| In the era of intelligence and automation,with the increasing penetration of flexible devices in the consumer goods market,people's interest in wearable optoelectronic devices is increasing rapidly.As an important part of consumer electronics devices,flexible optoelectronics devices have a growing demand in a large number of emerging areas,such as board-level optical interconnection,optomechanical tuning,epidermal monitoring,strain sensing,and conformal optics.In these applications,it is not only required that the internal components have extremely high adjustable controllability,but also have good bendability and stretch ability.For example,tunable micro-optics components in wearable optoelectronics need to have perfect reversibility while adapting to the high ductility of human skin up to 20%.However,the traditional optical components with fixed curvature cannot meet the needs of flexible optoelectronic devices,which has become a serious technical problem to the development of flexible optoelectronic devices.The solution of these problems depends on the development of new flexible optoelectronic materials and their manufacturing technology.Flexible materials represented by poly(dimethyl siloxane)(PDMS)have unique advantages such as high light transmittance in wide band,good photothermal stability and biocompatibility.In the aspect of flexible material manufacturing technology,lithography and nanoimprinting can be used to prepare high-precision micro-nano structures on the surface of flexible materials.However,the micro-nano structures fabricated on the surface are easy to be polluted by dust and other impurities because of electrostatic force.At the same time,improper adjustment during the tuning process will easily damage the micro-nano structures on the surface and reduce the optical performance of the component.In this paper,nanoimprinting and femtosecond laser direct writing(Fs LDW)technology are used to prepare micro-optical components on the surface and inside of PDMS respectively,so as to solve the problem that the surface of flexible optoelectronic materials is prone to dust.By means of mechanical drive(hydraulic and tension),bioinspired zoom compound eyes enable variable-focus imaging,appliable tension sensor,diffractive micro-optical components with dynamic binocular stereoscopic vision and three-dimensional reconstruction capability were prepared and controlled.The main research works of this paper are as follows:(1)Fabrication of PDMS based flexible micro-optical components.Different micro-optical components were fabricated on the surface and inside of PDMS by nanoimprinting and Fs LDW.On the one hand,the flexible microlens array(MLA)prepared on the surface of PDMS by nanoimprinting has 100% filling factor and good imaging ability.On the other hand,the diffraction grating(DG)and Fresnel zone plate(FZP)were fabricated by Fs LDW inside PDMS.Both micro-optical components have different optical properties.These internal components have good flexibility and can be cleaned easily.(2)The deformation of hydraulic drive PDMS lens is simulated by finite element analysis(FEA).The relationship between the focal length and the volume of lens is simulated.In this chapter,the hydraulic driving lens was introduced briefly.Then,with the help of COMSOL Multiphysics,the model of a two-dimensional axisymmetric PDMS lens is established by using FEA.The analysis shows that the volume of PDMS lens increases under the pressure of optical liquid.That is,when the radius of curvature of lens decreases,the diopter increases,and the focal length decreases.This conclusion provides a theoretical basis for the design and fabrication of bioinspired zoom compound eye in the next chapter.(3)Hydraulic driven bioinspired zoom compound eyes enable variable-focus imaging.In this chapter,by combining the biological structure of compound eyes with the regulation principle of human eyes,we solved the problem that the curvature of bioinspired compound eyes is fixed and cannot be zoomed into images.The PDMS MLA is integrated with microfluidic channel by plasma.The bioinspired compound eye is composed of about 1200 ommatidia.The imaging clarity of each ommatidia is basically the same.The maximum field of view(FOV)of the compound eye can reach 120°.The focal length of the main eye can be adjusted quickly by hydraulic driving.At the same time,the ommatidia can be used as the imaging unit to provide pixels for the variable-focus imaging of the main eye.In the experiment,this tunable micro-optical component was used to observe the objects at 1165 mm and 1833 mm.In this way,the variable-focus imaging ability of bioinspired zoom compound eye was verified.Since the whole structure of the bioinspired zoom compound eye is composed of PDMS with good biocompatibility,it is expected to be applied in the future such as endoscope and other medical imaging devices with limited space but high requirements on the field of vision.(4)Tension driven diffractive micro-optical components.Diffractive optical component has the advantages of small volume,light weight,foldable and high design freedom,which has become an indispensable part of optical system.However,the diffractive micro-optical components with fixed amplitude and phase have certain limitations on the miniaturization and integration of the flexible devices.In this chapter,the period,amplitude and phase of the diffractive micro-optical components are controlled by uniformly stretching the PDMS film.When the DG is tuned,the diffractive angle changes approximately linearly with the tension,and the normalized intensity of diffractive spot does not change obviously.At the same time,the component has good mechanical stability,and the optical properties remain stable after stretching-releasing cycle for 5000 times at 62.5%.When the FZP is adjusted,the optical properties are more abundant than those of the regular ones.On the one hand,three kinds of different foci with can be observed along the optical axis of the adjusted FZP,which provides a new idea for laser beam shaping.On the other hand,different regions on the deformed FZP can image one same object independently.Because there is a certain distance between the imaging areas,there will be an angle deviation when observing the same object.Using this imaging difference,the three-dimensional reconstruction of the measured object can be realized dynamically.Tunable diffractive micro-optical components with good morphology,optical properties,flexibility and biocompatibility,may have application prospects in conformal tension sensors and three-dimensional reconstruction of cell images.To sum up,the main work of this paper is to fabricate different micro-optical components on the surface and inside of PDMS by nanoimprinting and Fs LDW,respectively.The mechanical stress(hydraulic and tension)drive is used to realize the dynamic tuning of micro-optical components.Both the hydraulically driven bioinspired zoom compound eyes and the tension driven diffractive micro-optical components have good mechanical stability and adjustable optical properties.The research of tunable micro-optical components based on flexible material expands the new idea of optical design,and makes a beneficial exploration for the development of micro,integrated,intelligent,wearable flexible devices in the future. |
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