Presentation for optical wired and wireless communication.

1. RAHUL DOGRA
ECE-18/13
Communication is
connecting two distant
points to transmit and
receive data accurately.
Lasers are used in LC.PRE Known :
LASERs(Light Amplification
through Stimulated
Emission of Radiations)
Basic Communication
terminology

2. Introduction
• Laser communications systems are wireless or optical connections.
• Use Laser Beams to exchange information between two locations
• No fibers compulsion, a wireless technology
• Communication over long distances, such as between planets
• Laser Communication Terminals (LCTs) transmit a laser beam and are
capable of receiving laser beams.

3. Work Block Diagram
Signal Transmitter Laser
Receiver Signal

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

5. One-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 (Typical material Nd:YAG).
• Gas Lasers may also be used.

7. Receiver
The receiver involves:
• Telescope(‘antenna’)
• Signal processor
• Detector

8. Modulation by Transmitter
• AM
 Easy with gas lasers, hard with diodes
• PWM
• FSK for Pulse rate and PSK for Pulse width management.

9. Gain Systems
Transmitter
 Maximum output power
 Minimum divergence
Receiver
 Maximum lens area
 Clarity
 Tight focus on detector

10. Mounting Systems
• Mounts and stands need only be as accurate as beam divergence
• Since quarter turns (even eighth turns) are possible in mounting
threads, this is more than accurate enough
• Higher thread pitches allow shorter mounts which may be more stable
(against wind, vibration, wires)
• Mounts should be stable against natural varsities like rain, strong winds
etc.

11. Working Example of
LASER
COMMUNICATION

12. • The system is set up to
send voice data.
• A person's voice is input
into a conditioning
circuit to consume 8 bit
range of ADC
• Once the digital signal is
obtained from the ADC,
the MCU passes the
signal to the UART.

13. • 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.

14. • Not always possible to lay fiber lines
 Satellites
 Combat zones
 Physically / Economically not practical
 Emergencies
• Laser Communication is being incorporated even into fiber optic
networks whenever fiber is not practical.
Why not Fiber Optics?

15. • Bandwidth
• for Laser Communication 100 times greater than for RF.
=>More data travels at one time
• Power
• Laser beam is directed at target, much less transmission power required.
• Also the power loss is less.
• Size / Weight
• LC antenna is much smaller than RF.
• LC does not need Long towers
• Security
• Due to low divergence of laser beam, LC is more secure than RF.
Why not RF?

16. Applications
ISP (Internet Service Provider) Industrial Use

17. Applications
• Defense and sensitive areas.
• At airports for communication across the
runways.
• GPS through satellites then rf for different
users
• Free-space optical communication
• Space probe are being designed to use
optical rather than radio communication.
• Laser communication has also been
utilised on aircraft and high altitude
platforms.

18. 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.

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
• Snow
• 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.