に必要となる SDM アンプについて概要を紹介するものであり，2021 年 2 月に公表された第 1 版で使用されている図面の使用許諾を反映すると共に、エディトリアル修正をおこなって改正したものである。
この技術資料（TP）は，著作権法で保護対象となっている著作物である。
この技術資料（TP）の一部が，特許権，出願公開後の特許出願又は実用新案権に抵触する可能性があることに注意を喚起する。光産業技術振興協会は，このような特許権，出願公開後の特許出願及び実用新案権に関わる確認について，責任はもたない。

この技術資料は，一般財団法人光産業技術振興協会の標準に関する TP（技術資料）である。TP（技術資料）は，規格になる前段階，標準化の技術的資料，規格を補足する などのために公表するものである。

この技術資料に関して，ご意見・情報がありましたら，下記連絡先にお寄せください。
連絡先：一般財団法人光産業技術振興協会標準化室（3）

TP 33/AM: 2022

（4）

OITDA/TP（技術資料）

OITDA/TP 33/AM：2022
Optical fibre amplifier for space division multiplexing transmission
INTRODUCTION
Optical amplifiers (OAs) are essential components for developing a long-haul optical transmission system. IEC TC
86/SC 86C, therefore, has published many standards for OAs. Recently, a research project has been actively conducted
to develop space division multiplexing (SDM) fibre transmission systems that use multi-core, multi-mode fibre, etc..
An development effort is also made to fabricate

optical fibre amplifiers (OFAs)that are necessary for extending thetransmission distance, including a multi-core optical fibre amplifier, a few-mode optical fibre amplifier and a multicore and few-mode optical fibre amplifier. This technical paper provides with a better understanding of OFAs for SDM
fibre transmission systems.

1

Scope

This technical paper is written to provide general information on optical fibre amplifiers for space division multiplex
transmission such as multi-core transmission, few-mode transmission, and multi-core & few-mode transmission. The
paper describes the classificationand outlines of amplifiers, state-of-the-art development technologies, and specificfeatures and measurements.

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 61290-1 (all parts), Optical amplifiers - Test methods - Part 1: Power and gain parameters
IEC 61290-3 (all parts), Optical amplifiers - Test methods - Part 3: Noise figure parameters
IEC 61290-5 (all parts), Optical amplifiers - Test methods - Part 5: Reflectance parameters
IEC 61290-10-1, Optical amplifiers - Test methods - Part 10-1: Multichannel parameters - Pulse method using
an optical switch and optical spectrum analyzer
IEC 61290-10-2, Optical amplifiers - Test methods - Part 10-2: Multichannel parameters - Pulse method using
a gated optical spectrum analyzer
IEC 61291-1, Optical amplifiers – Part 1: Generic specification

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IEC 61291-2, Optical amplifiers - Part 2: Single channel applications - Performance specification template
IEC 61291-4, Optical amplifiers - Part 4: Multichannel applications - Performance specification template
IEC TR 61292-1, Optical amplifiers - Part 1: Parameters of amplifier components
IEC TR 61292-3, Optical amplifiers - Part 3: Classification, characteristics and applications
IEC TR 61292-8, Optical amplifiers - Part 8: High-power amplifiers
IEC TR 61931, Fibre optic – Terminology

3
3.1

Terms, definitions and abbreviated terms
Terms and definitions

For the purposes of this paper, the terms and definitions given in IEC 60050-731, IEC 61291-1, IEC TR 61931, andthe following apply.
3.1.1
erbium doped fibre amplifier
EDFA
amplifier with rare earth-doped fibre of which core is doped with erbium ions
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
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

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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
3.1.10multi-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 fibreEDFA

erbium-doped fibre amplifierFM

few-modeFMF

few-mode fibre

FRA

fibre Raman amplifier

GFF

gain flattening filterLDlaser diodeLPlinearly polarizedMC

multi-coreMCF

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

VOAvariable optical attenuator

WDM

wavelength division multiplexing

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XT

4crosstalkClassification of SDM OFASpace division multiplexing (SDM) fibre transmission includes multi-core fibre (MCF) transmission, few-mode fibre(FMF) transmission, and multi-core (MC) & few-mode fibre (FMF) transmission, and has the potential to overcome
capacity crunch and achieve an ultra-high exabit/s class capacity. A long-haul transmission system needs to have an
optical fibre amplifier (OFA) to maintain high-level optical signal power for SDM transmission that uses multi-core
EDFAs (MC-EDFAs), few-mode EDFAs (FM-EDFAs) and MC- & FM-EDFAs. When comparing with conventional
EDFAs, input and output fibres used for 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 and FM-EDF). [1-4]1 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 of SDM OFAs that consist of MC-OFAs and FM OFAs, as described in IEC TR
61292-3. The former has two types : MC-EDFA and MC-FRA, and the latter also has two types : FM-EDFA and FMFRA. Furthermore, as various mode multiplexing is under consideration for FMF transmission, FM OFAs have mutiple
mode types for amplification: linearly polarized (LP) mode, orbital-angular-momentum (OAM) mode, and coupledcore mode. MC & FM-OFAs can be achieved by combination of MC & FM-OFA techniques.
Multi-core EDFA
(MC-EDFA)
Multi-core OFA(MC-OFA)

Core pumped MC-EDFA

Cladding pumped MC-EDFA
Core & Cladding hybrid pumped MC-EDFA

Multi-core FRA(MC-FRA)SDM-OFA

Few-mode EDFA
(FM-EDFA)
Few-mode OFA(FM-OFA)

Few-LP mode EDFA
Orbital-angular-momentum EDFA
Coupled-core mode EDFA

Few-mode FRA(FM-FRA)Few-LP mode FRA
Orbital-angular-momentum mode FRA

Figure 1 – Classification of SDM OFA

5Multi-core OFA technology

5.1

Outline of multi-core EDFA

Figure 2 shows the concept of MC-EDFA. Although an EDFA for an MCF transmission system only needs an arrayed
EDFA (arrayed several conventional gain blokes) with fans in/out device, MC-EDFAs are now under developmentwith concept to achieve superior performance through the integration of optical components (which are described in
IEC TR 61292-1) and cores of EDFs, without any degradation in amplification properties such as the crosstalk (XT)
between optical signals (which propagates in each core), and the amplification efficiency. The XT characteristic is
1

The number in the square bracket shows the number of bibliographies

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particularly important, as several cores of EDFs need to be incorporated with high density. Furthermore, it is also
important to achieve the same amplification characteristics for each core. Use of MC-EDFA aims at making a systemthat is smaller with lower costs and lower power consumption than the arrayed EDFA.
Multi core fiber
Single mode core fiberElectrical

Integration of amplification medium

Gain block 1
Tap
coupler

WDM
coupler
EDF

Isolator
OpticalConnector
(MCF)

*ASE
rejection filter *GFF *VOAFan out

・
・
・

PD

・
・
・

・
・
・

Gain block N
Tap
coupler

Isolator*Pump
rejection filter

PD
Pump LD

Tap
coupler

WDM
coupler*ASE
rejection filter *GFF *VOAEDFIsolator

Integration of optical components

Tapcoupler

Isolator*Pump
rejection filter

PD
Pump LDFan inOpticalConnector
(MCF)

PD

*Optional components (can be placed elsewhere)
ASE rejection filter
Pump rejection filter
VOA: Variable optical attenuator
GFF: Gain flattening filter

Figure 2 – Concept of MC-EDFA
Figure 3 shows several amplification mediums and pump methods of the MC -EDFA. MC-EDF is now
actively under development. [3, 4] Some of the advantageous points held by MC-EDFA are that multicore
fibre fabrication technique would be applicable, and cost s and size can be reduced through manufacturing.
One of the challenging points is to make uniformed amplification characteristics in each core. There are two
types of MC-EDF: One is for a discrete pump only, and the other (that has a double cladding structure) isfor a cladding pump. In the former type, a pump method and optical components used for the conventional
EDFAs can be adapted. Additionally, it has a highly efficient pumping capacity and high-speed controlling
ability. In the latter one, it is a lower power consumption type and can be downsized by decreasing thenumber of pump laser diodes (LDs) used. We have also heard that a bundled EDF and a multi-element EDF
can be used as amplification media for MC-EDFAs.
Amp.
mediumBundled EDF

Double-cladding structure
BobbinPump
methodMulti-element EDF

Multi-core EDF

Coating

EDF

Cladding

Discrete pumping (core pumping)Core

1st Cladding

2nd Cladding

Coating

EDF

Discrete pumping and/or Cladding pumping
Cladding pumping

SignalPump

SignalPump

Figure 3 – Several amplification mediums and pump methods of MC-EDFA [Reprinted withpermission from [3]. © 2013 SPIE]
5.2

State-of-the-art multi-core EDFA development technology

5.2.1 Core pumped multi-core EDFA

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Figure 4 a) shows the configurations of core-pumped MC-EDFA with MC-EDF, and conventional WDM couplers, andFigure 4 b) shows one with MC-EDF and MC WDM coupler. Other optical components used for the construction
include a MC tap coupler that monitors the signal intensity of each core, a MC isolator, and optional components (canbe placed elsewhere) such as MC ASE rejection filters, MC pump rejection filters, MC variable optical attenuators(MC VOA), and MC Gain flattening filters (MC GFF).
The most important component is a MC-EDF that can be equipped with up to 19 cores with practical amplification
characteristics by modifying of MCF fabrication technique, according to a previous report. [3-7] One of the importantcharacteristics of MC-EDFs is crosstalk between each core.Crosstalk is caused by mode coupling between cores. In
general, most of crosstalk occurs depending on a distance between each core and an EDF length. As a length of MCEDF used as a transmission line is relatively shorter in the MC-EDFA than that in MCF, crosstalk of MC-EDFs can be
set to a larger value compared with other MCFs. A minimum core pitch of MC-EDF is 30 m according to a previous
report, for the purpose of keeping the adequate crosstalk value.
Several prototypes have already been launched, such as those equiped with a core-pumped MC-EDFA with MC-EDF
and conventional WDM couplers, and those with MC-EDF and newly developed MC WDM coupler. Figure 5 a), b),
and Figure 6 a), b) are examples to show configurations and amplification characteristics of a core-pumped MC-EDFA
with 7-core MC-EDF and conventional WDM couplers, and of core-pumped MC-EDFA with 19-core MC-EDF and
MC WDM coupler. [3, 5]
Other prototypes have also been demonstrated such as those of the core-pumped MC-EDFAs with a bundled EDF anda multi-element EDF. For the purpose of develoing a practical core-pumped MC-EDFA, uniformed amplification
characteristics are required between the cores, and the components such as the MC tap coupler, MC GFF and etc. are
indispensable, and each component should have a better performance and reliability and a lower price.
WDM
coupler
Isolator
OpticalConnector
MC Tap(MCF)
Coupler

Pump LDFan out

・
・
・

・
・
・

Fan inMC EDF*MC GFF

*MC
VOA

MC
Isolator*MC Pump
rejection filter
PD

PD

MC Tap
Coupler

OpticalConnector
(MCF)

・
・
・

・
・
・

PD

*MC ASErejection filterPD

WDM
coupler
Isolator
Pump LD

Multi core fiber
Single mode core fiberElectrical*Optional components (can be placed elsewhere)
MC ASE rejection filter
MC Pump rejection filter
MC VOA: Variable optical attenuator
MC GFF: Gain flattening filter

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a) Using conventional WDM couplers
OpticalConnector(MCF)*MC ASErejection filter

MC Tap MC MC WDM
Coupler Isolator coupler
MC EDF
・
・
・

PD
Pump
LD

MC
Isolator*MC Pump
rejection filter

MC Tap
Coupler

OpticalConnector
(MCF)

・
・
・

・
・
・

PD

*MC GFF

*MC
VOA

PD

PD

Pump
LD
Multi core fiber
Single mode core fiberElectrical*Optional components (can be placed elsewhere)
MC ASE rejection filter
MC Pump rejection filter
MC VOA: Variable optical attenuator
MC GFF: Gain flattening filterb) Using MC WDM couplers
Figure 4 – Configurations of Core pumped MC-EDFA

figure (dB)noisefigure(dB)
Gain
noise
Gain
&&

a) Configuration
35

30
25

XT Core #Core 0Core 4
Core 1
Core 5
Core 2
Core 6
Core 3

Gain

20
15
10

Noise figure

5
0
11530
530 11535
535 11540
540 11545
545 11550
550 11555
555 11560
560

Wavelength (nm)Wavelength(nm)b) Amplification characteristics
Figure 5 – Configuration and amplification characteristics of core pumped MC -EDFA with 7-core
MC-EDF and conventional WDM couplers [Reprinted with permission from [3]. © 2013 SPIE]

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WDM
coupler

Photo. of isolator

EDFA

Isolatora) Configuration
15

100 mW pump

25

100 mW pump
NF (dB)20
15-15 dBm input

3

1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)

15

20
15

-15 dBm input

30

20
15

Max. pump

12

Gain (dB)

NF (dB)

96-10 dBm input

5

3

1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)

30

20
15
10

-10 dBm input

5-10

1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)15Max. pump
NF (dB)

25
20
15-5 dBm input

12

Max. pump

96

l = 1 550 nm-5 dBm input

3-30

1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)

30

20

20

20

Gain (dB)30

l = 1 530 nm-10 dBm input

010

l = 1 550 nm-10 dBm input0

3

NF (dB)12

NF (dB)-1012

NF (dB)

-10

6

6

100

200 300 400
Pump power (mW)

500

9
6
3

3
0

l = 1 565 nm-10 dBm input

0

12

9

-20
-10
0
Input power (dBm)

10

-10

9

20

9

30

10

-5 0 5 10 15
Output power (dBm)

123

1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)l = 1 550 nm

Max. pump

6

10

Max. pump

25

NF (dB)

Gain (dB)-15 dBm input
1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)15Max. pump

25

10

Gain (dB)

93

1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)30

Gain (dB)Max. pump

12

6

10

5

-15 dBm input
1 520 1 530 1 540 1 550 1 560 1 570
Wavelength (nm)Max. pump

25

NF (dB)

Gain (dB)

30

5

9
6

10
5

12

Gain (dB)Gain (dB)

30

0

100

200 300 400
Pump power (mW)

500

0

100

200 300 400
Pump power (mW)500b) Amplification characteristics
Figure 6 – Configuration and amplification characteristics of core pumped MC -EDFA with 19-core
MC-EDF and MC WDM coupler [Reprinted with permission from [5]. © 2014 Optica (formerly
OSA)]

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5.2.2 Cladding-pumped multi-core EDFA
Figure 7 shows configurations of a cladding-pumped MC-EDFA. To construct this amplifier, a MC-EDF fora cladding pump and a pump light combiner are required in addition to the optical components shown in the
core-pumped MC-EDFA.
The cladding pump technique is used to increase the output of optical amplifiers as described in IEC TR
61292-8 Optical amplifiers – Part 8. It is thought that costs and power consumption can be reduced in a MCEDFA, as the cores can be pumped collectively.
An MC-EDF designed for cladding pumping has a double cladding structure that comprises the cores, aninner cladding, and outer claddings. It has been reported that an MC -EDF with cladding pumping can haveup to 32-cores [3, 4, 6 to 9].
To accomplish cladding pumping, the pump light is coupled to an inner cla dding of the MC-EDF with thehelp of a specially designed pump light combiner. Since the inner cladding area is much larger than the corearea, a high-power multimode LD can be used to inject the pump light into the inner cladding. The pumplight combiner is known from other cladding pumping techniques and can be a fused bundled fibre pump
combiner, a lens system combiner, or a tapered fibre side -coupled combiner, as shown in Figure 8a), 8b)
and 8c). Several prototypes of the cladding-pumped MC-EDFAs have been reported. Figure 9 shows anexample of the configuration and amplification characteristics of an EDFA with a 32 -core cladding-pumped
MC-EDF [9].
A practical cladding-pumped MC-EDFA should have uniform amplification characteristics in the various
EDF cores should, and its optical components should have better performance and reliability and lower costthan conventional EDFAs.

Figure 7 – Configuration of cladding-pumped MC-EDFA
Pump
light

Double clad MC EDF

SignalLens

Pump light(multi mode)

Multi mode fibre

Fused bundle
fiber part

Multi mode fibreSDM
signalLens
MCF

Double clad MC EDF

Dichroic
mirrorSingle mode fibrea) Fused bundled fibre pump combiner
Multi mode fibre
Pump
light

b) Lens system combiner

Tapered fiber side-coupled part

Double clad
MC EDF

SDM
signalLens

MC EDF (uncoated)c) Tapered fiber side-coupled combiner
Figure 8 – Pump light combiner

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TP 33/AM: 2022a) Configuration
920

NF (dB)

Gain (dB)

30

10

0
1 530

6

3

1 540

1 550

1 560

Wavelength (nm)

0
1 530

1 540

1 550

1 560

Wavelength (nm)b) Amplification characteristics
Figure 9 – Configuration and amplification characteristics of EDFA with 32-core cladding pumped
MC-EDF [Reprinted with permission from [9]. © 2017 Optica (formerly OSA)]
5.2.3 Core and cladding hybrid-pumped MC-EDFA
A cladding-pumped MC-EDFA pumps all the cores simultaneously, and has the potential to realize lower
power consumption. However, it cannot adjust the pump power for each core, as the performance of eachcore changes depending on the number of input signal channels and incident power. If a core and a cladding
hybrid-pumped MC-EDFA are combined, it enables lower power consumption of cladding pumping andcore pumping that can adjust individual pump power to each core. [11]Figure 10 a) and Figure 10 b) show two types of configurations of a core and a cladding hybrid-pumped
multi-core EDFA. In Type 1, one MC-EDF for a cladding pump is bidirectionally pumped to both a clad
and a core. In Type 2, a cladding pumped MC-EDFA and a core pumped MC-EDFA are connected in cascade.
Both types of prototypes have already been developed, and a MC-EDFA with lower power consumption and
excellent controllability of each core has already been launched. Currently, efforts have been made to further
reduce power consumption by optimizing the distribution ratio between the cladding pump power and thecore pump power.

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OpticalConnector(MCF)

MC WDM
coupler for
MC Tap MC
Coupler Isolator cladding pump

MC EDFfor cladding pump

Pump
LD

Pump
LD

MC
Isolator*MC Pump
rejection filter
・
・
・

PD

*MC
VOA

MC Tap
Coupler

OpticalConnector
(MCF)

・
・
・

・
・
・

PD

*MC ASEMC WDM rejection filter*MC GFFcoupler

PD

PD

Pump
LD
*Optional components (can be placed elsewhere)
MC ASE rejection filter
MC Pump rejection filter
MC VOA: Variable optical attenuator
MC GFF: Gain flattening filter

Multi core fiber
Single mode core fiberElectricala) Type 1
Cladding pumped
MC EDFA

Core pumped
MC EDFAb) Type 2
Figure 10 – Configuration of Core and Cladding hybrid pumped MC -EDFA
5.3

State-of-the-art remotely-pumped MC-EDFA and MC-FRA development technology

Remotely-pumped MC-EDFAs and MC-FRAs use optical fibre amplification technologies that have alreadybeen established. A remotely-pumped MC-EDFA can be worked by stimulating the MC-EDF placed between
the transmission MCFs from a distance. On the other hand, a MC-FRA can be worked by introducing Raman
pumping into individual transmission MCF cores, and it is confirmed that effectiveness of the FRA can beachieved by improving the SNR (Signal-to-Noise Ratio) for transmission signal by the Raman amplification.
Figure 11 a) and b) show configurations and SNR improvements by a remotely-pumped MC-EDFA and a
MC-FRA. [12]12TP 33/AM: 2022a) Configurations
12

DOSNR (dB)

10
8
6
4
Remotely pumped MC-EDFA

2

MC FRA

0
-2
0

500

1 000

1 500

Pump power (mW)b) SNR improvement
Figure 11 – Configurations of Core and Cladding hybrid-pumped MC-EDFA [Reprinted withpermission from [12]. © 2013 IEEE]
5.4

Specific features and measurement

Basic optical characteristics of MC-EDFAs (minimum relevant parameters for transmission characteristics
are described in IEC 61291-2 and IEC 61291-4) include a signal gain, noise characteristics, etc. that can beevaluated based on IEC 61290-1 series, IEC 61290-3 series, IEC 61290-5 series, by using optical fan-in andoptical fan-out, as shown in Figure 12. In addition, characteristics of the core-pumped MC-EDFAs can bemeasured by individually pumping those of each core, but in the cladding-pumped MC-EDFAs and hybridpumped MC-EDFAs, the characteristics of the measured core are affected by the state of a signal inputting
to the core that is different from the measured one. Therefore, it is necessary to pay attention to these points
when making an evaluation.
As several cores in a MC-EDFA that are embedded in a common cladding suffer from XT from other cores,
a XT evaluation method is required to measure a crosstalk component precisely. There are two methods ofevaluating XT both of which can identify a signal incident occurred on each core by wavelength or a timeunit. Figure 13 a) and 13 b) show the concept of these methods with different wavelengths and by a time
separation of signals. In the former one, IEC 61290-1-1 can be used to compare the output signal intensity
ratio for each wavelength [13], and in the latter one, IEC 61290-10-1 and IEC 61290-10-2 can be used tocompare the output signal intensity ratio for each time to evaluate XT.

13
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Input signal to

Output signal fromcore 1core 2

core 1core 2MC EDFA・・・

Fan in・・・

Fan out

Multi core fiber
Single mode core fibercore Ncore N

Figure 12 – Multi-core EDFA evaluation setup for basic optical characteristics
Input signal tocore 1l1
Wavelength
Intensity

core 2

core 2

core 1

l1 l2
Wavelength

XT
Intensity

Intensity

core 1

Intensity

Output signal fromcore 2

l1 l2
Wavelengthl2
Wavelengtha) Using different wavelengths
Input signal to

Output signal fromcore 1core 1Time

Intensity

Intensity

core 1Time

XT

core 2

core 2Time

Intensity

Intensity

core 2Timeb) By time separation of signals
Figure 13 – XT evaluation method with different wavelengths

66.1

Few-mode OFA technology
Outline of few-mode EDFAIn the conventional single mode transmission, communication s only used the LP 01 mode, but for the purposeof increasing the transmission capacity, a mode-division multiplexing (MDM) system is used over FMFs toperform communications using multiple modes. The LP mode, the OAM mode, and the coupled-core mode
are candidates of multiplexing modes [see Figure 14 a), b) and c)]. [2, 6, 14-16] Additionally, MDM

14
TP 33/AM: 2022

generally uses MIMO (Multi-Input Multi-output) techniques to restore deteriorated signals caused by modecrosstalk to the original signals. It has been pointed out that the performance of MIMO system is affectedby a mode-dependent loss (MDL) or a mode-dependent gain (MDG). Accordingly, optical amplifiers for the
MDM system is indispensable to control a MDG in addition to satisfying the basic requirements for
amplifiers such as a gain and noise figures.
Figure 15 shows configurations of FM-EDFAs. Optical components required for the construction include a
FM EDF with equal amplification characteristics for each mode and a low MDG, a FM WDM coupler
capable of amplification characteristics for each mode, a FM tap coupler that monitors the signal intensityof each mode, a MC isolator, and other optional components (can be placed elsewhere) such as a MC ASE
rejection filter, a MC Pump rejection filter, a MC VOA and a MC GFF.
For achieving low MDG characteristics, it is necessary to use components that have low MDG characteristics.
Particularly, it is essential to have a FM EDF with excellent performance. In addition, a FM VOA that canadjust a MDG may be required in many cases to change a loss for each mode.

p_LP01

s_LP01

s_LP11

s_LP21

s_LP31

s_LP41a) LP modesb) OAM modes [Reprinted with permission

from [15]. © 2006 APS]c) Coupled-core modes [Reprinted with permission from [16]. © 2016 IEEE]
Figure 14 – Image of each mode propagating through the core15
TP 33/AM: 2022
OpticalConnector(FMF)*FM ASErejection filter

FM Tap FM FMWDM
Coupler Isolator coupler
FM EDF
・
・
・

PD
Pump
LD

FM
Isolator*FM Pump
rejection filter

FM Tap
Coupler

OpticalConnector
(MCF)

・
・
・

・
・
・

PD

*FM GFF

*FM
VOA

PD

PD

Pump
LD
FMF
Single mode core fiberElectrical*Optional components (can be placed elsewhere)
FM ASE rejection filter
FM pump rejection filter
FM VOA: FM variable optical attenuator
FM GFF: FM gain flattening filter

Figure 15 – Configuration of FM-EDFA
6.2

State-of-the-art few-mode EDFA development technology

6.2.1 Few-LP mode EDFAFM EDFs with low MDG characteristics are now under development, and studies have been made to identify
a proper pumping method. Mode amplification exceeding the LP 01 mode can be provided by increasing acore diameter of the conventional EDFs (step core index and step erbium doping profile structure) , althougha size of MDG becomes larger (10 dB higher MDG in the LP 01 signal mode compared to the LP 11 signalmode) [see Figure 16]. Therefore, it is necessary to reduce the MDG size. This large MDG is due todifference in overlap integral of a signal power profile and an activated erbium -ion profile, as shown in
Figure 17. While conventional EDFs have the same erbium doping profile with optical index profiles, thepower distribution of these two modes is quite different. If the EDF is pumped with the LP 01 mode light, an
activated erbium doping profile is expected to be close to the pumping light. The gain of an EDF depends
on the overlap integral of a signal power profile and an activated erbium doping profile. It leads to a huge
MDG found in few-mode EDFAs with conventional EDFs.

30
Gain/NF [dB]

25

LP01

20
15

Gain

LP01Pump

LP11
NF

10
5
0
1520

1530

1540 1550 1560
Wavelength [nm]1570

Figure 16 – An example of gain and NF of 2-LP FM-EDFA (large core, step core index and step
erbium doping profile structured conventional EDF) [Reprinted with permission from [17]. © 2014
John Wiley and Sons]
Two approaches are proposed to reduce the MDG of FM EDF. One is to apply a higher-order pump lightintensity mode. [18, 19] The activated erbium-ion profile varies in terms of pumping power distribution.
For example, when using the LP 21 mode for pumping, the gain of the LP 11 signal mode could be larger thanthat of the LP 01 mode. The MDGs of 2.5 dB to 1 dB were obtained for a step core index profile FM EDF byapplying LP 11 and LP 21 mode pumping, respectively. The other approach is to change an erbium doping
profile and a core index of FM-EDF. [17, 20-22] If the erbium doping profile is adjusted to the pump lightintensity of higher-order modes such as a ring erbium doping profile, 4-LP signal mode amplification with
1 dB MDG is expected in theory. Furthermore, another proposal is made that uses a ring-core EDF having
a ring-like profile for both the core index and the erbium doping profile. A theoretical study has shown that
almost identical gains could be obtained for 6-LP modes by using a ring-core EDF. The ring-core FM EDF

16
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has been proven to reduce the MDG experimentally for a 2-LP mode EDF. Figure 17 a), b) and 18 a), b)
show configuration and amplification characteristics of 2-LP mode. An EDFA prototype that consists of aring-core FM EDF, a FM WDM coupler and two MC isolators has achieved a MDG of less than 1.0 dB
between LP 01 and LP 11 signal mode, and some of three-mode EDFAs [20, 21]
In addition, a FM VOA is under development using a spatial light modulator and a long period fibre grating.
The MDG can be controlled in a range between -7 dB to +5 dB by changing the ratio of the LP 01 to LP 11pump modes with long period fibre grating. [23] Currently, research is underway to further increase thenumber of modes.
RC-EDF
FMF-WDM

FMF

LP01 yPBC

SpliceFMF

xx

LP11 yx(b) coupler
WDM

LP01 yxSingle-Mode
980-nm LDs

LP11 ySpliceLP01 yFMF

FMF-WDM

LP11 yxxDichroic Mirror
FMF

Ring core EDF

FMF

Relative Refractive Index Difference

1.5

01

LP Mode Signal Intensity
11

1

0.05

0.5
0
−10

1550 nm LP01 & LP11980-nm, LP01 , LP11 or LP21
Replaceable Phase Plate

1550 nm LP01 & LP11

LP Mode Signal Intensity

−5

0

5

Signal Intensity (a.u.)

FMF

Relative Refractive
Index Difference (%)

(a)

0
10

Radial Position (m)Rotation

980-nm, LP01

SMFa) Configuration
LP01 Pumping
LP01 Signal

LP11 Pumping
22−5 dBm/mode−10 dBm/mode−15 dBm/mode−20 dBm/mode−25 dBm/mode

14
12

10
8
6

12
18
10
16
8
14
6
12

4
10
1530

1540

1550

14

20
12

Gain (dB)

Input Signal Power

16

(c)

14

20

Gain (dB)Gain (dB)1218

Noise Figure (dB)

20

22

(b)

14

Noise Figure (dB)

(a)

18
10
16
8
14
6
12

4
10
11530
530

1560

Wavelength (nm)

11540
540

1550
1 550

Noise Figure (dB)22

LP21 Pumping

4
10
11530
530

1560
1 560

Wavelength (nm)

11540
540

11550
550

1 560
1560

Wavelength (nm)LP11 Signal

10
16
8
14
6
12

12
18
10
16
8
14
6
12

4
10
11530
530

11540
540

11550
550

1 560
1560

Wavelength (nm)

(f)

14

20
12

Gain (dB)18

20

Gain (dB)Gain (dB)12

Noise Figure (dB)

20

22
14

(e)

18
10
16
8
14
6
12

4
10
11530
530

1540
1 540

1550
1 550

1560
1 560

Wavelength (nm)Noise Figure (dB)

22
14

(d)

Noise Figure (dB)

22

4
10
11530
530

11540
540

1550
1 550

1560
1 560

Wavelength (nm)

Amplification characteristicsb) Amplification characteristics
Figure 17 – Configurations and amplification characteristics of 2-LP mode EDFA’s prototype which
consisted with ring-core FM EDF, FM WDM coupler and two MC isolators [Reprinted withpermission from [20]. © 2015 Optica (formerly OSA)]17
TP 33/AM: 2022

25

25

20

20

Gain (dB)Gain (dB)a) Configurations

15
10
5
0

15
10
5

1 530

1 540

1 550

1 560

0

1 530

Wavelength (nm)

1 540

1 550

1 560

Wavelength (nm)b) Amplification characteristics
Figure 18 – Configurations and amplification characteristics of 3-LP mode EDFA’s prototype which
consisted with ring-core FM EDF [Reprinted with permission from [21]. © 2013 Optica (formerly
OSA)]
6.2.2 OAM mode EDFA and Coupled-core mode EDFA
It is reported that an EDFA with the OAM mode has been achieved that uses a ring-core EDF structure, oran annular-core photonic lantern structure and FMFs. [24-26] In the former, simulations have shown that
18-OAM mode amplification with a low MDG can be achieved. Some experiments have also been conducted
for 2-OAM mode amplification. In the latter, although experiments of 2-OAM mode amplification havebeen conducted [see Figure 19 a) and b)], some issues still exist with MDG. In addition, An OAM-mode
OFA for one OAM mode is reported that uses a PbS-doped ring-core fibre with approximately 3 dB of on/off
signal gain at 1 550 nm. [27]
It is also reported that coupled-core mode EDFAs are achieved by using a coupled-core EDF. [28, 29] Someexperiments have demonstrated that coupled-core amplification can be achieved either with a core or acladding pump.

18
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Fabricatedannularcore PL

Annularcore PL

6 LP mode FMFa) Experimental setup

0

200

400

600

800

1 530

1 540

1 550

1 560

b) Amplification characteristics
Figure 19 – Configurations and amplification characteristics of 2-OAM mode EDFA [Reprinted withpermission from [26]. © 2017 Author]
6.3

State-of-the-art FM FRA development technology

Distributed Raman amplification in an FMF requires a small MDG as well as a relatively flat gain over thesignal band in the same way as an FM-EDFA.
A FRA for 2-LP modes has been proved in an FMF transmission experiment [see Figure 20 a) and b)]. [30]
The experiment shows that the MDG could be minimized by optimizing the modal pump power distributionof LP 01 and LP 11 modes. Studies have also started to achieve Raman amplification for high-order modetransmission for over 2-LP modes. [31] Studies on OAM FRAs also have commenced, and some experiments
resulted in several dB of on/off signal gains for 2-OAM modes. [32, 33]

19
TP 33/AM: 2022

a) Experimental arrangement of mode multiplexer with a backward Raman pump couplerb) On-off Gain of the Raman amplification, and equivalent noise figure at the FMF end
Figure 20 – 2-LP modes FM FRA experiment [Reprinted with permission from [30]. © 2011
Nokia Corporation]
6.4

Specific features and measurement

Basic optical characteristics of FM-EDFAs (minimum relevant parameters for Transmission characteristics
are described in IEC 61291-2 and IEC 61291-4) include a signal gain, noise characteristics, etc. that can beevaluated based on IEC 61290-1 series, IEC 61290-3 series, IEC 61290-5 series, by using mode converters,a mode combiner and a mode splitter, as shown in Figure 21. However, if using the setup illustrated in
Figure 15 for measurement, it cannot discriminate between different LP mode output signals with mixed
intra-mode such as LP 11a and LP 11b . Thus, for characterising the MDG, the amplitude and phase transfer
matrix of the amplifier should be measured between each input/output pair across all the wavelengths. [34].
In addition, the crosstalk characteristics between modes can be evaluated by separating the wavelength anda time unit, as is the case of MC-EDFA [see Figure 13]. The wavelength separating method may use IEC
61290-1-1. For comparing the output signal intensity ratios for each wavelength, IEC 61290-10-1 and IEC
61290-10-2 can be used in the time separating method to compare the output signal intensity ratio s for eachtime unit for the purpose of evaluating XT.
Furthermore, when a propagation matrix evaluation in the amplifier is required in MIMO transmission, it isnecessary to have a new evaluation method not available in the current IEC document s.

20
TP 33/AM: 2022
Input signal

Output signal

Mode 1Mode 1Mode 2Mode 2・・・Mode N

Mode
combiner

FM EDFAMode
Splitter

・
・
・

FMF
Single mode core fiber (LP01)
Mode converter(LP01 ↔ Mode #, #: 1~N )Mode N

Figure 21 – FM-EDFA evaluation setup for basic optical characteristics

7

MC and FM-OFA technology

MC & FM-EDFAs that incorporate the MC-EDF and FM-EDF technologies is also under development. [3538] For example, we can see a newly created multi-core with a ring core, and it is confirmed that sevencores with a low MDG and 2-LP mode amplification is available, as shown in Figure 22 a) and b). Currently,
the number of modes and cores has increased, and amplification using MC & FM-EDFs with 7-core – 6modes, etc. are also demonstrated. We believe that the number of EDF cores and modes would continue toincrease in the future. It is also necessary to develop optical components for producing this amplifier.

a) Configurationsb) Amplification characteristics
Figure 22 – MC-EDFA with FM cores [Reprinted with permission from [36]. © 2017 IEEE]

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Yamada, and Toshio Morioka, “Transmission Over 1050-km Few-Mode Fiber Basedon Bidirectional
Distributed Raman Amplification,” IEEE J. Lightwave Technol., Vol. 34, No. 1, p p. 196-204, 2016.
[36] Y. Amma, T. Hosokawa, H. Ono; K. Ichii, K. Takenaga; S. Matsuo, and M. Yamada, “ Ring-Core
Multicore Few-Mode Erbium-Doped Fiber Amplifier,” IEEE Photonics Technology Letters, vol. 29, no. 24,
pp. 2163-2166, 2017.
[37] Y. Jung, M. Wada, K. Shibahara, S. Jain, I. A. Davidson, P. Barua, J. R. Hayes, T. Sakamoto, T. Mizuno,
Y. Miyamoto, Y. Sasaki, K. Saitoh, K. Nakajima, and D. J. Richardson, “ High Spatial Density 6-Mode 7Core Fiber Amplifier for L-Band Operation,” IEEE J. Lightwave Technol., Vol. 38, No. 11, pp. 2938-2943,
2020.
[38] Y. Wakayama, D. Soma, S. Beppu, S. Sumita, K. Igarashi, and T. Tsuritani, “ 266.1-Tbit/s Transmission
Over 90.4-km 6-Mode Fiber With Inline Dual C+L-Band 6-Mode EDFA,” IEEE J. Lightwave Technol., Vol.
37, No. 2, pp. 404-410, 2019.

24
TP 33/AM: 2022

OITDA/TP 33/AM：2022

Optical fibre amplifier for space division multiplex transmission
解説

この解説は，本体に記載した事柄を説明するもので，技術資料（TP）の一部ではない。

1

今回の改正までの経緯
近年，通信容量の飛躍的な増加を目的に，マルチコアファイバやマルチモードファイバを伝送路として用いる空間分割多重(SDM) の研究・開発が進められている。このため、一般財団法人光産業技術振興協会・
光増幅器及びダイナミックモジュール標準化部会では，日本国内の光ファイバ増幅器の製造者ならびにユーザ，光ファイバ増幅器の部品製造者などにとって，次世代の光増幅器の 1 つとして考えられている SDM
アンプについての有益な情報が提供できる技術資料に関して 2020 年 4 月から 2021 年 2 月にかけて審議
し，下記項目を解説している第 1 版を 2021 年 2 月に公開した。
✓

SDM アンプの分類およびその概要✓

最先端の開発技術および開発された増幅器構成と増幅特性例✓

SDM アンプの測定方法

初版公開後，光増幅器及びダイナミックモジュール標準化部会にて，引用する図面の使用許諾に関する疑問が提起されたため，記載する図面の使用許可を得る作業を進め，必要に応じて図面の描き直し又は削除を行うことを合意した。第 2 版は，2021 年 10 月から審議が行われ，2022 年 4 月に公開された。

2

今回の改正の趣旨
今回の第 2 版改正の主な変更点は，本技術資料で使用する図面の使用許諾を反映したフィギュアキャ

プションへの変更と使用許諾が得られなかったことにより生じた図面の変更である。また、図面等においてエディトリアル修正を行う必要が生じた点である。

3

主な項目及び改正点の説明
主な項目及び改正点は，次のとおりである。

a)Scope（箇条 1）
この技術資料は，マルチコアファイバ技術及びフューモードファイバ技術を適用した SDM 増幅器
についてまとめている。第 2 版における変更はない。

b)

Normative references（箇条 2）
関連する IEC 61290 規格群，IEC 61291 規格群，IEC 61292 規格群及び IEC 60050-731 を引用している。第 2 版における変更は，規格群の番号順に整列したことである。

c)

Teams, definitions and abbreviated teams（箇条 3）
この TP に記載する主な SDM 光増幅器の用語及び定義を規定している。第 2 版における変更はな

2
TP 33/AM：2022 解説

い。
d)Classification of SDM OFA（箇条 4）
SDM OFA の分類を記載している。第 2 版における変更は，図 1 の誤記を修正したことである。

e)Multi-core OFA technology（箇条 5）
マルチコア光ファイバ増幅器の技術を記載している。第 2 版における変更は，以下の通りである。
⚫

図 3，図 5，図 6，図 9，図 11 に対して，使用許諾を反映したフィギュアキャプションへの変
更。

f)

⚫

図 8 に対して，使用許諾が得られなかったためオリジナル図面への変更。

⚫

図 5，図 6，図 9，図 11 内の数字を，半角の空白を用いて 3 桁ごとに記載することへ変更。

Few-mode OFA technology（箇条 6）
フューモード光ファイバ増幅器の技術を記載している。第 2 版における変更は，以下の通りである。
⚫

図 14，図 16，図 17，図 18，図 19，図 20 に対して，使用許諾を反映したフィギュアキャプシ
ョンへの変更。

⚫

図 16，図 17，図 18，図 19 内の数字を，半角の空白を用いて 3 桁ごとに記載することへ変更。

g) MC and FM OFA technology（箇条 7）
マルチコアファイバ技術及びフューモードファイバ技術を用いた光ファイバ増幅器の技術例を記載している。第 2 版における変更は，以下の通りである。
⚫

4

図 22 に対して，使用許諾を反映したフィギュアキャプションへの変更。

その他
本技術資料は，IEC/TC 86/SC86C に TR 原稿として提案を予定している。

5

TP 作成・検討メンバ
技術資料（TP）第 2 版・検討メンバの構成表を，次に示す。
氏名
所属
山 田
誠
大阪公立大学高 橋 英 憲株式会社ＫＤＤＩ総合研究所
小 野 浩 孝湘南工科大学
（執筆者

6

山田 誠）

原案作成部会の構成表
原案作成部会の構成表（一般財団法人光産業技術振興協会 光増幅器及びダイナミックモジュール標準化部会）を，次に示す。
光増幅器及びダイナミックモジュール標準化部会
（議長）
（メンバ）

氏名
山 田
小 熊
小 島
小 西

健
良

誠
史
学
明

所属
大阪公立大学日本電気株式会社
横河計測株式会社
三菱電機株式会社

構成表

3
TP 33/AM：2022 解説（オブザーバ）

（事務局）

小 野
佐 藤
神 徳
鹿 間
渋 谷
清 水
鈴 木
高 橋
高 橋
田 中
藤 崎
三 浦
宮 内
吉 田
池 田
磯 野
来見田
清 水
水 本
宮 端
山 口
瀬戸山
浦 野
間 瀬

浩
功
正
光

孝
紀
樹
太
隆
誠
裕 一
英 憲
博 之
正 人
文 雄
寿太郎
彰
実
和 浩
秀 樹
淳 也
祐 貴
哲 弥*
茂
修 司
徹
章
昇 次

湘南工科大学(2022 年 4 月～)
古河電気工業株式会社(～2022 年 3 月)
古河電気工業株式会社(2022 年 4 月～)
日本電信電話株式会社
株式会社白山NTT エレクトロニクス株式会社
富士通株式会社
株式会社 KDDI 総合研究所
沖電気工業株式会社
住友電気工業株式会社
パナソニック コネクト株式会社
日本モレックス合同会社
IEC/TC 86 委員
近畿大学
経済産業省 商務情報政策局 情報産業課
IGS コンサルティング
国立研究開発法人産業技術総合研究所
一般財団法人日本規格協会
東京工業大学(～2022 年 3 月)
経済産業省 産業技術環境局
キーサイトテクノロジー株式会社(～2022 年 3 月)
一般財団法人光産業技術振興協会
一般財団法人光産業技術振興協会(～2022 年 3 月)
一般財団法人光産業技術振興協会(2022 年 4 月～)（執筆者 山田 誠）

禁無断転載

この OITDA 規格の TP（技術資料）は，一般財団法人光産業技術振興協会
ファイバオプティクス標準化部会 光ファイバセンサ専門部会で審議・取纏めたものである。
この資料についてのご意見又はご質問は，下記にご連絡ください。

TP（技術資料）：
空間分割多重伝送用光ファイバ増幅器（Optical fibre amplifier for space division multiplexing
transmission）

TP 番号：OITDA/TP 33/AM:2022
第2版
公表日：2022 年 4 月 25 日

発行者：一般財団法人光産業技術振興協会
住所：〒112-0014 東京都文京区関口 1-20-10
住友江戸川橋駅前ビル 7F
電話：03-5225-6431 FAX：03-5225-6435