The Study Of Micro-Optical Devices And Its Optical Properties Based On Femtosecond Laser Direct Writing

With the rapid development of modern science and intelligent manufacturing technology,functional diversification,module integration,miniaturization and low power consumption have become the development direction of functional devices and instruments.Compared with traditional optical devices,micro-optical devices have the advantages of compact structure,small volume,arrayability and integration.They have important application prospects in the fields of optical imaging,biomedicine,information storage and laser technology.Especially with the continuous emergence of micro-optical devices combined with new concepts and technologies,the research scope of micro-optics field is expanded,and higher requirements are put forward for micro/nano manufacturing technology.At present,there are many methods to fabricate micro-optical devices,such as UV exposure,electron beam exposure,ion beam etching,nano imprinting and femtosecond laser direct writing.Among them,femtosecond laser direct writing is a maskless lithography technology with simple process and machining accuracy beyond the diffraction limit.It can realize the preparation of complex threedimensional structures.It is complementary to other micro/nano manufacturing technologies,and provides a huge development space for micro-optical devices.Therefore,in this paper,we built a set of high-precision and fast femtosecond laser direct writing system,and studied the related processing technology.Some micro-optical devices have been fabricated by this system,including a high fill factor microlens array for shack Hartmann wavefront sensor;a radius phase shift spiral zone plate for generating perfect vortex beams;and a multi-value phase grating for generating a three-dimensional controllable focus array.The main research contents and innovations of this paper are as follows:(1)A femtosecond laser direct writing system based on two-photon absorption is designed and built.According to the performance requirements,the hardware system,software system and processing mode are optimized,and the processing technology of different lithographic materials is studied.(2)Aiming at the disadvantage of the low fill factor of ordinary microlens array,which leads to low energy utilization,three kinds of microlens arrays with different fill factors are designed and prepared.The optical performance test results show that the optical performance of high fill factor microlens array(fill factor 100%)is the best.The high fill factor microlens array is used in shack Hartmann wavefront sensor to measure the wavefront phases of plane wave and vortex rotation respectively.The experimental values are in good agreement with the theoretical values.(3)Radius phase shift spiral zone plate and elliptical spiral zone plate with high diffraction efficiency are designed and fabricated.By adjusting the radial phase shift control parameters,the bright ring radius of circular symmetric perfect vortex beam can be adjusted;The shape of bright ring of asymmetric perfect vortex beam can be adjusted by adjusting the long and short axis scale factor of elliptic spiral phase plate.The interference experiments verify that the topological charge number of the perfect vortex beam generated by the spiral phase plate is consistent with the theoretical design.This work provides a reference for the design and preparation of the spiral phase plate generating the perfect vortex beam with arbitrary shape.(4)Based on the theory of diffractive optics,the traditional Damman grating is optimized and improved,and a multi-value phase grating with higher diffraction efficiency and higher spot uniformity is designed and fabricated;At the same time,a multi-value phase zone plate with axial light splitting function is designed,and a three-dimensional multi-value phase grating is further designed by combining the multi-value phase zone plate and twodimensional multi-value phase grating,which realizes the distribution of three-dimensional diffraction spot array with high diffraction efficiency and high uniformity.