基于傅里叶变换光学系统的动态多光束干涉光刻

Dynamic Multi-Interference Lithography Incorporating Modulated Optical Fourier Transform System

变参量微纳结构在二维平面内交叉、分段排布可以实现超表面器件的多路复用和多功能集成。为实现交叉、分段变参量微纳结构的干涉制备,提出了孔径光阑与相位元件联合调制的傅里叶变换光学系统。利用透镜的傅里叶变换特性和相位元件衍射光线的几何传播特性,阐明了傅里叶成像面上交叉、分段分布的多干涉光场的生成方法与调控规律。同时,针对目标分布的变参量微纳结构,反演设计了多像素孔径光阑与基于光栅和变参量光栅的相位元件,实验获得了交叉、分段分布的多干涉光场。将多干涉光场与微缩投影结合可制备分段排布的纳米光栅。将动态调控的多干涉光场分时复用可制备分段排布的变参量纳米光栅。

Objective While space-variant micro/nano structures are segmented or interleaved in a two-dimensional plane,they demonstrate integrated performance as a multi-function or multiplexing meta-device.Among present technologies,projection lithography and interference lithography are effective for the rapid fabrication of micro/nano structures.By highresolution masks,projection lithography produces space-variant micro/nano structures quickly.However,the area of its fabricated micro/nano structures is seriously limited by variation ranges of parameters.For interference lithography,the structural profile and period can be varied by changing intensities and interference angles of light beams,respectively.Nevertheless,their corresponding micro/nano structures change in a limited range with low resolution,in addition to their complex optical setups.Combining projection lithography with interference lithography,this paper reports an optical Fourier transform system modulated by phase element to dynamically produce micro/nano structures in a wide variation range and achieves structural period variation of less than 1 nm.It merely produces structures pixel by pixel and dimension of every pixel is constant.Then,space-variant phase element is utilized as the phase element,where multi-interference light fields are generated to fabricate different micro/nano structures in different shaped pixels.However,their structural parameters and pixels cannot be customized or changed in real time.Therefore,this paper proposes a method to parallel produce micro/nano structures with independent changed structural parameters and pixels,which can be utilized to generate flexible arranged space-variant micro/nano structures for multi-function or multiplexing meta-devices.Methods An optical Fourier transform system jointly modulated by aperture diaphragms and a phase element is proposed.With the Fourier transform principle of lenses and the geometric propagation characteristics of diffraction beams in the phase element,the generation and manipulation of multi-interference light fields in the imaging plane are discussed.The theoretical analysis shows that multi-interference light fields are determined by the distributions of aperture diaphragms and the transmission of phase elements,where the pixelated aperture diaphragms are responsible for the distribution of light fields,and the transmission of a phase element contributes to the structural parameters of each interference light fields.Furthermore,the magnification between the imaging plane and the aperture diaphragm plane as well as the one between the image plane and the transmission plane of a phase element is different,which means that the variation in aperture diaphragms and the phase element manipulates the interference light fields independently.Then,two methods for the generation and manipulation of multi-interference light fields are discussed.When modulated by multipixel aperture diaphragms and a phase element,multi-interference light fields are generated to parallel produce the same structure within different pixels.Pixels and the infilled structural parameters can be dynamically changed by varying aperture diaphragms and manipulating the phase elements.When modulated by multi-pixel aperture diaphragms and a space-variant phase element,multi-interference light fields are generated to simultaneously produce different structures within different pixels.The same rules are obeyed in the manipulation of the light fields except that the change in the aperture diaphragms can vary the structural pattern inside each pixel.Therefore,incorporating the analyzed methods and rules for the generation and manipulation of the interference light fields,aperture diaphragms and the phase element can be inversely designed to produce customized light fields for flexible assembled micro/nano structures.Results and Discussions With the inversely designed methods mentioned above,symmetrical rectangular apertures are utilized as aperture diaphragms and a grating eliminating 0th transmission is acted as the phase element(Table 1)to modulate an optical Fourier transform system.Theoretical results show that three segmented interference light fields with targeted fringe frequency are produced simultaneously,while their light field distribution and interfered fringe frequency change as expected by pre-designed variation in apertures and the position of the grating(Fig.5).Meanwhile,multi-pixel apertures and a grating with space-variant orientations are designed to modulate the Fourier transform system,and types of demand-interleaved interference light fields are generated for the fringes with their orientations flexibly arranged(Fig.7).Experimentally,aperture diaphragms and phase elements fabricated as designed are placed in the optical Fourier transform system,and segmented/interleaved interference light fields,coincident with the theoretical ones,are detected in its imaging plane(Fig.9).Combining the multi-interference light fields with the miniature projection,arrays of segmented nano-gratings are fabricated consequently.With the time division multiplexing of dynamically controlled multi-interference light fields,segmented nano-gratings of nine pixels are fabricated with measured pixel dimensions of 142.705μm×142.689μm,75.102μm×75.264μm,27.576μm×27.505μm as well as structural periods of 472 nm,375 nm and 275 nm(Fig.10).Conclusions Incorporating planar segmented or interleaved space-variant micro/nano structures,meta-device demonstrates multi-function or multiplexing performance.To fabricate customized distributed and space-variant micro/nano structures with interference,this paper proposes an optical Fourier transform system,which is jointly modulated by aperture diaphragms and a phase element.With the Fourier transform principle of lenses and the geometric propagation characteristics of diffraction beams in the phase element,the methods for the generation and manipulation of flexibly distributed multi-interference light fields in the imaging plane are analyzed.Apertures and a grating,as well as apertures and a grating with space-variant parameters,are inversely designed as aperture diaphragms and a phase element respectively to obtain the required distribution of variant micro/nano structures.Theoretical and experimental results verify that with the inversely designed aperture diaphragms and the phase element modulating the optical Fourier transform system,target interference light fields for arrays of segmented or interleaved micro/nano structures can be realized.Combined with the multi-interference light fields and the miniature projection,arrays of segmented nano-gratings are fabricated in sequence.With the time division multiplexing of dynamically controlled multi-interference light fields,nanogratings with three periods are fabricated segmentally,which shows great potential for the rapid fabrication of multifunctional meta-devices.