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Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
Laser Communications
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Laser Communications

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Laser communications offer a viable alternative to RF communications for inter satellite links and other applications where high-performance links are a necessity.

Laser communications offer a viable alternative to RF communications for inter satellite links and other applications where high-performance links are a necessity.

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  • 1. Introduction • Laser communications systems are wireless connections through the atmosphere. • Use Laser Beams to transmit information between two locations • No fibers need, a wireless technology • Communication over long distances, e.g. between planets • Laser Communication Terminals (LCTs) transmit a laser beam and are capable of receiving laser beams.
  • 2. How does it Work ? Signal Transmitter Laser Receiver Signal Visit www.seminarlinks.blogspot.com to download
  • 3. Laser Transmitter and Receiver Laser Transmitter Receiver Optical fiber link Direct Link
  • 4. One-way Laser communication system
  • 5. 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.
  • 6. Receiver The receiver involves: • Telescope(‘antenna’) • Signal processor • Detector  PIN diodes  Avalanche Photo Diodes(APD)  Single or multiple detectors
  • 7. Modulation • AM  Easy with gas lasers, hard with diodes • PWM • PFM  Potentially the highest bandwidth(>100kHz)
  • 8. Gain Systems Transmitter  Maximum output power  Minimum divergence Receiver  Maximum lens area  Clarity  Tight focus on detector
  • 9. 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
  • 10. Mounting Systems • 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, 2000 etc.
  • 11. • Thus system is set up to send voice data. • A person's voice gets put into a conditioning circuit so that the full eight bit range of the analogue to digital converter is utilized. • Once the digital signal is obtained by the ADC, the MCU passes the signal to the uart.
  • 12. • The UART sets a transmit pin high or low according to the serial protocol. • Some conditioning is applied to this signal as well in order to ensure constant current to the laser. • On the receiver side, the signal is read by a photo transistor and basically the signal goes through an opposite sequence to output a sound instead of receiving one and using the DAC will change the digital signal to an analog one.
  • 13. • Not always possible to lay fiber lines  Satellites  Combat zones  Physically / Economically not practical  Emergencies • Laser Communication being incorporated into fiber optic networks when fiber is not practical. Why not Fiber Optics?
  • 14. • Bandwidth • for Laser Communication (LC) is 100 times greater than for RF. • Power • in LC is directed at target, so much less transmission power required. • Also the power loss is less. • Size / Weight • LC antenna is much smaller than RF. • Security • Due to low divergence of laser beam, LC is more secure than RF. Why not RF?
  • 15. Applications ISP (Internet Service Provider) Industrial Use
  • 16. Applications • Defense and sensitive areas. • At airports for communication across the runways. • Mass communication • Free-space optical communication • Space probe are being designed to use optical rather than radio communication. • Laser communication has also been demonstrated on aircraft and high altitude platforms.
  • 17. Lunar Atmosphere and Dust Environment Explorer (LADEE) • Lunar Laser Communication Demonstration (LLCD) equipment on LADEE set a space communication bandwidth record in October 2013. • Early tests using a pulsed laser beam to transmit data over the 385,000 kilometres (239,000 mi) between the Moon and Earth. • Passed data at a "record-breaking download rate of 622 megabits per second (Mbps)“ • Demonstrated an error-free data upload rate of 20 Mbps from an Earth ground station to LADEE in Lunar orbit.
  • 18. Security Aspects • Free space laser communications systems have narrow optical beam paths, which are not accessible unless viewing directly into the transmitter path. • Any potential eavesdropping will result in an interruption of the data transmission. • The existence of laser beams cannot be detected with spectrum analyzers.
  • 19. 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
  • 20. 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
  • 21. Conclusion • With the dramatic increase in the data handling requirements for satellite communication services, laser • inter satellite links offer an attractive alternative to RF with virtually unlimited potential and an unregulated spectrum. • The system and component technology necessary for successful inter satellite link exists today.
  • 22. Thank YouVisit www.seminarlinks.blogspot.com to download

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