1、 TIA STANDARD FOTP-235 IEC 61280-2-8 Fibre Optic Communication Subsystem Test Procedures Digital Systems Part 2-8: Determination of Low BER Using Q-Factor Measurements TIA-455-235 FEBRUARY, 2004 TELECOMMUNICATIONS INDUSTRY ASSOCIATION Representing the telecommunications industry in association with
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17、ITHOUT LIMITATION ANY AND ALL INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES (INCLUDING DAMAGES FOR LOSS OF BUSINESS, LOSS OF PROFITS, LITIGATION, OR THE LIKE), WHETHER BASED UPON BREACH OF CONTRACT, BREACH OF WARRANTY, TORT (INCLUDING NEGLIGENCE), PRODUCT LIABILITY OR OTHERWISE, EVEN IF ADV
18、ISED OF THE POSSIBILITY OF SUCH DAMAGES. THE FOREGOING NEGATION OF DAMAGES IS A FUNDAMENTAL ELEMENT OF THE USE OF THE CONTENTS HEREOF, AND THESE CONTENTS WOULD NOT BE PUBLISHED BY TIA WITHOUT SUCH LIMITATIONS. 61280-2-8 IEC:2003(E) adopted as TIA-455-235 iCONTENTS 1 Scope 1 2 Definitions and abbrevi
19、ated terms.1 3 Measurement of low bit-error ratios 2 4 Variable decision threshold method 5 5 Variable optical threshold method.14 Annex A (normative) Calculation of error bound in the value of Q .19 Annex B (informative) Sinusoidal interference method21 Figure 1 A sample eye diagram showing pattern
20、ing effects.4 Figure 2 A more accurate measurement technique using a DSO that samples the noise statistics between the eye centres .5 Figure 3 Bit error ratio as a function of decision threshold level 6 Figure 4 Plot of Q-factor as a function of threshold voltage.7 Figure 5 Set-up for the variable d
21、ecision threshold method.9 Figure 6 Set-up of initial threshold level (approximately at the centre of the eye) 9 Figure 7 Effect of optical bias.15 Figure 8 Set-up for optical link or device test16 Figure 9 Set-up for system test 17 Figure 10 Extrapolation of log BER as function of bias .18 Figure B
22、.1 Set-up for the sinusoidal interference method by optical injection 23 Figure B.2 Set-up for the sinusoidal interference method by electrical injection.24 Figure B.3 BER Result from the sinusoidal interference method (data points and extrapolated line) 25 Figure B.4 BER versus optical power for th
23、ree methods .26 Table 1 Mean time for the accumulation of 15 errors as a function of BER and bit rate .2 Table 2 BER as function of threshold voltage .11 Table 3 fias a function of Di11 Table 4 Values of linear regression constants 12 Table 5 Mean and standard deviation.13 Table 6 Example of optical
24、 bias test.17 Table B.1 Results for sinusoidal injection .23 (61280-2-8 IEC:2003(E) adopted as TIA-455-235 iiINTERNATIONAL ELECTROTECHNICAL COMMISSION _ FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES DIGITAL SYSTEMS Part 2-8: Determination of low BER using Q-factor measurements FOREWORD 1) The
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32、nt 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 o
33、n 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. 61280-2-8 IEC:2003(E) adopted as TIA-455-235 iiiThe committee has decided that the contents of this p
34、ublication 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) adopted as TIA-455-235 1FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES DIGITAL SYSTEMS Part 2-8: Determination of low BER us
35、ing 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 m
36、ethod, 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 ra
37、tio 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 th
38、e 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 (61280-2-8 IEC:2003(E) adopted as TIA-455-235 2PRBS Pseudo
39、-random binary sequence 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 (BER) may typically lie in the reg
40、ion 1012to 1020, 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 measu
41、rement 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
42、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 Bits/s 1061071081091010101110121013101410151,0M 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
43、75 s 750 s 2,1 h 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
44、min 8,3 h 3,5 d 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 time
45、s 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 manne
46、r, 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 regressio
47、n 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 error function (erfc). This means that very small changes in the impairment lead to ver
48、y large changes in BER; for example, in the region of a BER value of 1015a change of approximately 1 dB in the level of impairment results in a 61280-2-8 IEC:2003(E) adopted as TIA-455-235 3change of three orders of magnitude in the BER. A further difficulty is that a method based on extrapolation i
49、s 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 not
