A Revolutionary New Technology

This is based on light wave communication through hair thin strands of glass or plastic named as optical fiber. These are cylindrical wave guide system, which can be operated in optical frequency. It is transforming world communication net work.

Manufacturing of Optical Fibers

it can be made out of glass, silica or plastic core of diameter 10 to 100 mm with refractive index n1. The core is surrounded by a plastic covering with refractive index n2. N2 less than n2, N1-n2 is of the order 10*-3. The refractive indices are 1.52 and 1.48. for giving safety and strength a plastic coating called jacket is provided.

The glass core is of the diameter 10-600 microns, gladding thickness is between 123-630 microns and that of jacket 250-1040. For plastic fiber, diameters range between 750-2000.

The Working of Optical Fibers

The light wave travels through optical fibers by the phenomenon known as total internal reflection. The phenomenon which is responsible for brilliance of diamonds, and precious stones, mirage, etc. total internal reflection is the returning of light in same denser medium when light is incident on interface of two medium having different densities at an angle of incidence in denser medium greater than critical angle. Critical angle is that angle for which angle of refraction is 90degree.

Transmission of Light in Optical Fiber

Consider one end of an optical fiber in which light enters at an angle greater than critical angle, the light will be reflected internally and it continues reflecting and passes through the fiber. Optical fiber is also called optical wave guide.

Acceptance Angle and Acceptance Cone

It is the maximum angle at which the light wave can make for total internal reflection possible and light wave guided and propagate through the fiber.

Acceptance angle forms a cone since it can be launched from anywhere a circular base.

Modes of Propagation

Light is an electromagnetic wave, mode describes EM field pattern along the light path inside the fiber. When axial electric field is zero, and axial magnetic field is not zero it is in transverse electric mode. When axial electric field is not zero and magnetic field is zero then it is in transverse magnetic mode. if both fields are non zero then it is in hybrid mode.

Fiber Attenuation  

It is loss of light energy due to impurities or bend, absorption or scattering.

Advantages of Optical Fiber

  • Light weight and occupy less space than coaxial cable
  • Low attenuation than in coaxial cables
  • Longer life
  • Stronger against environmental hazards
  • Composed of dielectric material so immune against electric and magnetic field
  • Transmission speed is high
  • Number of signal channels can be accommodated whose band width is larger
  • Little signal linkage so cross talk is not possible
  • Safe against high voltage
  • Because of non conductivity and non inductivity no interference with other communication system
  • More economical than copper wire
  • No corrosion
  • Easily bent or twist

Disadvantages

Alone it is useless only work with electronics devices. There is need of metallic cables. They need special tools to handle

O F in Telecommunication

In telecommunication a very large number of electrical signals is to be carried at same time. The electrical is first converted to light signal and finally it is converted to electrical signals. Light signal is transmitted through fiber optical cables. Here the fiber is strengthened, it is to be pulled through under ground ducts. Joining of fibers is done by arc discharge. Melted and fusing together.

Uses of O F

In telecommunication, O F sensor is used to measure temperature and pressure. In medical investigations to see inside the human body.