Doug Lung NIST offers timing signals via RF at frequencies ranging from 60 kHz to 20 MHz. While suitable for many timekeeping applications, greater precision is required for scientific work, geodesy (altitude mapping) and navigation. This week NIST reported a demonstration of Ultraprecise Time Signals over a Wireless Optical Channel. “By bouncing eye-safe laser pulses off a mirror on a hillside, researchers at the National Institute of Standards and Technology (NIST) have transferred ultraprecise time signals through open air with unprecedented precision equivalent to the "ticking" of the world's best next-generation atomic clocks.”
The signal transfer demonstration used optical frequency combs on two low-power infrared laser beams. The frequency comb generates a steady stream of ultrashort optical pulses with a spacing that can be synchronized with the “ticks” of an optical atomic clock.
If you are wondering how the link deals with turbulence in the atmosphere, NIST says that because the turbulence affects both directions equality, it can be canceled out. It can also handle signal losses due to temporary obstruction of the light path. NIST said the method should be able to operate a much longer distances, possibly over future ground-to-satellite optical communications links.
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