Design Of Dynamic Tuning Optical Meta-elements Based On Moiré Effect

The optical control method of devices designed and manufactured by early traditional optical technology basically stayed in the "static state",which means that their functionalities are fixed and cannot be changed.With the development of optical technology and related applications,more and more fields such as optical communication,laser beam shaping,adaptive optics,etc.have urgent needs for tunable optical systems.While,the metasurfaces emerged recent year was also in the early stage of "static" manipulation for a beam.To realize dynamically tunable metasurfaces,researchers have proposed many different technical solutions so far.However,these methods are also accompanied by problems such as complex structure,design difficulty,and limited adjustment range.Therefore,in this paper,a dynamic tunable method based on the Moiréeffect is proposed,which is convenient in tuning,large in scope and simple in design.Furthermore,this method is applied to design the tunable blazed grating,tunable spiral phase plate,and continuous-zoom metalens.The method of dynamically tunable metasurfaces and optical elements based on the Moiré effect proposed in this paper not only opens a new road to realize the tunable manipulation of metasurfaces,but also provides a novel idea for designing various tunable optical elements.The main research contents in the paper are summarized as follows:(1)Interaction mechanism between metasurfaces based on geometric phase and light wave.The sub-wavelength cell structure of the geometric phase metasurfaces and the phase manipulation mechanism of the periodic array on incident light waves are clarified theoretically in the paper.The electromagnetic simulation software CST and Comsol are used to verify the derived theory for incident light with a wavelength of 633 nm,also,the sub-wavelength cell structure with a polarization conversion efficiency exceeding 95%was optimized,which laid the foundation for further research.(2)The principle and method of dynamic tuning metasurfaces based on moiré effect are explored.According to theoretical derivation and analysis,it is proposed that superimposing and changing the phase distribution by connecting two metasurfaces phase plates and adjusting the relative rotation angle between the two metasurfaces,so that the phase of incident wavefront is continuously and dynamically controlled.For this method of implementing a dynamically tunable metasurface based on moiré effect,the mathematical model of the phase distribution required for metasurfaces was explored and the changing rule in the dynamic modulation process was clarified.(3)Designed and simulated three kinds of dynamically tunable optical elements based on moiré effect.Three optical elements,i.e.tunable blazed grating,tunable spiral phase plate and continuous-zoom metalens,were designed using the geometric phase metasurfaces and the moiré effect-based tuning method.Simulations were performed by the electromagnetic simulation software FDTD Solutions and the mathematical software Matlab to verify functionalities of these three optical elements,meanwhile,their characteristics are analyzed and discussed.