Traditionally, photon diodes must be relatively large in order to produce the strong rotation of light polarization that is required to control the flow of light. As an alternative, the Stanford team created rotation in crystal using another light beam instead of a magnetic field. In this all-optical, magnet-free scheme, the light beam was polarized so that its electrical field took on a spiral motion, which, in turn, generated rotating acoustic vibrations in the crystal that gave it magnetic-like spinning abilities and enabled more light to be emitted. To make the structure both small and efficient, the researchers manipulated and amplified the light with nanoantennas and nanostructured materials.
The researchers designed arrays of ultrathin silicon disks that worked in pairs to trap the light and enhance its spiraling motion until it exited the diode. This enhanced the transmission of light moving forward. When illuminated in the reverse direction, the acoustic vibrations in the crystal spun in the opposite direction and helped to cancel out any light trying to exit.
The researchers said that theoretically, there is no limit to how small this system could be. For their simulations, they imagined structures as thin as 250 nm, demonstrating nanoscale nonreciprocal transmission of free-space beams at near-infrared frequencies with a 250-nm thick silicon metasurface as well as a fully subwavelength plasmonic gap nanoantenna.
"Achieving compact, efficient photonic diodes is paramount to enabling next-generation computing, communication, and even energy conversion technologies." Assc. Prof. Jennifer Dionne
The team believes these research results could provide a foundation for compact, nonreciprocal communication and computing technologies, from nanoscale optical isolators and full-duplex nanoantennas to topologically protected networks.“One grand vision is to have an all-optical computer where electricity is replaced completely by light and photons drive all information processing,” researcher Mark Lawrence said. “The increased speed and bandwidth of light would enable faster solutions to some of the hardest scientific, mathematical, and economic problems.”
The researchers are also interested in how their work could influence the development of neuromorphic computers. This goal would require additional advances in other light-based components, such as nanoscale light sources and switches.
“Our nanophotonic devices may allow us to mimic how neurons compute — giving computing the same high interconnectivity and energy efficiency of the brain, but with much faster computing speeds,” professor Jennifer Dionne said.
The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-11175-z).
