under water optical communication

7/25/2019 under water optical communication

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A Technical Seminar report on

Underwater optical communication

Submitted in partial fulfillment of the requirements for the award of the degree of

BACHELOR OF TECHNOLOGY

InELECTRONICS CO!!UNICATION ENGINEERING

By

YELGAN"ULA #RATHYUSHA $%%&$A'(%)

"E#ART!ENT OF ELECTRONICS CO!!UNICATION ENGINEERING

*YOTHISH!ATHI INSTITUTE OF TECHNOLOGY

SCIENCE+Appro,ed -. AICTE/New "el0i1 A22iliated to *NTU/H.dera-ad3

Nu4tulapur1 5arimna6ar/7'7()$

%'$%/%'$8


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*YOTHISH!ATHI INSTITUTE OF TECHNOLOGY

SCIENCE+Appro,ed -. AICTE/New "el0i1 A22iliated to *NTU/H.dera-ad3

Nu4tulapur1 5arimna6ar/7'7()$

"E#ART!ENT OF ELECTRONICS CO!!UNICATION ENGINEERING

CERTIFICATE

This is to certify that the project work entitled UNDERWATER OPTICAL

COMMUNICATION is a bonafide work carried out by YELGANDULA

PRATHYUSHA, bearing Roll o!"12271A0428, in partial fulfillment of the

requirements for the degree of #BATCHELOR OF TECHNOLOGY in

#ELECTRONICS & COMMUNICATION ENGINEERING by the $awaharlal

ehru Technological uni%ersity, &yderabad during the Academic year #201!201"#

The results embodied in this report ha%e not been submitted to any other

'ni%ersity for the award of any degree or diploma!

HO"

#ro29 "9RA:I5IRAN BABU !9Tec01 !ISTE

#ro2e44or Head

"epartment o2 ECE


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CONTENTS;

1. ABSTRACT

2. INTRO"UCTION

3. O#TICAL CO!!UNICATION

3.1 Free space optics communication concepts

3.2 Optical water parameters

3.3 Evaluation criterion for optical communication

3.4 Figure of merit for underwater platform

4. BASIC CO!#ONENTS AN" BU"GETS OF

UN"ER


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(.1. )ardware setup

(.2. *ir results

(.3. Underwater results

&9 CONCLUSION

)9 FUTURE


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1. ABSTRACT

T&is report presents t&e work accomplis&ed during a 'emester pro+ect at t&e ,-R

#aorator/ of E%F#. T&is pro+ect aims at implementing an underwater optical

communication s/stem etween a root and a surface platform for video transmission.

Firstl/ we present t&e fundamental p&/sics of different waves0 t&en we discuss and

compare t&e pros and cons for adopting different communication carriers acoustic

radio and optical and t&e final c&oice in optical communication. To estalis& an

underwater communication s/stem we develop an optical s/stem comining t&e

"anc&ester modulation wit& 3 att &ig& power lig&t emitting diode emitting lig&t in

lue part of visile spectrum. T&is report s&ows t&e design and e5perimental results in

air and underwater.

%9 INTRO"UCTION;

ireless underwater communication is a c&allenging task. "ost commonl/ used

met&ods w&ic& are well estalis&ed for digital communication in air do not work in

water.

6onventionall/ underwater communications are ac&ieved using an acoustic

met&od. *coustic communication is t&e most versatile and widel/ used tec&ni7ue in

underwater environments due to t&e low attenuation of sound in water. T&is is especiall/

true in t&ermall/ stale deep8water settings. On t&e ot&er &and t&e use of acoustic

waves in s&allow water can e adversel/ affected / temperature gradients surface

amient noise and multipat& propagation due to reflection and refraction. T&e muc&

slower speed of acoustic propagation in water aout 1!99 m:s compared wit& t&at ofelectromagnetic and optical waves is anot&er limiting factor for efficient

communication and networking.

*vailale radio modules operate in t&e ); range t&e attenuation in water for

&ig& fre7uenc/ radio especiall/ in electricall/ more conductive salt water is e5tremel/

&ig&. * wa/ around t&is is using ultra low fre7uenc/ long wave radio for w&ic& t&e

attenuation is manageale ut t&e ma5imum andwidt& is significantl/ limited.


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Optical communication s/stems can &ave s&orter ranges ecause of greater

attenuation of lig&t propagating t&roug& water t&e/ ma/ provide &ig&er andwidt& up

to several &undred


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>9 O#TICAL CO!!UNICATION;

-n t&is 6&apter we s&ow t&e optical c&aracteristics in air and

underwater conditions. T&e intention of t&is c&apter is provide t&e t&eoretical ase for

anal/;ing our final design and e ale to develop it t&oug&t t&ese parameters.

3.1. FREE '%*6E O%T-6' 6O""U>-6*T-O> 6O>6E%T'=

Free space optics F'O is a line8of8sig&t #O' link t&at utili;es t&e use of

lasers or lig&t emitting diodes #E$s to make optical connections t&at can

send:receive data information.

F'O &as attractive c&aracteristics of dense spatial reuse low power usage per

transmitted it and relativel/ &ig& andwidt&. #E$?s lasers p&oto detectors are

availale toda/ c&eapl/ and in large volumes.

T&e main disadvantage of F'O communication is t&at t&e transmission

medium is uncontrolled. T&e effects of atmosp&eric distortions scintillation weat&er

and attenuation can onl/ e minimi;ed or compensated / t&e transmitter:receiver

&ardware. -ssues for F'O communications are listed in t&e Tale 2.1

A-4orption radual loss in intensit/ of an/ kind of

flu5 t&roug& a medium due to wavelengt&

dependent particle asorption in t&eAli6nment I44ue4 #O' eams are ver/ narrow w&ic& causes

ma+or issues wit& alignment. Tracking is

re7uired for moving links and even on!ulti/#at0 di4per4ion T&e pat& a p&oton takes is ideall/ a

straig&t line ut due to scattering t&ep&oton ma/ e redirect several times

#0.4ical O-4truction4 #iving organisms t&at enter into t&e

eams pat& causing dropping of it or

Scatterin6 #ig&t eing redirected / particle roug&l/

same si;e as t&an t&e propagating

Scintillation Tur-ulence @ariation of t&e refractive inde5 along t&e

propagation pat& caused / temperature

and densit/ variations leading to large

Ta-le >9$ I44ue4 2or FSO communication7


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3.2. O%T-6*# *TER %*R*"ETER'=

To consider t&e design of underwater optical communications s/stems for

propagation of lig&t in water and t&e lig&t noise ackground we must first develop

two asic lig&t8in8water attenuation parameters.

T&e first of t&ese is t&e eam attenuation coefficient designated / c w&ic&

descries t&e attenuation of a collimated eam of lig&t.

It I9 e5pAc( E7uation 2.1

w&ere -9B t&e original lig&t irradiance watts:m

2

-tB t&e transmitted irradiance

;B t&e pat& lengt&.

Fi6ure >9$ Illu4tration o2 -eam attenuation coe22icient

T&is parameter is wavelengt& dependent wit& t&e minimum value in t&e

optical transmission window of water around 4C9 nm for clear ocean water and &as a

values of 9.92 m81

.

Fi6ure >9% Spectral attenuation coe22icient 2or optical radiation%


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T&e second of t&e asic lig&t in water attenuation parameters is designated / < and

descries t&e attenuation of diffuse lig&t.

It I9 e5pA)( E7uation 2.2

w&ere -9B t&e original lig&t irradiance watts:m2

-tB t&e transmitted irradiance

;B t&e pat& lengt&.

Fi6ure >9> Illu4tration o2 di22u4e attenuation coe22icient%

T&is parameter is especiall/ useful for calculating t&e attenuation of sunlig&t

in ocean waters for ackground noise calculations. @alues of < are classified

according t&e so8called Derlov water t/pes w&ic& range from t&e clear oceanO and

coastal water t/pes6.

Fi6ure >9( *erlo, Ocean and coa4tal 5 4pectra%


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T&is parameter is also wavelengt& dependent wit& t&e ma5imum transmission

s&ifting from aout 4C9 nm in t&e lue portion of t&e spectrum for t&e clearest ocean

water wit& a minimum value of < aout 9.992 m81

.


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3.3. E@*#U*T-O> 6R-TER-O> O%T-6*# 6O""U>-6*T-O>=

T&e main parameters in underwater communications are s&own in t&e

evaluation criterion for optical communication= 'ignal8to8noise '>R noise

e7uivalent power >E% and it rate ,R.

T&e '>R is defined as t&e ratio of a signal power to t&e noise power

corrupting t&e signal

*t SR

eA3)

r

+2

cos

E7uation 2.3

tan2

4r

2

*

Fi6ure >97 Illu4tration o2 SNR e?uation4

T&is e7uation assumes t&e eam pattern of t&e transmitter is a constant for

angles up to t&e 38d, &alfwa/ point and ;ero e/ond t&at angle.

T&e ,R is related to '>R

2

Transmitter "edium Receiver


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2qSPbg BWen F

2qSPsig BWen F

BR B- log.1 SR E7uation 2.4

&ere , is t&e s/stem andwidt& and t&e ot&er terms are defined as aove.

T&e >E% is given / a summation of several noise terms. T&e first of t&eseterms is t&e amient lig&t ackground s&ot noise. To calculate t&is noise term we first

calculate t&e upwelling solar radiance #sol

/sol R/fac

e5pA)+

E7uation 2.!

T&e optical power on t&e detector is given /

2+

21012

2/

*gb sol

1(

E7uation 2.(

T&e >E% of t&e solar ackground s&ot noise is given /

*bgGsn

S

E7uation 2.H

#ikewise t&e >E% of t&e signal s&ot noise is given /

*sigGsn

S

E7uation 2.I


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(2qIdark detG 2F 21I )BW dcen

In _ amp BWen

P2

bg _ snsig _ sndark _ snamp _ nP2P

2P

2

&ere %sig is Optical power of signal.

T&e >E% of dark current s&ot noise is given /

*darkG

sn

S3det E7uation 2.C

T&e >E% of t&e preamplifier is given /

*ampG n S3d

etE7uation 2.19

&ere -nGamp is t&e preamplifier current noise

densit/. Finall/ t&e total >E% is given /

*tot

E7uation 2.11

E%total we are ale to calculate '>R and ,R. -n t&ese underwater

optical s/stems andwidt&s of up to several &undred kps ma/ e ac&ieved.

3.4. F-URE OF "ER-T FOR U>$ER*TER % # * T F O R " =

T&e use of figure of merit FO" for underwater communication &as

primaril/ +ust focused on=

3.4.1. %ower of t&e transmitter

3.4.2. #oss of t&e medium

3.4.3. 'ensitivit/ of t&e receiver

E7uation 2.12


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Firstl/ t&e FO"T5 is determined /

bit

Amp &our*latform+ensity&w1

4assplatform2olumeplatform Surface Areaplatform


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014t5 sec

*owert

5

E7uation

2.13

Amp &ourT6 system +ensityT5 4assT52olumeT5

SurfaceAreaT5

bitRange

T&e first term se c

*owert5

-s appropriate if t&e power and s p a c e

Range


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6onstraints of t&e platform are not considered. ,its per second times range is t&e it

rate lengt& product discussed aove. is t&e solid angle of t&e emitter for isotropic

acoustic s/stem t&is can e 4. T&e %owerT5 is t&e amount of power t&atis supplied

to t&e transmitter t&us it is t&e amount of power t&at is devoted to making using opticalor acoustic power to send information.

T&e second termAmp &our*latform+ensity&w1

4assplatform2olumeplatform Surface Areaplatform

Amp &ourT5system +ensityT5 4assT52olumeT5

SurfaceAreaT5

e5press t&e impact of weig&t and si;e of t&e s/stem on t&e overall platform. &ere

*mp )ours%latform is t&e numer of availale *mp )ours in a powerlimited s/stem

@olume%latform and 'urface%latform are t&e availale volume and surface area of t&e

platform. *mpsT5s/stem is t&e total electrical current in amps including

computational power for signal processing.

'econdl/ t&e FO"Environ is determined /

014n%iron f -a%elengthabsorptionscatteringetc... SolarGBackground E7uation

2.14

T&is term e5pressed in d,:m is independent of t&e p&/sical c&aracteristic of t&etransmitter and receiver platforms ut does consider t&eir relative p&/sical positions in

t&e environment and t&e impact of water t/pe and time of da/ solar ackground.

For t&e optical s/stems t&e asorption and scattering model gives t&e magnitude

of t&e functionf for attenuation8limited s/stems. T&e effects of solar ackground are

dependent on t&e geometr/ ut are asicall/ t&e reduction in '>R due to s&ot noise on

t&e receiver.

Finall/ t&e FO"R5 is determined /


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bitrate Aperture012Amp&our*latform+ensity&w1

4assplatform2olumeplatform SurfaceAreaplatform

014t5

E7uation

2.1!

*ower

R5

Amp&ourR5system +ensityR5 4assR52olumeR5

SurfaceAreaR5

T&e FO" is similar to t&e transmitter instead of considering t&e solid angle oft&e emitted eam t&e field of view FO@ of t&e *perture is considered. * certain

amount of optical energ/ per it is re7uired to &ave a detectile signal and is

e7uivalent to t&e it8rate divided / t&e receiver power.


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Inputsignal

!dulat!r "ri#er $%" $ens

(9 BASIC CO!#ONENTS AN" BU"GETS OF UN"ER'"-TTER=

T&e asic components of t&e underwater optical communication transmitter

are

%latform window

Fi6ure (9$ Component4 o2 underwater communication tran4mitter

For t&e transmitter we &ave t&e modulator w&ic& modulates of t&e input signal. T&is

modulation can e software or &ardware.

T&e driver is necessar/ to transmit t&e signal to t&e #E$ in t&e rig&t fre7uenc/ and

amplitude.

>ewl/ developed &ig& power #E$s emit sustantial lig&t and are t/picall/ ver/ ine5pensive.

6urrentl/ #E$' can emit up to several watts of power into an angle of several tens of degrees.


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&utsignal

Plat'!rm ind! !llect!r "etect!r Signal pr!cessing "em!dulat!r

T&e lens collimated allow efficientl/ collimate t&e lig&t into a determinate eam wit& more

precision.

T&e transmitted lig&t eam e5its t&roug& t&e platform window into t&e water.

4.2. RE6E-@ER=

T&e asic components of t&e underwater optical communication transmitter

are

Fi6ure (9% Component4 o2 underwater communication recei,er

*t t&e receiver located on anot&er platform t&e eam enters t&e platform window after

eing attenuated / t&e water medium.

T&e received lig&t after t&e window going t&roug& t&e collection optics onto t&e detector.

T&e detector is a p&otodiode1 a t/pe of p&otodetector capale of converting lig&t into eit&er

current or voltage depending upon t&e mode of operation. 6OT' p&otodiodes suc& as avalanc&e

p&otodiodes *%$s can e used as detectors w&ic& can respond to pulses as narrow as several

nanoseconds. T&e p&otodiode needs to &ave a alance etween speed and sensitivit/.


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T&e signal processing stage takes t&e current from t&e p&otodiode. T&is is preamplified / a

transimpedance amplifier T-*. *fter t&at t&e signal is filtered amplified and processed.

T&e demodulator reali;es t&e demodulation of t&e input signal. T&is modulation can e

software or &ardware.

4.3. U>$ER*TER O%T-6*# #->< ,U$ET=

*fter e5posin a asic description of an underwater optical communication we

can s&ow t&e udgets in t&is kind of s/stems. eat&er wavelengt& of t&e #E$

distance etween emitter and receiver underwater currents scattering attenuation

asorption detectors and data rates are +ust a few of t&e t&ings t&at must e

considered.

T&e main motivation of t&is pro+ect was to uild an underwater link model

after anal/;ing t&e different communication t/pes t&e conclusion was t&at t&e optical

communication is t&e most useful in t&is case &owever as descried aove scattering

and variale optical 7ualities need e considered. T&ese var/ing properties c&ange

wit& time and location w&ic& in turn could affect t&e amount of lig&t lost.

T&e main optical properties t&at can influence communication are summari;ed

in t&e diagram elow.


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Wa#elengt*

"ept*

Water type(Geographic location)

$arge Particle!ncentrati!n

Pr!babilit+Functi!ns

Scattering

!e,cients

Seas!n

Small Particle!ncentrati!n

*l!r!p*+ll!ncentrati!n

-umic .cid!ncentrati!n

Ful#ic .cid!ncentrati!n

Organic Absorption Mechanisms

Pure ater

.bs!rpti!n and Scattering

Total Attenuation Absorption ! "cattering

Fi6ure (9> Functional -oc@ dia6ram o2 t0e total attenuation underwater7


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/ransmitter Inputs edium Inputs 0ecei#er Inputs

tput P!er 0ise /ime Beam "i#ergence urrent "ra !ltage Suppl+$ine Widt* P!inting $!ss

/ $%3S

4uantum %,cienc+ &ptical 0esp!nsi#el+ .rea

$%3S 0

Water /+pe 0ange "ept* Seas!n Wa#elengt**l!r!p*+ll 7 .cid !nc7 Particle !nc7

Ind70e'racti!n Scattering .bs!rpti!n

T&ese parameters will e used to construct a power link udget for a t&eoretical

underwater optical link. Furt&ermore t&e optical properties of t&e water will affect t&e

performance of t&e &ardware used.

-n addition to t&ese optical parameters t&e communication s/stems areimportant for uilding a compre&ensive model of t&e optical s/stem.

Fi6ure (9( Bloc@ dia6ram Lin@ Bud6et7

*ccording to t&ese udgets in t&e c&apter ! we will make specific c&oices for

t&e components descries in t&e paragrap&s 4.1 and 4.2.


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79 "ESIGN AN" CIRCUITRY;

T&e asic idea of t&is pro+ect was to create a fast ut relativel/ ine5pensive

wa/ to reali;e an underwater video transmission. T&ere were two parts to t&e pro+ect.

T&e first part is t&e s/stem is t&e electrical circuits including receiver and transmitter.

T&e second part is t&e mec&anical:optical enclosures t&at &ouse t&e lens and copper

o5es containing t&e receiver and transmitter circuits.

!.1. TR*>'"-TTER=

T&e main prolem in an optical transmitter design is t&e upper fre7uenc/ atw&ic& t&e lig&t source can e modulated. 'everal factors limit it t&ese include t&e

time constants fre7uenc/ response of t&e driving circuitr/ t&e p&/sics of t&e diode

itself and t&e c&aracteristics of t&e medium. *ll t&ese factors must e solved t&roug&

a summar/ etween modulation driving and lig&t source.

T&e final transmitter design for an underwater optical communication is

elow.

Fi6ure 79$ Tran4mitter Bloc@ "ia6ram +Up3/Tran4mitter 2inal de4i6n +down3


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T&e full circuit diagram and part list are in *ppendi5 * and , respectivel/.

T&e signal arrives from t&e camera F%* we consider t&is signal w&it a &ig&

7ualit/ so it?s not necessar/ filter it and amplif/ it. ,efore t&e signal is transmitted is

necessar/ modulate it / a ""H4)6I(" JOR ate wit& a clock signal and drive it/ stacking seven H4)694 -6s. T&e signal is t&en read/ for transmission via t&e lue

#E$.

!.1.1. "O$U#*T-O>=

Optical modulation is one of t&e ke/s for reali;ing suc& &ig& performance

optical network. $igital communications emplo/ing #E$ as optical carriers generall/

&aving carrier fre7uencies in t&e "ega&ert; range t&at permit enoug& &ig& modulation

andwidt&s for video transmission.

T&e optical modulation is used to modulate a eam of lig&t converting t&e

electrical signal arra/ into t&e lig&t signal arra/ and including information into t&e

signal.

One t/pe of optical modulation categori;ation is according to t&e wa/ ofotaining t&e modulation of intensit/ of a lig&t eam=

!.1.1.1. $irect modulation= "odulate t&e current driving t&e lig&t source.

!.1.1.2. E5ternal modulation= "odulation performed / a lig&t modulator.

T&e easiest wa/ to reali;e t&e modulation is direct modulation oviousl/ ut

for &ig& fre7uenc/ t&ere are prolems wit&

$epending on t&e parameter of a lig&t eam w&ic& is manipulated t&e

modulation ma/ e categori;ed into=

!.1.1.3. *mplitude modulation

!.1.1.4. %&ase modulation

!.1.1.!. %olari;ation modulation

T&e first step to c&oose t&e rig&t modulation is defining t&e main

c&aracteristics of our communication. -n our pro+ect t&e main reason to use


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modulation is lose of signal detection t&roug& t&e transmitter is in moving alwa/s we

are not going to know if we are receiving a K9? or we lost t&e signal.

'o after stud/ and anal/;e t&e papers t&e conclusion is t&at we need a simple

modulation to &ave t&e ma5imum efficienc/ in t&e transmission. T&e minimal numerof code data is two and t&e most efficienc/ eas/ and useful as we can see in a

commercial model is "anc&ester.

e propose a modulation ased on "anc&ester coded in order to reduce t&e

low power optical fluctuation it is possile implement it t&roug& )ardware and

ecause or signal come from a F%* t&at could give us t&e clock signal necessar/ for

t&e modulation.

T&e data K1? and K9? of "anc&ester code &ave K19? and K91? patterns

respectivel/ it &as less optical power fluctuation t&an -RL sc&eme.

"ata !anc0e4ter Code

9 911 19

Ta-le 79$ !anc0e4ter Codi2ication

T&e "anc&ester code is otained / t&e comination of t&e non8return8to ;ero

>RL data and clock0 it can e easil/ generated wit& an e5clusive OR JOR gate.

"ata Cloc@ Code

9 9 99 1 11 9 1

1 1 9Ta-le 79% S.4tem Codi2ication

-n our s/stem we use a clock wit& t&e doule fre7uenc/ to reali;e t&e

modulation and !9M dut/ c/cle.


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Cloc# ($%)

&ata

&0 Gate

MM'C*+

Enco,ing ,ata

Fi6ure 79% S.4tem Codi2ication

T&e design for t&e modulation is elow. To uild t&e design t&e commercial

JOR gate c&osen was ""H4)6I(".

Fi6ure 79> Codi2ication -loc@ dia6ram

T&e ""H4)6I( EJ6#U'-@E OR JOR gate utili;es advanced silicon8gate

6"O' tec&nolog/ to ac&ieve operating speeds similar to e7uivalent #'8TT# gates

w&ile maintaining t&e low power consumption and &ig& noise immunit/ c&aracteristic

of standard 6"O' integrated circuits. T&ese gates are full/ uffered and &ave a fan8

out of 19 #'8TT# loads. T&e H4)6 logic famil/ is functionall/ as well as pin out

compatile wit& t&e standard H4#' logic famil/. *ll inputs are protected from damage

due to static disc&arge / internal diode clamps to @66 and ground. T&e electronic

c&aracteristics are

T/pical propagation dela/= C ns

ide operating voltage range= 28(@

#ow input current= 1 N* ma5imum #ow 7uiescent current= 29 N* ma5imum H4 'eries


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Output drive capailit/= 19 #'8TT# loads

%ackage t/pe= 'O-6 14

T&e voltage range is appropriate for our design0 in our case we will use ! @.

T&e low input current is necessar/ to &ave a low power in t&e transmitter and t&e

dela/ is acceptale. T&e election of 'O-6 14 is ecause all t&e transmitter was uild

in 'O-6 tec&nolog/.

!.1.2. #E$=

T&e main reason to c&oose as lig&t source of a #E$ is ecause #E$ is an

omnidirectional lig&t source and in our communication s/stem t&e transmitter is in

moving. -n our case we will use a &ig&8powered #E$. Recentl/ &ig&8powered #E$s

&ave een commerciali;ed for applications re7uiring &ig& efficient.

For t&e election of t&e #E$ we must consider t&at for optical communication

purpose t&e following aspects s&ould e considered=

!.1.2.1. Optical wavelengt&

!.1.2.2. Optical output power

!.1.2.3. Reliailit/

!.1.2.4. ,eam parameter

!.1.2.!. #uminous flu5

'uperflu5 #E$s are a revolutionar/ energ/ efficient and ultra compact new

lig&t source comining t&e lifetime and reliailit/ advantages of #ig&t Emitting

$iodes wit& t&e rig&tness of conventional lig&ting.


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T&ere are t&ree #E$ wavelengt&s t&at could e considered for

underwater applications ,lue 6/an and reen

Fi6ure 79( Relati,e inten4it. ,49 wa,elen6t0

T&e wavelengt& c&osen is lue ecause presents a minimal asorption

value underwater.

-n man/ #E$ applications t&e c&aracteristics of t&e output eam are

not t&at important0 &owever in an optical communications s/stem t&e ailit/ to

collimate a eam is ver/ important. T&e 'uperflu5 #E$s &ave a similar setup

as a t/pical #E$ ut adding a good lens wit& t&e epo5/ is possile forming a

collimated eam wit& minimal distortion.

'o after t&e election of lue 'uperflu5 #E$ t&e ne5t step was to

c&oose t&e power. T&e first design was reali;ed wit& a 1.( att 'uperflu5

#E$ ,321I9. -s t&e minimal value possile for a transmission and we can?t

forget t&e emplacement of t&e transmitter an underwater root for t&is reason

t&e electronic power is essential. ,ut t&e results weren?t appropriates ecause

t&e ma5imum distance was 2 cm. T&e possile development was design a lens

s/stem to focus t&e lig&t ut t&e transmission location doesn?t allow locate a

ig s/stem. For t&is reason we decided c&ange t&e #E$ to 3att 'uperflu5

#E$ wit& a commercial lens and tr/ develop t&e lens s/stem in a future

pro+ect.

'o Finall/ t&e 'uperflu5 #E$ use in t&e final design was #J)#8%,9C. T&e ne5t tale s&ows t&e different etween t&e final #E$ and t&e

previous one


29/49

!odel #ower

"i44ipation

+ LE"

compari4on

T&e ad point is t&e power dissipation ut in t&e future we will tr/

developing t&e lens s/stem to use a low power one.

'o t&e final election is t&e #J)#8%,9C #E$ wit& t&e p&/sic c&aracteristics

Ta-le (9( LE" complete c0aracteriation4

*ccording wit& t&e t&ermal indications in t&e datas&eet was necessar/ include a

dissipater in t&e design wit& for t&ermal dissipation.

T&e ""H4)694 inverters utili;e advanced silicon gate 6"O' tec&nolog/ to

ac&ieve operating speed similar to #'8T## gates wit& t&e low power consumption of

standard 6"O' integrated circuits. T&e package is elow.


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Fi6ure 798 HeA in,erter pac@a6e dia6ram9

T&e electric c&aracteristics are elow

e are going to need H99 m* to drive t&e )ig&8powered #E$ so if eac& pin

suppl/ 2!m* we are going to need 2I inverters e7ual to seven packages. 'o t&e

design is seven &e5 inverters in parallel like t&e figure.

Fi6ure 79& Recei,er "ri,er Sc0ematic


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79$9>

LENS;

T&e lenses are for our s/stem like antennas for microwaves t&e gaindependent on #E$ geometr/ and si;e. T&e main prolem is again t&e

transmitter emplacement we can include ig lens in t&e transmitter ecause it

is located in t&e underwater root.

-f t&e transmitter roadcast angle and t&e receiver FO@ are ot&

narrow t&e '>R of t&e received pulse is &ig&er ut t&e pointing accurac/ of

transmitter and receiver is critical. -f &owever t&e transmitter roadcast

angle and:or t&e receiver FO@ is wide pointing is less critical0 '>R is lower

wit& t&e transmitted p&otons spread out into a wider angle and some

covertness could e lost. )owever t&is is proal/ not an issue wit& t&ese

s&ort communications.

For t&is reason we improve t&e effectiveness of t&e optical s/stem

wit& a Fraen acr/lic concentrator on t&e #E$ to create a cone of lig&t wit& an

internal angle of 39 degrees. T&is increases distance ate t&e e5pense of

transmission angle. T&e reduction in t&e transmission angle can e solved

including more p&otodiodes or developing a lens s/stem in t&e receiver.

T&e lens use to t&e final design is F)'8)",18##918;.


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Fi6ure 79) FHS/H!B$/LL'$/ 4c0eme


33/49

'o after appl/ t&e lens we are going to otain a signal wit& a luminous

Fi6ure 79 Luminou4 c0aracteri4tic len4

!.2. RE6E-@ER=

T&e receiver detects t&e lig&t via t&e p&oto detector. T&e low

current signal triggers a dual gate transistor >TE41! w&ic& takes t&e current from

t&e 12 @ rail and transmits it to t&e >E!C2 video amplifier. T&e >E!C2 cleans t&e

incoming rounded signal to a s7uare wave. %in I of t&e >E!C2 is t&e ot&er part of t&e

differential output and carries t&e data stream t&roug& a pre8amp circuit consisting of

a pair of common emitter connected transistor. T&e signal is t&en sent to a 4t&

,utterwort& low pass filter #T1!(I-> and a &ig& fre7uenc/ amplifier.

Fi6ure 79$ Recei,er Bloc@ "ia6ram +Up3/Recei,er 2inal de4i6n +down3


34/49

!.2.1 %)OTO$-O$E=

e tested several different p&oto diodes %$,861!I ,%21 and '#$8

H9,2 and got t&e est results wit& t&e diode '#$8H9,2 w&ic& &as a good trade

off etween speed and sensitivit/.

T&e planar p&otodiode is designed to operate in eit&er p&otoconductive or

p&otovoltaic modes. T&is diode incorporates a , filter t&at re+ects infrared

wavelengt&s and appro5imates t&e response of t&e &uman e/e. )ig& sensitivit/ and

low dark current allow use in low irradiance applications. T&e p&otodiode measures

3.( mm J 3.( mm 9.149 J 9.149 and is supplied on a ceramic ase wit& a clear

epo5/ dome package.

Fi6ure 79$$ #0otodiode dimen4ion4 4en4iti,it.

T&e electrical c&aracteristics of t&e p&otodiode

Ta-le 797 Electrical c0aracteri4tic4 p0otodiode


35/49

-n t&e final design we will implement a design wit& five p&otodiodes to

increase t&e reception area like in t&e figure 4.12.

Fi6ure 79$% #0otodiode location 4.4tem

T&e final value of t&e parameter Pd will depend in t&e ma5imum angular

coverage of t&e emitter and it could e useful in a future application to control t&e

position of t&e surface platform

!.2.2. '->*# TRE*T"E>T=

T&e low current signal triggers a dual gate transistor >TE41!

w&ic& takes t&e current from t&e 12 @ rail and transmits it to t&e >E!C2

video amplifier.

T&e >E!C2 cleans t&e incoming rounded signal to a s7uare wave.

%in I of t&e >E!C2 is t&e ot&er part of t&e differential output and carries

t&e data stream t&roug& a pre8amp circuit consisting of a pair of common

emitter connected transistor.

T&e signal is t&en sent to a 4t&

,utterwort& low pass filter

#T1!(I->. T&e #TQ1!(I is an eas/8to8use active8R6 filter uilding

lock wit& rail8to8rail inputs and outputs. T&e internal capacitors of t&e

-6 and t&e , product of t&e internal low noise op amps are trimmed

suc& t&at consistent and repeatale filter responses can e ac&ieved.

it& a single resistor value t&e #T1!(I provides a pair of matc&ed 28

pole ,utterwort& lowpass filters wit& unit/ gain suitale for -:c&annels.


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,/ using une7ual8valued e5ternal resistors t&e two 28pole

sections can create different fre7uenc/ responses or gains. -n addition

t&e two stages ma/ e cascaded to create a single 48pole filter wit& a

programmale response. 6apale of cutoff fre7uencies up to 19");

t&e #T1!(I is ideal for antialiasing or c&annel filtering in &ig&8speed

data communications s/stems.

Fi6ure 79$> (t0 Order Lowpa44 Filter Butterwort0

*fter t&e filtering it could e possile reali;e an amplification.

-n our case we don?t know t&e power restrictions in t&e surface

platform we decided don?t reali;e t&is stage ecause t&e &ig&

fre7uenc/ amplifier re7uires more power t&an t&e ot&er receiver?s

part.

!.2.3. $E"O$U#*T-O>=

T&e easiest wa/ to demodulate t&e signal is to use a microcontroller. $ue to

time restrictions and since demodulation can easil/ e a part of t&e future work

concerning t&e software of our communication it is not implemented in t&is current

work.


37/49

!.2.4. LENS;

%lano86onve5 %6J #enses &ave a positive focal lengt& making t&em ideal

for collecting and focusing lig&t in imaging applications. T&e/ are also useful in avariet/ of applications involving emitter detectors lasers and fier optics.

Fi6ure 79$7 #lano Con,eA Len4e4

*vailale in a wide variet/ of diameters and focal lengt&s our election wasdiameter e7ual to 1 mm and 6enter T&ickness 6T e7ual 9.! mm. e are going to

use one for eac& p&otodiode.

T&is election is t&e most important in t&e final results ecause t&e final

signal reception is completel/ depended on t&e lens s/stem. For t&is reason we

decided use a standard one to anal/;e t&e results and include t&e improvement of

t&is s/stem in t&e future work ecause t&e main point of t&is pro+ect was t&e

p&/sical electrical la/er and improve t&is point is stud/ing t&e results for differentdiameters.


38/49

89 E=#ERI!ENTAL "ATA;

'i5 e5periments were carried out to measure t&e ma5imum range and coverage of

t&e optical digital link in air and underwater. T&e range is defined as t&e ma5imum distance

etween transmitter #E$ and receiver p&otodiode. Furt&ermore e5periments were

carried out to investigate &ow transfer rate and dut/ c/cle e&ave at distances greater t&an

t&e range of t&e link. T&e e5periment setup and t&e individual results are outlined in t&e

following sections.

(.1. )*R$*RE 'ETU%=

-n order to avoid an/ unwanted interference sender and receiver were p&/sicall/

separated and t&e used wires were s&ort as possile.

For transmission a &ig& fre7uenc/ pulse generator was connected to t&e optical

transmitter w&ic& generate a /te stream. T&e transmitter was powered / a laorator/

power suppl/. T&e receiver circuit was powered / a laorator/ power suppl/ too and

connected to an oscilloscope w&ic& anal/;ed t&e received stream.

T&e closest distance etween emitter and receiver unit was etween t&e #E$ and t&e

p&oto diode. T&e receiver s/stem was fi5ed and to measure t&e range onl/ t&e #E$ was

moved.

For t&e e5periments in air t&e #E$ and t&e p&oto diode were aligned &ori;ontall/

and positioned on a tale wit& a possile reflecting surface ut it was t&e est possiilit/.

T&e e5periments was carried out in normal indoor lig&ting conditions mainl/ fluorescent

tues.

For t&e underwater e5periments we &ad an important limitation we &aven?t a

platform to sumerge t&e s/stem underwater. For t&is reason t&e e5periment was carried out

in a rectangular pool wit& w&ite wall w&ic& 9.91 meters deep 9.(9 meter widt& 1.19 meters

lengt& and t&ickness ! mm in eac& wall as figure !.1 s&ows.


39/49

Fi6ure 89% Emitter co,era6e in air9

T&e receiver and emitter were out of water in t&e walls surface to decrease effects

of t&e reflecting. e reali;e t&e e5periments wit& clear water wit& no visile pollution.

it& t&ese conditions we can do onl/ two distances e5periments wit& 9( meter and 11

meter. T&e e5periment was reali;ed wit& t&e same environmental lig&t wit& t&e

e5periments in air.

(.2. *-R RE'U#T'=

T&e range in t&is conte5t means t&e ma5imum distance etween transmitter and

receiver w&ic& still allows error8free transmission of data. For t&ese e5periments we use

a 4(9 nm lue emitter wit& a forward voltage of 3.H@ and a current of (99m*. T&e

region of interest for t&e e&aviour of transfer rate and error range is from 49 cm and 299

cm.

T&e first e5periment is focused to find t&e most ade7uate rate for t&is we measure

t&e received signal depending t&e emitting fre7uenc/. Figure !.1 s&ows t&e results.


40/49

Fi6ure 89% Emitter co,era6e in air9

*s e5pected t&e range decreases wit& t&e fre7uenc/. T&e final election of t&e

fre7uenc/ will depend of different factors0 one of t&em is t&e t/pe of modulation. T&e

modulation efficienc/ will influence in t&e decision etween rate and range of

application. -f we use a t/pe of modulation like "anc&ester modulation we will emitting

in a &alf of t&e fre7uenc/ reall/ it?s for t&is reason we will e more interested in t&is case

in develop t&e rate efore t&an t&e range. -n ot&er case if we implement a

communication protocol we can dispose around t&e ma5imum efficienc/ in

communication. T&is is going to focus t&e s/stem development in ot&er wa/.

For t&e ma5imum anal/;ed rate 2&; we decided to stud/ t&e dut/ c/cle influence

depending of t&e distance etween emitter and receiver. Figure !.2 s&ows t&e results.


41/49

Fi6ure 89> Emitter co,era6e in air +2D%!H3 ,49 "ut. C.cle

T&e anal/;e of $ut/ 6/cle influence is focused to find t&e etter transmission wit&

t&e minimal power consumption in t&e emitter w&at it?s mean wit& more dut/ c/cle we

&ave etter results due to we are emitting a signal wit& more 1 t&an 9 more lig&t in an/ case.

T&e &ig& power rating permits it to e used in a low dut/ c/cle mode allowing an intense

pulse of lig&t generated for a s&ort period of time ut in our case we &ave a ig power

restriction in t&e receiver t&at pro&iit t&is case. T&e prolem to include &ig& dut/ c/cle is

t&e power consumption in t&e transmitter less t&an &ig& power rating ut enoug& to e

considered.

T&e results in our e5periment s&ow t&at we &ave an optimal value around H98 I9

more pronounced in longer distances.

(.3. U>$ER*TER RE'U#T'=


42/49

T&e prolems t&at we &ave limit t&e trut&fulness of t&ese e5periments ut t&e

final results are logic ecause all t&e e5periments were reali;ed in t&e same situation so

we can take conclusion of t&em.

T&e same e5periments as descried efore were conducted in water ut onl/ in

t&e two distances t&at we dispose. T&e first e5periment is focused to find t&e most

ade7uate rate for t&is we measure t&e received signal depending t&e emitting fre7uenc/.

Figure !.4 s&ows t&e results.

Fi6ure 89( Emitter co,era6e underwater

To our surprise t&e received signal increased even t&oug& t&ere s&ould e

asorption and coupling losses in water and losses in t&e wall. T&e increased intensit/ at

t&e receiver can e e5plained in t&e refle5ion / t&e rig&t pool walls. e also e5pect less

&ig& fre7uenc/ noise disturing t&e receiver in t&e outdoor environment ecause

underwater t&e attenuation in &ig& for t&is range.

T&e important result is t&at clear water attenuation in fres& water does not &ave a

ig impact on t&e range of optical communication in a s&ort range.

For 1 "); and 2"); we decided to stud/ t&e dut/ c/cle influence depending oft&e distance etween emitter and receiver. Figures !.! and !.( s&ows t&e results.


43/49

Fi6ure 897 Emitter co,era6e underwater +2D$!H3 ,49 "ut. C.cle

Fi6ure 898 Emitter co,era6e underwater +2D%!H3 ,49 "ut. C.cleT&e results in our e5periment s&ow t&at we &ave an optimal value around

(IM in (9 cm communication and I(M in 119 cm communication. e can


44/49

0ecei#er

/ransmitter

d

oserve &ow it?s more pronounced in longer distances t&e dut/ c/cle influence in

underwater too.

T&e last e5periment reali;ed was stud/ t&e perpendicular coverage of t&e

emitter w&at it means more or less t&e angular range. e propose c&ange t&e distancePd of t&e figure !.I and anal/;e t&e received signal.

Fi6ure 89& EAperiment 4ituation

T&e figures (.I and (.H s&ow t&e results.


45/49

Fi6ure 89& #erpendicular Co,era6e Emitter underwater +2D$!03

Fi6ure 89) #erpendicular Co,era6e Emitter underwater+2D%!03

*s e5pected t&e lens election is fundamental ecause we lose t&e signal

radicall/ w&en t&e receiver is out of emitter range. -t could e possile amplified t&e

emitter range to (9S ut it suppose less signal in t&e received. e can?t increase t&e


46/49

power alimentation in t&e emitter so t&e development must e centre in t&e receiver

lens stud/ and develop a s/stem like we propose efore in t&e Figure !.14


47/49

&9 CONCLUSION;

T&e presented optical communication s/stem is suitale for underwater

applications since &ig& fre7uenc/ radio wave is &ig&l/ asored in water and

acoustic communication s/stems are relativel/ low andwidt&. e can do a

classification of t&e optical communication s/stems present in t&e iliograp&/ in two

groups. T&e first one present a limitation in si;e ut normall/ t&e power suppl/ isn?t a

&andicap for t&is reason it?s possile implement t&e communication wit& a &ig&8

power #E$. T&e second group present a limitation in power suppl/ and limit t&e

transmitted rate around !99 k); and t&e range in less t&an one metre. Our main

prolem is t&at we cannot include our s/stem in an/ of t&ese groups we &ave an

important si;e limitation ecause our emitter is located in a small root and we can?t

increase t&e range include ig lens as it?s usual to do. -n t&e ot&er wa/ we &ave a

power limitation ecause t&e power suppl/ must e inside t&e root and we can?t

include a 1* power suppl/. For t&ese reasons our pro+ect is inside of a new optical

communication field. it& t&is situation our s/stem presents several limitations due

to lack of stud/ in t&is field and lack of time ut t&e main point is t&at we can sa/ t&at

according wit& t&e results t&is communication is possile to e implementedincreasing t&e stud/ of some points.

T&e e5periments &ave s&own t&at t&e range is not decreased w&ile working in

underwater for t&e lue wavelengt& and &ig& power #E$ emitters can e used for

&ig&8speed optical communication wit& an appropriate lens.

T&e wide angular coverage 39S ecause it?s t&e used lens in t&e transmitter

doesn?t allow more t&an 19 cm range around t&e perpendicular point of movement.'o to allow omnidirectional coverage it?s necessar/ to include an improved lens

s/stem in t&e receiver and a s/stem wit& several p&oto diodes to increase t&e

detection range.

T&e power consumption of 3 in t&e transmitter is t&e ma5imum limit to

include in t&e final emplacement t&e root. 'o for t&is reason it?s necessar/ an

anal/sis aout &ow was possile to increase t&e power consumption. Once t&e lens

stud/ was finis&ed it could e necessar/ to reali;e t&is anal/sis ecause finall/ wemust include a small atter/ and it could e a prolem.


48/49

T&e results depending of t&e rate s&ow t&at depending t&e final s/stem

necessities we will define t&e ade7uate one. T&e e5periments s&ow t&at t&e s/stem

&as a good response in t&e range etween !99 k); and 1.!9 "); could e increase

to 2 "); if t&e lens s/stem was more efficient. 'o &ere we &ave t&e most important

conclusion t&e main point to increase t&e full s/stem must e reali;e a complete

anal/sis aout t&e lens s/stem.

*ccording wit& t&e initial pro+ect re7uirements we &ave completed t&e

electronic &ardware farication w&ic& means design and uild a full underwater

communication s/stem. T&ere are two points from t&e initial re7uirements t&at aren?t

completed t&e farication of an underwater platform to reali;e t&e underwater

e5periments and an anal/sis to determine t&e most efficient lenses s/stem. epropose t&ese points in t&e future work.


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)9 FUTURE

under water optical communication

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