  Atomic vapors offer many opportunities for manipulating electromagnetic
signals across a broad range of the electromagnetic spectrum. Here, a microwave
signal with an audio-frequency modulation encodes information in an optical
signal by exploiting an atomic microwave-to-optical double resonance, and
magnetic-field coupling that is amplified by a resonant high-Q microwave
cavity. Using this approach, audio signals are encoded as amplitude or
frequency modulations in a GHz carrier, transmitted through a cable or over
free space, demodulated through cavity-enhanced atom-microwave interactions,
and finally, optically detected to extract the original information. This
atom-cavity signal transduction technique provides a powerful means by which to
transfer information between microwave and optical fields, all using a
relatively simple experimental setup without active electronics.
