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.   

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