EN IEC 61280-2-8:2021

SLOVENSKI STANDARD
01-junij-2021
Nadomešča:
SIST EN 61280-2-8:2004
Postopki preskušanja optičnega komunikacijskega podsistema - Digitalni sistemi -
2-8. del: Ugotavljanje nizkega razmerja bitne napake (BER) s pomočjo meritev Q-
faktorja (IEC 61280-2-8:2021)
Fibre optic communication subsystem test procedures - Digital systems - Part 2-8:
Determination of low BER using Q-factor measurements (IEC 61280-2-8:2021)
Prüfverfahren für Lichtwellenleiter-Kommunikationsuntersysteme - Teil 2-8: Digitale
Systeme - Bestimmung von geringen Bitfehlerraten (BER) mit Hilfe von Q-Faktor
Messungen (IEC 61280-2-8:2021)
Procédures d’essai des sous-systèmes de télécommunications fibroniques - Partie 2-8:
Systèmes numériques - Détermination de faibles valeurs de BER en utilisant des
mesures du facteur Q (IEC 61280-2-8:2021)
Ta slovenski standard je istoveten z: EN IEC 61280-2-8:2021
ICS:
33.180.01 Sistemi z optičnimi vlakni na Fibre optic systems in
splošno general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61280-2-8

NORME EUROPÉENNE
EUROPÄISCHE NORM
April 2021
ICS 33.180.10 Supersedes EN 61280-2-8:2003 and all of its
amendments and corrigenda (if any)
English Version
Fibre optic communication subsystem test procedures - Part 2-8:
Digital systems - Determination of low BER using Q-factor
measurements
(IEC 61280-2-8:2021)
Procédures d'essai des sous-systèmes de Prüfverfahren für Lichtwellenleiter-
télécommunications fibroniques - Partie 2-8: Systèmes Kommunikationsuntersysteme - Teil 2-8: Digitale Systeme -
numériques - Détermination de faibles valeurs de BER en Bestimmung von geringen Bitfehlerraten (BER) mit Hilfe
utilisant des mesures du facteur Q von Q-Faktor Messungen
(IEC 61280-2-8:2021) (IEC 61280-2-8:2021)
This European Standard was approved by CENELEC on 2021-04-06. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2021 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61280-2-8:2021 E

European foreword
The text of document 86C/1708/FDIS, future edition 2 of IEC 61280-2-8, prepared by SC 86C "Fibre
optic systems and active devices" of IEC/TC 86 "Fibre optics" was submitted to the IEC-CENELEC
parallel vote and approved by CENELEC as EN IEC 61280-2-8:2021.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2022-01-06
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2024-04-06
document have to be withdrawn
This document supersedes EN 61280-2-8:2003 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of the International Standard IEC 61280-2-8:2021 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 61281-1 NOTE Harmonized as EN IEC 61281-1

IEC 61280-2-8 ®
Edition 2.0 2021-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Fibre optic communication subsystem test procedures –

Part 2-8: Digital systems – Determination of low BER using Q-factor

measurements
Procédures d’essai des sous-systèmes de télécommunications fibroniques –

Partie 2-8: Systèmes numériques – Détermination de faibles valeurs de BER en

utilisant des mesures du facteur Q

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 33.180.10 ISBN 978-2-8322-9497-0

– 2 – IEC 61280-2-8:2021 © IEC 2021
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms, definitions, and abbreviated terms . 6
3.1 Terms and definitions . 6
3.2 Abbreviated terms . 7
4 Measurement of low bit-error ratios . 7
4.1 General considerations . 7
4.2 Background to Q-factor . 8
5 Variable decision threshold method . 10
5.1 Overview. 10
5.2 Apparatus . 13
5.3 Sampling and specimens . 13
5.4 Procedure . 13
5.5 Calculations and interpretation of results . 15
5.5.1 Sets of data . 15
5.5.2 Convert BER using inverse error function . 16
5.5.3 Linear regression . 17
5.5.4 Standard deviation and mean . 18
5.5.5 Optimum decision threshold . 18
5.5.6 BER optimum decision threshold . 18
5.5.7 BER non-optimum decision threshold . 19
5.5.8 Error bound . 19
5.6 Test documentation . 19
5.7 Specification information . 19
6 Variable optical threshold method . 19
6.1 Overview. 19
6.2 Apparatus . 20
6.3 Items under test . 20
6.4 Procedure for basic optical link . 20
6.5 Procedure for self-contained system . 21
6.6 Evaluation of results . 22
Annex A (normative) Calculation of error bound in the value of Q . 24
Annex B (informative) Sinusoidal interference method . 26
B.1 Overview. 26
B.2 Apparatus . 26
B.3 Sampling and specimens . 26
B.4 Procedure . 27
B.4.1 Optical sinusoidal interference method . 27
B.4.2 Electrical sinusoidal interference method . 28
B.5 Calculations and interpretation of results . 29
B.5.1 Mathematical analysis . 29
B.5.2 Extrapolation . 29
B.5.3 Expected results . 30
B.6 Documentation . 31

IEC 61280-2-8:2021 © IEC 2021 – 3 –
B.7 Specification information . 31
Bibliography . 32

Figure 1 – Sample eye diagram showing patterning effects . 9
Figure 2 – More accurate measurement technique using a DSO that samples noise
statistics between eye centres . 10
Figure 3 – Bit error ratio as a function of decision threshold level . 11
Figure 4 – Plot of Q-factor as a function of threshold voltage . 12
Figure 5 – Set-up for the variable decision threshold method . 14
Figure 6 – Set-up of initial threshold level (approximately at the centre of the eye) . 14
Figure 7 – Effect of optical bias . 20
Figure 8 – Set-up for optical link or device test . 21
Figure 9 – Set-up for system test . 21
Figure 10 – Extrapolation of log BER as a function of bias . 23
Figure B.1 – Set-up for the sinusoidal interference method by optical injection . 27
Figure B.2 – Set-up for the sinusoidal interference method by electrical injection . 29
Figure B.3 – BER result from the sinusoidal interference method (data points and
extrapolated line) . 30
Figure B.4 – BER versus optical power for three methods . 31

Table 1 – Mean time for the accumulation of 15 errors as a function of BER and bit rate . 7
Table 2 – BER as a function of threshold voltage . 16
Table 3 – f as a function of D . 17
i i
Table 4 – Values of linear regression constants . 18
Table 5 – Mean and standard deviation . 18
Table 6 – Example of optical bias test . 22
Table B.1 – Results for sinusoidal injection . 28

– 4 – IEC 61280-2-8:2021 © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 2-8: Digital systems –
Determination of low BER using Q-factor measurements

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
misinterpretation by any end user.
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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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.
IEC 61280-2-8 has been prepared by subcommittee 86C: Fibre optic systems and active
devices, of IEC technical committee 86: Fibre optics. It is an International Standard.
This second edition cancels and replaces the first edition published in 2003. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) correction of errors in Formula (8) in 5.5.2 and in a related formula in 5.5.3;
b) correction of errors in the references to clauses, subclauses, figures, procedures, and in
the Bibliography;
c) alignment of the terms and definitions in 3.1 with those in IEC 61281-1.

IEC 61280-2-8:2021 © IEC 2021 – 5 –
The text of this International Standard is based on the following documents:
FDIS Report on voting
86C/1708/FDIS 86C/1711/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
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 document 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.

– 6 – IEC 61280-2-8:2021 © IEC 2021
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

Part 2-8: Digital systems –
Determination of low BER using Q-factor measurements

1 Scope
This part of IEC 61280 specifies two main methods for the determination of low BER values by
making accelerated measurements. These include the variable decision threshold method
(Clause 5) and the variable optical threshold method (Clause 6). In addition, a third method,
the sinusoidal interference method, is described in Annex B.
2 Normative references
There are no normative references in this document.
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
amplified spontaneous emission
ASE
optical power associated to spontaneously emitted photon amplified by an active medium in an
optical amplifier
3.1.2
bit error ratio
BER
P
e
number of errored bits divided by the total number of bits, over some stipulated period of time
3.1.3
intersymbol interference
ISI
overlap of adjacent pulses as caused by the limited bandwidth characteristics of the optical
devices in a fibre optic link
3.1.4
Q-factor
Q
ratio of the difference between the mean voltage of the 1 and 0 rails, to the sum of their standard
deviation values
IEC 61280-2-8:2021 © IEC 2021 – 7 –
3.2 Abbreviated terms
AC alternating current
CW continuous wave (normally referring to a sinusoidal wave form)
DC direct current
DSO digital sampling oscilloscope
DUT device under test
PRBS pseudo-random binary sequence
SNR signal-to-noise ratio
4 Measurement of low bit-error ratios
4.1 General considerations
Fibre optic communication systems and subsystems are inherently capable of providing
exceptionally good error performance, even at very high bit rates. The mean bit error ratio (BER)
−12 −20
may typically lie in the region 10 to 10 , depending on the nature of the system. While this
type of performance is well in excess of practical performance requirements for digital signals,
it gives the advantage of concatenating many links over long distances without the need to
employ error correction techniques.
The measurement of such low error ratios presents special problems in terms of the time taken
to measure a sufficiently large number of errors to obtain a statistically significant result. Table 1
presents the mean time required to accumulate 15 errors. This number of errors can be
regarded as statistically significant, offering a confidence level of 75 % with a variability of 50 %.
Table 1 – Mean time for the accumulation of 15 errors
as a function of BER and bit rate
Mean times for the accumulation of 15 errors
Bit rate BER
−5 −6 −7 −8 −9 −10 −11 −12 −13 −14 −15
10 10 10 10 10 10 10 10 10 10 10
1,0 Mbit/s 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7d 17 d 170 d 4,7 47
years years
2,0 Mbit/s 75 ms 750 ms 7,5 s 75 s 750 s 2,1 h 21 h 8,8 d 88 d 2,4 24
years years
10 Mbit/s 15 ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7 d 17 d 170 d 4,7
years
50 Mbit/s 3,0 ms 30 ms 300 ms 3,0 s 30 s 5,0 min 50 min 8,3 h 3,5 d 35 d 350 d
100 Mbit/s 1,5 ms 15 ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7 d 17 d 170 d
500 Mbit/s 300 μs 3 ms 30 ms 300 ms 3,0 s 30 s 5,0 min 50 min 8,3 h 3,5 d 35 d
1,0 Gbit/s 150 μs 1,5 ms 15 ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7 d 17 d
10 Gbit/s 15 μs 150 μs 1,5 ms 15 ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7 d
40 Gbit/s 3,8 μs 38 μs 380 μs 3,8 ms 38 ms 380 ms 3,8 s 38 s 6,3 min 63 min 10,4 h
100 Gbit/s 1,5 μs 15 μs 150 μs 1,5 ms 15ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h

– 8 – IEC 61280-2-8:2021 © IEC 2021
The times given in Table 1 show that the direct measurement of the low BER values expected
from fibre optic systems is not practical during installation and maintenance operations. One
way of overcoming this difficulty is to artificially impair the signal-to-noise ratio at the receiver
in a controlled manner, thus significantly increasing the BER and reducing the measurement
time. The error performance is measured for various levels of impairment, and the results are
then extrapolated to a level of zero impairment using computational or graphical methods
according to theoretical or empirical regression algorithms.
The difficulty presented by the use of any regression technique for the determination of the
error performance is that the theoretical BER value is related to the level of impairment via
the inverse complementary error function (erfc). This means that very small changes in the
impairment lead to very large changes in BER; for example, in the region of a BER value of
−15
10 , a change of approximately 1 dB in the level of impairment results in a change of three
orders of magnitude in the BER. A further difficulty is that a method based on extrapolation is
unlikely to reveal a levelling off of the BER at only about 3 orders of magnitude below the lowest
measured value.
It should also be noted that, in the case of digitally regenerated sections, the results obtained
apply only to the regenerated section whose receiver is under test. Errors generated in
upstream regenerated sections may generate an error plateau which may have to be taken into
account in the error performance evaluation of the regenerator section under test.
As noted above, two main methods for the determination of low BER values by making
accelerated measurements are described. These are the variable decision threshold method
(Clause 5) and the variable optical threshold method (Clause 6). In addition, a third method,
the sinusoidal interference method, is described in Annex B.
It should be noted that these methods are applicable to the determination of the error
performance in respect of amplitude-based impairments. Jitter may also affect the error per-
formance of a system, and its effect requires other methods of determination. If the error
performance is dominated by jitter impairments, the amplitude-based methods described in this
document will lead to BER values which are lower than the actual value.
The variable decision threshold method is the procedure which can most accurately measure
the Q-factor and the BER for optical systems with unknown or unpredictable noise statistics. A
key limitation, however, to the use of the variable threshold method to measure Q-factor and
BER is the need to have access to the receiver electronics in order to manipulate the decision
threshold. For systems where such access is not available, it may be useful to utilize the
alternative variable optical threshold method. Both methods are capable of being automated in
respect of measurement and computation of the results
4.2 Background to Q-factor
The Q-factor is the signal-to-noise ratio (SNR) at the decision circuit and is typically expressed
as [1] :
μμ−
1 0
Q= (1)
σσ+
where
µ and µ are the mean voltage levels of the "1" and "0" rails, respectively;
1 0
____________
Figures in square brackets refer to the Bibliography.

IEC 61280-2-8:2021 © IEC 2021 – 9 –
σ and σ are the standard deviation values of the noise distribution on the "1" and "0" rails,
1 0
respectively.
An accurate estimation of a system’s transmission performance, or Q-factor, shall take into
consideration the effects of all sources of performance degradation, both fundamental and
those due to real-world imperfections. Two important sources are amplified spontaneous
emission (ASE) noise and intersymbol interference (ISI). Additive noise originates primarily from
ASE of optical amplifiers. ISI arises from many effects, such as chromatic dispersion, fibre non-
linearities, multi-path interference, polarization-mode dispersion and use of electronics with
finite bandwidth. There may be other effects as well; for example, a poor impedance match can
cause impairments such as long fall times or ringing on a waveform.
One possible method to measure Q-factor is the voltage histogram method in which a digital
sampling oscilloscope is used to measure voltage histograms at the centre of a binary eye to
estimate the waveform’s Q-factor [2]. In this method, a pattern generator is used as a stimulus
and the oscilloscope is used to measure the received eye opening and the standard deviation
of the noise present in both voltage rails. As a rough approximation, the edge of visibility of the
noise represents the 3σ points of an assumed Gaussian distribution. The advantage of using
an oscilloscope to measure the eye is that it can be done rapidly on real traffic with a minimum
of equipment.
The oscilloscope method for measuring the Q-factor has several shortcomings. When used to
measure the eye of high-speed data (of the order of several Gbit/s), the oscilloscope’s limited
digital sampling rate (often in the order of a few hundred kilohertz) allows only a small minority
of the high-speed data stream to be used in the Q-factor measurement. Longer observation
times could reduce the impact of the slow sampling. A more fundamental shortcoming is that
the Q estimates derived from the voltage histograms at the eye centre are often inaccurate.
Various patterning effects and added noise from the front-end electronics of the oscilloscope
can often obscure the real variance of the noise.
Figure 1 shows a sample eye diagram made on an operating system. It can be seen in this
figure that the vertical histograms through the centre of the eye show patterning effects (less
obvious is the noise added by the front-end electronics of the oscilloscope). It is difficult to
predict the relationship between the Q measured this way and the actual BER measured with
a test set.
NOTE The data for measuring the Q-factor are obtained from the tail of the Gaussian distributions.
Figure 1 – Sample eye diagram showing patterning effects

– 10 – IEC 61280-2-8:2021 © IEC 2021
Figure 2 shows another possible way of measuring Q-factor using an oscilloscope. The idea is
to use the centre of the eye to estimate the eye opening and use the area between eye centres
to estimate the noise. Pattern effect contributions to the width of the histogram would then be
reduced. A drawback to this method is that it relies on measurements made on a portion of the
eye that the receiver does not really ever use.

Figure 2 – More accurate measurement technique using a DSO
that samples noise statistics between eye centres
It is tempting to conclude that the estimates for σ and σ would tend to be overestimated and
1 0
that the resulting Q measurements would always form a lower bound to the actual Q for either
of these oscilloscope-based methods. That is not necessarily the case. It is possible that the
histogram distributions can be distorted in other ways, for example, skewed in such a way that
the mean values overestimate the eye opening – and the resulting Q will actually not be a lower
bound. There is, unfortunately, no easily characterized relationship between oscilloscope-
derived Q measurements and BER performance.
5 Variable decision threshold method
5.1 Overview
This method of estimating the Q-factor relies on using a receiver front-end with a variable
decision threshold. Some means of measuring the BER of the system is required. Typically, the
measurement is performed with an error test set using a pseudo-random binary sequence
(PRBS), but there are alternate techniques which allow operation with live traffic. The
measurement relies on the fact that for a data eye with Gaussian statistics, the BER may be
calculated analytically as follows:
 
 |V −−μ | |V μ |
th 1 th 0
PV( ) erfc + erfc
  (2)
  
e th
 
2 σσ
 10 
 
=
IEC 61280-2-8:2021 © IEC 2021 – 11 –
where
P is the BER;
e
V is the decision threshold level;
th
µ ,µ and σ , σ are the mean and standard deviation of the "1" and "0" data rails;
1 0 1 0
erfc(.) is the complementary error function given by
∞
−−β / 22x /
(3)
erfc( x) e dβ≅ e
∫
2π x 2π
x
The approximation is nearly exact for x > 3.
The BER, given in Formula (2), is the sum of two terms. The first term is the conditional
probability of deciding that a "0" has been received when a "1" has been sent, and the second
term is the probabil
...