Optical amplifiers - Part 1: Parameters of amplifier components

IEC/TR 61292-1:2009(E) is a technical report, and applies to optical components of rare-earth doped fibre amplifiers. It provides information about the most relevant parameters of optical components especially for erbium doped fibre amplifiers (EDFAs). This second edition cancels and replaces the first edition published in 1998. It is a technical revision with updates reflecting new technology.

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IEC/TR 61292-1
Edition 2.0 2009-04
TECHNICAL
REPORT
Optical amplifiers –
Part 1: Parameters of amplifier components
IEC/TR 61292-1:2009(E)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC/TR 61292-1
Edition 2.0 2009-04
TECHNICAL
REPORT
Optical amplifiers –
Part 1: Parameters of amplifier components
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
ICS 33.160.10; 33.180.30 ISBN 978-2-88910-480-2
® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 3 ----------------------
– 2 – TR 61292-1 © IEC:2009(E)
CONTENTS

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

1 Scope and object ..............................................................................................................5

2 Normative references........................................................................................................5

3 Abbreviations....................................................................................................................5

4 OFA components ..............................................................................................................6

5 Terms and definitions .......................................................................................................6

5.1 Active fibre ..............................................................................................................6

5.2 Pump laser ..............................................................................................................8

5.3 WDM coupler.........................................................................................................11

5.4 Optical isolator ......................................................................................................12

5.5 ASE rejection filter.................................................................................................13

5.6 Pump rejection filter...............................................................................................13

5.7 Gain flattening filter (GFF) .....................................................................................14

5.8 Tap coupler ...........................................................................................................15

5.9 PIN-photodiode (PIN-PD).......................................................................................16

5.10 Variable optical attenuator (VOA)...........................................................................17

5.11 Optical connectors.................................................................................................18

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

Figure 1 – Example of the components inside an EDFA operating in a co-propagating

pumping scheme.....................................................................................................................6

---------------------- Page: 4 ----------------------
TR 61292-1 © IEC:2009(E) – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL AMPLIFIERS –
Part 1: Parameters of amplifier components
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.

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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.

The main task of IEC technical committees is to prepare International Standards. However, a

technical committee may propose the publication of a technical report when it has collected

data of a different kind from that which is normally published as an International Standard, for

example "state of the art".

IEC 61292-1, which is a technical report, has been prepared by subcommittee 86C: Fibre optic

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

This second edition cancels and replaces the first edition published in 1998. It is a technical

revision with updates reflecting new technology.
---------------------- Page: 5 ----------------------
– 4 – TR 61292-1 © IEC:2009(E)
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
86C/853/DTR 86C/871/RVC

Full information on the voting for the approval of this technical report can be found in the report

on voting indicated in the above table.

A list of all parts of the IEC 61292 series, published under the general title Optical amplifiers,

can be found on the IEC website.

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

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

maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this technical report may be published later.
---------------------- Page: 6 ----------------------
TR 61292-1 © IEC:2009(E) – 5 –
OPTICAL AMPLIFIERS –
Part 1: Parameters of amplifier components
1 Scope and object

This part of IEC 61292, which is a technical report, applies to optical components of rare-earth

doped fibre amplifiers. It provides information about the most relevant parameters of optical

components especially for erbium doped fibre amplifiers (EDFAs).

The object of this technical report is to provide introductory information for a better

understanding of EDFA operation and applications.
2 Normative references

The following referenced documents are indispensable for the application 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/TR 61931, Fibre optic – Terminology

ITU-T Recommendation G. 650.1, Definition and test methods for linear, deterministic

attributes of single-mode fibre and cable
NOTE A list of informative references is given in the Bibliography.
3 Abbreviations
For the purposes of this document, the following abbreviations apply.
ASE amplified spontaneous emission
EDFA erbium-doped fibre amplifier
EDF erbium-doped fibre
OFA optical fibre amplifier
OA optical amplifier
RMS(r.m.s) root mean square
LD laser diode
TEC thermo-electric cooler
FBG fibre Bragg grating
FWHM full-width at half maximum
WDM wavelength division multiplexing
GFF gain flattening filter
PIN-PD PIN-photodiode
VOA variable optical attenuator
EDF erbium doped fibre
PDL polarization dependent loss (variation)
PMD polarization mode dispersion
MTBF mean time between failure
---------------------- Page: 7 ----------------------
– 6 – TR 61292-1 © IEC:2009(E)
FIT failure in time
4 OFA components

The parameters relevant for a satisfactory understanding of OFA operation are covered by the

following optical component definitions:
– active fibre;
– pump laser;
– wavelength division multiplexing (WDM) coupler;
– optical isolator;
– amplified spontaneous emission (ASE) rejection filter;
– pump rejection filter;
– gain flattening filter (GFF);
– tap coupler;
– PIN-photodiode (PIN-PD);
– variable optical attenuator (VOA);
– optical connectors.
Figure 1 provides an example of the component layout for an OFA.
WDM coupler Active fibre
(Input)
Optical
connector
λ λ λ
(Output)
ASE rejection Pump rejection Gain flattening
Optical
Pump laser
filter* filter* filter*
connector
Tap coupler
Optical Variable
PIN-PD*
isolator* optical
attenuator*
*Optional components (can be placed elsewhere)
IEC 660/09
Figure 1 – Example of the components inside an EDFA operating
in a co-propagating pumping scheme
5 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
5.1 Active fibre

The active fibre is used as gain media in OFA. Rare earth ion is generally doped in the core

region of fibre to produce signal amplification, an Er ion is applied for 1550-nm band OFA

such as an erbium doped fibre amplifier (EDFA). Erbium doped fibre (EDF) absorbs light with a

---------------------- Page: 8 ----------------------
TR 61292-1 © IEC:2009(E) – 7 –

wavelength of 980 nm or 1 480 nm for pumping, and emits infrared light with a wavelength in

the 1 550-nm region. Optical amplification is realized utilizing stimulated emission of 1 530-nm

luminescence.
5.1.1
active fibre maximum input signal power

optical power level associated with the input signal above which the active fibre gets damaged,

causing impossibility of normal operation
5.1.2
active fibre insertion loss at out-of-band wavelength
active fibre insertion loss for a signal at out-of-band wavelength
5.1.3
active fibre polarization-dependent gain variation

maximum fibre gain variation due to variation of the state of polarization of the input signal

5.1.4
active fibre PMD

maximum PMD at the signal wavelength which is launched into the input port of the active fibre

and exits from signal output port of the active fibre, expressed in ps (pico second)

NOTE 1 When an optical signal travels through an optical fibre, optical component or subsystem (such as an OFA),

the change in the shape and width of the pulse due to the differential group delay (DGD) (the propagation delay

difference between the two principal states of polarization (PSPs)) and to the waveform distortion for each PSP, is

due to PMD. PMD, together with polarization dependent loss (PDL) and polarization dependent gain (PDG), may

introduce large waveform distortions leading to an unacceptable bit error ratio increase.

NOTE 2 The level of PMD may depend on temperature and operating conditions.
5.1.5
active fibre mode field diameter
as in ITU-T Recommendation G.650.1 and IEC/TR 61931
5.1.6
active fibre cut-off wavelength
as in ITU-T Recommendation G.650.1 and IEC/TR 61931
5.1.7
active fibre cladding diameter
as in ITU-T Recommendation G.650.1 and IEC/TR 61931
5.1.8
active fibre cladding non-circularity
as in ITU-T Recommendation G.650.1 and IEC/TR 61931
5.1.9
active fibre mode field concentricity error
as in ITU-T Recommendation G.650.1 and IEC/TR 61931
5.1.10
active fibre composition

composition of the active fibre, intended as the host glass composition as well as the dopant

element and its concentration
5.1.11
active fibre length

length of the active fibre. Changing fibre length can optimize gain characteristics of EDFA

---------------------- Page: 9 ----------------------
– 8 – TR 61292-1 © IEC:2009(E)
5.1.12
active fibre dopant distribution

concentration of dopant rare-earth ions in the fibre as a function of the fibre radial coordinate

5.1.13
pumping efficiency

for a given active fibre, the slope of the gain versus pump optical power curve under specified

operating conditions
5.1.14
saturation pump power

for a given active fibre, the pump optical power level above which the small-signal gain shows

no further increase
5.1.15
threshold pump power

the minimum pump optical power necessary to reach a small-signal gain equal to 1 in a given

active fibre when the fibre length is short enough so that the pump optical power remains

constant along the fibre
5.1.16
active fibre operating temperature

temperature to be maintained for normal operating condition, given in the relevant detail

specification

NOTE Amplification characteristics of active fibre strongly depend on its temperature. Thus, EDF in the many

EDFA unit is maintained with the certain constant temperature. Many EDFA units include heater device or TEC in

order to control active fibre temperature. Fibre operating temperatures of 40 ˚C ~ 70 ˚C are usually specified as

operating temperature. Some of fixed gain EDFAs (especially smaller packaged EDFA), do not include this feature.

5.2 Pump laser

A pump laser is used to provide excitation energy for active fibre. By introducing the strong

pumping light from a pump laser to active fibre, the signal light will be amplified by stimulated

emission from a rare-earth ion such as Er in EDF.
5.2.1
pumping wavelength

nominal wavelength of the emission spectrum of the pump laser. In EDFA, 980 nm and

1 480 nm are commonly used for pumping wavelength
5.2.2
pumping scheme

set-up of the EDFA characterized by the direction of pump optical power propagation with

respect to signal direction

NOTE Usually, three schemes are used: co-propagating, where the pump and the signal propagate through the

active fibre in the same direction; counter-propagating, where the signal and the pump propagate through the active

fibre in opposite directions; bi-directional, where two pumps propagate simultaneously through the active fibre in

both directions. Regarding pumping schemes other than pump direction, a polarization combining scheme and a

wavelength combining scheme are considered for detailed design to enlarge pump power. However, a single laser

diode pump scheme is described as a classic example in this technical report.
5.2.3
pumping power
optical power associated with the pump, injected into the active fibre
5.2.4
centre wavelength

pump efficiency of EDF depends on the overlap integral of EDF absorption spectrum and pump

LD spectrum, so the centre wavelength of pump laser is crucial for EDF pumping
---------------------- Page: 10 ----------------------
TR 61292-1 © IEC:2009(E) – 9 –
a) centroidal wavelength

Regarding many pump LDs of 980 nm and 1 480 nm, centroidal wavelength λ is applied for

avg

centre wavelength λ . The centroidal wavelength is the mean or average wavelength of an

optical spectrum of pump LD. The definition of centroidal wavelength is described as follows:

⎛ ⎞
⎜ ⎟
λ = P λ
avg ∑ i i
⎜ ⎟
i =1
⎝ 0⎠
where
λ is the wavelength of the i peak point (nm) ;
i corresponds to mode number for output spectra of pump LD;
P is the power of the i peak point (nW) ; and
P is the total power summed for all peak points (nW):
P = P
0 ∑ i
i = 1
N is the number of peak points.
b) peak wavelength

Regarding some pump LDs of 980 nm and 1 480 nm with FBG stabilizer, peak wavelength

λ is applied for centre wavelength λ . The peak wavelength corresponds to the maximum

peak c

power value of the optical spectrum of pump LD. The definition of peak wavelength is

described as follows:
λ = λ
c peak
NOTE Refer to IEC 61280-1-3 for details.
5.2.5
pumping spectral width

pump efficiency of EDF depends on the overlap integral of EDF absorption spectrum and pump

LD spectrum, so the pumping spectral width of pump laser is crucial term for EDF pumping in

order to quantify power band width of pump LD.
a) RMS spectral width

Regarding many pump LDs of 980 nm and 1 480 nm, RMS spectral width Δλ is applied for

rms
spectral width. The definition of RMS spectral width is described as follows:
N 2
⎡ ⎤
Δλ = P(λ − λ )
rms ⎢ ∑ i i c ⎥
i=1
⎣ 0 ⎦
b) full-width at half maximum

Regarding some pump LDs of 980 nm and 1 480 nm with FBG stabilizer, full-width at half

maximum (FWHM) Δλ is applied for spectral width. The definition of FWHM spectral width

fwhm
is described as follows:
---------------------- Page: 11 ----------------------
– 10 – TR 61292-1 © IEC:2009(E)

1) The positive difference of the closest spaced wavelengths, one above and one below

the peak wavelength λ , at which the spectral power density is 3 dB down from its

peak
peak value.

2) The difference of the half-power wavelengths can be determined as follows; since the

laser may not have modes at these wavelengths, they may be obtained by interpolation.

3) Connect the tip of each mode to the tips of adjacent modes; draw a horizontal line 3-dB

down from the peak power point.

4) The two or more intersection points define the half-power wavelengths. The maximum

difference in half-power wavelengths is Δλ .
fwhm
NOTE Refer to IEC 61280-1-3 for details.
5.2.6
wavelength stability

rate of variation of pumping wavelength with respect to operating and environmental conditions

5.2.7
threshold current

driving current at which the pump laser starts to lase. Practically, this value is specified as the

crossing condition between the spontaneous emission and las
...

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