Fiber Optic

Introduction to Fibre Optics

Fibre is an integral part of modern day communication infrastucture and can be found along roads, in buildings, hospitals and machinary. The fibre itself is a strand of silica based glass, it's dimensions similar to those of a human hair, surrounded by a transparent cladding. Light can be transmitted along the fibre over great distances at very high data rates providing an ideal medium for the transport of information.

Fibre Basics
Fibre Structure - It has an inner glass core with an outer cladding. This is covered with a protective buffer and outer jacket. This design of fibre is light and has a very low loss , making it ideal for the transmission of information over long distances.

Light in a fibre - The light propagates along the fibre by the process of total internal reflection. The light is contained within the glass core and cladding by careful design of their refractive indices. The loss along the fibre is low and the signal is not subject to electromagnetic interference which plagues other methods of signal transmission, such as radio or copper wire links.

Types of fiber-optic cables

Single Mode Fibre
The simplest type of optical fiber is called single-mode. It has a very thin core about 5-10 microns (millionths of a meter) in diameter. In a single-mode fiber, all signals travel straight down the middle without bouncing off the edges (red line in diagram). Cable TV, Internet, and telephone signals are generally carried by single-mode fibers, wrapped together into a huge bundle. Cables like this can send information over 100 km (60 miles).

Multi-Mode Fibre
Another type of fiber-optic cable is called multi-mode. Each optical fiber in a multi-mode cable is about 10 times bigger than one in a single-mode cable. This means light beams can travel through the core by following a variety of different paths (purple, green, and blue lines) - in other words, in multiple different modes. Multi-mode cables can send information only over relatively short distances and are used (among other things) to link computer networks together.

A brief history of fiber optics

*1840s: Swiss physicist Daniel Colladon (1802-1893) discovered he could shine light along water pipe. The water carried the light by internal reflection.
*1870: An Irish physicist called John Tyndall (1820-1893) demonstrated internal reflection at London's Royal Society. He shone light into a jug of water. When he poured some of the water out from the jug, the light curved round following the water's path. This idea of "bending light" is exactly what happens in fiber optics. Although Colladon is the true grandfather of fiber-optics, Tyndall often earns the credit.
*1930s: Heinrich Lamm and Walter Gerlach, two German students, tried to use light pipes to make a gastroscope-an instrument for looking inside someone's stomach.
*1950s: In London, England, Indian physicist Narinder Kapany (1927-) and British physicist Harold Hopkins (1918-1994) managed to send a simple picture down a light pipe made from thousands of glass fibers. After publishing many scientific papers, Kapany earned a reputation as the "father of fiber optics."
*1957: Three American scientists at the University of Michigan, Lawrence Curtiss, Basil Hirschowitz, and Wilbur Peters, successfully used fiber-optic technology to make the world's first gastroscope.
*1960s: Chinese-born US physicist Charles Kao (1933-) figured out how to make a very pure fiber-optic cable that can carry telephone signals over long distances.
*1960s: Researchers at the Corning Glass Company made the first fiber-optic cable capable of carrying telephone signals.
*1977: The first fiber-optic telephone cable was laid between Long Beach and Artesia, California.
*1997: A huge transatlantic fiber-optic telephone cable called FLAG (Fiber-optic Link Around the Globe) was laid between London, England and Tokyo, Japan.

Brief overview of Fibre Optic Advantages over Copper:

o SPEED: Fiber optic networks operate at high speeds - up into the gigabits
o BANDWIDTH: large carrying capacity
o DISTANCE: Signals can be transmitted further without needing to be "refreshed" or strengthened.
o RESISTANCE: Greater resistance to electromagnetic noise such as radios, motors or other nearby cables.
o MAINTENANCE: Fiber optic cables costs much less to maintain.

In recent years it has become apparent that Fiber Optics are steadily replacing copper wire as an appropriate means of communication signal transmission. They span the long distances between local phone systems as well as providing the backbone for many network systems. Other system users include cable television services, university campuses, office buildings, industrial plants, and electric utility companies.
A fiber-optic system is similar to the copper wire system that fiber-optics is replacing. The difference is that fiber-optics use light pulses to transmit information down fiber lines instead of using electronic pulses to transmit information down copper lines. Looking at the components in a fiber-optic chain will give a better understanding of how the system works in conjunction with wire based systems.
At one end of the system is a transmitter. This is the place of origin for information coming on to fiber-optic lines. The transmitter accepts coded electronic pulse information coming from copper wire. It then processes and translates that information into equivalently coded light pulses. A light-emitting diode (LED) or an injection-laser diode (ILD) can be used for generating the light pulses. Using a lens, the light pulses are funneled into the fiber-optic medium where they transmit themselves down the line.
Think of a fiber cable in terms of very long cardboard roll (from the inside roll of paper towel) that is coated with a mirror.
If you shine a flashlight in one you can see light at the far end - even if bent the roll around a corner.
Light pulses move easily down the fiber-optic line because of a principle known as total internal reflection. "This principle of total internal reflection states that when the angle of incidence exceeds a critical value, light cannot get out of the glass; instead, the light bounces back in. When this principle is applied to the construction of the fiber-optic strand, it is possible to transmit information down fiber lines in the form of light pulses.