1. Introduction

The idea of communicating by light was around for a long time, long before fiber optics. It took many years for the ideas behind fiber optics to evolve from conventional optics. Even at that time, people were thinking of making special optical devices than of optical communications. Form basic science, everyone knows that light travels in straight lines. Even though lenses can bend light and mirrors can deflect it, light still travels in straight lines between the optical devices. Many inventions have croped up as a result of this principle, such as telescopes, microscopes and cameras. However, there are times when light is needed to probe inside corners that are not in straight lines. This problem arose long before the solution was found. The need to pipe light from place to place, for communicating, viewing, illuminating and other purposes led to the invention of fiber optics.

1.2 Basics Of Fiber Optics

Fiber optics is a hybrid field. It started as a spin-off of classical optics. The basic concept of a fiber is optical and fiber bundles are used as optical components. As fiber became a communication medium, the field used concepts and terminology from electronic communications. Transmitters and receivers convert signals from electrical to optical format and back. They are part optics and part electronics. For good understanding of fiber optics, one must master the field of optics. Other important fields are communications and electronics. The first step is to understand optics.

Core: the inner light-carrying member. Cladding: the middle layer, which serves to confine the light to the core. Buffer: the outer layer which serves as a "shock absorber" to protect the core and cladding from damage. The concentric layers of an optical fiber include the light-carrying core, the cladding and the protective buffer.

The working of optical fibers depend on basic properties of optics and the interaction of light with matter. From a physical standpoint, light can be seen as either electromagnetic waves or photons, which is a quantum of electromagnetic energy. This is a famous wave particle duality of physics. The most useful point for optics often is to consider light as rays travelling in straight lines between optical elements, which can reflect or bend(refract) them. Light is only a small part of electromagnetic radiation. The nature of all electromagnetic radiation is the same; it can be viewed as photons or waves and travels and travels at the speed of light, which is 300,000 km/s. The difference between radiation in difference parts of the spectrum is a quantity that can be measured in several ways; as length of waves, energy of photons or as oscillation frequencies of electromagnetic fields. Most optical fibers used transmit light in the near infrared light at wavelengths of 800-1600 nm. The silica glasses used in most fibers are transparent at these wavelengths. Plastic fibers transmit best at visible wavelengths, but they are not as transparent as those wavelengths as glass fibers are in the infrared. Special fibers, which are currently in development, are made of materials other than silica and can transmit light at longer infrared wavelengths. Some special grade silica can transmit some near ultraviolet light.

1.3 Refractive Index and Total Internal Reflection

The most important optical measurement for any transparent material is its refractive index(n). The refractive index is the ratio of the speed of light in vacuum to the speed of light in the medium:
n = Cv/Cm
where C_v is the speed of light in vacuum

C_m is the speed of light in the medium.
The speed of light in a material is always slower than in vacuum, so the refractive index is greater than one in the optical part of the spectrum. Although light travels in straight lines through optical materials, light is bent at the surface. This happens as the refractive index changes as it moves from one medium to another. When the angle of incidence exceeds a critical value, where the sine of the angle equals one ( Snell's Law) the light will undergo total internal reflection and be bounced back into the glass, as shown in the figure below.

Once light reflects down a fiber, it will continue to do so.

It is this phenomenon of total internal reflection that keeps light confined in optical fibers and also happens to be the basic concept behind the optical fiber.

1.4 Why Fiber Optics ?

The fundamental difference between a fiber optic communication system and other types is that signals are transmitted as light. Conventional electronic communication relies on electrons passing through cables. Microwave communication relies on microwaves travelling through open space. High transmission capacity and long transmission distance are two major advantages of fiber optics compared with metal cables. However, different factors can dictate the choice of fiber for other applications. The wide variety of fiber optic systems have led to many applications and some of them are:

Connections between chips and circuits in computers (which will be the main aspect of this project).

Links among computers used for purposes such as computer aided design.

Local Area Networks operating at speeds too high or over distances too long for the use of metal cables.

.

High speed interconnections between computers and peripheral devices, or between computers.

Transmission for difficult environments, especially those plagued with electromagnetic interference.

These are a few of the current fiber optic applications. More are sure to come as technology develops. The main application that will be dealt with in this project is fiber optic connections within computers.

---