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 DD IEC/PAS 61280-2-10:2003 This Draft for Development was published under the authorit
2、y 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 reproduces 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 Deve
3、lopment series of publications and is of a provisional nature because it is considered that further experience is required in its application before it is converted into a British Standard. It should be applied on this provisional basis, so that information and experience of its practical applicatio
4、n 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 organization operating under a given procedure. Comments arising from the use of this Draft for Development are requested so that UK experience
5、 can be reported to the international organization responsible for the Technical Specification. A review of this publication will be initiated not later than 3 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. N
6、otification 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 the end of the review period, the responsible BSI Committee will decide whether to support the conversion into an international standard, t
7、o 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 GEL/86/3, Fibre optic systems and active devices, at British Standards House, 389 Chiswick High Road, London W4 4AL, giving the document ref
8、erence and clause number and proposing, where possible, an appropriate revision of the text. A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international publications referred to in this docume
9、nt 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 Online. Summary of pages This document comprises a front cover, an inside front cover, the IEC/PAS
10、 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. Amendments issued since publication Amd. No. Date Comments PRE-STANDARD Fibre optic communication subsystem test procedures Part 2-10: Dig
11、ital systems Time-resolved chirp and alpha-factor measurement of laser transmitters PUBLICLY AVAILABLE SPECIFICATION IEC/PAS 61280-2-10 Edition 1.0 2003-01 INTERNATIONAL ELECTROTECHNICAL COMMISSION Reference number IEC/PAS 61280-2-10 DDIEC/PAS61280210:2003 2 Cpoyrgi th 002I ,3EC CONTENTS FOREWORD.3
12、1 Scope.4 2 Background 4 3 Definition of time-resolved chirp .4 4 Modeling transmitter behaviour.5 5 Overview of chirp measurement methods .6 6 Frequency discriminator method.9 6.1 Apparatus9 6.1.1 Pattern Generator9 6.1.2 EDFA 9 6.1.3 Polarization controller9 6.1.4 Interferometer10 6.1.5 Optical os
13、cilloscope.10 6.2 Procedure .10 7 Monochromator method11 7.1 Apparatus11 7.1.1 Pattern generator 11 7.1.2 EDFA 11 7.1.3 Monochromator .11 7.1.4 Optical oscilloscope.11 7.2 Procedure .11 8 Alpha-factor calculations 12 8.1 Alpha factor vs. time, (t)12 8.2 Average alpha factor, avg .13 8.3 Alpha factor
14、 vs. power, (P) 13 9 Documentation .14 10 Abbreviations .14 Annex A Verification of TRC setup and calculations15 Annex B Optical transmitter modulation methods .16 B.1 Directly modulated laser16 B.2 Electro-absorption modulator.17 B.3 Mach-Zehnder modulator.18 BIBLIOGRAPHY .20 DDIEC/PAS61280210:2003
15、2poCyrigh 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 org
16、anization 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 activi
17、ties, 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
18、 participate 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 a
19、s possible, 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
20、 specifications, 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 reg
21、ional standards. 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 w
22、ith one of 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 concerni
23、ng the evidence, 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 o
24、f this patent 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
25、 optic systems 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 PAS Report on voting 86C/475A/PAS 86
26、C/496/RVD Following 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 exte
27、nded for a single 3-year period, following which it shall be revised to become another type of normative document, or shall be withdrawn. DDIEC/PAS61280210:20033 4 Cpoyrgi th 002I ,3EC FIBRE OPTIC COMMUNICATION SUBSYSTEM TEST PROCEDURES Part 2-10: Digital systems Time-resolved chirp and alpha-factor
28、 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 alpha-factor, a measure of transient chirp, is derived from the measured TRC data. Also covered is a means to verify the TRC se
29、tups 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 effects of chirp on the transmission of signals is of great importance to the system designer. Chirp can have two separate outc
30、omes 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 or negative path penalty, which ultimately decreases or increases the distance over which the signal can propagate in a system w
31、ithout 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 transmitted spectrum limiting the channel spacing by interfering with adjacent channels in an ultra-dense WDM environment, even at short
32、-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 negative path penalty corresponds to an apparent increase of receiver sensitivity. The path penalty is manifested as a shift of the sy
33、stems 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 to laser chirp to maintain a specified bit error ratio (BER) in a system with specified dispersion. Measuring chirp penalty dire
34、ctly 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 from a path penalty measurement. A path penalty measurement involves substituting a fibre of known chromatic dispersion into the
35、 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 is dominated by the chirp penalty term. This has led many transmitter and system designers and manufacturers to estimate the ch
36、irp (or dispersion) penalty using time-resolved chirp data directly or with derived modeling parameters. IEC technical report 61282-8 (to be published) describes the estimation of dispersion penalty from measured time-resolved chirp data 8. In order to bring the cost of DWDM transmission systems dow
37、n, 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 7. 3 Definition of time-resolved chirp Time-resolved chirp (also referred to as dynamic chirp) is the time variation of the inst
38、antaneous 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), is used in conjunction with f(t) to completely describe the optical signal. DDIEC/PAS61280210:20034poCyrigh t 002I ,3EC 5 Measure
39、ments are acquired in the time 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 fre
40、quency waveform, f(t), indicates 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
41、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 respectively. A general equation for chirp is given by 1: ) ( 4 ) ( 2 1 P K P P dt dP t f (1) where is the alpha-factor and K 1a
42、nd K 2are adiabatic terms. Considering only transient chirp, and solving for alpha-factor: P P dt dP dt d P dt dP t f P 2 2 ) ( 4 (2)where dt d t f 2 1 ) ( Equation (2) indicates that transient chirp produces a phase shift ( ) proportional to the normalized power change ( P/P) and a frequency transi
43、ent that is directly proportional to the rate at which the phase or power changes. DDIEC/PAS61280210:20035 6 Cpoyrgi th 002I ,3EC 5 Overview of chirp 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 tr
44、ansmission system. Synchronization must be provided to the measurement system in the form of a trigger signal. Three methods theoretically can provide the same values of f(t) and P(t). They are the frequency discriminator, frequency- resolved- optical gating (FROG), and monochromator methods.Figure
45、2 Simplified diagram for the frequency discriminator method In the frequency discriminator method 23, a Mach-Zehnder interferometer followed by an optical oscilloscope are typically configured as shown in Figure 10. An optical oscilloscope, sometimes called a digital communications analyser (DCA) co
46、nsists 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 conve
47、rt frequency deviations into amplitude variation by tuning the interferometer so that the nominal laser frequency is positioned at the quadrature points of the sinusoidal function (Points A and B in Figure 11) and corresponding waveforms are measured on the optical oscilloscope. The optical signal p
48、ower of the laser transmitter is given by: 2 ) ( ) ( ) ( t V t V t P B A (3) The chirp is calculated by taking the difference of the quadrature waveforms and correcting for the sinusoidal characteristic of the interferometer: 2 ) ( ) ( ) ( t V t V t V B A (4) ) ( ) ( ) ( arcsin 2 FSRt P t V f(t) (5)
49、 Optical input Variable time delay 6.5ps DCA Trigger input Optical Oscilloscope 6.5ps DCA Optical oscilloscope DDIEC/PAS61280210:20036poCyrigh t 002I ,3EC 7 Figure 3 The frequency discriminator method requires measurement at the quadrature point of the interferometer The frequency-resolved optical gating (FROG) method uses an optical gate followed
