Design Of Broadband Achromatic Focusing Lens Based On Optical Metasurface

The metasurface is a new type of artificial two-dimensional sub-wavelength electromagnetic material,with natural material do not have physical characteristics,and small volume,light weight,thin thickness,through the shape of the artificial sub-wavelength structure characteristics,geometric parameters and the design of the layout arrangement optimization,which can realize the target devices needed for the amplitude,phase and polarization of flexible control,the mode of electromagnetic wave is convenient excellent control,makes the surface structure in a variety of optical applications gradually shows its advantages,and improve the function of traditional lens large volume,low monotone and integration characteristics,promote to achieve the goals of the development of the optical system miniaturization,integration.In recent years,achromatic metasurface structure optical devices have been developed one after another,but the multifunctional metasurface lens in the broadband domain still needs to be further studied.The use of polarizer in traditional optical system inevitably weakens the energy of incident light and increases the complexity of optical system.The use of spatial light modulator also hinders the high integration of optical system.Therefore,in this paper,a non-achromatic metalens with the same numerical aperture is designed for comparative analysis to study the polarimetric sensitive achromatic reflective super-structural penetration.At the same time,the basic transmission achromatic focusing metalens and the amplitude modulated achromatic metalens are studied.The main research contents of this paper include:In order to avoid the energy loss of the incident light caused by the introduction of the polarizer in the traditional optical system,the problem of chromatic aberration of the Lens in the wide frequency domain and the problem that some of the metasurface structures are constrained by the polarization state of the beam,an achromatic metalens without polarization sensitivity is designed.Based on the theory of phase compensation and the transmission phase method,the square nanocell structures with different widths and the corresponding phase databases are constructed and arranged,and the whole structure is optimized by using the Particle swarm optimization,a metalens with the same numerical aperture but with chromatic dispersion is designed for comparison,and the achromatic effect of the metalens on the constant focusing of 500 nm to 550 nm in the visible wavelength band is realized,it is proved that the metalens has the same wave-front in different polarized light,and the designed non-polarization sensitive achromatic metalens is proved effectively.A transmission achromatic metalens is designed by geometric phase method,which can achieve achromatic effect from 500 nm to 595 nm in visible light band.Because the introduction of Spatial light modulator in the traditional optical system is unfavorable to the requirement of high integration of the optical system,the geometric phase type metasurface is designed,and two perpendicular cuboids are chosen as the basic units,by changing the rotation angle with the center of the unit as the axis,according to the special modulation relationship between the modulation phase of the cross-polarized light and the rotation angle in the geometric phase principle,the phase of the metalens is regulated,at the same time,the amplitude of the metalens is adjusted by changing the geometric parameters of the basic unit,and an Achromatic metalens operating from 535 nm to 600 nm in the visible light band is designed and analyzed.In this paper,the design mechanism of the metalens is explained and compared in theory,and the performance of the metalens is verified by using simulation tools,this work has potential applications in the fields of holographic imaging,super-resolution focusing and other optical imaging.