What is index fiber, Physics

What is index fiber? How you define the modes in an optical fiber? Give a relation between core diameter and numerical aperture.

Ans.:  The index profile of a single mode fiber is usually a step index type. Where the refractive index is constant throughout the core. In such a fiber the refractive index profile abruptly changes at the junction of the core and the cladding Because of this abrupt change they are called step index fibers. In the graded-index fiber, the highest index is at the centre and decreases gradually until it reaches the index number of the cladding that is near the surface. From these terms there are three types of optical fibers:  1. Multimode step-index fiber (MMSIF) 2. Multimode graded-index fiber (MMGIF) 3. Single-mode step-index fiber, (SMSIF) The multimode step-index fiber (MMSIF) has a large core diameter ranging from 100 um due to which there are many paths through which light can travel. Therefore, the light ry travelling the straight path through the centre reaches the end before the other rays, which follow a zig-zag path. The difference in the length of time it takes the various light rays to exist the fibre is called modal dispersion. A typical structure and index profile of a multimode step index fibre are shown in figure. The multimode graded index fiber is an improvement on the multimode step index fiber. Because light rays travel faster through the lower index of refraction, light at the fiber core travels more slowly than the light nearer the surface. Therefore, both light rays arrive at the exits point at almost the same time thus reducing modal dispersion. A typical graded index fiber has core diameters ranging from 50 to 85 um and a cladding diameter of 125 um. Fig. shows the typical structure and index profile of a multimode graded index fiber. Graded index fibers can be manufactured with a variety of different index grading profiles. One of the most popular profile functions is the alpha profile function. In which the index of refraction within the core is made to vary radically as where n is the core index at radial distance r from the core axis, n is the index at the core axis, is the normalized difference between the core and cladding indexes, d is the core diameter and is the grading profile index number. Graded index fibers generally will not support as many modes as the corresponding step index fibers. When a finite value of alpha is used, then the number of supported modes for a large number of modes is reduced according to the expression:  Graded index fibers are almost always used as multimode fibers and can give better performance as single mode fiber if designed carefully. The single mode step index fiber is widely used for wide band communication application have a light ray can travel in only one path making modal dispersion zero. This fiber has a very fine thin core of uniform refractive index of a higher value which is surrounded by a cladding of lower refractive index. Typical single mode step index fiber has a core diameter in the range 5 to 10 um with standard cladding diameter of 125 um. Fig. shows the typical structure and index profile of a single mode step index fiber. 

Posted Date: 6/30/2012 11:45:54 PM | Location : United States







Related Discussions:- What is index fiber, Assignment Help, Ask Question on What is index fiber, Get Answer, Expert's Help, What is index fiber Discussions

Write discussion on What is index fiber
Your posts are moderated
Related Questions
what is the biot law give the mathmatical description.

Q. Orbital Velocity for Low Earth Orbit Neglecting air friction an object will sustain a low altitude orbit when the centrifugal force due to its motion in a circular orbit is

Consider a particle of energy E is incident from the left on a rectangular potential barrier of height and width and on both sides of this barrier at which means that no force act

Is photon a particle or a wave? What is its rest mass? Can X-ray generate photoelectric effect? Determine the work function of a metal production photo electrons with X-rays of

A 1.6 kg man swings from a 2 meter rope at an angle of 45 degrees after swinging 20 degrees past the center point, the rope is cut by a razor. The man goes flying through the air

characteristics of schottky diode

Universal age paradox Two most straightforward methods of computing the age of the Universe through redshift measurements, and stellar evolution yield incompatible results. Re

Q. Define Fermi energy. Write down the expression for Fermi Dirac distribution law. Deduce an expression for Fermi energy of a system of free particles. Sol. The Fermi Energy

B-Infrared (IR)  Radiant Heat Heat radiation can be achieved by using infrared (IR) radiation it penetrates about 3mm in the skin. excessive exposure can cause erythema(redden