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

June 27, 2011
Matt Kirchner, a University of Colorado graduate student, fine-tunes an ultra-stable microwave generator that he helps operate at NIST. Credit: Burrus/NIST

By combining advanced laser technologies in a new way, physicists at the National Institute of Standards and Technology (NIST) have generated microwave signals that are more pure and stable than those from conventional electronic sources. The apparatus could improve signal stability and resolution in radar, communications and navigation systems, and certain types of atomic clocks.

Described in , NIST's low-noise apparatus is a new application of combs, tools based on ultrafast lasers for precisely measuring , or colors, of light. Frequency combs are best known as the "gears" for experimental next-generation atomic clocks, where they convert to lower microwave frequencies, which can be counted electronically.

The new low-noise system is so good that NIST scientists actually had to make two copies of the apparatus just to have a separate tool precise enough to measure the system's performance. Each system is based on a continuous-wave laser with its frequency locked to the extremely stable length of an with a high "quality factor," assuring a steady and persistent signal. This laser, which emitted yellow light in the demonstration but could be another color, is connected to a frequency comb that transfers the high level of stability to microwaves. The transfer process greatly reduces—to one-thousandth of the previous level—random fluctuations in the peaks and valleys, or phase, of the electromagnetic waves over time scales of a second or less. This results in a stronger, purer signal at the exact desired frequency.

The base microwave signal is 1 gigahertz (GHz, or 1 billion cycles per second), which is the repetition rate of the ultrafast laser pulses that generate the frequency comb. The signal can also be a harmonic, or multiple, of that frequency. The laser illuminates a photodiode that produces a signal at 1 GHz or any multiple up to about 15 GHz. For example, many common radar systems use signals near 10 GHz.

NIST's low-noise oscillator might be useful in radar systems for detecting faint or slow-moving objects. The system might also be used to make operating at , such as the current international standard cesium atom clocks, , more stable. Other applications could include high-resolution analog-to-digital conversion of very fast signals, such as for communications or navigation, and radio astronomy that couples signals from space with arrival times at multiple antennas.

Explore further: Atomic fountain clocks are becoming still more stable

More information: T.M. Fortier, M.S. Kirchner, F. Quinlan, J. Taylor, J.C. Bergquist, T. Rosenband, N. Lemke, A. Ludlow, Y. Jiang, C.W. Oates and S.A. Diddams. Generation of ultrastable microwaves via optical frequency division. Nature Photonics. Published online June 26, 2011.

Related Stories

Atomic fountain clocks are becoming still more stable

March 18, 2009

They are at present the most accurate clocks in the world: Caesium fountain clocks furnish the second accurate to 15 places after the decimal point. Until they reach this accuracy, caesium fountain clocks, however, need a ...

Atomic clock signals may be best shared by fiber-optics

March 2, 2007

Time and frequency information can be transferred between laboratories or to other users in several ways, often using the Global Positioning System (GPS). But today's best atomic clocks are so accurate—neither gaining nor ...

Enhanced LIDAR improves range, vibration measures

February 2, 2006

Scientists at the National Institute of Standards and Technology have demonstrated the use of an ultrafast laser "frequency comb" system for improved remote measurements of distance and vibration. The technology, described ...

Optical Atomic Clock: A long look at the captured atoms

February 5, 2008

Optical clocks might become the atomic clocks of the future. Their "pendulum", i.e. the regular oscillation process which each clock needs, is an oscillation in the range of the visible light. As its frequency is higher than ...

Recommended for you

Quantum data takes a ride on sound waves

September 22, 2017

Yale scientists have created a simple-to-produce device that uses sound waves to store quantum information and convert it from one form to another, all inside a single, integrated chip.

A way to measure and control phonons

September 22, 2017

(Phys.org)—A team of researchers with the University of Vienna in Austria and Delft University of Technology in the Netherlands has developed a technique using photons for controlling and measuring phonons. In their paper ...


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.