Researchers at the California Institute of Technology have a developed a new method that uses a pair of laser beams, instead of a quartz crystal, to tune oscillators. The achievement could provide a better frequency reference to future consumer electronics and high-end navigation and radar systems.
Present in nearly all electronic devices, oscillators are electronic circuits that create precise frequencies used, among other things, to send signals to and from radio and television transmitters or to help wristwatches and quartz clocks keep time. To function properly, these valuable components rely on quartz crystals to provide a frequency reference, which vibrate at relatively low frequencies at or below the range of megahertz.
However, modern technology is quickly outgrowing the abilities of quartz crystals, say researchers in the laboratory of Kerry Vahala, the Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics at Caltech. Instead, they have developed a method to stabilize microwave signals in the gigahertz range that uses a pair of laser beams as a reference. Known as electro-optical frequency division, the new technique builds off the method of optical frequency division developed at the National Institute of Standards and Technology more than a decade ago.
“Our new method reverses the architecture used in standard crystal-stabilized microwave oscillators—the ‘quartz’ reference is replaced by optical signals much higher in frequency than the microwave signal to be stabilized,” Vahala said.
The technique is similar to a gear chain on a bicycle that transfers the motion of pedaling from a small, fast-moving gear to a significantly larger wheel, explains Jiang Li, who a Kavli Nanoscience Institute postdoctoral scholar at Caltech and one of two lead authors on the paper along with graduate student Xu Y.
“Electrical frequency dividers used widely in electronics can work at frequencies no higher than 50 to 100 GHz. Our new architecture is a hybrid electro-optical ‘gear chain’ that stabilizes a common microwave electrical oscillator with optical references at much higher frequencies in the range of terahertz or trillions of cycles per second,” Li said.
To the naked eye, the optical reference in question is a laser that looks like a tiny disk. Measuring only 6 mm in diameter, it is particularly suited for use in compact photonics devices, electronic-like devices powered by photons instead of electrons, says study coauthor Scott Diddams, physicist and project leader at the National Institute of Standards and Technology.
“There are always tradeoffs between the highest performance, the smallest size, and the best ease of integration. But even in this first demonstration, these optical oscillators have many advantages; they are on par with, and in some cases even better than, what is available with widespread electronic technology,” Vahala said.
The accompanying paper, “Electro-Optical Frequency Division and Stable Microwave Synthesis,” is published in the journal Science. Other authors of the paper include Hansuek Lee, who is a visiting associate at Caltech.
The research was sponsored by DARPA’s ORCHID and PULSE programs, the Caltech Institute for Quantum Information and Matter (IQIM) and the Caltech Kavli NanoScience Institute.
