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Light

Amplification by

Stimulated Emission of Radiation 2

LASER stands for Light Amplification by Stimulated Emission of Radiation.A highly coherent, monochromatic and perfectly parallel beam of light.

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First successful laser was constructed by T.H. Maiman in 1960 using Ruby Laser.

A few other lasers are helium-neon laser, carbon dioxide laser, dye laser, junction laser, etc.

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RUBY LASER

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What Is Laser Communication? Laser communications systems are

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

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Free Space Laser Communication

Transmitting information via a laser beamVideoDataSound

Terrestrial / Space based systems

010001100110111011001111001010000010101110010001111001011011

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How Does it Work?How Does it Work?

Signal Transmitter

Receiver Signal

Laser

laser

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Photo resistor

High Level design

Conditioning MCU MCU

ConditioningConditioning

UART UARTA/D

PORT

Laser Laser DiodeDiode

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What is the What is the Transmitter?Transmitter? The transmitter involvesThe 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)

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Laser DiodeLaser Diodes include Photodiodes for feedback to ensure consistent output.

Obtained by polishing the two sides of a junction diode.

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The receiver involves:- Antenna Signal Processor Detector PIN diodes Avalanche Photo Diodes (APD) Single or Multiple Detectors

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Why Laser Communication?Current high speed communications technology:

RadioFiber Optics

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Beam Divergence = 3 mrad

Diameter = 3 mBeam area = 70686 cm2

Distance = 1km

Receive area = 200 cm2

Transmit Power

Receiver sensitivity

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Why not Fiber Optics?Not always possible to lay fiber lines

Physically / Economically not practicalEmergencies

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

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Why not RF?Bandwidth

for Laser Communication (LC) is 100 times greater than for RF.

Powerin LC is directed at target, so much less

transmission power required. Also the power loss is less.

Size / WeightLC antenna is much smaller than RF.

SecurityDue to low divergence of laser beam, LC is more

secure than RF.16

Current Applications Current Applications 1. Defense and sensitive areas.1. Defense and sensitive areas.2. In surgery.2. In surgery.3. Mass communication3. Mass communication

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

4. In industry.4. In industry.5. In nuclear power production.5. In nuclear power production.6. In weather forecasting.6. In weather forecasting.7. NASA7. NASA

Satellite - satelliteSatellite - satellite Earth – satelliteEarth – satellite

Earth

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Groundstation Description

Control System (data and tracking)Telescope & LASER MountsLASER & Transmission OpticsReceiving Package (photodetector)

Utilize Science Team’s Telescope & Processing Capability for LASER CommunicationTransmission & Receiving Package.

Satellite Description

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Bits Bit Encoderto Symbol LASER

TransferOptics

Channel(Atmos.)

ReceivingOpticsAmplifier

Symbol Recovery

Error Correction

Bits

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Demerits Of Laser CommunicationRequire direct line-of-sight.Operational distance is also a variable

if there are intervening materials such as rain, smoke, fog, glass etc.

Limited wavelength range.

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