In one line
A fibre optic communication system converts an electrical signal into light at the transmitter, sends it through an optical fibre, and converts it back to an electrical signal at the receiver.
Explained simply
It is like sending a message with a torch: you switch the torch on and off in a pattern (transmitter), the light travels down a "light pipe" (fibre), and your friend's eyes read the flashes (receiver). Real systems do this billions of times per second.
How it works
- Information source: voice, video or data, converted into an electrical signal.
- Transmitter: an encoder/modulator puts the signal in a suitable (usually digital) form and drives a light source, an LED or laser diode, which converts electrical pulses into light pulses.
- Source-to-fibre coupler: launches the light into the fibre within its acceptance cone.
- Optical fibre (channel): carries light by total internal reflection over long distances.
- Repeaters or optical amplifiers: placed at intervals to boost the weakened signal (for example erbium-doped fibre amplifiers).
- Fibre-to-detector coupler and photodetector: a PIN photodiode or avalanche photodiode converts light pulses back into electrical current.
- Receiver: amplifier, demodulator/decoder and filters recover the original signal.
- Destination: phone, TV or computer.
Quick example
When you stream a video, the data from a server may travel thousands of kilometres through single-mode fibres at 1550 nm, being amplified along the way, before reaching the local exchange and finally your Wi-Fi router.
Common mistakes
- Drawing the block diagram without a light source or detector.
- Calling the photodetector a "light source" or mixing up LED and photodiode roles.
- Leaving out repeaters/amplifiers in long-distance systems.
How MU asks it
Asked as "Draw and explain the block diagram of fibre optic communication system" (5 marks). Draw the blocks in a line (source, modulator, light source, fibre, repeater, detector, demodulator, destination) and write two lines on each block.