Nano-kirigami And Its Photonics Applications

Three-dimensional(3D)micro-/nano-fabrication technology can greatly promote the development of modern micro-/nano-photonics,which builds up the platform for the control and manipulation of photons as well as the development of next generation information technology.In this thesis,we investigate a focused ion beam(FIB)based nano-kirigami technology with exotic 3D geometric transformation characteristics,which enables unconventional 3D micro-/nano-structures with exceptional optical functionalities.Inspired from the traditional paper cutting arts,we develop a one-step and on-site nano-kirigami method with nanoscale accuracy.By selectively using high-dose milling and low-dose irradiation with gallium ion based FIB on a suspended gold film,corresponding “cutting” and “transformation” processes were achieved,and rich 3D shape transformation such as 3D buckling,rotation and twisting is realized,which results in exotic 3D structural geometries.After analyzing the physical processes during the FIB irradiation,we develop a comprehensive bilayer residual stress distribution model which can well predict the structural transformation.Based on the scanning mode of FIB and the topological morphology of the structure,the nano-kirigami can be classified into local-irradiation/global-irradiation and tree-type/close-loop,respectively.Nano-kirigami in different types have their own characteristics and advantages in various applications.Based on the tree-type nano-kirigami,we design a structure(EOT-SRR)that is composed of vertical split ring resonator(SRR)along one edge of the planar metallic hole.Prominent Fano resonances are successfully induced by the 3D conductive coupling between the vertical SRR and the planar hole.Through analyzing the transmission spectra and the surface current distributions,we figure out the physical origin of the Fano resonances,and demonstrate the advantages of 3D conductive coupling over the traditional capacity coupling in plasmonic systems.The experimental measurements are in good agreement with the numerical simulations,which clearly proves the robustness of the Fano resonance and the reliability of the nano-kirigami method.By breaking the symmetry of EOT-SRR structure,we obtain triple Fano resonances in an asymmetric SRR structure(EOT-aSRR).By sharing the same continuum state of triple Fano resonances,the original complex six-body system can be simplified into a four-body system and described by a four harmonic oscillators model.The wavelength of the corresponding Fano resonance can be tuned by changing the height of one arm of the aSRR structure.As a result,strong anti-crossing phenomena which originates from the strong coupling between Fano resonances are clearly observed in numerical simulation,theoretical calculation and experimental measurement,and the optical spectra are all in good agreement.Based on the characteristics of global irradiation based close-loop nano-kirigami,we design and fabricate an exotic 3D pinwheel structure with exotic twisting and rotation geometric features.The induced electric moment and magnetic moment are parallel or antiparallel in structures with different handedness,which induce giant optical chiral responses.As a result,the 3D pinwheels exhibit strong circular birefringence,which is equivalent to 310,000°/mm(in units of polarization rotation per unit thickness)at 1.95 ?m,and is much larger than the chiral metamaterials and planar structures reported in literatures.Considering the special phase difference of cross-polarized transmission between left-handed(LH)and right-handed(RH)3D pinwheel structures,a binary grating is formed through alternately patterning pinwheels with different handedness.The linearly binary grating can diffract cross-polarized transmitted light while keep the co-polarized light passing through along the original path.Benefited from the intrinsic and uniaxial property of the pinwheels,the binary grating can work on arbitrary orientation angle and form an ultrathin radial diffraction grating.