Design And Application Of Metasurface Device Based On Coding Unit For Decoupling Phase And Polarization

Decoupling phase and polarization of light,as one of development trends of optical elements,can process multi-dimensional information and achieve multi-channel functions.However,the geometrical optical elements and diffractive optical elements decouple phase and polarization with the cost of volume,due to a single parameter can just be modulated by one element.Therefore,decoupling phase and polarization by traditional elements hinders the miniaturization of optical system.The metasurface,a novel planar element composed of sub-wavelength structures,can control light by horizontal properties,such as size,shape,and rotation angle.The metasurface paves a novel path to decouple phase and polarization with a single-layer device,due to the advantages like ultra-thin and great degrees of freedom.However,the present metasurface for decoupling phase and polarization are still limited by two defects.Firstly,the modulation model employed in hybrid coding unit for broadband is limited by weak ability of modulation,due to the lack of flexibility.Secondly,the decoupling model for single coding unit rely on the property of silicon,result in low modulation accuracy in other materials.The two limitations hinder application of the metasurface for decoupling phase and polarization.Here,the decoupling methods are theoretically researched by establishing a generalized model and analyzing different functions.The decoupling method are experimentally verified by charactering a group of fabricated metasurface.The single layer metasurfaces are also applied in parallel polarization imaging.The main research contents of the thesis include:1.The phase theory and fabrication of amorphous TiO₂ coding unit were researched.The mechanisms of propagation phase and Pancharatnam-Berry phase are researched by finite-difference time-domain method.The effect on the two phases from rotation angle was discussed.A generalized model for decoupling phase and polarization is established which are based on the two phases.In order to decouple phase and polarization,the requirements for fabrication of nanofins are proposed by analyzing the phase theory.The fabrication process for TiO₂ nanofins with high aspect ratio is researched,and the key parameters in core process are optimized.The results provide theoretical guidance and experimental basis for the design,fabrication,and characterization of the coding unit for decoupling phase and polarization in visible.2.To achieve broadband decoupling phase and polarization,the hybrid coding unit based on all-rotation-angle-coding is proposed.The hybrid coding unit is based on Pancharatnam-Berry phase and obtained from the generalized model.In the hybrid coding unit,rotation angles of two nanofins,as the degrees of freedom for design,can control phase and polarization with broadband ability.In addition,a method to adjust relative intensities between multi-channel field is proposed.A group of polarization double-foci metalenses are simulated and charactered to verify the proposed method.The results demonstrate that the all-rotation-angle-coding based hybrid coding unit can decouple phase and polarization in the whole visible and control relative intensities between multi-channel fields.The single-layer metasurface is applied in parallel polarization detection.The results are corresponding with conventional polarization imaging,which demonstrates the ability to achieve parallel polarization imaging.3.To decouple phase and polarization with high efficiency,the single coding unit combining propagation-phase-coding and rotation-angle-coding was investigated.The single coding unit is based on propagation phase and obtained from the generalized model.The size and rotation angle of nanofins,as the degrees of freedom for design,are utilized to modulate phase and polarization.To design a group of nanofins with high efficiency and high accuracy,the sizes of nanofins are optimized by compensate the disturbance of phase caused by rotation angle.A group of polarization multi-foci meta-axicons are simulated and charactered.The results demonstrate that the single coding unit can decouple phase and polarization with high efficiency and high signal-noise-ratio.The single metasurface is applied into the parallel polarization imaging system as an illumination element.The measured results are equal to the polarization characteristic of tested sample with slightly error.The results demonstrate that it is feasible to achieve parallel polarization imaging by a single metasurface.