Introduction
A thin wire made up of silica which is used to transmit signal in the form of light signal is known as optical fiber. As, instead of metal wires, fibres are used, transmission over longer distances are possible. Optical fibres are now used for fibre optic internet, tv services, telecommunications etc.
There are different types of fibre optic network.
1) FTTH- Fibre To The Home
Here signal is delivered directly to home.
2) FFTB- Fibre To The Building- here signal is delivered on a shared property. One needs another cable to deliver the signal to home.
3) FTTC- Fibre To The Curb
The signal is transmitted to the curb near home.
Transmission in the form of light signal has many advantage over electrical transmission.
A) Less attenuation- This means less signal loss during transmission from one end to other.
B) High bandwidth- Means the data transfer rate is higher as compared to electrical transmission.
C) Unlike electrical signal, light signal is immune to electromagnetic interference.
D) As these are light signals they do not carry current hence cannot generate spark.
Overall optical transmission is profitable, fast and safe mode of transmission.
It has some disadvantages also:-
1) Optical fibres are not flexible hence they break on too much bending.
2) They are very expensive to install.
3) They are not robust as wire.
4) Optical fibres are very tender hence highly susceptible to damage during installation.
Working principles
The principle behind light transmission through optical fibre is total internal reflection. When angle of incidence is greater than limiting angle called critical angle, the ray reflects back in the same medium, this phenomenon is known as total internal reflection. This technique of bending light in same medium is used in optical fibre. The light ray travel along the fibre.
The fibre consist of a core and a cladding layer. In optical fibre cladding is a layer made up of material of lower refracting index, which is in close contact with core made up of higher refractive index. The cladding helps light to travel inside the core. Total internal reflection takes place at the boundary of cladding and core. In single mode fibre cladding has a refractive index of 1.444 and that of core is 1.4475. As for total internal reflection angle of incidence should be greater than critical angle therefore only light that enters the fibre within a certain range of angles can travel down the fibre. This range is called acceptance cone.
Uses of Fibre Optic cable
1) Internet- Optical fibre is used to transfer data at very high speed. They transfer more data in lesser time as compared to copper wire.
2) Medical field- Fibre optic cables have enormous use in medical field. Mostly they are used in endoscopy. Using optical fibre for lightening purpose during surgery reduces the number and size of incisions made.
3) Decorations- Optical fibres are very attractive and colourful hence are largely used for decorations on various occasion. They are available on low cost and are easy to operate.
4) Defense- They are used for wiring in SONAR, aircraft, hydrophone etc. As data transfer rate is very high in case of optical fibre therefore they are used for data transmission in high level data security in fields of military and aerospace applications.
5) Automotive industry- Optical fibres are used in vehicles both interior and exterior. They consume less space and has good illuminating power. They are used for safety purpose also. They transport signals between different parts of the vehicle at very high speed so they can be used in airbags.
