Difference between LED and LASER

Difference between LED and LASER

Difference between LED and LASER, in this post the basic differences between LED and LASER. But before that, some basic information about LED and LASER is discussed before the differences.

LED

The LED is a semiconductor p–n junction device that gives off spontaneous optical radiation when subjected to electronic excitation. The electronic excitation is achieved by applying a forward bias voltage across the p–n junction. This excitation energizes electrons within the material into an ‘excited’ state which is unstable. When the energized electrons return to the stable state, they release energy in the process and this energy is given off in the form of photons.

The radiated photons could be in the UV, visible or IR part of the electromagnetic spectrum depending on the energy band-gap of the semiconductor material. In LEDs, the conversion process is fairly efficient, thus resulting in very little heat compared to incandescent lights.

Advantages of LED

  1. Simple design.
  2. Ease of manufacture
  3. Simple system integration
  4. Low cost
  5. High reliability
  6. Simple fabrication
  7. simple drive circuitry
  8. Linear light output against current characteristics
  9. Less temperature-dependent.

Disadvantages of LED

  1. Refraction of light at the semiconductor/air interface.
  2. The average lifetime of radiative recombination is only a few nanoseconds, therefore modulation BW is limited to only a few hundred megahertz.
  3. Low coupling efficiency usually low optical power coupled into fiber (µW).
  4. Large chromatic dispersion.

LASER

Laser, which is the acronym for light amplification by stimulated emitted radiation, is a device that amplifies (generated) light, as the name suggests, but they are rarely used for this purpose in practice.

Lasers are used mainly as an optical oscillator with light bouncing back and forth in an optical cavity. One end of the cavity is made to have almost 100% reflection while the other is significantly less to allow the emission of monochromatic light (not exactly single wavelength but a very narrow band of wavelengths, typically 0.1–5 nm). In the operation of a laser, certain vital conditions are required to be met before lasing can take place.

Advantages of Laser

  1. Simple economic design
  2. High optical power
  3. Production of light can be precisely controlled
  4. Can be used at high temperature
  5. High coupling efficiency
  6. Low spectral width (3.5 nm).
  7. High radiance compared to LED.
  8. Modulation capabilities upto GHz range.
  9. Ability to maintain the intrinsic layer charecterics over long periods.

Disadvantages of Laser

  1. At the end of the fiber, a speckle pattern appears as two coherent light beams add or subtract their electric field depending upon their relative phase.
  2. The laser diode is extremely sensitive to overload currents and at high transmission rates.

Difference between LED and LASER

ParametersLEDLASER
Full FormLight Emitting DiodeLight Amplification by Stimulated Emission of Radiation
Principle of operationSpontaneous emissionStimulated emission
Optical Output PowerLow PowerHigh Power
Optical spectral widthBroad spectrum (25-100 nm)Much narrower (0.01-5 nm)
Modulation BandwidthTens of kHz to hundreds of MHzTens of kHz to tens of GHz
E/O conversion efficiency10-20 %30-70 %
Eye sefetyConsidered to safeMust be rendered eye safe
DirectionalityBeam is broader and spreadingBeam is directional and is highly collimated
ReliabilityHighModerate
CoherenceNon-coherentCoherent
Temperature dependenceLittle temperature dependenceVery temperature dependence
Drive and control circuitrySimple to use and controlThreshold and temperature compensation circuitry
Harmonic distortionLED has high harmonic distortionLASER has less harmonic distortion
Receiving filterWide- increase noise floorNarrow- lower noise floor
Life time105 hours104 hours
CostLowHigh
ApplicationsModerate distance low data rate.Long distance high data rates.

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