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Voice communication using Fiber Optic Analog Link

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To Study the Voice communication usingFiber Optic Analog Link.

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Fiber Optic Voice Communication

The human voice consists of sound made by a human being using the vocal folds for talking, singing, laughing, crying, screaming, etc. Its frequency ranges from about 50Hz to 12KHz.In that voice signal converting electrical signal using microphone transducer. And this electrical signal used in electronic circuits in voice communication. After doing all process the electrical signal converting voice signal again using speakers.


The heart of the transmitter is a light source. The major function of a light source is to convert an information signal from its electrical form into light. Today’s fiber-optic communications systems use, as a light source, either light-emitting diodes (LEDs) or laser diodes (LDS). Both are miniature semiconductor devices that effectively convert electrical signals into light. They need power-supply connections and modulation circuitry. All these components are usually fabricated in one integrated package. Transistor based driver circuit need for this type LEDs.

Optical fiber

The transmission medium in fiber-optic communications systems is an optical fiber. The optical fiber is the transparent flexible filament that guides light from a transmitter to a receiver. An optical information signal entered at the transmitter end of a fiber – optic communications system is delivered to the receiver end by the optical fiber.

Model Diagram for Plastic Fiber cable

This is multi mode plastic fiber cable, in this fiber cable core diameter 1000 micron and fiber cladding index 1.402.


The key component of an optical receiver is its photo detector. The major function of a photo detector is to convert an optical information signal back into an electrical signal (Photocurrent). The photo detector in today’s fiber – optic communications systems is a semiconductor photodiode (PD). This miniature device is usually fabricated together with its electrical circuitry to from an integrated package that provides power-supply connections and signal amplification.


  • Connect +15V adapter to both transmitter and receiver module
  • Switch (sw1) ON the transmitter Module
  • Connect the Mic on P4 connecter.
  • Connect the CRO Probe, positive to P6 and negative to P7 Ground.
  • Now check the mic pre amplifier output on CRO and vary the Amplitude pot meter min to max range.
  • Connect P6 and P8 using patch chord.
  • Connect P9 and P10 using patch chord.
  • Connect the 1 m Plastic fiber cable between transmitter module LED to receiver module Photo Diode.
  • Switch (sw1) ON the receiver Module.
  • Connect P2 and P4, P5 and P9 in receiver module using patch chord.
  • Connect the speaker on P12 connecter in receiver module.
  • Check the Audio power amplifier output on test point P11.
  • Now we get the transmitted voice signal at speaker.

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