In the 1940s, researchers learned how to precisely control the frequency of microwaves, which enabled radio transmission to transition from relatively low-fidelity amplitude modulation (AM) to high-fidelity frequency modulation (FM). This accomplishment, called microwave frequency synthesis, brought about many advanced technologies now critical to the military, such as wireless communications, radar, electronic warfare, atomic sensors and precise timing. Today, optical communications employ techniques analogous to those of pre-1940 AM radio, due to the inability to control frequency precisely at optical frequencies, which are typically 1,000 times higher than microwaves. The higher frequency of light, however, offers potential for 1,000-fold increase in available bandwidth for communications and other applications.
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