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Advantages & disadvantages of Internal light modulation,External light modulation

This page compares Internal light modulation vs External light modulation along with their differences. It mentions advantages (i.e. benefits) and disadvantages (i.e. drawbacks) of Internal light modulation and External light modulation types.

Introduction: The modulation of light is a process by which irradiance (viz. amplitude, phase, pulse width etc.) or direction of light changes during the path or medium. The different light modulation techniques are used in various applications such as fiber optic communications, optical switching, Q-switch laser etc.

Internal modulation vs External modulation

• Internal modulation : The light output from light sources (e.g. LED, Laser etc.) are directly controlled by injecting or driving current. Simple circuit is used for this purpose.
• External modulation: In this method, both amplitude/phase of the light from sources can be modulated externally. Processes such as electro-optic, magneto-optic or acousto-optic are employed for this purpose. Polarization status changes in the presence of external force field viz. electric or magnetic or acoustic. Consecutively phase or irradiance of light beam gets modified.
• Refer difference between Direct modulation vs external modulation >>.

optical direct modulation optical external modulation

Benefits or advantages of Internal light modulation

Following are the benefits or advantages of Internal light modulation:
➨It uses somple circuit for modulation purpose.
➨It is very cost effective method.

Drawbacks or disadvantages of Internal light modulation

Following are the drawbacks or disadvantages of Internal light modulation:
➨It can be used up to frequency of about 40 GHz.
➨It shifts emission frequency by changing the driving current.
➨Limited modulation is achieved by amplitude variation primarily.

Benefits or advantages of External light modulation

Following are the benefits or advantages of External light modulation:
➨Higher device speed, which is controlled by property of the modulator.
➨Emission frequency remains unaffected unlike internal modulation.
➨In this method, both amplitude and phase modulation are possible.

Drawbacks or disadvantages of External light modulation

Following are the drawbacks or disadvantages of External light modulation:
➨Large size of the modulator in scale of micro-electronics standards.



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