Ingo Sieber

Fabrication of microinjection-molded miniature freeform Alvarez lenses

Microinjection molding is a mass production method to fabricate affordable optical components. However, the intense nature of this process often results in part deformation and uneven refractive index distribution. These two factors limit the precision of replicated optics. In order to understand the influences of injection molding on freeform optical devices, in this study, finite element method (FEM) was employed to investigate the miniature microinjection-molded Alvarez lenses. In addition, an innovative metrology setup was proposed to evaluate the optical wavefront patterns in the molded lenses using an interferometer-based wavefront measurement system. This measurement setup utilized an optical matching liquid to reduce or eliminate the lenses surface power such that the wavefront pattern with large deviation from the freeform lenses can be measured by a regular wavefront setup. The FEM simulation results were also used to explain the differences between the nominal and experimentally measured wavefront patterns of the microinjection-molded Alvarez lenses. In summary, the proposed method combining simulation and wavefront measurements is shown to be an effective approach for studying injection molding of freeform optics.

Investigation of a thermoelectric power supply for the Artificial Accommodation System

Presbyopia and cataract are increasing concerns in the aging society. Both age-related ailments go along with a loss of ability to accommodate. A new approach to restoring the patients ability to accommodate is the Artificial Accommodation System which will be implanted into the capsular bag to replace the human crystalline lens. Depending on the actual need for accommodation, the Artificial Accommodation System autonomously adapts the refractive power of its integrated optical element. As the Artificial Accommodation System is an active implant, its subsystems have to be supplied with electrical energy. After a short introduction to thermoelectricity, this paper investigates the possibility of a thermoelectric power supply system for the Artificial Accommodation System. This energy-harvesting approach to powering micro-mechanical systems provides the possibility of an unattended, lifetime power supply of the whole system which promises to have the best possible patient compliance.

Design of freeform optics for an ophthalmological application

Optical freeform surfaces are gaining importance in different optical applications. A huge demand arises e.g. in the fields of automotive and medical engineering. Innovative systems often need high-quality and high-volume optics. Injectionmoulded polymer optics represents a cost-efficient solution. However, it has to be ensured that the tight requirements with respect to the system’s performance are met by the replicated freeform optics. To reach this goal, it is not sufficient to only characterise the manufactured optics by peak-to-valley or rms data describing a deviation from the nominal surface. Instead, optical performance of the manufactured freeform optics has to be analysed and compared with the performance of the nominal surface. This can be done by integrating the measured surface data of the manufactured freeform optics into the optical simulation model. The feedback of the measured surface data into the model allows for a simulation of the optical performance of the optical subsystem containing the real freeform optics manufactured. Hence, conclusions can be drawn as to whether the specifications with respect to e.g. imaging quality are met by the real manufactured optics. This approach will be presented using an Alvarez-Humphrey optics as an example of a tuneable optics of an ophthalmological application. The focus of this article will be on design for manufacturing the freeform optics, the integration of the measured surface data into the optical simulation model, simulation of the optical performance, and analysis in comparison to the nominal surface.

Robust Design of an Optical Micromachine for an Ophthalmic Application

This article describes an approach to the robust design of an optical micromachine consisting of a freeform optics, an amplification linkage, and an actuator. The robust design approach consists of monolithic integration principles to minimize assembly efforts and of an optimization of the functional components with respect to robustness against remaining assembly and manufacturing tolerances. The design approach presented involves the determination of the relevant tolerances arising from the domains manufacturing, assembly, and operation of the micromachine followed by a sensitivity analysis with the objective of identifying the worst offender. Subsequent to the above-described steps, an optimization of the functional design of the freeform optics with respect to a compensation of the effects of the tolerances is performed. The result leads to a robust design of the freeform optics and hence ensures a defined and optimal minimum performance of the micromachine in the presence of tolerances caused by the manufacturing processes and the operation of the micromachine. The micromachine under discussion is the tunable optics of an ophthalmic implant, an artificial accommodation system recently realized as a demonstration model at a scale of 2:1. The artificial accommodation system will be developed to replace the human crystalline lens in the case of a cataract.

Optical performance simulation of free-form optics for an eye implant based on a measurement data enhanced model

This paper describes the application of a modeling approach for precise optical performance prediction of free-form optics-based subsystems on a demonstration model of an eye implant. The simulation model is enhanced by surface data measured on the free-form lens parts. The manufacturing of the free-form lens parts is realized by two different manufacturing processes: ultraprecision diamond machining and microinjection molding. Evaluation of both processes is conducted by a simulation of the optical performance on the basis of their surface measurement comparisons with the nominal geometry. The simulation results indicate that improvements from the process optimization of microinjection molding were obtained for the best manufacturing accuracy.

Robust Design of a Lens System of Variable Refraction Power with Respect to the Assembly Process

The aim of this paper is to show that a compensation of manufacturing tolerances by means of the functional design is reasonable. The approach is discussed exemplarily in the application of a lens system of variable refraction power considering the assembly tolerances. This approach is based on the steps sensitivity analysis, tolerance analysis, and design optimisation and will result in a robust design with respect to the assembly process.

Optical design and tolerancing of an ophthalmological system

Tolerance analysis by means of simulation is an essential step in system integration. Tolerance analysis allows for predicting the performance of a system setup of real manufactured parts and for an estimation of the yield with respect to evaluation figures, such as performance requirements, systems specification or cost demands. Currently, optical freeform optics is gaining importance in optical systems design. The performance of freeform optics often strongly depends on the manufacturing accuracy of the surfaces. For this reason, a tolerance analysis with respect to the fabrication accuracy is of crucial importance. The characterization of form tolerances caused by the manufacturing process is based on the definition of straightness, flatness, roundness, and cylindricity. In case of freeform components, however, it is often impossible to define a form deviation by means of this standard classification. Hence, prediction of the impact of manufacturing tolerances on the optical performance is not possible by means of a conventional tolerance analysis. To carry out a tolerance analysis of the optical subsystem, including freeform optics, metrology data of the fabricated surfaces have to be integrated into the optical model. The focus of this article is on design for manufacturability of freeform optics with integrated alignment structures and on tolerance analysis of the optical subsystem based on the measured surface data of manufactured optical freeform components with respect to assembly and manufacturing tolerances. This approach will be reported here using an ophthalmological system as an example.

Konzept und Realisierung eines optischen Mikrosystems zur Wiederherstellung der Akkommodation

Zusammenfassung Akkommodation, die Fähigkeit von der Nähe bis in die Ferne scharf zu sehen, ist mit ca. 50 Jahren so stark eingeschränkt, so dass wir eine Sehhilfe, z.u202fB. eine Brille, verwenden müssen. Ein neuer Ansatz zwischen unendlich und Lesedistanz eine stufenlose Akkommodation wiederherzustellen, ist die Implantation eines optischen Mikrosystems anstelle einer Intraokularlinse. Es werden Konzept und Realisierung des Systems als Funktionsmodell im Maßstab 2:1 beschrieben.

Robust Design Approach in Micro Optics

The aim of this paper is to present the robust design approach in micro optics. Not only functional requirements have to be considered in robust design. All aspects of the manufacturing chain as well as operational and environmental effects have to be accounted for in the design phase already. Two fundamental issues characterise this approach: ensuring manufacturability and ensuring operability. The focus of this paper will be on the latter issue of ensuring the operability of the produced subsystem. The approach will be discussed using a micro optical test case as an example.

Construction kit for microoptical systems on the basis of microoptical benches

Manufacturing test structures of microsensors and microactuators is very expensive in terms of time and materials. In a conventional design process, this limits the number of design variants to be considered. For this reason, computer-supported design techniques are gaining importance in microsystems technologies. In contrast to microelectronics which may be considered two-dimensional in first approximation, a number of microoptical systems extend over three dimensions. As a consequence, a monolithic setup of such systems is not possible, as this would give rise to topological and geometric problems. Another reason for the modular concept of complex microoptical systems is the lacking of a uniform material system (in contrast to microelectronics). The modular setup of these hybrid systems results in an isolated manufacture of the individual components and their later assembly in a single system. An important aspect of construction is to ensure a certain functionality of the combined system, which is closely linked with the geometry of the structure and the application conditions. To maintain the overall function of a microsystem under the given manufacturing conditions and application environments to be expected, the system design has to be checked for interactions and adjusted accordingly. Hence, simulation of microsystems as a function of performance-reducing impacts plays a crucial role. The concept presented in this paper is the computer-aided design of a modular system on the basis of a microoptical construction kit of reusable models of fundamental microoptical elements.