1、 IEC/TR 61292-7 Edition 1.0 2011-11 TECHNICAL REPORT Optical amplifiers Part 7: Four wave mixing effect in optical amplifiers IEC/TR 61292-7:2011(E) THIS PUBLICATION IS COPYRIGHT PROTECTED Copyright 2011 IEC, Geneva, Switzerland All rights reserved. Unless otherwise specified, no part of this public
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10、l amplifiers Part 7: Four wave mixing effect in optical amplifiers INTERNATIONAL ELECTROTECHNICAL COMMISSION S ICS 33.160.10; 33.180.30 PRICE CODE ISBN 978-2-88912-803-7 Registered trademark of the International Electrotechnical Commission 2 TR 61292-7 IEC:2011(E) CONTENTS FOREWORD . 3 INTRODUCTION
11、. 5 1 Scope and object 6 2 Normative references . 6 3 Abbreviated terms 6 4 FWM effect in EDFAs . 7 4.1 General . 7 4.2 Introduction of the FWM effect . 7 4.3 FWM crosstalk enhancement in EDFA . 8 Annex A (informative) A technique for measurement of four wave mixing effect in OAs . 10 Annex B (infor
12、mative) Underestimation of FWM crosstalk by reduced number of WDM inputs . 18 Bibliography 21 Figure 1 Example of generation of FWM light . 8 Figure 2 Examples of EDFA with FWM effect . 9 Figure A.1 Basic measurement set-up 10 Figure A.2 Measurement flow chart 14 Figure A.3 Calculation of crosstalk
13、. 16 Figure B.1 Total number of combinations and number of combinations without the FWM channel that contribute to the FWM product generation for each channel number 19 Figure B.2 Total channel number dependence of the ratio of the number of the combinations under the condition f F= f rover the tota
14、l number of combinations . 19 Figure B.3 Calculated FWM signal power when all the signal channels are input and excluding the channel that coincides with the FWM channel . 20 Figure B.4 Dependence of the difference between the FWM signal powers for signals with all the channels and without the FWM c
15、hannel on the total channel number for various EDF dispersion values 20 Table A.1 Recommended test conditions . 12 TR 61292-7 IEC:2011(E) 3 INTERNATIONAL ELECTROTECHNICAL COMMISSION _ OPTICAL AMPLIFIERS Part 7: Four wave mixing effect in optical amplifiers FOREWORD 1) The International Electrotechni
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27、has collected data of a different kind from that which is normally published as an International Standard, for example “state of the art“. IEC 61292-7, which is a technical report, has been prepared by subcommittee 86C: Fibre optic systems and active devices, of IEC technical committee 86: Fibre opt
28、ics. The text of this technical report is based on the following documents: Enquiry draft Report on voting 86C/1029/DTR 86C/1036/RVC Full information on the voting for the approval of this technical report can be found in the report on voting indicated in the above table. 4 TR 61292-7 IEC:2011(E) Th
29、is publication has been drafted in accordance with the ISO/IEC Directives, Part 2. A list of all parts of IEC 61292 series, under the general title Optical amplifiers, can be found on the IEC website. The committee has decided that the contents of this publication will remain unchanged until the sta
30、bility 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. A bilingual version of this publication may be issued at a later date. TR
31、61292-7 IEC:2011(E) 5 INTRODUCTION The four-wave mixing (FWM) effect is known as one of the major restrictions in DWDM transmission systems. Although observation, conditions for generation, and evaluation methods have been reported in the literature, no international standards have been published on
32、 this subject, and manufacturers and users evaluate this phenomenon using their own techniques. This technical report is dedicated to the subject of four-wave mixing (FWM) effects in optical amplifiers. It provides an overview of the FWM effect and references information on test methods. The technol
33、ogy of optical amplifiers is quite new and still emerging; hence amendments and new editions to this technical report can be expected. 6 TR 61292-7 IEC:2011(E) OPTICAL AMPLIFIERS Part 7: Four wave mixing effect in optical amplifiers 1 Scope and object This part of IEC 61292, which is a technical rep
34、ort, applies to optical amplifiers (OAs) using active fibres and waveguides, containing rare-earth dopants, currently commercially available. It provides guidance on crosstalk caused by the four-wave mixing (FWM) effect. The object of this technical report is to provide introductory information for
35、understanding of the crosstalk issue raised by the FWM effect. This report also presents a measurement method in Annex A. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references,
36、only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 61290-10-4: Optical amplifiers Test methods Part 10-4: Multichannel parameters Interpolated source subtraction method using an optical spectrum analyzer NOTE
37、A list of informative references is given in the Bibliography. 3 Abbreviated terms ASE amplified spontaneous emission AWG arrayed waveguide CW continuous wave DFB distributed feed-back (laser diode) DOP degree of polarization DWDM dense wavelength division multiplexing ECL external cavity laser (dio
38、de) EDF erbium-doped fibre EDFA erbium-doped fibre amplifier FWM four-wave mixing MUX multiplexer OA optical amplifier OFA optical fibre amplifier O-MUX optical multiplexer OSA optical spectrum analyzer ROADM reconfigurable optical add/drop multiplexer SPM self-phase modulation VOA variable optical
39、attenuator WDM wavelength division multiplexing WSS wavelength selective switch XPM cross-phase modulation TR 61292-7 IEC:2011(E) 7 4 FWM effect in EDFAs 4.1 General The EDFA is a crucial element to configure photonic network systems based on WDM transmission because the EDFA compensates for loss in
40、 node devices such as ROADMs and WSSs, and expands capacity and distance which leads to large scale networks. Therefore the EDFA is required to amplify many channels of dense WDM signals and is also required to produce higher power for respective channels in order to compensate for loss in node devi
41、ces and transmission fibre. These demands have recently led to adverse deterioration of WDM signals caused by the nonlinear effect in the EDF. Previously this nonlinear effect was not thoroughly considered because the effect on signal deterioration was small. As for the L-band EDFA, the emission cro
42、ss section at 1,58 m is extremely small as compared to that at 1,55 m. As reported, the L-band amplifier requires a ten times longer EDF length in order to realize the 20-dB to 30-dB gain needed for practical use. Thus critical problems of signal deterioration by nonlinear effects were noted by the
43、long fibre length amplification in L-band 1. The FWM effect in multi-channel amplification is usually observed in an EDFA composed of long EDF, or in a high power EDFA. This technical report provides a method and procedure to measure crosstalk caused by the FWM (four-wave mixing) effect in the EDFA.
44、 4.2 Introduction of the FWM effect The nonlinear effects in EDF originate in the 3rd polarization of permittivity, the same as in transmission fibre, and lead four-wave mixing (FWM), cross-phase modulation (XPM) and self-phase modulation (SPM) 26. In FWM, wavelength-multiplexed signals generate noi
45、se on other channels. Therefore, crosstalk is imposed between the signal and the noise products generated by FWM in DWDM transmission systems. Figure 1 is a schematic diagram explaining the generation of FWM products. When the signal lights of three different wavelengths are launched into EDFA, new
46、lights (idler) are generated by the FWM effect. The newly generated wavelengths do not correspond with any of the above mentioned three wavelengths. When signal frequencies are f p , f q , and f r , generated idler light caused by FWM is expressed as follows. r q p r q, p, F f f f f f + = =(1) The g
47、enerated FWM products overlap with signal wavelength, and crosstalk is imposed on the signal. Besides FWM idler generation by three wavelengths, FWM products are generated when two signals with different wavelengths are launched into EDFA. This FWM effect resulting from two signal wavelengths is cal
48、led degenerate four-wave mixing. 8 TR 61292-7 IEC:2011(E) + + FWM r q p pqr f f f f + = p f q f r f ppr f qqr f qqp f rrp f pqr f qqr f ppq f prq f rpq f qrp f rqp f rrq f + +Figure 1 Example of generation of FWM light 4.3 FWM crosstalk enhancement in EDFA On a fundamental level, the origin of nonli
49、near response in the material is related to harmonic motion of bound electrons under the influence of an applied field. As a result, the induced polarization P from the electric dipoles is not linear in the electric field E, and is expressed in following Formula 2. + + + = E E E E E E P 3 2 1 (2) The first term represents the linear effect; the second term represents second order non- linearity; and third term represents third ord
