Manipulating Polarization And Phase Of Light By Microstructures

Polarization and phase are two important properties of light.In recent years,the manipulations of light field based on metallic microstructures,such as holes,slits,grooves and protuberances,have been taken more research interests with the development of the microfabrication technology.Due to the strong dependence of surface plasmon polaritons(SPPs)excited by the metallic microstructures on these structures,the manipulation of light field in the micro-or nano-meter scale can be realized by using metallic microstructures.Thus,it also attracts the research interest in designing the micro optical elements.The size of optical devices can be reduced greatly based on the micro optical elements,and this will improve the development of the optical integrated devices.The research for manipulating polarization and phase of light by using microstructures has been become a hotspot in nanophotonics.This thesis chooses silver as the material supporting the excitation of the surface plasmon polaritons,and focus to manipulate phase and polarization of light by using the metallic microstrucutres composed of subwavelength rectangular holes.The innovative studies include the detection of the polarization state,the transformation between the polarization states and the generation of the plasmonic vortex which are realized using the microstructures.The specific studies are listed as follows:1.Polarization states of light is the focus of research in this thesis,and the polarization states of light are described in detail in the introduction.Firstly,the incident light is classified according to the polarization states,and the conversion between different polarization states is analyzed in detail from the angle of phase,.The Jones matrices are used to mathematically describe the completely polarized light and the common polarizing devices.Then,the characteristics of the SPPs,the excitation and detection methods of SPPs are introduced in the thesis.The excitation of SPPs depends on the polarization state of incident light and the designedmicrostructure,and the metallic microstructure plays a key role in the propagation of SPPs.Therefore,this thesis lists some fabrication methods for the manufacturement of the microstructures and some examples of the light manipulation using metallic microstructures.Finally,this thesis introduces the vector beams and the vortex beams which can be formed when the polarization and phase of light are manipulated by microstructures.2.As a nature property of light,the polarization of light has been used in many areas.It’s important to know the polarization states of light before the polarization is used.Therefore,the detection of the polarization states is one main work of this thesis.In Section two of this thesis,the polarization state analyzer is designed,which is composed of a series of rectangular holes with large length-width radio.These holes are arranged on an Archimedes’ spiral trajectory and the length of rectangular holes are always towards the center of the spiral.Not only can the analyzer detect the polarization state of the incident light,but it can determine the polarization direction of linearly polarized light,the rotation direction of circularly polarized light and the ellipticity and the ellipse rotation angle of the elliptically polarized light.In theoretical analysis,the mathematics expressions of the transmitted filed of the microstructure with different polarized light illumination are given based on the dipole model.In order to confirm the property of the polarization states analyzer,the numerical simulations are given by the finite time domain difference method,and the simulated results verify the theoretical predictions that the analyzer can analyze the polarization state of the incident light.3.Conversion between the polarization states is favorable for the practical applications of polarized light.Therefore,the third chapter of this thesis is studied about the conversion of polarization states based on metallic microstructures.Firstly,an rectangular hole is optimized to realize the transformation between the linearly polarized light and the circularly polarized light.Then,a series of rectangular holes rotated and arranged in an Archimedes’ spiral trajectory form a microstructure that can change the circularly polarized light into the vector light.The rectangular hole on different position changes the circularly polarized light into the linearly polarizedlight with different polarization direction,and the Archimedes’ spiral can counteract the spin momentum carried by circularly polarized light.The detail deduction of the field using Jones matrices and the superposition principle of field predicts the conversion from the circularly polarized light to radially and the azimuthally polarized light.Numerical simulations and experimental measurement results show that the radially polarized light can be obtained when the rectangular holes are arranged in a right-handed Archimedes’ spiral and illuminated by the left-handed circularly polarized light,and the azimuthally polarized light can be obtained when the rectangular holes are arranged in a left-handed Archimedes’ spiral with righthanded circularly polarized light illumination.4.Due to carrying orbital angular momentum,the optical vortex with spiral phase front has been used in many areas.The plasmonic vortex generation based on microstructures is studied in Section four of this thesis.The microstructure is composed with optimized rectangular holes etched in the silver film,which are parallel to each other and arranged in a circle or an Archimedes ’ spiral.The plasmonic vortex with spiral phase can be generated when the microstructure is illuminated by ±45o linearly polarized light with homogeneous phase.The formulas of the electric filed near the center of the structure is theoretically analyzed based on the superposition of field,and the spiral phase term indicates the generation of the plasmonic vortex.And the theoretical analysis also demonstrates that the plasmonic vortex with different topological charge can be obtained by changing the trajectory of the rectangular holes.The simulation results show that the spiral phase can be obtained when the microstructure is illuminated by the linearly polarized light with certain polarization direction.5.The summary of the research results and innovation points of this thesis are given,and the deficiency and the unconquered difficulties are illustrated in this section.The following research directions are also proposed.