Fiber-Optics

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Fiber-Optics

Fiber
Chad Richmond Aaron Parker Billy Spies
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Optical Media

• How data is transmitted over fiber-optics.

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1. To understand how optical media work, we have to
   look at light first.

• The light used in optical fiber networks is one
  type of electromagnetic energy. When an electric
  charge moves back and forth, or accelerates, a
  type of energy called electromagnetic energy is
  produced. This energy in the form of waves can
  travel through a vacuum, the air, and through
  some materials like glass. This is how data is
  transmitted through optical cable.

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How Data Is Carried
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• Light waves
• Reflection
• When a ray of light (the incident ray) strikes
  the shiny surface of a flat piece of glass, some
  of the light energy in the ray is reflected.
  Ideally, all the light needs to be reflected.
• Refraction
• When a light strikes the interface between two
  transparent materials, the light divides into two
  parts. Part of the light ray is reflected back
  into the first substance, with the angle of
  reflection equaling the angle of incidence. The
  remaining energy in the light ray crosses the
  interface and enters into the second substance.
  This is called refraction.

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Applying Light
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• A light ray that is being turned on and off to
  send data (1s and 0s) into an optical fiber must
  stay inside the fiber until it reaches the far
  end. The ray must not refract into the material
  wrapped around the outside of the fiber. The
  refraction would cause the loss of part of the
  light energy of the ray. A design must be
  achieved for the fiber that will make the outside
  surface of the fiber act like a mirror to the
  light ray moving through the fiber. If any light
  ray that tries to move out through the side of
  the fiber were reflected back into the fiber at
  an angle that sends it towards the far end of the
  fiber, this would be a good "pipeline" or "wave
  guide" for the light waves.

• Light can only travel through a piece of fiber if
  it meets these conditions
• Transmitted light must hit the core and the
  outer jacket at an angle lt 90 or lt critical
  angle.
• The inner core of a piece of fiber must have an
  index of refraction greater than that of the
  outer casing (cladding).

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Applying Light (pt 2)
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• Achieving the second condition we just mentioned
  in a piece of fiber, the index of refraction
  part, is easy. Glass already has a greater index,
  is cheap, and is an ideal reflector/refractor, so
  they use glass probably 100 of the time.
• The first condition, or the angle of incidence,
  brings us to something called modes of fiber.
  Now, weve heard of multi-mode fiber and
  single-mode fiber, but just what is a mode?

Modes
A mode is, by definition, the pathway that a blip
of light takes to travel from the origin point,
or Chads flashlight which we saw earlier, to the
destination, which was represented by
Parks. There are two different types of modes
1. Single-Mode Fiber and 2. Multi-Mode Fiber
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Types of Modes
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Transmission
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Okay, so we understand how the light can go
through the fiber, and the different types of
fiber, but we still dont know how it understands
what the light is saying!

• How it transmits light
• The transmitter receives electrical impulses
  from a router, switch, or hub.
• Then, the transmitter converts the 1s and 0s to
  their equivalent light impulses. For example, a
  0 might be a darker pulse then a 1, which
  would be a brighter impulse

• How it receives light
• The receiver on the other end of the fiber-optic
  cable acts like a photovoltaic cell when light
  hits it, electricity is created much like the
  solar cell on most calculators.
• First, an impulse of light must be detected by
  the receiver, then it determines the intensity of
  the light and then converts that into the
  appropriate voltages and sends them off as 1s and
  0s again.

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Loss of Data
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Problems with Data Transmission Fiber-optic cable
is not affected by the sources of external noise
that cause problems on copper media because
external light cannot enter the fiber except at
the transmitter end. The cladding is covered by a
buffer and an outer jacket that stops light from
entering or leaving the cable.
3.) Another factor that causes attenuation of the
light signal is manufacturing irregularities or
roughness in the core-to-cladding boundary. Power
is lost from the light signal because of the less
than perfect total internal reflection in that
rough area of the fiber. Any microscopic
imperfections in the thickness or symmetry of the
fiber will cut down on total internal reflection
and the cladding will absorb some light energy.
4.) Dispersion of a light flash also limits
transmission distances on a fiber. Dispersion is
the technical term for the spreading of pulses of
light as they travel down the fiber.
1.) Although fiber is the best of all the
transmission media at carrying large amounts of
data over long distances, fiber is not without
problems. When light travels through fiber, some
of the light energy is lost. The farther a light
signal travels through a fiber, the more the
signal loses strength. This attenuation of the
signal is due to several factors involving the
nature of fiber itself. The most important factor
is scattering. The scattering of light in a fiber
is caused by microscopic non-uniformity
(distortions) in the fiber that reflects and
scatters some of the light energy. 2.) Absorption
is another cause of light energy loss. When a
light ray strikes some types of chemical
impurities in a fiber, the impurities absorb part
of the energy. This light energy is converted to
a small amount of heat energy. Absorption makes
the light signal a little dimmer.

• 4 Main Causes of Lost Data
• Light scattering
• Absorption of data
• Cable irregularities
• Dispersion of light

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Pros and Cons
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• Pros of using Optical Fiber
• Transmits much more data faster.
• Fiber tends to lose much less data then copper or
  wireless media.
• The size of fiber media are smaller then copper
  media.
• The distances fiber can be transmitted over is
  much greater then other media.
• Fiber-optics use light to carry data, which is
  one of the more easy medium to carry information

• Cons of using Optical Fiber
• More fragile then copper or wireless media.
• Fiber can be expensive the cladding and glass
  pipelines break a lot, resulting in constant
  maintenance.
• Fiber can only go so far until signal dispersion
  renders a signal unusable.