We present the design of a varifocal freeform optics consisting of two lens bodies each with a helical-type surface structure of azimuthally varying curvatures. This arrangement allows for tuning the optical refraction power by means of a mutual rotation of the lens bodies around the optical axis. Thus, the refraction power can be tuned continuously in a defined range. The shape of the helical-type surfaces is formed by a change in curvature subject to the azimuthal angle α. At the transition of the azimuthal angle from α = 2π to α = 0, a surface discontinuity appears. Since this discontinuity will seriously affect the imaging quality, it has to be obscured. In the initial state, i.e., zero-degree rotation, the curvatures of the opposing surfaces result in a specific refraction power, which is constant over the entire circular aperture. Rotating one of the lens bodies by an angle φ around the optical axis will change the opposing curvatures and result in a change of refraction power. Two circular sectors with different tunable optical refraction powers are formed, thus resulting in a tunable bifocal optics. Obscuring the minor sector will result in a tunable monofocal rotation optics. In contrast to conventional tunable lens systems, where additional space for axial or lateral lens movement has to be allocated in design, rotation optics allowing for a more compact design. A performance analysis of the rotation optics based on simulations is presented in dependence on aperture size as well as approaches to compensate for spherical aberrations.
This paper presents the design of a novel varifocal freeform optics consisting of two lens bodies each with a helical-type surface structure of azimuthally varying curvatures. This arrangement allows for tuning the optical refraction power by means of a mutual rotation of the lens bodies around the optical axis. Thus, the refraction power can be tuned continuously in a defined range. The shape of the helical-type surfaces is formed by a change in curvature subject to the azimuthal angle α. At the transition of the azimuthal angle from α = 2π to α = 0, a surface discontinuity appears. Since this discontinuity will seriously affect the imaging quality, it has to be obscured. In the initial state, i.e. zero-degree rotation, the curvatures of the opposing surfaces result in a specific refraction power, which is constant over the entire circular aperture. Rotating one of the lens bodies by an angle φ around the optical axis will change the opposing curvatures and result in a change of refraction power. Two circular sectors with different tunable optical refraction powers are formed, thus resulting in a tunable bifocal optics. Obscuring the minor sector will result in a tunable monofocal rotation optics. In contrast to conventional tunable lens systems, where additional space for axial or lateral lens movement has to be allocated in design, rotation optics allowing for a more compact design. A simulative performance analysis of the rotation optics in dependence of the maximum rotation angle will be presented as well as an approach to design-for-manufacture.
This paper presents a refractive optical system consisting of two lens bodies with helical surface structures, which allows for tuning the optical refraction power by means of a mutual rotation of the lens bodies around the optical axis. Thus, the refraction power can be tuned continuously in a certain range. The helical surfaces are shaped by changing the radius of curvature as a function of to the polar angle. Combination of such two surfaces results in an optics with refraction power being tunable by a mutual rotation. This optical system is multifocal with at least two sectors with different individually tunable refraction powers. To obtain a monofocal rotation optics, obscuration of one of the lens sectors is necessary. Conventional lens systems providing tunable refraction power do so by mutual axial or lateral shift of the lenses or the lens parts. Hence, additional space for lens movement is needed in the mechanical design. Since the rotational optics allows for adjustment of the refraction power by a mutual rotation of the lens parts, no displacement of lenses is needed and a more compact design is obtained.
The paper presents an approach to a cost-efficient modularly built non-dispersive optical IR-gas sensor (NDIR) based on a construction kit. The modularity of the approach offers several advantages: First of all it allows for an adaptation of the performance of the gas sensor to individual specifications by choosing the suitable modular components. The sensitivity of the sensor e.g. can be altered by selecting a source which emits a favorable wavelength spectrum with respect to the absorption spectrum of the gas to be measured or by tuning the measuring distance (ray path inside the medium to be measured). Furthermore the developed approach is very well suited to be used in teaching. Together with students a construction kit on basis of an optical free space system was developed and partly implemented to be further used as a teaching and training aid for bachelor and master students at our institute. The components of the construction kit are interchangeable and freely fixable on a base plate. The components are classified into five groups: sources, reflectors, detectors, gas feed, and analysis cell.
Source, detector, and the positions of the components are fundamental to experiment and test different configurations and beam paths. The reflectors are implemented by an aluminum coated adhesive foil, mounted onto a support structure fabricated by additive manufacturing. This approach allows derivation of the reflecting surface geometry from the optical design tool and generating the 3D-printing files by applying related design rules. The rapid fabrication process and the adjustment of the modules on the base plate allow rapid, almost LEGO®-like, experimental assessment of design ideas.
Subject of this paper is modeling, design, and optimization of the reflective optical components, as well as of the optical subsystem. The realization of a sample set-up used as a teaching aid and the optical measurement of the beam path in comparison to the simulation results are shown as well.
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.
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.
Efficient and reliable optical design requires knowledge of the production chain, the materials used, and the environmental circumstances in the field of operation. This is realized in the comprehensive modelling approach consisting of three steps: • Design for manufacturing, i.e. the model must be adjusted to the process chain. Knowledge of design rules is required. • Robust design, i.e. optimization of the functional design with the objective of a compensation of the tolerance influences on the system’s performance. Knowledge of the tolerances of the individual process steps is required. • Reliable design with respect to environmental and operational effects, respectively. Coupling of an optical and mechanical simulation tool is required to form the optical simulation environment. The availability of process knowledge such as e.g. design rules and manufacturing tolerances is ensured by coupling of the optical simulation environment with a process knowledge database. Integration of measured surface data in this simulation environment enables a realistic simulation and analysis of real, manufactured optics. This approach allows e.g. for the evaluation of replication methods such as precision molding or injection molding against high-precision manufacturing methods, e.g. diamond turning.
Designing optical subsystems not only requires consideration of the optical properties of the optical components but also
examination of the properties of the mechanical subsystem structures such as e.g., alignment or mounting structures. This
is essential since most optical subsystems extend over three dimensions and are realized in modular setups, where the
optical components are mounted and adjusted by means of mechanical structures. Hence, the contour accuracy of these
structures is crucial for the adjusted alignment of the optical components and therefore for the system’s performance.
The contour accuracy depends on both the fabrication processes and the operational conditions of the optical subsystem.
This leads to our concept of comprehensive modeling and simulation where not only optical properties are to be
simulated but as well the influences of the mechanical system structures on the optical performance.
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.
In contrast to microelectronics which may be considered two-dimensional in first approximation, micro-optical systems
extend over three dimensions. Due to the lack of a uniform material system, complex micro-optical systems are
constructed using a modular concept. The modular setup of such hybrid systems results in an isolated manufacture of the
individual components and their later assembly in a single system.
Designing a micro-optical system, all relevant requirements and constraints defined by the manufacturing processes and
the application of the system in a real ambience must be considered. Furthermore, every individual manufacturing step
adds its own tolerances to the system. To maintain the overall function of a system under the given manufacturing
conditions, the system design has to be robust with respect to the expected tolerances. The system's robustness will result
from considering process knowledge in the state of modeling already. Process knowledge of non-silicate manufacturing
processes is collected and stored in a knowledge database. On basis of these data, process-dependent inaccuracies and
tolerances can be used to design robust functional components and functional units (subsystems).
This approach of robust, tolerance compensating design is applied to the design of an infrared gas sensor, a micro-optical
distance sensor, and a lens of variable refraction power.
In succession of a benchmark study for the modeling of micro-optical components in the Network of Excellence on Micro-Optics (NEMO) we define a novel systematic approach for the evaluation of modeling results and the combination of different modeling approaches and modeling expertise. The method is applied for an optical bridge system, comprising both refractive and diffractive optical components. We work with different intermediate planes at which the field distributions obtained with different simulation tools are rigorously compared. Therefore all participating partners have programmed the necessary tools that allow the exchange of obtained field distributions. First evaluation results are discussed in detail.
A novel design for a compact and robust micro optical distance sensor is presented. It is suitable for mass fabrication by micro molding known form the LIGA technique [1] and automatic assembly. Due to a modular design approach a distributed fabrication of the device modules is currently implemented. This allows a separate fabrication of the modules at several manufacturers each one being an expert for the special technology needed to fabricate the module. During the design phase not only the optical specification of the sensor system but also all requirements given by the manufacturers, such as easy manufacturability with high throughput as well as defined interfaces need to be considered.
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 becoming more and more important in microsystems technologies. The modular structure of hybrid systems requires single components to be manufactured in isolation and later combined into one total system. Combining single components into one overall system is bound to be subject to certain tolerances. The concept presented in this paper is the computer-aided design of a modular system rugged enough to be employed in mass fabrication. In mass fabrication, it is not the ideal arrangement of individual components which results in the most effective system. Instead, tolerances in position individual optical elements need to be taken into account already in modeling. Furthermore, environmental influences like e.g. variations of the temperature can have an impact on the performance of the optical function module.
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 becoming more and more important in microsystems technologies. In this paper, a system model of an IR gas sensor is presented. This model allows designs to be optimized, e.g. for use of the analysis chamber also to detect other gases with different absorption characteristics.
Manufacturing test structures of microsystems is a very expensive process, both in terms of time and money. For this reason, computer—supported design technologies ensuring continuous support in all design phases and, consequently, also consistency, are becoming increasingly important in microsystems technology. The modular structure of hybrid systems requires single components to be manufactured in isolation and later combined into one total system. Combining single components into one overall system is bound to be subject to certain tolerances. The concept presented in this paper is the computer—aided design of a modular system rugged enough to be employed in mass fabrication. In mass fabrication, it is not the ideal arrangement of individual components which results in the most effective system. Instead, tolerances in positioning individual optical elements need to be taken into account already in modeling. Furthermore environmental influences like e.g. variations of the temperature can have an impact on the performance of the micro—optical function module.
Manufacturing test structures of microsystems and microcomponents is very expensive in terms of time and materials. In conventional design processes, this limits the number of design variants to be considered. For this reason, computer-supported design techniques are becoming more and more important in microsystems technology. The article describes a micro-optical structure as an example demonstrating the factors which disturb the operation of a micro-optical module, and derives a theoretical description of the system under consideration which allows the system parameters to be optimized with respect to the disturbing influences by means of an evolutionary search method.
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