Using unidirectional cubic nanoantennas to direct the output from nanoemitters, researchers at Monash University in Australia have described a method to accurately focus light at the nanoscale. The practical upshot of which is substantial progress towards guided, ultra-narrow beams needed for the new world of nanoelectromechanical systems (NEMS) and the eventual production of entire lab-on-a-chip devices.

According to the researchers, nanoscale directed beams of light incorporated in microscale NEMS lab-on-a-chip equipment offer the potential to assist in measuring bacterial levels in food, to help identify airborne pollutants, or even support the diagnosis of cancer.

Apart from the nanoscale light being used as an illumination source in microfluidic analysis, it may also find use in other NEMS mechanisms being developed, such as in the minute deflection registers of ultra-sensitive force detectors or even providing the motivation for light-powered spinning devices to drive these micro-machines.

"These unidirectional nanoantennas are most suitable for integrated optics-based biosensors to detect proteins, DNA, antibodies, enzymes, etc., in truly portable lab-on-a-chip platforms of the future," said Debabrata Sikdar, a postgraduate student from Monash University working on the project. "They can also potentially replace the lossy on-chip IC (integrated circuit) interconnects, via transmitting optical signals within and among ICs, to ensure ultrafast data processing while minimizing device heating."

Cubic in shape, the newly-devised nanoantennas are claimed to perform better than previous spherical versions at guiding an ultra-narrow beam of light where it is needed, with little or no loss due to heating and scattering. The team also claims that being constructed of insulating, instead of conducting or semiconducting materials as the spherical types were – besides being more effective – the cubes are also easier to fabricate.

To test their theories on this new efficiency, the researchers placed the approximately 200-nanometer wide dielectric (nonconductive) nanoncubes in a simulation where they were located in the path of visible and near-infrared light sources. Arranged in a chain of interspaced modules, the space between the cubes can be modified to finely-tune the width and focus of the light beams as required for varying applications. According to the researchers, changing the distance between the nanocubes alters the angular width of the beam and improves directionality.

"Unidirectional nanoantennas induce directionality to any omnidirectional light emitters like microlasers, nanolasers or spasers [spaser stands for surface plasmon amplification by the stimulated emission of radiation – they are similar to lasers, but employ tiny oscillations of electrons rather than photons of light], and even quantum dots," said Sikdar. "Analogous to nanoscale spotlights, the cubic antennas focus light with precise control over direction and beam width."

The research team plans to begin fabricating unidirectional cubic NEMS antennas at the Melbourne Center for Nanofabrication in the not-too-distant future.

"We would like to collaborate with other research groups across the world, making all these wonders possible," said Sikdar.

The results of this research were recently published in the Journal of Applied Physics