Manipulation Of Light With High Index Dielectric Nanostructures

Efficient manipulation of light,including its phase,amplitude and polarization,is always of fundamental importance in the research of optics.With the rapid progress in nanosicience and nanotechnology,many types of nanostructures have been fabricated and widely used in applications for manipulating optical field within subwavelength scale.Due to the strong field enhancement caused by plasmonic resonance,most tra-ditional nanostrctures are composed by metallic structures and rely on their electric reponse to control optical fields.However,metallic structures are always suffer from strong Ohm losses.It is known that introducing manetic responses into optical systems can bring an extra dimension for the manipulation of the optical field.High refractive index dielectric nanostructures have drawn unprecedented attention during recent years due to its low losses and magnetic response in optical regime.This thesis mainly fo-cuses on the manipulation of light with high refractive index dielectric nanostructures:from dielectirc nanoparitcles to dielectric nanoparticle array also called metasurface.The main research works of this dissertation are summerized as follows:1.The scattering properties of an single isolated dielectric nanocube are invesgated and the induced electric dipole resonance and magnetic dipole resonance are identified.Unidirectional scattering can be achieved by properly choosing the working wavelength when the electric dipole mode and magnetic dipole mode are equal amplitude and in phase.By futher altering the geometrical size of the nanocue,the electric dipole res-onace and magnetic dipole resonance can be overlapped in the resonnace region thus leading to a resonantly unidirectional scattering.Furthemore,a broadband undirectional scattering is achieved by structuring the dielectric nanocuboids into a chain.2.Based on the dipole-dipole interaction model,we study the scattering properties of two coupled silicon nanocube(nanodimer)incident by a Gaussian beam.The far-field scattering results from the interplay of the antenna dipole moments induced by the incident electromagnetic fields which are related to the relative position.By measuring the lateral scattering intensity contrast ratio,one can identify the relative position be-tween the center of the incident beam and the center of the dielectric nanodimer.This study will pave way to a novel position detection and displacement sensing with suitable nanodimer.3.Metasurfaces are 2D arrays composed by subwavelegnth nanoparticles with spe-cial pattern.They are widely focused on for their ability for flexible light manipulation(phase,amplitude and polarization)over subwavelength propagation distances.Based on Jones matrix,we study the transmission properties of metasurface formed by silicon nanocuboid with different size and rotation angle.By properly choosing the nanoparti-cles and arranging the in-plane distribution,arbitrary wavefront can be obtained.Here,we design and fabricate two kinds of metasurfaces for generating radial/azimuthal polar-ization beam corresponding to polarization manipulation and Airy beam corresponding to phase manipulation.4.We introduce a classification of metasurfaces based on their symmetry proper-ties and to link them to their specific Jones matrix.We show that all metasurfaces can be divided into only five distinct classes,each having an individual form of Jones ma-trix and specific eigenstates.Based on this,we design a two-layered metasuface,whose eigenstates are circular polarization,to obtain giant optical activity.Unlike traditional optical activity,the polartiztion rotation angle can vary from-900° to 90° only by chang-ing the structure lateral size.This work may offer a way for new optical polarization convertor.Highlights of this dissertation are as following:1.We develope a semianalytical method based on polarizability tensors to analyze the scattering properties of nanoparticles and the transmission and reflection properties of metasurfaces formed by the naonopaticles.This method is valid only when the size of the nanoparticle is much smaller than the incident wavelength.2.We propose a nanoscale displacement detection method based on the interac-tion of Gaussian beam with a dielectric nanodime.By measuring the lateral scattering intensity contrast ratio,one can identify the relative position between the center of the incident beam and the center of the dielectric nanodimer.The detection sensitivity is about tens of nanometers and can be enhanced by using HG10 mode.3.We obtain giant optical activity using a two-layered dielectric metasurface.Un-like traditional chiral material which increases the transmitting polarization rotation an-gle by lengthen the structure along the propagation,our structure altering the rotation angle by changing the lateral size of the structure.