《IEC-PAS-61280-2-10-2003.pdf》由会员分享，可在线阅读，更多相关《IEC-PAS-61280-2-10-2003.pdf（24页珍藏版）》请在三一文库上搜索。
1、 PRE-STANDARD Fibre optic communication subsystem test procedures Part 2-10: Digital systems Time-resolved 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
2、 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 Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/06/2007 09:53:47 MSTNo reproduction or networking permitt
3、ed without license from IHS -,-,- Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/06/2007 09:53:47 MSTNo reproduction or networking permitted without license from IHS -,-,- PRE-STAND
4、ARD Fibre optic communication subsystem test procedures Part 2-10: Digital systems Time-resolved 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
5、 N I C A L C O M M I S S I O N Reference number IEC/PAS 61280-2-10 Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/06/2007 09:53:47 MSTNo reproduction or networking permitted without
6、 license from IHS -,-,- 2 Copyright 2003, IEC CONTENTS FOREWORD.3 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.
7、3 Polarization controller9 6.1.4 Interferometer10 6.1.5 Optical oscilloscope.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
8、vs. time, (t)12 8.2 Average alpha factor, avg.13 8.3 Alpha factor 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
9、Mach-Zehnder modulator.18 BIBLIOGRAPHY .20 Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/06/2007 09:53:47 MSTNo reproduction or networking permitted without license from IHS -,-,-
10、Copyright 2003, IEC 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 organ
11、ization 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 activiti
12、es, 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 p
13、articipate 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
14、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 s
15、pecifications, 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 regio
16、nal 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 wit
17、h 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 concerning
18、 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 of
19、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 o
20、ptic 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 86C/
21、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 extend
22、ed for a single 3-year period, following which it shall be revised to become another type of normative document, or shall be withdrawn. Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 0
23、3/06/2007 09:53:47 MSTNo reproduction or networking permitted without license from IHS -,-,- 4 Copyright 2003, IEC 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
24、 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 setups and calculations (Annex A) and a review of laser modulation metho
25、ds 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 can interact
26、 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 both the sig
27、n 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 of receive
28、r 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 BER-curves towards higher or lower input power levels. A positiv
29、e 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 directly is difficult because it requires a chirp-free transmitter with th
30、e 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 signal path and measuring the additional power (SNR) required to achi
31、eve 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 chirp data directly or
32、 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 down, lower cost transmitters are being designed and deployed. Controllin
33、g 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 instantaneous optical frequency of a transmitter. It is typically expresse
34、d 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. Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IHS Employees/1111111001
35、, User=listmgr, listmgr Not for Resale, 03/06/2007 09:53:47 MSTNo reproduction or networking permitted without license from IHS -,-,- Copyright 2003, IEC 5 Measurements are acquired in the time domain using a trigger that is synchronous with a PRBS modulation pattern. As described above, there are t
36、wo 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 the data. Figure 1 shows
37、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 frequency shift term. An abrupt shift in phase becomes a transient in frequency. The two terms are generally refe
38、rred 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 terms. Considering only transient chirp, and solving for alpha-factor: P P dt dP dt d P dt dP tf P = = 22 )( 4 (2) whe
39、re 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 is directly proportional to the rate at which the phase or power changes. Copyright International Electrotechnical Commission Prov
40、ided by IHS under license with IECLicensee=IHS Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/06/2007 09:53:47 MSTNo reproduction or networking permitted without license from IHS -,-,- 6 Copyright 2003, IEC 5 Overview of chirp measurement methods Time-resolved chirp measurements requ
41、ire 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 of f(t) and P(t). They are the frequency
42、 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 oscilloscope are typically configured as shown in F
43、igure 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 spacin
44、g is called the free spectral range (FSR). In this method, the interferometer is used to convert 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
45、11) and corresponding waveforms are measured on the optical oscilloscope. The optical signal power of the laser transmitter is given by: 2 )()( )( t V t V tP BA + = (3) The chirp is calculated by taking the difference of the quadrature waveforms and correcting for the sinusoidal characteristic of th
46、e interferometer: 2 )()( )( t V t V t V BA = (4) )( )( )( arcsin 2 FSR tP t V f(t) = (5) Optical input Variable time delay 6.5ps DCA Trigger input Optical Oscilloscope 6.5ps DCA Optical oscilloscope Copyright International Electrotechnical Commission Provided by IHS under license with IECLicensee=IH
47、S Employees/1111111001, User=listmgr, listmgr Not for Resale, 03/06/2007 09:53:47 MSTNo reproduction or networking permitted without license from IHS -,-,- Copyright 2003, IEC 7 Figure 3 The frequency discriminator method requires measurement at the quadrature point of the interferometer The frequen
48、cy-resolved optical gating (FROG) method uses an optical gate followed by an optical spectrum analyser (OSA) as shown in Figure 4. The optical gate is set to a particular position in time, ti, and a spectrum is measured on the OSA. By varying the optical gate time, Table 1 can be completed. The weighted-average frequency (sometimes called the centre-of- mass frequency) is calculated as follows: = =