Introduction to Receiver Design
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The basic structure of an optical receiver is similar to that of a radio receiver: an aerial (the photodiode) picks up the signal and converts it to a voltage prior to low noise preamplification; a post amplifier provides amplification; a filter restricts the system bandwidth; a detector restores the original signal. Most optical links use direct detection – the optical receiver (the photodiode) directly demodulates the light. This is different to coherent detection which is the preferred detection method in radio systems. (Long-haul optical links use coherent detection. These are examined when we consider current and future systems in the final chapter.) Although most of the work presented in this chapter is concerned with digital links, analogue receivers are also considered.