Study On The Optical Devices Based On Hyperbolic And Planar Metamaterials

In the past few decades,people have been constantly exploring the applications of metamaterials in optical functional devices based on their powerful control over electromagnetic waves(EMWs),such as absorbers,modulators,and polarization-control devices et al.As the members of the metamaterials "family",the appearance of hyperbolic and planar metamaterials have drawn much attention.Based on their unique optical properties,hyperbolic and planar metamaterials have potential application prospects in many fields,including sub-wavelength imaging,spontaneous radiation enhancement,and wave-front controlling et al.In this thesis,we have studied the optical devices based on hyperbolic and planar metamaterials,including hyperbolic metamaterial(HMM)based broadband absorbers and wavefront control devices,and planar metamaterial based slow-light and Airy beam generator.The main contents and innovations are as follows:(1)In the research of HMM based broadband absorbers,considering the limitation of the working bandwidth of a single-sized HMM absorber,this thesis proposes that the bandwidth of the absorber can be greatly broadened by cascading multiple defferent-sized HMM waveguide arrays.In the reseach of optical absorber,we propose to incorporate three different-sized tapered HMM waveguides,each of which works at a different and wide absorption band,into a unit absorption cell.Numerical simulation demonstrates that the absorber presents the capability of working with an ultra-wide frequency band ranging from 1 to 30 THz,and keeps the absorption efficiency over 80%.In the reseach of microwave absorber,this thesis proposes to cascade two different-sized tapered HMM waveguides into a new absorber unit.In this way,the corresponding absorption bands of each HMM waveguide will be cascaded together to effectively broaden the working band of the absorber.Both the numerical and experimental results demonstrate that in such a design strategy,the low absorption bands of a single-sized tapered HMM waveguide array can be effectively eliminated,resulting in a largely expanded absorption bandwidth ranging from 2.3 to 40 GHz.(2)In the research of HMM based wave-front control devices,this thesis proposes the use of HMM waveguides to control the phase and amplitude of EMWs to design highly efficient transmissive wavefront control devices.This thesis firstly studies the characteristics of the modes supported by the HMM waveguide array.Based on this research,we have investigated the mechanism of the amplitude and phase modulation of EMWs by use of HMM waveguides.For circularly polarized EMWs,we have designed and fabricated a beam deflector and a focusing lens in the microwave band,where the experimental results are in excellent agreement with the numerical simulations.Differetnt from conventional structures based on dilelectric and plasmonic metasurfaces,the scheme requires neither high-index materials nor plasmonic resonances.By scaling down the HMM meta-devices,the proposal can be extended to operate at optical frequencies.We have further designed the beam deflector and focusing lens at 1550 nm wavelength.For the beam deflector,it can achieve a diffraction efficiency of 95.1% and a conversion efficiency of 77.9% at 1550 nm wavelength,which are much higher than those of single-layer plasmonic metasurfaces and comparable to those with dielectric high-aspect-ratio metasurfaces recently reported.For linearly polarized EMWs,we have designed and fabricated a spatial Airy beam generator in the microwave band.Both the numerical and experimental results demonstrate the effectiveness of the Airy beam generator.Moreover,we have conducted corresponding research on the optical properties of the spatial Airy beam.(3)In the research of graphene planar metamaterial based slow-light device,considering the intrinsic constraints of the surface plasmon polaritons(SPP)slow-light at the metal/dielectric interface as narrow band and no tunability,we give a proposal for plasmonic rainbow trapping based on a novel structure comprised of a silica–graphene–silica on a sloping silicon substrate.In the study of graphene broadband slow-light device,the dispersion relations of graphene SPP can be controlled by adjusting its chemical potential.By applying a certain bias voltage between the silicon substrate and graphene layer,the chemical potential of graphene varies continuously along the propagation direction of SPP,thus enabling the continuous control of SPP dispersion relations.The simulation based on the finite element algorithm confirms that the structure achieves a slow-light effect in the broadband frequency range of 143-180.8THz.Meanwhile,the group velocity of the slow-light can be reduced to be 1000 times smaller than light velocity in air.Considering the tunability of graphene layer,the trapped SPP waves could be released by increasing the bias voltage.(4)In the research of metallic metasurface based Airy beam generator,considering the polarization dependence of those surface Airy beam generators,this thesis proposes a new type of metasurface structure to achieve a polarization-controlled Airy beam generator.We have investigated the mechanism of the phase modulation of excited SPP under linearly and circularly polarized incidences by use of a meta-atom(paired nanoslit resonators).Based on the mechanism of phase modulation,a polarization-controlled Airy beam generator is designed.Numerical simulation based on finite-difference time-domain method shows that the metasurface structure can generate the Airy SPP under different polarization states,including x-,y-,left-handed circular polarized,and right-handed circular polarized incidences.Besides,we have studied the optical properties of the Airy SPP,including nondiffracting,self-healing,and autofocusing effects.