Effects could influence the future development of processors, electronic devices and communication networks
Brillouin scattering – a phenomenon named after the French physicist Léon Brillouin (1889-1969) – occurs when light waves and mechanical vibrations interact within a material. It is observed when photons – the elementary particles of the electromagnetic force (or, roughly speaking, particles of light) – fall on a material medium, emitting or absorbing phonons, which are the vibrational energy that arises from the collective oscillation of atoms.
In fiber optic telecommunications, Brillouin scattering is one of the factors that limit the information transmitted, especially in long-distance communication lines, where a few milliwatts (thousandth of a watt) of power are enough for the photons to return to the emitting source in instead of heading to the receiver.
Researchers from the Gleb Wataghin Institute of Physics (IFGW) at the State University of Campinas (Unicamp) have been studying this and other optomechanical effects – resulting from the interaction of light with mechanical movements – with the aim of manipulating them.
Thiago Pedro Mayer Alegre, professor in the Department of Applied Physics, is one of the group's main researchers and spoke about the interaction between light and sound in photonic structures at FAPESP Week New York, held in conjunction with the City University of New York (CUNY) and the Wilson Center October 26-28 at the CUNY Graduate Center.
“The increase in confinement provided by physical structures can be used to tune or strengthen the dynamic coupling between photons, electrons and phonons. In photonic structures, this improvement enables a series of new functionalities, such as changing the color of light in non-linear effects, generating radiofrequency signals, suppressing stimulated scattering of light and manipulating mesoscopic phonon modes,” said Alegre.
In condensed matter physics, mesoscopic physics describes phenomena that occur on a scale intermediate between the macroscopic and the microscopic. According to Alegre, any of these functionalities requires great control over the design and manufacture of the microstructure that shapes the optical and acoustic spectra of the phonons, as well as their interaction.
“We have obtained very important results in research, such as in the design and manufacture of nanometric waveguides [structures that guide waves, such as electromagnetic waves or sound waves] and optomechanical cavities that can amplify or suppress these interactions,” he said.
Photonics has applications in the most diverse areas, such as energy, manufacturing, robotics, displays (smartphone screens, for example), health and communications. The first devices developed based on photonic principles were semiconductor light-emitting diodes, in the 1960s, and optical fiber with very low attenuation, in the following decade.
With support from FAPESP, Alegre and colleagues developed a new type of optomechanical device that uses a microscopic silicon disk to confine optical and mechanical waves.
The new device is compatible with commercial manufacturing processes and could be a solution to improve sensors that detect force and movement. The device was described in an article published in the magazine Optics Express.
“The way we designed the device allows us to increase the levels of interaction between the light and mechanical waves that pass through it. In this way, the device could have both practical applications and support our basic research, helping to answer some questions such as what happens in the transition between the quantum microscope world and the classical macroscopic world,” Alegre told FAPESP Agency.
The device created by the researchers, based on a silicon disk 24 microns in diameter and supported on a central silicon dioxide pedestal so that the disk vibrates, has a shape similar to a dartboard, with nanometric concentric circular grooves. This format allows you to confine light and mechanical waves in the device using separate mechanisms (Read more at: http://agencia.fapesp.br/24687/).
IFGW-Unicamp researchers also theoretically developed a silicon photonic device that could enable the interaction between optical and mechanical waves that vibrate in the range of tens of gigahertz (GHz).
Result of the projects "Nanophotonics in semiconductors of Groups IV and III-V" e "Optomechanics in photonic and phononic crystals", both with support from FAPESP, the device was described in an article in the journal Scientific Reports.
The researchers proposed, through computer simulations, a device to explore Brillouin scattering and that could be transposed to photonic microchips (Read more at: http://agencia.fapesp.br/25000/).
Metamaterials
Andrea Alu, director of the Advanced Science Research Center (ASRC) at the CUNY Graduate Center, spoke at FAPESP Week New York about research carried out by his group to control light in metamaterials. These are artificial materials modified in such a way that they acquire desired properties that do not exist naturally.
“We have a complete and ambitious basic research program aimed at introducing and developing new revolutionary ideas and concepts that allow us to model, design, analyze, manufacture and characterize metamaterials for the next generation of integrated electromagnetic and photonic systems,” he said.
ASRC researchers employ new theoretical tools (including analytical and numerical methods), fabrication techniques for nanometer-scale objects, two-dimensional materials, advances in the fundamental physics of the interaction of light and matter in metamaterials, and optomechanics.
“The study of light at the nanoscale has become a vibrant field of research, as scientists now master the flow of light at length scales far below the optical wavelength, surpassing the classical limits imposed by diffraction,” Alu said.
Find out more about FAPESP Week New York at: www.fapesp.br/week2018/newyork.
