Research On The Manipulation And Applications Of Optical Surfaces Waves

The manipulation of light is a wavefront shaping technique,which takes use of optical devices to control the amplitude,phase,polarization,frequency and coherence of light.It has attracted great attention in super-resolution optical microscopy,precision measurement,medical detection,microdynamics,quantum communication and integrated photonics.With the development of science and technology,the manipulation of light based on traditional optical elements is difficult to satisfy the needs of miniaturization due to the huge volume and complexity of optical systems.Recently,photonic devices fabricated on optical thin film have become a hot topic to realize the functions of traditional optical devices in optics and optical engineering.Optical surface waves are electromagnetic waves that propagate at the surface of optical thin film,such as surface plasmonic polaritons at the noble metal/dielectric interface,Bloch surface waves in the defect layer of dielectric photonic crystal thin film.Optical surface waves own large propagation wavevector,surface electric field enhancement,sensitivity to the environment and subwavelength localization,so they have been widely applied in micro/nano photonic devices,surface enhanced Raman scattering,dark field imaging,optical tweezers and high sensitivity biosensors through manipulating their polarization,phase and amplitude.This thesis begins from the electromagnetic properties of optical surface waves and studies the research on the manipulation and application of optical surface waves with leakage radiation optical microscopy.In this paper,a high-precision metrology measurement technique is proposed to resolve the cross-section of nanowires.Broadband optical waveguide devices(Mode converter and Power splitter)are realized in visible wavelengths.A new method for trapping and controlling single particle has been accomplished in focused Bloch surface waves and an optical chip is designed for generating tunable optical lattices.The main research works are as follows:1.The optical devices(mode converter and power splitter)of mode-divisionmultiplexing technique are realized on the dielectric photonic crystal film platform.Low refractive waveguide over photonic crystal film can sustain guided Bloch surface waves due to the existence of forbidden band,which extends the range of materials for waveguides.Taking use of perturbation theory and coupling mode equations,the equivalent coupling coefficient method is proposed to design disk/hole structure which can be fabricated on optical waveguide.The results show that a partial or complete conversion between two lowest modes can be achieved by adjusting the coupling distance,which can realize the mode converters(working band of mode purity>90%is 590～680 nm)and multi-mode interference coupler.Finally,simulated results shows multi-mode interference coupler can be used in power beam splitter(The working band of 8:2 beam splitter ratio is 530～710 nm).2.A device for precise measurement of dielectric nanowires’ morphology based on asymmetric excitation of optical surface waves is invented.The model,a row of linearly polarized dipoles with gradient phase,is built to clarify asymmetric propagation of optical surface waves,and this phenomenon can be used to accurately measure the cross-section of nanowires.The width information of the nanowire is successfully retrieved by combining the calibration curve calculated by the finite-difference timedomain method and the optimal polarization angle measured by the leakage radiation optical microscope,whose transverse accuracy is less than 7 nm(3.69 nm,4.38 nm and 6.83 nm).This topography measurement technique can independently measure the width and height of nanowires without complex algorithm.Additionally,the influence about azimuth angle of incident light,the shape of nano wire and the robustness of width measurement are also analyzed.3.The focused Bloch surface waves excited by annular azimuthally polarized beam is proposed to capture and manipulate single mesoscopic metal or single dielectric particle.The constructed beam is used to excite the focused Bloch surface wave efficiently with oil objective,which can form a strong local field.The field is used as optical tweezer to accomplish the stable capture of single mesoscopic particle.The trapping principles of Rayleigh gold particles and mesoscopic gold particles are not the same.Through theoretical analysis and numerical simulation,it can be seen that Rayleigh gold particles are mainly affected by gradient optical force while the scattering optical force is the main force exerted on mesoscopic gold particles.In addition,by comparing the capturing stiffness of single gold particle between focused Bloch surface wave optical tweezers and focused surface plasmons optical tweezers,it can be concluded that focused Bloch surface wave optical tweezers can trap single mesoscopic gold particle more stable.4.A tunable optical lattice chip and microfluidic system,which can be used for sorting hundred-nanometer chiral particles and studying multi-body interactions,is designed.Plasmonic chiral metasurfaces are constructed on a metal thin film to simulate multi-beam interference.Because the initial phase of surface plasmon polaritons excited by metasurface is sensitive to the incident beam,the distribution of topological optical lattices in real space can be controlled by manipulating the polarization and the vortex phase of incident beam.Both theoretical and simulated results show that the interaction of plasmonic chiral metasurfaces and incident beam with different polarization and vortex phase can generate five kinds of topological optical lattices.All results show that these optical lattices can realize not only electric gradient optical forces but also magnetic gradient optical forces and spin density optical forces on dipolar chiral particles.The particles with different chirality can be effectively sorted in the z direction.The innovations of this thesis are as follows:1.The equivalent coupling coefficient theory is used to design the microstructures and study the optical waveguide devices.The high purity mode converter and high ratio power splitter are realized on the photonic crystal film platform.2.The linearly polarized dipole array model is proposed to study the phenomenon that the polarization of incident field can manipulate the asymmetric excitation of optical surface waves.Taking use of this phenomenon,a device is invented to accurately measure the geometric size of subwavelength nanowires with a lateral accuracy better than 7 nm experimentally.3.Ring-shaped laser beam with an azimuthal polarization is used to achieve efficient excitation of Bloch surface waves on photonic crystal film.The focused Bloch surface wave tweezer is proposed to solve the trouble that traditional tweezer is difficult to stably capture the mesoscopic gold particles.Additionally,focused Bloch surface wave tweezer can capture single particle in a large range and move the captured particle to any position.4.Combining the metasurfaces’ geometric phase and propagating phase,a new method for generating optical lattices is proposed.Through manipulating the polarization and phase distribution of the incident beam,the initial phase of surface plasmon polaritons exited by metasurfaces can be tuned.Then the purpose of controlling a variety of optical lattice is accomplished.This method propose a new routine to realize period distribution of optical field.