IEC 61 290 4 3 Edition 1 0 201 5 05 INTERNATIONAL STANDARD Optical amplifiers – Test methods Part 4 3 Power transient parameters – Single channel optical amplifiers in output power control IE C 6 1 2[.]
I E C 61 90-4-3 ® Edition 201 5-05 I N TE R N ATI ON AL STAN DAR D colour i n si de Opti cal am pl i fi ers – Test m eth o d s Part 4-3: Power tran si en t param eters – Si n g l e ch an n el opti cal am pl i fi ers i n IEC 61 290-4-3:201 5-05(en) ou tpu t power tro l TH I S P U B L I C AT I O N I S C O P Y R I G H T P R O T E C T E D C o p yri g h t © I E C , G e n e v a , S w i t z e rl a n d All rights reserved Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from either IEC or IEC's member National Committee in the country of the requester If you have any questions about IEC copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or your local IEC member National Committee for further information IEC Central Office 3, rue de Varembé CH-1 21 Geneva 20 Switzerland Tel.: +41 22 91 02 1 Fax: +41 22 91 03 00 info@iec.ch www.iec.ch Ab o u t th e I E C The International Electrotechnical Commission (I EC) is the leading global organization that prepares and publishes International Standards for all electrical, electronic and related technologies Ab o u t I E C p u b l i ca t i o n s The technical content of IEC publications is kept under constant review by the IEC Please make sure that you have the latest edition, a corrigenda or an amendment might have been published I E C Catal o g u e - websto re i ec ch /catal o g u e The stand-alone application for consulting the entire bibliographical information on IEC International Standards, Technical Specifications, Technical Reports and other documents Available for PC, Mac OS, Android Tablets and iPad I E C pu bl i cati on s search - www i ec ch /search pu b The advanced search enables to find IEC publications by a variety of criteria (reference number, text, technical committee,…) It also gives information on projects, replaced and withdrawn publications E l ectroped i a - www el ectro ped i a o rg The world's leading online dictionary of electronic and electrical terms containing more than 30 000 terms and definitions in English and French, with equivalent terms in additional languages Also known as the International Electrotechnical Vocabulary (IEV) online I E C G l o ssary - std i ec ch /g l o ssary More than 60 000 electrotechnical terminology entries in English and French extracted from the Terms and Definitions clause of IEC publications issued since 2002 Some entries have been collected from earlier publications of IEC TC 37, 77, 86 and CISPR I E C J u st Pu bl i sh ed - websto re i ec ch /j u stpu bl i sh ed Stay up to date on all new IEC publications Just Published details all new publications released Available online and also once a month by email I E C Cu stom er Servi ce Cen tre - websto re i ec ch /csc If you wish to give us your feedback on this publication or need further assistance, please contact the Customer Service Centre: csc@iec.ch I E C 61 90-4-3 ® Edition 201 5-05 I N TE R N ATI ON AL STAN DAR D colour i n si de Opti cal am pl i fi ers – Test m eth o d s Part 4-3: Power tran si en t param eters – Si n g l e ch an n el opti cal am pl i fi ers i n ou tpu t po wer trol INTERNATIONAL ELECTROTECHNICAL COMMISSION ICS 33.1 80.30 ISBN 978-2-8322-2670-4 Warn i n g ! M ake su re th a t yo u o btai n ed th i s pu bl i c ati o n fro m an au th ori zed d i stri bu to r ® Registered trademark of the International Electrotechnical Commission –2– I EC 61 290-4-3: 201 © I EC 201 CONTENTS FOREWORD Scope N orm ati ve references Term s, defi n itions and abbrevi ations Term s and defi n i ti ons Abbreviati ons Apparatus Test set-u p Ch aracteristics of test equ ipm en t Test sam ple Procedure Test preparati on Test dition s Calcu lations Test resu l ts 1 Test settin gs 1 Test data Ann ex A (inform ati ve) Overview of power transient events in sin g le chan n el EDFA A Backgroun d A Ch aracteristic i n pu t power behavi our A Param eters for ch aracterizi n g transient behaviour Ann ex B (inform ati ve) Backgrou nd on power tran si en t phen om ena i n a sing l e ch an n el EDFA B Am plifi er ch ns i n optical n etworks B Typical optical am pl ifier desig n B Approach es to address detecti on errors Ann ex C (inform ative) Sl ew rate effect on transi en t gai n response 23 Bibl i ograph y 24 Fig u re – Power transi ent test set-u p Fig u re – OA output power transient response of a) in put power increase 1 Fig u re A – Exam ple OA i n pu t power transi ent cases for a receiver applicati on Fig u re A – I nput power m easurem ent param eters for a) i n pu t power i ncrease an d b) input power decrease Fig u re A – OA ou tpu t power transient response of a) in pu t power i ncrease and b) input power decrease Fig u re B – Transien t response to a) i npu t power drop (in verse step transi en t) with transien t trol, b) deacti vated (constan t pum p power) , an d c) activated (power control) 21 Fig u re B – Transien t response to a) i npu t power rise (step transi ent) wi th transien t trol , b) deacti vated (constan t pum p power) , an d c) activated ( power trol) 22 Tabl e – Exam pl es of transi ent control m easu rem ent test conditions I EC 61 290-4-3:201 © I EC 201 –3– I NTERNATI ON AL ELECTROTECH NI CAL COMMI SSI ON OPTICAL AMPLIFIERS – TEST METHODS Part 4-3: Power transient parameters – Single channel optical amplifiers in output power control FOREWORD ) Th e I n ternati on al El ectrotechn i cal Com m i ssi on (I EC) i s a worl d wi d e org an i zati on for stan dardi zati on com pri si n g al l n ati on al el ectrotech ni cal com m i ttees (I EC N ati onal Com m i ttees) The obj ect of I EC i s to prom ote i n ternati on al co-operati on on al l q uesti on s concern i n g stand ardi zati on i n th e el ectri cal an d el ectron i c fi el ds To thi s en d and i n addi ti on to other acti vi ti es, I EC pu bl i sh es I n ternati on al Stan dards, Tech n i cal Speci fi cati ons, Tech ni cal Reports, Pu bl i cl y Avai l abl e Speci fi cati on s (PAS) an d Gu i des (h ereafter referred to as “I EC Publ i cati on (s) ”) Th ei r preparati on i s entru sted to tech n i cal com m i ttees; an y I EC N ati on al Com m i ttee i nterested i n th e su bj ect deal t wi th m ay parti ci pate i n th i s preparatory work I nternati on al , g overn m ental an d n on g overn m ental org an i zati ons l i si n g wi th th e I EC al so parti ci pate i n thi s preparati on I E C col l aborates cl osel y wi th th e I n tern ati onal Org an i zati on for Stan d ardi zati on (I SO) i n accordan ce wi th di ti on s determ i ned by ag reem en t between th e two org an i zati on s 2) Th e form al deci si on s or ag reem en ts of I EC on tech ni cal m atters express, as n earl y as possi bl e, an i nternati on al sen su s of opi ni on on th e rel evant su bj ects si n ce each tech ni cal com m i ttee h as representati on from al l i n terested I EC N ati on al Com m ittees 3) I EC Pu bl i cati ons h ave th e form of recom m endati on s for i ntern ati on al u se an d are accepted by I EC N ati onal Com m i ttees i n th at sense Whi l e al l reasonabl e efforts are m ade to ensure th at th e tech n i cal content of I EC Publ i cati on s i s accu rate, I EC can n ot be h el d respon si bl e for th e way i n wh i ch th ey are used or for an y m i si nterpretati on by an y en d u ser 4) I n order to prom ote i n tern ati onal u ni form i ty, I EC N ati on al Com m i ttees un d ertake to appl y I EC Pu bl i cati on s transparentl y to th e m axi m um exten t possi bl e i n th ei r nati on al an d reg i on al publ i cati ons Any d i verg ence between an y I EC Pu bl i cati on an d the correspon di ng nati on al or reg i on al pu bl i cati on sh al l be cl earl y i n di cated i n the l atter 5) I EC i tsel f d oes n ot provi de an y attestati on of form i ty I n depend ent certi fi cati on bodi es provi de form i ty assessm ent servi ces an d, i n som e areas, access to I EC m arks of form i ty I EC i s not respon si bl e for an y servi ces carri ed out by i n d epen den t certi fi cati on bodi es 6) Al l u sers sh ou l d en su re th at th ey h ave th e l atest edi ti on of thi s publ i cati on 7) N o l i abi l i ty shal l attach to I EC or i ts di rectors, em pl oyees, servants or ag en ts i ncl u di n g i n di vi du al experts an d m em bers of i ts tech n i cal com m i ttees and I EC Nati on al Com m i ttees for any person al i nj u ry, property d am ag e or other dam ag e of any n atu re wh atsoever, wheth er di rect or i n di rect, or for costs (i n cl u d i n g l eg al fees) and expenses ari si ng out of th e pu bl i cati on, u se of, or rel i an ce upon, th i s I EC P ubl i cati on or an y oth er I EC Publ i cati ons 8) Atten ti on i s drawn to th e N orm ati ve references ci ted i n th i s publ i cati on U se of the referen ced pu bl i cati ons i s i n di spensabl e for th e correct appl i cati on of th i s publ i cati on 9) Atten ti on i s drawn to th e possi bi l i ty th at som e of th e el em en ts of th i s I EC Publ i cati on m ay be the su bj ect of paten t ri g hts I EC sh al l n ot be h el d responsi bl e for i denti fyi ng an y or al l such paten t ri g h ts I n tern ati on al Stan dard I EC 61 290-4-3 has been prepared by su bcom m ittee 86C: Fi bre optic system s and acti ve devices, of I EC techn ical com m ittee 86: Fi bre optics This I ntern ation al Standard is to be used i n conj u ncti on with I EC 61 291 -1 : 201 2, on th e basis of wh ich it was establ ish ed The text of th is stan dard is based on the fol lowi n g docum en ts: FDI S Report on voti n g 86C/1 31 0/FDI S 86C/1 329/RVD Fu l l inform ati on on th e voti ng for th e approval of th is stan dard can be fou nd in th e report on voting in dicated in th e above table This publicati on has been drafted i n accordance wi th th e I SO/I EC Directi ves, Part –4– I EC 61 290-4-3: 201 © I EC 201 A l ist of al l parts of th e I EC 61 290 series, pu blish ed u nder th e g eneral titl e Test methods ) can be foun d on the I EC website Optical amplifiers – The com m ittee h as decided that the ten ts of th is pu blicati on will rem n unch ang ed u ntil th e stabil i ty date in dicated on the I EC website un der "h ttp://webstore i ec ch " i n th e data related to th e specific pu blicati on At th is date, th e pu bl ication wi ll be • reconfi rm ed, • wi thdrawn , • repl aced by a revised edi ti on, or • am ended A bi l in g ual versi on of th is pu bl icati on m ay be issu ed at a l ater date IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates that it contains colours which are considered to be useful for the correct understanding of its contents Users should therefore print this document using a colour printer _ ) Th e fi rst edi ti on s of som e of th ese parts were pu bl i sh ed u n d er th e g en eral ti tl e specification or Optical amplifier test methods Optical fibre amplifiers – Basic I EC 61 290-4-3:201 © I EC 201 –5– OPTICAL AMPLIFIERS – TEST METHODS Part 4-3: Power transient parameters – Single channel optical amplifiers in output power control Scope This part of I EC 61 290 appl ies to output power control led optical l y am plified, el em en tary su bsystem s I t appl ies to optical fibre am pl ifi ers (OFA) u si n g acti ve fi bres contain i n g rare- earth dopan ts, presentl y com m ercial l y avai labl e, as i ndi cated i n I EC 61 291 -1 , as wel l as altern ative optical am pl ifiers that can be used for sing l e chann el ou tpu t power trol led operati on, such as sem icon ductor optical am pl ifiers (SOA) The obj ect of th is standard is to provi de th e g eneral backgrou n d for optical am pl ifi er (OA) power transien ts an d its m easurem ents an d to i n dicate th ose I EC standard test m eth ods for accu rate an d rel iabl e m easurem en ts of th e fol lowi ng transient param eters: a) b) c) d) Transient power response Transient power overcom pensati on response Stead y-state power offset Transient power response tim e The stim u lu s an d respon ses beh aviours u n der considerati on incl u de: 1) 2) 3) 4) 5) 6) Ch ann el Ch ann el Ch ann el Ch ann el Ch ann el Ch ann el power power power power power power i ncrease (step transi ent) reducti on (i n verse step transi ent) i ncrease/reducti on (pu lse transient) redu ction /i ncrease (in verse pulse transi ent) increase/reducti on/i ncrease (l i g htn i ng bolt transien t) reducti on /increase/redu ction (in verse l ig h tn in g bol t transi en t) These param eters have been incl uded to provi de a com plete descri ption of th e transi ent beh aviour of an outpu t power transien t controlled OA The test defi n iti on defi ned h ere are appl icable if th e am pl ifi er is an OFA or an altern ati ve OA H owever, th e description i n Ann ex A of th is docum en t concentrates on th e ph ysical perform ance of an OFA an d provides a detail ed description of th e beh avi our of OFA; it does n ot gi ve a sim ilar description of oth er OA types Normative references The foll owi ng docum en ts, i n wh ole or i n part, are norm ati vel y referenced i n th is docum en t and are in dispensabl e for i ts appl ication For dated references, on l y the editi on cited appli es For un dated references, th e l atest editi on of th e referenced docum en t (i nclu ding an y am endm ents) appli es I EC 61 291 -1 : 201 2, Optical amplifiers – Part 1: Generic specification –6– 3.1 I EC 61 290-4-3: 201 © I EC 201 Terms, definitions and abbreviations Terms and defi nition s For the purposes of th is docum en t, the foll owi ng term s an d defi n iti ons apply 3.1 input signal optical sig n al th at is inpu t to the OA 3.1 input power excursion relati ve i n pu t power difference i n dB before, duri ng an d after th e i npu t power stim u lus event th at causes an OA transi en t power excursion 3.1 input power rise time tim e it takes for the i n put optical si gn al to rise from % to 90 % of the total difference between th e i n itial an d final sig n al levels durin g an i ncreasi ng power excu rsion event Note to entry: see Fi g u re A 3.1 input power fall time tim e it takes for th e in put optical sig n al to fal l from % to 90 % of the total difference between th e i n iti al an d fi nal sig n al levels du rin g a decreasi n g power excu rsi on event Note to entry: see Fi g u re A 3.1 slew rate m axim um rate of chan ge of th e i nput optical si g nal durin g a power excursi on even t 3.1 transi ent power response m axim um or m in im um deviation (oversh oot or u ndersh oot) in dB between the OA’s targ et power and th e observed power excursi on i nduced by a ch ang e in an i n pu t ch an n el power excu rsion Note to entry: On ce th e ou tput power of an am pl i fi ed ch an n el devi ates from i ts targ et power, the trol el ectroni cs i n th e OA sh oul d attem pt to com pensate for th e power di fferen ce or tran si en t power respon se, bri n g i n g the OA ou tpu t power back to i ts ori g i n al targ et l evel 3.1 transient power settling time am oun t of tim e taken to restore the power of th e OA to a stabl e power l evel close to the targ et power level Note to en try: Th i s param eter i s m easu red from the ti m e wh en sti m ul u s event th at created th e power fl uctuati on to the ti m e at wh i ch th e OA power respon se i s stabl e an d wi th i n speci fi cati on 3.1 transient power overcompensation respon se m axim um devi ati on i n dB between the am plifi er’s targ et outpu t power an d the power resul tin g from the trol el ectron ics i nstabili ty Note to en try: Tran si ent power overcom pen sati on respon se occu rs after a power excu rsi on, wh en an am pl i fi er’s trol el ectron i cs attem pts to bri ng th e power back to th e am pl i fi er’ s targ et l evel The trol process i s i terati ve, an d trol el ectron i cs m ay i n i ti al l y overcom pen sate for th e power excursi on u nti l su bsequ entl y reach i n g th e desi red targ et power l evel I EC 61 290-4-3:201 © I EC 201 –7– Note to en try: The transi en t power overcom pensati on respon se param eter i s g en eral l y of l esser m ag n i tud e th an th e transi en t power respon se and h as th e opposi te si g n 3.1 stead y state power offset difference in dB between th e fin al an d in iti al output power of th e OA, pri or to the power excursi on stim u lu s event Note to en try: Norm al l y, th e steady state power l evel fol l owi n g a power excu rsi on di ffers from the OA power before th e i n put power sti m u l us even t Th e tran si en t trol l er attem pts to overcom e th i s offset usi ng feedback 3.2 Abbreviation s AFF AG C APC ASE ASEP BER DFB DWDM EDF EDFA GFF NEM NSP O/E OA OD OFA OSA OSN R PDs PI D SOA SAR Sig P SOP VOA WDM 4.1 ASE flatteni n g fil ter au tom atic g n controller au tom atic power trol am pl ifi ed spon tan eous em ission am pl ifi ed spon tan eous em ission power bit error ratio distri bu ted feedback (l aser) dense wavel en gth di visi on m ul tipl exing Erbiu m -doped fibre Erbium -doped fibre am pl i fier gain flatten in g fi lter network equ ipm en t m an u facturers network service providers optical-to-el ectrical optical am pl ifi er optical dam ag e optical fi bre am pl ifier optical spectrum an al yser optical sig n al -to-n oise rati o ph otodiodes proporti onal i n tegral deri vati ve sem iconductor optical am plifi er sig n al-to-ASE rati o sig n al power state of polari zati on variabl e optical attenu ator wavelen gth division m u ltiplexi ng Apparatus Test set-up Fi gu re sh ows a g en eric set-up to ch aracterise th e transi ent response properties of ou tput power controll ed si n g le chan nel OAs –8– Laser sou rce Pol ari zati on scram bl er VOA Opti cal m odu l ator I EC 61 290-4-3: 201 © I EC 201 OA un d er test Fun cti on g en erator Chan n el passban d fi l ter O/E verter Osci l l oscope IEC Figure – Power transient test set-up 4.2 Characteristics of test equipment The test equ ipm ent listed below is n eeded, with th e requ ired characteristics a) Laser source for suppl yin g th e OA i nput sig n al wi th th e foll owin g ch aracteristics : – Abi li ty to su pport th e ran ge of sig nal wavelen g ths for wh ich th e OA u nder test is to be tested Th is cou l d be provided for exam pl e by a tu neable laser, or a bank of distribu ted feedback (DFB) lasers – An achi evabl e averag e ou tpu t power such that at th e input to th e OA u nder test th e power wi l l be above th e m axim um specified i n put power of th e OA, i ncl udi n g loss of an y subsequ ent test equ i pm ent between th e laser source an d OA u n der test b) Pol arizati on scram bler to random i ze the incom ing pol arizati on state of th e laser sou rce, or to trol i t to a defin ed state of polari zati on (SOP) Th e pol ari zation scram bler is option al c) Variable optical atten uator (VOA) with a d yn am ic ran g e su fficient to su pport th e requ ired ran g e of su rvi vi n g sig nal levels at wh ich the OA u nder test is to be tested N OTE I f the ou tpu t power of th e l aser sou rce can be vari ed over th e requi red dynam i c ran g e, th en a VOA i s n ot n eed ed d) Optical m odu l ator to m odify th e OA i npu t si g nal to th e defi n ed power excursion wi th th e fol l owi ng ch aracteristics – Exti nction ratio at rewrite with ou t puttin g n um ber hig her th an the m axim u m drop l evel for wh ich th e OA un der test is to be tested – Swi tch i n g tim e fast en ou gh to su pport th e fastest slew rate for wh ich th e OA u n der test is to be tested e) Ch ann el pass-ban d fi lter: an optical fi lter desig n ed to distin g u ish the sig nal waveleng th wi th th e fol lowi n g characteristics N ote th e use of a ch an n el pass-ban d fi lter is option al – Abi li ty to su pport th e ran ge of sig nal wavelen gths for wh ich th e OA u nder test is to be tested Th is cou l d be provi ded for exam pl e by a tun eabl e fil ter, or a seri es of discrete fil ters – dB pass-ban d of at least ±20 G H z cen tred arou n d th e sig nal wavel en gth – At least 20 dB atten uati on level below th e m i n i m um inserti on l oss across the en ti re specified transm issi on ban d of the OA u n der test except with in a rang e of ±1 00 G H z cen tred arou nd th e si gn al wavelen g th f) Opto-electron ic (O/E) vertor to detect the fi ltered ou tpu t of th e OA u nder test with the foll owi ng ch aracteristics – A sufficien tl y wi de optical and el ectrical bandwidth to support the fastest slew rate for wh ich th e OA is to be tested – A li near response with i n a ±5 dB rang e of all sig n al levels for wh ich th e OA u nder test is to be tested – 12 – f) 8.2 I EC 61 290-4-3:201 © I EC 201 I n put optical wavel en gth λ i n Test data The fol l owing test data shal l be recorded a) I n put optical power, Pi n trace b) Output optical power Pout trace c) d) e) f) g) h) i) j) k) l) m) Sig n al-to-ASE rati o (SAR) at operati n g condition before an d after excursi on OFA laser pum p power before an d after excursi on OA reported i npu t power before an d after inpu t excursion (where avai labl e) OA reported ou tpu t power before and after in pu t excursion OA reported i nternal tem perature (wh ere avai labl e) Measu rem ent accu racy of each pi ece of test equ ipm ent Tem perature of test sam ple Transient power response Transient power overcom pensati on Stead y state power offset Transient power response tim e I EC 61 290-4-3: 201 © I EC 201 – 13 – Annex A (informative) Overview of power transient events in single channel EDFA A.1 Background The i npu t si gn al to a term inal OFA is n orm all y a si ng l e ch an n el erbi um doped fibre am plifier (EDFA) with a wi de d yn am ic rang e as a resu l t of chan nel power excursi ons throug h ou t th e network Th e i npu t sig nal wi l l accum u late fast power vari ations wh i ch are caused by concaten ati on of transient oversh oot/u n dersh oot excursi ons from the precedi ng ch n of im perfect EDFA th at tran sport ch ann els Th ose well -kn own g ain transi en ts arise as a resu lt of add/drop events throu g h ou t th e n etwork, even thoug h each EDFA is o perated i n constant g ain m ode wi th state of th e art gai n transi en t suppressi on (typicall y, l ess th an ±1 dB g ain oversh oot/u n dersh oot from each EDFA) The tem poral steepn ess and over/un dersh oot m agn itu de of th ose transients wil l accum ulate with th e num ber of EDFAs passed , an d even tu all y a transient even t with consi derable power variations wi l l arri ve at the i nput of th e term i nal EDFA The sh ape of th is sin gl e-ch an n el power transi en t even t is directl y dependent on th e transi en t output power sh ape of the precedi ng in li ne EDFAs A.2 Characteristic input power behaviour The ch aracteristic in put power beh aviour of a sin g l e ch an n el term in al OFA is sh own i n Fig u re A , wh ich is a consequence of add/drop even ts i n th e preceding am plifi er chain Th e fig ure specifical l y represen ts tim e dependence of th e i n put power ch an g es with exam ple tim ing s The step, pu lse and l i gh tn i n g bolt transient power response, an d power offset response are particul arl y critical to carri ers an d network equ i pm ent m anufacturers (N EM) , g i ven th at the term in al OA is im m ediatel y foll owed by a ch ann el recei ver A properl y desi g ned OA wi ll have sm all valu es for th ese transi en t param eters – 14 – I EC 61 290-4-3:201 © I EC 201 I n pu t power, dBm dBm I nput power, −3 T(ri se) = 50 µ s −1 −1 Ti m e, µ s T(ri se) = 50 µ s −1 T(fal l ) = 50 µ s I n pu t power, (2) P ul se −1 I nput power, (1 ) Step I nverse −3 dBm dBm N orm al Ti m e, µ s T(ri se) = 50 µ s −1 −1 −1 Ti m e, µ s T(ri se) = 50 µ s −1 I n pu t power, dBm dBm I n pu t power, (3) Li g htni ng bol t T(fal l ) = 00 µ s T(fal l ) = 50 µ s T(ri se) = 50 µ s Ti m e, µ s −3 −3 T(ri se) = 50 µ s Ti m e, µ s T(ri se) = 00 µ s −1 T(fal l ) = 50 µ s Ti m e, µ s T(fal l ) = 50 µ s −1 IEC NOTE As an exam pl e of recei vers, these are exam pl e n um bers Figure A.1 – Example OA input power transient cases for a receiver application Specific m easurem en t param eters of th e in put power ch an g es are detail ed in Fi g ure A wi th reference to th e l ig htn in g bolt scen ario I nput power to OFA, l i n ear a u I EC 61 290-4-3:201 © I EC 201 – 15 – 90% change 0% change Rise time Power increase Fall time Ti m e, 0% change s 90% change IEC a) Input power increase I n pu t power to OFA, l i n ear a u Power decrease 90% change 0% change 0% change Rise time Ti m e, s Fall time 90% change IEC b) Input power decrease Figure A.2 – Input power measurement parameters for a) input power increase and b) input power decrease I t is im portant that a si n g le ch ann el OA pl aced next to a recei ver is operated in au tom atic power trol (APC) m ode in order to su ppress these i n pu t power transi ent excursi ons Th is is referred to as outpu t power transient trolled operati on M oderate transi ent power excursi ons i ncident on the recei ver are m an ageabl e, dependi ng on th e receiver d yn am ic ran g e an d th e bandwi dth of th e recei ver au tom atic gai n trol l er (AG C) H owever, excessi ve optical powers at th e recei ver eith er can resu lt i n data m iss-readi ngs g i vi ng u n wanted bit errors or can perm anen tl y dam ag e th e recei ver A.3 Parameters for characterizing transient behaviour The param eters g enerall y used to ch aracteri ze th e transi en t behavi our of a power control l ed OA for th e case of ch an nel step increase/reducti on are defi n ed in Figu re A Fi g ure A 3a) specificall y represen ts the tim e depen dence of th e ou tpu t power of th e OA wh en the i n pu t power is rapi dl y i ncreased Likewise, th e transient power beh aviour for the case wh en the input power is rapidl y decreased is sh own in Fig u re A 3b) The im portant transi en t param eters are transien t power overshoot/un dersh oot, transi ent power response settl i ng tim e an d stead y state power offset For a power-con trol led am plifi er, a reducti on in i npu t power resu lts in an ou tpu t power u n dersh oot, and an increase in outpu t resu l ts in an output power oversh oot Th is is in contrast to a gain-con trol l ed am plifier, wh ere a – 16 – I EC 61 290-4-3:201 © I EC 201 Tran si en t po wer res po n se Power, dBm reducti on i n in pu t power resu l ts in a gai n oversh oot, an d an increase in in pu t power results i n a g n u n dersh oot Stead y state power offset Tran si en t power respo n se ti m e Ti m e, s IEC Power, dBm a) Channel input power increase Tran si en t power respo n se ti m e Transient power overcompensation response Stead y state po wer offset Tran si en t power respon se ti m e Tran si en t power respo n se Ti m e, s IEC b) Channel input power decrease Figure A.3 – OA output power transient response of a) input power increase and b) input power decrease I EC 61 290-4-3:201 © I EC 201 – 17 – Annex B (informative) Background on power transient phenomena in a single channel EDFA B.1 Amplifier chains in optical networks Optical n etworks com m on l y i ncorporate a ch ain of optical am pl ifiers to m an age fi bre loss as wel l as l osses i ncurred by optical com pon en ts provi din g fu ncti ons such as dispersion com pensation or ch ann el add/drop As the n etwork is devel opi n g in to a m esh structure, chan nels m ay pass throug h a n um ber of different optical paths before arrivi ng at a recei ver wi th a consequ en tial im pact of un expected power variations du e to com pou n ded com pensation of ch ann el add-drops wi th i n n etworks com pon ents, especiall y transi ent trol of i n-lin e optical am pl ifi ers The resi li ence of the recei ver to th ese u nexpected optical power variations is key to a correctl y function i ng optical n etwork I t is com m on in existin g G b/s system s for th e last li n e am plifi er i n th e WDM li nk to be a pream plifier wi th th e en tire dense wavel eng th divisi on m u ltiplexin g (DWDM) com b bein g am plifi ed col lectivel y N evertheless, there is an i ncreasin g n eed for am pl ifiers on each chan nel to pre-am pl ify furth er th e optical chan n el prior to th e recei ver This sing l e ch an n el OFA is i nserted to h el p m eet th e strin gent optical si gn al-to-noise ratio (OSN R) requ irem en ts of m odern m odu l ati on form ats and overcom e the l osses of speciali zed optical com pon ents , i ncl u din g optical discri m inators or dem odu lators, pol arization dem ultipl exers, tu n eabl e dispersion com pensators, an d tun eable fi lters i n the receiver ch ain The total ou tput power of th is si n g le-ch an n el OFA is com posed of si g nal power an d am plifi ed spon tan eous em ission (ASE) noise The si g nal power an d ASE power is som etim es u nfi ltered an d n ot attenu ated by an optical band-pass filter, dem ul tiplexer or speci alized com pon ents down stream of th e OFA This is particu larl y tru e for colourl ess recei vers, wh ich are broadband and n ot wavelen g th specific B.2 Typical optical amplifier design The typical desig n of an optical l y am plifi ed recei ver consists of a chan nel selector, an OFA, a ph oton detector, a l im itin g am pl ifier, an d an electrical low pass fil ter Pre- am plifi er OFAs h ave becom e an integral part of optical receivers since th eir perform ance boosts th e sensitivity of th e recei ver photon detector H owever, n oise is g en erated with in a pre-am p EDFA as a resu lt of spontaneous de-exci tation of the excited erbium ions As the ions h ave a fin ite excited state lifetim e, som e retu rn spontan eou sl y to th e grou nd state em ittin g a ph oton that is incoh eren t with respect to th e incom in g optical si gn al, as opposed to a photon g en erated by stim u lated em issi on Thi s backg rou n d n oise is known as am pl ified spontaneous em ission (ASE) , an d i t is the dom i nan t noise elem ent in pre-am plifi er EDFAs Optical power transi ents are su b-m i llisecon d flu ctu ati ons in n etwork power levels th at are caused by even ts su ch as pl an n ed or acci den tal chan nel loadin g chang es, passi ve l oss variations, or n etwork protecti on switch in g I n a dyn am ic n etworki n g en vironm en t, optical am pl ifiers n eed to be able to com pensate for such power vari ations i n order to avoid poten tial degradation of qu al ity of service For instance, i n a n etwork reconfig urati on scen ario, th e nu m ber of DWDM chan n els at th e i n pu t of an OFA m ay su dden l y decrease, i ncreasin g th e am pl ifier’s popu l ati on i n version with a correspon din g i ncrease i n g n, in a m atter of m icrosecon ds Th is gain ch an g e resu lts in chan nel power overshoot wh i ch is detrim en tal to network service provi ders (N SPs) , g i ven th at their n etworks wil l no lon ger operate at th e gai n level for wh ich they were optim i zed, poten tial l y i m pactin g service qual i ty Power flu ctu ations accum u late with each OFA i n th e system an d, if left u n abated, wi l l en ter a si ng le chan nel OFA upstream of a receiver and wil l be am pl ifi ed, cau sing th e transi ent to enter th e receiver This can resul t i n a cum u lati ve transi ent oversh oot or un dershoot at th e recei ver that can grow to exceed th e d yn am ic ran ge of th e recei ver The subsequ ent i ncrease in bit error ratio (BER) – 18 – I EC 61 290-4-3:201 © I EC 201 resu l ts i n qu al ity of service degradati on or, in som e circum stances, can even dam ag e a recei ver as a resu lt of excessi ve optical power Lin e OFA in th e optical repeaters al ong th e transm ission system typicall y operate in constan t gai n m ode An OFA th at is operatin g with constan t gain wi l l repl icate and am pl ify ch ann el power transi en ts enteri n g the in put at th e outpu t, wh ich is detrim en tal for a sin g l e ch an n el am pl ifi er in an am pl ifi ed recei ver It is im perative th at an y si ng le chan nel OFA situ ated cl ose to a recei ver be operated in constan t ou tpu t power m ode i n order to suppress transien ts Th is is referred to as power transien t controlled operation M oderate transien t power excursions i nciden t on the receiver are m anag eable, depen di ng on the recei ver d yn am ic ran ge an d the ban dwi dth of the recei ver au tom atic g n control ler (AG C) , bu t an excessi vel y l arg e power excu rsi on can : a) exceed the absol ute m axim um optical power rati ng of th e recei ver, leadi ng to poten ti al catastroph ic optical dam ag e (OD) (particu l arl y resu lti ng from power oversh oot) ; b) exceed th e m axim u m operati n g optical power rati ng of the recei ver, leadi ng to eye open in g pen alty an d a burst of errors leadi n g to an outage (particu l arly resu lting from power oversh oot waveform s) ; c) drop below th e m in im um operati n g optical power rati n g of the recei ver, leadin g to eye open in g pen alty and a burst of errors, leadin g to an ou tag e (particul arl y resu lti ng from power u ndershoot waveform s) ; d) rapidl y osci llate between cases b) an d c) above, causi n g an ou tag e (parti cu larl y resu lti n g from li g htn in g bolt power waveform s) In additi on to am pl ifyi n g optical ch an n els carryi n g data, an OFA g en erates an d transm its ASE noise The optical data si gn al is typicall y centred on on e or m ore wavelen gths correspon di n g to th e chan n els stan dardised by th e I nternati on al Telecom m unicati on s U n i on (I TU) I n trast, th e ASE is typical l y g enerated across a m uch broader wavelen gth ran ge, for exam ple arou n d 40 nm , wh ich is substan tial l y wi th in th e g ain ban dwidth reg ion of th e OFA The level of ASE depends u pon the optical si gn al chan nel g ain , th e overal l popu lation in versi on an d tem perature of the erbium doped fibre (EDF) Furth er, the l evel of ASE produ ced by th e OFA wil l also vary du e to th e loss variabi lity of oth er optical com ponents wi thi n th e OFA, since passi ve l osses affect th e g n requ ired i n the EDF to attai n a target g n in th e OFA A m easure of th e am ou nt of ASE rel ati ve to th e si gn al power entering a sin g le ch ann el receiver is defin ed as th e si g nal to ASE ratio (SAR) Th is is calcu lated as: SAR = SigP (dB) ASEP wh ere SAR is the sig n al to ASE rati o i n dB; SigP is the sig n al power exiti n g th e OFA i n dBm ; ASEP is the total ASE power exitin g th e OFA i n dBm I deal l y, th e SAR of an am plifier is al ways posi tive because th e si gn al power is greater than th e su m of th e ASE power exiti n g th e OFA I t is preferred that hi g h er levels of SAR are ach ieved as this is beneficial to l ow bi t error rate detection of sig n al data, and si ng l e ch ann el pream pl ifier OFA are desi g n ed to m axim i ze SAR Si n ce operation al condi tions affect the am ou nt of ASE, the val u e of SAR wil l also be operati onal Since the OFA is em pl oyed as a si n g le ch ann el am plifi er, th e g n sh ape wi th respect to wavelen gth of th e OFA m ay or m ay n ot be g n flatten ed Even with i deal g n flatten in g , th e gai n of the EDF varies with in put chan nel waveleng th Therefore, ASE g enerated by th e OFA