Holographic Liquid Crystals for Nanophotonics

Abstract

Nanotechnology offers a new paradigm in ways of controlling light in optical systems. Optically enhanced effects such plasmonic resonances and nano-antennas combined with diffraction and photonic bandgap effects can create new mechanisms to enhance the performance of modulation technologies in applications such as three dimensional displays. The power of these optical effects can then be made even more effective by adding in a variable refractive index material such a liquid crystal. This allows the optical properties to be tuned or modulated and creates a new class of optical devices which utilise features on the nano-scale. This chapter pulls together the various strands that have been developed in this area to make an initial investigation into these types of devices. The power of diffraction is introduced to propagate light in a manner which ideally suits nanotechnology. This is then combined with the algorithms used to create computer generated holograms to demonstrate that the diffraction process is indeed the key to the optical control mechanisms at length scales of the order of the wavelength of the light. The key properties of carbon nanotubes and liquid crystals are then introduced to provide the means to create enhanced diffraction through resonant effects which can then be tuned through the variable refractive index properties of the liquid crystals. The most important property of the nanotechnology is the ability to have electrically conductive structures on the nanometre length scale, which allows the rules of electric field interaction to ne manipulated by plasmonics. These effects are demonstrated using both conducting multiwall carbon nanotubes as well as silver nano-antennas. Plasmonic resonance in arrays of nanotubes show the predicted wavelength cut off due to a negative dielectric constant. The same effects are then linked with diffraction to create quasi-crystalline diffraction patterns and fully synthetic computer generated holograms. These effects are expanded further with the silver nano-antennas, where the enhanced resonance effects allow the control of polarisation as well as the wavefront through diffraction. Finally the liquid crystal element of variable refractive index is added to the devices to control the resonance and tune its performance. While this is still at a very early stage of research, it already demonstrates the power and versatility created by the combination of these different optical effects.