The document discusses laser communications, outlining its principles of operation, including one-way systems that transmit data through free space. It highlights the advantages, such as high bit rates and security, while also addressing challenges like atmospheric interference. Overall, laser communications present a promising alternative to traditional RF communications for various applications.

1. RAHUL KUMAR
ECE
226320070
Seminar
On
Laser Communications

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
Laser Transmitter Receiver
Optical fiber link
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. 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

11. 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

12. 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

13. 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.

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. 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.

16. References
 www.studymafia.org
 www.google.com
 www.wikipedia.com

17. Thanks