IEC 61290-4-1:2011
(Main)Optical amplifiers - Test methods - Part 4-1: Gain transient parameters - Two-wavelength method
Optical amplifiers - Test methods - Part 4-1: Gain transient parameters - Two-wavelength method
IEC 61290-4-1:2011 applies to erbium-doped fibre amplifiers (EDFAs) and optically amplified elementary sub-systems. It applies to OAs using active fibres (optical fibre amplifiers, OFAs), containing rare-earth dopants. These amplifiers are commercially available and widely deployed in service provider networks.
Amplificateurs optiques - Méthodes d'essai - Partie 4-1: Paramètres de gain transitoire - Méthode à deux longueurs d'onde
La CEI 62190-4-1:2011 s'applique aux amplificateurs à fibre dopée à l'erbium (EDFA) et aux sous-systèmes élémentaires à amplification optique. Elle s'applique aux AO utilisant des fibres actives (amplificateurs à fibres optiques, AFO), contenant des dopants aux terres rares. Ces amplificateurs sont disponibles sur le marché et sont largement déployés dans les réseaux de prestataires de service.
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IEC 61290-4-1
®
Edition 1.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical amplifiers – Test methods –
Part 4-1: Gain transient parameters – Two-wavelength method
Amplificateurs optiques – Méthodes d’essai –
Partie 4-1: Paramètres de gain transitoire – Méthode à deux longueurs d'onde
IEC 61290-4-1:2011
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IEC 61290-4-1
®
Edition 1.0 2011-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical amplifiers – Test methods –
Part 4-1: Gain transient parameters – Two-wavelength method
Amplificateurs optiques – Méthodes d’essai –
Partie 4-1: Paramètres de gain transitoire – Méthode à deux longueurs d'onde
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX R
ICS 33.180.30 ISBN 978-2-88912-614-9
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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– 2 – 61290-4-1 © IEC:2011
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope and object . 6
2 Normative references. 6
3 Terms, definitions and abbreviations . 6
3.1 General . 6
3.2 Terms and definitions . 9
3.3 Abbreviated terms . 10
4 Apparatus . 11
5 Test specimen . 11
6 Procedure . 11
7 Calculations . 12
8 Test results . 12
Annex A (informative) Background on transient phenomenon in optical amplifiers . 13
Annex B (informative) Slew rate effect on transient gain response . 16
Bibliography . 19
Figure 1 – Definitions of rise and fall times (a) in the case of a channel addition event,
and (b) in the case of a channel removal event . 7
Figure 2 – OFA transient gain response for (a) a channel removal event, and (b) a
channel addition event . 8
Figure 3 – Generic transient control measurement setup . 11
Figure A.1 – EDFA pump control for a chain of 5 EDFAs and 4 fibre spans . 14
Figure A.2 – EDFA spectral hole depth for different gain compression . 15
Figure A.3 – EDFA spectral hole depth for different wavelengths . 15
Figure B.1 – Transient gain response at various slew rates . 17
Figure B.2 – 16 dB add/drop (rise time = 10 µsec) . 18
Figure B.3 – 16 dB add/drop (rise time = 1 000 µsec) . 18
Table 1 – Examples of add and drop scenarios for transient control measurement . 12
Table 2 – Typical results of transient control measurement . 12
Table B.1 – Transient gain response for various rise time and fall time (16 dB add/drop) . 17
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61290-4-1 © IEC:2011 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL AMPLIFIERS –
TEST METHODS –
Part 4-1: Gain transient parameters –
Two-wavelength method
FOREWORD
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International Standard IEC 61290-4-1 has been prepared by subcommittee 86C: Fibre optic
systems and active devices, of IEC technical committee 86: Fibre Optics.
The text of this standard is based on the following documents:
CDV Report on voting
86C/956/CDV 86C/1011/RVC
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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A list of all parts of the IEC 61290 series, published under the general title Optical amplifiers –
Test methods can be found on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until the
stability 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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.
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61290-4-1 © IEC:2011 – 5 –
INTRODUCTION
This part of IEC 61290-4 is devoted to the subject of Optical Amplifiers (OAs). The technology
of optical amplifiers is quite new and still emerging; hence amendments and new editions to
this standard can be expected.
Each abbreviation introduced in this standard is explained in the text at least the first time it
appears. However, for an easier understanding of the whole text, a list of all abbreviations used
in this standard is given in 3.3.
Background information on the transient phenomenon in erbium-doped fibre amplifiers and the
consequences on fibre optic systems is provided in Annex A and on slew rate effects in
Annex B.
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OPTICAL AMPLIFIERS –
TEST METHODS –
Part 4-1: Gain transient parameters –
Two-wavelength method
1 Scope and object
This part of IEC 61290-4 applies to erbium-doped fibre amplifiers (EDFAs) and optically
amplified elementary sub-systems. It applies to OAs using active fibres (optical fibre amplifiers,
OFAs), containing rare-earth dopants. These amplifiers are commercially available and widely
deployed in service provider networks.
The object of this part of IEC 61290-4 is to provide the general background for EDFA transients
and related parameters, and to describe a standard test method for accurate and reliable
measurement of the following transient parameters:
• Channel addition/removal transient gain overshoot and transient net gain overshoot
• Channel addition/removal transient gain undershoot and transient net gain undershoot
• Channel addition/removal gain offset
• Channel addition/removal transient gain response time constant (settling time)
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 61291-1, Optical amplifiers – Part 1: Generic specification
NOTE A list of informative references is given in the Bibliography.
3 Terms, definitions and abbreviations
3.1 General
When the input power to an OFA operating in saturation changes sharply, the gain of the
amplifier will typically exhibit a transient response before settling back into the required gain.
This response is dictated both by the optical characteristics of the active fibre within the OFA
as well as the performance of the automatic gain control (AGC) mechanism.
Since a change in input power typically occurs when part of the DWDM channels within the
specified transmission band are dropped or added, definitions are provided that describe a
dynamic event leading to transient response. Rise and fall time definitions are shown in
Figure 1.
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61290-4-1 © IEC:2011 – 7 –
100 %
of change
90 %
of change
10 %
of change
Rise
time
Time
Channel
Channel
addition start
addition end
(a) IEC 1582/11
10 %
of change
90 %
of change
100 %
of change
Fall
time
Time
Channel
Channel
removal start
removal end
(b)
IEC 1583/11
Figure 1 – Definitions of rise and fall times (a) in the case of a channel addition event,
and (b) in the case of a channel removal event
The parameters generally used to characterize the transient gain behaviour of a gain controlled
EDFA for the case of channel removal are defined in Figure 2(a). The figure specifically
represents the time dependence of the gain of one of the surviving channels when channels
Input power to EDFA
Input power to EDFA
(linear a.u.)
(linear a.u.)
---------------------- Page: 9 ----------------------
Transient gain response time
constant (settling time)
– 8 – 61290-4-1 © IEC:2011
are removed. Likewise, the transient gain behaviour for the case when channels are added is
shown in Figure 2(b). The main transient parameters are: transient gain response time
constant (setting time), gain offset, transient net gain overshoot, and transient gain net
undershoot. The transient gain overshoot and undershoot are particularly critical to carriers and
network equipment manufacturers (NEMs) given that the speed and amplitude of gain
fluctuations compound through the network as the optical signal passes through an increasing
number of cascaded amplifiers. Properly designed optical amplifiers have very small values for
these transient parameters.
Net gain
overshoot
Gain
Gain
overshoot
stability
Final
gain
Gain offset
Initial
Gain
Net gain
gain
undershoot
undershoot
Time
(a)
IEC 1584/11
Net gain
Gain
Overshoot
overshoot
Initial
Gain offset
gain
Final
gain
Gain
stability
Gain
Net gain
undershoot
undershoot
Transient gain response time
constant (settling time)
Time
(b)
IEC 1585/11
Figure 2 – OFA transient gain response for (a) a channel removal event,
and (b) a channel addition event
Gain (dB)
Gain (dB)
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61290-4-1 © IEC:2011 – 9 –
3.2 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61291-1 and the
following apply.
3.2.1
surviving (pre-existing) signal
optical signal that remains (exists) after (before) drop (add) event
3.2.2
saturating signal
optical signal that is switched off (on) by the drop (add) event
3.2.3
drop (add) level
amount in dB by which the input power decreases (increases) due to dropping (adding) of
channels
3.2.4
add rise time
time it takes for the input optical signal to rise from 10 % to 90 % of the total difference
between the initial and final signal levels during an add event (see Figure 1(a))
3.2.5
drop fall time
time it takes for the input optical signal to fall from 10 % to 90 % of the total difference between
the initial and final signal levels during a drop event (see Figure 1 (b))
3.2.6
initial gain
gain of the surviving (pre-existing) channel before a drop (add) event
3.2.7
final gain
steady state gain of the surviving (pre-existing) channel a very long time (i.e. once the gain has
stabilized) after a drop (add) event
3.2.8
gain offset
Change in dB of the gain between initial and final state, defined as final gain – initial gain
NOTE Gain offset may be positive or negative for both channel addition and removal events
3.2.9
gain stability
specified peak-to-peak gain fluctuations of the OFA under steady state conditions (i.e. not in
response to a transient event)
3.2.10
transient gain response time constant (settling time)
amount of time required to bring the gain of the surviving (pre-existing) channel to the final gain
NOTE 1 This parameter is the measured time from the beginning of the drop (add) event that created the transient
gain response, to the time at which the surviving (pre-existing) channel gain first enters within the gain stability
band centred on the final gain.
NOTE 2 Hereon this will also be referred to as settling time
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3.2.11
transient gain overshoot
difference in dB between the maximum surviving (pre-existing) channel gain reached during the
OFA transient response to a drop (add) event, and the lowest of either the initial gain and final
gain
NOTE Hereon this will also be referred to as gain overshoot
3.2.12
transient net gain overshoot
difference in dB between the maximum surviving (pre-existing) channel gain reached during the
OFA transient response to a drop (add) event, and the highest of either the initial gain and final
gain. The transient net gain overshoot is just the transient gain overshoot minus the gain offset,
and represents the actual transient response not related to the shift of the amplifier from the
initial steady state condition to the final steady state condition
NOTE Hereon this will also be referred to as net gain overshoot
3.2.13
transient gain undershoot
difference in dB between the minimum surviving (pre-existing) channel gain reached during the
OFA transient response to a drop (add) event, and the highest of either the initial gain and final
gain
NOTE Hereon this will also be referred to as gain undershoot
3.2.14
transient net gain undershoot
difference in dB between the minimum surviving (pre-existing) channel gain reached during the
OFA transient response to a drop (add) event and the lowest of either the initial gain and final
gain.
NOTE 1 The transient net gain undershoot is just the transient gain undershoot minus the gain offset and
represents the actual transient response not related to the shift of the amplifier from the initial steady state
condition to the final steady state condition.
NOTE 2 Hereon this will also be referred to as net gain undershoot
3.3 Abbreviated terms
AGC automatic gain control
AOM acousto-optic modulator
BER bit error ratio
DFB distributed feedback
DWDM dense wavelength division multiplexing
EDFA erbium-doped fibre amplifier
FWHM full width half maximum
NEM network equipment manufacturer
NSP network service provider
O/E optical-to-electronic
OA optical amplifier
OFA optical fibre amplifier
OSNR optical signal-to-noise ratio
SHB spectral-hole-burning
VOA variable optical attenuator
WDM wavelength division multiplexing
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61290-4-1 © IEC:2011 – 11 –
4 Apparatus
Figure 3 shows a generic setup to characterize the transient response properties of OAs.
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Figure 3 – Generic transient control measurement setup
5 Test specimen
The OA shall operate at nominal operating conditions. If the OA is likely to cause laser
oscillations due to unwanted reflections, optical isolators should be used to bracket the OA
under test. This will minimize signal instability and measurement inaccuracy.
6 Procedure
In the setup shown, the input signal power into the amplifier being tested is the combination of
two distributed feedback (DFB) lasers with wavelengths approximately 1 nm apart. Each
channel is subsequently adjusted with a variable optical attenuator (VOA) to the desired optical
input power levels. One optical modulator driven by a function generator acts as an on/off
switch, to simulate add and drop events. The two optical channels are subsequently combined
onto the same fibre before the signal is directed to the amplifier being tested. A tuneable filter,
an optical-to-electronic (O/E) converter and an oscilloscope are placed in tandem at the output
of the amplifier. The surviving channel is selected with the tuneable filter and its transient
response is monitored with the O/E converter and oscilloscope. A waveform similar to the one
shown in Figure 2 is displayed on the oscilloscope’s screen.
To simulate a drop event at the input of the amplifier being tested, the two lasers are set so
that their total input power is equal to the amplifier’s typical input power (e.g. 1 dBm).
Therefore, the two lasers at –2 dBm each represent 20 optical channels having –15 dBm power
per channel. When the function generator turns the modulator into the “off” position, the
second laser is completely suppressed, changing the system’s channel loading. For instance,
when one laser is switched off it simulates a 3 dB “drop” or a change in the system’s channel
loading from 40 channels to 20 channels. Similarly, when the modulator is changed into an “on”
state, the addition of a second laser simulates a 3 dB add in optical power, or a change in the
system’s channel loading from 20 channels to 40 channels. For other transient control
measurements, the VOAs can be adjusted accordingly so that the input power levels will differ
by an appropriate value.
Several transient control measurements can be performed, according to the operating
conditions and specifications that are provided. Measurements may also be taken for various
add and drop scenarios as shown in Table 1. These measurements are typically performed
over a broad range of input power levels.
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– 12 – 61290-4-1 © IEC:2011
Table 1 – Examples of add and drop scenarios for transient control measurement
Channels
Scenario Total channels Surviving channels
added/dropped
20 dB add/drop 100 1 99
16 dB add/drop 40 1 39
13 dB add/drop 40 2 38
10 dB add/drop 40 4 36
6 dB add/drop 40 10 30
3 dB add/drop 40 20 20
7 Calculations
The results of the transient measurement are the following parameters:
• Channel addition/removal transient gain overshoot and transient net gain overshoot
• Channel addition/removal transient gain undershoot and transient net gain undershoot
• Channel addition/removal gain offset
• Channel addition/removal transient gain response time constant (settling time)
These parameters can be extracted from the oscilloscope display, as described in Figure 2.
8 Test results
Table 2 shows typical measurement conditions and transient control measurement results of C-
band EDFAs. The measurement conditions include gain, surviving channel wavelength, input
power, transient type (e.g., 3 dB drop, 1 dB add), and different transient parameters. In order to
characterize the EDFA transient, the user should choose the measurement conditions to
adequately characterize the dynamic range of the OA.
Typical values of transient parameters are listed in the last row of the table.
Table 2 – Typical results of transient control measurement
Amplifier gain (dB) Surviving channel wavelength (nm)
Transient gain
Input Transient net Transient net gain
Transient event response time Gain offset
power gain overshoot undershoot
description constant (dB)
(dBm) (dB) (dB)
(µsec)
3 dB add or drop -4 0,5 0,2 10 -0,2
x dB add or drop
y dB
Typical values <1 <0,5 <100 <0,5
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61290-4-1 © IEC:2011 – 13 –
Annex A
(informative)
Background on transient phenomenon in optical amplifiers
Optical power transients are sub-millisecond fluctuations in network power levels that are
caused by events such as channel loading changes, passive loss variations, and network
protection switching. In a dynamic networking environment, optical amplifiers need to be able
to compensate for such power variations in order to avoid potential degradation of quality of
service. For instance, in a network reconfiguration scenario, the number of DWDM channels at
the input of an EDFA may suddenly decrease, increasing the amplifier’s inversion and therefore
its gain, in a matter of microseconds. This gain change is detrimental to network service
providers (NSPs) given that their networks will no longer operate in the gain level for which
they were optimized, potentially impacting service quality. An increase in bit error ratio (BER) is
a typical manifestation of quality of service degradation. A reduction in channel power can
decrease the optical signal-to-noise ratio (OSNR), while an increase in the power can enhance
degradation due to non-linear effects in transmission fibre and increased signal shot noise
, from shot noise from amplified input signal.
factor, F
shot,sig
Three factor
...
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