Wavelength Demultiplexing And Handedness Modulation Based On Subwavelength Metallic Structure

Surface plasmon polaritons(SPP) at the interface of metal and dielectric mediumwhich are excited and manipulated in the subwavelength metallic structures can be em-ployed to design novel plasmonic devices. This kind of devices has already attractingresearch interests in the recent years due to its advantages such as high performance, s-mall scale, easy-control and easy-integration. Coupling between the subwavelength struc-tures and incident light exhibits a complicated mechanism which shows different opticalresponse with different permittivity of material, shape and size of metallic structure, wave-length and polarization state of illumination electromagnetic waves. But there is still a lotof space to utilize the dispersion and handedness dependent properties of subwavelengthmetallic structures compared with current plasmonic devices. The handedness is corre-sponding to the mirror symmetry which can be found in polarization state of incidentlight, geometry of metallic structure and electromagnetic resonance mode.In this dissertation, wavelength demultiplexing and handedness of circular polariza-tion demultiplexing 1D and 2D diffraction optical elements which modulate wave prop-agation in the free space are studied to show the ability of utilizing dispersion and hand-edness properties of subwavelength metallic structure artificially. Then subwavelengthmetallic structure with opposite handedness of symmetry breaking and displacement cur-rent loop of magnetic mode are studied for spectrum engineering under excitation withvaried polarization state, incident angle and rotation angle of light. The works are sum-marized as follows:Wavelength demultiplexing focusing 1D plasmonic lens composed of metal-dielectric-metal(MDM) waveguides are designed. The wavefront modulation of MDM waveguidewith varied width is investigated analytically. The focusing lens which can focus the lightwith different wavelength to separated locations are designed by a simulated annealingalgorithm. The results are verified by numerical simulation. The lens avoids the sophisti-cated resonators and provide a candidate way to design photon routing devices.Wavelength multiplexing and handedness of circular polarization Terahertz(THz)hologram composed of C-shaped subwavelength metallic antennas. Simulated anneal-ing algorithm are modified and improved to design the hologram.The C-shaped antennaswith different radius and cut angles are used to achieve wavelength demultiplexing THzhologram which generate different character patterns at the observation plane accordingto the incident wavelength; The C-shaped antennas with different rotation angles are usedto achieve handedness demultiplexing THz hologram which generate different characterpatterns according to the handedness of incident circular polarization. The samples arefabricated and measured to show the reliability of the design. The wavefront modulationof each metallic antenna are fully utilized. The results can guide the design of colorful dis-play devices based on red, green and blue color demultiplexing and handedness analyzerof circular polarization based on measuring diffraction intensityOptical magnetic mode enhancement in metallic nanocluster with opposite hand-edness of symmetry breaking. A Quasi-static multi-pole expansion of vector potentialmethod is adopted to describe scattering spectrum of nanoquadrumer. The effects ofhandedness of symmetry breaking, s-/p-polarization and incident angle are analyzed andexplained by coupling mode theory. Magnetic mode are enhanced by manipulating thehandedness of symmetry breaking. Circular dichroism based on magnetic mode is alsoproposed. The results show handedness of symmetry breaking can benefit the applicationof optical activity and optical magnetic materials.Magnetic mode with opposite handedness of circulating current loop in asymmetri-cal planar Terahertz split-ring resonator(SRR). The magnetic modes with opposite hand-edness of current loop are excited at different rotation angle of linear polarization light andmanipulated to achieve resonance peaks with high Q-factor and figure of merit(FOM) byFano resonance. The results propose a new approach for THz thin film bio-sensing andnonlinear optics studies.In conclusion wavelength demultiplexing and handedness demultiplexing metallicdiffraction optics elements are studied by using analytic equations, numerical simulationand sample preparing and testing. The reliability of numerical modeling of wavefrontmodulation cells, calculating methods of wave propagation, modification of optimizationalgorithm, sample fabrication and measurement in THz imaging system are demonstrated.The tailoring of spectrum based on handedness of symmetry breaking and magnetic modeare also studied in metallic nanoclusters and THz SRRs at kinds of polarization state ofillumination light theoretically and experimentally which will benefit the further researchabout optical properties of handedness.