Study On Generation Of Cylindrical Vector Beam By Using Subwavelength Nanostructured Grating Polarizer

Cylindrical vector beams are the most typical spatially non-homogeneous polarized beams.In modern optics,cylindrical vector beams have been widely used in imaging,measurement,sensing and information processing.The polarization of light is a phenomenon which result from the photon spin.Macroscopically,the generation of spatially non-homogeneous light,including cylindrical vector beams,implies that the photon spin is manipulated on the microscopic level.Such manipulation is significant in exploring the physical essence of light.Therefore,the generation of cylindrical vector beams is one of the important research directions in modern optical technology.In this research,high-quality the cylindrical vector beams were generated by using subwavelength nanostructure grating polarizers.The polarizer was a microminiaturized and integrated deviece which was in accordance with the development direction of modern optical research.In this dissertation,the research status in the field of developing subwavelength nanostructured grating polarizers was summarized,and the existing problems in this field were also studied.The following innovative achievements have been obtained:1.Applying the rigorous coupled-wave analysis theory,the interaction between incident polarized light and subwavelength nanostructured grating was systematically analyzed,and the mathematical model of subwavelength nanostructured grating was established.Using the subwavelength scale grating model,the effect on the transmission and reflection from the polarizer was analyzed,which was involved by change of the physical parameters about the gratings and the incident light.According to the analysis results,it was concluded that: when the grating period is less than the wavelength of the incident light to a certain extent,the transmission energy of the grating will concentrate on the 0th order,and the energy of other orders of the transmission will approach to 0.After the incident light passes through the subwavelength gratings,the phase difference between the x-direction polarization component and the y-direction polarization component of the transmission of the 0th order will occur.Based on the rigorous coupled-wave analysis theory,the accurate calculation of this phase difference was realized,and the theoretical basis for designing and developing subwavelength nanostructured grating polarizer was established.2.A method for designing subwavelength nanostructured grating polarizer was proposed.The method included the design of local structure of subwavelength gratings and the design of spatial distribution of gratings on the polarizer surface.The geometric structure of subwavelength grating was determined by local structure design,which converted the circularly polarized light to linearly polarized light in a specific direction locally.In the part of designing the spatial distribution of subwavelength gratings,the mathematical correspondence between the grating distribution on the polarizer surface and the expected cylindrical vector beam was established.The corresponding grating distributions of different types of cylindrical vector beams were obtained by using this mathematical relation.3.Several polarizers with different spatial distribution of subwavelength gratings were designed by using the design method proposed in this dissertation.Among them,the polarizer with four-zone configuration was simple in design and easy to manufacture.It generated approximate radially and azimuthally polarized light which were applied to the occasions where the polarization of the output beam were not required strictly.The polarizer with concentric ring configurations and the polarizer which generate radially and angularly polarized light can generate four kinds of basic cylindrical vector beams totally.Finally,two kinds of composite structure polarizers were designed.They generated two particular types of cylindrical vector beams.These two cylindrical vector beams were innovative in polarization state distribution and focusing characteristics,and have high application value in optical technology.4.The process and method of fabricating subwavelength nanostructured grating polarizers were discussed in detail.Using optical nano-fabrication technology,subwavelength nanostructured grating polarizer made of indium-tin-oxide which generated radially and angularly polarized light was fabricated.The experimental scheme for testing the subwavelength nanostructured grating polarizer was designed,and the test optical system was set up on an optical platform.The polarizer was tested in this optical system.It was proved that the polarizer can convert the incident 532 nm circularly polarized light into radially polarized light and azimuthally polarized light.5.On the basis of functional verification of the device,the Stokes parameters and polarization parameters of the output beam from the palorizer were further measured.The factors affecting the optical performance of the polarizer,including the angle of incident light and the fabricating accuracy,are analyzed.The optical characteristics of the device were evaluated based on the measurement results.It was concluded that the local polarization orientation deviation and ellipsometry of the radially polarized beam and the azimuthally polarized beam generated by the device were very small.Finally,by comparing with metal grating polarizer,it is proved that the polarized designed in this reserch has higher energy efficiency.