Laser Laser CommunicationCommunication

What Is Laser Communication?What Is Laser Communication?

Laser communications systems are Laser communications systems are wireless connections through the wireless connections through the atmosphere. They work similarly to atmosphere. They work similarly to fiber optic links, except the fact that, fiber optic links, except the fact that, in lasers, beam is transmitted through in lasers, beam is transmitted through free space. free space.

LLightight

AAmplification bymplification by

SStimulatedtimulated

EEmission of mission of

RRadiationadiation

Free Space Laser Free Space Laser CommunicationCommunication

► Transmitting information via a laser beamTransmitting information via a laser beam VideoVideo DataData SoundSound

► Terrestrial / Space based systemsTerrestrial / Space based systems

010001100110111011001111001010000010101110010001111001011011

How Does it Work?How Does it Work?

Signal Transmitter

Receiver Signal

Laser

laser

Photo resistorPhoto resistor

High Level designHigh Level design

Conditioning MCU MCU

ConditioningConditioning

UART UARTA

/D

PO

RT

Laser DiodeLaser Diode

What is the Transmitter?What is the Transmitter?

►The transmitter involves:The transmitter involves: Signal processing electronics Signal processing electronics

(analog/digital)(analog/digital) Laser modulator Laser modulator Laser (visible, near visible wavelengths)Laser (visible, near visible wavelengths)

RUBY LASER

Laser DiodeLaser Diode

Laser Diodes include Photodiodes for feedback to insure consistent output.

ModulationModulation

►AMAM Easy with gas lasers, hard with diodesEasy with gas lasers, hard with diodes

►PWM (Pulse Width Modulation)PWM (Pulse Width Modulation)►PFM (Pulsed FM)PFM (Pulsed FM)

Potentially the highest bandwidth Potentially the highest bandwidth (>100kHz)(>100kHz)

What is the Receiver?What is the Receiver?

►The receiver involves:The receiver involves: Telescope (referred to as ‘antenna’)Telescope (referred to as ‘antenna’) Signal processorSignal processor DetectorDetector

Often both ends will be equipped

with a receiver and transmitter

--PIN diodesPIN diodes

-Avalanche Photo Diodes (APD)-Avalanche Photo Diodes (APD)-Single or multiple detectors-Single or multiple detectors

Avalanche photodiode-2Avalanche photodiode-2

Stabilisation of working point of APD:.

Gain =75Temperature stabilisation.

Thermoelectrically cooler stabilisation

system is inside of APD module

AVALANCHE PHOTO DIODE

System ComparisonSystem Comparison(OC3 1km products)(OC3 1km products)

OpticalAccess ICS LightPointer

Transmit Power (mW) 10 (10 dBm) 100 (20 dBm) 4 (6 dBm)

Beam Diverg (mrad) 2.5 11 3

Receive Area (cm^2) 52 232 200

Min Recv Power (nW) 100 (-40 dBm) 32 (-45 dBm) 50 (-43 dBm)

Price $19.5k $25k $24k

Why Laser Communication?Why Laser Communication?

► Current high speed communications Current high speed communications technology:technology: RadioRadio Fiber OpticsFiber Optics

Laser Link GeometryLaser Link GeometryCritical Design ParametersCritical Design Parameters

Beam Divergence = 3 mrad

Diameter = 3 m

Beam area = 70686 cm2

Distance = 1km

Receive area = 200 cm2

Transmit Power

Receiver sensitivity

►Not always possible to lay fiber linesNot always possible to lay fiber lines SatellitesSatellites Combat zonesCombat zones Physically / Economically not practicalPhysically / Economically not practical EmergenciesEmergencies

LC being incorporated into fiber optic LC being incorporated into fiber optic networks when fiber is not practical.networks when fiber is not practical.

Why not Fiber Optics?Why not Fiber Optics?

► BandwidthBandwidth for Laser Communication (LC) is 100 times greater for Laser Communication (LC) is 100 times greater

than for RF.than for RF.

► PowerPower in LC is directed at target, so much less in LC is directed at target, so much less

transmission power required. Also the power loss transmission power required. Also the power loss is less.is less.

► Size / WeightSize / Weight LC antenna is much smaller than RF.LC antenna is much smaller than RF.

► SecuritySecurity Due to low divergence of laser beam, LC is more Due to low divergence of laser beam, LC is more

secure than RF.secure than RF.

Why not RF?Why not RF?

Current Applications Current Applications

►Defense and sensitive areas. Defense and sensitive areas. ►At airports for communication across At airports for communication across

the runways.the runways.►Mass communicationMass communication

►400 TV channels400 TV channels►40,000 phone conversations40,000 phone conversations

►NASANASA Satellite - satelliteSatellite - satellite Earth - satelliteEarth - satellite Earth

Groundstation DescriptionGroundstation Description► Control System (data and tracking)Control System (data and tracking)► Telescope & LASER MountsTelescope & LASER Mounts► LASER & Transmission OpticsLASER & Transmission Optics► Receiving Package (photodetector)Receiving Package (photodetector)

•Utilize Science Team’s Telescope & Processing Capability for LASER Communication•Transmission & Receiving Package.

Satellite Description

Uplink/Downlink Data Uplink/Downlink Data Processing SequenceProcessing Sequence

Bits Bit Encoderto Symbol LASER

TransferOptics

Channel(Atmos.)

ReceivingOpticsAmplifier

Symbol Recovery

Error Correction

Bits

Opportunities For Student Involvement

•LASER Research

•LASER Modulation Circuitry

•Encoding/Decoding Circuitry

Contact InformationContact Information

•Matthew Johnson (mjohnson@u.arizona.edu)• Freddy Valenzuela (acv@bigdog.engr.arizona.edu)• Http://www.physics.arizona.edu/ssp/sti

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