Fabrication And Research Of Multi-Functional Microlens Array Based On 3D Lithography

As a novel micro-optical element,microlens array(MLA)has attracted much attentions of experts and technicians in various fields benefiting from advantages of the high integration,wide field of view(FOV)and miniaturization.Nowadays,it has been widely applied in various fields,consumer electronics,scientific research,national defense technology,for instance.However,the functional requirements of MLA in various fields are becoming more and more strict.Therefore,to meet various requirements,multi-functional MLA has been developed by researchers.Each function of multi-functional MLA is realized by the complex microstructure,which brings new challenges to traditional MLA fabrication methods.A 12-bit laser direct writing lithography(LDWL)technology has the advantages of high exposure gray scale,high production efficiency,and high processing accuracy.Therefore,it is very perfect for preparing large-area,complex morphology and high aspect ratio microstructures.Undoubtedly,what the technological advantages bring are new opportunities to the fabrication of multi-functional MLA.In the 3D lithography technology,the exposure process is the vital step.Therefore,the exposure mechanism,the nonlinearity of exposure depth and the facula model were studyied.Combined with the analysis of process advantages,a 3D LDWL technological system for fabricating multi-functional MLA was established.Without increasing the manufacturing complexity,various aspherical microlens arrays(AMLA)prepared based on this technology have a low surface roughness(6 nm)and were processed at one-step,and the shape deviation was reduced to 0.3%;a zoom MLA with the complex morphology was fabricated,and its pattern was transferred to a curved substrate to form an artificial hyper compound eye(AHCE)with zoom functions on both planar and curved surfaces;the superhydrophobic structure with the high aspect ratio was integrated between the microlenses,and the MLA with a waterproof function was realized.The main contents are:(1)AMLA features of the low dispersion and diffraction-limited imaging quality,which plays a crucial part in high-end optical sensing,communications,and advanced optical imaging.We demonstrated the fabrication of a large-format AMLA based on the3 D lithography.Its size is up to 30 mm × 30 mm.Without affecting its roughness,its relative profile deviation was reduced to 0.3% by a proposed method.In particular,we prepared an off-axis MLA and MLAs with different filling factors(100%,97%,and78%)due to high fabrication degree.In addition,using the above technology,the MLA pattern was transferred to the optically transparent material,thereby preparing a nakedeye 3D film with an excellent display effect,which provides a new way to realize flexible naked-eye 3D display technology at low cost.(2)To realize the zoom imaging function on both flat and curved surfaces,we prepared a novel AHCE based on a zoom MLA fabricated by the 3D lithography and an ultraviolet light(UV)curing technology.It’s a bionic design inspired by the ancient creature,trilobite.Compared to a dragonfly or butterfly,the trilobite’s compound eyes not only have a large FOV,but also a zoom function due to the photosensitive unit consisted of ommatidia with different focal lengths.Inspired by this concept,we designed and fabricated an AHCE.For this AHCE,its basic unit is composed of five microlenses with different sizes and curvatures,and the different micro-lenses are regarded as five ommatidia with different focal lengths.The five ommatidia are formed into a photosensitive unit to realize the zoom function.In addition to the zoom function,we found that object information can be shared between different photosensitive units,which confirmed the biologists’ conjecture.Using this information sharing function,we have realized the flat zoom imaging function.We further measured its working parameters.Its FOV is 62°,the information received angle is 37.2° and the angle resolution is 3.08°.This AHCE facilitates the development of advanced miniature optics with a large FOV and zoom function.Its unique information sharing capabilities also provide us with a new method to collect environmental information.(3)The MLA,as an optical imaging element,has been widely used in various optical devices.However,in humid environments,the images formed by such devices become blurred,which limits their application environments.In general,to improve the surface dewetting performance of microlenses,complex fabrication methods are required to integrate superhydrophobic structures between microlenses.A superhydrophobic structure requires a discontinuous rough surface,and a microlens requires a continuous smooth surface.The traditional preparation method requires many different processing methods to prepare a surface with the contradictory property microstructures.Using the 3D lithography technology,the superhydrophobic MLA with contradictory properties on the surface was fabricated within one-step.The MLA we prepared has the following advantages: 1.The superhydrophobic MLA with contradictory property surface was processed and formed within one-step.2.The fabricated MLA has a high filling factor.3.The prepared superhydrophobic MLA has a transmittance over 90% and a good imaging function.4.The experiment shows that the MLAs with period of 50～100 μm have excellent superhydrophobic properties.For MLA with period = 80 μm,the contact angle of water droplets is more than 153 °,and the sliding angle is less than 9 °.The superhydrophobic structure allows the water droplets on the surface of the MLA to leave quickly.5.Superhydrophobic MLA was made of flexible materials,so it also maintained excellent optical and superhydrophobic properties when it was bent.We applied the humidifier to simulate the real humid outdoor environment,and its waterproof ability proves its great application potential in the humid environment.Firstly,based on the exposure mechanism and model,a 3D lithography process system was established.The AMLA was fabricated via optimizing the microlens profile.Secondly,a zoom MLA with complex morphology of periodic units was fabricated.Finally,the hydrophobic structures were integrated into the microlenses,and the super hydrophobic MLA was prepared.The fabricated multi-functional MLAs were studied by combination of simulation optimization and experimental verification.As a result,this high degree of freedom micro/nano machining method is suitable for processing MLA with complex morphology to realize the preparation of multi-functional MLA.This dissertation proposed a new technical route for the fabrication of multi-functional MLA,which promotes the development of multi-functional micro optical elements.