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Unprecedented accuracy:
RLE researchers achieve breakthrough in drift-free
timing synchronization
For Immediate Release
TUESDAY, 04 November 2008
Contact:
William Smith, Assistant Director for Finance and Sponsor
Relations
Phone: +1.617.253.5621
Email: whs@mit.edu
CAMBRIDGE,
MA. 11.04.2008
MIT Research Laboratory of Electronics
(RLE) engineers have achieved a dramatic breakthrough
in drift-free synchronization based on mode-locked
lasers. This achievement is an important milestone
in transitioning mode-locked laser-based synchronization
systems from the laboratory into real-world facilities.
Their work, reported in Nature Photonics on November
2nd, could bring unprecedented capabilities to large-scale
facilities that need femtosecond accuracy for many
hours of continuous operation. In particular, advanced
X-ray free-electron lasers (FELs)—some
already under construction and others planned in the
near future—immediately require such extremely
high timing accuracy. Another potential beneficiary
of the new RLE findings could be phased-array antennas
for radio astronomy such as the Atacama Large Millimeter
Array (ALMA) currently under construction.
The principal
investigator of the team announcing these findings, Franz X.Kärtner,
Professor of Electrical Engineering and senior member
of the RLE Optics and Quantum Electronics Group, said, "When
we started this work four years ago most people in
the field thought this was impossible to do. Now, we
have already demonstrated precision and stability that
enables a new generation of light sources with vastly
improved performance. In fact, significant funding
for this work came from European facilities that are
in the process of implementing these systems."
Femtosecond (10-15 s) mode-locked lasers have revolutionized
many fields of science, most recently by enabling high-precision
optical frequency measurements using frequency combs.
Owing to their ultra-low noise properties, mode-locked
lasers have been expected to clock large-scale scientific
facilities requiring extremely high timing accuracy
that conventional electronic clocking cannot provide.
However, lack of long-term stable synchronization
techniques has hindered the realization of this pervasive
clocking idea. None of the previous work has demonstrated
drift-free remote synchronization over hundreds of
meters with femtosecond timing accuracy maintained
over extended periods of time, which is an essential
prerequisite for running such large-scale facilities.
In their Nature Photonics paper, the RLE researchers
present a comprehensive set of novel large-scale synchronization
techniques that achieve, for the first time, sub-10-femtosecond
timing accuracy maintained over more than 10 hours
and over distances of more than 300 m. The demonstrated
relative timing stability in timing distribution, optical-optical
synchronization, and optical-microwave synchronization
represents multiple orders of magnitude improvement
compared to previous work.
Said Jungwon Kim, the lead
author of the paper, "It is really exciting to
see the techniques developed in our lab are already
tested and becoming installed in real accelerator facilities
around the world."
The equivalent accuracy of synchronization is keeping
the timing with less than a second accumulated error
since the birth of the universe.
As the demand for
higher timing accuracy increases, the technique developed
by the RLE researchers will find more applications
in commercial applications such as communication and
computation networks and precise tracking/positioning
systems.
The lead author of the paper is Dr. Kim (PhD
'07), a postdoctoral associate in RLE. Other authors
are Electrical Engineering and Computer Science graduate
students Jonathan A. Cox and Jian Chen, and Professor
Kärtner, all members of RLE.
The research was funded
by the European Union, under the EuroFEL program; the
U.S. Office of Naval Research (ONR), under the Multidisciplinary
University Research Initiative (MURI) program; the
U.S. Air Force Office of Scientific Research (AFOSR);
the U.S. Defense Advanced Research Projects Agency
(DARPA); the University of Wisconsin; and the Samsung
Scholarship Foundation.
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