3 Light transmission, sources and detectors
3.1 Introduction

Optical communication systems transmit information by means of light. Compared to copper wire used in electrical communications, optical fibres have lower cost, weigh less, have less attenuation and dispersion and provide more bandwidth. Optical fibre can support ultra-high data rates: Terabits per second and can be used to transmit light and thus information over long distances. Moreover, there are no problems associated to EMC (Electromagnetic Compatibility) interference immunity and there is no fire hazard because of the pass of electricity through the communication channel is eliminated.

Figure 5 shows the typical block diagram of an optical communication system. The electrical signal (information) controls the source of light; the light emitted by the source is coupled to the transmission channel: Optical fibre, waveguide or free space. The light is transmitted through the transmission channel up to the light detector that is coupled with the channel. The light detector transforms the light into electrical signal and the information is received.

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Fig. 5. Optical communication system block diagram.