Agustin Santiago-Alvarado

Analysis and design of an adaptive lens

This study presents the design and analysis of a lens with a variable focal length, which we will call an adaptative lens. This lens is formed of two transparent elastic surfaces with a transparent liquid medium between them. The mechanical design of the lens considers the variation of liquid pressure between the surfaces. This causes changes in curvature radii and in the axial thickness, generating variations in the focal length of the lens. An analysis is given of changes in lens power with respect to changes in pressure. Finally, a model of the human eye is presented using this adaptative lens as crystalline.

Calculating petal tools by using genetic algorithms

To pass from a spherical surface to a conic one, it is possible to use a petal tool or a small solid tool that is placed at different time intervals at several radial zones of the glass. Genetic algorithms are applied to calculate the angular sizes of the incomplete annular tools that make up the petal tools. We also present the desired wear results carried out with the petal tool that was designed on the basis of the dwell times of complete annular tools. These dwell times are calculated by using base functions that are generated with annular tools and by applying the genetic algorithms.

Design of a single flat null-screen for testing a parabolic trough solar collector

Abstract. We present a null-screen design for testing the shape quality of the reflecting surface of a parabolic trough solar collector (PTSC). This technique is inexpensive, the whole surface is tested at once, and it is easy to implement. For this, we propose the design of a flat null-screen perpendicular to the optical axis of the PTSC in such a way that it allows testing of the full aperture; we compute the caustic associated with the reflected light rays on the desired surface and analyze the parameters that determine the null-screen dimensions. Additionally, we perform a numerical simulation to analyze the accuracy of the method by introducing random displacement errors into the measured data. Accuracies >0.35  mrad were found to evaluate the quality of surfaces with this method. The errors in the determination of the coordinates of the centroids of the reflected images must be measured with an accuracy >0.5  pixels, and the errors in the coordinates of the spots of the null-screen must be <0.5  mm.

Improving fast aspheric convex surface tests with dynamic null screens using LCDs.

A method for testing fast aspheric convex surfaces with dynamic null screens using LCDs is shown. A flat null screen is designed and displayed on an LCD monitor with drop-shaped spots in such a way that the image, which is formed by reflection on the test surface, becomes an exactly square array of circular spots if the surface is perfect. Any departure from this geometry is indicative of defects on the surface. Here the whole surface is tested at once. The position of the spots on the LCD can be changed in a dynamic way, to perform point-shifting of the image spots. The proposed procedure improves the dynamic point-shifting method. As has been shown previously, this process reduces the numerical error during the integration procedure, thereby improving the sensitivity of the test. The positioning accuracy for the screen spots is related to the LCDs spatial resolution. Results of the evaluation of a parabolic convex surface with f/#=0.22 are shown.

Measurement of aberrations of a solid elastic lens using a point-diffraction interferometer

There has been a considerable recent increase in the use of variable focal length lenses (VFLLs), especially as microlenses in photographic objectives, endoscopes, microscope objectives, etc. One distinguishing feature of these VFLLs is the presence of a mechanism whereby the shape of the lens and its geometrical parameters can be changed. A new type of variable focal length lens is introduced made from elastic material. It is placed inside a mechanical mount where radial forces can be applied to its perimeter. We also present the optomechanical design and the measurement of wavefront aberrations to the third and fifth order of a solid elastic lens (SEL). A point-diffraction interferometer is used as a wavefront sensor to test changes of the lens. Geometrical changes in the lens produce changes in the aberrations. Finally, the aberrations found in the SEL (without any application of stress) are compared with aberrations obtained by means of numerical ray trace. Some experimental results are also shown.

Design and analysis of an adaptive lens that mimics the performance of the crystalline lens in the human eye

Tunable lenses are optical systems that have attracted much attention due to their potential applications in such areas like ophthalmology, machine vision, microscopy and laser processing. In recent years we have been working in the analysis and performance of a liquid-filled variable focal length lens, this is a lens that can modify its focal length by changing the amount of water within it. Nowadays we extend our study to a particular adaptive lens known as solid elastic lens (SEL) that it is formed by an elastic main body made of Polydimethylsiloxane (PDMS Sylgard 184). In this work, we present the design, simulation and analysis of an adaptive solid elastic lens that in principle imitates the accommodation process of the crystalline lens in the human eye. For this work, we have adopted the parameters of the schematic eye model developed in 1985 by Navarro et al.; this model represents the anatomy of the eye as close as possible to reality by predicting an acceptable and accurate quantity of spherical and chromatic aberrations without any shape fitting. An opto-mechanical analysis of the accommodation process of the adaptive lens is presented, by simulating a certain amount of radial force applied onto the SEL using the finite element method with the commercial software SolidWorks®. We also present ray-trace diagrams of the simulated compression process of the adaptive lens using the commercial software OSLO®.

Use of linear programming to calculate dwell times for the design of petal tools

Two constraints in the design of a petal tool are, the angles that define it must all be positive, and wear must never be greater than the desired wear. The first constraint is equivalent to that of the positive dwell times of a small solid tool. In view of this foregoing, we present a design of petal tools that are used to generate conic surfaces from their nearest spheres and that correct the profile of a surface that is polished. We study optimal angular sizes of a petal tool, which are found after we use linear programming to calculate the optimal dwell times of a set of complete annular tools placed in different zones of the glass surface. We report numerical results of designed petal tools.

The design, construction and characterization of a solid elastic lens

Recent times have seen the production of normal and micro liquid lenses with variable focal length. These have been specially made with transparent elastic materials and liquid medium between them, or with a dielectric liquid medium inside the cavity. Change in the volume of the liquid medium, in the first case, or the application of an electric field as in the second, produced a change in the optical parameters of the lens. The present study offers the opto-mechanical design, manufacture and characterization of a solid elastic lens made of Polydimethylsiloxane (PDMS). To do so, we have prepared a mechanical support frame to hold all of the components of the lens and also allow for the application of radial stress on its periphery. In order to ensure a well-finished lens surface a high quality optical glass mold has also been constructed. Finally, we will present an analysis of the properties of this type of lens when it undergoes variations of radial stress. The experimental results are presented.

Analysis and design of an optical spherometer with an adaptive lens

The inability of an optical spherometer to measure large curvature radii in optical convex surfaces is well known. This is because the movement of the optical component or the instrument cannot be physically carried out since this would involve crossing each other. This study proposes the opto-mechanical design of a spherometer that will have a source light, a beam splitter, and a liquid lens composed of a plane surface and a transparent elastic membrane with a liquid medium between them. By changing the volume of the liquid the shape of the membrane and the thickness of the lens will change. The present study offers a paraxial analysis of the relationships obtained to measure the curvature radius together with its uncertainty as a function of changes in the volume. The study also presents the work range of the instrument. The instrument is focused on the vertex of the surface and on the center of curvature with aid an intensity detector.

Characterization of a tunable liquid-filled lens with minimum spherical aberration

Tunable lenses have become very popular elements due their capacity of change their focal length by only modifying their shape. This characteristic is very useful in different applications in the field of optics. The development of tunable lenses consists on several phases: first, to find a suitable material, second, to obtain an optimal analysis and design, and third, to find the way to change the lens shape and characterization. In this work we present the characterization of a tunable lens, formed by spherical profiled elastic membranes and a liquid medium between them. The proposed liquidfilled tunable has a design such that the spherical aberration is the least to different focus. The development of an optomechanical system to change the lens shape is presented.