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Laser Communication
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.
Light
Amplification by
Stimulated
Emission of
Radiation
Free Space Laser Communication
►Transmitting information via a laser beam
Video
Data
Sound
►Terrestrial / Space based systems
010001100110
111011001111
001010000010
101110010001
111001011011
How Does it Work?
Signal Transmitter
Receiver Signal
Laser
laser
Photo resistor
High Level design
Conditioning MCU MCU
Conditioning Conditioning
UART UART A/D
PO
RT
Laser Diode
What is the Transmitter?
►The transmitter involves:
Signal processing electronics (analog/digital)
Laser modulator
Laser (visible, near visible wavelengths)
RUBY LASER
Laser Diode
Laser Diodes include
Photodiodes for
feedback to insure
consistent output.
Modulation
►AM
Easy with gas lasers, hard with diodes
►PWM (Pulse Width Modulation)
►PFM (Pulsed FM)
Potentially the highest bandwidth (>100kHz)
What is the Receiver?
►The receiver involves:
Telescope (referred to as ‘antenna’)
Signal processor
Detector
Often both ends will be equipped
with a receiver and transmitter
-PIN diodes
-Avalanche Photo Diodes (APD)
-Single or multiple detectors
Avalanche photodiode-2
Stabilisation of working point of APD:
.
Gain =75
Temperature stabilisation.
Thermoelectrically cooler stabilisation
system is inside of APD module
AVALANCHE PHOTO DIODE
System Comparison (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?
►Current high speed communications technology:
Radio
Fiber Optics
Laser Link Geometry Critical 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 lines Satellites
Combat zones
Physically / Economically not practical
Emergencies
LC being incorporated into fiber optic networks when fiber is not practical.
Why not Fiber Optics?
►Bandwidth for Laser Communication (LC) is 100 times greater than
for RF.
► Power in LC is directed at target, so much less transmission
power required. Also the power loss is less.
► Size / Weight LC antenna is much smaller than RF.
► Security
Due to low divergence of laser beam, LC is more secure than RF.
Why not RF?
Current Applications
►Defense and sensitive areas.
►At airports for communication across the runways.
►Mass communication ►400 TV channels
►40,000 phone conversations
►NASA Satellite - satellite
Earth - satellite Earth
Groundstation Description
►Control System (data and tracking)
►Telescope & LASER Mounts
► LASER & Transmission Optics
►Receiving Package (photodetector)
•Utilize Science Team’s Telescope & Processing
Capability for LASER Communication
•Transmission & Receiving Package.
Satellite Description
Uplink/Downlink Data Processing Sequence
Bits Bit Encoder
to Symbol LASER Transfer
Optics
Channel
(Atmos.)
Receiving
Optics Amplifier Symbol
Recovery
Error
Correction
Bits
Opportunities For Student Involvement
•LASER Research
•LASER Modulation Circuitry
•Encoding/Decoding Circuitry
Contact Information
•Matthew Johnson ([email protected])
• Freddy Valenzuela ([email protected])
• Http://www.physics.arizona.edu/ssp/sti
For more information regarding
laser communication: