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Optical Fiber
AUTO3160 - Optics and Spectroscopy
Spring 2012
Miguel Angel Chourio
Master’s degree in Telecommunication Engineering
University of Vaasa, Finland
What is a Optical Fiber
Single Mode Optical Fiber
Multimode Optical Fiber
Single mode Vs. Multimode Fiber
Snew’s Law - Total Internal Reflection
How is glass optical Fiber made
Optical Fiber
 Optical Fiber uses glass to guide the light impulses from
source to destination.
 Optical Fiber provides a very large bandwidth data rates.
 Based on its requirements and needs, Networks communication
are implemented as
o Copper
o Optical Fiber
o Wireless (Signal are propagated over the air)
Glass Fiber Structure
 The core vary its dimensions either the fiber is single or multimode.
• The Cladding surronds or cover the core and is designed to prevent light
loss from the fiber.
• Since the light can only travel in one direction over the optical cable, two
fibers are required to support full duplex operations
• Light enter into the core and its cladding along the fiber
Ray Light explanation
 Typically, the core size on Multiple Fiber are large enough so that,
multiple light ray can enter to the core at different angles along the fiber.
 Multimode fiber employ Light Emitting Diodes (LEDs) with its proper
angles to represent the transmitted data as bits along the media.
 Due the light enters the fiber at different angles, it takes different amount
of time to travel down the fiber, and it may become confuse at the
receiver side.
 This effect known as modal dispersion, limit the length of multimode
fiber segments.
Ray Light explanation
 In “Single Fiber”, the core is so tiny that only one light ray
which is perpendicular to the cable may be propagate along.
 Single Fiber employs a single Ray of Light as source
generator to propagate the signals, because the laser is uni-
directional and travels along the center of the fiber.
Single mode vs. Multimode Fibers
• Small core
• Less dispersion
• Carry a single ray of light, usually
generated from a laser.
• Employ for long distance applications
• Uses as Backbone and distances of
several thousands meters.
• Larger core than single mode cable.
• Allows greater dispersion and therefore,
loss of signal.
• Used for shorter distance application,
but shorter than single-mode (up to
• It uses LED source that generates
differtes angles along cable.
• Often uses in LANs or small distances
such as campus networks.
Waveguide calculation of Fiber Mode
 Here is fiber mode calculation based on Waveguide Calculation by Fiber
Optics for Sale Company (USA)
 V number determines the numbers of guided modes.
• When V number is smaller than
2.405 only one mode can be guided
by the fiber, this is called single
mode fiber.
• When V Numer is larger than 2.405
severals modes can be guided by the
• As higer V number as larger
number of modes, this is called
Multimode Fiber
Multimode Fibers is more complex
 The multimode fiber keeps the same structure as single mode
unlike the sieze of the core glass is bigger.
The x (axes )shows fiber raduis
The y (axes ) shows refractive index
The core usually has a refractive index n1 = 1.48
The cladding has a refractive index n2 = 1.06
This is called Step-index fiber
Refractive index profile in multimode fibers
Snew’s Law - Total Internal Reflection
 Snew’s Law describe the relation between the angles of
incidents and refractions.
 When the Light Ray pass from a higher index material to a
lower index material, light refraction occurs.
 When light incidents at interface between the core and the
cladding has differents angles some power are reflacting back
and some power enter into the cladding
 As the angle is increases larger than the
target no more light enter into the
Cladding layer and all the light reflect back
into the core. This is called “Total Internal
Optical Fiber manufacturer
 Generally it consists on 2 steps by
Glass Fiber preform
Fiber Manufacturing
• 1st Step a preform is made and it has quite exactly the same proportion
core as the cladding material.
• 2nd Step the preform pass through a monitor to deploy the final fiber
into a drum to be storage and distributed.
Special fiber drawing tower
 Optical Implementation
Technology offers byYangtze
Optical Fibre and Cable
Company Ltd. (YOFC) a
Chinese company established in
May 1988.
Optical Fibers Applications
• Nowadays, Optical Fibers connects the world under the sea and over the
• Basically all digital communications travels via fiber.
• A single fiber can carry more communications than the biggest copper
Optical Fibers Applications
 Telecommunications | Internet | Fiber at Home
 Video Streaming | Data Centers | Computer Networks
 Video and Audio
 Military | Governments | Airports |Hospital
 Intelligent | Public transportations
 Everywhere
 Optical Fiber = Optical + Fiber “ At Speed of Light”
 Single Mode Fiber provides higher data rates speed and more
distance than Single Mode
 Single Mode uses a single Ray of Light while Multimode Fiber
employ Light Emitting Diodes (LEDs) to propagate the
 At present, the fiber application might be infinite, however a
deep analysis and design is recommended before implement a
[1] Yangtze Optical Fibre and Cable Company Ltd. (YOFC)
[2] CISCO Networking Academy Program CCNA 1 and 2 book, 3rd Edition,
Indianapolis – CISCO press, 2003.
[3] About Optical Fiber, link:
[4] Eugene Hecht – Optics , International Edition, Pearson Education
 Thank you
 Kiitos
 Tack