IEC 61290-10-5:2014

IEC 61290-10-5 ®
Edition 1.0 2014-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical amplifiers – Test methods –
Part 10-5: Multichannel parameters – Distributed Raman amplifier gain and noise
figure
Amplificateurs optiques – Méthodes d'essai –
Partie 10-5: Paramètres à canaux multiples – Gain et facteur de bruit des
amplificateurs Raman répartis
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IEC 61290-10-5 ®
Edition 1.0 2014-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Optical amplifiers – Test methods –

Part 10-5: Multichannel parameters – Distributed Raman amplifier gain and

noise figure
Amplificateurs optiques – Méthodes d'essai –

Partie 10-5: Paramètres à canaux multiples – Gain et facteur de bruit des

amplificateurs Raman répartis
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX S
ICS 33.180.30 ISBN 978-2-8322-1581-4

– 2 – IEC 61290-10-5:2014 © IEC 2014
CONTENTS
FOREWORD . 3
1 Scope and object . 5
2 Normative references . 5
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviated terms . 7
4 DRA gain and noise figure parameters – Overview . 7
5 Apparatus . 9
5.1 General . 9
5.2 Multi-channel signal source . 10
5.3 Polarization controller . 11
5.4 Optical spectrum analyser . 11
5.5 Optical power meter . 12
5.6 Tuneable narrowband source . 12
5.7 Broadband optical source . 12
5.8 Optical connectors and jumpers . 12
6 Test sample . 12
7 Procedure . 12
7.1 Overview. 12
7.1.1 Channel on-off gain . 12
7.1.2 Pump module channel insertion loss and channel net gain . 13
7.1.3 Channel equivalent noise figure (NF) . 13
7.2 Calibration . 13
7.2.1 Calibration of optical bandwidth . 13
7.2.2 Calibration of OSA power correction factor . 15
7.3 Measurement . 15
7.4 Calculation . 17
7.4.1 Channel on-off gain . 17
7.4.2 Channel net gain . 17
7.4.3 Channel equivalent NF. 17
8 Test results . 17
Annex A (informative) Field measurements versus laboratory measurements . 19
Annex B (informative) Pump depletion and channel-to-channel Raman scattering . 20
Bibliography . 21

Figure 1 – Distributed Raman amplification in co-propagating (left) and count-
propagating (right) configurations . 9
Figure 2 – Measurement set-up without a pump module. 10
Figure 3 – Measurement set-up for counter-propagating configuration . 10
Figure 4 – Measurement set-up for co-propagating configuration . 10
Figure 5 – Possible implementation of a multi-channel signal source . 11

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL AMPLIFIERS –
TEST METHODS –
Part 10-5: Multichannel parameters –
Distributed Raman amplifier gain and noise figure

FOREWORD
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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 61290-10-5 has been prepared by 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/1142/CDV 86C/1233/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.

– 4 – IEC 61290-10-5:2014 © IEC 2014
A list of all parts in 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 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.
OPTICAL AMPLIFIERS –
TEST METHODS –
Part 10-5: Multichannel parameters –
Distributed Raman amplifier gain and noise figure

1 Scope and object
This part of IEC 61290 applies to distributed Raman amplifiers (DRAs). DRAs are based on
the process whereby Raman pump power is introduced into the transmission fibre, leading to
signal amplification within the transmission fibre through stimulated Raman scattering.
A detailed overview of the technology and applications of DRAs can be found in
IEC TR 61292-6.
A fundamental difference between these amplifiers and discrete amplifiers, such as EDFAs, is
that the latter can be described using a black box approach with well-defined input and output
ports. On the other hand, a DRA is basically a pump module, with the actual amplification
process taking place along the transmission fibre. This difference means that standard
methods described in other parts of IEC 61290 for measuring amplifier parameters, such as
gain and noise figure, cannot be applied without modification.
The object of this standard is to establish uniform requirements for accurate and reliable
measurements, using an optical spectrum analyser (OSA), of the following DRA parameters:
a) channel on-off gain;
b) pump unit insertion loss;
c) channel net gain;
d) channel signal-spontaneous noise figure.
The measurement method is largely based on the interpolated source subtraction (ISS)
method using an optical spectrum analyser, as described and elaborated in IEC 61290-10-4,
with relevant modifications relating to a DRA.
All numerical values followed by (‡) are suggested values for which the measurement is
assured. Other values may be acceptable but should be verified.
NOTE General aspects of noise figure test methods are reported in IEC 61290-3.
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 60825-1, Safety of laser products – Part 1: Equipment classification and requirements
IEC 61291-1, Optical amplifiers – Part 1: Generic specification
IEC 61291-4, Optical amplifiers – Part 4: Multichannel applications – Performance
specification template
– 6 – IEC 61290-10-5:2014 © IEC 2014
IEC TR 61292-4, Optical amplifiers – Part 4: Maximum permissible optical power for the
damage-free and safe use of optical amplifiers, including Raman amplifiers
3 Terms, definitions and abbreviations
3.1 Terms and definitions
3.1.1
Raman pump power
optical power produced by the DRA to enable Raman amplification of signal channels
Note 1 to entry: The Raman pump power shall be at a lower wavelength than the signal channels.
3.1.2
fibre span
length of fibre into which signal channels and Raman pump power are introduced, and Raman
amplification of the signal channels takes place via stimulated Raman scattering
3.1.3
co-propagating configuration
forward pumping configuration
configuration whereby the Raman pump power is coupled to the input of the fibre span such
that the signal channels and Raman pump power propagate in the same (forward) direction
3.1.4
counter-propagating configuration
backward pumping configuration
configuration whereby the Raman pump power is coupled to the output of the fibre span such
that the signal channels and Raman pump power propagate in opposite directions
3.1.5
pump module
module that produces Raman pump power and couples it into the connected fibre span
Note 1 to entry: If the pump module is connected to the input of the fibre span, then both the incoming signal
channels and Raman pump power are coupled to the fibre span.
Note 2 to entry: If the pump module is connected to the output of the fibre span, then the pump power is coupled
into the fibre span, while the signal channels exiting the fibre span pass through the pump module from the input
port to the output port.
Note 3 to entry: In this standard, the convention will be used whereby the input port of the pump module is
defined as the port into which the signal channels enter, while the output port is defined as the port through which
the signal channels exit. Thus, in co-propagating configuration the Raman pump power exits the pump module from
the output port, while in counter-propagating configuration the Raman pump power exits the pump module from the
input port.
3.1.6
channel on-off gain
G
on-off
ratio of the channel power at the output of the fibre span when the pump module is
operational to the channel power at the same point when the pump module is not operational
3.1.7
pump module channel insertion loss
IL
ratio of the channel power at the input of the pump module to the channel power at the output
of the pump module
3.1.8
channel net gain
G
net
channel on-off gain minus the pump module channel insertion loss, in dB
3.1.9
channel equivalent noise figure
NF
sig-ASE,eq
channel noise figure due to signal-spontaneous beat noise (see IEC 61290-3) of an equivalent
discrete amplifier placed at the output of the fibre span which has the same channel gain as
the DRA channel on-off gain, and generates the same amount of ASE as that generated by
the DRA at the output of the fibre span.
3.2 Abbreviated terms
ASE amplified spontaneous emission
DRA distributed Raman amplifier
EDFA Erbium doped fibre amplifier
FWHM full-width half-maximum
GFF gain flattening filter
ISS interpolated source subtraction
NF noise figure
RBW resolution bandwidth
OSA optical spectrum analyser
OSNR optical signal-to-noise ratio
PCF power correction factor
SMF single-mode fibre
SSE source spontaneous emission
VOA variable optical attenuator
4 DRA gain and noise figure parameters – Overview
NOTE Unless specifically stated otherwise, all equation and definitions in this clause and onwards are given in
linear units, and not dB.
Figure 1 shows the application of DRAs in co-propagating (forward pumping) and counter-
propagating (backward pumping) configurations. As a general rule, counter propagating
configuration is much more widely used compared to co-propagating configuration.
As with any amplifier, one of the main parameters of interest is the channel gain (see
IEC 61291-1 and IEC 61291-4). However, unlike discrete amplifiers, where the channel gain
is simply defined as the ratio of the channel power at the output port to the channel power at
the input port, with a DRA, the situation is more complex. In principle, the DRA includes both
the pump module, which supplies the pump power, and the fibre span, where the actual
amplification takes place. Thus, one option for defining channel gain is to define it as the ratio
of the channel power at point C (Figure 1) to the channel power at point A, while the pumps
are operational. However, since this definition also include the fibre span loss, which is often
larger than the gain supplied by the Raman pumps, this definition is not very useful.
A much more useful quantity is the channel on-off gain, which is defined as the ratio of the
channel power at the output of the fibre span when the Raman pumps are on to the channel
power at the same point but when the pumps are off (see the graphs in Figure 1).

– 8 – IEC 61290-10-5:2014 © IEC 2014
P
on
G =
(1)
on−off
P
off
In practice, the channel on-off gain may be measured at any point following the fibre span, for
example point C for co-propagating configuration, or points B and C for the counter-
propagating configuration.
Another parameter of interest for DRAs is the pump module channel insertion loss, which is
defined as the ratio of the channel power at the input port of the pump module to the channel
power at the output port of the pump module (points A and B for co-propagating configuration,
and points B and C for counter propagating configuration).
P
pump unit input
IL=
(2)
P
pump unit output
Since no amplification takes place within the pump module, this is just passive insertion loss,
and is not affected by the status of the pumps (on or off).
The channel on-off gain and pump module channel insertion loss can be combined into a
single quantity, the channel net gain, which is defined in dB as
G (dB)=G (dB)−IL(dB) (3)
net on−off
The channel net gain is particularly useful for counter-propagating configuration, as it may be
directly measured in linear units as the ratio of the channel power at point C when the pumps
are on to the channel power at point B when the pumps are off. When the pump module
includes a gain flattening filter (GFF) to tailor the spectral shape of the Raman gain, then the
channel net gain includes the effect of the GFF, as opposed to the channel on-off gain which
does not (i.e. the channel on-off gain has a non-flat dependence on the channel wavelength).
For the co-propagating configuration, the channel net gain has less physical meaning, and it
is more common to separately define the channel on-off gain and pump module channel
insertion loss.
Another important parameter relevant to a DRA is the channel equivalent noise figure (NF)
due to signal-spontaneous beat noise. This quantity is only relevant to counter-propagating
configuration. The channel equivalent NF of a DRA is defined as the NF of an equivalent
discrete amplifier placed at the output of the fibre span, which provides the same amount of
channel gain as the DRA channel on-off gain, and generates the same amount of amplified
spontaneous emission (ASE) as that generated at the fibre span output by the DRA. The
channel equivalent noise figure (in dB) due to signal-spontaneous beat noise is given by (see
IEC 61290-3):
NF = 10log (ρ /(G hν))
(4)
sig−ASE,eq 10 ASE,B on−off
where
ρ is the ASE spectral density at the channel wavelength λ (in both polarization
ASE,B
modes) measured at the output of the fibre span (point B in the counter-propagating
configuration of Figure 1);
ν=c /λ is the channel frequency;
h is Planck’s constant.
Using the relation between the channel on-off gain and the channel net gain, it is easily
shown that the channel equivalent NF is also given by

NF = 10log (ρ /(G hν))
sig−ASE,eq 10 ASE,C net (5)
where
ρ is now measured at point C.
ASE,C
Counter-propagating configuration
Co-propagating configuration
Fibre span
Fibre span
Signal Signal
A C A C
B B
Pump Pump
module module
Pump Pump
30  30
Pump
Pump
Signal with pump on
Signal with pump on
20  20
Signal with pump off
Signal with pump off
10  10
0   0
–10
–10
–20
–20
On-off On-off
gain gain
–30 –30
0 50 100 150 0 50 100 150
Position along span  (km) Position along span  (km)
IEC  1389/14
NOTE The graphs show the evolution of pump and signal along the fibre span.
Figure 1 – Distributed Raman amplification in co-propagating (left)
and count-propagating (right) configurations
When measuring DRA gain and NF, the following issues should be considered:
a) The purpose of the measurement: whether the purpose is to measure the DRA
performance in relation to a specific span of fibre in the field, or characterize DRA
performance with respect to a generic fibre type in the laboratory. This is elaborated in
Annex A.
b) Whether or not the input signal configuration can affect the measurement due to pump
depletion and/or signal-signal Raman scattering. This is elaborated in Annex B.
5 Apparatus
5.1 General
Figures 2 through 4 show the measurement set-up for measurement of DRA parameters in
counter-propagating and co-propagating configurations. The various components comprising
the set-up (as well as other components used for calibration) are described in the following
subclauses.
Power  (dBm)
Power  (dBm)
– 10 – IEC 61290-10-5:2014 © IEC 2014
Fibre span
Signal
Multi-channel Polarization
OSA
signal source controller
IEC  1390/14
Figure 2 – Measurement set-up without a pump module

Fibre span
Signal
Pump
Multi-channel Polarization
OSA
module
signal source controller
Pump
IEC  1391/14
Figure 3 – Measurement set-up for counter-propagating configuration

Fibre span
Signal
Pump
Multi-channel Polarization
OSA
module
signal source controller
Pump
IEC  1392/14
Figure 4 – Measurement set-up for co-propagating configuration
5.2 Multi-channel signal source
Figure 5 shows a possible implementation of a multi-channel signal source. This optical
source should consist of n laser sources where n is the number of channels for the test
configuration. The full width at half maximum (FWHM) of the output spectrum of each laser
source shall be narrower than 0,1 nm (‡) so as not to cause any interference to adjacent
channels. The suppression ratio of the side modes of the single-line laser shall be higher than
35 dB (‡). The output power fluctuation shall be less than 0,05 dB (‡), which is more easily
attainable with an optical isolator placed at the output port of each source. The wavelength
———————
Suggested value.
accuracy shall be better than ±0,1 nm (‡) with stability better than ±0,01 nm (‡). The
spontaneous emission power within a 1 nm window surrounding the laser wavelength should
be at least 40 dB below the laser output power.
The purpose of the channel combiner is to multiplex all the laser sources onto a single fibre.
The channel combiner should have polarization dependent loss better than 0,5 dB (‡), and
wavelength dependent loss better than 1 dB (‡).The reflectance from this device shall be
smaller than –50 dB (‡) at each port.
λ
Variable
Laser
optical
source
attenuator
λ
n
IEC  1393/14
Figure 5 – Possible implementation of a multi-channel signal source
The multi-channel signal source should provide the ability to control the power of each
individual laser, so as to achieve a desired power configuration of the channels. This can be
achieved either through direct control of each laser source, or by placing a variable optical
attenuator (VOA) after each laser source. The multi-channel signal source should preferably
also provide the ability to control the power of all the sources simultaneously, e.g. using a
variable optical attenuator (VOA) as shown in Figure 5. If one or more VOA is used, then its
attenuation range and stability shall be over 40 dB (‡) and better than 0,1 dB (‡), respectively.
The reflectance from this device shall be smaller than –50 dB (‡) at each port. If a VOA is
placed after the channel combiner, the wavelength flatness over the full range of attenuation
shall be less than 0,5 dB (‡).
5.3 Polarization controller
This device shall be able to convert any state of polarization of a signal to any other state of
polarization. The polarization controller may consist of an all-fibre polarization controller or a
quarter-wave plate rotatable by a minimum of 90°, followed by a half-wave plate rotatable by a
minimum of 180°. The reflectance of this device shall be smaller than –50 dB (‡) at each port.
The insertion loss variation of this device shall be less than 0,5 dB (‡). The use of a
polarization controller is considered optional, but may be necessary to achieve the desired
accuracy for cases when the DRA exhibits significant polarization dependent gain.
5.4 Optical spectrum analyser
The optical spectrum analyser (OSA) shall have polarization sensitivity less than 0,1 dB (‡),
stability better than 0,1 dB (‡) and wavelength accuracy better than 0,05 nm (‡). The linearity
should be better than 0,2 dB (‡) over the device dynamic range. The reflectance from this
device shall be smaller than –50 dB (‡) at its input port. The OSA shall have sufficient
dynamic range and support sufficiently small resolution bandwidth (RBW) to measure the
noise between channels. For 100 GHz (0,8 nm) channel spacing, the dynamic range shall be
greater than 55 dB at 50 GHz (0,4 nm) from the signal.
Channel combiner
– 12 – IEC 61290-10-5:2014 © IEC 2014
5.5 Optical power meter
This device, which may be required for the calibration of the OSA, shall have a measurement
accuracy better than 0,2 dB (‡), irrespective of the state of polarization, within the operational
wavelength bandwidth of the DRA and within the power range from –40 dBm to +20 dBm (‡).
5.6 Tuneable narrowband source
This device, which may be required for the calibration of the OSA, shall be tuneable over the
operational wavelength bandwidth of the DRA (for example, 1 530 nm to 1 565 nm). The full
width at half maximum (FWHM) of the output spectrum of the narrowband source shall be
narrower than 0,1 nm (‡).The wavelength accuracy shall be better than ±0,1 nm (‡) with
stability better than ±0,01 nm (‡). The output power fluctuation shall be less than 0,1 dB (‡).
The output power shall remain stable to within 0,1 dB (‡) while tuning the wavelength over the
measurement bandwidth range (typically 10 nm).
5.7 Broadband optical source
This device, which may be required for the calibration of the OSA, shall provide broadband
optical power over the operational wavelength bandwidth of the DRA (for example, 1 530 nm
to 1 565 nm). The output spectrum shall be flat with less than a 0,1 dB (‡) variation over the
measurement bandwidth range (typically 10 nm). The output power fluctuation shall be less
than 0,1 dB (‡).
For example, the ASE generated by an optical fibre amplifier with no input signal applied
could be used as a broadband optical source.
5.8 Optical connectors and jumpers
Optical connectors and jumpers, which may be used to connect the various components in
Figures 2 through 4, should have a connection loss repeatability better than 0,1 dB (‡).
Preferably, the reflectance from optical connectors when used shall be smaller than –50 dB
(‡). Preferably, jumper length shall be short (<2 m), and jumpers shall remain undisturbed
during the duration of the measurement in order to minimize state of polarization change.
6 Test sample
The DRA under test, which consists of both the pump module and the fibre span, shall
operate at nominal operating conditions. Care shall be taken in maintaining the state of
polarization of the input light during the measurement. Changes in the polarization state of the
input light may result in input optical power changes because of the slight polarization
dependency expected from all the used optical components, leading to measurement errors
Due to high Raman pump power typically used in the measurement, laser safety procedures
should be implemented and followed as described in IEC 60825-1. In addition, extra care
should be taken with respect to connector cleanliness and avoidance of fibre bends, as
described in IEC TR 61292-4.
Connection loss between the pump module and fibre span should be minimized as much as
possible (preferably <0,2 dB) in order not to affect the measurement results.
7 Procedure
7.1 Overview
7.1.1 Channel on-off gain
For measuring the channel on-off gain, the following parameters shall be measured:

a) The signal power level for each channel when the pump module is off (i.e. not emitting
Raman pump power), using the set-up shown in Figure 3 for counter-propagating
configuration, or the set-up shown in Figure 4 for co-propagating configuration.
b) The signal power level for each channel when the pump module is on (i.e. emitting Raman
pump power), using the set-up shown in Figure 3 for counter-propagating configuration, or
the set-up shown in Figure 4 for co-propagating configuration.
7.1.2 Pump module channel insertion loss and channel net gain
For measuring the pump module channel insertion loss and the channel net gain, the
following parameters shall be measured:
a) The signal power level for each channel according to the set-up shown in Figure 2.
b) The signal power level for each channel when the pump sources within the pump module
are off (i.e. not emitting Raman pump power), using the set-up shown in Figure 3 for
counter-propagating configuration, or the set-up shown in Figure 4 for co-propagating
configuration.
c) The signal power level for each channel when the pump sources within the pump module
are on (i.e. emitting Raman pump power), using the set-up shown in Figure 3 for counter-
propagating configuration, or the set-up shown in Figure 4 for co-propagating
configuration
7.1.3 Channel equivalent noise figure (NF)
For measuring the channel equivalent NF for counter-propagating configuration, the following
parameters should be measured:
a) The signal power level for each channel using the set-up shown in Figure 2.
b) The source spontaneous emission (SSE) spectral power density at the wavelength of each
channel using the set-up shown in Figure 2.
c) The signal power level for each channel when the pump module is on (i.e. emitting Raman
pump power) using the set-up shown in Figure 3.
d) The ASE spectral power density at the wavelength of each channel when the pump
sources within the pump module are on (i.e. emitting Raman pump power) using the set-
up shown in Figure 3.
The noise-equivalent bandwidth of the OSA is required for the measurement of SSE and ASE
spectral power density. If not specified by the manufacturer to sufficient accuracy, it may be
calibrated using one of the two methods below. The noise-equivalent bandwidth of a
wavelength filter is the bandwidth of a theoretical filter with rectangular pass-band and the
same transmission at the centre wavelength that would pass the same total noise power as
the actual filter when the source power density is constant versus wavelength.
7.2 Calibration
7.2.1 Calibration of optical bandwidth
7.2.1.1 General
The noise-equivalent bandwidth, B , can be calibrated using one of the following two
o
methods, based on the use of either a tuneable narrowband optical source or a broadband
optical source.
For both methods, the following approximate equation permits converting the optical
bandwidth from the wavelength domain, ∆λ (λ ), to the frequency domain, B (λ ):
BW s o s
−1 −1
( ) [( ( ) ) ( ( ) ) ]
B λ = cλ −∆λ λ / 2 − λ +∆λ λ / 2 (6)
o S s BW s s BW s
– 14 – IEC 61290-10-5:2014 © IEC 2014
where c is the speed of light in free space.
Once the noise-equivalent bandwidth has been determined as above, the OSA resolution
bandwidth should remain unchanged throughout the measurement procedure.
The OSA resolution bandwidth shall be chosen such that it is narrow enough to accurately
measure ASE between any two channels of the multi-channel signal source with sufficiently
large dynamic range dynamic range.
7.2.1.2 Calibration using a tuneable narrowband optical source
The steps listed below shall be followed:
a) Connect the output of a tuneable narrowband optical source directly to the OSA.
b) Set the OSA centre wavelength to the signal wavelength to be calibrated, λ .
s
c) Set the OSA span to zero (fixed wavelength).
d) Set the OSA resolution bandwidth to the desired value, RBW.
e) Set the narrowband optical source wavelength to λ , within the range from
λ −RBW−δ
i S
to , choosing δ large enough to ensure that the end wavelengths fall outside
λ + RBW+δ
S
the OSA filter pass-band.
f) Record the OSA signal level, P(λ ), in linear units.
i
g) Repeat steps e) and f), incrementing the narrowband optical source wavelength through
the wavelength range by the tuning interval, ∆λ, selected according to the accuracy
requirements as described below.
h) Determine the optical bandwidth according to the following equation:
P(λ)
i
∆λ (λ )= ∆λ (7)
BW S ∑
P(λ )
S
i
The procedure may be repeated for different signal wavelengths, or for each wavelength of
the multichannel source.
The accuracy of this measurement is related to the tuning interval of the narrowband optical
source (∆λ) and power flatness over the wavelength range. A tuning interval smaller than
0,1 nm is advisable. The optical power should not vary more than 0,4 dB over the wavelength
range.
7.2.1.3 Calibration using a broadband optical source
This method requires that the OSA have a rectangular shape bandwidth-limiting filter, when
the resolution bandwidth is at the maximum value. The steps listed below shall be followed:
Connect the output of a narrowband optical source directly to the OSA. If adjustable, as in
a)
the case of a tuneable laser, set the wavelength of the source to a specific wavelength,
λ .
s
b) Set the OSA resolution bandwidth to the maximum value, preferably not larger than
10 nm.
c) Using the OSA, measure the FWHM of the OSA bandwidth by scanning over the
narrowband signal, ∆λ .
RBWmax
d) Connect the output of a broadband optical source directly to the OSA.
e) Keep the OSA resolution bandwidth at the maximum value.
f) Using the OSA, measure the output power level, P (in linear units), at the given
RBWmax
wavelength, λ .
s
g) Set the OSA resolution bandwidth to the desired value.
h) Using the OSA, measure the output power level, P (in linear units), at the given
RBW
wavelength, λ .
s
i) Determine the optical bandwidth according to the following equation:
P
RBW
∆λ (λ )= ∆λ (λ )
(8)
BW S RBWmax S
P
RBWmax
j) The procedure may be repeated for different signal wavelengths, or for each wavelength
of the multichannel signal source.
NOTE It is assumed that the measurement at the maximum resolution bandwidth, ∆λ , is accurate.
RBWmax
7.2.2 Calibration of OSA power correction factor
Follow the steps listed below to calibrate the OSA power correction factor (PCF). The power
correction factor calibrates the OSA for absolute power.
λ .
a) Adjust the multi-channel signal source to output a single channel at signal wavelength,
s
Connect the output of the multi-channel signal source directly to the input of the optical
power meter, and measure P (in dBm). Alternatively, the set-up in Figure 2 may be
PM
used, with the OSA replaced by the optical power meter.
b) Disconnect the optical power meter, connect the OSA instead, and measure P

OSA
(in dBm).
c) Determine the power calibration factor, PCF in dB, according to the following equation:
PCF(λ )= P −P (9)
s PM OSA
For the multi-channel signal source, turn λ on and all other lasers off. Follow steps (a)
through (c) above. Then turn λ on and all other lasers off. Repeat until a power calibration
factor is obtained for all n wavelengths.
7.3 Measurement
The measurement procedure for all parameters (channel on-off gain, channel net gain,
channel equivalent NF) is described in the following steps. If the channel equivalent NF is not
required, then steps b), c) and d) may be omitted (if the OSNR is high enough, see NOTE 1
below, then steps j) and k) may also be omitted). If only channel on-off gain is required, then
only steps f) through k) need be performed.
a) Connect the measurement set-up as shown in Figure 2.
b) Set the resolution bandwidth of the OSA to the calibrated value. Do not change this
setting throughout this procedure.
c) Adjust the relative power levels of each laser of the multichannel source, as well as the
absolute power level of all lasers using the VOA, according to the detailed specification.
Typically, the lasers shall be set to have equal power output.
d) Measure the s
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