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