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
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| 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.