Signals May Be Best Shared by Fiber-Optics

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 also will 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 by Jun Ye's group at JILA, a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder.

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 requires days of measurement averaging to accurately compare today's best frequency standards. Moreover, considerable fiber-optic infrastructure already exists. For instance, the new knowledge is based largely on research performed on a 3.45-km fiber link installed in underground conduits and steam tunnels.

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.

COMPAMED.de; Source: National Institute of Standards and Technology (NIST)