Advanced Fibre Optics

1
Advanced Fibre Optics

• Aroon Pasricha
• And
• Gnanamohan Gnanasegaram

2
Overview

• Introduction
• Composition of optical fibre
• Operation of the fibre optic system
• Advantages and disadvantages
• Analog and digital communication
• Two main types of cables
• Pulse Spreading
• Transmission Loss
• Interviews
• Conclusions

3
Introduction

• Fibre optics is being used to transmit
  television, voice, and digital data signals by
  light waves over flexible hair like threads of
  glass and plastic. It has evolved into a system
  of great importance and use since the 1980s.
• The advantages of fibre optics compared to
  coaxial cable or twisted pair cable, are endless.
  Millions of dollars are being spent to put
  light wave communication systems into operation,
  as a result of its performance.

4
Composition of optical fibre

• Silica based glass or plastic filaments are spun
  and packed into bundles of several hundreds or
  thousands. Bundles may be put together as rods
  or ribbons and sheets.
• These bundles are flexible and can be twisted and
  contorted to conduct light and images around
  corners
• The thin glass center of the fibre where the
  light travels is called the core.
• The outer optical material surrounding the core
  that reflects the light back into the core is
  called the cladding.
• In order to protect the optical surface from
  moisture and damage, it is coated with a layer of
  buffer coating.

Cross section of a bundle
5
Operation of the fibre optic system

• Light is ejected into the glass core at the
  correct angle and transmitted it will reflect
  back repeatedly with internal reflections, even
  when the rod is curved. Light cannot escape from
  a fibre optics cable. A bundle of rods of fibres
  is capable of taking an image projected at one
  end of the bundle and reproducing it at the other
  end.

Reflected path of light in the glass rod
6
Operation of the fibre optic system

• In a fibre optic system, there are a few major
  components to perform the task of communication.
• The Input Modulator is needed this modulates the
  incoming signal with a light beam.
• A light emitting device is used it can be either
  a light emitting diode (LED) or a semiconductor
  laser diode.
• A fibre optic cable is used as a transportation
  medium.
• A fibre optic system converts an electrical
  signal to an infrared light signal, and then
  transmits the signal onto an optical fibre.
• An Output Modulator is used to separate the
  signal from the light beam.
• Special connectors must be used to couple the
  light from the source to the fibre and from the
  fibre to the detector.

7
Advantages and Disadvantages

• ADVANTAGES
• Fibre optic cables have a much greater bandwidth
  than metal cables.
• Fibre optic cable is less susceptible to signal
  degradation than copper wire.
• Fibre optic cables weigh less than a copper wire
  cable.
• Data can be transmitted digitally.
• Lower-power transmitters can be used instead of
  the high-voltage electrical transmitters used for
  copper wires.
• Unlike electrical signals in copper wires, light
  signals from one fibre do not interfere with
  those of other fibres in the same cable.
• Because no electricity is passed through optical
  cable it is non-flammable, and immune to
  lightning.
• Impossible to tap into a fibre optics cable,
  making it more secure

8
Advantages and Disadvantages

• DISADVANTAGES
• Fibre optics are that the cables are expensive to
  install.
• The termination of a fibre optics cable is
  complex and requires special tools.
• They are more fragile than coaxial cable.

9
Analog and Digital Communication

• An analog signal changes continuously, while a
  digital signal can be at only a certain number of
  discrete levels.
• Conventionally, analog is used for audio and
  video communication.
• Analog technology has been used because our ears
  detect continuous fluctuations in sound levels,
  not just the presence or absence of sound.
• Going through a system where the analog signal
  can not be successfully reproduced outputs a
  distorted signal which is what happens when we
  get a distorted voice on the telephone or radio.
• Digital transmission works the best both analog
  and digital signals are found in audio and
  telephone systems.
• Analog signals are converted to digital before
  transmission and then back to analog signals.

10
Two main types of cables

• Step Index Fibre
• This cable has a specific index of refraction for
  the core and the cladding.  It causes
  deformations due to the various paths lengths of
  the light ray.  This is called modal distortion.
  It is the cheapest type of cabling. Within the
  cladding and the core, the refractive index is
  constant.
• Graded Index Fibre
• In graded index fibre, rays of light follow
  sinusoidal paths. Although the paths are
  different lengths, they all reach the end of the
  fibre at the same time. Multimode dispersion is
  eliminated and pulse spreading is reduced. Graded
  Index fibre can hold the same amount of energy as
  multimode fibre. The disadvantage is that this
  takes place at only one wavelength.

11
Pulse Spreading

• Optical fibres that carry data consist of pulses
  of light energy following each other. The fibre
  has a limit as to how many pulses per second can
  be sent to it and be expected to emerge intact at
  the other end. This is known as pulse spreading
  which limits the Bandwidth of the fibre.
• The pulse sets off down the fibre with a square
  wave shape. As it travels along the fibre, it
  progressively gets wider and the peak intensity
  decreases.

12
Transmission Loss

• The transmission loss or attenuation of an
  optical fibre is perhaps the most important
  characteristic of the fibre this determines if a
  system is practical. It controls (1) spacing
  between repeaters and (2) the type of optical
  transmitter and receiver to be used.
• As light waves travel down an optical fibre, they
  lose part of their energy because of various
  imperfections in the fibre. These losses are
  measured in decibels per kilometers (dB/km).

13
Interviews

• Kushner, Jeff, Fibre Solutions Specialist,
  CORNING
• Stated fibre optics is a revolution that may
  affect our lives as much as computers and
  integrated circuits have. Fibre optics is being
  compared in importance with microwave and
  satellite transmissions in the advanced world of
  communications.
• Ali, Zafar, Configuration Supervisor, Unisys
  Canada Inc.
• stated that fibre optics will make using devices
  that use services such as two-way television that
  was too costly before the development of fibre
  optics easier to use with better quality. In
  addition to an incredible bandwidth, fibre optics
  has smaller and lighter cables than conventional
  copper-conductor systems, with immunity to
  electrical noise, and numerous other advantages.

14
Conclusion

• The age of optical communications is a new era.
  In several ways fibre optics is a pivotal
  breakthrough from the electric communication we
  have been accustomed to. Instead of electrons
  moving back and forth over a regular copper or
  metallic wire to carry signals, light waves
  navigate tiny fibres of glass or plastic to
  accomplish the same purpose.
• With a bandwidth and information capacity a
  thousand times greater than that of copper
  circuits, fibre optics may soon provide us with
  all the communication technology we could want in
  a lifetime, at a cost efficient price.
• Any new communication system that does not use
  fibre optics, or consider its use, is obsolete
  even before it has been built. It is apparent
  that the average technician may also become
  superseded if he or she fails to master fibre
  optics. After all, the technician will be
  responsible for repairing and maintaining fibre
  optic systems wherever they are used, not the
  engineer.

15
THE END