Focusing light at nanoscale
Normally, light cannot be focused to a spot smaller than the diffraction limit which is half its wavelength. However, in recent years researchers have succeeded in this direction by coupling it to plasmonic nanostructures in which conductive electrons can oscillate collectively at the surface of metals, called surface particle plasmons. The phenomenon is studied as a part of a subject known as “nanoplasmonics”, based on tailored metallic nanostructures.
Plasmonic waveguides
Electron plasmons are formed when electrons oscillate back and forth (like an electron dipole) while magnetic plasmons are formed when electrons oscillate in a circular fashion (like a magnetic dipole).
Magnetic plasmonic wave guiding networks are better than electronic ones when it comes to small size and they are superior to their photonic counterparts because they can focus light to wavelengths dramatically below the so-called diffraction limit.
Researchers at Rice University have made magnetic plasmon-based waveguides composed of “fused” organic molecules called heptamers. Magnetic plasmons could propagate over distances of several microns along a conjugated chain of heptamers. The heptamers are artificial molecules composed of ring-like components and generate unique ring currents that circulate around the structures when illuminated with light from a laser operating at 1500 nm. The fused heptamers share two gold nanoparticles that act as a mutual link for efficient current exchange between the two neighboring heptamers,
Wave guiding networks
Researchers showed that the fused heptamers could be used as building blocks for magnetic plasmonic waveguiding networks and succeeded in making a steerer device that can direct plasmons around bends with large angles and a Y-splitter than can transport plasmons along two separate optical paths. The Y-splitter can also act as an interferometric device to switch plasmon propagation on and off.
Applications
The structures could be used as a blueprint for a new generation of nanoscale photonic devices that could find applications in areas such as low-loss energy transport, data storage and near-field microscopy. Also tailored metallic nanostructures can be made for making tiny optoelectronics devices.