This is a map of Germany showing the path of the 920-km-long optical fiber link from Max Planck Institute of Quantum Optics to the Federal Institute of Physical and Technical Affairs. The red houses represent amplifier stations. Credit: Stefan Droste, Max Planck Institute of Quantum Optics |
Atomic
clocks based on the oscillations of a cesium atom keep amazingly steady
time and also define the precise length of a second. But cesium clocks
are no longer the most accurate. That title has been transferred to an
optical clock housed at the U.S. National Institute of Standards and
Technology (NIST) in Boulder, Colo. that can keep time to within 1
second in 3.7 billion years. Before this newfound precision can redefine
the second, or lead to new applications like ultra-precise navigation,
the system used to communicate time around the globe will need an
upgrade. Recently scientists from the Max Planck Institute of Quantum
Optics, in the south of Germany, and the Federal Institute of Physical
and Technical Affairs in the north have taken a first step along that
path, successfully sending a highly accurate clock signal across the
many hundreds of kilometers of countryside that separate their two
institutions.
The
researchers will present their finding at Conference on Lasers and
Electro Optics (CLEO: 2012), taking place May 6-11 in San Jose, Calif.
“Over
the last decade a new kind of frequency standard has been developed
that is based on optical transitions, the so-called optical clock,” says
Stefan Droste, a researcher at the Max Planck Institute of Quantum
Optics. The NIST optical clock, for example, is more than one hundred
times more accurate than the cesium clock that serves as the United
States’ primary time standard.
Extremely
precise time keeping—and the ability to communicate the world time
standard across long distances—is vital to myriad applications,
including in navigation, international commerce, seismology, and
fundamental quantum physics. Unfortunately, the satellite-based links
currently used to communicate that standard are not up to the task of
transmitting such a stable signal, so the second retains its less
precise measure. Optical fiber links could work better, but had
previously been tested only over short distances, such as those
separating buildings on the same campus or within the same urban area.
“The
average distance between institutes that operate frequency standards in
Europe is on the order of a few thousand kilometers,” notes Droste.
“Spanning these great distances with an optical link is challenging not
only because of the additional degradation of the transferred signal,
but also because multiple signal conditioning stations need to be
installed and operated continuously along the link path.” Droste and his
colleagues were able to overcome the challenges by installing nine
signal amplifiers along a 920-km-long fiber link. They successfully
transferred a frequency signal with more than 10 times the accuracy than
would be required for today’s most precise optical clocks.
CLEO:
2012 presentation CTh4A.1. “Optical Frequency Transfer via 920 km Fiber
Link with 10?19 Relative Accuracy” by Stefan Droste et al. is at 4:30
p.m. on Thursday, May 10 in the San Jose Convention Center.
Source: Optical Society of America
