SIST EN 61280-2-2:2006
(Main)Fibre optic communication subsystem test procedures -- Part 2-2: Digital systems - Optical eye pattern, waveform and extinction ratio measurement
Fibre optic communication subsystem test procedures -- Part 2-2: Digital systems - Optical eye pattern, waveform and extinction ratio measurement
This part of IEC 61280 describe a test procedure to measure the eye pattern and waveform parameters such as rise time, fall time, overshoot, and extinction ratio. Alternatively, the waveform may be tested for compliance with a predetermined waveform mask.
Prüfverfahren für Lichtwellenleiter-Kommunikationsuntersysteme -- Teil 2-2: Digitale Systeme - Messung des optischen Augendiagramms, der Wellenform und des Extinktionsverhältnisses
Procédures d'essai des sous-systèmes de télécommunications à fibres optiques -- Partie 2-2: Systèmes numériques - Mesure du diagramme de l'oeil optique, de la forme d'onde et du taux d'extinction
Décrit une procédure d'essai pour mesurer le diagramme de l' il et les paramètres de la forme d'onde tels que le temps de montée, le temps de descente, le taux de dépassement et le taux d'extinction. Sinon, la forme d'onde peut être déterminée avec un masque de forme d'onde prédéterminé.
Postopki preskušanja optičnega komunikacijskega podsistema – 2-2. del: Digitalni sistemi – Merjenje po vzorcu optičnega očesa, valovne oblike in hitrosti ugašanja (IEC 61280-2-2:2005)
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Standards Content (Sample)
SIST EN 61280-2-2:2006SLOVENSKImarec 2006
STANDARDPostopki preskušanja optičnega komunikacijskega podsistema – 2-2. del: Digitalni sistemi – Merjenje po vzorcu optičnega očesa, valovne oblike in hitrosti ugašanja (IEC 61280-2-2:2005)Fibre optic communication subsystem test procedures - Part 2-2: Digital systems - Optical eye pattern, waveform, and extinction ratio measurement (IEC 61280-2-2:2005)©
Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljenoReferenčna številkaSIST EN 61280-2-2:2006(en)ICS33.180.01
EUROPEAN STANDARD
EN 61280-2-2 NORME EUROPÉENNE EUROPÄISCHE NORM
July 2005 CENELEC European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung
Central Secretariat: rue de Stassart 35, B - 1050 Brussels
© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61280-2-2:2005 E
ICS 33.180.01 Supersedes EN 61280-2-2:1999
English version
Fibre optic communication subsystem test procedures Part 2-2: Digital systems -
Optical eye pattern, waveform and
extinction ratio measurement (IEC 61280-2-2:2005)
Procédures d'essai des sous-systèmes de télécommunications à fibres optiques Partie 2-2: Systèmes numériques - Mesure du diagramme de l'œil optique,
de la forme d'onde et du taux d'extinction (CEI 61280-2-2:2005)
Prüfverfahren für Lichtwellenleiter-Kommunikationsuntersysteme Teil 2-2: Digitale Systeme -
Messung des optischen Augen-diagramms, der Wellenform und
des Extinktionsverhältnisses (IEC 61280-2-2:2005)
This European Standard was approved by CENELEC on 2005-04-01. 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-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 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, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EN 61280-2-2:2005 - 2 - Foreword The text of document 86C/642/FDIS, future edition 2 of IEC 61280-2-2, 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 was approved by CENELEC as EN 61280-2-2 on 2005-04-01. This European Standard supersedes EN 61280-2-2:1999. Significant changes include updating the extinction ratio measurement and eye-mask definitions to coincide with TIA OFSTP-4A and inclusion of methods for return-to-zero (RZ) eye measurements. 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)
2006-02-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)
2008-04-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 61280-2-2:2005 was approved by CENELEC as a European Standard without any modification. __________
- 3 - EN 61280-2-2:2005
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies. Publication Year Title EN/HD Year ITU-T Recommendation G.957 1999 Optical interfaces for equipments and systems relating to the synchronous digital hierarchy - - A1 2003
- -
NORME INTERNATIONALECEIIEC INTERNATIONAL STANDARD 61280-2-2Deuxième éditionSecond edition2005-04 Procédures d'essai des sous-systèmes de télécommunications à fibres optiques – Partie 2-2: Systèmes numériques – Mesure du diagramme de l'œil optique, de la forme d'onde et du taux d'extinction
Fibre optic communication subsystem test procedures – Part 2-2: Digital systems – Optical eye pattern, waveform and extinction ratio measurement Pour prix, voir catalogue en vigueur For price, see current catalogue IEC 2005
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Copyright - all rights reserved Aucune partie de cette publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit de l'éditeur. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Electrotechnical Commission,
3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, SwitzerlandTelephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch
Web: www.iec.ch CODE PRIX PRICE CODE U Commission Electrotechnique InternationaleInternational Electrotechnical Commission
61280-2-2 IEC:2005 – 3 –
CONTENTS FOREWORD.5
1 Scope and object.9 2 Normative reference.9 3 Apparatus.9 3.1 Time-domain optical detection system.11 3.2 Oscilloscope synchronization system.19 3.3 Pulse pattern generator.19 3.4 Optical power meter.19 3.5 Optical attenuator.19 3.6 Jumper cable.21 4 Test sample.21 5 Procedure.21 5.1 Method 1: Basic waveform measurement.21 5.2 Method 2: Extinction measurement method using the histogram function.23 6 Calculation.25 6.1 Method 1: Basic waveform measurement definitions.25 6.2 Method 2: Extinction calculation method using the histogram function.33 6.3 Eye-diagram analysis using a mask.33 7 Test result.37 7.1 Required information.37 7.2 Available information.39 7.3 Specification information.39
Annex A (informative)
Oscilloscope synchronization system.43
Bibliography.51
Figure 1 – Optical eye pattern, waveform, and extinction ratio measurement configuration.9 Figure 2 – Time-domain optical detection system.11 Figure 3 – Illustration of NRZ and RZ eye-diagram parameters.33 Figure 4 – Example of eye pattern measured with 0,75/T low-pass filter.35 Figure 5 – Example of eye pattern measured with 3,0/T low-pass filter.37 Figure 6 – Eye diagram with vertical histogram data collected from the central 20 % window.37 Figure A.1 – Oscilloscope synchronization system.43
Table 1 – Frequency response characteristics.17 Table 2 – Typical parameters for the measurement shown in Figure 4.39 Table 3 – Typical parameters for the measurement shown in Figure 5.41
61280-2-2 IEC:2005 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
FIBRE OPTIC COMMUNICATION SUBSYSTEM
TEST PROCEDURES –
Part 2-2: Digital systems – Optical eye pattern,
waveform and extinction ratio measurement
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with an IEC Publication. 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. International Standard IEC 61280-2-2 has been prepared by subcommittee 86C: Fibre optic systems and active devices, of IEC technical committee 86: Fibre optics. This second edition cancels and replaces the first edition published in 1998. This second edition constitutes a technical revision. Significant changes include updating the extinction ratio measurement and eye-mask definitions to coincide with TIA OFSTP-4A and inclusion of methods for return-to-zero (RZ) eye measurements.
61280-2-2 IEC:2005 – 7 –
The text of this standard is based on the following documents: FDIS Report on voting 86C/642/FDIS 86C/661/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. IEC 61280 consists of the following parts under the general title Fibre optic communication subsystem test procedures 1) : Part 1:
General communication subsystems 2) Part 2: Digital systems 3) Part 4: Cable plant and links 4) Part 3
is in preparation.
The committee has decided that the contents of this publication will remain unchanged until the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to the specific publication. At this date, the publication will be
• reconfirmed; • withdrawn; • replaced by a revised edition, or • amended. ___________ 1) The general title of the IEC 61280 series has changed. Previous parts were published under the general title Fibre optic communication subsystem basic test procedures 2) The title of Part 1 has changed. Parts 1-1 and 1-3 were published under the title Test procedures for general communication subsystems. 3) The title of Part 2 has changed. Parts 2-1, 2-2, 2-4 and 2-5 were published under the title Test procedures for digital systems. 4) The title of Part 4 has changed. Part 4-2 was published under the title Fibre optic cable plant.
61280-2-2 IEC:2005 – 9 –
FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES –
Part 2-2: Digital systems – Optical eye pattern,
waveform and extinction ratio measurement
1 Scope
This part of IEC 61280 describes a test procedure to measure eye pattern and waveform parameters, such as rise time, fall time, overshoot, and extinction ratio. Alternatively, the waveform may be tested for compliance with a predetermined waveform mask.
2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ITU-T Recommendation G.957:1999, Optical interfaces for equipments and systems relating to the synchronous digital hierarchy Amendment 1 (2003) 3 Apparatus The primary components of the measurement system are a photodetector, a low-pass filter, an oscilloscope, and an optical power meter, as shown in Figure 1.
Pulse pattern generator Optical transmitter Optical attenuator (Clock) Data Jumper cable Jumper cable Optical interface point Time-domain optical detection system Trigger O/E convertor Low-pass filter Oscilloscope Optical power meter IEC
1 519/98
Figure 1 – Optical eye pattern, waveform, and extinction ratio measurement configuration
61280-2-2 IEC:2005 – 11 –
3.1 Time-domain optical detection system The time-domain optical detection system displays the intensity of the optical waveform as a function of time. The optical detection system is comprised primarily of an optical-to-electrical (O/E) converter, a linear-phase low-pass filter, and an oscilloscope. The detection system is shown in Figure 2. More complete descriptions of the equipment are listed in the following subclauses. OptionalamplifierOpticalsignalinputOpticalinterfacepointOptical toelectricalconverterOscilloscopeverticalOscilloscopesynchronizationsignalTriggerResistivesignalsplitter(optional)Tosynchronizationsystem(optional)Low-passfilterIEC
1 520/98 Figure 2 – Time-domain optical detection system 3.1.1 Optical-to-electrical (O/E) converter The O/E converter is typically a high-speed photodiode, followed by electrical amplification. The O/E converter is equipped with an appropriate optical connector to allow connection to the optical interface point, either directly or via an optical jumper cable.
The O/E converter (including any optional amplification following the O/E converter) shall be able to reproduce the optical waveform with sufficient fidelity to ensure a meaningful measure-ment. Precise specifications are precluded by the large variety of possible implementations, but general guidelines are as follows: a) acceptable input wavelength range, adequate to cover the intended application; b) input optical reflectance, low enough to avoid excessive back-reflection into the transmitter being measured;
For example, assume that an optical transmitter is specified to tolerate –24 dB reflectance maximum. If the input reflectance of the O/E converter is –30 dB, the converter can be directly connected to the transmitter. If, however, the input reflectance of the O/E converter is –14 dB, a common value, the effective reflectance can be lowered to –24 dB (or less) by inserting either an optical isolator or a low-reflectance attenuator of 5 dB (or more) between the transmitter and the O/E converter.
61280-2-2 IEC:2005 – 13 –
c) responsivity, adequate to produce a readable display on the oscilloscope;
For example, assume that a non-return-to-zero (NRZ) optical data stream with an average optical power of –15 dBm is to be measured. If the sensitivity of the oscilloscope is 10 mV per division, a responsivity of 790 V/W is required in order to produce a display of 50 mV peak-to-peak (that is, five divisions peak-to-peak).
d) optical noise-equivalent power, low enough to result in an accurately measurable display on the oscilloscope;
For example, assume that a non-return-to-zero (NRZ) optical data stream with an average optical power of –15 dBm is to be measured. If the effective noise bandwidth of the measurement system is 470 MHz, and if the displayed root-mean-square noise is to be less than 5 % of the eye pattern peak-to-peak height, the optical noise-equivalent power shall be 145 pW Hz-1/2 or less.
e) lower cut-off (–3 dB) frequency, 0 Hz;
DC coupling is necessary for two reasons. First, extinction ratio measurements cannot otherwise be performed with sufficient accuracy. Second, if AC-coupling is used, low-frequency spectral components of the measured signal (below the lower cut-off frequency of the O/E converter) may cause significant distortion via amplitude modulation of the detected waveform. f) upper cut-off (–3 dB) frequency, greater than the bandwidth of the low-pass filter following the O/E converter;
In order to ensure repeatability and accuracy, a low-pass filter of known characteristics is inserted in the signal path before the oscilloscope. This filter alone should primarily determine the effective system bandwidth. However, the response of the entire measure-ment system should conform to the desired frequency response. g) transient response, overshoot, undershoot, and other waveform aberrations should be minor so as not to interfere with the measurement;
The low-pass filter following the O/E converter should primarily determine the system transient response. h) output electrical return loss, high enough so that reflections from the low-pass filter following the O/E converter are adequately suppressed, from 0 Hz to a frequency significantly greater than the bandwidth of the low-pass filter;
A time-domain measurement may be very inaccurate if significant multiple reflections are present. Many passive, low-loss, low-pass filters, in addition to being reflective in the stop band, have frequency responses that are strongly dependent on the termination impedances at the input and output. A minimum value of 15 dB for the return loss is recommended when passive low-pass filters are employed following the O/E converter. The effective output return loss of the O/E converter may be improved with in-line electrical attenuators, at the expense of reduced signal levels. Finally, the return loss specification extends to d.c., since otherwise, a d.c. shift in the waveform will occur, causing extinction ratio measurements to be in error. 3.1.2 Resistive signal splitter (optional) If the trigger signal for the oscilloscope is to be derived from the optical waveform itself, it is necessary to tap into the signal path at some point. A resistive signal splitter (power divider) at the location indicated in Figure 2 provides a branch from which to derive the trigger signal.
61280-2-2 IEC:2005 – 15 –
3.1.3 Linear-phase low-pass filter Generally, one of the primary purposes of measuring the optical eye pattern is to verify certain performance requirements such as rise and fall time, overshoot, etc. If the measurement system bandwidth is much greater than needed, high frequency (and probably insignificant) details of the waveform will tend to obscure the desired measurement. Also, since different measurement setups would have different bandwidths, repeatability between setups would be almost impossible to achieve.
In order to ensure repeatability and accuracy, a low-pass filter of known characteristics is inserted in the signal path prior to the oscilloscope. This filter alone should primarily determine the effective system bandwidth. The type of measurement being performed determines the bandwidth of the low-pass filter. The bandwidth and transfer function characteristics of the low-pass filter should be explicitly stated in the detail specifications. One type of eye pattern measurement effectively simulates the signal that would result at the output of a bit-rate-specific optical receiver. For NRZ format signals this type of receiver typically has a bandwidth that is somewhat less than the clock frequency. For this type of measurement, a low-pass filter of –3 dB bandwidth of 0,75/T (where T is the bit interval, in seconds, of the data signal) is often used. The resulting eye pattern is compared to a "mask" to verify compliance with specification. For RZ (return-to-zero) format signals spectral content may be significantly higher than the NRZ signal at the same optical bit rate. This may require the reference bandwidth to be in excess of the clock frequency. A different type of eye pattern measurement involves measuring the rise time, fall time, pulse width, and other time-domain parameters of an optical transmitter unit. For this type of measurement, the system bandwidth shall be greater than described above. The –3 dB bandwidth of the low-pass filter in this case needs to be high enough to allow verification of maximum rise and fall times (for example, one-third of a bit intervals), but low enough to eliminate unimportant high-frequency waveform details. For NRZ signals a low-pass filter bandwidth of 3,0/T is a typical compromise value for this type of measurement. RZ signals can require a bandwidth of 5,0/T as a typical compromise. Regardless of the type of eye pattern measurement, the filter should have a linear phase response at frequencies up to and somewhat beyond the filter –3 dB bandwidth. If the phase response is linear (implying that the group delay is constant) up to frequencies of high attenuation, slight variations in filter bandwidths should not significantly affect the waveform measurements (see Table 1).
Example low-pass filter specifications for a 0,75/T filter are as follows (Exact filter specifications are typically found within the communication standard defining transmitter performance): – characteristic impedance: 50 Ω nominal; – –3 dB bandwidth: 0,75/T, Hz; (Further study required for RZ format) – filter type:
fourth-order Bessel-Thomson (further study required for RZ format)
61280-2-2 IEC:2005 – 17 –
Table 1 – Frequency response characteristics Frequency divided by bit rate Nominal attenuation dB Attenuation tolerance dB Maximum group delay distortion s 0,15 0,1 0,3 – 0,30 0,4 0,3 – 0,45 1,0 0,3 – 0,60 1,9 0,3 0,002T 0,75 3,0 0,3 0,008T 0,90 4,5 0,3 0,025T 1,00 5,7 0,3 0,044T 1,05 6,4 0,39 0,055T 1,20 8,5 0,64 0,100T 1,35 10,9 0,90 0,140T 1,50 13,4 1,15 0,190T 2,00 21,5 2,0 0,300T 3.1.4 Oscilloscope The oscilloscope that displays the optical eye pattern should have a bandwidth well in excess of the bandwidth of the low-pass filter, so that the oscilloscope is not the bandwidth-limiting item of the measurement system. The oscilloscope is triggered either from a local clock signal that is synchronous with the optical eye pattern, or from a synchronization signal derived from the optical waveform itself. Figures 4 and 5 illustrate oscilloscope bandwidths that are commonly used in eye pattern measurements. The oscilloscope shall have a vertical-channel histogram function for extinction ratio measurement. 3.1.5 Overall system response The eye pattern measurement is obviously a time-domain measurement, and needs to accurately represent the optical waveform. This should be done without introducing undesirable overshoot, ringing, and other waveform aberrations. While the individual components of the measurement system are most conveniently specified in the frequency-domain, the final assembled system may also be required to meet certain time-domain performance limits.
Even an ideal fourth-order Bessel-Thomson filter will have an overshoot of about 1 %, and a rise time (10 % to 90 %) of about 0,35/B, where B is the bandwidth in Hertz. In view of this, the overall measurement system shall be required to demonstrate performance similar to the following when stimulated by an ideal step function signal: −
rise time, fall time (10 % – 90 %): 0,43/B maximum, 0,29/B minimum; −
rise time, fall time (20 % – 80 %):
0,35/B maximum, 0,23/B minimum; −
overshoot, undershoot: 5 % maximum.
61280-2-2 IEC:2005 – 19 –
3.2 Oscilloscope synchronization system A stable synchronization signal is essential for accurate eye pattern measurement. Ideally, the optical transmitter unit provides the synchronization signal. However, since this synchronization signal may not be present at an optical interface point, it may be necessary to derive the signal from the optical waveform itself.
Some oscilloscopes will allow triggering from transitions in the detected data pattern, either internally (from the vertical channel) or externally (from a separate trigger input). While conveniently simple, this method is not recommended for performing accurate measurements. Optical waveforms are usually fairly "noisy", and by triggering on transitions in the data pattern, the observed eye pattern will be changed by the precise adjustment of the trigger threshold. An oscilloscope typically will trigger on either a rising or a falling edge (but not both). For a PRBS data pattern, only 1 of every 4 bit transitions will produce a trigger event. Thus 75 % of the data is never measured even if the pattern repeats. Also, jitter in the optical waveform itself will be difficult to observe, since the triggering process may mask jitter. Jitter on the signal being measured is common to the trigger signal and can be effectively common-moded out. Finally, the bandwidth of the transition detector in many oscilloscopes may be insufficient to allow reliable, repeatable triggering. When a stable synchronization signal is not available, a more reliable method of using the optical waveform for oscilloscope synchronization is to use an external oscillator which is "locked" to the optical signal. This is similar to the method used to recover the clock in an optical receiver, but is accomplished with commercially available test equipment rather than with custom circuitry. This method provides a very stable trigger signal, and allows jitter in the optical waveform to be viewed directly. A detailed description of an oscilloscope synchronization system and associated equipment is given in Annex A. Care must be taken in choosing the response bandwidth of the trigger extraction system to achieve an accurate jitter measurement. 3.3 Pulse pattern generator The pulse pattern generator shall be capable of providing a pseudo random bit sequence and programmable word patterns to the system consistent with the signal format (pulse shape, amplitude, etc.) required at the system input electrical interface of the transmitter device. 3.4 Optical power meter An optical power meter shall be used which has a resolution of at least 0,1 dB, and which has been calibrated for th
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