Seminar Space

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ACKNOWLEDGEMENT

ABSRAC

INRODUCION 2 FEARES OF LASER COMMNICAIONS SYSEM 7

3 OPERAION 0 4 ACQISIION AND RCKING 5 OPICAL NOISE 6 SYSEM CHARACERISICS AND DESCRIPON LINK PARAMETERS RNSMIER PARMEERS 8 9. CHANNEL PARAMEERS 1 RECEIVER PARAMEERS DEECOR PARAMEERS AN EXAMPLE 3 APPLICAIONS

4 ADVANAGES AND DISADVANAGES

CONCLSIONS REFERENCES

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ACKOWLEDGEMENTS

am thankl and express my hea-ll gratitude to BM.S INSTITUTE OF

TECOLOGY for provding an opporunity o llling my most cherished desire of

reaching my goals and thus helping me to wsh me a bright career

wish to acknowledge my grattude to our respected Princpal Dr. S Venkateswaran for

creating a good opportunty to show the talent of an individual n ths nsttution under his

ale guidance

I express 1Y hearfelt grattude to our HOD and my project guide Prof Ramana Murthy

MV or hs gudance and constant superson of my work! express my heafelt gratude

to Prof Ramana Murty MV and Mr MS Sowmya Shree for ther guidance and

constant supevsion of my work

also thank to our lectures of LCOMMUNICAO depament n clearing my

doubts and helping me to attan the completon of my technical seminar

nally not to orget my ends who always nspred me and encouraged me take ths lecture

opic as success

Shahaaz. T

lBY06TE047

4 DEPT OF TeE, BMSI


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ABSTRACT

Laser communications offe vable alteative to commuicatons fo inte-

satelite links and othe applications whee high-pefomance lnks ae necessity. High

data rae, small antenna size narow beam dvergence and a narow eld of view are

chaacteistics of aser communicaion that offe a numbe of potential advantages fo

system design

Free space optical communcations s a ne-of-sght (LOS) technology hat transmits a

modulated beam of visbe o inared lght though he amosphere for boadband

communications In a manne smlar to be opical communications, ee space optics

uses a ight emitting dode ED) o laser (light amplication by stimulated emisson of

adiaton) pont souce fo data tansmsson Howeve n ee space optics an energy

beam s collmated and ansmited hrough space aher han being guided hrough an

optical cable. These beams of light, operating in the Terahertz poton of he spectm,

ae focused on a eceiving lens connected to a high senstivity eceive though an

optica ber

Unlike radio and micowave sysems, ee space optical communications reques no

specrum icensing and inteference to and om othe systems is not a conce In

addition the point-o-poin lase signal is extemey dicult to ntecept making it

deal for cove communicatons ree space optca communications offer daa raes

comparable to be optical communications a a acton of the depoyment cost whle

exemely naow lase beam widths povide no limt to he numbe of ee space

optcal lnks hat may be installed in a given location

5 DEPT OF TeE, BMSI


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INTRODUCTON

Lasers have been consdered for space communcatons snce ther realizaton n

1960. However, t was soon recognzed that although the laser had potental or teanse o ata a exeely hgh raes specc advanceens were neee n

component peroance an systes engneerng, patcularly or space-qualedJ

harware

Avances n syste archtecture data orattng an coponent technoogy

over he pas ee ecaes have ae aser comuncaons n space not ony a vable

but aso an atractve appoach to nter satelle lnk applcatons

The hgh data rate and large normaton throughput avalable wth laser

councaons are any tes geater han n raoeuency (RF) systes The sal

antena se eures ony a smal ncease n the weght and voue o host vehce In

aon, ths eatue substantally reuces blocage o eds o vew o he ost

esrable areas on satelltes The saller antenas, wth aeters typcally less than 30c ceae ess oentu dsurbance o any sensve satele sensos Fewe on boa consuabes ae eure over the long ete because there are ewer sturbances to the satelle copaed wth larger an heaver RF systems The narow

beam vergence o aods ntererenceee and secue opeaton

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FEATURES OF LASER COMMNICAION SYSEM

Direct or indirect modulation techniques may be empoyed depending on the type of

laser employed. The sorce output passes through optcal system into the channel

he optical system typically ncludes transfer, beam shaping and telescope optics The

receiver beam comes in through the optical system and is passed along to detectors and

sgnal processing electroncs.

here are also terminal control electroncs that must control the gimbals and

other steerng mechanisms and servos to keep the acuston and tracing system

operatn n the designed modes of operaton.

10

Aperur 8diameter

6

4

2

ptcal

105 06 0 08 09 0

Data a

igure 2. elescope apeture Vs. data rae fomilimee wave

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I Te extemely hig antenna gai made possible by te naow beams enables

sall teescope apertures to be used. Plots of apetre diameter Vs data ate fo

Iillimete and optica waves ae sown in Fig 2 A lase comunication sstem

opeating at I Gb/s equies an apetue of appoimately 30 cm. In contast a GbsI

milliete wave system equies a signicanly lage apeture, 2-2.75m.Te lase beam

widt can be made as naow as te diaction limit of te optics allows is s given by te bea widt eqal to 1.22 times te waveengt of te ligt, divided by te adius

of te output beam apeue is antenna gain is poporiona to te ecipocal of te

bea widt squaed e most important point ee is tat to acieve te potentialdifactionliited bea widt given by te telescope diameter a singlemode ig

beaqulity laser souce is equied, togete wit very igquality optical

coponents tougout te tansmitting subsyste

Te beam quality cannot be bette tan te wost element in te optical cain,

so te possible antenna gain will be esticted not only by te lase souce itself, but also

by any of te optical eleents including te na irro or teescope piay. Because

o te equieent for bot ig efciency and ig bea quaity any lases tat ae

sutabe in ote appications ae unsuitable fo ong distance eespace counication n ode to comunicate adequate powe must be eceived by te detecto to distinguis signal o noise

Lase powe tansie optical syste losses, pointing syste impefections,tansite and receive antenna gains eceive losses and eceive tracking losses ae

al factos in estabising receiver powe Te reqired optica powe is detemined by

data rate, detecto sensitivity moduation fomats, noise and detection metods



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-Probabilty

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f deecio Sgna +

Bakrd akrud I

dak re+ dk cre

I Threshld

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Meared phre de me

I Figure 3. Dstbton of dton poabltyVs photo cnt n t psn of sna

When the receiver is detecting signals, it is actually making decisions as to the nature of

the signa (when digita signal are being sent it distinguishes between ones and zeos).

Fig 3. shows the probability o detection vs measured photo current in a decision time

There are two distributions: one when a signa is present (including the amount o

photocurent due to background and dak current in the detector and one when there is

no signal present (including only the non signa curent sources A threshold must be

set that maximizes the success rate and minimizes the ero rate One can see that

diferent types of eors wil occur Even when there is no signal pesent the uctuation



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I of the non signal sources wi perodicay cause he threshold to be exceeded. This isthe error of stating that a signal is present when there s no signa resent The signadisbuton may aso fa on the other side of te treshod, so errors statng that nosigna is resent w occur even when a signa s resent For aser communication

systems n genera one wants to equaize these two eror tyes In the acquisition mode

however, no atemt is made to equaize these erors since this woud increase

acuisiton tme

OPERION

ree sace aser communicatons systems are wreess connections throug te

atmoshere ey work simiar o ber otc cabe systems ecet the beam is

transmitted though oen sace he carrer used for te transmission of this signa is

generated by eter a g ower LED or a aser dode he aser systems oerate n te

near nared region of te sectrum e aser ght across the i is at a waveength of

between 780 - 920 r. wo arae beams are used, one for transmssion and one for

receton

Figur 4: MAGNM 5 Hgh-Seed Laser-Communication System (Source:SA Potoncs)

10 DEPT OF eE, BMSIT


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ACOUISITIN

Beamwidth

Uncerait

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AND TRACKING

here are three basic steps to laser communication: acquisition, tracking, and

communications. Of the three, acquisition is generaly the most dicult; angular

tracking is usually the easiest ommunications deends on bandwidth or daa rate bu

is generally easier than acqusition unless very hgh data rates are required cquisition

is the most dicult because laser beams are typically much smaller than the area of

uncertainty Satellites do not know exactly where they are or where the other platform is

located, and since everything moves with some degree of uncertainty they cannot take

vey long to search or the reference is lost nstablity of the Platforms also causes

uncerainty in time n the ideal acquisition method, shown in Figue4, the beam width

of he source is greate than the angle of uncerainty in the location of receiver. he

receiver eld of includes the location uncertainty of the transmitter.

this ideal method requires a signicant amount of laser power

Unfortunately

ansm Al ofty

igure 5. The ideal acquston meto

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fd w

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It is possible to operate a number of laser types at hig peak power and low

duty cycle to make acquisition easier Ths is because a lower plse rate is needed foracqusiton than for tracing and communicatons.J

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I High peak power pulses more easiy overcome the receiver set theshold andkeep the false alarm rate low A low duty cyce transmitter gives high peak powe, yet

requres less average power and s thus a suitale source for acquisition As the

uncetanty area becomes less it becomes more feasible to use a continuous source of

acqusiton especially if the acquisition time does not have to be sho

OPTICAL NOSE

Noise characteristics play an impotant role in laser communication

systems At optical equencies noise characteristics are signicantly different than

those at rado equences n the R doman quantum nose is qute low whle therma

noise predominates and does not vary wth equency in the microwave regionowever as the wavelength gets shorter quantum noise ncreases lineary, and in the

aser regme thermal noise drops off vey rapidlybecoming insignicant at optical

wavelengths Because there s so tte energy in a photon at radio equences, it taes

many probems to equal the therma nose The quantum noise is actualy the statistical

uctuations of the photons which s the limting sensitivity at optical equenciesI owever in optica recevers employing direct detection and avalanche photodiodes

the detecton process does not approach the quantum mt performance For ths ype of

Ioptica receiver, the therma noise due to the preamplier is usually a signcant

contibutor to the total noise power

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Free space optical communcatio nks, atmospheric turbuence causes

uctuations in oth the intensity and the phase of the received ight signa imparingink performance_ Atmospheric urbuence can degrade he performance of ee-space

optica ins particulary over ranges of the order of 1 km or onger

In homogeneities the temperature and pressure of the atmosphere ead to

variations of the reacive index aong the ransmission path. This inde I

homogeneiies can deteriorate the quaity of the received image and can cause

ucuaions in oth the intensiy and the phase o the received signa

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These ucuations can ead o an increase in the ink error proaiity imiting

the perfonance of communication systems Aeroso scatteing effecs caused y rain

snow and fog can aso degrade the performance of freespace systems The primary

ackground noise is the sun he soar spectra radiance etends om the utra vioet to

he inared wih he pea in the visie portion of he specum

Atmospheric scattered sunight sunit couds the panes, he moon and the

Earh ackground hav simia radiances; the sun's adiance is much higher and a star

eds much ower. A star ed is an area of the sky ha incudes a numer of stars fI one wee ae o oo ony at an individua sar one woud nd righness simiar to

I hat of he sun u a star ed as a whoe is composed of sma point sources of ight

I the stars in he ed, against a dark area having no ackground eve

The ackground is reduced y maing oh the ed of view and the specra

widh as narow as possie or direc detection sysems narrow ed of view specra

ters on the order of 20A *( nm) are typica Heterodyne systems wi enabe rther

reduction u wih an increase in termina compeity However some systems can e

signauanumnoise imied rather than ackgroundimited without having to resor

to heterodyne detecion



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I I SYSTEM CHARACTERISTICS AND DESCRIPTION

Here we dscuss specic key sysem characerstcs whch, which when

quaned ogeher gve a dealed descrpon of a ypca councaon sysem. J

Key sysem characersics are idened and subsequeny quanied for a

pacuar apcaon n he s par of hs secon we denfy he key arameers ha

make p a nk abe sng In he second par we w descrbe how a n anayss s

used o provde a descripon of a aser comuncaons cross-nk operaing a 10

s This Qw daa rae is only used as an exampe and gives a pon of reference for

sysems of smar performance

IKey sysem characeriscs or paraeers mus be dened and quaned o

y descrbe e sysem Crica arameers can be grouped in o ve ajor

aegores: ln ransmer cannel recever and deecor parameers Freesace aser

communicaon s a ver exble means o connec end sers o a gband wd daa

newor va groundbased ermnas on op of budings or o bring a variey of daa

services o remoe ocaions via saelle erminals in space

I Exea nuences on he oca nk due o amospherc urbuence andI vbraons n he ansmer's envronmen requre some mehod of beam cono o

sabze he ocal nk and manain a hgh ansmsson rae. Lqud cysa (C)opics can ovde a comac and lowpower soluion o beam conrol in laser

comuncaons sysems



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J LINK PARAMETERS

I The link parameters ae the type of lase, wavelength, type of link, and equiredsigna citeia. Athough vitually every laser type has been consideed at one time ofJ

Ianothe today the lases typically used in ee space lase communicatons system ae

eithe semiconducto laser diodes solid state lases o be ampies/lases Lase;-

souces ae typicaly descibed as opeaing in eithe single o multple longitudinal

modes In single ongitdinal mode opeation the ase emits adiation at a singe

fequency, whie in multiple longitudinal mode opeation multiple eqencies ae emitted Single-mode souces ae equied in coherent detection systems and typically

have specta widths o the orde of to kHz-OMHz Mutimode souces are employed

in diect detection systems and typicay have specta widths om 5 to 10 nm

Semiconducto ases have been in deveopment for the thee decades and have only

recently (within last ve yeas) demonstated the leves of perfomance needed fo

eiabe opeaton as diect souces

Typicaly opeating in the 800-900 nm range galium asenide/gallium

auminium asenide, GaAs/GaAlAs mateial system), their inherently high efciency

approaching 0%) and sma sie made this technoogy attactive Howeve key issues

have been the ietimes, asymmetic beam shape and output powe Research into

integrated phased arays poved to be moe challenging than rst anticipated focing

the use of single emittes and ouput powers in the 00-50mW ange nheent beam comines employing wavelengthdivision multipex o othe techniques wee

employed fo those applications equiing geate powe



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Sod stae lases have oered hghe powe evels and he ablty o operae in

hgh peak powe modes fo acquson. When dode ases ae used o opcally pumpthe lasng meda gace degadaon and hghe overal elaly (compaed o lamppumped sysems) s acheved A vaey o maeas have een poposed o ase

ansmes; howeve, neodymum doped yum aumnum gae (Nd:YAG) s he

mos widey developed Opeaing a 1064m hese ases eque an exeal

modulao eadng o a slgh ncease n complexiy and elaly The modulao

mus e capale o opeang a equed puse aes as wel as handlng he powe levels

om he lase

Wh he apd deveopmen o eesa e communcaons a wde aay oI componens s avaae o poenal applcaon n space These nclude deecosI ases mulpexes ampes dve elecocs opca peampes and ohes

Opeang a 500 nm eum doped e ampes (EDFA) have een developed oI

commeca opcal e comncaons ha oe levels o peomance cossen

wh may ee-space lase communcaos appcaons (00m age) Issues hee

evolved aoud he space quacao o eesal compoens ad he dese oI acheve as much peomance (e lase powe) as possle o keep elescope apeues

J small

hee ae hee asc k ypes acquson ackg ad commucaos he

majo deeces eee he k pes ae eeced n he equed sga cea oJ each Fo acquson he cea ae ypcally he acquson me ase alam ae

poay o deeco ad a mulpe deeco scheme s used how many

deecons m (o he oa nume possle n) ae equed o he ackng lnk he key

consdeao s he amoun o angle eo nduced y he eceve ccuy

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This angle eor is commonly efeed to as nose effective length (NEA), an

depends on the signal-to-noise atio (SNR the angula sensitivity o the ackng

detecto, and the chaacteisics of the tacking contol loops. Fo the commnicatons

ink the key consideations ae te eqed data and bit eo ates Aso of pime

ipoance, once a ase type is seected, is te odlation oat sed to pess

infomation on the lase caie

,.- '

Figure 6. Poto of 155-_m hgh powe diode lase SO syste by eabeam

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he transmsson parameters consst of certan key laser characterstcs, osses

ncurred n the transmt optical path transmt antenna gan and transmt pontng loss.

The key laser characterscs ncude peak and average optca power puse rate ad

puse wdth In a pused conguraton the peak laser power and duty cycles are

speced whe n contnues-wae appcatons the aerage power s speced. In a

pulsed applcaton the puse rate and wdth descrbe the aser's tempora performance

In contnues-wae appcatons such as coherent communcaton employng equency

sh keyng (FSK) or phase shft keyng (PSK), the puse rate and wdth descrbe the

symbo rate and symbo duraton of the data mpressed on the aser carrer

ransmt optca path oss s made up of optcal transmsson osses and oss due

to the wae-ont quaty of the ransmttng optcs degradng the theoretca fareld

on-axs gan he wae ont eror oss s anaogous to the surface roughness oss

assocated wth anteas he optcal transmt antenna gan s exacty anaogous to

J the antena gan n systems, and descrbes the on-axs gan reate to an soropcradator wth the dstrbuton of the transmtted aser radaton denng the ansmt

antenna gan

he aser sources sutabe to the eespace aser communcatons tend to

exhbt a Gaussan ntensty dstrbuton n the man obe he reducton n the far-eld

sgna strength due to transmtter ms-pontng s the transmtter pontng oss For each

nk n a aser system appontng budget must be determned he pontng budget s

typcally composed of bas (sowy ayng) and random (more rapdy aryng)

components he bas components are the algnment and detector gan msmatch erors;

the random components are the NEA and resdua error due to base moton

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Fo a system employing a Gaussian beam, whee the poining oss is

pedominanty a bias the on-axis tansmitted gain-pointing oss podct is maximized

when the/e2 beam width s set equa to, appoxmately 2.8 times the pointing eo

Inceasing antena diamete the (deceasing the e beam wth) wi degrade

pefomance Wen ponting eo s a combination of bias ad andom tems a

somewhat moe compex expession must be evauated. The point to stess hee is that

once the ponting eo is detemned the system beam width must be sed

appopiatey

_ CHANNEL PARAMETERS The channe paametes fo an optca nte sateite ink (S) consist of the! ange and assocated oss backgound specta adance and specta iadance. Snce

-J ths ace deas with SLs osses due to the atmosphee ae not consideed These

osses can be qute age and mitgaton of the effects compex. The ange oss is simpy

RL (/(4pR2, whee R is the sepaaton between the two patfoms in metes and 1 is=

the waveength The backgound eve depends on the eative atitdes of the patfoms

Ithe time of the yea and the waveength seected

IRECEIVER PARAMETERS

The eceive paametes ae the eceive antenna gain the eceive optica path

oss the optica te bandwdth and the eceive ed of vew The eceive antenna

gan s gven by GR (PDR) 2 whee D s the effectve eceive diamete diametes in=

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r1 The receive optical pah oss is simply the optical tansmission oss fo

systems employig diect detection techniques. Howeve, fo ase systems employing

coheent optica detection (ehe homodyne o heteodyne) thee is an additional loss

due to wave ont erro The pesevation o the wave ont quaity is essential fo

optical mixing of the eceived signal and local oscillato elds on the detecto sufaceI

To st ode the oss expession is the same as that peviousy dened fo the ansmit

wave font eo The optical lte bandwidth species the spectal width of the narrow band pass lte employed in optical inte satellite inks Optical lte edce the amont

of nwanted backgound enteing the system The optica width of the te mst be

compatibe with the spectal width of the lase soce In addition to soce

consideations, the minimm width also be detemined by the acceptable tansmission

level of the lte; typicaly the tansmission of the lte deceases with specta width

he na eceive paamete to be discssed is the angula eld of view

(FOY in adians which imits the backgound powe of an extended soce incident

on the detecto To maximize backgond ejection the FOY shold be as small as

possibe since fo he tpaly small angles consdeed 1 mad h backgond

powe incident on the detecto is popotional to FOY oweve the minimum FOY is

limited by optical design constaints and the eceive pointing capability

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DETECOR PARAMEERS

The detector parameters are the type of detector, gain o the detector (f any)J quantum ecency heterodyne mxng efcency(for coherent detecton only) nose

due to the detector nose due to the followng preampler and (for track lnks) anguar

J senstvty or slope factor of the detector

For optcal ISLs based on semconductor laser dodes or Nd: a Y AG laser thedetector of choce s a p-tpe-ntrnscntype (PN) or an avalanche photo dode (APD).

A P photodode can be operated n the photovotac or photoconductve mode and

has no nteal gan mechansm AnAPD s always operated n the photoconductve mode and has ntea gan by

I vre of the avalanche multplcaton process At shorer wavelengths (SI0-900 nm)

PINs and APDs made of scon show the best response but at onger waveengths

(13001550 nm) InGaAs and Ge APDs have sgncantly more excess nose than

comparable slcon devces For applcaton requrng gan and operatng at Nd YAG

waveengths scon APD s tpcay peee becaue of ts ntea gan However f gan s not requred an InGaAs PIN woud be preferred because of the hgher quantm

efcency The quantum ecency h of the detector s the efcency wth whch the

detector convers ncdent photons to electrons The ean output curent for both PINs

and APDs s proporonal to the quantm ecency

By denton quantum efcences are always less than unty For scondetectors operatng at GaAlAs wavelengths h 0.S50.9, whle at the Nd YAG=

-wavelength h maybe only 04 For InGaAs etectors operated at InGaAsP and NdAG

wavelengths h s about OAnother detector parameter to consder s the nose due to

the detector alone Typcally n detector there s a DC current even n the absence of

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sgnal or background. Ths DC "dar current, as t is commonly caled produces a

shot-nose current just as he sgnal and bacground currents do.

In an APD there are two contrbutors to the toal dar current: an unmulpled

I crrent and a mtped current. The multpcaton s provded by the avalanche gan

mechansm and as expected, for ypcal operatng gans (>50) the multpled term s

domnant In a PIN photodode here s only the nmltpled term The output of the

detector s npu to a preampler that converts the detector sgnal current no a voltage

and ampes t to a worale leve for rther processng. Beng the rs element pas

the detector, the nose due to the preampler has a sgncant effect on te system's

senstvty he selecton of preampler desgn (transmpedance or hgh mpedance)

I ntea transstor desgn (bpoar or FE), and devce materal (GaAs or slconI depends on a nmber o actors Transmpedance desgns have greater dnamc range,I' bt are nomnally less senstve than hghmpedance desgns

Eremely hgh bandwdth and large normaton throughput s avaable many

tmes greater than R communcaton Modulaton of helm-Neon laser (equency 4.7

x 104 rests n a channel bandwdth of4700 GHz, whch s enogh to carr a mllon

smutaneos V channel

Smal antenna sze reqres ony a smal ncrease n weght and volume of the

satelte hs reduces blocage of eds of vew of most desabe areas on satetes.

Laser satelte communcaton eqpment can provde advantages of 3: 1 n mass and 2 I

n power relatve to mcrowave systems narrow beam dvergence affords nterference

ee and secure operaton The exstence o laser beams cannot be deected wth

J specrum analyzers



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AN EXAMPLE

Hee we give a simple example of hoe the parametes jus descibed ae used in

link analysis to design a lase communicaions system caable suppoting a ll duplex

Mb/s geosynchonous obi cosslink. The detaied link analysis is no coveed in

this aticle but employs he entie element desced aove o size the system,

howeve a lnk analysis fo the communicatons nction was pefomed.

he souce peak powe equemen3

dB of the system magIn wasdetemined to be 0.6 W A semiconduco lase dode eam combine is assumed fo he

ansmitte souce employing fou lases at 150 mW each A 5 n apetue was

deemined to poduce a beam wdh compaible wih he ne-tack poning budget of

4 ad he poinng budge was detemined by assumng a acking sysem

employing boh ne-steeing mios and a gimballed elescope he tansmi and

eceive optics efciencies ae epesenaves of nominal values achievable otally in

simila sysems Silicon bipola tansisos may come om a moe maue echnology

bu GaAs FEs have a highe bandwidh capabiliy and ae inheenly adiaon

esistan

he peak eceived signal powe was detemined to be l64 nW om the

assumed paamete values gven he diode lase souce is modulaed diecly in a

Manchese modulaion fomat by changing he dive cuen to he diodes he link

employs a ae 1 constain length 7 convolutional code wih Viebi decoding and

had decsons his pemits he link to opeate a a highe channel symbol eo ae

( 4), but sll poduce a decoded b eo ae of 0-6 the code employed yields

appoxmately 2 dB of codng gan fo diect detection lase communcations link A

quadan APD was selected as he deeco because of its compactness high eliability



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and high sensiiviy (compaed o a PIN phoodiode). he desied counicaions

signal was obained y summing he fou quadrans I is assumed ha 06W of lase

powe is adequae o suppot he acquisiion and tack ncions This example IS

epesenaive o a ypica ase communicaions sysem fo saelie applicaions1

ALCATOS,- Depending on he climaic zone whee he ee space lase communicaions

sysems ae used, hey can span disances up o 15 km a low bi aes o povide bi

aes up o 22 Mps a shoe disances he sysems ae poocol anspaen allowingJansmission of digial compue daa (LAN ineconnec, video, voice ove IP,

Imulipexed daa o AM hey ae suiable fo empoay conneciviy needs such as

1a convenions spoing evens copoae and univesiy campuses, disase scenes o

miliay opeaions

ADVATAGES AD DSADVATAGES

II

Fee space lase communicaions links eliminae he need fo secuing igh of

J ways and buied cable insallaions As he equipmens opeae wihin he nea inaed specum hey ae no subjec o govemen icensing and no specum fees have o be

paid accoding o . 7 in [3] equies ony he use of he equency specum below

3'000 GH a licence Addiionally since no adio inefeence sudies ae necessayhe sysems ae quickly deployable he naow lase eam widh pecludes inefeence1

Jwih ohe communicaion sysems of his ype Fee space lase communicaions

sysems povide only ineconnecion beween poins ha have diec lne-of-sigh11

hey can ansmi hough glass, howeve fo each glass suface he ligh inensiy is

educed due o a mixue of absopion and eacion hus educing he opeaional

I



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,distance of a system. Occasionally, sho inteuptions or unavailability events lasting

fom some ous up to a few days can occ

CONCLUSIO

The system and component technology necessay fo success inte

satellite lase communication link exist today The gowing equiements fo efcient

and secue communications have led to nceased inteest in the opeational deployment

of lase coss lnks fo commecial and miitay satellite systems in both low eah and

geosynchonous obits With the damatic incease in the data handing equiement fo

satellite communication sevices lase inte satellite links offe an atactive alteative

to R with viually unlimited gowth potential and an unegulated spectm The

demonstation pogams undeway in he United States Euope and Japan will show

the way fo tue lage-scale applications of lase communications to satellite coss

links

Jrl

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I 25 DEPT OF TeE, BMSIT

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, REFERENCES

1 I communicatons Magazine. Augst 2000 free space laser communications:Laser cross-ink systems and technology by David L Begley, Ball Aerospace &technologies coporation.

2 Chaotc ree-Space Laser Communcaton over a Turbulen Channel By N FRulov 1 M A Vorontsov and ling institute for Nonlnear Scence Universiy ofCalifoia San Diego La Jolla Califoia 92093 Army Research aboratory AdelphiMaryland 20783

3 ree Space Optcsor Laser Communication through the Air BY Denns KllngerOptics

&

Photonics News_

October 2002

4. Hgh datarate laser transmtters for freesace laser Communcatons BY AI Biswas H Hemmat and J R Lesh Optical Communications Group et Propulsion

Laboratory Califoia Institute of Technoogy

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