Monday, January 20, 2020

Block Diagram of Fiber optic Communication System (FOC)

  • The optical fiber communication system for either digital or analog transmission.
  • The transmitter consists of an information encoder or signal shaping circuit preceding a modulation or electronic driver stage which operates the optical source.

Block Diagram of  Fiber  optic Communication System (FOC)
  • Light emitted from the source is launched into an optical fiber.
  • The light emerging from the far end of the transmission medium is converted back into an electrical signal by an detector.
  • Detector is positioned at the input of the receiver. 
  • The electrical signal is than amplified prior to decoding or demodulation to obtain original information signal. 
  • There  is requirement for electrical interfacing at either end of optical link and at present the signal processing is usually performed electrically. 
  • The information signal to be transmitted may be voice, video or computer data.
  • The first step is to convert the information into a from compatible with the communications medium. 
  • This is done by converting continuous analog signal such as voice and video signal into a series of digital pulses. 
  • An ADC is used to convert analog into digital.
  • Then digital pulse are used to fiash a powerful light source off and on very rapidly.   
  • In low- cost systems for short distance communication LED is a light source. 
  • LED is semiconductor device it emits light.
  • Color of light emitted depends on material used to construct LED.
  •  Another commonly used light source is the solid-state laser.
  • LASER is also a semiconductor device which generates single-frequency light beam.
  • The light beam pulses are than fed into a fiber-optic cable. 
  • At the receiving end , a light sensitive device i.e. photocell or  light detector is used to detect the light pulses.
  • light detector converts the light pulses into electrical signal.
  • The electrical pulses are amplified and reshaped back into digital from.
  • They are fed to a decoder, such as DAC where the original voice or video is recovered.
  • in very long transmission systems, repeater units must be used along the way. 
  • Since the light is greatly attenuated when it travels over long distances, at some point it may be too weak to be received reliably.
  • To overcome to attenuation problem, special relay stations are used to pick up the light beam, convert it back into electrical pulse that are amplified , and than  re-transmit the pulses on another light beam.   


If you have any doubts,please let me know