Controlling light localization with nanophotonic metamaterials.
University of Southampton, Faculty of Physical and Applied Sciences,
Light localization plays an important role in developing high resolution imaging and precision technologies in nanophotonics. In order to create and control nanoscale light localizations, this thesis has investigated into two research topics with different types of nanophotonic metamaterials: precise control of near-field light localizations and subwavelength light concentration beyond the near field.
For the first topic, (i) I have demonstrated for the first time that a planar fish-scale metamaterial can be used as a controllable template for nanoscale light localizations. By tuning the polarization and wavelength of an incident light beam, the positions of energy hot-spots on the landscape of the metamaterial can be efficiently controlled. Moreover, it has been found that the locations of the hot-spots show a high correlation with the nanostructure, the unit cell size, and the dipole absorption resonance of the fish-scale metamaterial.
In an array of discrete asymmetrically split-ring meta-molecules system, (ii) I have also demonstrated for the first time that the well-isolated subwavelength energy hot-spots can be created and positioned on the metamaterial landscape by the coherent control of a monochromatic continuous light beam with a spatially modulated phase profile. Due to the strong optically induced interactions between meta-molecules, a well-isolated energy hot-spot of a fraction of wavelength has been created. By simply tailoring the phase profile, the hot-spot positions on the metamaterial can be prescribed and moved at will from one meta-molecule to another in a digital fashion with an accurate moving step around lambda/2. In my experiments, (iii) I have integrated a scanning near-field optical microscope and a spatial light modulator to demonstrate the coherent control process. Via this approach, an energy concentration on the nanoscale and accurate control of the energy hot-spots have been achieved.
For the second topic, based on optical super-oscillation, (iv) I have first created an isolated focused spot by using a super-oscillating binary masks with radially symmetric quasi-periodic arrangement of nanoholes. The well-isolated focused spot around 0.45 lambda has been acquired in a wide field of view about 90 lambda. (v) Discovering another exploitation of nanohole arrays, it has been shown that a quasi-periodic nanohole array can be used as a conventional lens with a high numerical aperture around 0.89.
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