LED & laser

Name – Bhupender singhRoll no. – 13ECE06subject – Optical communication

Content

• INTRODUCTION TO LED • LED WORKING• USE OF LED IN OPTICAL FIBER• LASER• LASER WORKING• USE OF LASER IN OPTICAL FIBER • COMPARSION OF LED & LASER

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. 

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 electrons. 

• 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.

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.

Optical fiber communication

LASER• 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 spot.

• A laser is a coherent and focused beam of photons. 

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 directional.

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 are used. 

• 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.

COMPARSION OF LED & LASER

Thank you