|Overlaid scanning electron microscopy (SEM) and optical images show an ENGRAVE nanowire that is periodically modulated at one end. (Images courtesy of UNC-Chapel Hill)
Researchers from the University of North Carolina at Chapel Hill have created a spectrally selective silicon (Si) photonic wire potentially useful in optical computing.1 The Si wires are several hundred nanometers in diameter and form a new type of nanoscale light switch that can turn on and off the transmission of a specific wavelength of light over long on-chip distances.
"In the past there hasn't been a controlled method for selectively sending light down nanoscale wires, so optical technology has either used much larger structures or wasted a lot of light in the process," says James Cahoon, associate professor of chemistry in the College of Arts and Sciences at UNC-Chapel Hill. "We found a way to turn on and off the transmission of a specific color of light, and it represents an important step towards the more controlled, effective use of light that would enable optical computing."
The research team developed the Encoded Nanowire Growth and Appearance through VLS and Etching (ENGRAVE) technique, which can create complex shapes in nanowires. They then achieved selective light transmission through precise diameter modulation with the ENGRAVE technique. This was the first report of direct use of a Mie resonance, a light scattering property of nanowires, for guiding light in a nanowire.
In particular, a periodic geometric perturbation in th Si nanowire couples a Mie resonance to a bound-guided state (BGS) of the wire, producing a dip in the scattering spectrum (and a rise in the amount of guided light at that wavelength). The device can work at telecommunications wavelengths.
The team believes its findings can enable downsizing of the optical components needed to develop computers based on light. By miniaturizing these components, they can be more easily integrated with the existing electronic components in computers. Additionally, the wavelength of light conducted by the wires in this study is sensitive to environmental changes. Thus, these structures could be used as a new type of optical sensor.
1. Seokhyoung Kim et al., Nature Communications (2018); https://doi.org/10.1038/s41467-018-05224-2