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1、DRAFT FOR DEVELOPMENT DD IEC/PAS 61280-2-10: 2003 Fibre optic communication subsystem test procedures Part 2-10: Digital systems Time-resolved chirp and alpha-factor measurement of laser transmitters ICS 33.180.01 ? Licensed Copy: London South Bank University, London South Bank University, Tue Dec 1
2、2 04:24:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI DD IEC/PAS 61280-2-10:2003 This Draft for Development was published under the authority of the Standards Policy and Strategy Committee on 28 February 2003 BSI 28 February 2003 ISBN 0 580 41312 8 National foreword This Draft for Development reprod
3、uces verbatim IEC/PAS 61280-2-10:2003 This publication is not to be regarded as a British Standard. It is being issued in the Draft for Development series of publications and is of a provisional nature because it is considered that further experience is required in its application before it is conve
4、rted into a British Standard. It should be applied on this provisional basis, so that information and experience of its practical application may be obtained. A PAS is a Technical Specification not fulfilling the requirements for a standard, but made available to the public and established in an org
5、anization operating under a given procedure. Comments arising from the use of this Draft for Development are requested so that UK experience can be reported to the international organization responsible for the Technical Specification. A review of this publication will be initiated not later than 3
6、years after its publication by the international organization so that a decision can be taken on its status at the end of its 3-year life. Notification of the start of the review period will be made in an announcement in the appropriate issue of Update Standards. According to the replies received by
7、 the end of the review period, the responsible BSI Committee will decide whether to support the conversion into an international standard, to extend the life of the Technical Specification for another 3 years or to withdraw it. Comments should be sent in writing to the Secretary of BSI Subcommittee
8、GEL/86/3, Fibre optic systems and active devices, at British Standards House, 389 Chiswick High Road, London W4 4AL, giving the document reference and clause number and proposing, where possible, an appropriate revision of the text. A list of organizations represented on this committee can be obtain
9、ed on request to its secretary. Cross-references The British Standards which implement international 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 Ele
10、ctronic Catalogue or of British Standards Online. Summary of pages This document comprises a front cover, an inside front cover, the IEC/PAS title page, pages 2 to 20, an inside back cover and a back cover. The BSI copyright date displayed in this document indicates when the document was last issued
11、. Amendments issued since publication Amd. No. DateComments Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 04:24:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI PRE-STANDARD Fibre optic communication subsystem test procedures Part 2-10: Digital systems Time-resol
12、ved chirp and alpha-factor measurement of laser transmitters P U B L I C L Y A V A I L A B L E S P E C I F I C A T I O N IEC/PAS 61280-2-10 Edition 1.0 2003-01 I N T E R N A T I O N A L E L E C T R O T E C H N I C A L C O M M I S S I O N Reference number IEC/PAS 61280-2-10 DD IEC/PAS 61280210:2003 L
13、icensed Copy: London South Bank University, London South Bank University, Tue Dec 12 04:24:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 2 Cpoyrgi th 002I ,3EC CONTENTS FOREWORD.3 1Scope.4 2Background 4 3Definition of time-resolved chirp .4 4Modeling transmitter behaviour.5 5Overview of chirp measur
14、ement methods .6 6Frequency discriminator method.9 6.1Apparatus9 6.1.1Pattern Generator9 6.1.2EDFA 9 6.1.3Polarization controller9 6.1.4Interferometer10 6.1.5Optical oscilloscope.10 6.2Procedure .10 7Monochromator method11 7.1Apparatus11 7.1.1Pattern generator 11 7.1.2EDFA 11 7.1.3Monochromator .11
15、7.1.4Optical oscilloscope.11 7.2Procedure .11 8Alpha-factor calculations 12 8.1Alpha factor vs. time, ?(t)12 8.2Average alpha factor, ?avg.13 8.3Alpha factor vs. power, ?(P) 13 9Documentation .14 10Abbreviations .14 Annex A Verification of TRC setup and calculations15 Annex B Optical transmitter mod
16、ulation methods .16 B.1Directly modulated laser16 B.2Electro-absorption modulator.17 B.3Mach-Zehnder modulator.18 BIBLIOGRAPHY .20 DD IEC/PAS 61280210:2003 2 Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 04:24:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI poCy
17、righ t 002I ,3EC 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES Part 2-10: Digital systems Time-resolved chirp and alpha-factor measurement of laser transmitters FOREWORD 1)The IEC (International Electrotechnical Commission) is a worldwide organizat
18、ion for standardization comprising all national electrotechnical committees (IEC National Committees). The object of the 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,
19、the IEC publishes International Standards. 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 parti
20、cipate in this preparation. The 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 the IEC on technical matters express, as nearly as possi
21、ble, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested National Committees. 3)The documents produced have the form of recommendations for international use and are published in the form of standards, technical specifi
22、cations, technical reports or guides and they are accepted by the National Committees in that sense. 4)In order to promote international unification, IEC National Committees undertake to apply IEC International Standards transparently to the maximum extent possible in their national and regional sta
23、ndards. Any divergence between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the latter. 5)The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any equipment declared to be in conformity with one of
24、 its standards. 6)The International Electrotechnical Commission (IEC) draws attention to the fact that it is claimed that compliance with this document may involve the use of a patent concerning the double-pass monochromator described in clauses 2.4 and 4.1. IEC takes no position concerning the evid
25、ence, validity and scope of this patent right. The holders of this patent right has assured the IEC that they are willing to negotiate licenses under reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this respect, the statement of the holder of this pate
26、nt right is registered with the IEC. Information may be obtained from: Agilent Technologies Palo Alto CA USA A PAS is a technical specification not fulfilling the requirements for a standard, but made available to the public. IEC-PAS 61280-2-10 has been prepared by subcommittee 86C: Fibre optic syst
27、ems and active devices, of IEC technical committee 86: Fibre optics The text of this PAS is based on the following document: This PAS was approved for publication by the P-members of the committee concerned as indicated in the following document: Draft PASReport on voting 86C/475A/PAS86C/496/RVD Fol
28、lowing publication of this PAS, the technical committee or subcommittee concerned will investigate the possibility of transforming the PAS into an International Standard. This PAS shall remain valid for an initial maximum period of 3 years starting from 2002-08. The validity may be extended for a si
29、ngle 3-year period, following which it shall be revised to become another type of normative document, or shall be withdrawn. DD IEC/PAS 61280210:2003 3 Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 04:24:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 Cpoyrgi
30、th 002I ,3EC 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 sets forth standard procedures for measuring time-resolved chirp on laser transmitters. The calculation of
31、 alpha-factor, a measure of transient chirp, is derived from the measured TRC data. Also covered is a means to verify the TRC setups and calculations (Annex A) and a review of laser modulation methods and the relationship of TRC to performance in a transmission system. 2 Background Understanding the
32、 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 can interact with the fibre dispersion to broaden or narrow the pulse along the fibre. This will cause a positive
33、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 both the sign of the chirp and the sign of the fibre dispersion. The second is that chirp can broaden the transmit
34、ted 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 of receiver sensitivity due to distortion of the signal waveform during its transmission over the path. A negati
35、ve path penalty corresponds to an apparent increase of receiver sensitivity. The path penalty is manifested as a shift of the systems BER-curves towards higher or lower input power levels. A positive chirp penalty is defined as the additional signal-to-noise ratio (SNR) required at the receiver due
36、to laser chirp to maintain a specified bit error ratio (BER) in a system with specified dispersion. Measuring chirp penalty directly is difficult because it requires a chirp-free transmitter with the identical intensity pattern as the DUT. Because of this difficulty, chirp penalty is often inferred
37、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 (SNR) required to achieve the specified BER. This measurement is tedious and time consuming and assumes that the measurement
38、 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 chirp data directly or with derived modeling parameters. IEC technical report 61282-8 (to be published) describes the estima
39、tion of dispersion penalty from measured time-resolved chirp data 8. 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 is key to their success in the network
40、7. 3 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. It is typically expressed as ?f(t), the difference from the average optical frequency. The instantaneous optical power, P(t),
41、is used in conjunction with ?f(t) to completely describe the optical signal. DD IEC/PAS 61280210:2003 4 Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 04:24:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI poCyrigh t 002I ,3EC 5 Measurements are acquired in the ti
42、me domain using a trigger that is synchronous with a PRBS modulation pattern. As described 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), indi
43、cates that the frequency of the laser is also varying as the laser is modulated with the data. Figure 1 shows a typical TRC result. Figure 1 A typical TRC measurement 4 Modeling transmitter behaviour In a modulated signal, the frequency variation can be modeled as the sum of phase shift term and fre
44、quency shift term. An abrupt shift in phase becomes a transient in frequency. The two terms are generally referred to as transient and adiabatic respectively. A general equation for chirp is given by 1: )( 4 )( 2 1 P K P P dt dP tf? ? ? (1) where ? is the alpha-factor and K1 and K2 are adiabatic ter
45、ms. Considering only transient chirp, and solving for alpha-factor: P P dt dP dt d P dt dP tf P ? ? ? ? ? ? ? ?22 )( 4 (2) where dt d tf ? ?2 1 )(? Equation (2) indicates that transient chirp produces a phase shift (?) proportional to the normalized power change (?P/P) and a frequency transient that
46、 is directly proportional to the rate at which the phase or power changes. DD IEC/PAS 61280210:2003 5 Licensed Copy: London South Bank University, London South Bank University, Tue Dec 12 04:24:57 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 6 Cpoyrgi th 002I ,3EC 5 Overview of chirp measurement metho
47、ds 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 provide the same values
48、of ?f(t) and P(t). They are the frequency discriminator, frequency- resolved- optical gating (FROG), and monochromator methods. Figure 2 Simplified diagram for the frequency discriminator method In the frequency discriminator method 23, a Mach-Zehnder interferometer followed by an optical oscillosco
49、pe are typically configured as shown in Figure 10. An optical oscilloscope, sometimes called a digital communications analyser (DCA) consists of a broadband optical-to- electrical converter and a sampling oscilloscope. The differential delay between the two paths creates sinusoidal amplitude versus frequency variation. The frequency spacing is called the free spectral range (FSR). In this method, the interferometer is used to convert freq