Future electronics may depend on lasers, not quartz

Move over, quartz crystals! New research may allow lasers to replace quartz in gen-next electronics, scientists say.
Nearly all electronics require devices called oscillators that create precise frequencies - frequencies used to keep time in wristwatches or to transmit reliable signals to radios.
For nearly 100 years, these oscillators have relied upon quartz crystals to provide a frequency reference.
Now, researchers in the laboratory of Kerry Vahala at California Institute of Technology, have developed a method to stabilise microwave signals in the range of gigahertz, or billions of cycles per second - using a pair of laser beams as the reference, in lieu of a crystal.

Quartz crystals "tune" oscillators by vibrating at relatively low frequencies - those that fall at or below the range of megahertz, or millions of cycles per second, like radio waves.
Quartz crystals are so good at tuning these low frequencies that years ago, researchers were able to apply a technique called electrical frequency division that could convert higher-frequency microwave signals into lower-frequency signals, and then stabilise these with quartz.

The new technique, dubbed electro-optical frequency division, is based on the method of optical frequency division, developed a decade ago.
"Our new method reverses the architecture used in standard crystal-stabilised microwave oscillators - the 'quartz' reference is replaced by optical signals much higher in frequency than the microwave signal to be stabilised," Vahala said.

Jiang Li, a Kavli Nanoscience Institute postdoctoral scholar at Caltech and one of two lead authors on the paper, along with graduate student Xu Yi likens the method to a gear chain on a bicycle that translates pedalling motion from a small, fast-moving gear into the motion of a much larger wheel.
"Electrical frequency dividers used widely in electronics can work at frequencies no higher than 50 to 100 GHz," Li said.
"Our new architecture is a hybrid electro-optical 'gear chain' that stabilises 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.

The optical reference used by the researchers is a laser that, to the naked eye, looks like a tiny disk.
At only 6 mm in diameter, the device is very small, making it particularly useful in compact photonics devices - electronic-like devices powered by photons instead of electrons, said Scott Diddams, physicist and project leader at the National Institute of Standards and Technology in the US and a coauthor on the study.
The new technique is described in a paper published in the journal Science.