Post on 24-Jun-2015
description
SUBMITED BY-SUBMITED BY- SAI DEBASIS MOHANTYSAI DEBASIS MOHANTYREGD NO-1101219426REGD NO-110121942677THTH SEM SEMET 2ET 2
Organization1. Introduction.
2. Basic principle.
3. What is LASER Communication?
4. Free Space Laser Communication
5. Why Laser Communication?
6. A Simple Laser comm. System
6.1. Transmitter
6.2. Modulation
6.3. Receiver
7. Current Application.
8. FSO
7.1. What is FSO?
7.2. Advantages of FSO
9. SUMMARY
10. References
INTRODUCTION
LASER ?
“LIGHT AMPLIFICATION BY SIMULATED EMMISSION OF RADIATION”
BASIC PRINCIPLE
ABSORPTION
SPONTANEOUS EMISSION
STIMULATED EMISSION
POPULATION INVERSION
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
Video
Data
Sound
Terrestrial / Space based systems
010001100110111011001111001010000010101110010001111001011011
DIRECTIONAL TRANSMISSION:
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
How Does it Work?
laser
What is the Transmitter?
►The transmitter involves: Signal processing electronics (analog/digital) Laser modulator Laser (visible, near visible wavelengths)
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
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)
Avalanche photodiode-2
Stabilisation of working point of APD:.
Gain =75Temperature stabilisation.
Thermoelectrically cooler stabilisation
system is inside of APD module
AVALANCHE PHOTO DIODE
Why Laser Communication?
Current high speed communications technology:
Radio
Fiber Optics
Why not Fiber Optics?
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 RF? 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.
Current Applications
►Defense and sensitive areas. ►FSO Communication.►At airports for communication across the
runways.►Mass communication
►400 TV channels►40,000 phone conversations
►NASA Satellite - satellite Earth - satellite
FSO
line-of-sight technology.uses LASERS and Photo detectors. optical connections between two points—without
the fiber.
FSO units consist
-optical transceiver with a laser (transmitter)
-Photo detector (receiver)
-provide full duplex capability.
ADVANTAGES OF FSO SYSTEMS
No licensing required. Very low installation cost. No sunk costs. No capital overhangs. Highly secure transmission possible. High data rates @ 2.5 -10 Gbps.
SUMMARY
Basic principle of laser action discussed.
Laser communication system used in satellite communication.
Provide higher data rates , high security & lesser antenna size.
FSO used for lesser link length ~ 4km.
FSO links –designed carefully due to safety issues.
Opportunities For Student Involvement
•LASER Research
•LASER Modulation Circuitry
•Encoding/Decoding Circuitry