chapter 7- system design consideration

8/17/2019 Chapter 7- System Design Consideration

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1. Link Power Budget (Attenuation)

2. Bandwidth Budget (Dispersion)

Chapter 7: Syste DesignConsideration


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!pti"a# transitter$re"ei%er "ir"uit

!pti"a# power$#oss ode# &or a point$to$point #ink. 'he #osses o""ur at "onne"torsat sp#i"es and in the *er.


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'ransission attenuation 'he transission attenuation is the tota# (in

dB) *etween two gi%en inter&a"es.


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'ransission attenuation+,ap#e o& attenuation to *e "onsidered in

a *er opti" point$to$point #ink.


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Link power *udget 'he opti"a# power re"ei%ed at PD depends

on the aount o& #ight "oup#ed into the*er and the #osses o""urred in the *erand at the "onne"tors and sp#i"es.

'he #ink #oss *udget deri%ed &ro these-uentia# #oss "ontri*utions o& ea"he#eent in the #ink.

+a"h o& these #oss e#eents is e,pressed inde"i*e#s (dB) as

where Pin and Pout are the opti"a# power

eanating into and out o& the #oss e#eent


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Power arginA #ink power argin is usua##y pro%ided in

the ana#ysis to a##ow &or "oponent agingteperature /u"tuations and #osses.

'ypi"a# power argin o& 0 to dB is used&or the syste whi"h is not e,pe"ted toha%e additiona# update in the &uture.


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Link #oss *udgetLink #oss *udget is the tota# opti"a# power

#oss P ' that is a##owed *etween the #ight

sour"e and photode"tor.

& Ps is the opti"a# power eerging &ro theend o& the *er /y#eads atta"hed to the#ight sour"e and P3 is the re"ei%er

sensiti%ity then:$

4here is the "onne"tor #oss is the *erattenuation (dB5k) L is the transissiondistan"e and the syste argin is nora##y

taken as 0 dB.


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Power *udget (suary)

A systeati" ethod to design an opti"a##ink with respe"t to attenuation "an *esuari6e in the &o##owing way.


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Design e,ap#eA data rate o& 2 8*ps and a *it error rate o& 1$9 is

used. or the re"ei%er a si#i"on pin photodiodeoperating at ; n is "hosen. ro the re"ei%ersensiti%ities %s *it rate graph the re-uired input signa#is $ "ore diaeter.Ca#"u#ate the a##owa*#e power #oss in the syste.

Assue &urther that a 1 dB #oss o""urs when the i*er/y#ead is "onne"ted to the "a*#e and another 1 dB #oss

o""urs at the "a*#e$to$photodete"tor inter&a"e.n"#uding a 0 dB syste argin and *er attenuationo& ?.; dB5k e%a#uate the possi*#e transissiondistan"e@


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3e"ei%er sensiti%ities %s *it rate


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+,ap#eA *er #ink in"#udes %e sp#i"es at .2

dB5sp#i"e &our "onne"tors at .2dB5"onne"tor transitter power o& $1dB and re"ei%er sensiti%ity o& $2; dB.

Copute the #ength o& the *er that shou#d*e used i& sing#e ode *er "a*#e withattenuation o& .? dB5k is "hosen and there-uired power argin is ? dB.


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Bandwidth


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8a,iu *it rate


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Bandwidth and *it rate


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Bandwidth$#ength produ"t 'he #onger the *er #ength in%o#%ed the

greater the dispersion.

Dispersion or pu#se *roadening is spe"ied asns or ps per k

Bandwidth$#ength produ"t is a gure o& erit&or "oparing dierent systes. nits aretypi"a##y 86.k or =6.k

Suary o& B35B4 re#ation:$

Data rate/bit rate

Dispersion +#e"tri"a# !pti"a#

3e"tangu#ar shapepu#se

=aussianshapepu#se

Data rate/bit rate

Dispersion +#e"tri"a# !pti"a#

3e"tangu#ar shapepu#se

=aussianshapepu#se


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Pro*#e


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Pro*#e so#ution


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3ise tie *udget3ise$tie *udget ana#ysis is used to

deterine the dispersion #iitation o& anopti"a# *er #ink.

n this approa"h the tota# rise tie t sys o&

the #ink is the root$su$s-uare o& the riseties &ro ea"h "ontri*utor to the pu#serise$tie degradation.

or non$return$to$6ero (3E) dataor return$to$6ero (3E) data

where 3 is the data rate5*it rate.


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3ise tie *udget 'he rise tie *udget is asse*#e as:$

where is transitter rise tie (#ight sour"e)is the *er rise tie whi"h "onsist o& tota#dispersion rise tie &or a gi%en *er and isre"ei%er rise tie (photodiode).

3e"a## that:$

where is the ?dB e#e"tri"a# *andwidth o& there"ei%er.


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'ota# dispersion rise tie 'he pu#se *roadening in the u#tiode inde, *er

"an *e o*tained as *e#ow:$

where is a oda# dispersion and is a "hroati"dispersion. ote that the is the su o& ateria# andwa%eguide dispersion and "an a#so *e &ound using

owe%er the rise tie o& oda# dispersion"a#"u#ation and ana#ysis in u#tiode *er*e"oe ore "op#i"ated.

( ) 21

22

mod chromal f t σ σ +=


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8oda# dispersion rise$tieA %ariety o& epiri"a# e,pression &or oda# dispersion

ha%e *een de%e#oped. ro pra"ti"a# e#d e,perien"e ithas *een &ound that the *andwidth in the #ink o& #ength L"an *e e,pressed to a reasona*#e appro,iation *y theepiri"a# re#ation:$

where the paraeter - ranges *etween .; and 1 and isthe *andwidth o& a 1$k #ength "a*#e. A %a#ue o& -F.;indi"ates that the steady$state oda# e-ui#i*riu has *een

rea"hed whereas -F1 indi"ates #itt#e ode i,ing. 'hereasona*#e estiate is -F.7.

or ?$dB opti"a# *andwidth o& the *er #ink and #etting *ethe oda# dispersion rise tie then:$


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Design e,ap#eContinue &ro the pre%ious e,ap#e. Assue that the

L+D with its dri%e "ir"uit has a rise tie o& 1; ns. 'aking a typi"a# L+D spe"tra# width o&


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+,ap#eA #o"a# data #ink to *e insta##ed has the

&o##owing "hara"teristi"sG a,iu *it rate?2 8*psG #ine "ode 3EG *er 02.;512; >Ginsta##ation #ength 2kG operating

wa%e#ength 1? nG rise tie o& #ightwa%e e-uipent < ns and LD spe"tra#width o& 2 n. 4i## this *er support there-uired *it rate@

chapter 7- system design consideration

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