1、 g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g55g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58procedures Part 2-10: Digital systems Time-resolved chirp and alpha-factor measurement of laser tra
2、nsmittersThe European Standard EN 61280-2-10:2005 has the status of a British StandardICS 33.180.01Fibre optic communication subsystem test BRITISH STANDARDBS EN 61280-2-10: 2005BS EN 61280-2-10:2005This British Standard was published under the authority of the Standards Policy and Strategy Committe
3、e on 23 December 2005 BSI 23 December 2005ISBN 0 580 47098 9request to its secretary.Cross-referencesThe British 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 Corresp
4、ondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards 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 i
5、tself confer immunity from legal obligations.Summary of pagesThis document comprises a front cover, an inside front cover, the EN title page, pages 2 to 22, an inside back cover and a back cover.The BSI copyright notice displayed in this document indicates when the document was last issued.Amendment
6、s issued since publicationAmd. No. Date Comments present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK.A list of o
7、rganizations represented on this subcommittee can be obtained on National forewordThis British Standard is the official English language version of EN 61280-2-10:2005. It is identical with IEC 61280-2-10:2005.The UK participation in its preparation was entrusted by Technical Committee GEL/86, Fibre
8、optics, to Subcommittee GEL/86/3, Fibre optic systems and active devices, which has the responsibility to: aid enquirers to understand the text;EUROPEAN STANDARD EN 61280-2-10 NORME EUROPENNE EUROPISCHE NORM September 2005 CENELEC European Committee for Electrotechnical Standardization Comit Europen
9、 de Normalisation Electrotechnique Europisches Komitee fr 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 61280-2-10:2005 E ICS 33.180.01 En
10、glish version Fibre optic communication subsystem test procedures Part 2-10: Digital systems Time-resolved chirp and alpha-factor measurement of laser transmitters (IEC 61280-2-10:2005) Procdures dessai des sous-systmes de tlcommunications fibres optiques Partie 2-10: Systmes numriques Mesure de la
11、fluctuation de la longueur donde rsolue dans le temps et du facteur alpha des metteurs laser (CEI 61280-2-10:2005) Prfverfahren fr Lichtwellenleiter-Kommunikationsuntersysteme Teil 2-10: Digitale Systeme Messung von zeitaufgelstem Chirp und Alphafaktor von Lasersendern (IEC 61280-2-10:2005) This Eur
12、opean Standard was approved by CENELEC on 2005-08-01. 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 referenc
13、es 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 memb
14、er 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, Ital
15、y, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom. Foreword The text of document 86C/663/FDIS, future edition 1 of IEC 61280-2-10, prepared by SC 86C, Fibre optic systems and active devices, of IEC TC 86,
16、 Fibre optics, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61280-2-10 on 2005-08-01. 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) 2006-
17、05-01 latest date by which the national standards conflicting with the EN have to be withdrawn (dow) 2008-08-01 The International Electrotechnical Commission (IEC) and CENELEC draw attention to the fact that it is claimed that compliance with this document may involve the use of a patent concerning
18、the double-pass monochromator described in Subclauses 2.4 and 4.1. The IEC and CENELEC take no position concerning the evidence, validity and scope of this patent right. The holder of this patent right has assured the IEC that he is willing to negotiate licences under reasonable and non-discriminato
19、ry terms and conditions with applicants throughout the world. In this respect, the statement of the holder of this patent right is registered with the IEC. Information may be obtained from: Agilent Technologies Palo Alto, CA USA Attention is drawn to the possibility that some of the elements of this
20、 document may be the subject of patent rights other than those identified above. IEC and CENELEC shall not be held responsible for identifying any or all such patent rights. _ Endorsement notice The text of the International Standard IEC 61280-2-10:2005 was approved by CENELEC as a European Standard
21、 without any modification. _ EN 61280-2-10:2005 2 3 EN 61280-2-10:2005 CONTENTS 1 Scope 4 2 Background 4 3 Abbreviations .5 4 Definition of time-resolved chirp5 5 Modelling transmitter behaviour 6 6 Overview of chirp measurement methods 7 7 Frequency discriminator method .10 8 Monochromator method 1
22、2 9 Alpha-factor calculations.14 10 Documentation .15 Annex A (informative) Verification of TRC set-up and calculations.16 Annex B (informative) Optical transmitter modulation methods17 Figure 1 A typical TRC measurement .6 Figure 2 Simplified diagram for the frequency discriminator method. .7 Figur
23、e 3 The frequency discriminator method requires measurement at the quadrature point of the interferometer .8 Figure 4 In the FROG method, the spectrum from an optically-gated signal is measured on an OSA9 Figure 5 Simplified block diagram for the monochromator method. 9 Figure 6 To obtain low disper
24、sion, a double-pass configuration is typically used10 Figure 7 Set-up for the frequency discriminator method 10 Figure 8 Set-up for the monochromator method 12 Figure 9 An example plot of alpha versus time for an EML 14 Figure 10 Alpha factor versus power for (a) a DM laser and (b) an EML 15 Figure
25、A.1 Pure phase modulation observed on (a) an OSA and (b) a TRC measurement set-up .16 Figure B.1 Schematic representation of a directly modulated laser. .17 Figure B.2 A directly modulated laser has significant transient and adiabatic chirp 18 Figure B.3 Schematic representation of an EML .19 Figure
26、 B.4 Chirp of an EML with normal transient chirp.19 Figure B.5 Chirp of an EML with an additional transient characteristic .20 Figure B.6 Schematic representation of a Mach-Zehnder modulator 21 Figure B.7 Chirp measurement on a Mach-Zehnder modulator showing only transient chirp.21 Table 1 Instantan
27、eous frequency, f for each time slot, t and the calculated weighted-average frequency, f(t).i i8 EN 61280-2-10:2005 4 FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES Part 2-10: Digital systems Time-resolved chirp and alpha-factor measurement of laser transmitters 1 Scope This part of IEC 61280 s
28、ets forth standard procedures for measuring time-resolved chirp (TRC) on laser transmitters. The calculation of alpha-factor, a measure of transient chirp, is derived from the measured TRC data. Also covered is a means to verify the TRC set-ups and calculations (Annex A) and a review of laser modula
29、tion methods and the relationship of TRC to performance in a transmission system. 2 Background Understanding the effects of chirp on the transmission of signals is of great importance to the system designer. Chirp can have two separate outcomes in transmission systems. The first is that the chirp ca
30、n interact with the fibre dispersion to broaden or narrow the pulse along the fibre. This will cause a positive or negative path penalty, which ultimately decreases or increases the distance over which the signal can propagate in a system without regeneration. The sign of the penalty depends upon bo
31、th the sign of the chirp and the sign of the fibre dispersion. The second is that chirp can broaden the transmitted spectrum limiting the channel spacing by interfering with adjacent channels in an ultra-dense WDM environment, even at short-haul distances. The path penalty is the apparent reduction
32、of receiver sensitivity due to distortion of the signal waveform during its transmission over the path. A negative path penalty corresponds to an apparent increase of receiver sensitivity. The path penalty is manifested as a shift of the systems bit error ratio (BER) curves toward higher or lower in
33、put power levels. A positive chirp penalty is defined as the additional signal-to-noise ratio (SNR) required at the receiver due to laser chirp to maintain a BER in a system with specified dispersion. Measuring chirp penalty directly is difficult because it requires a chirp-free transmitter with the
34、 identical intensity pattern as the device under test (DUT). Because of this difficulty, chirp penalty is often inferred from a path penalty measurement. A path penalty measurement involves substituting a fibre of known chromatic dispersion into the signal path and measuring the additional power (SN
35、R) required to achieve the specified BER. This measurement is tedious and time consuming and assumes that the measurement is dominated by the chirp penalty term. This has led many transmitter and system designers and manufacturers to estimate the chirp (or dispersion) penalty using time-resolved chi
36、rp data directly or with derived chirp parameters that are either modelled or measured. 5 EN 61280-2-10:2005 In order to bring the cost of DWDM transmission systems down, lower cost transmitters are being designed and deployed. Controlling the amount of chirp present in these lower cost transmitters
37、 is key to their success in the network. 113 Abbreviations BER Bit-error ratio DCA Digital communications analyser DFB Distributed feedback laser DM Directly modulated laser DUT Device under test DWDM Dense wavelength-division multiplexing EAM Electro-absorption modulator EDFA Erbium-doped fibre amp
38、lifier EML Electro-absorption modulated laser FFT Fast Fourier transform FROG Frequency-resolved optical gating FSR Free spectral range NRZ Non-return-to-zero OSA Optical spectrum analyser PMF Polarisation maintaining fibre PRBS Pseudo-random binary sequence SLM Single longitudinal mode SNR Signal-t
39、o-noise ratio SOP State of polarisation TRC Time-resolved chirp WDM Wavelength-division multiplexing 4 Definition of time-resolved chirp Time-resolved chirp (also referred to as dynamic chirp) is the time variation of the instantaneous optical frequency of a transmitter. Chirp is also expressed in t
40、he literature by temporal rate of change of the phase of the propagating electromagnetic wave; as such it is a time derivative and bares units of inverse of time (Hz). 2 It is typically expressed as f(t), the difference from the average optical frequency. The instantaneous optical power, P(t), is us
41、ed in conjunction with f(t) to completely describe the optical signal. 1)Figures in square brackets refer to the bibliography. EN 61280-2-10:2005 6 Measurements are acquired in the time domain using a trigger that is synchronous with a pseudo-random binary sequence (PRBS) modulation pattern. As desc
42、ribed above, there are two components of TRC measurement. The optical waveform, P(t), is that which would be displayed with a wide-band optical receiver and oscilloscope. The chirp or frequency waveform, f(t), indicates that the frequency of the laser is also varying as the laser is modulated with t
43、he data. Figure 1 shows a typical TRC result. (Hz) (W) ChipsHzPowerWTime (s) 3.E+092.E+091.E+090.E+001.E+09 2.E+09 3.E+09 4.E+09 5.E+09 0.00E+00 2.00E10 4.00E10 6.00E10 8.00E10 1.00E09 1.20E09 1.40E09 1.60E09 8.E04 7.E04 6.E04 5.E04 4.E04 3.E04 2.E04 1.E04 0.E+00 IEC 1066/05 Figure 1 A typical TRC m
44、easurement 5 Modelling transmitter behaviour In a modulated signal, the frequency variation can be modelled as the sum of phase shift term and frequency shift term. An abrupt shift in phase becomes a transient in frequency. The two terms are generally referred to as transient and adiabatic respectiv
45、ely. A general equation for chirp is given by 2: 21dd4)(PKPPtPtf +=(1) where f(t) is the difference from the average optical frequency, is the alpha-factor, P is the instantaneous optical power, and K1and K2are adiabatic terms. Considering only transient chirp, and solving for alpha-factor: PPtPtPtP
46、tfP= 22)(4dddddd(2) where ttfdd21)(= 7 EN 61280-2-10:2005 Equation (2) indicates that transient chirp produces a phase shift () proportional to the normalized power change (P/P) and a frequency transient that is directly proportional to the rate at which the phase or power changes. 6 Overview of chi
47、rp measurement methods Time-resolved chirp measurements require to be modulated with a bit stream to simulate the way in which the device is used in a transmission system. Synchronization must be provided to the measurement system in the form of a trigger signal. Three methods theoretically can prov
48、ide the same values of f(t) and P(t). They are the frequency discriminator, frequency-resolved-optical gating (FROG), and monochromator methods. The time-average alpha may also be measured using non-time-resolved methods such as the small signal method of Devaux 3 and others. Optical input Variable
49、timedelay 6.5psDCA Trigger input Optical Optical oscilloscope IEC 1067/05 Figure 2 Simplified diagram for the frequency discriminator method In the frequency discriminator method 45, a Mach-Zehnder interferometer followed by an optical oscilloscope are typically configured as shown in Figure 3. An optical oscilloscope, sometimes called a digital commu
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