IEC 61290-4-3:2018

IEC 61290-4-3 ®
Edition 2.0 2018-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical amplifiers – Test methods –
Part 4-3: Power transient parameters – Single channel optical amplifiers in
output power control
Amplificateurs optiques – Méthodes d'essai –
Partie 4-3: Paramètres de puissance transitoire – Amplificateurs optiques
monocanaux commandés par la puissance de sortie

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IEC 61290-4-3 ®
Edition 2.0 2018-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical amplifiers – Test methods –

Part 4-3: Power transient parameters – Single channel optical amplifiers in

output power control
Amplificateurs optiques – Méthodes d'essai –

Partie 4-3: Paramètres de puissance transitoire – Amplificateurs optiques

monocanaux commandés par la puissance de sortie

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.30 ISBN 978-2-8322-5639-8

– 2 – IEC 61290-4-3:2018 © IEC 2018
CONTENTS
FOREWORD . 3
1 Scope . 5
2 Normative references . 5
3 Terms, definitions and abbreviated terms . 6
3.1 Terms and definitions . 6
3.2 Abbreviated terms . 7
4 Apparatus . 8
4.1 Test set-up . 8
4.2 Characteristics of test equipment . 8
5 Test sample . 9
6 Procedure . 9
6.1 Test preparation. 9
6.2 Test . 10
7 Calculations . 10
8 Test results . 11
8.1 Test setting conditions . 11
8.2 Test data . 12
Annex A (informative) Overview of power transient events in single channel EDFA . 13
A.1 Background. 13
A.2 Characteristic input power behaviour . 13
A.3 Parameters for characterizing transient behaviour . 16
Annex B (informative) Background on power transient phenomena in a single channel
EDFA . 17
B.1 Amplifier chains in optical networks . 17
B.2 Typical optical amplifier design . 17
B.3 Approaches to address detection errors . 19
Annex C (informative) Slew rate effect on transient gain response . 23
Bibliography . 24

Figure 1 – Power transient test set-up. 8
Figure 2 – OA output power transient response of a) input power increase and b)
decrease . 11
Figure A.1 – Example OA input power transient cases for a receiver application . 14
Figure A.2 – Input power measurement parameters . 15
Figure A.3 – OA output power transient response . 16
Figure B.1 – Transient response to input power drop . 21
Figure B.2 – Transient response to input power rise . 22

Table 1 – Template for transient control measurement test conditions . 10

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL AMPLIFIERS – TEST METHODS –

Part 4-3: Power transient parameters –
Single channel optical amplifiers in output power control

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
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6) All users should ensure that they have the latest edition of this publication.
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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.
International Standard IEC 61290-4-3 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 2015. This edition
constitutes a technical revision.
This edition includes the following significant technical change with respect to the previous
edition: alignment of the measure of amplified spontaneous emission (ASE) relative to signal
power with the definition in IEC 61290-3-3.

– 4 – IEC 61290-4-3:2018 © IEC 2018
The text of this International Standard is based on the following documents:
FDIS Report on voting
86C/1505/FDIS 86C/1512/RVD
Full information on the voting for the approval of this International Standard can be found in
the report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
This International Standard is to be used in conjunction with IEC 61291-1:2012.
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.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this 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.
OPTICAL AMPLIFIERS – TEST METHODS –

Part 4-3: Power transient parameters –
Single channel optical amplifiers in output power control

1 Scope
This part of IEC 61290 applies to output power controlled optically amplified, elementary
sub-systems. It applies to optical fibre amplifiers (OFAs) using active fibres containing
rare-earth dopants, presently commercially available, as indicated in IEC 61291-1, as well as
alternative optical amplifiers that can be used for single channel output power controlled
operation, such as semiconductor optical amplifiers (SOAs).
The object of this document is to provide the general background for optical amplifiers (OAs)
power transients and their measurements and to indicate those IEC standard test methods for
accurate and reliable measurements of the following transient parameters:
a) transient power response;
b) transient power overcompensation response;
c) steady-state power offset;
d) transient power response time.
The stimulus and responses behaviours under consideration include the following:
1) channel power increase (step transient);
2) channel power reduction (inverse step transient);
3) channel power increase/reduction (pulse transient);
4) channel power reduction/increase (inverse pulse transient);
5) channel power increase/reduction/increase (lightning bolt transient);
6) channel power reduction/increase/reduction (inverse lightning bolt transient).
These parameters have been included to provide a complete description of the transient
behaviour of an output power transient controlled OA. The test definitions defined here are
applicable if the amplifier is an OFA or an alternative OA. However, the description in
Annex A concentrates on the physical performance of an OFA and provides a detailed
description of the behaviour of an OFA; it does not give a similar description of other OA
types. Annex B provides a detailed description background of the dynamic phenomenon in
output power controlled amplifiers under transient conditions and Annex C details the impact
of speed of transient inputs.
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 61291-1, Optical amplifiers – Part 1: Generic specification

– 6 – IEC 61290-4-3:2018 © IEC 2018
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
input signal
optical signal that is input to the OA
3.1.2
input power excursion
relative input power difference before, during and after the input power stimulus event that
causes an OA transient power excursion
Note 1 to entry: Input power excursion is expressed in dB.
3.1.3
input power 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 increasing power excursion event
Note 1 to entry: See Figure A.2 a).
3.1.4
input power fall time
time it takes for the input optical signal to fall from 90 % to 10 % of the total difference
between the initial and final signal levels during a decreasing power excursion event
Note 1 to entry: See Figure A.2 b).
3.1.5
slew rate
maximum rate of change of the input optical signal during a power excursion event
Note 1 to entry: See Annex C.
3.1.6
transient power response
maximum or minimum deviation (overshoot or undershoot) between the OA’s target power
and the observed power excursion induced by a change in an input channel power excursion
Note 1 to entry: Once the output power of an amplified channel deviates from its target power, the control
electronics in the OA should attempt to compensate for the power difference or transient power response, bringing
the OA output power back to its original target level.
Note 2 to entry: Transient power response is expressed in dB.
3.1.7
transient power response time
amount of time taken to restore the power of the OA to a stable power level close to the target
power level
Note 1 to entry: This parameter is measured from the time when the stimulus event created the power fluctuation
to the time at which the OA power response is stable and within specification.

3.1.8
transient power overcompensation response
maximum deviation between the amplifier’s target output power and the power resulting from
the control electronics’ instability
Note 1 to entry: Transient power overcompensation response occurs after a power excursion, when an amplifier’s
control electronics attempts to bring the power back to the amplifier’s target level. The control process is iterative,
and control electronics may initially overcompensate for the power excursion until subsequently reaching the
desired target power level.
Note 2 to entry: The transient power overcompensation response parameter is generally of lesser magnitude than
the transient power response and has the opposite sign.
Note 3 to entry: Transient power overcompensation response is expressed in dB.
3.1.9
steady state power offset
difference between the final and initial output power of the OA, prior to the power excursion
stimulus event
Note 1 to entry: Normally, the steady state power level following a power excursion differs from the OA power
before the input power stimulus event. The transient controller attempts to overcome this offset using feedback.
Note 2 to entry: Steady state power offset is expressed in dB.
3.2 Abbreviated terms
AFF ASE flattening filter
AGC automatic gain controller
APC automatic power control
ASE amplified spontaneous emission
ASEP amplified spontaneous emission power
BER bit error ratio
DFB distributed feedback (laser)
DWDM dense wavelength division multiplexing
EDF erbium-doped fibre
EDFA erbium-doped fibre amplifier
GFF gain flattening filter
NEM network equipment manufacturers
NSP network service providers
O/E optical-to-electrical
OA optical amplifier
OD optical damage
OFA optical fibre amplifier
OSA optical spectrum analyser
OSNR optical signal-to-noise ratio
PDs photodiodes
PID proportional integral-derivative
SOA semiconductor optical amplifier
Sig_ASE signal-to-ASE ratio
SigP signal power
SOP state of polarization
VOA variable optical attenuator
WDM wavelength division multiplexing

– 8 – IEC 61290-4-3:2018 © IEC 2018
4 Apparatus
4.1 Test set-up
Figure 1 shows a generic set-up to characterise the transient response properties of output
power controlled single channel OAs.
OA
Channel pass-
Optical
Polarization
under
Laser source VOA
band filter
modulator
scrambler
test
VOA
Function generator
O/E converter
Oscilloscope
IEC
Figure 1 – Power transient test set-up
4.2 Characteristics of test equipment
The test equipment listed below is needed, with the required characteristics:
a) Laser source for supplying the OA input signal with the following characteristics.
– ability to support the range of signal wavelengths for which the OA under test is to be
tested. This could be provided for example by a tuneable laser, or a bank of distributed
feedback (DFB) lasers;
– an achievable average output power such that at the input to the OA under test, the
power will be above the maximum specified input power of the OA, including loss of
any subsequent test equipment between the laser source and OA under test.
b) Polarization scrambler to randomize the incoming polarization state of the laser source, or
to control it to a defined state of polarization (SOP). The polarization scrambler is
optional.
c) Variable optical attenuator (VOA) with a dynamic range sufficient to support the required
range of surviving signal levels at which the OA under test is to be tested.
NOTE If the output power of the laser source can be varied over the required dynamic range, then a VOA is
not needed.
d) Optical modulator to modify the OA input signal to the defined power excursion with the
following characteristics;
– extinction ratio at rewrite without putting a number higher than the maximum drop level
for which the OA under test is to be tested;
– switching time fast enough to support the fastest slew rate for which the OA under test
is to be tested.
e) Channel pass-band filter: an optical filter designed to distinguish the signal wavelength
with the following characteristics. Note that the use of a channel pass-band filter is
optional:
– ability to support the range of signal wavelengths for which the OA under test is to be
tested. This could be provided for example by a tuneable filter, or a series of discrete
filters;
– 1-dB passband of at least ±20 GHz centred around the signal wavelength;

– more than 20 dB attenuation level below the minimum insertion loss across the entire
specified transmission band of the OA under test, except within a range of ±100 GHz
centred around the signal wavelength.
f) VOA before the optical-to-electrical (O/E) converter to ensure the maximum power is
within the linear response range.
g) Optical-to-electrical (O/E) convertor to detect the filtered output of the OA under test with
the following characteristics:
– a sufficiently wide optical and electrical bandwidth to support the fastest slew rate for
which the OA is to be tested;
– a linear response within a ±5 dB range of all signal levels for which the OA under test
is to be tested.
h) Oscilloscope to measure and capture the transient response of the optically filtered output
of the OA under test, with a sufficiently wide electrical bandwidth to support the fastest
slew rate for which the OA is to be tested.
i) Function generator to generate the input power transient waveforms to drive the optical
modulator, with electrical pulse width short enough and electrical slew rate high enough to
support the fastest slew rate for which the OA under test is to be tested.
5 Test sample
The OA shall operate under nominal operating conditions. If the OA is likely to cause laser
oscillations due to unwanted reflections, optical isolators should be used to isolate the OA
under test. This will minimize signal instability.
6 Procedure
6.1 Test preparation
In the set-up shown in Figure 1, the input optical signal power injected into the amplifier being
tested is generated from a suitable laser source. The optical power is passed through an
optional polarization scrambler to allow randomization or control of the signal polarization
state and is subsequently adjusted with a VOA to the desired optical input power levels. The
signal then passes through an optical modulator driven by a function generator that provides
the desired input power test waveform to stimulate the transient input power excursions. The
signal is then injected into the amplifier being tested. A channel pass-band filter (such as a
tuneable optical filter, fixed optical filter or similar component) may be used to select only the
relevant channel wavelength under test, followed by an O/E converter and an oscilloscope at
the output of the amplifier. The output channel selected by the optional channel pass-band
filter including its transient response is monitored with the O/E converter and oscilloscope.
Waveforms similar to those shown in Figure A.3 are captured via the oscilloscope for
subsequent computer processing.
Prior to measurement of the transient response, the input power waveform trace shall be
recorded. Use the set-up of Figure 1 without the OFA under test. The input optical connector
from the optical modulator is connected to the channel pass-band filter.
For this test, to stimulate a power excursion at the input of the OA under test, the source laser
power at the OA input is set at some typical power level. The function generator waveform is
chosen to increase or decrease the input power to the OA under test with power excursions
and slew rate relevant to the defined test condition. For example, for a typical number in the
case of an optical receiver, the input power to the OA could be increased by 7 dB in a
timeframe of 50 µs and then held at this power value to simulate a power increase transient
power response (step transient) condition as shown in Figure A.1 a). For alternative transient
control measurements, the signal generator waveform is controlled appropriately, and the
VOA is adjusted accordingly.
– 10 – IEC 61290-4-3:2018 © IEC 2018
6.2 Test
Several sequential transient control measurements can be performed according to the OA’s
specified operating conditions. Examples of power excursion scenarios are shown in Table 1.
These measurements are typically performed over a broad range of input power levels.
Table 1 – Template for transient control measurement test conditions
Scenario Power excursion Slew rate
dB
µs
Input power step transient increase/reduction 3, 7 500, 200, 50
Input power pulse transient 3, 7 500, 200, 50
Input power lightning bolt transient ± 3, ± 7 500, 200, 50

7 Calculations
Transient parameters can be calculated by processing amplifier output power transient
waveforms shown in Figure 2 a) and b), using the following criteria:
– transient power response (dB) = B – A;
– transient power overcompensation response (dB) = G – A;
– steady state power offset (dB) = E – A;
– transient power response time (μs) = D – C.

B
E
A
G
C D
Time (s)
IEC
a) Channel input power increase
G
A
E
B
C D
Time (s)
IEC
b) Channel input power decrease
Figure 2 – OA output power transient response
of a) input power increase and b) decrease
8 Test results
8.1 Test setting conditions
The following test setting conditions shall be recorded:
a) arrangement of the test set-up;
b) details (make and model) of each piece of test equipment;
c) set-up condition of each piece of test equipment (e.g. operating speed of polarization
scrambler, resolution bandwidth of optical spectrum analyzer (OSA));
d) mounting method of test sample;
e) ambient conditions for the test sample;
f) input optical wavelength λ .
in
Power (dBm)
Power (dBm)
– 12 – IEC 61290-4-3:2018 © IEC 2018
8.2 Test data
The following test data shall be recorded:
a) input optical power, P trace;
in
b) output optical power P trace;
out
c) signal-to-ASE ratio (Sig_ASE) at operating condition before and after excursion;
d) OFA laser pump power before and after excursion;
e) OA reported input power before and after input excursion (where available);
f) OA reported output power before and after input excursion;
g) OA reported internal temperature (where available);
h) measurement accuracy of each piece of test equipment;
i) temperature of test sample;
j) transient power response;
k) transient power overcompensation;
l) steady state power offset;
m) transient power response time.

Annex A
(informative)
Overview of power transient events in single channel EDFA
A.1 Background
The input signal to a terminal OFA is normally a single channel erbium-doped fibre amplifier
(EDFA) with a wide dynamic range as a result of channel power excursions throughout the
network. The input signal will accumulate fast power variations, which are caused by
concatenation of transient overshoot/undershoot excursions from the preceding chain of
imperfect EDFA that transport channels. Those well-known gain transients arise as a result of
add/drop events throughout the network, even though each EDFA is operated in constant gain
mode with state-of-the-art gain transient suppression (typically, less than ±1 dB gain
overshoot/undershoot from each EDFA). The temporal steepness and over/undershoot
magnitude of those transients will accumulate with the number of EDFAs passed, and
eventually a transient event with considerable power variations will arrive at the input of the
terminal EDFA. The shape of this single-channel power transient event is directly dependent
on the transient output power shape of the preceding inline EDFAs.
A.2 Characteristic input power behaviour
The characteristic input power behaviour of a single channel terminal OFA is shown
in Figure A.1 a), b) and c), which is a consequence of add/drop events in the preceding
amplifier chain. The figure specifically represents time dependence of the input power
changes with example timings. The step, pulse and lightning bolt transient power response,
and power offset response are particularly critical to carriers and network equipment
manufacturers (NEM), given that the terminal OA is immediately followed by a channel
receiver. A properly designed OA will have small values for these transient parameters.
Specific measurement parameters of the input power changes are detailed in Figure A.2 with
reference to the lightning bolt scenario.

– 14 – IEC 61290-4-3:2018 © IEC 2018
Normal Inverse
−10
−3
a) Step
−17
−10
Time (s)
Time (s)
−10
−3
b) Pulse
−17
−10 Time (s)
Time (s)
−3
−3
−10
Time (s)
c) Lightning bolt
Time (s)
−10
−17
−17
IEC
NOTE As an example of receivers, these are example numbers.
Figure A.1 – Example OA input power transient cases for a receiver application
Input power (dBm)
Input power (dBm)
Input power (dBm)
Input power,  dBm
Input power,  dBm Input power,  dBm

Power increase
90% change
10% change
Fall time
10% change
90% change
Input power
rise time
Time (µs)
IEC
a) Input power increase
Power decrease
90% change
Input power
10% change
fall time
Rise time
10% change
90% change
Time (µs)
IEC
b) Input power decrease
Figure A.2 – Input power measurement parameters
It is important that a single channel OA placed next to a receiver is operated in automatic
power control (APC) mode in order to suppress these input power transient excursions. This
is referred to as output power transient controlled operation. Moderate transient power
excursions incident on the receiver are manageable, depending on the receiver dynamic
range and the bandwidth of the receiver AGC. However, excessive optical powers at the
receiver either can result in data misreadings giving unwanted bit errors or can permanently
damage the receiver.
Input power to OFA linear, arbitrary units
Input power to OFA linear, arbitrary units

– 16 – IEC 61290-4-3:2018 © IEC 2018
A.3 Parameters for characterizing transient behaviour
The parameters generally used to characterize the transient behaviour of a power controlled
OA for the case of channel step increase/reduction are defined in Figure A.3. Figure A.3 a)
specifically represents the time dependence of the output power of the OA when the input
power is rapidly increased. Likewise, the transient power behaviour for the case when the
input power is rapidly decreased is shown in Figure A.3 b).
The important transient parameters are transient power overshoot/undershoot, transient
power response settling time and steady state power offset. For a power-controlled amplifier,
a reduction in input power results in an output power undershoot, and an increase in output
results in an output power overshoot. This is in contrast to a gain-controlled amplifier, where a
reduction in input power results in a gain overshoot, and an increase in input power results in
a gain undershoot.
Transient power response
Steady state power offset
Transient power response time
Time  (s)
IEC
a) Channel input power increase
Transient power response time
Transient power
overcompensation
response
Steady state power offset
Transient power response time
Transient power response
Time  (s)
IEC
b) Channel input power decrease
Figure A.3 – OA output power transient response
Power (dBm)
Power (dBm)
Annex B
(informative)
Background on power transient phenomena
in a single channel EDFA
B.1 Amplifier chains in optical networks
Optical networks commonly incorporate a chain of optical amplifiers to manage fibre loss as
well as losses incurred by optical components providing functions such as dispersion
compensation or channel add/drop. As the network is developing into a mesh structure,
channels may pass through a number of different optical paths before arriving at a receiver
with a consequential impact of unexpected power variations due to compounded
compensation of channel add-drops within networks components, especially transient control
of in-line optical amplifiers. The resilience of the receiver to these unexpected optical power
variations is key to a correctly functioning optical network.
It is common in existing 10 Gb/s systems for the last line amplifier in the WDM link to be a
preamplifier with the entire dense wavelength division multiplexing (DWDM) comb being
amplified collectively. Nevertheless, there is an increasing need for amplifiers on each
channel to pre-amplify further the optical channel prior to the receiver. This single channel
OFA is inserted to help meet the stringent optical signal-to-noise ratio (OSNR) requirements
of modern modulation formats and overcome the losses of specialized optical components,
including optical discriminators or demodulators, polarization demultiplexers, tuneable
dispersion compensators, and tuneable filters in the receiver chain. The total output power of
this single-channel OFA is composed of signal power and amplified spontaneous emission
(ASE) noise. The signal power and ASE power is sometimes unfiltered and not attenuated by
an optical band-pass filter, demultiplexer or specialized components downstream of the OFA.
This is particularly true for colourless receivers, which are broadband and not wavelength
specific.
B.2 Typical optical amplifier design
The typical design of an optically amplified receiver consists of a channel selector, an OFA, a
photon detector, a limiting amplifier, and an electrical low pass filter. Pre-amplifier OFAs have
become an integral part of optical receivers since their performance boosts the sensitivity of
the receiver photon detector. However, noise is generated within a pre-amplifier EDFA as a
result of spontaneous de-excitation of the excited erbium ions. As the ions have a finite
excited state lifetime, some return spontaneously to the ground state emitting a photon that is
incoherent with respect to the incoming optical signal, as opposed to a photon generated by
stimulated emission. This background noise is known as ASE, and it is the dominant noise
element in pre-amplifier EDFAs.
Optical power transients are sub-millisecond fluctuations in network power levels that are
caused by events such as planned or accidental channel loading changes, passive loss
variations, or 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 OFA may suddenly decrease, increasing the
amplifier’s population inversion with a corresponding increase in gain, in a matter of
microseconds. This gain change results in channel power overshoot which is detrimental to
network service providers (NSPs), given that their networks will no longer operate at the gain
level for which they were optimized, potentially impacting service quality. Power fluctuations
accumulate with each OFA in the system and, if left unabated, will enter a single channel OFA
upstream of a receiver and will be amplified, causing the transient to enter the receiver. This
can result in a cumulative transient overshoot or undershoot at the receiver that can grow to
exceed the dynamic range of the receiver. The subsequent increase in bit error ratio (BER)
results in quality of service degradation or, in some circumstances, can even damage a
receiver as a result of excessive optical power.

– 18 – IEC 61290-4-3:2018 © IEC 2018
Line OFA in the optical repeaters along the transmission system typically operate in constant
gain mode. An OFA that is operating with constant gain will replicate and amplify channel
power transients entering the input at the output, which is detrimental for a single channel
amplifier in an amplified receiver.
It is imperative that any single channel OFA situated close to a receiver be operated in
constant output power mode in order to suppress transients. This is referred to as power
transient controlled operation. Moderate transient power excursions incident on the receiver
are manageable, depending on the receiver dynamic range and the bandwidth of the receiver
AGC, but an excessively large power excursion can
a) exceed the absolute maximum optical power rating of the receiver, leading to potential
optical damage (OD) (particularly resulting from power overshoot),
b) exceed the maximum operating optical power rating of the receiver, leading to eye
opening penalty and a burst of errors leading to an outage (particularly resulting from
power overshoot waveforms),
c) drop below the minimum operating optical power rating of the receiver, leading to eye
opening penalty and a burst of errors, leading to an outage (particularly resulting from
power undershoot waveforms), or
d) rapidly oscillate between cases b) and c) above, causing an outage (particularly resulting
from lightning bolt power waveforms).
In addition to amplifying optical channels carrying data, an OFA generates and transmits ASE
noise. The optical data signal is typically centred on one or more wavelengths corresponding
to the channels standardised by the International Telecommunications Union (ITU). In
contrast, the ASE is typically generated across a much broader wavelength range, for
example around 40 nm, which is substantially within the gain bandwidth region of the OFA.
The level of ASE depends upon the optical signal channel gain, the overall population
inversion and temperature of the erbium-doped fibre (EDF). Further, the level of ASE
produced by the OFA will also vary due to the loss variability of other optical components
within the OFA, since passive losses affect the gain required in the EDF to attain a target gain
in the OFA.
A measure of the amount of ASE relative to the signal power entering a single channel
receiver is defined as the signal to ASE ratio (Sig_ASE). This is calculated as:
P
out
Sig _ ASE=
P
ASE
where
Sig_ASE is the signal to ASE ratio;
P is the signal power exiting the OFA;
out
P is the total ASE power exiting the OFA.
ASE
Ideally, the Sig_ASE of an amplifier is always posit
...