The Detection reference article from the English Wikipedia on 24-Apr-2004
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Detection

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In general, detection is the extraction of intelligence from a carrier signal in a communication system.

In opto-electronic systems, the generation of an electrical signal in response to a received optical input. For example, the optical signal received from an optical fiber is converted to an electrical signal in a detector, often a photodiode.

In radio systems, the extraction of an AM signal from its carrier frequency.