2. Basic principle.
3. What is LASER Communication?
4. Free Space Laser Communication
5. Why Laser Communication?
6. A Simple Laser comm. System
7. Current Application.
7.1. What is FSO?
7.2. Advantages of FSO
“LIGHT AMPLIFICATION BY SIMULATED
EMMISSION OF RADIATION”
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. “
Free Space Laser Communication
Transmitting information via a laser beam
Terrestrial / Space based systems
Narrow divergence of the FSO transmit path
(shown in red) as compared to a typical Radio
Frequency (RF) path (shown in blue).
Free Space Optic Link Equation:
Preceived = received power
Ptransmit = transmit power
Areceiver = receiver area
Div = beam divergence (in radians)
Range = link length
What is the Transmitter?
►The transmitter involves:
Signal processing electronics (analog/digital)
Laser (visible, near visible wavelengths)
What is the Receiver?
►The receiver involves:
Telescope (referred to as ‘antenna’)
-Avalanche Photo Diodes (APD)
-Single or multiple detectors
Often both ends will be equipped
with a receiver and transmitter
“Laser Diodes include
feedback to insure
Easy with gas lasers, hard with diodes
PWM (Pulse Width Modulation)
PFM (Pulsed FM)
Potentially the highest bandwidth (>100kHz)
AVALANCHE PHOTO DIODE
Stabilisation of working point of APD:
Thermoelectrically cooler stabilisation
system is inside of APD module
Why Laser Communication?
Current high speed communications technology:
Why not Fiber Optics?
Not always possible to lay fiber lines
Physically / Economically not practical
LC being incorporated into fiber optic networks
when fiber is not practical.
Why not RF?
for Laser Communication (LC) is 100 times greater than for
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.
Due to low divergence of laser beam, LC is more secure than
►Defense and sensitive areas.
►At airports for communication across the
►400 TV channels
►40,000 phone conversations
Satellite - satellite
Earth - satellite
uses LASERS and Photo detectors.
optical connections between two points—without
FSO units consist
-optical transceiver with a laser (transmitter)
-Photo detector (receiver)
-provide full duplex capability.
ADVANTAGES OF FSO
No licensing required.
Very low installation cost.
No sunk costs.
No capital overhangs.
Highly secure transmission possible.
High data rates @ 2.5 -10 Gbps.
Basic principle of laser action discussed.
Laser communication system used in satellite
Provide higher data rates , high security & lesser
FSO used for lesser link length ~ 4km.
FSO links –designed carefully due to safety issues.
Opportunities For Student
•LASER Modulation Circuitry