新型可控焦距液体透镜阵列

为了提高成像品质,提出了一种新型液体透镜阵列镜头。先将油滴沉入弹性体底部形成具有可控焦距的单个液体平凸透镜,再通过唯一平台实验液体透镜阵列,制作液体透镜阵列。通过控制滴入硅胶基底的硅油液体体积大小,控制单个微透镜的折射面曲率和透镜焦距。通过位移平台,控制阵列中微透镜的排布和个数。透镜阵列制作方法简单且成本低,透镜抗挤压能力强,焦距可控,阵列规整,在制造过程中,可以控制镜头光圈和初始焦距,因此是一种实用性较高的透镜阵列。     

紫外成像器件中衍射微透镜阵列设计与研制

为了提高紫外成像器件的填充因子,解决凝视型高性能紫外成像器件的核心技术问题,根据标量衍射理论设计了用于128×128日盲型紫外成像器件的微透镜阵列,其工作中心波长为350nm,单元透镜F数为3.56。采用组合多层镀膜与剥离的工艺方法制备衍射微透镜阵列,对具体的工艺流程和制备误差进行了分析,测量了衍射微透镜阵列的光学性能。实验结果表明:衍射微透镜阵列的衍射效率为86%,与理论值95%有偏差,制备误差主要来自对准误差和线宽误差。紫外衍射微透镜阵列的整体性能满足了微透镜阵列与紫外成像阵列的单片集成要求。     

仿复眼视觉系统的研究进展

复眼是昆虫重要的光感受器,由成千上万的小眼构成,具有大视野的动目标快速检测能力。仿复眼的多孔径系统在机器人视觉导航、大视角测量和全景成像等领域应用广泛。首先介绍了复眼的生物机理、成像特性及现有的大视场成像系统;其次介绍了微透镜阵列的仿复眼光学设计现状,分析了微透镜阵列的大视角与多景深的全景成像质量,指出目前曲面微透镜一体化制造存在的成像缺陷;最后提出结合曲面与平面微透镜阵列实现大视角、多景深分辨率的仿复眼系统的可行性。该成像系统不仅可以实现全景范围内的清晰成像,而且还具有全景范围内的目标位置估计能力。     

Fabrication of Microlens Array and Its Application:A Review

Microlens arrays are the key component in the next generation of 3D imaging system, for it exhibits some good optical properties such as extremely large field of view angles, low aberration and distortion, high temporal resolution and infinite depth of field. Although many fabrication methods or processes are proposed for manufacturing such precision component, however, those methods still need to be improved. In this review, those fabrication methods are categorized into direct and indirect method and compared in detail. Two main challenges in manufacturing microlens array are identified: how to obtain a microlens array with good uniformity in a large area and how to produce the microlens array on a curved surface? In order to effectively achieve control of the geometry of a microlens,indirect methods involving the use of 3D molds and replication technologies are suggested. Further development of ultraprecision machining technology is needed to reduce the surface fluctuation by considering the dynamics of machine tool in tool path planning. Finally, the challenges and opportunities of manufacturing microlens array in industry and academic research are discussed and several principle conclusions are drawn.     

微透镜阵列莫尔放大作用及其防伪特征的研究

为了研究微透镜阵列防伪膜的工作原理和防伪作用,首先,从最基本的莫尔条纹相关理论着手,推导出有关莫尔条纹特性的公式;然后,再将微透镜阵列防伪膜的微透镜阵列和微缩文字阵列看作两个具有固定周期的光栅,将莫尔条纹相关公式应用到微透镜阵列防伪膜上,研究了莫尔放大作用和透镜放大作用的匹配问题;最后,通过实验制备出了样品,得到了微透镜阵列防伪膜制备过程中的关键因素。     

Design,fabrication and testing of a compact large-field-of-view infrared compound eye imaging system by precision glass molding

Bionic artificial compound eyes inspire a promising field of miniaturized imaging systems. In this research, a novel infrared (IR) three-dimensional (3D) compound eye imaging system, consisting of a double-side molded 3D microlens array and an aperture array, was designed and fabricated by combining modulated slow-tool-servo diamond turning and precision glass molding. To facilitate the complex profiles on the mold inserts, two novel slow-tool-servo strategies were adopted, namely virtual-axis based diamond broaching and adaptive diamond turning. This microlens array consists of 3 × 3 channels for a field of view of 48° × 48° with a thickness of 1.8 mm. The freeform microlens array on a flat surface was employed to steer and focus the incident light from all three dimensions to a two-dimension (2D) infrared imager. Using raytracing, the profiles of the freeform microlenses of each channel were optimized to obtain the best imaging performance. To avoid crosstalk among adjacent channels, a 3D printed three-dimensional micro aperture array was mounted between the microlens array and the IR imager. The imaging tests of the infrared compound-eye imaging system using the molded chalcogenide glass lenses showed that the asymmetrical freeform lenslets were capable of steering and forming images within the designed field of view. Compared to a conventional infrared camera, this novel microlens array can achieve a considerably larger field-of-view while maintaining low manufacturing cost without sacrificing image quality.     

Characteristics of stand-alone microlenses in fiber-based fluorescence imaging applications

Microlens-ended fibers, which have found tremendous interest in the recent past, find potential biomedical applications, in particular, in endoscopic imaging. The work presented in this paper focuses on the stand-alone microlenses along with custom-fabricated specialty optical fiber, such as imaging fiber, for probe imaging applications. Stand-alone self-aligned microlenses have been fabricated employing microcompression molding and then attached at the end facet of imaging fiber. A detailed characterization of the fabricated microlens is carried and it demonstrates appropriate focusing ability, high fluorescence collection efficiency and imaging ability for biomedical applications. The surface roughness of the microlens is found to be 25 nm with a minimum spot size of 38 μm. The probe imaging system is found to be able to image the fluorescence microspheres of 10 μm size. The collection efficiency of the fiber probe with lens found to be enhanced by three times approximately.     

基于同名点间距变换的三维显示参数匹配

传统集成成像系统以重构场景为记录场景的镜像,而当用相机阵列代替透镜阵列获取元素图像时,两种阵列参数的不匹配会破坏上述镜像关系.为了得到相机阵列获取的元素图像经透镜阵列重构后的物像关系,本文提出用同名点间距计算集成成像重构像距的方法.该方法通过获取端场景物距、相机焦距等参数,得到同名点间距,并等效至重构端透镜阵列系统来实现光学参数的匹配.理论计算表明,同名点间距不同,得到的重构像距也不同.对与透镜阵列参数匹配的同名点间距进行变换处理,即可精确再现不同重构像距的景物.最后,通过实验验证了本文所提方法的有效性.     

Highly uniform manufacturing method for large-area microlens arrays

The microlens array is a key microstructure component in imaging systems, such as in light field cameras. A resolution of the light field camera can facilitate the use of a small-area microlens array. However, fabricating a large-area microlens array with a highly accurate and consistent surface finish is still difficult and high-cost. A low-cost manufacturing method is proposed in this study, where the mould core of the microlens array is fabricated with high precision and high uniformity by cylindrical ultra-precision diamond turning. The proposed tool path strategy is employed to achieve superior surface quality and avoid the dynamic vibration of an unsmooth path. Light field camera prototypes are developed using a commercial DSLR camera with a fabricated microlens array. The successful performance of the prototypes confirms that the proposed manufacturing method satisfies the application demands of large-area microlens arrays.     

Characterisation of a standard CCD video camera devoted to the design of an efficient particle image velocimetry instrument

A particle image velocimetry (PIV) instrument using a video frame grabbing system and two unsynchronised CCD video arrays was constructed. In the optical device, the two CCD are positioned at two perpendicular axes, with an image splitter located at their intersection and a single imaging lens in front of it. An optical characterisation of each CCD array and the imaging lens is needed to ensure that the field of view is similar for each vision system. Firstly, the experimental method of Cornu was used to deduce the basic optical parameters of the imaging lens. A simple video model was then performed to extract the unknown optical parameters of the device such as the angular field of view, the efficient dimensions of each CCD array and the transfer function from the CCD to the TV screen. An identification method based on global magnification measurements allowed the resolution of the micrometric stages needed for the spatial calibration step of the final instrument, to be deduced. Experimental tests have shown that the aberration in image formation was minimum with this configuration.     

Polarized light field microscopy: an analytical method using a microlens array to simultaneously capture both conoscopic and orthoscopic views of birefringent objects

For the comprehensive analysis of anisotropic materials, a new approach, called 'polarized light field microscopy' is introduced. It uses an LC-PolScope to which a microlens array was added at the image plane of the objective lens. The system is patterned after the 'light field microscope' that achieves both lateral and axial resolution in thick specimens in a single camera exposure. In polarized light field microscopy, the microlens array generates a hybrid image consisting of an array of small conoscopic images, each sampling a different object area. Analysis of the conoscopic images reveals the birefringence of each object area as a function of the propagation direction of transmitted light rays. The principles and utility of the instrument that we are calling 'light field LC-PolScope' are demonstrated with images of a thin, polycrystalline calcite film, revealing the azimuth and inclination angle of the optic axis for many crystals simultaneously, including crystals with diameters as small as 2 microm. Compared to traditional conoscopy and related methods, the vastly improved throughput and quantitative analysis afforded by the light field LC-PolScope make it the instrument of choice for measuring 3D birefringence parameters of complex structures.     

Vacuum suction aid for microlens array formation using LIGA-like process

Microlens array fabrication using a vacuum suction process combed with the LIGA-like process is presented in this paper. The circular patterned array was designed on a photomask and transferred onto a substrate using photoresist patterning. Electroforming technology was used to convert the photoresist patterns into a metallic molds with an array of nozzles. Liquid JSR resist was spun onto the substrate joining the metallic mold to remove microlens array under vacuum conditions. The exposure energy and vacuum pressure were essential parameters in the microlens array manufacturing process. Microlens arrays with 50 μm in diameter at −50 cm-Hg vacuum pressure and 100 μm in diameter at −60 cm-Hg vacuum pressure were successfully formed. The produced microlens arrays presented smooth measured surface profiles coincident with the optical lens geometry.     

Vacuum suction aid for microlens array formation using LIGA-like process

Microlens array fabrication using a vacuum suction process combed with the LIGA-like process is presented in this paper. The circular patterned array was designed on a photomask and transferred onto a substrate using photoresist patterning. Electroforming technology was used to convert the photoresist patterns into a metallic molds with an array of nozzles. Liquid JSR resist was spun onto the substrate joining the metallic mold to remove microlens array under vacuum conditions. The exposure energy and vacuum pressure were essential parameters in the microlens array manufacturing process. Microlens arrays with 50 μm in diameter at -50 cm-Hg vacuum pressure and 100 μm in diameter at -60 cm-Hg vacuum pressure were successfully formed. The produced microlens arrays presented smooth measured surface profiles coincident with the optical lens geometry.     

Two dimensional photoacoustic imaging based on an acoustic lens and the peak-hold technology

A new method of photoacoustic (PA) imaging based on an acoustic lens and the peak-hold technology is presented in this article. A fast PA imaging system, which consists of an acoustic lens, a 64-element linear transducer array, and a peak detection-and-hold circuit, is developed to obtain the two dimensional (2D) PA images of the experimental samples. By utilizing an acoustic lens, the PA signals generated from the sample are directly imaged on the imaging plane and collected by the 64-element linear transducer array which changes the PA signals into the corresponding electronic signals. Then the electronic signals are converted into a one dimensional image using the peak detection-and-hold circuit. After vertical scanning with a step motor on the imaging plane, the 2D PA image of the sample is achieved successfully. The results show that the images reconstructed in this experiment agree well with the original samples. Compared to other methods, this PA imaging system can acquire the PA images more rapidly without any complex algorithms, and it may provide a more convenient method for future in vivo noninvasive imaging of tissues and clinic diagnosis.     

集成成像系统中高填充率微透镜阵列的设计与加工

针对目前微透镜设计与加工中存在的问题,本文提出了一种大尺寸、高填充率的微透镜阵列设计与加工方法,并成功应用于基于手机屏幕的三维集成成像显示系统。根据焦面模式下的集成成像原理,建立了透镜阵列参数与集成成像显示关键参数的关系,并设计了高填充率透镜阵列的孔径与焦距。采用超精密铣削方法加工出金属母板,通过纳米压印和图形转移复制的方法,在涂有UV固化胶的PET透明膜上得到了高填充率的微透镜阵列膜,并将其应用于基于手机显示屏的集成成像系统。测试结果表明,在5.7英寸全高清手机屏幕上,直接覆盖孔径为0.526mm、焦距为2mm、填充率为100%的透镜阵列,可以实现立体图像出屏距离达4cm、视场角为12.5°的集成成像显示效果。系统的设计与透镜阵列的制作完全满足集成成像要求,裸眼观看立体图像清晰、逼真,系统集成度高,使用方便。     

大视场并列型仿生复眼光学系统

为了实现大视场微型仿生复眼系统的增材制造,对仿生复眼的成像原理、微透镜阵列与中继系统的设计以及复眼系统的机械结构进行了研究。根据仿生复眼的光学原理设计出单个微透镜,并完成微透镜阵列。通过设计中继系统,使曲面阵列所成的曲面像转换成平面像,从而被平面探测所接收。将微透镜阵列与中继系统组合并对其进行优化。为了满足复眼系统3D增材制造工艺,对其机械结构进行设计。整个复眼系由3481个紧密拼接的正六边形微透镜组成,每个微透镜的视场为4°,通光口径为110μm,整个复眼的视场为123.7°。在120 lp/mm处,复眼各视场的MTF值均大于0.3,各视场点列图的RMS半径均小于艾里斑半径。该系统成像质量良好,公差分析结果表明其像质满足成像要求,满足增材制备工艺需求。     

Recording and controlling the 4D light field in a microscope using microlens arrays

By inserting a microlens array at the intermediate image plane of an optical microscope, one can record four-dimensional light fields of biological specimens in a single snapshot. Unlike a conventional photograph, light fields permit manipulation of viewpoint and focus after the snapshot has been taken, subject to the resolution of the camera and the diffraction limit of the optical system. By inserting a second microlens array and video projector into the microscope's illumination path, one can control the incident light field falling on the specimen in a similar way. In this paper, we describe a prototype system we have built that implements these ideas, and we demonstrate two applications for it: simulating exotic microscope illumination modalities and correcting for optical aberrations digitally.     

曲面复眼成像系统的研究

研究了两种曲面复眼成像系统,并首次将曲面场镜阵列引入曲面复眼成像系统,使其边缘视场的成像质量进一步提高,视场角进一步加大。进行了成像系统的建模以及光线追迹,两种结构的视场角分别达到60°和88°,整个系统的体积分别为0.9 mm×0.9 mm×0.5 mm和0.9 mm×0.9 mm×0.75 mm。文中给出了用激光直写设备在曲面基底上进行光刻来制作曲面微透镜阵列的方法。     

基于相机阵列的三维集成成像记录系统

基于三维集成成像理论以及相机阵列和显示透镜阵列之间的对应关系,利用几何成像理论和光线追踪方法对不匹配全光学集成成像记录系统进行了理论分析,得到了主要记录参数(记录距离和相机间隔)和集成成像显示特性之间的关系。提出了一种非匹配系统中相机阵列记录系统参数的设计方法,并设计了相机阵列记录系统。计算得到了系统的关键参数为记录距离49.6cm,相机间隔25mm。对提出的方法进行了实验验证,结果表明,提出的相机阵列光学记录系统能够完整记录场景的三维信息,三维显示特性基本达到了设计指标,相机阵列的主要记录参数与集成成像三维显示特性的关系符合理论分析,验证了提出方法及系统设计的可行性。提出的系统可为不匹配全光学集成成像系统显示提供大场景、高分辨率微图像阵列。     

基于发光二极管配光曲线设计自由曲面透镜

针对头盔显示器(HMD)液晶像源的特殊要求,选择了一款小尺寸、高光效的发光二极管(LED)作为背光光源。基于此LED的光强分布曲线,利用非成像光学理论设计了双自由曲面透镜阵列,以期进一步提高背光光效。首先对单个LED设计了3款不同半径的双自由曲面透镜,形成了亮度均匀的圆形光斑。然后对单个透镜进行切割,形成矩形光斑,并用4个矩形透镜拼接成透镜阵列。选择了效果最优的透镜进行了加工和测试。结果表明:与传统的采用两层扩散膜的背光结构相比,采用透镜阵列和两层扩散膜后的背光的光能利用率提高了13.94%,背光亮度提高了96.4%,非均匀性由23.8%略提高到23.1%,半亮度视角由37°降低到19°。用设计的透镜及其阵列对LED光源发出的光线进行准直,易形成高亮度的均匀矩形光斑,满足头盔显示器液晶像源背光的要求。