OPTICAL MODULATORS

  •  An Optical Modulator is used for modulating optical signal by changing the properties of light
  • Depending on the properties of light changed,there are Intensity modulators,Phase modulators and polarization modulators.
  • There are two types of modulation techniques for optical signals. They are  direct Modulation and External modulation
Direct Modulation 


Fig 1*
  • The Message signal is Superimposed on the bias current which modulates the laser beam
  • It causes issues like Frequency chirping,Pulse spreading and Loss of Information

External Modulation



Fig 2*
  • The laser beam is modulated by an external optical modulator
  • It is used in High end systems
  • It is most complex and expensive 
The below figure shows the classification of Optical Modulators



Fig 3*
  • Refractive Modulator-by varying refractive index of the modulating Material
  • Absorptive Modulator-by varying absorption coefficient of the material

*Figure courtesy:Google Images

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