连续变焦微型液体柱透镜系统的设计与制备

Design and Fabrication of a Continuous Zoom Liquid Micro-Cylindrical Lens System

设计并制备了一种具有较大变倍比及较高成像质量的充液式连续变焦微型柱透镜系统。该系统由埋入聚二甲基硅氧烷基片的两片对称弯月柱透镜及一片双凸柱透镜构成:两弯月柱透镜边缘位置胶合形成空腔,改变注入其中的液体折射率,可实现柱透镜系统的连续变焦;双凸柱透镜的优化设计可控制柱透镜系统整个变焦范围内的像差。当柱透镜系统中注入的液体折射率由1.3330变化到1.5530时,可实现系统后焦距由52.292~4.972 mm的连续平滑变化。整个变焦范围内,柱透镜系统径向弥散斑均方根半径始终小于5μm,接近衍射极限。对柱透镜系统的可能公差进行了详细分析,证实了该设计的可行性,并完成了透镜系统的加工制备及后焦距、调制传递函数曲线的测量。该变焦系统具有变倍比高、体积小、结构简单稳定、成像质量高等优势,可用于集成化的微型设备中。

Objective In order to improve the adaptability of cylindrical lenses and expand their application fields,a continuous zoom liquid microcylindrical lens system was fabricated.Cylindrical lenses are widely used in engineering fields such as beam shaping,scanning equipment,and holographic display due to their irreplaceable ability in beam manipulation.However,the commonly used focal length of cylindrical lenses is always fixed,and most of the research on zoom systems always focuses on the commonly used symmetric circular lenses,while zoom cylindrical lenses are relatively unexplored.Therefore,a series of liquid zoom cylindrical lenses have been designed in our previous study,including compoundtype and capillarytype liquid core zoom cylindrical lenses.They change the refractive index of the core by changing the type or concentration of the liquid filled in the hollow area of the lens and then achieve the variable focal length.However,the compoundtype lens has a large size and is not easy to integrate.The capillarytype micro cylindrical lens system has a short focal length and small zoom range,which limit its application.To address the above problems,we aim to design and fabricate a new type of liquid zoom cylindrical lens system based on a polydimethylsiloxane(PDMS)substrate,which is characterized by a high zoom ratio,stable structure,small volume,and easy integration.The continuous zoom liquid microcylindrical lens system can be used to replace the fixed focus cylindrical lens in beam manipulation,providing a higher degree of freedom and adaptability and applied in the accurate measurement of liquid refractive index and liquid diffusion coefficient.Methods The design and fabrication of a continuous zoom liquid microcylindrical lens system mainly include four processes:establishment and optimization of the initial structure,zoom ability and imaging quality evaluation,tolerance analysis,and processing and fabrication.In this paper,the capillarytype liquid core microcylindrical lens based on a PDMS substrate designed in our previous work is selected as the original structure,and its parameters are quadrupled as the initial structure to lengthen the focal length.When the refractive index of the liquid filled in the capillary varies by changing the type or concentration of the liquid,the focal length of the lens system changes,which can be considered as the different zoom states of the system and simulated by using the multiple structures in ZEMAX.We set the curvature radii,thicknesses,and glass material types of the cylindrical lens in the zoom system as variables and establish the evaluation function to optimize the system structure iteratively.We also analyze the optimized system′s zoom ability and imaging quality until a high zoom ratio and good imaging quality over the zoom range are obtained.Then,the tolerance analysis,including curvature radius,decentering,as well as thickness of every surface in the molding process,and tilting of each cylindrical lens in the installation process,are performed to evaluate the feasibility of the design.We send the designed cylindrical lenses for processing and embed them into a PDMS substrate to complete the preparation.The setup of the observation system is complete,and then the zoom ability and the imaging quality of the continuous zoom liquid microcylindrical lens system based on a PDMS substrate are measured to verify the feasibility of the design scheme.Results and Discussions The zoom lens system we have designed is composed of two symmetrical meniscus lenses and a biconvex cylindrical lens,which are all embedded in a PDMS substrate(Fig.2).The edges of the two meniscus lenses are glued to form a cavity,and the focal length of the system can be changed continuously by varying the refractive index of the liquid filled in the cavity.The rationally designed biconvex cylindrical lens can control the aberrations of the cylindrical lens system in the whole zoom range.The detailed parameters are listed in Table 1.The dimension of the PDMS substrate is 14.7 mm×6.0 mm×10.0 mm.When the refractive index of the liquid injected into the cylindrical lens system changes from 1.3330 to 1.5530,the back focal length of the system changes from 52.292 mm to 4.972 mm continuously and smoothly(Fig.3).In the whole zoom range,the radial root mean square radius of the diffuse spot of the cylindrical lens system is always less than 5μm(Fig.5),and the MTF curves are close to the diffraction limit in most zoom structures(Fig.6).The possible tolerance of the cylindrical lens system is analyzed in detail(Figs.7-10),and permissible tolerance is given.Then,the fabrication of the lens system(Fig.11),as well as the measurement of the back focal length(Fig.12)and the MTF curves(Fig.13)are completed.The measured values and curves are close to the simulation results.Conclusions A continuous zoom liquid microcylindrical lens system based on a PDMS substrate is designed and fabricated in this paper,and a cavity is used to inject liquid;a biconvex cylindrical lens is used to control the aberrations,and the square PDMS substrate ensures the stability of the lens system.Both the simulation and measured results have confirmed its high zoom ratio and great imaging quality.Compared with the original structure,the zoom range is enlarged by about 5 times while ensuring the imaging quality.The zoom system has the advantages of a high zoom ratio,small size,simple and stable structure,and high imaging quality,which can be used in integrated microdevices.