Research On Spatial Second-order Derivation Calculation And Image Edge Detection Based On Dielectric Metasurfaces

It is the development of artificial intelligence technology that has led to a sharp increase in data around the world.These data need to be processed or converted in order to express more accurate information.However,the traditional electronic circuits for information processing have certain limitations for some demands such as high speed and low power consumption.On the other hand,the analog optical computing based on dielectric metasurface can perform information processing with the above requirements.Therefore,it is considered in this study as one of the most promising alternatives.The main view of spatial analog optical computing is now to be used to perform the common arithmetic operations including spatial derivation,Laplace operator and image edge detection,nevertheless,there are still two challenges needed to be overcome.One of them is how to design the system of 2D image edge detection with a large spatial bandwidth,which is suited for linearly polarized light and unpolarized light.The other challenge corresponds to how to design a Laplacian calculator with the spatial resolution of wavelength-scale.For the purposes,we conducted the following researches on the design of these two types of arithmetic units to solve those difficulties:(1)The metasurface consisting of a single layer of dielectric nanodisks embedded in a homogeneous material is introduced and studied in this thesis.And we find that the spatial dispersion excited by the electric dipole resonance in the metasurface can be used to tailor the optical transfer function of the spatial second-order derivation.Furthermore,benefited from the mechanism of electric dipole resonance,the metasurface can perform the two-dimensional image edge detection for linearly polarized light and unpolarized light at visible wavelengths,which follows a large spatial bandwidth and a high efficiency.Relevant numerical simulations show the effectiveness of the structure which realizes the elementary operations,namely,second-order derivation and image edge detection.(2)The dielectric metasurface is introduced and studied in order to perform the Laplace operation for incident electric field.By exciting the quasi-bound states in the continuum,an optical transfer function for nearly-perfect isotropic second-order derivation is achieved with a spatial resolution of wavelength-scale.By means of numerical simulation,it is verified that the metasurface has the functions of performing spatial second-order derivation,Laplace operator and image edge detection for unpolarized light.In addition,its working wavelength can be shifted to other wavebands by adjusting the size of the structure,thus the design is flexible and can be applied to different occasions.In my research,the electromagnetic simulation software based on finite element method is used to analyze the mechanisms of the metasurfaces,and to obtain optical transfer functions.Furthermore,we introduce and employ the optical transfer functions in MATLAB software for simulation of algorithm.The research works show that the results of simulation are consistent with the theoretical results,which proves the validity and feasibility of the design schemes in the thesis.The two dielectric metasurfaces introduced reach the above-mentioned design requirements,paving the way to the application of real-time computing with high throughput.