20 February 2018

Element of optical fiber transmission link

In this block diagram that are a different block can be used in optical fiber communication. General block diagram of optical communication system consists of following important blocks :
  •     Transmitter
  • .    Information channel
  • .    Receiver
Block diagram of OFC systems

Message origin :

  • Generally, message origin is from a transducer that converts a nonelectrical message into an electrical signal.
  • Common examples microphones for the room a transducer that converts a non-electrical include microphones for converting sound waves into currents and video (TV) cameras for convert images into the current.
  • In the data transfer between computers, the message already in electrical form.

Modulator :

The modulator has two main functions :

  • Modulator converts the electrical message into the proper format
  • Modulator impresses this signal onto the wave generated by the carrier source
  • Two distinct categories of modulation are used i.e. analog and digital modulation system

Carrier source :

  • Carrier source generates the wave on which the information is transmitted. This wave is called the carrier.
  • In fiber optic system, a laser diode ( LD ) or a light emitting diode ( LED ) is used for the carrier.

Channel coupler :

  • Coupler feeds the power into the information channel. In channel coupler the  atmospheric optical fiber system is a lens used for collimating the light emitted by the transmitter side and  also have directing this light towards the receiver.
  • This channel coupler must be efficiently transfer the modulated light beam from the source to the optic fiber device.  
  • One of the advantages of this design is that it possibility of high losses.

Information channel :

  • The information channel is the path between the transmitter and receiver. In fiber-optic communications, a glass or plastic fiber is the channel.
  • Amplifiers are needed in very long links to provide sufficient power to the receiver. Repeaters can be used only for digital systems.

Optical detector :

  • The information being transmitted is detected by a detector. In the fiber optic system, the optic wave is converted into an electric current by a photodetector.
  • The current developed by the detector. this current is proportional to the power in the incident optic wave. Detector output current contains the transmitted information.
  • This detector output is then filtered to remove the constant bias and then amplified.

Signal processing :

  • Signal processing includes filtering, amplification. Proper filtering maximizes the ratio of signal to unwanted power.
  • For a digital system, decision circuit is an additional block. The bit error rate (BER) should be very small for quality communications.

Message output :

  • The electrical form of the message emerging, from the signal processor, are transformed into a sound wave or visual image.
  • Sometimes these signals are directly usable when computers or other types of  machines are connected through a fiber system.