Laser communication systems transmit information via laser beams through the atmosphere, providing a wireless alternative to fiber optic cables. They involve laser transmitters that emit laser signals, and receivers with telescopes and detectors that receive the signals. Modulation techniques like amplitude modulation are used to encode data onto the laser beams. Applications include long distance communication between planets or satellites, as was demonstrated by the LADEE mission which achieved a record breaking 622 Mbps data transmission between the Moon and Earth using laser communication.

1. B.MANIKANTA REDDY
19E11A0405
ECE-4A

2. 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.

3. How does it Work ?
Signal Transmitter Laser
Receiver Signal

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

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. • 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.

10. • 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.

11. Applications
ISP (Internet Service Provider) Industrial Use

12. 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.

13. 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.

14. 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.