An academic-industrial team in Japan has connected three laboratories in a 100-kilometer region with an optical telecommunications fiber network stable enough to remotely interrogate optical atomic clocks. This type of fiber link is poised to expand the use of these extremely precise timekeepers by creating an infrastructure that could be used in a wide range of applications such as communication and navigation systems.

«The laser system used for optical clocks is extremely complex and thus not practical to build at multiple locations,» said Tomoya Akatsuka, a member of the research team from telecommunications company Nippon Telegraph and Telephone Corporation (NTT). «With our network scheme, a shared laser would enable an optical clock to operate remote clocks with much simpler laser systems.»

In The Optical Society (OSA) journal Optics Express, researchers from NTT, the University of Tokyo, RIKEN, and NTT East Corporation (NTT East), all in Japan, report the new low-noise fiber link.

«Optical clocks and optical fiber links have reached the stage where they can be put into practical use,» said Akatsuka. «Our system is compatible with existing optical communication systems and will help accelerate practical applications. For example, because optical clocks are sensitive to gravitational potential, linked clocks could be used for highly sensitive detection of early signs of earthquakes.»

Dealing with noise

Because of optical clocks’ extremely high precision, noise is a critical issue when linking optical clocks over a long fiber link. Even small vibrations or temperature variations can introduce noise into the network that skews the laser signal enough that it no longer reflects what originally came from the optical clock.

Story Source: Materials provided by The Optical Society. Note: Content may be edited for style and length.