OPTICAL AMPLIFIERS

  •  An Optical Amplifier amplifies optical signal without converting it to electronic signal
  • They can be placed anywhere along the Optical length of the fiber
  • They can be bidirectional
  • Optical Multiplexing is possible
  • They accept signals of different wavelength and provides Amplification
  • They use Stimulated Emission like LASER .But Optical amplifiers do not have Feedback mechanism.

All Optical Amplifiers have an Active medium.There is an external source called Pump to supply energy to the medium.This raises the electrons in the active medium to higher energy levels.The incoming photon from the signal(input signal which is to be amplified) will excite the electrons to lower energy level resulting in the emission of photons thereby amplifying the signal

Applications of Amplifier

  • In Line amplifier- They are used in between Transmitter and receiver to increase the distance between them
  • Pre Amplifier-They are used before the receiver to improve its sensitivity
  • Transmission Booster- If Optical Amplifier cannot be connected at the transmitter side,then transmission booster can be used to transmit signal for long distance
  • signal booster-Weak signal cannot be sent to multiple users simultaneously.So, a Signal booster is used

Types of Optical Amplifier

  • Semiconductor Optical Amplifier
  • Raman Optical Amplifier

Semiconductor Optical amplifier

  • Group III and V semiconductor materials are used as the active medium 
  • It is an InGaASP Laser that operates below its threshold value
  • By varying the composition of the semiconductor,gain can be varied.
  • They work in O band and C band
  • They are small in size and consume less power
  • It acts as a Traveling wave amplifier.During the passage of signal through the Amplifier,the signal gains energy

Erbium Doped Fiber Amplifier

  • Erbium ions have quantum levels that allows them to get stimulated to emit photons in 1540 nm
  • The fiber core is heavily doped with Erbium ions which provides amplification
  • A LASER pump energy is given at 980nm/1480 nm
  • High energy is mixed with the weak signal by a wavelength selective coupler
  • The Erbium ions in the fiber absorb energy by laser pumping and gets excited to higher energy levels.These excited ions decay quickly to the meta stable state.Then,by stimulated emission and absorption,weak signal is amplified.

Advantages-EDFA

  • Commercially available in C Band (1530-1560nm) and O Band(1570-1610 nm)
  • High Gain
  • No distortion at High bit rates and immunity to cross talk
  • Do not need High speed electronics

Disadvantages-EDFA

  • Difficult to Integrate with other Componenets
  • Gain equalizer is required for Multi stage Amplification

WATCH THIS VIDEO  

to know how EDFA was developed    https://youtu.be/v_Xkn14XWcQ

Animation 










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