Communication is the exchange of information through transmission and reception of messages. The basic elements of communication are an information source, transmitter, communication channel, and receiver. There are different types of electronic communication including simplex, half duplex, and full duplex. Analog signals vary continuously while digital signals change in discrete steps. Channel multiplexing and modulation techniques like frequency division multiplexing and time division multiplexing allow efficient transmission of multiple signals over a single medium. Optical fiber communication systems transmit information as light pulses along optical fibers and have advantages over traditional metal cable systems like increased bandwidth and lower signal attenuation.

1. What is Communication
 Communication is the process of exchanging information.
 Sending and receiving of messages from one place to
another is called communication.
 The basic elements involved in communication—
1. Information Source
2. Transmitter
3. Communication Channel
4. Receiver

2. Types of Electronic Communication
Simplex
This type of communication is one-way. Examples are:
 Radio
 TV broadcasting
 Beeper (personal receiver)
Half Duplex
The form of two-way communication in which only one party
transmits at a time is known as half duplex. Examples are:
 Police, military, etc. radio transmissions
 Citizen band (CB)
 Family radio
 Amateur radio
Full Duplex
• Most electronic communication is two-way and is referred to as Full-
duplex.
• When people can talk and listen simultaneously, it is called full
duplex. The telephone is an example of this type of communication.

3. Types of Communication
 Analog Communication
AM, FM, PM etc.
 Digital Communication
ASK, FSK, PSK, QPSK etc.
 Microwave Communication
Communication through radio/microwaves/frequencies
 Optical Communication
Communication through Light

4. Basic Block Diagram of Communication System
Noise degrades or interferes with transmitted information
Figure: General Model of All Communication Systems

5. Basic Concepts of Communication
Analog Signals
 An analog signal is a smoothly and continuously varying
voltage or current. Examples are:
Sine wave Voice Video (TV)
Analog and Digital Signals

6. Basic Concepts of Communication
Digital Signals
 Digital signals change in steps or in discrete increments. Most digital
signals use binary or two-state codes. Examples are:
 Telegraph (Morse code)
 Continuous wave (CW) code
 Serial binary code (used in computers)
Analog and Digital Signals

7. Channel Multiplexing and Modulation
Modulation and multiplexing are electronic
techniques for transmitting information efficiently
from one place to another.
Modulation makes the information signal more
compatible with the medium.
Multiplexing allows more than one signal to be
transmitted concurrently over a single medium.

8. Channel Multiplexing and Modulation
Figure: Multiplexing and Modulation at The Transmitter

9. Channel Multiplexing and Modulation
Frequency Division Multiplexing
 Each signal is modulated to a different carrier frequency
 Carrier frequencies separated so signals do not overlap
(guard bands)

10. Channel Multiplexing and Modulation
Time Division Multiplexing
 Multiple digital signals interleaved in time domain.
 Time slots preassigned to sources and fixed.

11. Modulation Formats
NON-RETURN-TO-ZERO- In Communication, a non-return-to-zero (NRZ) line
code is a binary code in which ones are represented by one significant
condition, usually a positive voltage, while zeros are represented by some other
significant condition, usually a negative voltage, with no other neutral or rest
condition.
RETURN-TO-ZERO- (RZ or RTZ) describes a line code used in communications
signals in which the signal drops (returns) to zero between each pulse.

12. 12
Need of Fiber Optic Communications
 Fiber communication promised extremely high data rates,
which allow high capacity transmission quickly.
 It also had the potential for transmission over long
distances without the need to amplify and retransmit along
the way.
 Speed limit of electronic processing, limited bandwidth of
copper/coaxial cables.
 Optical fiber has very high-bandwidth (~30 THz)
 Optical fiber has very low loss (~0.25dB/km @1550nm)
 suitable for long-distance transmission

13. Increase of the bit rate distance
product BL for different
communication Technologies
over time.
Evaluation of Lightwave Communication Systems
A figure of merit of communication
systems is the bit rate–distance product,
BL, where B is the bit rate and L is the
repeater spacing.

14. Frequency and Wavelength Graph

15. 15
Optical Communication
amplitude
wavelength
position/distance
 electromagnetic wave
 carry energy from one point to another
 travel in straight line
 described in wavelength (usually in mm or nm)
 speed of light in vacuum = 3108 m/s

16. Block Diagram of Optical Fiber
Communication System
Figure: Basic Block Diagram of Optical Communication System

17. Block Diagram of Optical Fiber
Communication System

18. Optical Transmitter

19. Optical Modulator

20. Optical Receiver

21. Advantages of optical fiber communication
 Increased Bandwidth and Channel Capacity
 Low Signal Attenuation
 Immune to Noise
 No Crosstalk
 Lower Bit Error Rates
 Signal Security
 Electrical Isolation
 Reduced Size and Weight of Cables
 Radiation Resistant and Environment Friendly
 Resistant to Temperature Variations etc.

22. Disadvantages of optical fiber
communication
 Specialist skills needed
 Cost of installation
 Cost of transmission equipment from electrical to
optical signals
 Optical fibers can not carry electrical power

23. Applications of optical fiber communication
 As fibers are very flexible, they are used in flexible digital cameras.
 Fibers are used in mechanical imaging i.e. for inspection of mechanical welds in
pipes and engines of rockets, space shuttles, airplanes.
 Fibers are used in medical imaging such as endoscopes and laparoscopes.
 Fibers can be used under sea communication.
 Fibers are used in military applications such as aircrafts, ships, tanks etc.
 Nuclear testing applications use optical fiber phase sensors and transducers
 Fibers are used in public utility organizations like railways, TV transmission etc.
 Fibers are used in LAN systems of offices, industrial plants and colleges etc.
 Fibers are used in telecommunication such as voice telephones, video phones,
telegraph services, message services and data networks.

24. Queries……..
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