Research On Integrated And Multiplexed Photonic Devices With Silicon Metasurface

Metasurface,as a new kind of two-dimensional planar optical device,can control the amplitude,phase and polarization of the incident light through the scatterers array with subwavelength size on the interface.Compared with traditional optical devices,metasurface has the advantages of ultra-thin planar structures,small size,multifunctionality and easy integration.Metasurface has been one of the hot research field in optics due to its unique ability to control light,which provides a new and multi-degree of freedom micro-nano manipulation platform for the integration of optical devices.Compared with plasmonic metasurface,dielectric metasurface based on high refractive index nanostructures has low loss and great potential in practical photonic devices.Silicon,as a kind of high refractive index dielectric material,can be compatible with semiconductor process.Various functional photonic devices have been realized by silicon metasurface,such as metalens,holography,display,polarization control and new light field generation.Due to the unique advantages of silicon metasurface and its multi-dimensional optical manipulation ability,more and more attention has been paid to its integrated and multifunctional application in practice.In this thesis,we carry out research on multifunctional and integrated multiplexing photonic devices based on silicon metasurface.We focus on the practical application requirements in stimulated emission depletion(STED)microscopy,all-optical magnetic storage system,integrated polarization imaging and measurement,aiming at replacing multiple traditional functional devices.The main research results are as follows:1.A single-layer metalens is designed to respectively generate a solid focal spot and a doughnut-shaped focal spot at two wavelengths based on the phase modulation of metasurface,which can be used in STED microscopy.In order to rationally regulate the focusing intensity ratio of two focal spots in practical application,a method is proposed to control the focusing efficiency of two focal spots.The focusing intensity ratio of two focal spots can be controlled by increasing the difference between the phase provided by the scatterers and the target phase.2.A triplex metalens integrating the functions of an azimuthal polarization converter,a helical phase plate,and a focusing lens is proposed and fabricated to generate and focus the first-order azimuthally polarized vortex beam.The experimental results demonstrate that linearly polarized incident light at the wavelength of 633 nm can be converted into almost perfect circularly polarized focal spot by the metalens,which induces a pure longitudinal magnetization spot.This is the first experimental demonstration of a compact metasurface for all-optical magnetic storage system,which has potential application in high-density all-optical magnetic storage system.3.To satisfy the practical application of switching the direction of longitudinal magnetization field alternately in all-optical magnetic storage system,we propose and fabricate a triplex metalens with adjustable direction of longitudinal magnetization field by modulating the handness of incident circularly polarized light.We choose the tetratomic supercell as the unit structure of the metalens and utilize the interference of scatterers inside the supercell to control the transmittance and phase delay along the long axis and short axis of the supercell.The metalens can integrate the functions of the azimuthal polarization converter,the switching of positive and negative first-order vortice and the focusing lens.Experimental results demonstrate that the metalens can generate pure longitudinal magnetization field with adjustable direction by modulating the handness of incident circularly polarized light.4.In order to develop an integrated full Stokes parameters measuring instrument,a polarimeter based on silicon metasurface matrix grating is designed and fabricated,which combines the unique polarization modulation of the metasurface and the diffraction of the grating.The dependence of the Stokes parameters of the scattered field of the subwavelength nanoslits on the slit width is demonstrated by the metasurface polarimeter in experiment.Furthermore,a method is proposed to determine the width of the subwavelength nanoslits by measuring the full Stokes parameters of the scattered field after the subwavelength nanoslits,which beats the diffraction limit on the optical microscopy.Experimental results show that the metal slit with the width of 68 nm can be resolved at 633 nm.Highlights of the dissertation are as following:1.A triplex metalens for all-optical magnetic storage system is proposed on the demand for the miniaturization and integration of all-optical magnetic storage system,which integrates the functions of an azimuthal polarization converter,a helical phase plate,and a focusing lens.It is the first composite metalens for all-optical magnetic storage system.2.A triplex metalens with adjustable direction of longitudinal magnetization field by modulating the handness of incident circularly polarized light is proposed and fabricated on the demand for switching the direction of the longitudinal magnetization field alternately in all-optical magnetic storage system.Compared with the metalens which can only generate a single direction of longitudinal magnetization field,it is more compact and suitable for all-optical magnetic storage system.3.A polarimeter based on metasurface matrix grating on the demand for compact and integrated polarization measurement system is proposed and fabricated.Moreover,a method is proposed to determine the width of the subwavelength nanoslits by measuring the full Stokes parameters of the scattered field of the nanoslits,which beats the diffraction limit of optical microscope system.