IEC 61280-2-8:2021

IEC 61280-2-8 ®
Edition 2.0 2021-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures – Digital systems –
Part 2-8: Digital systems – Determination of low BER using Q-factor
measurements
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IEC 61280-2-8 ®
Edition 2.0 2021-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Fibre optic communication subsystem test procedures – Digital systems –

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

measurements
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.180.10 ISBN 978-2-8322-9530-4

– 2 – IEC 61280-2-8:2021 RLV © 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 . 9
5 Variable decision threshold method . 11
5.1 Overview. 11
5.2 Apparatus . 14
5.3 Sampling and specimens . 14
5.4 Procedure . 15
5.5 Calculations and interpretation of results . 16
5.5.1 Sets of data . 16
5.5.2 Convert BER using inverse error function . 17
5.5.3 Linear regression . 18
5.5.4 Standard deviation and mean . 19
5.5.5 Optimum decision threshold . 20
5.5.6 BER optimum decision threshold . 20
5.5.7 BER non-optimum decision threshold . 20
5.5.8 Error bound . 20
5.6 Test documentation . 20
5.7 Specification information . 21
6 Variable optical threshold method . 21
6.1 Overview. 21
6.2 Apparatus . 21
6.3 Items under test . 22
6.4 Procedure for basic optical link . 22
6.5 Procedure for self-contained system . 22
6.6 Evaluation of results . 23
Annex A (normative) Calculation of error bound in the value of Q . 25
Annex B (informative) Sinusoidal interference method . 27
B.1 Introduction Overview . 27
B.2 Apparatus . 27
B.3 Sampling and specimens . 27
B.4 Procedure . 28
B.4.1 Optical sinusoidal interference method . 28
B.4.2 Electrical sinusoidal interference method . 29
B.5 Calculations and interpretation of results . 30
B.5.1 Mathematical analysis . 30
B.5.2 Extrapolation . 30
B.5.3 Expected results . 31
B.6 Documentation . 32

B.7 Specification information . 32
Bibliography . 33

Figure 1 – Sample eye diagram showing patterning effects . 10
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 . 12
Figure 4 – Plot of Q-factor as a function of threshold voltage . 13
Figure 5 – Set-up for the variable decision threshold method . 15
Figure 6 – Set-up of initial threshold level (approximately at the centre of the eye) . 15
Figure 7 – Effect of optical bias . 21
Figure 8 – Set-up for optical link or device test . 22
Figure 9 – Set-up for system test . 23
Figure 10 – Extrapolation of log BER as a function of bias . 24
Figure B.1 – Set-up for the sinusoidal interference method by optical injection . 28
Figure B.2 – Set-up for the sinusoidal interference method by electrical injection . 30
Figure B.3 – BER result from the sinusoidal interference method (data points and
extrapolated line) . 31
Figure B.4 – BER versus optical power for three methods . 32

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 . 17
Table 3 – f as a function of D . 18
i i
Table 4 – Values of linear regression constants . 19
Table 5 – Mean and standard deviation . 19
Table 6 – Example of optical bias test . 23
Table B.1 – Results for sinusoidal injection . 29

– 4 – IEC 61280-2-8:2021 RLV © IEC 2021
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –
DIGITAL SYSTEMS –
Part 2-8: Digital systems –
Determination of low BER using Q-factor measurements

FOREWORD
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