Silicon nanoparticles that can manipulate light

A new study has shown how silicon nanoparticles can be controlled to achieve effective non-linear light manipulation, a breakthrough that could help introduce new optical devices with many functionalities, such as transmitting, reflecting or scattering incident light in a particular direction, depending on its intensity. Devices based on the nanoparticles could also allow flexible data processing in optical communication systems and be integrated into microchips to bring ultrafast all-optical signal processing in optical communication lines and new optical computers.

Devices that require electromagnetic waves for information transmission and processing require an antenna to receive or transmit signals in a specific direction. However, as incoming signals often need to be flexibly processed, it is key to have a reconfigurable antenna whose characteristics can be altered in a specific way during signal processing. Although quickly transmitting information through is already achievable, silicon-based electronics can’t process incoming data as fast as fiber optics; non-linear nanoantennas that operate at optical wavelengths could resolve this problem.

“It sheds light on non-linear response of optical silicon nanoantennas and provides insight on behavior of more complicated structures”Denis Baranov

To demonstrate non-linear switching, researchers from Moscow Institute of Physics and Technology in Dolgoprudny and ITMO University, St. Petersburg, whose work has appeared in ACS Photonics [Baranov et al., ACS Photonics (2016) DOI: 10.1021/acsphotonics.6b00358], examined a dielectric nanoantenna, an optically resonant spherical nanoparticle made from silicon. Although all spherical particles show resonances, their size determines its resonant wavelength. The first resonance, observed at the longest wavelength, is the magnetic dipole resonance.

Incident light of a specific wavelength induces a circular electric current in the particle. As silicon has a high refractive index, particles with diameters approaching 100 nm will show magnetic dipole resonance at optical frequencies, thus achieving enhanced optical effects at the nanoscale.

The team carried out photoexcitation of a silicon nanoparticle using a femtosecond laser pulse, with intense irradiation exciting electrons in the silicon nanoparticle into the conduction band, thereby changing the optical properties of the particle such that it enables unidirectional scattering of incident light. This allowed them to develop an analytical model explaining the ultrafast non-linear dynamics of the nanoantenna. As researcher Denis Baranov explains, “It sheds light on non-linear response of optical silicon nanoantennas and provides insight on behavior of more complicated structures.”

Silicon nanoparticles could therefore become the basis for ultrafast optical nanodevices, and the team is looking to apply the model to simulate the non-linear behavior of more complicated structures involving resonant silicon nanoparticles, thereby allowing the manipulation of light in unusual ways, such as rotating a beam in a desired direction depending on its intensity.