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Nonlinear Light Manipulation Could Provide Basis for Optical Nanodevices
Aug 2016
ST. PETERSBURG, Russia, Aug. 29, 2016 — Ultrafast nanoantenna switching between different light-scattering modes, caused by the interaction between an intense laser pulse and the silicon of a nanostructure, could lead to devices that would enable ultrafast all-optical signal processing.

To demonstrate ultrafast nanoantenna switching, researchers from ITMO University and the Moscow Institute of Physics and Technology (MIPT) manipulated the optical properties of a nonlinear silicon nanoantenna. They irradiated an array of silicon nanoparticles with a short and intense laser pulse and continuously measured the transmittance, altering the properties of the material and the behavior of the silicon nanoantenna and causing it to scatter light in the direction of the incident pulse.

Alexander Krasnok, Denis Baranov, Sergey Makarov

From left to right, Alexander Krasnok, Denis Baranov, Sergey Makarov — cooperative team of young scientists from ITMO University and Moscow Institute of Physics and Technology. Courtesy of ITMO University and Moscow Institute of Physics and Technology.

Thus, by exposing a particle to a short and intense pulse, the researchers found that its behavior as an antenna could be dynamically controlled.

Based on these results, the researchers developed an analytical model to describe the ultrafast nonlinear dynamics of the nanoantenna as well as the generation and relaxation of electron plasma in silicon. According to the model, a radical change in the scattering diagram of the antenna occurs within a short period of time – on the order of 100 femtoseconds (fs). Before the pulse arrival, the amount of energy scattered by the particle in the forward direction is nearly the same as in the backward direction. However, when driven by a short pulse, the antenna switches to almost perfectly unidirectional forward-scattering.

Electromagnetic antenna in transmitting (a) and receiving (b) modes.

Electromagnetic antenna in transmitting (a) and receiving (b) modes. Courtesy of ITMO University and Moscow Institute of Physics and Technology.

Theoretical predictions backed by the experimental data suggest that an antenna of this kind would have a bandwidth of about 250 Gbps, whereas conventional silicon-based electronics rely on components with bandwidths limited to only tens of Gbps.

“It is a top priority — and at the same time a major challenge — to develop such tunable antennas operating at infrared and optical frequencies." said Denis Baranov, a researcher at MIPT. "Nowadays, we can already transmit information through fiber optics at incredible speeds of up to hundreds of Gbps. However, silicon-based electronics are unable to process the incoming data at that rate. Nonlinear nanoantennas that work at optical wavelengths could help us to resolve this problem and make ultrafast all-optical signal processing possible.”  

Schematic representation of the system studied in the paper.

Schematic representation of the system studied in the paper. Photoexcitation of a silicon nanoparticle by a femtosecond laser pulse. Intense irradiation excites electrons in the silicon nanoparticle into the conduction band, which alters the optical properties of the particle (amplitudes of electric and magnetic dipole resonance) in a way that enables unidirectional scattering of incident light. Courtesy of ITMO University and Moscow Institute of Physics and Technology.

“The research shows that silicon nanoparticles might well become the basis for developing ultrafast optical nanodevices," said Sergey Makarov, a researcher at ITMO University. "Our model can be used to design nanostructures containing silicon particles that are more complex, which would enable us to manipulate light in a most unusual way. For example, we hope to eventually control not just the amplitude of an optical signal but also its direction. We expect to be able to ‘turn’ it by a specified angle on an ultrafast timescale.” 

Dynamical reconfiguration of a non-linear silicon nanoantenna.

Dynamical reconfiguration of a nonlinear silicon nanoantenna. This graph shows the front-to-back ratio (FBR) of a nanoparticle, i.e., the ratio of the power transmitted in the forward direction to the power transmitted in the backward direction. The light-blue shaded area in the background represents the envelope of the pulse intensity. The two insets contain the scattering diagrams of the antenna for two different times with the red arrows representing the incident beam. Courtesy of ITMO University and Moscow Institute of Physics and Technology.

The use of a nonlinear antenna, which could be switched by the incident light itself, lays the foundation for the development of novel optical devices with a wide range of functionalities. Silicon nanoparticle-based devices could be integrated into microchips to enable ultrafast, all-optical signal processing in optical communication lines and in the next generation of optical computers.

The research was published in ACS Photonics (doi: 10.1021/acsphotonics.6b00358)

Pertaining to optics and the phenomena of light.
The use of atoms, molecules and molecular-scale structures to enhance existing technology and develop new materials and devices. The goal of this technology is to manipulate atomic and molecular particles to create devices that are thousands of times smaller and faster than those of the current microtechnologies.
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
A small object that behaves as a whole unit or entity in terms of it’s transport and it’s properties, as opposed to an individual molecule which on it’s own is not considered a nanoparticle.. Nanoparticles range between 100 and 2500 nanometers in diameter.  
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