A device capable of transforming a signal from one form of energy to another, usually in such a way that the fidelity of the original information is maintained, or substantially so. A microphone, for example, is a transducer that converts acoustic energy into electric current, and a speaker is a transducer that converts electric current into acoustic energy. The transmission of sound through these paired transducers certainly results in some loss of fidelity, the level of which depends on their quality, their proper matching, and the quality of the circuit that interconnects them. A diode laser light source and an Avalanche PhotoDiode (APD) light detector are paired transducers that, in combination, convert electrical energy to optical energy and back to electrical energy in an optical network such as fiber optics or Free Space Optics (FSO).