Time Division Modulation In The Interference For The Spatial-variant Structures Of The Metalens

Metalens shows great potential of replacing traditional lens for its advantages in miniaturization and integration.To the state of art,the fabrication of space variant structures for metalenses mainly relies on the electron beam lithography,which can not provide large area structures for its low efficiency and high cost in fabrication.That causes the metalens still stay in lab without prospective applications.For the rapid fabrication of space-variant micro/nano structures,we propose an optical Fourier transform system jointly modulated by a filter diaphragm and a phase element in this paper.And at its image plane,the output interference light field is analyzed,utilizing its properties of the Fourier transform and geometrical light propagation.Besides,the variations in the output interference light field by changing the space diaphragms and displacing the phase element are discussed.Therefore,the principle of dynamic generation of the interference light field is clarified,and the real-time modulation in its distribution area and structural parameters are achieved.For the metalens based on the Pancharatnam-Berry phase principle,a grating structure with various parameters inside circular and annular distribution is designed.With the above-mentioned principle of dynamic generation and modulation in the output interference light field,the shape and dimension of the diaphragm as well as the structure and relative motion of phase element are derivated according to the space variant gratings.Then the designed diaphragm and phase elements are fabricated,inserted into a Fourier transform optical system.Through four time-multiplexed lithography,space variant gratings inside a circle and three rings for metalens are obtained.The measured results show that their corresponding distributed locations and dimensions as well as their structural orientations and periods are the same with the design.Furthermore,by combing the optical Fourier transform system with a tube lens,an objective lens and a precise displacement platform,an interference lithography system with miniature magnification is set up.By utilizing the same fabrication principle,2 × 2 and 3 ×3 meta-structures with space variant gratings for metalens arrays are fabricated,which provides a new method for replacing electron beam lithography in rapid fabrication of metalens arrays.In conclusion,the optical Fourier transform system jointly modulated by the space diaphragm and the phase element is proposed in this paper,which can dynamically modulate the interference light field by changing the diaphragm and moving or rotating the phase element.With the time-multiplexed fabrication,a large-area,space-variant micro/nano-structures can be fabricated quickly,which provides theoretical and technical basis for the rapid fabrication of meta-surface devices.