Design Of Sparse And Achromatic Lenses Based On Dielectric Metasurfaces

Metasurface,as a hot research area for sub-wavelength electromagnetic wavefront control,has the advantages of low profile,miniaturization and easy integration,which meet the requirements of modern electromagnetics and optics devices.Metasurface was widely used in radar scattering cross-section reduction,array antenna,electromagnetic stealth,holographic imaging,optical/electric lens and other fields to make up for many shortcomings of traditional devices,providing new degrees of freedom for the design and manufacturing.The design of optical/electric lenses was proposed in this thesis.A sparse metalens with randomly distributed meta-atoms and a dual-layer achromatic metalens were designed for microwave and optical imaging,respectively.Firstly,the design of one-or two-dimensional(1D or 2D)random and sparse metalenses with randomly distributed meta-atoms was proposed in the chapter 3.Then the idea of block matrix pencil method was innovatively introduced to overcame the mismatch between the excitation amplitude of the traditional array antenna and innovative metalens.The traditional pure random metalens used random function to generate the position of unit cell,which had non-uniqueness and uncertainty,relatively low efficiency,unstable performance,and can only achieve random position.The random and sparse metalens proposed in this paper can achieve double randomness of position and phase.The metalens we proporsed can obtain the determinacy of the design results and the stability of the metalens performance.The focusing efficiency is better than the traditional pure random metalens.Besides,the random and sparse metalens can achieve polarization insensitivity.which pave the new way for the development of random and sparse metasurfaces.Then,a broadband achromatic metalens based on double-layer metasurface was proposed in the chapter 4.Then the dispersion can be easily compensated by using a dual-layer metalens with plano-convex and plano-concave liked metalens.The two stacked metalenses were both designed by using general meta-atoms which are high refractive index dielectric cylinders with varied radius.We introduced the effective Abbe number for metalens and use lens maker equations to design the dual-layer achromatic metalenses,which has focal length difference of less than 2?m across the visible wavelength range,average focusing efficiency of above 50%and the numerical aperture range from 0.18 to 0.53.The dual-layer achromatic metalens we proposed has the stronger universality and the better robustness than single layer achromatic metalenses.Some performances have been greatly improved,which provides a new idea for the design of optical imaging system.Finally,the random metalens and the dual-layer achromatic metalens proposed in this paper are promising for many potential applications in multi-functional flat optics devices.The former can be used as a millimeter wave imaging lens for security inspection systems and the latter can be used as a optical imaging lens for impact imaging system.