Miniaturised device helps steady electrical currents

Researchers at the California Institute of Technology (Caltech) have developed a device that can help steady the electrical currents needed to power high-end electronics and stabilise the signals of high-quality lasers.

The work marks the first time that such a device has been miniaturised to fit on a chip and may pave the way to improvements in high-speed communications, navigation and remote sensing.

The device provides a consistent light frequency that improves both optical and electronic devices when it is used as a reference, says Kerry Vahala, Ted and Ginger Jenkins Professor of Information Science and Technology and Applied Physics. Vahala is also executive officer for applied physics and materials science and an author on the study describing this new work, published in the journal Nature Communications. 

The researchers were able to stabilise the light’s frequency by developing a silica glass chip resonator with a specially designed path for the photons in the shape of what is called an Archimedean spiral. “Using this shape allows the longest path in the smallest area on a chip. We knew that if we made the photons travel a longer path, the whole device would become more stable,” says Hansuek Lee, a senior researcher in Vahala’s lab and lead author on the paper.

Frequency instability stems from energy surges within the optical resonator, which are unavoidable due to the laws of thermodynamics. Because the new resonator has a longer path, the energy changes are diluted, so the power surges are dampened - greatly improving the consistency and quality of the resonator’s reference signal, which, in turn, improves the quality of the electronic or optical device.

In the new design, photons are applied to an outer ring of the spiralled resonator with a tiny light-dispensing optic fibre; the photons subsequently travel around four interwoven Archimedean spirals, ultimately closing the path after travelling more than a metre in an area about the size of a quarter - a journey 100 times longer than achieved in previous designs. In combination with the resonator, a special guide for the light was used, losing 100 times less energy than the average chip-based device.

In addition to its use as a frequency reference for lasers, a reference cavity could one day play a role equivalent to that of the ubiquitous quartz crystal in electronics. Most electronics systems use an oscillator to provide power at very precise frequencies. In the past several years, optical-based oscillators - which require optical reference cavities - have become better than electronic oscillators at delivering stable microwave and radio frequencies. While these optical oscillators are currently too large for use in small electronics, there is an effort underway to miniaturise their key subcomponents - like Vahala’s chip-based reference cavity.

“A miniaturised optical oscillator will represent a shift in the traditional roles of photonics and electronics. Currently, electronics perform signal processing while photonics rule in transporting information from one place to another over fibre-optic cable. Eventually, oscillators in high-performance electronics systems, while outwardly appearing to be electronic devices, will internally be purely optical,” Vahala says.