Design, Fabrication And Applications Of General Aspherical Lens

With the development of technology, more and more kinds of lenses have been adopted in modern optical systems. Traditional spherical lens will lead to relative poor performance in some applications, such as collimating beam with large divergence angle and correcting an astigmatic laser diode beam, where specific lenses are needed, such as aspherical lens and cylindrical lens. But traditional fabrication method for spherical lens, such as grinding, cannot be simply applied to fabricate these new types of lens, new technologies such as molding method and single point diamond turning have been developed to overcome this problem. In this thesis, we will study the fabrication, measurement and application of aspherical lens which is based on modulating the lens shape by electric field, listed as follows:1. The experimental setup for the fabrication of aspherical lens is introduced, in which the liquid lens is modulated by applying electric field in the system, inspected by the measuring module and cured by UV light when its performance meets the requirements. Commercial software COMSOL based on finite element method (FEM) is employed to solve the deformation of droplet shape in an electric field. Level-set method and moving mesh method are used, respectively, the former can get the transition process of droplet deformation, while the latter can get the steady shape. Electrical force at the droplet interface under electrodes with different shapes is calculated to show the effects of electrode shape. Liquid lens shape on an elliptic substrate is solved both analytically and numerically. Analytical method reveals the relationship among the two curvatures, droplet volume, major axis length and minor axis length of the substrate. Numerical method based on Surface Evolver is then used to verify the analytical solution and study the effect of gravity. Phenomena of shrinkage of lens during UV curing are studied. Curve compensation is realized based on artificial neural network that maps the lens shape before UV curing to that after UV curing.2. Different kinds of aspherical lens are fabricated. Firstly is fiber collimator lens. A fiber is put in a glass tube, on the end surface of which a droplet is injected. The collimator lens can then be obtained by curing the droplet after modulating the lens shape by electric field. Secondly is logarithmic axicon (LA). A droplet is put on a biconcave substrate which is used to extend the focal length. Commercial optical software is employed to evaluate the performance of the LA. Characteristic of the fabricated LA is measured by experiments, showing that a focal line with high resolution is obtained. Phase retrieval is then used to retrieve the wavefront exiting the LA based on multiple plane intensity distribution measured by a CCD with low resolution and a home-built scanning optical probe system with high resolution. Finally is anamorphic lens. Non-axisymmetric substrate fabricated by machinery and3D printing is used to form the anamorphic lens shape. Characteristic of the lens for laser diode beam collimation and3D position detection is studied by experiments.4. Characteristic of LA is studied to show its application prospects in compound eye. Results show that the spot turns into cross bar under oblique illumination, which means that LA can be used to determine the positon of spot center. When the measuring plane is tilted, the spot on the plane is shown to be an elongation of the original spot in one dimension. Astigmatism is introduced in the simulation, showing that the phase can correct the astigmatism under large field of vie, which means it can be used in planar compound eye to get large field of view and large depth of field simultaneously. Application of cubic phase mask in compound eye is studied. Results show that the point spread function under small field of view is almost the same as that under normal illumination, meaning that it can be used in imaging, but under large field of view, the generated astigmatism will severely deteriorate the resolution. Ellipsoidal lens model is used to correct the astigmatism. Characteristic of single ellipsoidal lens for3D position detection is studied. Analytical solution and numerical solution of the spot shape under different fields of view are obtained. Effects of astigmatism on double helix point spread function are studied, results show that the effects are related to the orientation of the spot and it behalves like defocus in the orthogonal direction while it affects very little in the parallel direction.