IEC 61290-10-4:2007

INTERNATIONAL IEC
STANDARD
CEI
61290-10-4
NORME
First edition
INTERNATIONALE
Première édition
2007-05
Optical amplifiers –
Test methods –
Part 10-4:
Multichannel parameters –
Interpolated source subtraction method
using an optical spectrum analyzer

Amplificateurs optiques –
Méthodes d’essais –
Partie 10-4:
Paramètres à canaux multiples –
Méthode par soustraction de la source interpolée
en utilisant un analyseur de spectre optique
Reference number
Numéro de référence
IEC/CEI 61290-10-4:2007
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INTERNATIONAL IEC
STANDARD
CEI
61290-10-4
NORME
First edition
INTERNATIONALE
Première édition
2007-05
Optical amplifiers –
Test methods –
Part 10-4:
Multichannel parameters –
Interpolated source subtraction method
using an optical spectrum analyzer

Amplificateurs optiques –
Méthodes d’essais –
Partie 10-4:
Paramètres à canaux multiples –
Méthode par soustraction de la source interpolée
en utilisant un analyseur de spectre optique
PRICE CODE
Q
CODE PRIX
Commission Electrotechnique Internationale
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue
Pour prix, voir catalogue en vigueur

– 2 – 61290-10-4 © IEC:2007
CONTENTS
FOREWORD.3
INTRODUCTION.5

1 Scope and object.6
2 Normative references .6
3 Abbreviated terms .7
4 Apparatus.7
5 Test sample.8
6 Procedure .9
6.1 Calibration.9
6.1.1 Calibration of optical bandwidth.9
6.1.2 Calibration of OSA power correction factor .10
6.2 Measurement .11
6.3 Calculation .12
7 Test results .12

Annex A (normative) Limitations of the interpolated source subtraction technique due
to source spontaneous emission .13

Bibliography.17

Figure 1 – Apparatus for gain and noise figure measurement.7
Figure A.1 – DI subtraction error as a function of source spontaneous emission level.14
Figure A.2 – Spectral plot showing additive higher noise level from spontaneous
emission of individual laser sources and broadband multiplexer.16
Figure A.3 – Significantly reduced spontenous emmision using wavelength selective
multiplexer .16

61290-10-4 © IEC:2007 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
OPTICAL AMPLIFIERS –
TEST METHODS –
Part 10-4: Multichannel parameters –
Interpolated source subtraction method using
an optical spectrum analyzer
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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 61290-10-4 has been prepared by subcommittee 86C: Fibre optic
systems and active devices, of IEC technical committee 86: Fibre optics.
This standard shall be used in conjunction with IEC 61291-1. It was established on the basis
of the second (2006) edition of that standard.
The text of this standard is based on the following documents:
CDV Report on voting
86C/724/CDV 86C/742/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.

– 4 – 61290-10-4 © IEC:2007
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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 publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
61290-10-4 © IEC:2007 – 5 –
INTRODUCTION
This International Standard is devoted to the subject of optical amplifiers. The technology of
optical amplifiers is still rapidly evolving, hence amendments and new additions to this
standard can be expected.
– 6 – 61290-10-4 © IEC:2007
OPTICAL AMPLIFIERS –
TEST METHODS –
Part 10-4: Multichannel parameters –
Interpolated source subtraction method using
an optical spectrum analyzer
1 Scope and object
This part of IEC 61290 applies to all commercially available optical amplifiers (OAs) and
optically amplified subsystems. It applies to OAs using optically pumped fibres (OFAs based
on either rare-earth doped fibres or on the Raman effect), semiconductor optical amplifiers
(SOAs) and waveguides (POWA).
The object of this standard is to establish uniform requirements for accurate and reliable
measurements, by means of the interpolated source subtraction method using an optical
spectrum analyzer. The following OA parameters, as defined in Clause 3 of IEC 61291-1, are
determined:
• channel gain, and
• channel signal-spontaneous noise figure.
This method is called interpolated source subtraction (ISS) because the amplified
spontaneous emission (ASE) at each channel is obtained by interpolating from measurements
at a small wavelength offset around each channel. To minimize the effect of source
spontaneous emission, the effect of source noise is subtracted from the measured noise.
The accuracy of the ISS technique degrades at high input power level due to the spontaneous
emission from the laser source(s). Annex A provides guidance on the limits of this technique
for high input power.
An additional source of inaccuracy is due to interpolation error. Annex A provides guidance on
the magnitude of interpolation error for a typical amplifier ASE versus wavelength
characteristic.
NOTE 1 All numerical values followed by (‡) are suggested values for which the measurement is assured. Other
values may be acceptable but should be verified.
NOTE 2 General aspects of noise figure test methods are reported in IEC 61290-3.
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 61291-1:2006, Optical amplifiers – Part 1: Generic specification
IEC 61291-4: Optical amplifiers – Part 4: Multichannel applications – Performance
specification template
61290-10-4 © IEC:2007 – 7 –
3 Abbreviated terms
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, the following is a list of all
abbreviations used in this standard:
ASE Amplified spontaneous emission
DI Direct interpolation (technique)
FWHM Full-width half-maximum
ISS Interpolated source subtraction
NF Noise figure
RBW Resolution bandwidth
OA Optical amplifier
OFA Optical fibre amplifier
OSA Optical spectrum analyzer
POWA Planar optical waveguide amplifier
PCF Power correction factor
SOA Semiconductor optical amplifier
SSE Source spontaneous emission
4 Apparatus
4.1 Multichannel source
This optical source consists 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 the laser
sources 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
accuracy shall be better than ±0,1 nm (‡) with stability better than ±0,01 nm (‡). The
spontaneous emission level must be less than -43 dB/nm with respect to the total input power
for 0 dBm total input power and less than -48 dB/nm with respect to the total input power for
5 dBm total input power (‡). See Annex A for a discussion of the impact of the spontaneous
emission level on the accuracy of noise figure measurements.

λ
Calibration path
λ
dB
Variable Polarization
OA Optical
optical controller
under test spectrum
λ
n attenuator
analyzer
Multichannel source
IEC  746/07
Figure 1 – Apparatus for gain and noise figure measurement
Optical combiner
– 8 – 61290-10-4 © IEC:2007
4.2 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 0,2 dB (‡). The use of a
polarization controller is considered optional, but may be necessary to achieve the desired
accuracy for OA devices exhibiting significant polarization dependent gain.
4.3 Variable optical attenuator
The 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.
The wavelength flatness over the full range of attenuation shall be less than 0,2 dB (‡).
4.4 Optical spectrum analyzer
The optical spectrum analyzer (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 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.
4.5 Optical power meter
This device shall have a measurement accuracy better than 0,2 dB (‡), irrespective of the
state of polarization, within the operational wavelength bandwidth of the OA and within the
power range from –40 dBm to +20 dBm (‡).
4.6 Broadband optical source
This device shall provide broadband optical power over the operational wavelength bandwidth
of the OA (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). For
example, the ASE generated by an OA with no signal applied could be used.
4.7 Optical connectors
The connection loss repeatability shall be better than 0,1 dB (‡). The reflectance from this
device shall be smaller than –50 dB (‡).
4.8 Optical fibre jumpers
The mode field diameter of the optical fibre jumpers shall be as close as possible to that of
the fibres used as input and output ports of the OA. The reflectance from this device shall be
smaller than –50 dB (‡), and the device length shall be short (< 2m). The jumpers between
the source and the device under test should remain undisturbed during the duration of the
measurements in order to minimize state of polarization changes.
Subsequently, the combination of the multichannel optical source, the variable optical
attenuator, and the input polarization controller shall be referred to as the source module. The
polarization controller of the source module is optional and is required only when polarization
dependent performances are to be measured.
5 Test sample
The OA under test shall operate at nominal operating conditions. If the OA is likely to cause
laser oscillations due to unwanted reflections, use of optical isolators is recommended to
bracket the OA under test. This will minimize the signal instability and the measurement
inaccuracy.
61290-10-4 © IEC:2007 – 9 –
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
6 Procedure
This method is based on the optical measurement of the following parameters:
• the signal power level for each channel at the input of the OA under test;
• the signal power level for each channel at the output of the OA under test;
• the ASE power level for each channel at the output of the OA under test;
• the SSE power level for each channel at the input of the OA under test; and
• the optical bandwidth of the OSA.
The noise-equivalent bandwidth of the OSA is required for the calculation of ASE 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.
6.1 Calibration
6.1.1 Calibration of optical bandwidth
The noise-equivalent bandwidth, B , can be determined with the following methods. The
o
calibration can be performed using one of the following two methods, based on the use of
either a tuneable narrowband or a broadband optical source, respectively.
6.1.1.1 Calibration using a narrowband optical source
The steps listed below shall be followed.
a) Connect the output of a tuneable narrowband optical source directly to the OSA.
λ .
b) Set the OSA centre wavelength to the signal wavelength to be calibrated,
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 to
S
i
λ + RBW + δ , choosing δ large enough to ensure that the end wavelengths fall out of the
S
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, Δλ, selected according to the accuracy
requirements as described below.
h) Determine the optical bandwidth according to the following equation:
P()λ
i
Δλ ()λ = Δλ (1)
BW S ∑
P()λ
S
i
The procedure may be repeated for different signal wavelengths, or for each wavelength of
the multichannel source.
– 10 – 61290-10-4 © IEC:2007
The accuracy of this measurement is related to the tuning interval of the narrowband optical
source (Δλ) 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.
6.1.1.2 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 by scanning over the narrowband signal, Δλ .
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
Δλ ()λ = Δλ ()λ (2)
RBW S
BW S
P
RBWmax
j) The procedure may be repeated for different signal wavelengths, or for each wavelength
of the multichannel source.
For both methods, the following approximate equation permits converting the optical
bandwidth from the wavelength domain, Δλ (λ ), to the frequency domain, B (λ ):
BW s o s
−1 −1
[ ]
B()λ = c()λ − Δλ (λ)/ 2 −()λ + Δλ(λ)/ 2 (3)
o S s BW s s BW s
where c is the speed of light in free space.
NOTE 1 Once this value is determined, all OSA measurements are made with the same resolution bandwidth
setting as calibrated above, taking into consideration the optical filter in the OSA, if present. A resolution
bandwidth must be chosen such that the dynamic range is adequate to measure ASE between channels.
NOTE 2 If a narrow optical filter is included in the OA, then the OA should be included in the path between the
source and the OSA when calibrating B (λ ). The resolution bandwidth setting must be smaller than the optical filter
o s
bandwidth.
NOTE 3 It is assumed that the measurement at the maximum resolution bandwidth, Δλ , is accurate.
RBWmax
6.1.2 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.
a) Adjust the source module for a single channel at signal wavelength, λ . Connect the

s
output of the source module directly to the input of the optical power meter, and measure
P (in dBm).
PM
61290-10-4 © IEC:2007 – 11 –
b) Disconnect the output of the source module from the optical power meter, and connect the
output of the source module directly to the input of the OSA, and measure P (in dBm).

OSA
c) Determine the power calibration factor, PCF in dB, according to the following equation:
PCF()λ = P − P (4)
s PM OSA
NOTE For the multichannel 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.
6.2 Measurement
The measurement procedure is described in these steps.
a) Set the resolution bandwidth of the OSA to the calibrated value. Do not change this
setting throughout this procedure.
b) Connect the output of the source module directly to the OSA.
c) Adjust the relative power levels of each laser of the multichannel source to the contour
called out in the detail specification. Typically, the lasers would be set to have equal
power output. Set the total input power to that specified in the detail specification with the
optical attenuator.
d) Measure the source spontaneous emission power level at wavelengths offset to both sides
of each signal wavelength. The wavelength offset should be set to one-half the channel
OSA
spacing or less. Use linear interpolation to determine the noise power level, P ()λ
SSE s
in dBm, at each signal wavelength. Determine the calibrated source-spontaneous
emission power level, P ()λ in dBm, for each wavelength, according to the following
SSE s
equation:
OSA
P ()λ = P ()λ + PCF (5)
SSE SSE
OSA
e) Measure the power level of each signal, P ()λ in dBm. Determine the calibrated power
IN s
level of each input signal wavelength using the following equation:
OSA
() ()
P λ = P λ + PCF (6)
IN IN
f) Connect the source module to the input of the OA and connect the output of the OA to the
OSA, as shown in Figure 1.
g) Measure the uncorrected forward ASE power level at wavelengths offset to both sides of
each signal wavelength. The wavelength offset should be set to one-half the channel
OSA
()
spacing or less. Use linear interpolation to determine the noise power level, P λ
ASE s
in dBm, at each signal wavelength. Determine the calibrated total forward ASE power
level, P ()λ in dBm, for each channel wavelength, according to the following equation:
ASE
OSA
P ()λ = P ()λ + PCF (7)
ASE ASE
OSA
h) Measure the output signal power at each channel, P ()λ in dBm. Determine the
OUT s
calibrated signal output power at each wavelength, P ()λ in dBm, using the following
OUT s
equation:
OSA
() ()
P λ = P λ + PCF (8)
OUT OUT
i) Determine the corrected signal output power in dBm at each channel by subtracting the
noise power using the following equation:
P ()λ P ()λ
⎛ OUT ASE ⎞
⎜ ⎟
sig
10 10
P ()λ = 10log 10 − 10 (9)
OUT ⎜ ⎟
⎜ ⎟
⎝ ⎠
– 12 – 61290-10-4 © IEC:2007
λ) in dB, for each channel using the following equation:
j) Determine the channel gain, G(
sig
G()λ = P (λ) − P ()λ (10)
OUT IN
k) Determine the amplifier contribution to the total forward ASE power level at each signal
amp
wavelength, P ()λ in dBm, by subtracting the source-spontaneous emission power
s
ASE
level, which is increased by the gain at the amplifier output, from the calibrated total ASE
power level, according to the following equation:
P ()λ G()λ +P ()λ
⎛ ⎞
ASE SSE
⎜ ⎟
amp
10 10
P ()λ = 10log 10 − 10 (11)
⎜ ⎟
ASE
⎜ ⎟
⎝ ⎠
6.3 Calculation
Since the forward ASE power level is directly determined by the measurement procedures,
the calculations given below shall be followed for the determination of the channel signal-
spontaneous noise figure, NF .
sig-sp
Starting from the determined values of the OA contribution to the forward ASE power level,
amp
P ()λ (in dBm), gain, G(λ ) (in dB), and optical bandwidth, B (λ ) (in frequency units),
ASE s s o s
calculate the signal-spontaneous noise figure, NF in dB, for the chosen signal input

sig-sp
power, P , and signal wavelengths, λ , according to the following equation:
in s
amp
NF (P ,λ) = P ()λ −G()λ − 10log[]hνB()λ (12)
sig−sp in s s s o s
ASE
where h is Planck’s constant and ν the optical signal frequency.
NOTE The accuracy of this test method is very dependent on the accuracy at which connections can be broken
and remade as well as on the polarization dependence of the OSA.
7 Test results
The following details shall be presented:
a) Arrangement of test set-up (if different from the one specified in Clause 4)
b) Measurement technique; here: multichannel interpolation source subtraction
c) Wavelength range of the measurement
d) Type of optical source used
e) Input signal wavelengths, λ
s
f) Optical bandwidth, B
o
g) Indication of the optical pump power (if applicable)
h) Ambient temperature (if requested)
i) Input signal power and channel distribution, P (λ )
in s
j) Channel gain, G in dB
amp
k) Total forward ASE power level, P
ASE
l) Channel signal-spontaneous noise figure, NF
sig-sp
m) Error due to source spontaneous emission subtraction (from Annex A).

61290-10-4 © IEC:2007 – 13 –
Annex A
(normative)
Limitations of the interpolated source subtraction technique due to
source spontaneous emission
A.1 General
This interpolated source subtraction technique requires the subtraction of the amplified source
spontaneous emission from the total ASE noise measured on the OSA. This calculation is
shown in Step (k) of 6.2:
P ()λ G()λ +P ()λ
⎛ ASE SSE ⎞
⎜ ⎟
amp
10 10
P ()λ = 10log 10 − 10 (A.1)
ASE ⎜ ⎟
⎜ ⎟
⎝ ⎠
Under certain conditions, the two terms within the brackets can be very close in value. A small
measurement error in either term is magnified by the subtraction. The error is largest when
measuring low values of noise figure at high input power levels.
The magnitude of this error is to be calculated based on specific values for the measured
noise figure, source spontaneous emission level, and the uncertainty of measuring the noise
level. The following are noise power levels:
amp
)P = NF +G + 10log(hνB(dBm) (A.2)
sig −sp o
ASE
In linear units this is
amp
P
ASE
amp
P (linear) = 10(mW) (A.3)
ASE
The total measured uncorrected noise in linear units is
P
ASE
P (linear) = 10(mW) (A.4)
ASE
The source spontaneous emission in linear units is
P
SSE
P (linear) = 10(mW) (A.5)
SSE
For an uncertainty of α dB in measuring total noise and source spontaneous emission, the
error in amplifier noise is calculated as follows:
α /10 −α /10 G /10
10 P (linear) − 10 10 P (linear)
ASE SSE
+ error = 10log dB (A.6)
amp
P (linear)
ASE
−α /10 α /10 G /10
10 P (linear) − 10 10 P (linear)
ASE SSE
− error = 10log dB (A.7)
amp
P (linear)
ASE
– 14 – 61290-10-4 © IEC:2007
For a typical α value of 0,05 dB, the plots in Figure A.1 show the magnitude of the subtraction
error as a function of source spontaneous emission level.

DI subtraction error
Measured noise figure = 5 dB
0,8
0,7
0,6
0,5
0,4
0,3
0,2
0,1
–0,1
-50-49-48-47 -46-45-44-43-42-41-40-39 -38-37-36-35
–0,2
–0,3
–0,4
–0,5
–0,6
–0,7
–0,8
Source spontaneous emission power  (dB/nm)
IEC  747/07
NOTE A noise figure of 5 dB is assumed in the calculation.
Figure A.1 – DI subtraction error as a function of source spontaneous emission level
A.2 The effect of multiplexer type
There are two types of multiplexers used for combining the laser outputs for multichannel
sources. The selection will have a large impact on the uncertainty due to source spontaneous
emission power. The broadband multiplexer, which may be based on fused-fibre couplers,
has insertion loss for each channel is given by:
L = 10log()1/N + RdB (A.8)
BB BB
where N is the number of inputs and R is the excess insertion loss. A typical value for R
BB BB
is 0,5 dB. The total power, P , from the combined N sources, with each channel having an
T
identical output power P in dBm, is:
s
P = P −R (A.9)
T s BB
Source spontaneous emission passes through the multiplexer with its spectral characteristics
unmodified. At the combined output, the total signal-to-spontaneous-noise ratio will be
approximately equal to that of the individual lasers, but the signal-to-spontaneous ratio of
individual channels is degraded by about L dB.
BB
The second type of multiplexer is the wavelength-selective multiplexer, which uses fibre
Bragg grating, array waveguide, or dielectric filter technology. Unlike the broadband device,
the insertion loss for each channel, R is not inversely proportional to N. A typical value
WS
Error  (dB)
61290-10-4 © IEC:2007 – 15 –
could be 6 dB. Thus, the total power, P , from the combined N sources, with each channel
T
having an identical output power P in dBm, is:
s
()
P = P + 10log N −R (A.10)
T s WS
Because the wavelength-selective multiplexer presents a bandpass filter characteristic to
each channel, it filters the spontaneous emission from all sources. The individual signal to
spontaneous noise ratio is significantly improved on the combined output signal.
Two examples of multichannel source spectra are shown below. Figure A.2 is the spectrum of
eight DFB lasers combined with a broadband multiplexer. Figure A.3 is from sixteen DFB
lasers combined with a wavelength selective multiplexer.
The broadband-multiplexed source (Figure A.2) provides a minimum of 31 dB/nm signal-to-
spontaneous emission ratio on a per channel basis. It can provide up to −6 dBm total input
power to a test OA before ISS subtraction error is excessive (>0,1 dB).
The wavelength-selective multiplexed source (Figure A.3) provides a minimum of 60 dB/nm
signal-to-spontaneous emission ratio on a per channel basis. Such a spectrum can be used
up to +16 dBm total input power before the subtraction error is excessive.

– 16 – 61290-10-4 © IEC:2007
–5
–10
–15
–20
–25
–30
–35
–40
–45
1 524,8 1 525 1 525,2 1 525,4 1 525,6 1 525,8 1 526
Wavelength  (nm)
IEC  748/07
Figure A.2 – Spectral plot showing additive higher noise level from spontaneous
emission of individual laser sources and broadband multiplexer

–10
–20
–30
–40
–50
–60
–70
–80
1 535 1 540 1 545 1 550 1 555 1 560 1 565
Wavelength  (nm)
IEC  749/07
Figure A.3 – Significantly reduced spontenous emmision using wavelength selective
multiplexer
dB
dB
61290-10-4 © IEC:2007 – 17 –
Bibliography
IEC 61931: Fibre optic – Terminology
IEC 61290-1-1: Optical amplifiers –Test methods – Part 1-1: Power and gain parameters –
Optical spectrum analyzer method
IEC 61290-3: Optical fibre amplifiers – Basic specification – Part 3: Test methods for noise
figure parameters
___________
———————
A future edition is in preparation.

– 18 – 61290-10-4 © CEI:2007
SOMMAIRE
AVANT-PROPOS.19
INTRODUCTION.21

1 Domaine d'application et objet.22
2 Références normatives.22
3 Termes abrégés .23
4 Appareillage .23
5 Echantillon d’essai .25
6 Procédure .25
6.1 Étalonnage.25
6.1.1 Etalonnage de la largeur de bande optique.25
6.1.2 Étalonnage du facteur de correction de puissance de l’ASO .27
6.2 Mesures .27
6.3 Calculs .28
7 Résultats de l’essai .28

Annexe A (normative) Limites de la technique de soustraction de la source interpolée
due à l’émission spontanée de la source.30

Bibliographie.34

Figure 1 – Appareillage de mesure du gain et du facteur de bruit.23
Figure A.1 – Erreur de soustraction de DI en fonction du niveau d’émission spontanée
de la source.31
Figure A.2 – Avec un multiplexeur large bande, les émissions spontanées provenant
des sources laser individuelles s’additionnent, produisant un niveau de bruit plus
élevé, comme présenté sur ce tracé spectral .32
Figure A.3 – Avec un multiplexeur à sélection de longueur d’onde, l’émission
spontanée est significativement réduite .33

61290-10-4 © CEI:2007 – 19 –
COMMISSION ÉLECTROTECHNIQUE INTERNATIONALE
______________
AMPLIFICATEURS OPTIQUES –
MÉTHODES D’ESSAIS –
Partie 10-4: Paramètres à canaux multiples –
Méthode par soustraction de la source interpolée
en utilisant un analyseur de spectre optique

AVANT-PROPOS
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La Norme internationale CEI 61290-10-4 a été établie par le sous-comité 86C: Systèmes et
dispositifs actifs à fibres optiques, du comité d'é
...