Research On The Design Principle And Applications Of The Achromatic Metalens

As a common tool for focusing beams,lenses are widely used in various modern optical systems.However,the dispersion of the lens limits its working spectral width.Thus,achromatic lenses based on double cementation and lens groups are designed.However,they have the disadvantages of difficult processing and large size,which are not conducive to the integration of optical systems.Metasurfaces have been widely used in the research and development of various new optical devices in recent years due to their flexible wavefront control capabilities at subwavelength scales.Therefore,metalens based on metasurface provides a new solution for realizing ultra-thin and ultra-compact achromatic lenses.In this paper,the achromatic metalens is taken as the main research object.And three achromatic metalenses with different working bands,different sizes and different functions are proposed.The main research results and innovations of this paper are as follows:(1)A polarization-independent infrared achromatic metalens with a millimeter aperture is designed.This design combines the discrete multi-wavelength achromatic principle with a global optimization algorithm.By optimizing the phase distribution at 9 sampling wavelengths in the 8 ～12 μm band,the designed metalens can satisfy the focusing phase of each wavelength at the same time,thus achieving achromatic focusing.Subsequently,polarizationindependent achromatic metalens with a diameter of 1 mm and a numerical aperture of 0.23 were constructed using various four-fold symmetric meta-atoms.At the same time,achromatic metalenses of different sizes and numerical apertures are also designed.Their achromatic focusing performances are simulated and compared.(2)A high-magnification rotary zoom achromatic metalens is designed in the visible light.This design applies the zooming principle of Moiré lens to the design of achromatic metalens,useing two metasurfaces with zoom phases to form a rotating zoom metalens.The focal phase of the metalens is related to the relative rotation angle between the metasurfaces,and the focal length can be continuously adjusted by changing the rotation angle.Afterwards,the phase distributions of the two metasurfaces at 440 nm,540 nm and 640 nm are optimized by the global optimization algorithm,so that the constructed metalens can satisfy the zoom phase of three wavelengths simultaneously,eliminating the dispersion.In this paper,the 1-10×achromatic zoom performance of the metalens is verified by simulation.(3)A near-infrared achromatic metalens array for optical multi-parameter detection is proposed and implemented.In this design,two polarization-dependent achromatic metalens schemes are given for different phase control methods.This metalens array is composed of a variety of polarization-dependent metalenses,which can achieve achromatic focusing performance from 1310 nm to 1550 nm.At the same time,due to the polarization-dependent focusing characteristics of the superlens array,the polarization and wavefront information of the incident light can be restored by using the light intensity and centroid distribution of the focused spot with the restoration algorithm.In this paper,the achromatic focusing and multiparameter detection performance of the designed metalens array are verified by simulation.In addition,various experiments were carried out,the actual focal length of the processed samples was tested,and the different polarization states and phase gradients in the working spectrum were detected.