Spirals of light the key to faster electronics?

The work marks the first time that such a device has been miniaturised to fit on a single chip, and is expected to pave the way to improvements in high speed communications, navigation and remote sensing. The Caltech engineers describe their optical resonator as "the optical equivalent of a tuning fork". Good tuning forks control the release of their acoustic energy, ringing just one pitch at a particular sound frequency for a long time. This sustaining property is called the quality factor. The Caltech team transferred this concept to their optical resonator, focusing on the optical quality factor and other elements that affect frequency stability. They 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," explained lead researcher Professor Kerry Vahala. "We knew that if we made the photons travel a longer path, the whole device would become more stable." 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 US quarter—a journey 100 times longer than achieved in previous designs.