Photonics involves the control and use of photons in various applications. It includes optoelectronics, which uses light in electronics; quantum electronics, which involves light-matter interaction in devices like lasers; and quantum optics, which studies light's quantum properties. Photonic communications specifically applies these photonic technologies to transmit information over long distances using fiber optics. Fibers allow extremely wide bandwidth, are small and lightweight, provide immunity to electromagnetic interference, and enable transmission rates over 1 Gbit/s. Communication protocols and digital/analog transmission ensure error-free and efficient routing of data between senders and receivers.

1. Photonics
• Optoelectronics: refers to devices & systems that are
essentially electronics but involve lights, such as LED, liquid
crystal displays & array photodetectors.
• Quantum Electronics: is used in connection with devices &
systems that rely on the interaction of light with matter, such
as lasers & nonlinear optical devices.
• Quantum Optics: Studies quantum & coherence properties of
light.
• Lightwave Technology: describes systems & devices that are
used in optical communication & signal processing.
• Photonics: in analogy with electronics, involves the control of
photons in free space and matter.

2. Photonic Communications
• Photonics reflects the importance of the photon nature of light. Photonics
& electronics clearly overlap since electrons often control the flow of
photons & conversely, photons control the flow of electrons.
• The scope of Photonics:
1- Generation of Light (coherent & incoherent)
2- Transmission of Light (through free space, fibers, imaging systems,
waveguides, … )
3- Processing of Light Signals (modulation, switching, amplification,
frequency conversion, …)
4- Detection of Light (coherent & incoherent)
• Photonic Communications: describes the applications of
photonic technology in communication devices & systems,
such as transmitters, transmission media, receivers & signal
processors.

4. Why Photonic Communications?
• Extremely wide bandwidth: high carrier frequency ( a wavelength of
1552.5 nm corresponds to a center frequency of 193.1 THz!) &
consequently orders of magnitude increase in available transmission
bandwidth & larger information capacity.
• Optical Fibers have small size & light weight.
• Optical Fibers are immune to electromagnetic interference (high voltage
transmission lines, radar systems, power electronic systems, airborne
systems, …)
• Lack of EMI cross talk between channels
• Availability of very low loss Fibers (0.25 to 0.3 dB/km), high
performance active & passive photonic components such as
tunable lasers, very sensitive photodetectors, couplers, filters,
• Low cost systems for data rates in excess of Gbit/s.

5. Communication Protocols
 Data communication software is the software
that enables us to communicate with other
systems
 The procedure of data transformation in the form
of software is commonly called protocol.
 The data transmission software or protocols
perform the following functions for the efficient
and error free transmission of data.

6.  Data sequencing: A long message to be transmitted
is broken into smaller packets of fixed size.
 Data Routing: the process of finding the most
efficient route between source and destination
before sending the data.
 Flow control: All machines are not equally efficient
in terms of speed. Hence the flow control regulates
the process of sending data between fast sender and
slow receiver.
 Error Control: It ensures that data are transmitted
without any error.
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Data transmission software or
protocols (functions)

7. Three ways for transmitting data
• Simplex: In this mode the communication can take
place in one direction.
• Half-duplex: communication channel is used in both
directions, but only in one direction at a time.
• Full-duplex: In full duplex the communication channel
is used in both directions at the same time. Use of full-
duplex line improves the efficiency. Example of this
mode of transmission is the telephone line.
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8. • Fig. 2.1
Mathematics Department 8
Fig. 7.1

9. Digital and Analog Transmission
• Data is transmitted from one point to another
point by means of electrical signals that may be
in digital and analog form
• In analog signal the transmission power varies
over a continuous range with respect to sound,
light and radio waves
• digital signal may assume only discrete set of
values within a given range
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Analog signal is measured in Volts and its
frequency in Hertz (Hz).
A digital signal is a sequence of voltage
represented in binary form.
the technique by which a digital signal is
converted to analog form is known as modulation
And the reverse process, that is the conversion of
analog signal to its digital form, is known as
demodulation.
The device, which converts digital signal into
analog, and the reverse, is known as modem
Digital and Analog Transmission

11. Mathematics Department 11

12. Asynchronous and Synchronous
Transmission
• Data transmission through a medium can be either
asynchronous or synchronous.
• In asynchronous transmission data is transmitted
character by character as you go on typing on a
keyboard. Hence there is irregular gaps between
characters.
• in the synchronous mode, the saved data is
transmitted block by block. Each block can contain
many characters.
• Synchronous transmission is well suited for remote
communication
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13. Communication devices
• Wire pairs are commonly used in local
telephone communication and for short distance
digital data communication.
• They are usually made up of copper and the pair
of wires is twisted together
• Data transmission speed is normally 9600 bits
per second in a distance of 100 meter.
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14. Mathematics Department 14
• Coaxial Cables: Coaxial cable is groups of
specially wrapped and insulted wires that are
able to transfer data at higher rate.
• They consist of a central copper wire
surrounded by an insulation over which
copper mesh is placed.
• They are used for long distance telephone
lines and local area network for their noise
immunity and faster data transfer.

15. Microwave
• Microwave system uses very high frequency radio
signals to transmit data through space.
• The transmitter and receiver of a microwave system
should be in line-of-sight because the radio signal
cannot bend.
• With microwave very long distance transmission is not
possible. In order to overcome the problem of line of
sight and power amplification of weak signal, repeaters
are used at intervals of 25 to 30 kilometers between the
transmitting and receiving end.
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16. Communication Satellite
• A communication satellite is a microwave relay
station placed in outer space.
• In satellite communication, microwave signal is
transmitted from a transmitter on earth to the
satellite at space.
• The satellite amplifies the weak signal and transmits
it back to the receiver.
• The main advantage of satellite communication is
that it is a single microwave relay station visible from
any point of a very large area.
• In microwave the data transmission rate is 16 giga
bits per second. They are mostly used to link big
metropolitan cities.
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