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LASER
COMMUNICATION
SYSTEM
SWATHI S BABU
ROLL NO: 58
S3 EC
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Introduction
How does it Work?
One-way Laser communication system
Application
Advantages
Disadvantages
Conclusion
Reference
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Laser communications systems are wireless
connections through the atmosphere.
They work similarly to fiber optic links, except
the beam is transmitted through free space.
While the transmitter and receiver must
require line-of-sight conditions, they have the
benefit of eliminating the need for broadcast
rights and buried cables.
Optical fiber link
Laser Transmitter
Receiver
Direct Link
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The Transmitter involves a
signal processing circuit,
and a laser.
A laser diode is used to
create the laser signal.
Laser
Diodes
include
Photodiodes for feedback
to insure consistent output.
The receiver involves:
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Telescope(‘antenna’)
Signal processor
Detector
 PIN diodes
 Avalanche Photo Diodes(APD)
 Single or multiple detectors
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AM
Easy with gas lasers, hard with diodes
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PWM (Pulse Width Modulation)
Used by Ramsey in their kit
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PFM (Pulsed FM)
Potentially the highest bandwidth (>100kHz)
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Transmitter
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Maximum output power
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Minimum divergence
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Receiver
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Maximum lens area
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Clarity
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Tight focus on detector
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Sun shade over detector
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Shade in front of lens
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Detector spectral response
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Colored filters
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Absorb ~50% of available light
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Difficult to find exact frequency
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Mounts and stands need only be as accurate as beam
divergence
Good laser diodes will be 1-2mR (milliRadian)
A 32 pitch screw at the end of a 2' mount will yield 1mR per
revolution. Since quarter turns (even eighth turns) are
possible, this is more than accurate enough
Higher thread pitches allow shorter mounts which may be
more stable (against wind, vibration, wires)
1mR is 1.5' of divergence every 1000', 3' at 2000 ', etc.
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GPS and Compass
Scopes and Binoculars
Strobe lights, large handheld floods, headlights
HTs to yell when laser light is seen at remote
location
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Transmit voice for miles line-of-sight
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Use weak signal modes for ?cloud scatter?
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Transmit video with cheap pens
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Transmit high speed data without WEP
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Blind flies for easy extermination
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Ease of deployment
Can be used to power devices
License-free long-range operation (in contrast with radio
communication)
High bit rates
Low bit error rates
Immunity to electromagnetic interference
Full duplex operation
Protocol transparency
Increased security when working with narrow
beam(s)[citation needed]
No Fresnel zone necessary
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For terrestrial applications, the principal limiting factors are:
Beam dispersion
Atmospheric absorption
Rain
Fog (10..~100 dB/km attenuation)
Snow
Scintillation
Interference from background light sources (including the
Sun)
Shadowing
Pointing stability in wind
Pollution / smog
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Laser communications offers a viable alternative to RF
communications for inter satellite links and other
applications where high-performance links are a necessity.
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High data rate, small antenna size, narrow beam divergence,
and a narrow field of view are characteristics of laser
communications that offer a number of potential advantages
forsystem design.
www.google.com
www.wikipedia.com
Thanks