3D Printing of Customized Aspheric Lenses for Imaging

A simple and efficient process for fabricating customized aspheric lenses is reported, in which a stereolithographic 3D printer combined with the meniscus equilibrium post-curing technique is employed. Two kinds of UV-curable resins, DentaClear and HEMA, were used for printing aspheric lenses in our experiments. The printed DentaClear lens featured low surface profile deviation of ~74 μm and showed satisfactory optical imaging resolution of 50.80 lp/mm, i.e., 4.92 μm. The surface roughness of the printed lens with DentaClear was measured to be around 2 nm with AFM. The surface roughness was improved as a result of post-curing, which reduced the ripples on printed lens surfaces. In contrast, the printed HEMA lens exhibited a significant stair-stepping effect with a large surface profile deviation of ~150 μm. The ripples were somewhat apparent even if the printed HEMA lens surface was smoothed by means of post-curing. No sharp image can be obtained with the HEMA lens in the resolution testing. The composition of HEMA resin may be the reason for the relatively poor surface quality and optical properties.

Design of a stigmatic lens with minimal Fresnel losses

A method for designing double aspheric lenses enabling minimal Fresnel losses in the class of stigmatic lenses is considered. Minimization of the Fresnel losses is provided by ensuring equal ray-deviation angles on both aspheric surfaces of the lens. The design of the lens is reduced to the integration of an explicit ordinary differential equation. Simple analytical approximations for the lens profiles are also presented.

Effect of Elastic Modulus on the Accuracy of the Finite Element Method in Simulating Precision Glass Molding

Precision glass molding is a revolutionary technology for achieving high precision and efficient manufacturing of glass aspheric lenses. The material properties of glass, including elastic modulus and viscosity, are highly dependent on temperature fluctuations. This paper aims to investigate the effect of elastic modulus on the high-temperature viscoelasticity of glass and the accuracy of the finite element simulation of the molding process for glass aspheric lenses. The high-temperature elastic modulus of D-ZK3L glass is experimentally measured and combined with the glass cylinder compression creep curve to calculate the high temperature viscoelasticity of D-ZK3L. Three groups of viscoelastic parameters are obtained. Based on this, the molding process of the molded aspheric lens is simulated by the nonlinear finite element method (FEM). The surface curves of lenses obtained by simulation and theoretical analyses are consistent. The simulation results obtained at different initial elastic modulus values indicate that the elastic modulus has a great influence on the precision of the FEM-based molding process of glass aspheric lenses.

Development of a Cost-Efficient Computer Controlled Optical Surfacing Process for Correcting Aspheric Lenses using Tool Influence Function based Dwelltime Optimization

A Computer Controlled Optical Surfacing (CCOS) system has been developed for correcting form errors on aspheric surfaces. Experiments were carried out to find the correlation between different polishing parameters and polishing metrics such as removal rate, uniformity etc. Based on established polishing parameters, polishing process is developed to correct surface errors on planar, spherical and aspheric surfaces. A convolution model between TIF and dwell times was developed to simulate and solve for correction polishing. Surface accuracies of peak-to-valley (PV) 141 nm and root-mean-squared (RMS) 22 nm has been achieved for planar surface. For aspheric surface, current accuracy of 662 nm PV and of 115 nm RMS is achieved with further development ongoing.

Curved CMOS Image Sensors: Packaging Issues, Applications and Roadmaps

Since few years, there has been an increasing interest and demand in flexible electronics. Standard imaging system consists of an optical module (set of lenses) and an image sensor. For wide field of view applications, and due to the curved shape of lenses and mirrors, the flat image after being propagated through the optical system is not flat but curved, i.e. the off-axis light focuses in a curved manner. This problem is called Petzval Field Curvature Aberration (Petzval FCA). It is generally fixed by additional complex lenses to “flatten” the image plane. We propose another approach with a hemispherical curved sensor technology. It allows eliminating FCA directly at the sensor level and thus makes it possible to drastically simplify, and hence miniaturize, the optical system architecture. First, a brief state of the art on curved detectors will be detailed for different application fields. Bendable capacities of hydrid detectors (included interconnection layer) were fully investigated and tested in the past [1, 2]. Moreover, a hemi-spherically curved visible image sensor with better optical characteristics (image quality) was realized and patented by Sony Company in 2014 [3]. Recently, a tunable curving packaging technology, with new optical functions possibilities has been presented in Electronic Component and Technology Conference 2016 [4]. Then, CEA-LETI curving technologies will be explained to address fixed and tunable curvature packaging applications, included modeling and technical process steps. Characterization of curved sensors prototypes have been performed to understand mechanical and electro-optical bending limits and will be also presented in the paper. Based on an existing fisheye flat sensor optical design, a curved focal plane will be described, showing that it's possible to simplify the standard system from 14 lenses (11 types of optical glass) with 2 aspheric lenses, to only 9 lenses (−35%), 3 types of optical glasses, without aspheric surfaces. The benefits of a curved sensor will be summarized into two categories: those related to the optical system design and those related to the quality of images produced by a camera with curved sensor. Optical system:» Miniaturization of optical devices (volume, weight);» Simplification of the lenses alignment process (due to reduced number of lenses);» Suppression of aspheric lenses;» Wide field of view enhancement. Image quality:» More homogeneous image quality (reduced image noise);» Similar or improved resolution and higher sensitivity;» Corrected distortion occurring along the image edges. Finally, curved CMOS image sensor roadmaps and perspectives will be discussed: from a market point of view, application field surveys have been done on mass market applications (mobile, consumer…), photography, automotive… From a technical aspect, a curving technologies roadmap will be proposed, leaded by applications needs, on single chip, collective, and wafer level processes.