IEC 61280-2-8:2003

INTERNATIONAL IEC
STANDARD
61280-2-8
First edition
2003-02
Fibre optic communication subsystem test
procedures – Digital systems
Part 2-8:
Determination of low BER
using Q-factor measurements
Reference number
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INTERNATIONAL IEC
STANDARD
61280-2-8
First edition
2003-02
Fibre optic communication subsystem test
procedures – Digital systems
Part 2-8:
Determination of low BER
using Q-factor measurements
 IEC 2003  Copyright - all rights reserved
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– 2 – 61280-2-8  IEC:2003(E)
CONTENTS
FOREWORD . 4

1 Scope . 5

2 Definitions and abbreviated terms . 5

2.1 Definitions . 5

2.2 Abbreviations. 5

3 Measurement of low bit-error ratios . 6

3.1 General considerations . 6
3.2 Background to Q-factor . 7
4 Variable decision threshold method . 9
4.1 Overview . 9
4.2 Apparatus .12
4.3 Sampling and specimens .12
4.4 Procedure.12
4.5 Calculations and interpretation of results .13
4.6 Test documentation .17
4.7 Specification information .17
5 Variable optical threshold method.17
5.1 Overview .17
5.2 Apparatus .18
5.3 Items under test.18
5.4 Procedure for basic optical link .18
5.5 Procedure for self-contained system .19
5.6 Evaluation of results.20
Annex A (normative) Calculation of error bound in the value of Q .22
Annex B (informative) Sinusoidal interference method .24
Bibliography .30
Figure 1 – A sample eye diagram showing patterning effects . 8
Figure 2 – A more accurate measurement technique using a DSO that samples the
noise statistics between the eye centres . 8
Figure 3 – Bit error ratio as a function of decision threshold level .10
Figure 4 – Plot of Q-factor as a function of threshold voltage .10
Figure 5 – Set-up for the variable decision threshold method .12
Figure 6 – Set-up of initial threshold level (approximately at the centre of the eye) .12
Figure 7 – Effect of optical bias .17
Figure 8 – Set-up for optical link or device test.19
Figure 9 – Set-up for system test .19
Figure 10 – Extrapolation of log BER as function of bias .21
Figure B.1 – Set-up for the sinusoidal interference method by optical injection .25
Figure B.2 – Set-up for the sinusoidal interference method by electrical injection .27
Figure B.3 – BER Result from the sinusoidal interference method
(data points and extrapolated line) .28
Figure B.4 – BER versus optical power for three methods .29

61280-2-8  IEC:2003(E) – 3 –
Table 1 – Mean time for the accumulation of 15 errors as a function of BER and bit rate . 6

Table 2 – BER as function of threshold voltage .14

Table 3 – f as a function of D .14
i i
Table 4 – Values of linear regression constants .15

Table 5 – Mean and standard deviation.16

Table 6 – Example of optical bias test.20

Table B.1 – Results for sinusoidal injection.26

– 4 – 61280-2-8  IEC:2003(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

DIGITAL SYSTEMS –
Part 2-8: Determination of low BER

using Q-factor measurements
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organisation for standardisation comprising
all national electrotechnical committees (IEC National Committees). The object of the IEC is to promote
international co-operation on all questions concerning standardisation in the electrical and electronic fields. To
this end and in addition to other activities, the IEC publishes International Standards. 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 organisations liasing with
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Standardisation (ISO) in accordance with conditions determined by agreement between the two organisations.
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from all interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61280-2-8 has been prepared by subcommittee 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:
FDIS Report on voting
86C/485/FDIS 86C/505/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.
The committee has decided that the contents of this publication will remain unchanged
until 2010. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
61280-2-8  IEC:2003(E) – 5 –
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –

DIGITAL SYSTEMS –
Part 2-8: 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 4) and the variable optical threshold method (Clause 5). In addition, a third method,
the sinusoidal interference method, is described in Annex B.
2 Definitions and abbreviated terms
2.1 Definitions
For the purposes of this document, the following terms and definitions apply.
2.1.1
amplified spontaneous emission
ASE
impairment generated in optical amplifiers
2.1.2
bit error ratio
BER
the number bits in error as a ratio of the total number of bits
2.1.3
intersymbol interference
ISI
mutual interference between symbols in a data stream, usually caused by non-linear effects
and bandwidth limitations of the transmission path
2.1.4
Q-factor
Q
ratio of the difference between the mean voltage of the 1 and 0 rails, and the sum of their
standard deviation values
2.2 Abbreviations
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

– 6 – 61280-2-8  IEC:2003(E)
3 Measurement of low bit-error ratios

3.1 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
–12 –20
(BER) 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
BER
–6 –7 –8 –9 –10 –11 –12 –13 –14 –15
10 10 10 10 10 10 10 10 10 10
Bits/s
1,0M 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7d 17
...