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：2021
第1版

公表

2021 年 2 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）

TP 33/AM：2021

目

次
ページ

まえがき ........................................................................................................................................................................ 2
INTRODUCTION .......................................................................................................................................................... 3
1

Scope ...................................................................................................................................................................... 3

2

Normative references.............................................................................................................................................. 33

Terms, definitions and abbreviated terms ............................................................................................................... 4
3.1

Terms and definitions ..................................................................................................................................... 4

3.2

Abbreviated terms .......................................................................................................................................... 5

4

Classification of SDM OFA ................................................................................................................................... 6

5

Multi-core OFA technology .................................................................................................................................... 7

6

7

5.1

Outline of multi-core EDFA ........................................................................................................................... 7

5.2

State-of-the-art multi-core EDFA development technology ........................................................................... 8

5.2.1

Core pumped multi-core EDFA .................................................................................................................. 8

5.2.2

Cladding-pumped multi-core EDFA......................................................................................................... 11

5.2.3

Core and cladding hybrid-pumped MC-EDFA ......................................................................................... 13

5.3

State-of-the-art remotely-pumped MC-EDFA and MC-FRA development technology ............................... 13

5.4

Specific features and measurement .............................................................................................................. 14

Few-mode OFA technology .................................................................................................................................. 15
6.1

Outline of few-mode EDFA.......................................................................................................................... 15

6.2

State-of-the-art few-mode EDFA development technology ......................................................................... 16

6.2.1

Few-LP mode EDFA ................................................................................................................................ 16

6.2.2

OAM mode EDFA and Coupled-core mode EDFA .................................................................................. 19

6.3

State-of-the-art FM FRA development technology ...................................................................................... 19

6.4

Specific features and measurement .............................................................................................................. 20

MC and FM OFA technology ............................................................................................................................... 21

Bibliography ................................................................................................................................................................. 22(1)

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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。
この技術資料では，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。
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(2)

TP 33/AM：2021

OITDA/TP（技術資料）

OITDA/TP 33/AM：2021
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.
A 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 classification and 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 61290-1, Optical amplifiers - Test methods - Part 1: Power and gain parameters
IEC 61290-1-1, Optical amplifiers – Test methods – Part 1-1: Power and gain parameters – Optical spectrum
analyzer method
IEC 61290-1-2, Optical amplifiers – Test methods – Part 1-2: Power and gain parameters –Electrical spectrum
analyzer method
IEC 61290-1-3, Optical amplifiers – Test methods – Part 1-3: Power and gain parameters –Optical power meter
methodIEC 61290-3, Optical amplifiers - Test methods - Part 3: Noise figure parameters
IEC 61290-3-1, Optical amplifiers – Test methods – Part 3-1: Noise figure parameters – Optical spectrum
analyzer method
IEC 61290-3-2, Optical amplifiers – Test methods – Part 3-2: Noise figure parameters –Electrical spectrum
analyzer method
IEC 61290-3-3, Optical amplifiers - Test methods - Part 3-3: Noise figure parameters - Signal power to total ASE
power ratio

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IEC 61290-5-1, Optical amplifiers - Test methods - Part 5-1: Reflectance parameters - Optical spectrum analyzer
methodIEC 61290-5-2, Optical amplifiers - Test methods - Part 5-2: Reflectance parameters - Electrical spectrum
analyser method
IEC 61290-5-3, Basic specification for optical amplifier test methods - Part 5-3: Test methods for reflectanceparameters - Reflectance tolerance test method using electrical spectrum analyzer
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 agated optical spectrum analyzer
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 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 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

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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
3.1.10multi-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

MDL

mode-dependent loss

MIMO

multi-input multi-output

MDG

mode-dependent gain

MDM

mode-division multiplexing

NF

noise figure

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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

XT

crosstalk4

Classification 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 OFA(MC-OFA)

Multi-core EDFA
(MC-EDFA)

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(MC-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
1

The number in the square bracket shows the number of bibliographies

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5
5.1

Multi-core OFA technology
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 isparticularly 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
Isolator

OpticalConnector
(MCF)

*ASE
rejection filter *GFF *VOAEDFPDPump LDFan out・・・
WDM
coupler
Isolator
PD
Pump LD

Isolator
PD

・
・
・

・
・
・

Gain block N
Tap
coupler*Pump
rejection filter

Tapcoupler*ASE
rejection filter *GFF *VOA
EDF

*Pump
rejection filter

Integration of optical components

Fan inOpticalConnector
(MCF)

Tap
coupler

Isolator
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 costs 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.

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Amp.
mediumBundled EDF
BobbinPump
methodMulti-element EDF

Multi-core EDF
Double-cladding structure

Coating

EDF

Cladding

Core

Discrete pumping (core pumping)

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 [3, 4]
5.2

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

5.2.1 Core pumped multi-core EDFA
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 MC
EDF 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.

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WDM
coupler
Isolator
OpticalConnector
MC Tap(MCF)
Coupler

Pump LDFan out

・
・
・

・
・
・

*MC ASErejection filter

Fan inMC EDF*MCVOAMCIsolator

MC Tap
Coupler*MC Pump
rejection filter
PD

PD

OpticalConnector
(MCF)

・
・
・

・
・
・

PD

*MC GFFPD

WDM
coupler
Isolator

Multi core fiber
Single mode core fiberElectrical

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

MC Tap MC MC WDM
Coupler Isolator coupler
MC EDF*MC Pump
rejection filter

・
・
・

PD
Pump
LD

MC
Isolator

MC Tap
Coupler

・
・
・

・
・
・

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-EDFAa) Configuration

OpticalConnector
(MCF)

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Gain & noise figure(dB)

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35
30
25

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

Gain

20
15
10

Noise figure

501530 1535 1540 1545 1550 1555 1560

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 [3]a) Configuration

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TP 33/AM：2021b) Amplification characteristics
Figure 6 – Configuration and amplification characteristics of core pumped MC-EDFA with 19-core
MC-EDF and MC WDM coupler [5]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.
The MC EDF for a cladding pump has a double cladding structure that consists of cores, an inner cladding
and outer claddings. It is reported that the MC EDF for a cladding pump can have up to 32-cores. [3, 4, 69]
A pumping light is coupled to an inner cladding of MC-EDF for a cladding pump through a pump lightcombiner. Since the inner cladding area is much larger than the core area, a high-power multi-mode LD isused to install a pumping light in an inner cladding. A pump light combiner uses the cladding pump10

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techniques such as a fused bundled fibre pump combiner, a lens system combiner and a tapered fibre sidecoupled combiner, as shown Figure 8 a), b) and c). [7] Currently, we can see several prototypes of thecladding-pumped MC-EDFAs. Figure 9 a) and b) are examples to show configurations and amplification
characteristics of a EDFA with a 32-core cladding-pumped MC EDF. [9]For developing a practical cladding-pumped MC-EDFA, the amplification characteristics of the cores should
be uniformed, and the optical components should have better performance and reliability and a lower cost.

Figure 7 – Configuration of cladding-pumped MC-EDFAa) Fused bundled fibre pump combinerb) Lens system combinerc) Tapered fiber side-coupled combiner
Figure 8 – Pump light combiner [7]a) Configuration

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TP 33/AM：2021b) Amplification characteristics
Figure 9 – Configuration and amplification characteristics of EDFA with 32-core cladding pumped
MC EDF [9]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 anda 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.
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

・
・
・

PD

*MC
VOA

MC Tap
Coupler

OpticalConnector
(MCF)

・
・
・

・
・
・

PD

*MC ASEMC WDM rejection filter*MC GFFcoupler

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

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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]a) Configurationsb) SNR improvement
Figure 11 – Configurations of Core and Cladding hybrid-pumped MC-EDFA [12]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.

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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 1

1
Wavelength

XT

Intensity

core 2

core 2

core 1

1 2
Wavelength

Intensity

Intensity

core 1

Intensity

Output signal fromcore 2

1 2
Wavelength

2
Wavelengtha) Using different wavelengths

Input signal to

Output signal fromcore 1core 1Time

Intensity

Intensity

core 1Time

XT

core 2
core 2

Intensity

Intensity

core 2TimeTimeb) 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, communications only used the LP 01 mode, but for the purposeof increasing the transmission capacity, a mode-division multiplexing (MDM) system is used over FMFs to14

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perform 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
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.

a) Few-LP modeb) OAM modec) Coupled-core mode

Figure 14 – Image of each mode propagating through the core [15, 16]

OpticalConnector(FMF)*FM ASErejection filter

FM Tap FM FMWDM
Coupler Isolator coupler
FM EDF*FM Pump
rejection filter

・
・
・

PD
Pump
LD

FM
Isolator

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15

TP 33/AM：2021

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
20
15

Gain

LP01

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) [17]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
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.

a) Configuration

16

TP 33/AM：2021

14
12

8
6

1550

16

8

14

6

12

4
1540

10

1560

1540

Wavelength (nm)

10

16

8

14

6

12

4
1540

1550

1560

Wavelength (nm)20

Gain (dB)

12

18

10
1530

22

14

(d)

Noise Figure (dB)Gain (dB)

20

12

18

10

16

8

14

6

10
1530

1560

Wavelength (nm)LP11 Signal
22

1550

12

18

10

16

8

14

6

12
10
1530

22
20

4
1540

1550

4
1540

1550

1560

Wavelength (nm)

14

(e)

14

12

4

10
1530

(c)

Noise Figure (dB)

5 dBm/mode10 dBm/mode15 dBm/mode20 dBm/mode25 dBm/mode

12

18

20

1560

Wavelength (nm)

(f)

14
12

18

10

16

8

14

6

12
10
1530

Noise Figure (dB)

16

10

22

14

Gain (dB)

Input Signal Power(b)

Noise Figure (dB)18

20

LP21 Pumping

Gain (dB)

12

10
1530

22

14

Gain (dB)Gain (dB)20(a)

Noise Figure (dB)22

LP11 Pumping

Noise Figure (dB)

LP01 Pumping
LP01 Signal

4
1540

1550

1560

Wavelength (nm)b) 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 [20]a) Configurationsb) Amplification characteristics
Figure 18 – Configurations and amplification characteristics of 3-LP mode EDFA’s prototype which
consisted with ring-core FM EDF [21]17

TP 33/AM：2021

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.

a) Experimental setupb) Amplification characteristics
Figure 19 – Configurations and amplification characteristics of 2-OAM mode EDFA [26]6.3State-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]

18

TP 33/AM：2021a) 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 [30]
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 ratios 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 documents.

19

TP 33/AM：2021

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- and FM-EDFA [36]20

TP 33/AM：2021

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23

OITDA/TP 33/AM：2021

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

制定の趣旨
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 アンプについての情報を提供する。

2

制定の経緯
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。
本資料が，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ものと考える。同文書は，
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 アンプの測定方法について解説している。
本 OITDA 技術資料は，2020 年 4 月から 2021 年 2 月に光増幅器及びダイナミックモジュール標準化部会で審議された。

3

審議中に特に問題となった事項
この技術資料の作成にあたり，審議中に問題となった事項及び審議結果は，次のとおりである。

a)

マルチコアファイバ技術及びフュー（few）モード技術を中心に記載することにしていたが，読者の理解を促進するため，利得，出力，雑音指数などの性能例を記載する必要があるとの意見があった。審議の結果，国内研究機関の事例だけでなく，海外研究機関の事例を，出典を明確にすることでデータ
解1

2
TP 33/AM：2021 解説を引用することにした。

4

構成要素
主な項目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
についてまとめた。

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 を引用した。

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た。

d)Classification of SDM OFA（箇条 4）
SDM OFA の分類を記載した。

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た。

f)

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た。

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
した。

5

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。

6

TP 作成・検討メンバ

TP 作成・検討メンバの構成表を，次に示す。
氏名
所属
山 田
誠
大阪府立大学八重樫 浩 樹沖電気工業株式会社
高 橋 英 憲株式会社ＫＤＤＩ総合研究所
水 本 哲 弥東京工業大学小 野 浩 孝湘南工科大学
（執筆者

解

2

山田 誠）

3
TP 33/AM：2021 解説

7

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）

（オブザーバ）

（事務局）

氏名
山 田
小 熊
小 島
佐 藤
鹿 間
渋 谷
清 水
鈴 木
高 橋
田 中
長谷川
藤 崎
三 浦
水 本
宮 内
八重樫
吉 田
磯 野
岡 田
来見田
米 田
清 水
山 口
中 野
森
小 林

健
功
光

裕
英
正
清
文

誠
史
学
紀
太
隆
誠
一
憲
人
智
雄

寿太郎
哲 弥
彰
浩 樹
実
秀 樹
直 也
淳 也
竜 司
祐 貴
修 司
博 行
高 章
多 実

解

構成表

所属
大阪府立大学日本電気株式会社
横河計測株式会社
古河電気工業株式会社
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
住友電気工業株式会社
三菱電機株式会社
パナソニックシステムソリューションズジャパン
株式会社
日本モレックス合同会社
東京工業大学
IEC/TC 86 委員
沖電気工業株式会社近畿大学
富士通オプティカルコンポーネンツ株式会社
経済産業省商務情報政策局
国立研究開発法人産業技術総合研究所
経済産業省産業技術環境局
一般財団法人日本規格協会
キーサイトテクノロジー株式会社
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
一般財団法人光産業技術振興協会（執筆者 山田 誠）

3

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:2021

第1版

第 1 版 公表日：2021 年 2 月 26 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