This document describes how a basic one-way laser communication system works. It consists of a transmitter that uses amplitude modulation to vary the intensity of a laser beam according to an input audio signal. At the receiver, the varying laser intensity is detected by a photodiode or other optical sensor. The document discusses components of the transmitter and receiver, modulation techniques, advantages like high bandwidth and security, and challenges like beam dispersion and interference from other light sources.

1. AANM&VVRSRPOLYTECNICCOLLEGE,GUDLAVALLERU

2. Content
 Abstract
 Introduction
 How does it Work?
 One-way Laser communication system
 Application
 Advantages
 Disadvantages
 Conclusion
 Reference

3. Abstract
 Laser Communication System works on the
principle of “Amplitude Modulation” process.
 “Carrier Signal refers to Laser Beam”
“Amplitude refers to Intensity of Laser Beam”
“Input Signal refers to audio signal”
 This simple Laser Communication System
consists of two sectionsTransmitter and
Receiver.
 At the receiver this varying intensity can be
sensed by any optical sensors like Light
Dependent Resistor (LDR) or photo transistor or
Solar cell.

4. Introduction
 Laser communications systems are wireless
connections through the atmosphere.
 They work similarly to fiber optic links, except
the beam is transmitted through free space.
 While the transmitter and receiver must
require line-of-sight conditions, they have the
benefit of eliminating the need for broadcast
rights and buried cables.

6. TRANSMITTER

7. RECEIVER

8. Laser Transmitter and Receiver
LaserTransmitter Receiver
Optical fiber link
Direct Link

9. One-way Laser communication
system

10. Laser Transmitter
 The Transmitter involves a
signal processing circuit, and
a laser.
 A laser diode is used to
create the laser signal.
 Laser Diodes include
Photodiodes for feedback to
insure consistent output.

11. Receiver
The receiver involves:
 Telescope(‘antenna’)
 Signal processor
 Detector
 PIN diodes
 Avalanche Photo Diodes(APD)
 Single or multiple detectors

12. Modulation
 AM
Easy with gas lasers, hard with diodes
 PWM (PulseWidth Modulation)
Used by Ramsey in their kit
 PFM (Pulsed FM)
Potentially the highest bandwidth (>100kHz)

13. Gain Systems
 Transmitter
• Maximum output power
• Minimum divergence
 Receiver
• Maximum lens area
• Clarity
• Tight focus on detector

14. Filters
 Sun shade over detector
 Shade in front of lens
 Detector spectral response
 Colored filters
• Absorb ~50% of available light
• Difficult to find exact frequency

15. Mounting
 Mounts and stands need only be as accurate as beam
divergence
 Good laser diodes will be 1-2mR (milliRadian)
 A 32 pitch screw at the end of a 2' mount will yield 1mR
per revolution. Since quarter turns (even eighth turns) are
possible, this is more than accurate enough
 Higher thread pitches allow shorter mounts which may be
more stable (against wind, vibration, wires)
 1mR is 1.5' of divergence every 1000', 3' at 2000 ', etc.

16. Pointing
 GPS and Compass
 Scopes and Binoculars
 Strobe lights, large handheld floods, headlights
 HTs to yell when laser light is seen at remote location

17. Applications
 Transmit voice for miles line-of-sight
 Use weak signal modes for ?cloud scatter?
 Transmit video with cheap pens
 Transmit high speed data without WEP
 Blind flies for easy extermination

18. Advantages
 Ease of deployment
 Can be used to power devices
 License-free long-range operation (in contrast with radio
communication)
 High bit rates
 Low bit error rates
 Immunity to electromagnetic interference
 Full duplex operation
 Protocol transparency
 Increased security when working with narrow
beam(s)[citation needed]
 No Fresnel zone necessary

19. Disadvantages
 For terrestrial applications, the principal limiting factors are:
 Beam dispersion
 Atmospheric absorption
 Rain
 Fog (10..~100 dB/km attenuation)
 Snow
 Scintillation
 Interference from background light sources (including the
Sun)
 Shadowing
 Pointing stability in wind
 Pollution / smog

20. Conclusion
 Laser communications offers a viable alternative to RF
communications for inter satellite links and other
applications where high-performance links are a necessity.
 High data rate, small antenna size, narrow beam
divergence, and a narrow field of view are characteristics
of laser communications that offer a number of potential
advantages forsystem design.

21. References
 www.studymafia.org
 www.google.com
 www.wikipedia.com

22. ANYQUERIES