| Metasurface is two-dimensional artificial electromagnetic metamaterial that enable flexible manipulation of the amplitude,polarization,phase,frequency,angular momentum and other properties of electromagnetic waves by designing and arranging periodic or non-periodic subwavelength array structures on a flat surface to achieve unprecedented functionality.Compared with conventional optical components,matesurface-based optical devices have the advantages of low loss,thinness and compactness,and ease of high integration.In recent years,in order to cope with the demands of beam phase modulation,beam deflection,beam focusing and other applications,research on functional optical devices based on full dielectric metasurfaces has been carried out,and a large number of preliminary research results have been obtained.However,the reported related devices still have problems such as low efficiency,small operating bandwidth,and poor dynamic modulation ability,which greatly restrict the application of metasurface optics in practical environments.Therefore,further research on metasurface optical devices with high conversion efficiency,large operating bandwidth,and tunability is not only valuable for theoretical research,but also has important market application prospects.In this paper,we focus on two important research hotspots,beam splitting and beam focusing,and conduct in-depth research on high-performance optical devices based on full dielectric metasurfaces.The main research contents of the paper are as follows:(1)A broadband efficient optical beam splitter based on a fully dielectric metasurface is proposed.The design consists of two triangular nano-antenna arrays with opposite spatial distribution placed on a silica substrate.Simulations by the finite-difference time-domain method show that the anomalous transmission intensity of the structure is higher than 0.8 in the wavelength range of 1537-1826 nm,and the total transmission efficiency exceeds 90%.In this operating wavelength range,the beam splitting angle can reach 131.84° at a wavelength of 1826 nm.Especially,the anomalous transmission intensity of the structure is maintained above 0.92 while the conversion efficiency exceeds99% with an operating bandwidth of more than 125 nm.By optimizing the structure parameters,we can further improve the performance of the beam splitter.In addition,we propose for the first time the tuning of the device beam splitting characteristics by adding a refractive index(RI)material to the device surface.(2)A broadband efficient four-channel beam splitter based on a continuous type metasurface is proposed and demonstrated numerically.The structure consists of a cross-shaped aluminum antimonide nanoantenna placed on a polydimethylsiloxane substrate.Incident light passing through the structure is able to split a beam into four beams of equal intensity,with an anomalous transmission intensity exceeding 0.8 in the wavelength range of 761-835 nm,a conversion efficiency higher than 83%,and an anomalous refraction angle that can vary from 46.45° to 53.68° for any order of the beam.In addition,the four-channel beam splitter is tunable when the metasurface is designed as a discrete structure.At a wavelength of 874 nm,the period is increased from 1050 nm to1207 nm by stretching the elastic substrate,at which time the anomalous refraction angle can be tuned from 56.34° to 46.39°(3)A polarization-insensitive metalens based on a dielectric metasurface is designed.Firstly,a phase controller is designed,which consists of a vanadium dioxide nanopillar placed on a silica substrate to achieve full 2π phase control within a nanopillar radius of50-180 nm.Then,the spatial phase distribution is converted to a spatial radius distribution by the phase distribution equation of the metalens.A polarization-insensitive metalens with focal lengths around the set 40 μm at multiple wavelengths at both x and y incidence is achieved,and the focusing efficiency can reach 85.5% at the wavelength of 1070 nm. |
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