Optical Fiber Communication

“Optical Fiber Communication”
Presented By:
Ruchi Singh
Lecturer, Electronics Engineering
Govt. Polytechnic, Unnao
This work is licensed under a Creative Commons Attribution
NonCommercial- ShareAlike 4.0 International License.

Contents
 Introduction
 Need of Optical Fiber Communication
 Applications and Advantages of OFC
 Basics of OFC, System Block Diagram
 Elements of Fiber Optics
 Optical Fiber Waveguide
 Principle of Operation, RayTheory
 Types of Optical Fibers
 Transmission Characteristics
 Optical Components

tems
 Introduction & Information System Revolution
 Demand of Large bandwidth
 Why Optical FiberTechnology ?
 OpticalTransmission fundamentals
 How to Explode the optical fiber bandwidth ?
 Data rate requirements for high speed networks.
 Optical Fiber Solutions for today’s Systems &
Networks.
Course
Outlines

Introduction
Historical Development
Electrical era Optical era
 .Telegraph 1836  .Optical fibers 1978
 .Telephones 1876  .Optical amplifiers 1990
 .Coaxial cables 1840  .WDMTechnology 1996
 .Microwaves 1948  .Multiple Bands 2002
 Microwaves & Coaxial cables limited to B ~ 100
Mb/s .
 Optical systems can operates at Bit Rate > 10Tb/s.
 Improvement in Optical Fiber system capacity is
related to the Higher frequencies of Optical waves
(~ 200THz at 1.5 µm ).

Information Revolution
 Industrial revolution of 19th century gave way to
information revolution during the 1990s.
 Fiber-Optic Revolution is a natural consequence of
the Internet growth.
 Global, distributed and extensive in their reach
 More volatile and subjective to constant change
Five Generations
I. 0.8-μm systems (1980); Graded-index fibers
II. 1.3-μm systems (1985); Single-mode fibers
III. 1.55-μm systems (1990); Single-mode lasers
IV. WDM systems (1996); Optical amplifiers
V. L and S bands (2002); Raman amplification

Needs For Optical Systems
 Increased capacity of transmission (bit/sec).
 Minimize insertion loss (dB).
 Minimize polarization dependent loss (PDL).
 Minimize temperature dependence of the optical
performance (a thermal solutions).
 Minimize component packaging size (integrability).
 Modularity of components is an advantage
(versatility)

Facts of OpticalTransmission
BIT RATE INCREASING
TRANSMISSION DISTANCE INCREASING

EM spectrum-Region used for
Optical Communication

Optical Fiber Applications
 Medical
 Defense/Government/Shipboard communication
 Data Storage
 Telecommunications
 Networking/WAN & LAN computer networks
 Industrial/Commercial
 Broadcast/CATV/Closed circuitTV system
 Airplanes communication & control
 Local & long distance telephone system
 Nuclear plant interconnections
 Petroleum industries and plants
 LPG plants/Oil & Natural Gas Agencies

Advantages of Optical Fiber
 Enormous potential bandwidth
 Electrical isolation
 Signal security
 Immunity to interference and crosstalk
 Low transmission loss
 Signal security
 Low transmission loss
 System reliability and ease of maintenance
 Ruggedness and flexibility
 Potential low cost
 use of a light-wave carrier
 LongTransmission Distance, Save Energy
 Transmit Massive Amount of Information at One
Time

Fiber links offer over 1,000 times
as much bandwidth and distances
over 100 times
Distance Bandwidth Voice
Channels
Copper 2.5 KM 1.5 Mb/s 24
Optical
fiber
200 KM > 2.5 Gb/s >32,000

Basics of Optical fiber comm.
 In 1880 first time speech signal was transmitted by
Alexander Graham Bell using optical carrier wave,
called as photophone.
 Photophone: A Device transmits speech on a beam of
light, using mirrors & selenium detectors.
 Sophisticated techniques have been developed using
electromagnetic carrier waves from the optical range
of frequencies.
 Present optical communication systems uses LED,
Laser & Optical Fiber technologies.
 Optical frequency is typically 1014 Hz, which can
support wideband modulation. Compared to
microwave frequencies 109 Hz, the optical career can
offer 105 times more bandwidth.

Basics of Contd...
 Fiber Optics is a revolutionary development that has
changed the face of telecommunications around the
world.
 Transmission of data as a light pulses through
optical fiber (first converting electronic binary
signals to light and then finally converting back to
electronic signals).
 OFC system therefore consists of a transmitter or
modulator linked to the information source, the
transmission medium, and a receiver or
demodulator at the destination point.
 Transmitter
 Receiver
 Transmission medium(Optical fiber cable)

Optical fiber comm. system
General OFC system
Transmitter & Receiver Block diagrams
Optical Fiber communication channels

Elements of Fiber Optics
Transmission: The optical source which provides the
electrical–optical conversion may be either a
semiconductor laser or light-emitting diode (LED).
 Light Source; Infrared LED having properties
 850 nm, 1300 nm
 Low cost, easy to use
 Used for multi mode fiber
 Special edge emitting LEDs for single mode fiber
 Light Source; Laser Source having properties
 Coherence, Directionality
 Monochromaticity
 High Specific Intensity
 850 nm, 1300 nm, 1550 nm
 Very high power output
 Very high speed operation
 Very expensive
 Need specialized power supply & circuitry

Elements of Contd...
Reception: The receiver consists of an optical detector
which drives a further electrical stage and hence
provides demodulation of the optical carrier.
Photodiodes (p–n, p–i–n or avalanche);
Photo detector converts back to electrical pulses
 PIN DIODES
 850, 1300, 1550 nm
 Low cost
 APDs (Avalanche Photodiodes)
 850, 1300, 1500 nm
 High sensitivity, can operate at very low power
levels
 expensive

Elements of Contd...
Propagation: The transmission medium consists of an
optical fiber cable; in which Light propagates by mans of
total internal reflection.
 Optical Fiber consists of two concentric layers ; Core
– inner layer; Cladding – outer layer
 Refractive index of core is greater than cladding,
necessary for total internal reflection
 Light entering within acceptance angle propagates
through fiber
 Strikes core cladding interface > critical angle and
gets reflected completely.
 Fairly lossless propagation through bends also.
 Optical fiber
 Multimode (Graded Index 50/125 & 62.5/125  )
 Single mode (8.7 /125  )

Optical FiberWaveguides
 An optical fiber is a spatially inhomogeneous
structure for guiding light
 Cylindrical dielectric waveguide (non-conducting
waveguide) that transmits light along its axis, by the
process of total internal reflection (TIR).
 Waveguide showing a transparent core of refractive
index n1, surrounded by a transparent cladding of
slightly lower refractive index n2. (n1>n2)

Principle of Operation:
 A cylindrical dielectric waveguide in which light
propagates by the process of total internal reflection.
 It consists of a core surrounded by a cladding layer,
both of which are made of dielectric materials.
 To confine the optical signal in the core, the
refractive index of the core must be greater than that
of the cladding (n1>n2).
 The cladding supports the waveguide structure while
also, when sufficiently thick, substantially reducing the
radiation loss into the surrounding.
 The fibers facilitate the propagation of light along the
optical fiber depending on the requirement of power
and distance of transmission.
 The boundary between the core and cladding may
either be abrupt, in step-index fiber, or gradual, in
graded-index fiber.

Ray theory transmission
 Light propagates within an Optical Fiber by
using RayTheory.
 Refractive index: is defined as the ratio of the
velocity of light in a vacuum to the velocity of
light in the medium; n = c / v
 Snell’s Law: When light passes from one
transparent medium to another, it bends
according to Snell's law which is defined as:
n1sin(θ1) = n2sin(θ2)

Ray theory Contd...
 Refraction of light: When a ray is incident on the
interface between two dielectrics of different
refractive indices (e.g. glass–air), refraction
occurs, light ray changes its direction depends on
the refractive index of the mediums.
 If n2>n1; Refracted ray bends towards the
normal
 If n2<n1; Refracted ray bends away from the
normal

Ray theory Contd...
Critical angle θc :
 If n2>n1; Refracted ray bends towards the normal
 If n2<n1; Refracted ray bends away from the normal
 when the angle of refraction is 90° and the refracted
ray emerges parallel to the interface between the
dielectrics, the angle of incidence must be less than
90°. This is the limiting case of refraction and the
angle of incidence is now known as the critical angle
θc.
 The critical angle can be calculated from Snell's law,
putting in an angle of 90° for the angle of the
refracted ray θ2.This gives θ1:
critical angle; θc = θ1 = arcsin(n2/n1)

Ray theory Contd...
Total Internal Reflection(TIR):
 At angles of incidence greater than the critical
angle the light is reflected back into the originating
dielectric medium ,know asTIR .
 Light propagates in an optical fiber through TIR
reflection at the core–cladding interface.

Ray theory Contd...
Acceptance angle: θmax is the maximum angle to
the axis at which light may enter the fiber in order
to be propagated, and is often referred to as the
acceptance angle for the fiber.
 ray enters the fiber core at an angle θmax to the
fiber axis will propagates within fiber.
 rays which enters into the fiber core at an angle
greater than θmax will be eventually lost by
radiation.

Ray theory Contd...
Numerical Aperture: relates the acceptance angle
to the refractive indices, very useful measure of the
light-collecting ability of a fiber.

Types of Optical Fibers
The classification depends on the refractive index,
materials used and mode of propagation of light.
 Based on the refractive index:
1. Step Index Fibers: It consists of a core
surrounded by the cladding which has a single
uniform index of refraction.
2. Graded Index Fibers: The refractive index of the
optical fiber decreases as the radial distance
from the fiber axis increases.
 Based on the materials used:
1. Plastic Optical Fibers: Polymethyl-methacrylate
is used as a core material for the transmission of
the light.
2. Glass Fibers: It consists of extremely fine glass
fibers.

Types of Optical Contd...
 Based on the mode of propagation of light:
1. Single Mode Fibers: carry only one mode which
travels as a straight line at the center of the
core.
2. Multimode Fibers: carry more than one mode at
a specific light wavelength.
The mode of propagation and refractive index of
the core is used to form four combination types of
optic fibers as follows:
1. Single mode-Step index fibers
2. Single mode-Graded index fibers
3. Multimode-Step index fibers
4. Multimode-Graded index fibers

Types Of Optical Contd...
Single-mode step-index fiber
 Mode-field diameter 7 to 11 μm
 Cladding diameter: generally 125 μm
 Numerical aperture: 0.08 to 0.15
 Attenuation: 2 to 5 dB km−1
 Bandwidth: Greater than 500 MHz km
 Applications: high-bandwidth, medium- and long-
haul applications

Multimode-Step index fibers
• Core diameter: 100 to 300 μm
• Cladding diameter: 140 to 400 μm
• Numerical aperture: 0.16 to 0.5.
• Attenuation: 2.6 to 50 dB km−1
• Bandwidth: 6 to 50 MHz km.
• Applications: These fibers are best suited for short-
haul, limited bandwidth and relatively low-cost
applications’.

Single mode-Graded index fibers
 The Core diameter is 8 to 9mm
 All the multiple-mode or multimode effects are
eliminated
 However, pulse spreading remains
 Bandwidth range 100GHz-Km

Multimode-Graded index fibers
 Core diameter: 50 to 100 μm
 Cladding diameter: 125 to 150 μm
 Numerical aperture: 0.2 to 0.3
 Attenuation: 2 to 10 dB km−1
 Bandwidth: 200 MHz km to 3 GHz km
 Applications: short-haul and medium- to high-
bandwidth applications laser diodes respectively

The transmission characteristics play a major role in
determining the performance of the entire
communication system that are;
Attenuation and bandwidth
Attenuation Mechanisms:
 linear scattering
 non linear scattering
 material absorption
 fiber bends
Bandwidth: The number of bits of information
transmitted in a given time period and is largely
limited by signal dispersion within the fiber.
Dispersion: It is defined as the spreading of the light
pulses as they travel down the fiber.
 Intermodal Dispersion
 Intramodal /Chromatic Dispersion
Transmission Characteristics

Fiber alignment and joint;
 Multimode fiber joints
 Single-mode fiber joints
Fiber splices;
 Fusion splices
 Mechanical splices
 Multiple splices
Fiber connectors
 Cylindrical ferrule connectors
 Duplex and multiple-fiber connectors
 Fiber connector-type summary
Optical Components

Expanded beam connectors;
 GRIN-rod lenses
Fiber couplers
 Three- and four-port couplers
 Star couplers
 Wavelength division multiplexing couplers
Optical isolators
Optical circulators
Optical Components

 https://en.wikipedia.org/wiki/Optical_fiber
 https://www.fiberoptics4sale.com/blogs/archive-posts/95146054-
optical-fiber-tutorial-optic-fiber-communication-fiber
 Optical fiber communications: principles and practice / John M.
Senior
 Fiber-Optic Communication Systems, Govind P.Agrawal
 “Status of Optical Communication Technology and Future
Trends”, available at: www.qqread.net, 2013.
 G. P. Agrawal, Fiber-Optic Communication Systems, 3rd ed.
(Wiley, Hoboken, NJ, 2002)
 R. Ramaswami and K. Sivarajan, Optical Networks 2nd ed.
(Morgan, San Francisco, 2002).
 G. E. Keiser, Optical Fiber Communications, 3rd ed. (McGraw-
Hill,NewYork, 2000).
 G. P. Agrawal, Lightwave Technology: Components and Devices
(Wiley, Hoboken, NJ, 2004).
 G. P.Agrawal, Lightwave Technology:Telecommunication Systems
(Wiley, Hoboken, NJ, 2005).
References

Optical Fiber Communication

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