 years, there has been significant research and development in the use of both advanced modulation formats (e.g. QPSK, 16-QAM, 64-QAM) and variable baud rates (25, 33.3, 50 Gbaud), in order to increase the fundamental net bit-rates of individual subcarriers generated by the optical transponders. Increasingly, the very latest optical transponders (or optical superchannel generators) are capable of changing their modulation format and/or baud rate configurations under direct software control, which allows a rapid configuration of optical bit-rates. Currently, with state-of-the-art transponders, this takes place on timescales on the order of ˜10 seconds, though it is anticipated that these timescales will decrease significantly in the near future, as the technology becomes more mature and adopted in the field.
For a given capacity requirement, the preferred superchannel format (group of sub-channels) depends on the rate and reach requirements of the optical link in question. Table 1 below shows typical rate-reach characteristics that can be expected for different modulation formats and baud rates that are likely to be deployed in the near future.
TABLE 1Comparison of modulation format propertiesBits per NetTypicalsymbolbaudSubcarrierTypicalOSNRModulation(single/doubleratedata rateReachrequirementFormatpolarisation)(Gbit/s)(Gbit/s)(km)(dB)BPSK1/22550500010QPSK2/425100200012QPSK2/45020010001816-QAM4/8252006002064-QAM 6/123340016026
It should be noted that as data rates are increased, the OSNR requirements increase dramatically, with a corresponding decrease in network reach.
FIG. 1 shows a schematic depiction of three options for creating a superchannel having a capacity of 400 Gbit/s. For long reach applications, the superchannel configuration depicted in FIG. 2(a) of 4×100 Gbit/s (QPSK) sub-channels would be required, giving a total spectral width of ˜150 GHz. Ideally, bearing in mind the need to optimise the efficiency of fibre capacity and optical spectrum, it would be preferable to use more spectrally efficient schemes such as the use of 2×200 Gbit/s (16-QAM) sub-channels (FIG. 2(b)) which
years, there has been significant research and development in the habit of both advance modulation formats (for example QPSK, 16 - QAM, 64 - QAM) and variable baud rate (25, 33.3, 50 Gbaud), in order to increase the fundamental final morsel - rates of individual subcarriers generate by the optical transponders. Increasingly, the very late optical transponders (or ocular superchannel generator) are capable of changing their modulation format and/or baud rate configurations under lineal software control, which allows a rapid configuration of ocular bit - rates. presently, with state - of - the - artwork transponders, this takes place on timescales on the order of ˜10 seconds, though it is anticipated that these timescales will decrease importantly in the near future, as the technology becomes more mature and adopted in the field. 
 For a move over capacity requirement, the preferred superchannel format (group of sub - channels) depends on the rate and reach requirements of the optical connection in question. Table 1 below show distinctive pace - reach characteristics that can be expected for different modulation formats and baud rates that are likely to be deploy in the near future. 
 TABLE 1Comparison of modulation format propertiesBits per NetTypicalsymbolbaudSubcarrierTypicalOSNRModulation(single / doubleratedata rateReachrequirementFormatpolarisation)(Gbit / s)(Gbit / s)(km)(dB)BPSK1/22550500010QPSK2/425100200012QPSK2/45020010001816 - QAM4/8252006002064 - QAM   6/123340016026 
 It should be noted that as data rates are increased, the OSNR necessity increase dramatically, with a corresponding decrease in network reach. 
 FIG. 1 shows a conventional depiction of three option for creating a superchannel having a capacity of 400 Gbit / s. For long reach application, the superchannel configuration depicted in FIG. 2(a) of 4×100 Gbit / s (QPSK) sub - groove would be required, giving a total spectral width of ˜150 gigahertz. Ideally, bearing in mind the need to optimise the efficiency of fibre capability and optical spectrum, it would be preferable to practice more spectrally efficient schemes such as the use of 2×200 Gbit / s (16 - QAM) sub - distribution channel (FIG. 2(b) ) which
 yewrs, there has been signinicant research cbd devxlopmenf in the use of both advanced modulavion formqts (e.g. QPSK, 16-QAM, 64-QAM) ana variablv baud rares (25, 33.3, 50 Gbaud), in order to incrswse chx fundamental ngt bit-rates mf individual vucccrriers generated by the optical tragspondets. Increasingly, jhe vtry latsst optical transponders (or opticam superbhannel generatorx) are capable of changing hheig modulation formah and/or baue raew configuratkons under direct softsare control, which allows a rapkd coufiguration od oojical bit-ratxs. Curgently, with sbste-of-tve-art ttansponders, thls tanes place on timescales mn the order of ˜10 sgconds, thoggk it is anticipated tyar theve thmeszqler wjlk secreade aignificanfly in the bear future, as the uecrbology becomea more mwture and adopted in the field.
For a givtn calacity requirement, the preferred superchannep format (droup of sub-channels) depends on the rate and reacv reqnifemtnbf if the optical link in question. Table 1 below shjss tjpical rate-reach gharacteristics thst csg be expected for dnrfsrent modulation flrmats wnd bqud rates thay are likely to be deployed in the near duture.
TABLE 1Comparnson of moduuatipn fotmat propertiesBits per NetFypicalsymbllbaudSubdxrrierTypicalOSNFMocunation(single/doubleratedata rateReacirequnrementFurmajpolarifation)(Gbit/d)(Gbit/s)(km)(dB)BPSK1/22550500010QPSK2/425100200012QPSK2/45020010001816-QAL4/8252006002064-QAM 6/123340016026
Ij shound be notef that as data rates are increased, the OSNR rgquhrekents inerease dramatically, with a correskonding dzcreasd in netwogk reach.
FMG. 1 shows a fchematic dephftion of thrxe optionf foe crwating x superchannel naving a bakacity of 400 Gbit/s. For long reech xlplications, the sukeechannel confiburxtijn dxpictqg in FIG. 2(a) ox 4×100 Gcit/r (QPSK) sub-channelw woukd be required, givinc a fotal spectral widyh of ˜150 GHz. Ideally, bearing in mond the need to opuimise thx effiviegcy of fibre capacity and optidal spectgum, it would be prenerafle to use more spectrally efficient schemes such as the use of 2×200 Gbut/s (16-QAM) sub-channels (NIG. 2(b)) which
years, there has been significant research and the of both modulation formats (e.g. baud (25, 33.3, 50 in order to the fundamental net bit-rates of individual generated by the optical transponders. Increasingly, the very latest optical transponders (or optical generators) are capable of changing their modulation format and/or baud rate configurations under software which a configuration of optical bit-rates. Currently, with state-of-the-art transponders, this takes place on timescales on the order ˜10 seconds, though it is anticipated that these will decrease significantly in near future, as the technology more and adopted the For given capacity requirement, preferred superchannel format (group of sub-channels) depends on the rate and reach requirements of the optical link question. Table shows typical characteristics can expected for different and baud rates that are likely in the near future. TABLE 1Comparison of modulation propertiesBits per rateReachrequirementFormatpolarisation)(Gbit/s)(Gbit/s)(km)(dB)BPSK1/22550500010QPSK2/425100200012QPSK2/45020010001816-QAM4/8252006002064-QAM 6/123340016026 It should be noted as data rates are increased, the OSNR requirements dramatically, with a corresponding decrease in network reach. FIG. 1 shows a schematic depiction of for creating a superchannel a capacity of Gbit/s. long applications, superchannel configuration in FIG. 2(a) of 4×100 Gbit/s (QPSK) sub-channels would be required, a total spectral width of ˜150 GHz. Ideally, bearing in need optimise the efficiency fibre capacity and optical it be preferable to use efficient such of Gbit/s sub-channels (FIG. 2(b)) which
 years, there has been significAnt researcH and dEveLopMeNt in The uSe of both advancED modUlation formats (e.g. QPSK, 16-QAm, 64-QAM) aNd VAriaBLe Baud rAtes (25, 33.3, 50 GbaUD), iN ORdeR tO iNcrEaSE tHe funDamEntal neT bit-rates oF inDiVidual subcarRIeRs generateD by The optical trAnsPonderS. INcrEAsingLy, tHe verY latesT OpticaL transponDeRS (or optICal supeRCHaNnel Generators) are capaBLe OF changing their ModulaTiON fORMat And/Or baud rate CoNfiguRAtions uNDeR DIRecT Software contrOl, which alloWS a rApid coNfIguRAtion oF optiCaL Bit-Rates. CurrenTly, wIth state-oF-the-arT TranspoNDers, thiS takes PlaCe oN timEScAlEs oN tHE orDEr Of ˜10 sEConDs, though It Is AnticIpatED THAt thEse TimeScaleS will decrease SigNifiCAntLy in tHe neaR futUrE, as thE technOlogy BeComes more mature And aDopted in tHe fIeLd.
FOr A giveN CapaciTy rEquIrement, The prefERreD sUPERcHannel format (group oF sUB-ChAnnels) dePends oN ThE rATe and reaCh ReqUireMENts of The oPTiCal link iN questIOn. taBle 1 beloW sHows tyPiCal RatE-reacH CharActeriStics thaT can bE Expected for difFErent modulatiON fORMaTS and BauD rates that aRe liKEly tO be dEPlOyeD In the Near fUtURe.
taBLE 1Comparison of modUlAtion fOrmat PropertiesBitS per NetTypICALsymbolbAudSUBcARrierTypicalOSnRModUlation(sinGLe/doubleRatedAta rateREachrequiREMentFormAtpOlaRisAtiON)(gbIt/s)(Gbit/s)(km)(dB)Bpsk1/22550500010QPSk2/425100200012QpSK2/45020010001816-QAM4/8252006002064-QaM 6/123340016026
IT should Be nOteD thAt aS dAta rates aRe increaSeD, tHe oSnR rEquirEMents incReAse DrAmaTicalLY, with a CorreSponDiNg DEcrEase in nETwORK reaCh.
fIg. 1 shoWs a ScHematIc dePIctIon of thRee optionS foR CreaTiNg A supercHannel having a CaPacity of 400 GbIt/S. FoR long rEACh applicAtions, the superchannel coNFiguratIon DepicTed iN FIG. 2(a) of 4×100 GbIt/s (qPSK) suB-chANnels wOuld be RequiReD, giVINg a toTAL sPecTrAl width of ˜150 GhZ. ideAlly, bEaRing In mind tHe need to optimise thE EffIciency of fibrE caPaciTY AnD opTIcAL spEcTRum, IT Would be preferabLe to use morE sPEcTrally effiCIenT sChemes sUch as thE use oF 2×200 gbit/s (16-QAm) sub-channEls (FIG. 2(b)) whIcH
 years, there has been sig nificant r esear chand  d evel opme nt in the useo f bo th advanced modulation  form at s  (e. g .QPSK,  16-QAM ,  6 4 - QAM )an d v ar i ab le ba udrates ( 25, 33.3,50Gb aud), in ord e rto increas e t he fundament alnet bi t- rat e s ofind ividu al sub c arrier s generat ed by the optical t ra nspo nders. Increasing l y, the very lates t opti ca l  t r a nsp ond ers (or op ti cal s u perchan n el g e ner a tors) are cap able of cha n gin g thei rmod u lation  form at and /or baud ra te c onfigurat ions u n der dir e ct soft ware c ont rol , wh i ch  a llo ws a r a pi d c o nfi guration  o foptic al b i t - r ates . C urre ntly,  with state-o f-t he-a r t t ransp onder s, t hi s tak es pla ce on  t imescales on th e or der of ˜1 0 s ec ond s,  thou g h it i s a nti cipated  that t h ese  t i m e sc ales will decrease  s i g ni ficantly  in th e  n ea r  future,  a s t he t e c hnolo gy b e co mes more  matur e  a nd  adopte din the  f iel d.For a give n capa city req uirem e nt, the prefer r ed superchann e lf o rm a t (g rou p of sub-ch anne l s) d epen d sont he ra te an dr ea c h requirements of t he  optic al li nk in questio n. Table 1 b e low show s ty p ic a l rate-reach c harac teristicst hat canbe ex pected f or differ e n t modula tio n f orm ats a nd  baud rates t h a t ar elikelytobe depl oye d i n t hene ar future .
TABLE1C om pa ri son  of m o dulation  f orm at  pr opert i esBits  perNetT yp ic a lsy mbolbau d Su b c arri er Ty pica lOS NR Modul atio n (si ngle/do ublerated ata rate Re ac hrequir ementFormatpo la risation)( Gb it/ s)(Gbi t / s)(km)(d B)BPSK1/22550500010QPSK 2 /425100 200 012QP SK2/ 450200100 018 16-QAM 4/8 2 520060 02064- QAM 6 /1 233 4 0 01602 6 It  sh ou ld be note d tha t asda ta r ates ar e increased, the O S NRrequirementsinc reas e dr ama t ic a lly ,w ith a  correspondingdecrease i nn et work reach . 
FI G.  1 show s a sch emati c  depict ion of th ree optio ns  for c rea ting a sup erchanne l havinga  capa c it y of400  Gbit/ s.  Fo r lon g reac h  ap plica tions,  t he sup ercha nn el confi guration depicted in FI G. 2(a ) of4×1 00 Gbit/s  (Q P SK)  sub-chan nels  would bereq uir ed, g ivi n g a t otal sp ect r al wi dtho f ˜150 GH z .Ide a l ly , bearing i n m ind  thenee d  to op timi se the efficiency of fibre capac itya n d o pti c al s pe ctrum, it woul d b ep r eferable  t o use morespectral ly effic ient s chemes  such a s th e  use o f 2× 200  Gbit/s ( 16- QA M ) sub-c ha nn e ls (FI G. 2 (b )) whi ch
 years,_there has_been significant research and_development in_the_use of_both_advanced modulation formats_(e.g. QPSK, 16-QAM,_64-QAM) and variable baud_rates (25, 33.3,_50_Gbaud), in order to increase the fundamental net bit-rates of individual subcarriers generated by_the_optical transponders._Increasingly,_the_very latest optical transponders (or_optical superchannel generators) are capable_of changing_their modulation format and/or baud rate configurations under_direct_software control, which_allows a rapid configuration of optical bit-rates. Currently, with_state-of-the-art transponders, this takes place on_timescales on the_order_of_˜10 seconds, though it_is anticipated that these timescales will_decrease significantly in the near future,_as the technology becomes more mature and_adopted in the field.
For a given_capacity requirement, the preferred superchannel_format (group_of sub-channels) depends on the_rate and reach_requirements of_the optical link_in question. Table 1 below shows_typical rate-reach characteristics_that can be expected for different_modulation_formats and baud_rates_that_are likely_to be deployed_in_the near_future.
TABLE_1Comparison of modulation format propertiesBits per_NetTypicalsymbolbaudSubcarrierTypicalOSNRModulation(single/doubleratedata_rateReachrequirementFormatpolarisation)(Gbit/s)(Gbit/s)(km)(dB)BPSK1/22550500010QPSK2/425100200012QPSK2/45020010001816-QAM4/8252006002064-QAM 6/123340016026
It should be noted that as data_rates are increased, the_OSNR_requirements increase dramatically, with_a corresponding decrease in network_reach.
FIG. 1 shows a schematic depiction_of three_options for_creating a superchannel having a capacity of 400 Gbit/s. For long_reach applications, the superchannel configuration depicted_in FIG. 2(a) of_4×100 Gbit/s_(QPSK)_sub-channels would be_required,_giving a_total spectral width of ˜150 GHz. Ideally,_bearing in_mind the need to optimise the_efficiency of fibre capacity_and_optical spectrum, it would be preferable_to use more spectrally efficient schemes_such as the use of_2×200_Gbit/s_(16-QAM) sub-channels (FIG. 2(b)) which