What is an optical fibre?
Optical fibres are made of thin cylindrical strands of glass.
The diameter of a typical fibre is close to the diameter of a human hair.
These fibres can carry information, such as text, images, videos, telephone calls.
Also carries anything that can be encoded as digital information, across large distances almost at the speed of light.
Ultra-thin fibres seem very fragile.
But when manufactured correctly as a long thread surrounded by protectives, they serve the purpose in a durable way.
They are strong, light, and flexible, and ideal to be buried underground, drawn underwater, or bent around a spool.
Almost 60 years ago, physicist Charles Kao suggested that glass fibres could be a superior medium for telecommunication, replacing the copper wires of the time.
For his ground-breaking achievements concerning fibre optic communication, Dr. Kao received a part of the 2009 Nobel Prize in physics.
The refractive index is the property of a medium that determines how fast light can travel in it.
When a beam travels in the reverse direction, that is from glass to air, it’s possible that it won’t enter the air.
Instead, it will be completely reflected back within the glass.
This phenomenon, known as total internal reflection.
This is the basis of guiding light across long distances without a significant loss of optical power.
A fibre optic communication system consists of three parts,
A transmitter which encodes information into optical signals (in the form of rapidly blinking light pulses of zeros and ones).
An optical fibre that carries the signal to its destination.
A receiver which reproduces the information from the encoded signal.
Optical waves allow a high data-transmission rate.
Fibre cables are insensitive to external perturbations such as lightning and bad weather.
How were fibre optic cables developed?
In 1840, Jean-Daniel Colladon at the University of Geneva first demonstrated that light’s propagation can be restricted to a narrow stream of a water jet.
Jacques Babinet observed a similar effect in France and extended the idea to bent glass rods.
You may have seen such effects in water fountains lit by colourful beams of light.
Michael Faraday, demonstrated the effect in a water jet at the Royal Society in London in 1854. The effect is also visible in plastic-fibre Christmas trees.
We can guide light using total internal reflection with materials that have a higher refractive index than air.
As Babinet found, a better choice than water is thin glass rods thanks to their availability, durability, and convenience.
In 1954, fibre development made a significant leap forward.
Harold Hopkins and Narinder Singh Kapany at Imperial College London transmitted images using a 75-cm-long bundle of more than 10,000 optical fibres.
Two years later, Lawrence E. Curtiss at the University of Michigan developed the first glass-clad fibres.
His idea to coat the bare glass fibres with a cladding material with a low refractive index paved the way for long-distance data transmission. In the same year, Kapany coined the term ‘fibre optics’.
In 1960, Theodore Maiman built the first laser an excellent optical source further boosted research in optical communication.
In 1966, Kao and his colleagues found that the signals were attenuated due to impurities in the glass rather than the light being scattered.
In 1971, the American glass-making company Corning Glass Works achieved this value in a finished cable.
Nowadays, glass fibres are manufactured using the fibre-drawing technique.
In India, the Fibre Optics Laboratory at the Central Glass and Ceramic Research Institute, Kolkata, has a facility to manufacture high-quality silica-based optical fibres.
Today’s optical fibres have a typical loss of less than 0.2 dB/km.
What is the future of fibre cables?
Fibre optics technology has since been used in telecommunication, medical science, laser technology, and sensing.
With a goal to securing communication and promoting quantum science, the Government of India announced a national mission in the Union Budget of 2020.
The proposed budget for this ‘National Mission on Quantum Technologies and Applications’ is ₹8,000 crore over a period of five years.
The possibilities of fibre optic networks are growing at an accelerated rate, reaching all the way into our homes.
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