IEC 61290-4-3:2015

IEC 61290-4-3


®


Edition 1.0 2015-05



INTERNATIONAL



STANDARD




colour
inside


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

IEC 61290-4-3:2015-05(en)

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IEC 61290-4-3



®



Edition 1.0 2015-05







INTERNATIONAL





STANDARD











colour

inside










Optical amplifiers – Test methods

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

output power control



























INTERNATIONAL

ELECTROTECHNICAL


COMMISSION





ICS 33.180.30 ISBN 978-2-8322-2670-4



  Warning! Make sure that you obtained this publication from an authorized distributor.


® Registered trademark of the International Electrotechnical Commission

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– 2 – IEC 61290-4-3:2015 © IEC 2015


CONTENTS



FOREWORD . 3

1 Scope . 5

2 Normative references . 5


3 Terms, definitions and abbreviations . 6

3.1 Terms and definitions . 6

3.2 Abbreviations . 7

4 Apparatus . 7

4.1 Test set-up . 7
4.2 Characteristics of test equipment . 8
5 Test sample . 9
6 Procedure . 9
6.1 Test preparation. 9
6.2 Test conditions . 9
7 Calculations . 10
8 Test results . 11
8.1 Test settings . 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 . 15
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 . 11

Figure A.1 – Example OA input power transient cases for a receiver application . 14
Figure A.2 – Input power measurement parameters for a) input power increase and b)
input power decrease . 15
Figure A.3 – OA output power transient response of a) input power increase and b)
input power decrease . 16
Figure B.1 – Transient response to a) input power drop (inverse step transient) with
transient control, b) deactivated (constant pump power), and c) activated
(power control). 21
Figure B.2 – Transient response to a) input power rise (step transient) with transient
control, b) deactivated (constant pump power), and c) activated (power control) . 22

Table 1 – Examples of transient control measurement test conditions . 10

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IEC 61290-4-3:2015 © IEC 2015 – 3 –


INTERNATIONAL ELECTROTECHNICAL COMMISSION


____________




OPTICAL AMPLIFIERS – TEST METHODS



Part 4-3: Power transient parameters –

Single channel optical amplifiers in output power control



FOREWORD

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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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 International Standard is to be used in conjunction with IEC 61291-1:2012, on the basis
of which it was established.
The text of this standard is based on the following documents:
FDIS Report on voting
86C/1310/FDIS 86C/1329/RVD

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 –

1)
Test methods can be found on the IEC website.


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

the stability date indicated on the IEC website 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 publication may be issued at a later date.

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.


___________
1)
The first editions of some of these parts were published under the general title Optical fibre amplifiers – Basic
specification or Optical amplifier test methods.

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IEC 61290-4-3:2015 © IEC 2015 – 5 –


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 (OFA) 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 (SOA).
The object of this standard is to provide the general background for optical amplifier (OA)
power transients and its 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:
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 definition defined here are
applicable if the amplifier is an OFA or an alternative OA. However, the description in
Annex A of this document concentrates on the physical performance of an OFA and provides
a detailed description of the behaviour of OFA; it does not give a similar description of other

OA types.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61291-1:2012, Optical amplifiers – Part 1: Generic specification

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3 Terms, definitions and abbreviations


3.1 Terms and definitions


For the purposes of this document, the following terms and definitions apply.


3.1.1

input signal

optical signal that is input to the OA


3.1.2

input power excursion
relative input power difference in dB before, during and after the input power stimulus event
that causes an OA transient power excursion.
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
3.1.4
input power 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 decreasing power excursion event
Note 1 to entry: see Figure A.2
3.1.5
slew rate
maximum rate of change of the input optical signal during a power excursion event
3.1.6
transient power response
maximum or minimum deviation (overshoot or undershoot) in dB 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.

3.1.7
transient power settling 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 stimulus event that 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 in dB 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.

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IEC 61290-4-3:2015 © IEC 2015 – 7 –


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.

3.1.9

steady state power offset

difference in dB 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.

3.2 Abbreviations


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
SAR signal-to-ASE ratio

SigP signal power
SOP state of polarization
VOA variable optical attenuator
WDM wavelength division multiplexing
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.

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OA

Channel pass-
Optical
Polarization
under
Laser source
VOA
band filter
modulator
scrambler
test


O/E converter

Function generator

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 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 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.
– 1dB pass-band of at least ±20 GHz centred around the signal wavelength.
– At least 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) Opto-electronic (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.

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IEC 61290-4-3:2015 © IEC 2015 – 9 –


g) 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.

h) 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 and 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 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(1). For alternative transient
control measurements, the signal generator waveform is controlled appropriately, and the
VOA is adjusted accordingly.
6.2 Test conditions
Several sequential transient control measurements can be performed according to the optical
amplifier’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.

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Table 1 – Examples of transient control measurement test conditions


Scenario Power excursion Slew rate

Input power step transient increase/reduction 3 dB, 7 dB 500 µs, 200 µs, 50 µs

Input power pulse transient 3 dB, 7 dB
500 µs, 200 µs, 50 µs

Input power lightning bolt transient ±3 dB, ±7 dB 500 µs, 200 µs, 50 µs




7 Calculations


Transient parameters can be calculated by processing amplifier output power transient
waveforms shown in Figure 2, 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

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IEC 61290-4-3:2015 © IEC 2015 – 11 –




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
8 Test results
8.1 Test settings
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
Power, dBm
Power,  dBm

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f) Input optical wavelength λ
in


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 (SAR) 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

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IEC 61290-4-3:2015 © IEC 2015 – 13 –


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
...