Laser communication systems transmit information via laser beams through free space or the atmosphere, similarly to fiber optic links but without physical cables. They work by modulating laser signals and detecting the signals with sensors at the receiving end. Key benefits over radio frequency (RF) include higher bandwidth, directivity for more power and security, and smaller equipment. Current applications include satellite communication and situations where laying fiber is not practical. Students can be involved in laser research, modulation circuitry, and encoding/decoding systems.

1. Laser Communication
Laser Communication

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

3. L
Light
ight
A
Amplification by
mplification by
S
Stimulated
timulated
E
Emission of
mission of
R
Radiation
adiation

4. Free Space Laser Communication
Free Space Laser Communication
► Transmitting information via a laser beam
Transmitting information via a laser beam
 Video
Video
 Data
Data
 Sound
Sound
► Terrestrial / Space based systems
Terrestrial / Space based systems
010001100110
111011001111
001010000010
101110010001
111001011011

5. How Does it Work?
Signal Transmitter
Receiver Signal
Laser
laser

6. Photo
Photo
resistor
resistor
High Level design
High Level design
Conditioning MCU MCU
Conditioning
Conditioning
UART UART
A/D
PORT
Laser Diode

7. What is the Transmitter?
►The transmitter involves:
 Signal processing electronics (analog/digital)
 Laser modulator
 Laser (visible, near visible wavelengths)

8. RUBY LASER

9. Laser Diode
Laser Diode
Laser Diodes include
Photodiodes for
feedback to insure
consistent output.

10. Modulation
Modulation
►AM
AM
 Easy with gas lasers, hard with diodes
Easy with gas lasers, hard with diodes
►PWM (Pulse Width Modulation)
PWM (Pulse Width Modulation)
►PFM (Pulsed FM)
PFM (Pulsed FM)
 Potentially the highest bandwidth (>100kHz)
Potentially the highest bandwidth (>100kHz)

11. 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

12. Avalanche photodiode-2
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

13. System Comparison
System 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

14. Why Laser Communication?
Why Laser Communication?
► Current high speed communications technology:
Current high speed communications technology:
 Radio
Radio
 Fiber Optics
Fiber Optics

15. Laser Link Geometry
Laser Link Geometry
Critical Design Parameters
Critical Design Parameters
Beam Divergence = 3 mrad
Diameter = 3 m
Beam area = 70686 cm2
Distance = 1km
Receive area = 200 cm2
Transmit Power
Receiver sensitivity

16. ►Not always possible to lay fiber lines
Not always possible to lay fiber lines
 Satellites
Satellites
 Combat zones
Combat zones
 Physically / Economically not practical
Physically / Economically not practical
 Emergencies
Emergencies
 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?

17. ► Bandwidth
Bandwidth
 for Laser Communication (LC) is 100 times greater than
for Laser Communication (LC) is 100 times greater than
for RF.
for RF.
► Power
Power
 in LC is directed at target, so much less transmission
in LC is directed at target, so much less transmission
power required. Also the power loss is less.
power required. Also the power loss is less.
► Size / Weight
Size / Weight
 LC antenna is much smaller than RF.
LC antenna is much smaller than RF.
► Security
Security
 Due to low divergence of laser beam, LC is more secure
Due to low divergence of laser beam, LC is more secure
than RF.
than RF.
Why not RF?
Why not RF?

18. 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

19. Groundstation Description
Groundstation Description
► Control System (data and tracking)
Control System (data and tracking)
► Telescope & LASER Mounts
Telescope & LASER Mounts
► LASER & Transmission Optics
LASER & Transmission Optics
► Receiving Package (photodetector)
Receiving Package (photodetector)
•Utilize Science Team’s Telescope & Processing
Capability for LASER Communication
•Transmission & Receiving Package.
Satellite
Description

20. Uplink/Downlink Data Processing
Uplink/Downlink Data Processing
Sequence
Sequence
Bits Bit Encoder
to Symbol LASER
Transfer
Optics
Channel
(Atmos.)
Receiving
Optics
Amplifier
Symbol
Recovery
Error
Correction
Bits

22. Opportunities For Student Involvement
•LASER Research
•LASER Modulation Circuitry
•Encoding/Decoding Circuitry

23. Contact Information
Contact Information
•Matthew Johnson (mjohnson@u.arizona.edu)
• Freddy Valenzuela (acv@bigdog.engr.arizona.edu)
• Http://www.physics.arizona.edu/ssp/sti
For more information regarding
laser communication: