Swedish researchers are steering blue and red light in different directions using an array of sub-wavelength asymmetric nano-particles.
The technique is simple, can be applied right across a wafer, and could be used in sensors.
"We believe that our findings can significantly broaden the versatility of plasmonic devices and we envision possible practical implementations in meta-materials, directional emitters, photon couplers and sorters and in chemo-/bio-sensors," the team, from Chalmers University, told the Journal Nature Communications in a paper.
The structures, which are dotted across a glass substrate, all with the same orientation, are effectively optical antennas that impart different phase shifts to the two wavelengths.
An artist's view of colour routing from a bimetallic dimer supported by a glass substrate. The particles are roughly to scale, but red and blue mean little at this nanometre level.
Each consists of a 130nm gold disc next to a 110nm silver disc separated by a 15-20nm gap - a structure whose volume is around 100th of the wavelength cubed.
"The explanation for this exotic phenomenon is optical phase shifts," said researcher Timur Shegai. "The reason is that nanoparticles of gold and silver have different optical properties, in particular different plasmon resonances. Plasmon resonance means that the free electrons of the nanoparticles oscillate strongly in pace with the frequency of the light, which in turn affects the light propagation even though the antenna is so small."
Fabrication is apparently simple.
"The antennas can be fabricated densely over large areas using cheap colloidal lithography," said the University.
Plasmonics is a hot topic as it allows the control of light using small structures.
It can be applied in a variety of areas, said Chalmers professor Mikael Käll.
"One example is optical sensors, where you can use plasmons to build sensors which are so sensitive that they can detect much lower concentrations of toxins or signalling substances than is possible today," he said. "This may involve the detection of single molecules in a sample, for example, to diagnose diseases at an early stage, which facilitates quick initiation of treatment."