Module 2 : Ray Model
Lecture : Ray Model
  PROPAGATION OF LIGHT IN AN OPTICAL FIBER (RAY MODEL)
1.1 BASICS
1.
Optical fiber is basically a solid glass rod. The diameter of rod is so small that it looks like a fiber.
2.
 Optical fiber is a dielectric waveguide. The light travels like an electromagnetic wave inside the waveguide. The dielectric
waveguide is different from a metallic waveguide which is used at microwave and millimeter wave frequencies.
3.
 In a metallic waveguide, there is a complete shielding of electromagnetic radiation but in an optical fiber the
electromagnetic radiation is not just confined inside the fiber but also extends outside the fiber.
4.
 The light gets guided inside the structure, through the basic phenomenon of total internal reflection .
5.

The optical fiber consists of two concentric cylinders; the inside solid cylinder is called the core and the surrounding

  shell is called the cladding . (See Fig 1)
 

Figure1: Schematic of an optical fiber
 
6. For the light to propagate inside the fiber through total internal reflections at core-cladding interface, the refractive index of
  the core must be greater than the refractive index of the cladding. That is .
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