1. LASER COMMUNICATION SYSTEM
SWATHI S BABU
ROLL NO: 58
S3 EC

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

3. 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.

5. Laser Transmitter and Receiver
Optical fiber link
Laser Transmitter
Receiver
Direct Link

6. One-way Laser communication system

7. 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.

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

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

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

11. 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

12. 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.

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

14. 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

15. 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

16. 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

17. 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.

18. References

19. Thanks