Introduction to the Optical Fiber

Contents

Introduction

Total Internal Reflection

Numerical Aperture

Single & Multi mode fiber

Step Index and Graded Index Fiber

Optical Fiber Communication System

Applications of Optical Fibers

Problems on NA

1M Previous Years' Questions

Communication using electromagnetic waves is today the most reliable, economical, and fastest way of communicating information between different points. In any communication system, the information to be transmitted is generated at a source; gets transmitted through a channel such as atmosphere in radio broadcast, or electrical lines in telephone or wireless network in mobile communication, or optical fibers in a fiber-optic communication system; and finally reaches a receiver, which is the destination. Optical frequencies are extremely large compared to radio waves and microwaves. Hence a light beam acting as a carrier wave is capable of carrying far more information in comparison to radio waves and microwaves. Light wave communication using glass fibers can transmit information at capacities of larger than 1 Tb/s (which is roughly equivalent to transmission of about 15 million simultaneous telephone conversations). At the heart of an optical communication system is the optical fiber that acts as the transmission channel carrying the light beam loaded with information. The light beam gets guided through the optical fiber due to the phenomenon of total internal reflection (TIR).

Optical Fiber

The construction of optical fiber (OF) is very crucial. The average diameter of optical fibers are in the order of 0.25 to 0.5 mm. Figure 1 shows the construction of an optical fiber. It consist of mainly five components namely, core, cladding, coating, strengthening fibers and cable jacket. The cable jacket protect the optical fiber from external damage. Strengthening fiber provide the strength to the fiber. Coating helps to reduce the attenuation (loss) and act as a shield from external radiation.

total-internal-reflection 1

Figure 1. Different parts of an optical fiber

The optical signal is transmitted in the core which is surrounded co-axially by cladding. The refractive index of core (µ1) is greater than that of the cladding (µ2), so that due to the phenomenon of TIR and light signal will always pass through the core medium.