1、BRITISH STANDARD BS EN 61280-2-8:2003 Fibre optic communication subsystem test procedures Digital systems Part 2-8: Determination of low BER using Q-factor measurements The European Standard EN 61280-2-8:2003 has the status of a British Standard ICS 33.180.10 BS EN 61280-2-8:2003 This British Standa
2、rd was published under the authority of the Standards Policy and Strategy Committee on 15 May 2003 BSI 15 May 2003 ISBN 0 580 41824 3 National foreword This British Standard is the official English language version of EN 61280-2-8:2003. It is identical with IEC 61280-2-8:2003. The UK participation i
3、n its preparation was entrusted by Technical Committee GEL/86, Fibre optics, to Subcommittee GEL/86/3, Fibre optic systems and active devices, which has the responsibility to: A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The B
4、ritish Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards
5、Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the respo
6、nsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cov
7、er, the EN title page, pages 2 to 31 and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date CommentsEUROPEAN STANDARD EN 61280-2-8 NORME EUROPENNE EUROPISCHE NORM April 2003 CENELEC European C
8、ommittee for Electrotechnical Standardization Comit Europen de Normalisation Electrotechnique Europisches Komitee fr Elektrotechnische Normung Central Secretariat: rue de Stassart 35, B - 1050 Brussels 2003 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENE
9、LEC members. Ref. No. EN 61280-2-8:2003 E ICS 33.180.10 English version Fibre optic communication subsystem test procedures - Digital systems Part 2-8: Determination of low BER using Q-factor measurements (IEC 61280-2-8:2003) Procdures dessai des sous-systmes de tlcommunications fibres optiques - Sy
10、stmes numriques Partie 2-8: Dtermination du faible Taux dErreur Binaire (TEB) en utilisant les mesures du facteur Q (CEI 61280-2-8:2003) Prfverfahren fr Lichtwellenleiter- Kommunikationsuntersysteme - Digitale Systeme Teil 2-8: Bestimmung von geringen Bitfehlerverhltnissen (BERs) mit Hilfe von Q-Fak
11、tormessungen (IEC 61280-2-8:2003) This European Standard was approved by CENELEC on 2003-03-01. 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-
12、to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat 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
13、under the responsibility of a CENELEC member into its own language and notified to the Central Secretariat has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungar
14、y, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom. Foreword The text of document 86C/485/FDIS, future edition 1 of IEC 61280-2-8, prepared by SC 86C, Fibre optic systems and active devices, of IEC TC 86, Fibre optics
15、, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61280-2-8 on 2003-03-01. The following dates were fixed: latest date by which the EN has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2003-12-01 latest d
16、ate by which the national standards conflicting with the EN have to be withdrawn (dow) 2006-03-01 Annexes designated “normative“ are part of the body of the standard. Annexes designated “informative“ are given for information only. In this standard, annex A is normative and annex B is informative. _
17、 Endorsement notice The text of the International Standard IEC 61280-2-8:2003 was approved by CENELEC as a European Standard without any modification. _ Page2 EN6128028:2003 CONTENTS 1 Scope.5 2 Definitions and abbreviated terms .5 2.1 Definitions.5 2.2 Abbreviations.5 3 Measurement of low bit-error
18、 ratios.6 3.1 General considerations6 3.2 Background to Q-factor7 4 Variable decision threshold method.10 4.1 Overview.10 4.2 Apparatus13 4.3 Sampling and specimens .13 4.4 Procedure13 4.5 Calculations and interpretation of results14 4.6 Test documentation.18 4.7 Specification information18 5 Variab
19、le optical threshold method .18 5.1 Overview.18 5.2 Apparatus19 5.3 Items under test.19 5.4 Procedure for basic optical link 19 5.5 Procedure for self-contained system 20 5.6 Evaluation of results 21 Annex A (normative) Calculation of error bound in the value of Q23 Annex B (informative) Sinusoidal
20、interference method 25 Bibliography31 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 centres9 Figure 3 Bit error ratio as a function of decision threshold level.11 Figure 4 Plot
21、of Q-factor as a function of threshold voltage .11 Figure 5 Set-up for the variable decision threshold method .13 Figure 6 Set-up of initial threshold level (approximately at the centre of the eye) .13 Figure 7 Effect of optical bias .18 Figure 8 Set-up for optical link or device test 20 Figure 9 Se
22、t-up for system test.20 Figure 10 Extrapolation of log BER as function of bias22 Figure B.1 Set-up for the sinusoidal interference method by optical injection.26 Figure B.2 Set-up for the sinusoidal interference method by electrical injection .28 Figure B.3 BER Result from the sinusoidal interferenc
23、e method (data points and extrapolated line).29 Figure B.4 BER versus optical power for three methods30 Page3 EN6128028:2003 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 voltage15 Table 3 f ias a function of D i .15 Tabl
24、e 4 Values of linear regression constants.16 Table 5 Mean and standard deviation .17 Table 6 Example of optical bias test .21 Table B.1 Results for sinusoidal injection27 Page4 EN6128028:2003 FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES DIGITAL SYSTEMS Part 2-8: Determination of low BER using
25、 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 meth
26、od, 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
27、 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 m
28、ean 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 Page5 EN6128028:2003 3 Mea
29、surement 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 (BER) may typically lie in the region 10 12to 10 20 , depending
30、 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 r
31、atios 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 co
32、nfidence 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 Bits/s 10 610 710 810 910 1010 1110 1210 1310 1410 151,0M 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7d 17 d 170 d 4,7 years 47 years 2,0M 750 ms 7,5 s 75 s 750 s 2,1 h
33、 21 h 8,8 d 88 d 2,4 years 24 years 10M 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 50M 30 ms 300 ms 3,0 s 30 s 5,0 min 50 min 8,3 h 3,5 d 35 d 350 d 100M 15 ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7 d 17 d 170 d 500M 3 ms 30 ms 300 ms 3,0 s 30 s 5,0 min 50 min 8,3 h 3,5 d
34、35 d 1,0G 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 10G 150 s 1,5 ms 15 ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h 1,7 d 40G 38 s 380 s 3,8 ms 38 ms 380 ms 3,8 s 38 s 6,3 min 63 min 10,4 h 100G 15 s 150 s 1,5 ms 15ms 150 ms 1,5 s 15 s 2,5 min 25 min 4,2 h The times given in Table
35、 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 signific
36、antly 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. Th
37、e 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 error function (erfc). This means that very small changes in the impairment lead to very large changes
38、in BER; for example, in the region of a BER value of 10 15a 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
39、 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 platea
40、u which may have to be taken into account in the error performance evaluation of the regenerator section under test. Page6 EN6128028:2003 As noted above, two main methods for the determination of low BER values by making accelerated measurements are described. These are the variable decision thresho
41、ld 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. It should be noted that these methods are applicable to the determination of the error performance in respect of amplitude-based impair
42、ments. 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 standard will lead to BER values which are lower than the actual value
43、. 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 h
44、ave 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
45、 the results 3.2 Background to Q-factor The Q-factor is the signal-to-noise ratio (SNR) at the decision circuit and is typically expressed as 3 1 : 0 Q + = 1 0 1 (1) where 1and 0are the mean voltage levels of the “1” and “0” rails, respectively, and 1 and 0are the standard deviation values of the no
46、ise distribution on the “1” and “0” rails, respectively. An accurate estimation of a systems transmission performance, or Q-factor, must take into consideration the effects of all sources of performance degradation, both fundamental and those due to real-world imperfections. Two important sources ar
47、e 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 ele
48、ctronics 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
49、measure voltage histograms at the centre of a binary eye to estimate the waveforms Q-factor 4. 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
