Fabrication Of Complex Micro-optical Elements Based On Femtosecond Laser Two-photon Polymerization

Micro-optical components have the advantages of small volume and weight,low manufacturing cost,and excellent performance in practical applications,so they are used in display technology,light field operation and integrated optical system.In recent years,with the rapid development of micro-optics,micro-electronics,microelectromechanical systems and other fields,the application range of micro-optical elements has become more and more extensive.However,the development will encounter challenges.Due to the wide application of micro-optical devices,and the inability of existing processing methods to meet the manufacturing of more advanced devices,the current devices cannot meet certain practical needs in certain fields.Therefore,it is very important to fabricate micro-optical devices with more complex surface shape,better focusing effect and higher diffraction efficiency.There are limitations for the fabrication of complex components in the commonly used fabrication methods of micro-optical devices.Traditional preparation methods such as planar photolithography,ion beam etching technology and other technologies,though most of the processes have been successfully proven to be able to process microoptical elements at the micro-nano scale,but there will be problems such as The process is complex and requires a mask plate、most of them are Suitable for flat structures without too much fluctuation、the 3D structure is difficult to process,and the machining accuracy is low,and the surface quality of the structure is not satisfactory.Therefore,in order to solve the problems of complex technology and low machining accuracy,this paper proposes a processing method of femtosecond laser two-photon polymerization to fabricate complex 3D micro-optical devices.Femtosecond laser two-photon polymerization technology has high processing accuracy.Since the energy is mainly distributed in the center of the focus during the processing process,it can be used to process the micro/nano structures that smaller than the diffraction limit size.Moreover,the structure can be precisely designed before processing,and the laser scanning route can be controlled by the program,so in theory,any structure can be processed.In this paper,SU8 polymer materials are selected,t taking two optical elements,blazed grating and three-dimensional Kinoform refractive lens,as examples to demonstrate the unique advantages of the two-photon polymerization method.Firstly,by adjusting the laser scanning point spacing,single point exposure time and other parameters,a large,super-smooth and complex surface micro-optical device with the structure size of 80 μm×90 μm×90 μm and the roughness of 2 nm is realized.After selecting suitable processing parameters,grating structures with different periods and heights,that is,different blaze angles are prepared.The results prove that the structure can indeed concentrate most of the light energy passing through the grating to a specified energy level.Subsequently the Kinoform lens which can focus X-rays by refraction principle was prepared.During the experiment,the experimental parameters were adjusted to make the surface quality of the structure excellent,and the details can also be kept intact.Both structures are consistent with the expected design of the structure.This article proves the feasibility of the two-photon polymerization processing method for the processing of complex three-dimensional structures through experiments,which provides new ideas for micro-nano processing,and is bound to open a new door to the fields of micro-optics,microelectronics,micromechanics,etc.,and continue to promote its rapid development.