Laser communications ...................

ppt laser

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.

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

5. O ne-way Laser communication system

6. 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.

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

8. 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)

9. 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

10. 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

11. 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

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. 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. 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.

15. References www.studymafia.org www.google.com www.wikipedia.com

16. Thanks