The document discusses laser communication systems. It begins with an introduction that explains laser communication works similarly to fiber optic links but transmits a beam through free space instead of a cable. It then covers what laser communication is, how the one-way system works with a laser transmitter that modulates a signal and a receiver with a telescope and detector, and modulation techniques like OOK, PWM, and PFM. Applications are discussed along with advantages like high bandwidth and disadvantages like beam dispersion in the atmosphere.

1. Seminar
On
Laser
Communications
Prepared By:
P Saicharan Rao
14K81A0440
ECE-4A

2. Content
• Introduction
• What is Laser Communication
• How does it Work?
• One-way Laser communication system
• Processing of electrical signal to light
• 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.

4. What is LASER
Communication??
Laser communication 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.

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

7. One-way Laser communication system

8. 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.

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

10. 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)

11. The LASER Diode is being turned
ON/OFF quickly as needed according to the
OOK/PWM/PFM signal.
Modulation Techniques:
ON-OFF Keying(OOK)
Pulse Width
Modulation(PWM)
Pulsed Frequency
Modulation(PFM)
OOK
PWM
PFM

13. 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

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. Laser in navy

16. Military Defence

17. 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

18. 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

19. 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.

20. LASER COMMUNICATION
Thank you