'Comb on a chip' powers new atomic clock design

July 22, 2014
This image depicts NIST physicists Scott Diddams (left) and Scott Papp with a prototype atomic clock based on a chip-scale frequency comb. Diddams is holding the silicon chip, which fits into the clock apparatus on the table. With performance improvements and further reductions in size, the technology might eventually be used to make portable tools for measuring time and frequency. Credit: Burrus/NIST

Researchers from the National Institute of Standards and Technology (NIST) and California Institute of Technology (Caltech) have demonstrated a new design for an atomic clock that is based on a chip-scale frequency comb, or a microcomb.

The microcomb clock, featured on the cover of the inaugural issue of the new journal Optica, is the first demonstration of all-optical control of the microcomb, and its accurate conversion of to lower . (Optical frequencies are too high to count;microwave frequencies can be counted with electronics.)

The new clock architecture might eventually be used to make portable tools for calibrating frequencies of advanced telecommunications systems or providing microwave signals to boost stability and resolution in radar, navigation and scientific instruments. The technology also has potential to combine good timekeeping precision with very small size. The comb clock might be a component of future "NIST on a chip" technologies offering multiple measurement methods and standards in a portable form.

"The microcomb clock is one way we might get precision frequency metrology tools out of the lab and into real-world settings," NIST physicist Scott Diddams says.

Frequency combs produce precisely defined colors, or frequencies, of light that are evenly spaced throughout the comb's range. (The name comes from the spectrum's resemblance to the teeth of a pocket comb.) The original combs required relatively large lasers that produced rapid, extremely short pulses of light, but more recently NIST and other laboratories have developed much smaller microcombs.

A microcomb generates its set of frequencies from light that gets trapped in the periphery of a tiny silica glass disk, looping around and around the perimeter. These combs can be astonishingly stable. NIST has an ongoing collaboration in this area with Caltech researchers, who made the 2-millimeter-wide silica disk that generates the frequency comb for the new clock.

The new microcomb clock uses a laser to excite the Caltech disk to generate a , broadens the spectrum using nonlinear fiber, and stabilizes two comb teeth (individual frequencies) to energy transitions in rubidium atoms that "tick" at optical frequencies. (Conventional rubidium atomic clocks operate at much lower microwave frequencies.) The comb converts these optical frequency ticks to the microwave domain.

Thanks to the gear-like properties of the disk and the comb, the output is also 100 times more stable than the intrinsic ticking of the rubidium atoms. According to Diddams. "A simple analogy is that of a mechanical clock: The provide stable oscillations—a pendulum—and the microcomb is like a set of gears that synthesizes optical and microwave frequencies."

The center of the comb spectrum is locked to an infrared laser operating at 1560 nanometers, a wavelength used in telecommunications.

NIST researchers have not yet systematically analyzed the microcomb clock's precision. The prototype uses a tabletop-sized rubidium reference. The scientists expect to reduce the instrument size by switching to a miniature container of atoms like that used in NIST's original chip-scale . Scientists also hope to find a more stable atomic reference.

The microcomb chip was made by use of conventional semiconductor fabrication techniques and, therefore, could be mass produced and integrated with other chip-scale components such as lasers and atomic references. NIST researchers expect that, with further research, the microcomb clock architecture can achieve substantially better performance in the future.

Explore further: A quiet phase: NIST optical tools produce ultra-low-noise microwave signals

More information: S.B. Papp, K. Beha, P. Del'haye, F. Quinlan, H. Lee, K.J. Vahala and S.A. Diddams. A microresonator frequency comb optical clock. Optica 1, 10-14. July 22, 2014.

Related Stories

NIST shows how to make a compact frequency comb in minutes

July 11, 2013

Laser frequency combs-high-precision tools for measuring different colors of light in an ever-growing range of applications such as advanced atomic clocks, medical diagnostics and astronomy-are not only getting smaller but ...

Recommended for you

Using optical fiber to generate a two-micron laser

October 9, 2015

Lasers with a wavelength of two microns could move the boundaries of surgery and molecule detection. Researchers at EPFL have managed to generate such lasers using a simple and inexpensive method.

Perfectly accurate clocks turn out to be impossible

October 7, 2015

Can the passage of time be measured precisely, always and everywhere? The answer will upset many watchmakers. A team of physicists from the universities of Warsaw and Nottingham have just shown that when we are dealing with ...

The topolariton, a new half-matter, half-light particle

October 7, 2015

A new type of "quasiparticle" theorized by Caltech's Gil Refael, a professor of theoretical physics and condensed matter theory, could help improve the efficiency of a wide range of photonic devices—technologies, such as ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.