1. LED & laser
Name – Bhupender singh
Roll no. – 13ECE06
subject – Optical communication
• INTRODUCTION TO LED
• LED WORKING
• USE OF LED IN OPTICAL FIBER
• LASER WORKING
• USE OF LASER IN OPTICAL FIBER
• COMPARSION OF LED & LASER
3. INTRODUCTION TO LED
• A light-emitting diode (LED) is a two-lead semiconductor light source that
convert an electrical current into light.
• It is a p-n junction diode, which emits light when activated. When a
suitable voltage is applied to the leads.
• A light emitting diode (LED) is known to be one of the best optoelectronic
devices out of the lot.
4. LED WORKING
• A P-N junction can convert absorbed light energy into a proportional electric current.
The same process is reversed here (i.e. the P-N junction emits light when electrical
energy is applied to it). This phenomenon is generally called electroluminescence.
• Which can be defined as the emission of light from a semi-conductor under the
influence of an electric field.
• The charge carriers recombine in a forward-biased P-N junction as the electrons cross
from the N-region and recombine with the holes existing in the P-region.
• Free electrons are in the conduction band of energy levels, while holes are in the
valence energy band.
• Thus the energy level of the holes will be lesser than the energy levels of the
• Some portion of the energy must be dissipated in order to recombine the electrons
and the holes. This energy is emitted in the form of heat and light.
6. USE OF LED IN OPTICAL FIBER
• Light emitters are a key element in any fiber optic system.
• This component converts the electrical signal into a corresponding light signal that
can be injected into the fiber.
• LEDs are of interest for fiber optics because of five inherent characteristics:
1. They are small.
2. They possess high radiance (i.e., They emit lots of light in a small area).
3. The emitting area is small, comparable to the dimensions of optical fibers.
4. They have a very long life, offering high reliability.
5. They can be modulated (turned off and on) at high speeds.
• A laser is a device that emits light through a process of optical amplification based
on the stimulated emission of electromagnetic radiation.
• LASER stands for "light amplification by stimulated emission of radiation”.
• it emits light coherently, Spatial coherence allows a laser to be focused to a tight
• A laser is a coherent and focused beam of photons.
9. LASER working
• laser is created when the electrons in atoms in special glasses, crystals, or gases
absorb energy from an electrical current or another laser and become “excited.”
• The excited electrons move from a lower-energy orbit to a higher-energy orbit
around the atom’s nucleus.
• When they return to their normal or “ground” state, the electrons emit photons
(particles of light).
• its light contains only one wavelength (one specific color) and laser light is
10. USE OF LASER IN OPTICAL FIBER
• Where higher levels of performance are required, i.e. it is necessary that the fibre
optic link can operate over greater distances and with higher data rates, then lasers
• the light output is directional and this enables a much higher level of efficiency in
the transfer of the light into the fibre optic cable.
• lasers have a very narrow spectral bandwidth as a result of the fact that they
produce coherent light. This narrow spectral width enables the lasers to transmit
data at much higher rates.
• Laser diodes are often directly modulated. This provides a very simple and
effective method of transferring the data onto the optical signal.