Write a note on following: Coaxial Cable, Fiber Optics
Answer:-
Coaxial Cable:
Coaxial cable has better shielding and greater bandwidth than unshielded twisted pairs, so it can span
longer distances at higher speeds.
Two kinds of coaxial cable are widely used. One kind, 50-ohm cable, is commonly used when it is
intended for digital transmission from the start. The other kind, 75-ohm cable, is commonly used for
analog transmission and cable television.
Fiber Optics:
Fiber optics are used for long-haul transmission in network backbones, highspeed LANs (although so far,
copper has always managed catch up eventually), and high-speed Internet access such as FttH (Fiber to the Home).
An optical transmission system has three key components: the light source, the transmission medium, and
the detector. The transmission medium is an ultra-thin fiber of glass. The detector generates an electrical
pulse when light falls on it.
Fig(a): When a light ray passes from one medium to another—for example, from fused silica to air—the ray is refracted (bent) at the silica/air boundary. A light ray incident on the boundary at an angle α1 emerging at an angle β1. The amount of refraction depends on the properties of the two media (in particular, their indices of refraction)
Fig (b): The light is refracted back into the silica; none of it escapes into the air. Thus, a light ray incident at or above the critical angle is trapped inside the fiber. The fig shows the only one trapped ray, but since any light ray incident on the boundary above the critical angle will be reflected internally, many different rays will be bouncing around at different angles. Each ray is said to have a different mode, so a fiber having this property is called a multimode fiber.