Abstract:

Advances in nano- and microscale fabrication make possible artificial materials with extraordinary optical properties such as photonic crystal slabs and waveguides with ultraslow speed of light or ¡°left-handed¡± metamaterials. Planar nanostructures, which can be easily fabricated by electron-beam lithography, are currently attracting a special interest of the research community. The important challenge in tailoring optical properties of planar nanostructures is polarization control, which would be crucial for a number of applications. The pronounced changes in the polarization state of transmitted light wave can be achieved with chiral nanogratings, e.g. by using an ordered array of chiral nanoparticles much thinner than wavelength. Optical properties of metal nanogratings are governed by surface plasmons, i.e. by collective oscillation of conduction electrons in metal nanoparticles. We demonstrated that chiral metal gratings exhibit giant optical activity with specific rotation of about 104 �0†2/mm in the vicinity of the surface-plasmon resonance. Such a strong polarization effect in a thin quasi-two-dimensional object originates from the coupling of surface plasmons at the metal-dielectric and metal-vacuum interfaces of the chiral grating. However, in metal nanostructures, optical losses impose severe restrictions on photonic applications. This difficulty can be partially overcome using an all-dielectric chiral photonic crystal that surpasses metal nanogratings in terms of the rotation power and transparency. In the planar chiral photonic crystal, a dramatic enhancement of the optical activity originates from the coupling of the normally incident light wave with low-loss waveguide modes. We anticipate that the strong optical activity of chiral nanostructures will open new opportunities in polarization control for light emitters, polarization selective photo-sensors and polarization switching devices.
 
 
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