TYPES OF OPTICAL FIBER Part1:-

Fibers basically classified as two types on the basis of index profile no. of modes.

Index Profile:- a) Step Index b) Graded Index

Modes:- a) Single mode fiber b) multitude fiber

• The index profile is defined as the variation or graphical representation as the variation of refractive index across the fiber.
• A mode is defined as the stable field distribution of the light in the fiber in a particular distribution.

Index profile:-

(a)Step Index:-

a1) Step Index Fiber:-

• Index profile is constant through out the core and makes a step change /Abrupt change at core cladding interface.

n(r)= n1, r>a

n(r) = n2, r>=a

a2) Step Index Multi-mode Fiber:-

• In order to launch more number of modes the radius of the core is to be high i.e around 25 um.
• As the refractive index of modes the core is constant hence the velocity of all the modes will be same. Hence, the modes travelling Zig-Zag path will travel a long distance as compared to the fundamental mode which is travelling the straight path through the core axis. Hence, there will be propagation delay between the mode which will lead to inter- modal or modal of fiber based dispersion.
• The amount of dispersion depends on the delay difference between the arrival time of slowest m ode (longest path) and the fastest mode (shortest path) . ∂T= Tmax-Tmin ∂T=L n1²∆/C n2

• The pulse broadning and the delay between the modes depends on the length of the fiber because as the length increases the distance of the Zig-Zag mode is also increases. Hence, Pulse broadning increases.
• The inter-model dispersion does not depend on the radius of the core and cladding but depends on their refractive index.
• NOTE:- As the length of the fiber increases ∂T Increases. Hence, inter-model dispersion and BER also increases. Which results in to reduction transmission, capacity & Bandwidth, data rate of the fiber. Hence, Step index multimode fibers are for short distance communication.

Thanks & Regard, Rahul Mishra