NIST: Atomic Clock Signals May Be Best Shared by Fiber Optics
April 13, 2007 // Published as a news service by IHS
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Time and frequency information can be transferred between laboratories or to other users in several ways, often using the global positioning system (GPS).
The best option, however, may be to use lasers to transfer data over fiber-optic cables, according to scientists at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder.
The use of fiber-optic channels to transfer time signals allows accurate comparisons of distantly located atomic clocks of different types.
This could lead, for example, to enhanced measurement accuracy in experiments to determine whether so-called "constants of nature" are in fact changing.
Sharing of clock signals via fiber will also enable synchronization of components for advanced X-ray sources at linear accelerators, which may power studies of ultrafast phenomena in chemistry, biology, physics and materials science, or link arrays of geographically distributed radio telescopes to produce the power of a giant telescope.
Three state-of-the-art techniques for distributing ultra-stable time and frequency signals over fiber are described in a recent Review of Scientific Instruments article from NIST Fellow Jun Ye.
Microwave frequency signals such as from NIST's standard atomic clock can be distributed over fiber using a continuous-wave (CW) laser.
Another method can transfer more accurate optical frequency references, such as NIST's mercury ion clock or JILA's strontium clock, with a cw laser and disseminate signals to both optical and microwave users using an optical frequency comb. As a third option, microwave and optical frequency references can be transmitted simultaneously using a frequency comb.
Researchers said fibers can be far more stable - especially when efforts are made to cancel molecules along the transmission path - than the paths through free space used by GPS, which require days of measurement averaging to accurately compare today's best frequency standards.
Noting that gravitational effects may eventually limit ground-based atomic clocks, researchers suggest the future might entail creating a network of optical atomic clocks in space which might be used to make flawless distance measurements, transfer clock signals to different locations and accurately map the Earth's gravity distribution.
Source: National Institute of Standards and Technology (NIST).