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Design tools for Freeform optics
Abstract
Freeform Optical surfaces are defined as any non-rotationally symmetric surface or a symmetric surface that is rotated about any axis that is not its axis of symmetry. These surfaces offer added degrees of freedom that can lead to lower wavefront error and smaller system size as compared to rotationally symmetric surfaces. Unfortunately, freeform optics are viewed by many designers as more difficult and expensive to manufacture than rotationally symmetric optical surfaces. For some freeform surfaces this is true, but a designer has little or no feedback to quantify the degree of difficulty for manufacturing a surface. This paper describes a joint effort by Optical Research Associates (ORA) and the Precision Engineering Center (PEC) at North Carolina State University to integrate metrics related to the cost and difficulty of manufacturing a surface into the merit function that is used during the design of an optical system using Code V®. By incorporating such information into the merit function, it is possible to balance optical performance and manufacturability early in the design process.
... Besl [72] equivalently states that "a free-form surface has a well defined surface normal that is continuous almost everywhere except at vertices, edges and cusps". Freeform shapes are 41 interesting because their surfaces are designed in a way to improve the functional specifications of an object and meet its aesthetic requirements [8], [73], [74]. ...
... Le principe de notre algorithme se résume par une minimisation au sens des moindres carrés des distances qui tiennent à la fois compte de la géométrie et de la topologie. Plus explicitement, nous cherchons à minimiser la différence entre la variation de la position des points subdivisés d'une itération à l'autre et la distance séparant les données du polygone subdivisé : (73) où les points sont les points subdivisés, les vecteurs unitaires de distance et les les distances à l'itération . Les scalaires correspondent aux amplitudes par lesquelles les points de contrôle à l'itération doivent se déplacer (dans la direction normale des points de contrôle) afin d'obtenir un polygone de contrôle à l'itération qui garantira que la courbe B-Spline se rapproche des données. ...
Complex surfaces exhibit real challenges in regard to their design specification, their manufacturing, their measurement and the evaluation of their manufacturing defects. They are classified according to their geometric/shape complexity as well as to their required tolerance. Thus, the manufacturing and measurement processes used are selected accordingly. In order to transcribe significant information from the measured data, a data processing scheme is essential. Here, processing involves surface reconstruction in the aim of reconstituting the underlying geometry and topology to the points and extracting the necessary metrological information (form and/or dimensional errors). For the category of aspherical surfaces, where a mathematical model is available, the processing of the data, which are not necessarily organized, is done by fitting/associating the aspherical model to the data. The sought precision in optics is typically nanometric. In this context, we propose the L-BFGS optimization algorithm, first time used in metrological applications and which allows solving unconstrained, non-linear optimization problems precisely, automatically and fast. The L-BFGS method remains efficient and performs well even in the presence of very large amounts of data.In the category of general freeform surfaces and particularly turbine blades, the manufacturing, measurement and data processing are all at a different scale and require sub-micrometric precision. Freeform surfaces are generally not defined by a mathematical formula but are rather represented using parametric models such as B-Splines and NURBS. We expose a detailed state-of-the-art review of existing reconstruction algorithms in this field and then propose a new active contour deformation of B-Splines approach. The algorithm is independent of problems related to initialization and initial parameterization. Consequently, it is a new algorithm with promising results. We then establish a thorough study and a series of tests to show the advantages and limitations of our approach on examples of closed curves in the plane. We conclude the study with perspectives regarding improvements of the method and its extension to surfaces in 3D.
... In recent years, freeform optical lenses [1][2][3] and microstructured [4][5][6][7][8][9] and nanostructured [10][11][12][13][14][15] surfaces have attracted increasing attentions, due to their excellent optical qualities and promise in wide range of applications. Fast tool servo (FTS) assisted single point diamond turning has been extensively regarded as a very promising technology to fabricate these surfaces. ...
... The motion crosstalk means one direction movement of the two-DOF FTS will generate a disturbance to the other direction resulting in a shift in the position. Under open-loop control condition, giving the two actuators a sinusoidal command signal, respectively, the response is all recorded as shown in Figure 7. Motor [1] Act pos is the z-direction displacement, and motor [2] is the x-direction displacement. Theoretically, the crosstalk of the two-DOF FTS can be neglected because of the decoupling structure and high stiffness of the cross shape flexure hinge. ...
Fast tool servo (FTS) technology is considered as the most popular technology to fabricate freeform optical lenses and micro- and nano-structured surfaces. Aiming at the disadvantages of existing single DOF FTS systems, this paper described a two-DOF FTS. Cross shape flexure hinges are designed as the guide mechanism, and two voice coil motors (VCMs) are selected to drive the tool motion. The FTS offline performance is tested, and the following error is about less than 0.1 mu m; the motion resolution is 0.05 mu m. A sinusoidal surface is machined to verify the cutting performance of the novel FTS, and the surface roughness is Ra 27 nm. The test results show that the two-DOF FTS system works well on the fabrication of optical freeform surfaces.
... Recently, we are witnessing significant advances in the fabrication and optical testing of both diffractive optics and emerging freeform optics [34,35]. The free-form optical shapes or optical surfaces are designed with little to no symmetry: they are free from any constraints of symmetry in their form and shape. ...
The off-axis three-mirror optical system is derived from the classical Cooke triplet or a derivative of the inverse-telephoto lens. By properly arranging an internal reimaging mechanism or altering the location of the optical stop, one can create different versions of three-mirror optical systems. They include very compact configurations and wide field-of-view imagers. Insights into the optical design process, manufacturing, stray light management, and remote sensing applications are presented.
... Freeform optics, which refers to refractive or reflective optical elements with freeform surfaces, is considered a revolution in modern optics [1] . Freeform surfaces are those surfaces that do not have rotational or translational symmetries [2] . Compared with traditional optical surfaces, including spherical, aspherical, and cylindrical surfaces, freeform surfaces offer much greater design freedom, allowing optical systems to achieve previously unimaginable imaging [3][4][5] , illumination [6,7] , and laser beam shaping performances [8] . ...
... Freeform surface manufacturing requires at least three axes of motion [14,[18][19][20][21]. The Alvarez arrays in our system were fabricated with a multi-axis ultraprecision diamond milling center with a 50,000 RPM milling spindle. ...
Dynamic illumination using tunable freeform arrays can enable spatial light distributions of variable size with high uniformity from non-uniform sources through relatively small opposing lateral shifts applied to the freeform components. We present the design, manufacturing, and characterization of a tunable LED-based illuminator using custom freeform Alvarez arrays with commercially available optics to shorten the manufacturing cycle. The optomechanical design and manufacturing of the Alvarez lens arrays and mounting parts are presented in detail. The optical performance of the system is evaluated and compared with simulation results using a custom camera-based test station. Experimental results demonstrate and confirm the dynamic illumination concept with good uniformity.
... Thus, the unfeasible design geometries along with the machining technologies constraint should be accounted at the early stages by the designers and the manufacturers. Garrard et al [238] structured the interface between the optimization engine and manufacturing cost metric computation which added functionalities to Code V. Program using Code V macro-Plus language was made for the prediction of the magnitude of non-rotational surface component of the sag as manufacturing cost. An integrated design and optimization environment that brought together the existing optical performance predictions with automated feedback of manufacturing costs for FTS machined freeform surfaces. ...
Freeform optics has become the most prominent element of the optics industry. Advanced freeform optical designs supplementary to ultra-precision manufacturing and metrology techniques have upgraded the lifestyle, thinking, and observing power of existing humans. Imaginations related to space explorations, portability, accessibility have also witnessed sensible in today's time with freeform optics. Present-day design methods and fabrications techniques applicable in the development of freeform optics and the market requirements are focussed and explained with the help of traditional and non-traditional optical applications. Over the years, significant research is performed in the emerging field of freeform optics, but no standards are established yet in terms of tolerances and definitions. We critically review the optical design methods for freeform optics considering the image forming and non-image forming applications. Numerous subtractive manufacturing technologies including figure correction methods and metrology have been developed to fabricate extreme modern freeform optics to satisfy the demands of various applications such as space, astronomy, earth science, defence, biomedical, material processing, surveillance, and many more. We described a variety of advanced technologies in manufacturing and metrology for novel freeform optics. Next, we also covered the manufacturing-oriented design scheme for advanced optics. We conclude this review with an outlook on the future of freeform optics design, manufacturing and metrology.
... In addition, one aspherical or free-form optic might be able to replace several spherical optics at once. Therefore, optical components with smaller imaging errors, smaller dimensions and lower weight can be developed and manufactured (Garrard et al. [2]). Despite these advantages, their use is still often limited to high-priced components and special applications. ...
Quartz glass is frequently used for optical components, but traditional machining methods, particularly for aspherical optics, are often associated with long process times and high costs. One possible approach to achieve higher efficiencies and higher speeds in contactless processing is laser ablation using CO2 laser radiation. This study investigates the evolution of surface topography during laser ablation of quartz glass using nanosecond pulses from a Q-switched CO2 laser beam source. The special focus of a broad empirical study lay on ablation depth, ablation rate, ablation efficiency and resulting surface roughness for an ablation process using 300 ns laser pulses at a maximum laser power of 115 W and pulse frequencies up to 150 kHz. Ablation efficiency shows a characteristic logarithmic dependency on laser fluence. It was revealed that local heat accumulation significantly affects the optical penetration depth, which reduces the threshold fluence for multi-pulse laser ablation down to approx. 0.37 J/cm². Ablation rates of up to 1.48 mm³ min⁻¹ W⁻¹ were achieved, which exceeds results achieved for laser ablation using cw laser radiation or ultra-short pulses. An ablation rate of up to 170 mm³/min is a particularly noteworthy result. Therein, a maximum ablation efficiency of approx. 64% shows that the largest part of the incident laser energy was used for material ablation. Finally, based on a simplified model, numerical calculations and experimental results, pulse stability was identified to have a decisive impact on the evolution of the resulting surface roughness. The resulting surface roughness Sa is typically increased in pulsed laser processing and depends linearly on standard deviation of ablation depth and the square root of the number of ablation layers.
... Freeform optics are optical elements without an axis of rotational invariance, with arbitrary shape and possible additional surface structure (71,72). They allow increasing the performance of an optical system, e.g., in biomedical engineering or green energy, building systems with fewer surfaces and thus smaller dimensions and mass with the reduced necessity of assembly (73,74). ...
3D printing belongs to the emerging technologies of our time. Describing diverse specific techniques, 3D printing enables rapid production of individual objects and creating shapes that would not be produced with other techniques. One of the drawbacks of typical 3D printing processes, however, is the layered structure of the created parts. This is especially problematic in the production of optical elements, which in most cases necessitate highly even surfaces. To meet this challenge, advanced 3D printing techniques as well as other sophisticated solutions can be applied. Here, we give an overview of 3D printed optical elements, such as lenses, mirrors, and waveguides, with a focus on freeform optics and other elements for which 3D printing is especially well suited.
... In addition, one aspherical or free-form optic might be able to replace several spherical optics at once. Therefore, optical components with smaller imaging errors, smaller dimensions and lower weight can be developed and manufactured (Garrard et al. [2]). Despite these advantages, their use is still often limited to high-priced components and special applications. ...
Quartz glass is frequently used for optical components, but traditional machining methods, particularly for aspherical optics, are often connected to long process times and high costs. This study investigates laser ablation of quartz glass using nanosecond pulses from a Q-switched CO2 laser beam source. Based on a broad empirical basis, crucial process mechanisms were identified. An in-depth discussion concerning acting physical principles and relevant effects for laser based material ablation is provided. It was revealed that local heat accumulation significantly affects optical penetration depth of quartz glass in the interaction zone of laser beam and material. This has a significant effect on ablation rate and threshold fluence required for laser ablation. Pulse energy, pulse frequency, laser beam diameter and pulse distance are dominant process parameters, while track offset, and the number of ablation layers just play subordinate roles. An ablation rate of up to 170 mm3/min at average laser power of 115 W, pulse frequency of 150 kHz and scan speed of vscan = 750 mm/s are particularly noteworthy results. Furthermore, with an ablation efficiency of approx. 65 % the largest part of the incident laser energy was used for the ablation process. Finally, based on a simplified model, numerical calculations and experimental results, pulse (in-)stability was identified to have a decisive impact on the evolution of the resulting surface topography and surface roughness.
... In addition, one aspherical or free-form optic might be able to replace several spherical optics at once. Therefore, optical components with smaller imaging errors, smaller dimensions and lower weight can be developed and manufactured (Garrard et al. [2]). However, the production of glass optics with a non-spherical surface shape is complex and associated with high costs, particularly for small to medium lot sizes of less than 10,000 pieces (Chen et al. [3]). ...
A laser-based process chain is a possible solution to increase precision and reduce production time in optics manufacturing of components with complexly shaped surface. A new high precision laser ablation process was investigated using CO2 laser radiation and microsecond laser pulses. An average ablation depth of approx. 0.1 nm per laser pulse indicates that material ablation on an atomic/molecular scale was achieved. Four characteristic laser processing regimes and their related dominant physical process mechanisms were identified. The effect of crucial process parameters such as pulse energy, pulse duration and fluence on ablation depth and spatial resolution was empirically investigated. Ablation depths smaller than 10 nm per layer and a spatial resolution of less than 100 μm were achieved in areal laser ablation. The potential use of this high precision laser ablation process was studied for an iterative process cycle (laser beam figuring - LBF) consisting of contactless surface measurement and subsequent laser ablation. The feasibility of LBF for form correction of fused silica components was successfully demonstrated, while a reduction in average surface roughness from Sa = 10.3 nm to 3.5 nm was achieved. High stability in pulse energy is the key requirement for high precision in ablation depth.
This is an open access preprint article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/)
... As a new type of optical surface, an optical aspheric surface has obvious advantages, including correcting aberration, reducing the size and weight of the system, expanding the field of view, compared with a traditional regular surface, and has become a core component of modern optical systems [1][2][3]. In order to meet the actual optical performance of the components, it is necessary to rely on high-precision machining. ...
Optical aspheric components are inevitably affected by various disturbances during their precision machining, which reduces the actual machining accuracy and affects the optical performance of components. In this paper, based on the theory of multi-body system, we established a machining error model for optical aspheric surface machined by fast tool servo turning and analyzed the effect of the geometric errors on the machining accuracy of optical aspheric surface. We used the method of ray tracing to analyze the effect of the surface form distortion caused by the machining error on the optical performance, and identified the main machining errors according to the optical performance. Finally, the aspheric surface was successfully applied to the design of optical lens components for an aerial camera. Our research has a certain guiding significance for the identification and compensation of machining errors of optical components.
... An optical freeform surface is defined as any nonrotationally symmetric surface or a symmetrical surface that rotates around an asymmetrical axis [1]. Such surfaces can be designed in any shape, and in most cases, these surfaces have submicron profile accuracy and nanoscale surface quality [2]. ...
Optical freeform surface components have attracted much attention due to their high degree of design freedom and small size. However, the design and processing difficulty of such components limit its wide application in optics industry. In recent years, diamond turning has been considered an efficient method for processing optical freeform surfaces, but the research on tool path generation of this processing method is not systematic. Progressive addition lens (PAL) is a typical optical freeform surface and is widely used to correct people’s vision problems. Firstly, this paper introduces a method of designing PAL. Then, an optimized tool path generation method for diamond turning of the optical freeform surface is proposed, the equal angle method is used to select the discrete points, and a tool nose radius compensation method suitable for both slow slide servo (SSS) and fast tool servo (FTS) is adopted. Finally, the turning experiment is carried out with a single point diamond lathe, and a PAL surface with a roughness of 0.087 μm was obtained. The power and astigmatism distributions were measured using a Rotlex freeform verifier to verify the rationality of the optical design.
... Several optical elements can be fabricated and integrated together without an additional assembling process. Moreover, various freeform optical components can be realized, [56][57][58][59][60] because freeform optics often requires complex geometries that cannot be achieved with conventional symmetric shapes, 3D printing of freeform integrated optical components is attracting increasing attention in a variety of optical fields [61,62]. For example, it could be important for lightweight, head-mounted displays for virtual reality and augmented reality [63,64]. ...
Three-dimensional (3D) printing is a new paradigm in customized manufacturing and allows the fabrication of complex optical components and metaphotonic structures that are difficult to realize via traditional methods. Conventional lithography techniques are usually limited to planar patterning, but 3D printing can allow the fabrication and integration of complex shapes or multiple parts along the out-of-plane direction. Additionally, 3D printing can allow printing on curved surfaces. Four-dimensional (4D) printing adds active, responsive functions to 3D-printed structures and provides new avenues for active, reconfigurable optical and microwave structures. This review introduces recent developments in 3D and 4D printing, with emphasis on topics that are interesting for the nanophotonics and metaphotonics communities. In this article, we have first discussed functional materials for 3D and 4D printing. Then, we have presented the various designs and applications of 3D and 4D printing in the optical, terahertz, and microwave domains. 3D printing can be ideal for customized, nonconventional optical components and complex metaphotonic structures. Furthermore, with various printable smart materials, 4D printing might provide a unique platform for active and reconfigurable structures. Therefore, 3D and 4D printing can introduce unprecedented opportunities in optics and metaphotonics and may have applications in freeform optics, integrated optical and optoelectronic devices, displays, optical sensors, antennas, active and tunable photonic devices, and biomedicine. Abundant new opportunities exist for exploration.
... A relevant context for this discussion is the study of the surface shape of as-built optical surfaces with complex nominal shapes including aspheric and freeform optics [5][6][7]. The tool marks left by the associated fabrication steps are generally referred to as mid-spatial frequency structure (MSF). ...
In many applications it is natural to seek to extract a characteristic scale for a function’s variations by reference to a frequency spectrum. Although the moments of a spectrum appear to promise simple options to make such a connection, standard Fourier methods fail to yield finite moments when the function’s domain is itself finite. We investigate a family of Fourier-like bases with rapidly decaying spectra that yield well-defined moments for such cases. These bases are derived by considering classes of functions for which a normalised mean square derivative is stationary. They are shown to provide precisely the type of spectrum needed to complete a recent investigation of mid-spatial frequency structure on optical surfaces [K. Liang, Opt. Express 27, 3390-3408 (2019)].
... Practically, these surfaces have large degrees of asymmetry. To broaden the processing capacity of FTS, the surface should be decomposed into a rotational symmetry part and a nonrotational symmetry part [53,54]. The rotational symmetry part generally has a millimeter-level peak-to-valley (PV) value, and the non-rotationally symmetric part of the geometric feature scale is typically on the order of several hundred microns. ...
Fast tool servo (FTS) in ultra-precision machining (UPM) is an enabling and efficient technology for fabricating optical freeform surfaces or microstructures with submicrometric form accuracy and nanometric surface finish. There are many kinds of FTS in the different driving principle to present their various performances currently. Their kernel technologies influence the machining ability and accuracy of freeform surfaces, consequently receiving much research attention and interest. These technologies are generally summarized as the development of FTS structure, the advanced control algorithms, tool path planning, machining condition monitoring, and surface measurement and error compensation. This paper aims to survey the current state of the art in machining freeform optics by FTS. An analysis of the principle, performance, and application of FTS machining with regard to freeform optics is presented. And the key machining technologies for optical freeform surfaces by FTS are then introduced in detail. The challenges and opportunities for further studies are concluded according to the FTS machining difficult of optical freeform surfaces finally.
... Owing to their abundant degrees of freedom and strong ability of aberration correction, optical aspheric and freeform surfaces are strong candidates. From the geo- metrical viewpoint, 1 an optical freeform surface has nonrota- tionally symmetric features. From the aspect of fabrication and design, 2 an optical freeform surface is regarded as an optical surface that leverages a third independent axis during the fabrication process to form the optical surface with as- designed nonsymmetric features. ...
Modern advanced manufacturing and testing technologies allow the application of freeform optical elements. Compared with traditional spherical surfaces, an optical freeform surface has more degrees of freedom in optical design and provides substantially improved imaging performance. In freeform optics, the representation technique of a freeform surface has been a fundamental and key research topic in recent years. Moreover, it has a close relationship with other aspects of the design, manufacturing, testing, and application of optical freeform surfaces. Improvements in freeform surface representation techniques will make a significant contribution to the further development of freeform optics. We present a detailed review of the different types of optical freeform surface representation techniques and their applications and discuss their properties and differences. Additionally, we analyze the future trends of optical freeform surface representation techniques. © 2017 Society of Photo-Optical Instrumentation Engineers (SPIE).
... As a result of their unique physical, mechanical, chemical and thermal properties, many hard and brittle materials, including engineering ceramics, optical glass, single-crystal silicon, highstrength alloy steel, titanium alloys, and sapphire, have been widely used in manufacturing industries. 1 However, hard and brittle materials are difficult to cut, causing serious tool wear to appear during the cutting process, leading to deterioration of the cut surface quality, reduced processing accuracy, and even the collapse of the cutting blade. 2,3 Elliptical vibration cutting (EVC) is one of the most promising ways to cut a variety of different materials 4 because of the method's unique intermittent cutting and friction reversal characteristics. High-precision elliptical motion was difficult to achieve using the existing EVC devices, which thus limited their widespread application to precision and ultra-precision component processing. ...
Because of its unique intermittent cutting and friction reversal characteristics, elliptical vibration cutting (EVC) has become the most promising method for machining of otherwise difficult-to-machine materials in recent years. However, some problems remain in the research towards development of EVC devices. In this paper, with the intention of solving the existing problems of EVC devices, a nonresonant-type EVC device that is driven by two parallel piezoelectric stacks is developed. After the principle of the device is introduced, the stiffness of the EVC device is calculated, and device simulations and experimental evaluations are performed. In addition, the performance of the EVC device is also tested. The experimental results show that the maximum strokes of the two directional mechanisms operating along the X- and Z-axes can reach 16.78 μm and 15.35 μm, respectively, and the motion resolutions in the X-axis and Z-axis directions both reach approximately 50 nm. Finally, a curved surface cutting experiment is carried out to verify the performance of the developed device.
... Application of FTS was introduced to the compensation of motion errors of machine tools [26], it is also well-known that this technique was applied for freeform surface generation in recent decades [27]. It can be inferred from above that FTS machining has been recently focused on machining micro-structured surfaces but rarely on smooth surface, while most smooth surfaces are machined by diamond milling. ...
Optical freeform surfaces are of great advantage in excellent optical performance and integrated alignment features. It has wide applications in illumination, imaging and non-imaging, etc. Machining freeform surfaces on infrared (IR) materials with ultra-precision finish is difficult due to its brittle nature. Fast tool servo (FTS) assisted diamond turning is a powerful technique for the realization of freeform optics on brittle materials due to its features of high spindle speed and high cutting speed. However it has difficulties with large slope angles and large rise-and-falls in the sagittal direction. In order to overcome this defect, the balance of the machining quality on the freeform surface and the brittle nature in IR materials should be realized. This paper presents the design of a near-rotational freeform surface (NRFS) with a low non-rotational degree (NRD) to constraint the variation of traditional freeform optics to solve this issue. In NRFS, the separation of the surface results in a rotational part and a residual part denoted as a non-rotational surface (NRS). Machining NRFS on germanium is operated by FTS diamond turning. Characteristics of the surface indicate that the optical finish of the freeform surface has been achieved. The modulation transfer function (MTF) of the freeform optics shows a good agreement to the design expectation. Images of the final optical system confirm that the fabricating strategy is of high efficiency and high quality. Challenges and prospects are discussed to provide guidance of future work.
... In recent years, the optical freeform surfaces are becoming more and more popular in industrial application. Compared with conventional rotational symmetric optical surface, the optical free-form surface has some excellent performances [1]. Ultra-precision diamond turning using a fast tool servo is the most popular technique which can produce optical freeform surfaces [2][3][4]. ...
Optical free-form surfaces are becoming more and more popular in the industry application, which can be fabricated by diamond turning based on fast tool servo (FTS). It is an efficient, precise and low-cost processing method. In order to use diamond turning to fabricate the freeform optics, this paper develops a novel long range fast tool servo which is actuated by voice coil motor. The total range can reach up to 30 mm. The important parts of the FTS have been simulated and analyzed. The transfer function model identification of the FTS has been accomplished. Since the desired tool trajectories are approximately periodic signals in freeform surfaces turning, and the adaptive feedforward cancellation (AFC) control can achieve perfect tracking and disturbance rejection of periodic signals, the AFC control is designed to be added on the IMC-PID controller.
... Free-form surface is a kind of surface type without axis of rotational invariance and it has been applied in several fields, such as optical devices, turbine blade and injection molding. This kind of surface can be designed into arbitrary shapes, and regular or irregular surface structures [1,2,3]. Free-form surface applied in optical system has its prominent merits, such as simplifying the structure, improving the performance, much more integrations and excellent flexibility [2]. ...
The free-form surface closed to a sphere of brittle material has been used widely, but it is difficult for machining and the efficiency of processing is insufficient. In order to get a product, several processes are needed, such as rough machining, semi-finishing and finishing. Axisymmetric curved surface can take place of the free-form surface in roughing or semi-finishing for wiping off the mass allowance efficiently. Therefore, a spherical approximation algorithm of free-form surface closed to sphere is presented in which free-form surface optical lens will be replaced by a spherical surface in semi-finishing and get the approximate sphere of the free-form surface. It can be certified in the test that this method is simple and reliable. The efficiency and precision in machining is excellent and the distribution of allowance for finishing is uniform in the whole surface, which has great practical significance in machining of optical free-form surface of brittle materials.
... However, this method is not applicable to our off-axis mirror case because the mirror is no longer a part of the axially symmetric parent mirror. From a machining point of view, its sophisticated surface should be created from a raw freeform mirror surface [17][18][19]. Thanks to the advances of single point diamond turning (SPDT) technology, freeform mirrors can be directly manufactured by an ultraprecision diamond turning machining process [20][21][22][23][24]. ...
Freeform mirrors can be readily fabricated by a single point diamond turning (SPDT) machine. However, this machining process often leaves mid-frequency errors (MFEs) that generate undesirable diffraction effects and stray light. In this work, we propose a novel thin electroless nickel plating procedure to remove MFE on freeform surfaces. The proposed procedure has a distinct advantage over a typical thick plating method in that the machining process can be endlessly repeated until the designed mirror surface is obtained. This is of great importance because the sophisticated surface of a freeform mirror cannot be optimized by a typical SPDT machining process, which can be repeated only several times before the limited thickness of the nickel plating is consumed. We will also describe the baking process of a plated mirror to improve the hardness of the mirror surface, which is crucial for minimizing the degradation of that mirror surface that occurs during the polishing process. During the whole proposed process, the changes in surface figures and textures are monitored and cross checked by two different types of measurements, as well as by an interference pattern test. The experimental results indicate that the proposed thin electroless nickel plating procedure is very simple but powerful for removing MFEs on freeform mirror surfaces.
... Freeform surfaces, including smooth surfaces (e.g., F-theta surfaces) and microstructured functional surfaces (e.g., microlens arrays), are gaining ever-increasing applications in both imagining and nonimaging optical systems due to their prominent performances [1][2][3]. To satisfy practical industrial requirements, fast tool servo (FTS) or slow tool servo (STS) diamond turning has been introduced and is widely regarded as a very promising technique due to its capacity of efficiently generating optics with submicron form accuracy and nanometric roughness on a wide spectrum of engineering materials [3]. ...
The inherent residual tool marks (RTM) with particular patterns highly affect optical functions of the generated freeform optics in fast tool servo or slow tool servo (FTS/STS) diamond turning. In the present study, a novel biaxial servo assisted fly cutting (BSFC) method is developed for flexible control of the RTM to be a functional micro/nanotexture in freeform optics generation, which is generally hard to achieve in FTS/STS diamond turning. In the BSFC system, biaxial servo motions along the z -axis and side-feeding directions are mainly adopted for primary surface generation and RTM control, respectively. Active control of the RTM from the two aspects, namely, undesired effect elimination or effective functionalization, are experimentally demonstrated by fabricating a typical F-theta freeform surface with scattering homogenization and two functional microstructures with imposition of secondary phase gratings integrating both reflective and diffractive functions.
... In general, freeform aspheric surfaces can be defined as surfaces with no axis of rotational invariance (within or beyond the part). In this way, freeform surfaces may have an arbitrary shape, and regular or irregular surface structures [9,10]. In this investigation the starting design of the catadioptric collimator is rotationally symmetric; this makes the analysis and the explanation of the algorithm clearer, because, initially, we only have to determine two planar generating curves (one for the refracting surface and one for the TIR surface). ...
The aim of this paper is to develop a straightforward rigorous and flexible computational method to determine the coordinate points on an aspheric surface. The computational method chosen is based on the basic slope-point form of a straight-line equation [slope-point method (SPM)]. The practical instrumental example chosen to illustrate this method is a rotationally symmetric catadioptric collimator for a light-emitting diode (LED) source. This optical system has both a refractive and a totally internally reflective aspheric surface. It is a particularly illuminating example because it requires careful computational attention to the smooth transition between the refracting inner zones and the reflective outer zones of the aperture. The chosen SPM computational method deals satisfactorily with the transition points at the junction between the refractive and total internal reflecting (TIR) zones of the collimator. As part of this study, the effect of the position of the start point of the SPM surface evolution for the TIR zones of the collimator emerges as being particularly important, and the details of this are discussed. Finally, an extension of the basic SPM-based method is used to generalize the development of the catadioptric collimator surfaces to illustrate this general algorithm for aspheric surface design for an extended LED light source.
Freeform surfaces are known for their versatility in providing complex optical functionalities. The surface texture aspect ratio, representing the relationship between surface height variation and lateral feature size, is examined in relation to vari-focal lenses. Nanometric surface measurement techniques and 3D surface parameters are utilized to quantify the aspect ratio and evaluate its impact on optical performance. Experimental results demonstrate a significant correlation between higher aspect ratios and increased aberrations, leading to decreased optical quality. Controlling the surface texture aspect ratio during manufacturing is crucial for achieving optimal functional performance. This study contributes to the understanding of how the aspect ratio affects the performance of freeform surfaced optic components, providing insights for the design and fabrication of high-performance optical components. Future research can explore optimization strategies and advanced manufacturing techniques to enhance functional performance in optics and optical system design.
Most modern commodity imaging systems we use directly for photography—or indirectly rely on for downstream applications—employ optical systems of multiple lenses that must balance deviations from perfect optics, manufacturing constraints, tolerances, cost, and footprint. Although optical designs often have complex interactions with downstream image processing or analysis tasks, today’s compound optics are designed in isolation from these interactions. Existing optical design tools aim to minimize optical aberrations, such as deviations from Gauss’ linear model of optics, instead of application-specific losses, precluding joint optimization with hardware image signal processing (ISP) and highly parameterized neural network processing. In this article, we propose an optimization method for compound optics that lifts these limitations. We optimize entire lens systems jointly with hardware and software image processing pipelines, downstream neural network processing, and application-specific end-to-end losses. To this end, we propose a learned, differentiable forward model for compound optics and an alternating proximal optimization method that handles function compositions with highly varying parameter dimensions for optics, hardware ISP, and neural nets. Our method integrates seamlessly atop existing optical design tools, such as Zemax . We can thus assess our method across many camera system designs and end-to-end applications. We validate our approach in an automotive camera optics setting—together with hardware ISP post processing and detection—outperforming classical optics designs for automotive object detection and traffic light state detection. For human viewing tasks, we optimize optics and processing pipelines for dynamic outdoor scenarios and dynamic low-light imaging. We outperform existing compartmentalized design or fine-tuning methods qualitatively and quantitatively, across all domain-specific applications tested.
Holographic optical elements (HOEs) have a wide range of applications, including their emerging use in virtual and augmented reality displays, but their design and fabrication have remained largely limited to configurations using simple wavefronts. In this paper, we present a pipeline for the design, optimization, and fabrication of complex, customized HOEs that enhances their imaging performance and enables new applications. In particular, we propose an optimization method for grating vector fields that accounts for the unique selectivity properties of HOEs. We further show how our pipeline can be applied to two distinct HOE fabrication methods. The first uses a pair of freeform refractive elements to manufacture HOEs with high optical quality and precision. The second uses a holographic printer with two wavefront-modulating arms, enabling rapid prototyping. We propose a unified wavefront decomposition framework suitable for both fabrication approaches. To demonstrate the versatility of these methods, we fabricate and characterize a series of specialized HOEs, including an aspheric lens, a head-up display lens, a lens array, and, for the first time, a full-color caustic projection element.
We demonstrate an additive manufacturing approach to produce gradient refractive index glass optics. Using direct ink writing with an active inline micromixer, we three-dimensionally print multimaterial green bodies with compositional gradients, consisting primarily of silica nanoparticles and varying concentrations of titania as the index-modifying dopant. The green bodies are then consolidated into glass and polished, resulting in optics with tailored spatial profiles of the refractive index. We show that this approach can be used to achieve a variety of conventional and unconventional optical functions in a flat glass component with no surface curvature.
During the machining of freeform surfaces, the tool path will directly affect the machining accuracy of the surface, the execution of each axis of the machine tool, and the machining efficiency. Therefore, tool path planning is a very critical link in all types of diamond turning processes. In this paper, a new tool path generation strategy is proposed for machining freeform surfaces by quasi-intermittent vibration assisted swing cutting (QVASC) method. Due to the unique tool swing motion law of QVASC, the effective central angle of tool nose arc participating in the cutting is a parameter that is ignored by traditional cutting and is considered. This makes the generation of tool trajectories, tool geometry selection and freeform surfaces very different from traditional diamond cutting. According to the principle of QVASC, the tool parameters are analysed, and the tool position is designed in the cylindrical coordinate system. Interpolation was then performed by the Hermite spline interpolation theorem. The application of this strategy is discussed, and the sinusoidal surface, sinusoidal mesh surface and toric surface are taken as examples to simulate. The simulation succeeded in obtaining the tool path corresponding to the three curved surfaces processed by the QVASC method. The results prove that the tool trajectory generation strategy proposed in this paper is feasible. The proposed tool path generation strategy can provide a new reference for future freeform surfaces processing.
Freeform optical surfaces are advantageous to optical designers, as they provide additional degrees of freedom for optimization. The loss of rotational symmetry, however, makes measurement of freeforms more challenging. Herein, advances in interferometric areal measurement of freeform optical surfaces, including null tests, non‐null tests, near‐null tests, and adaptive null tests, are reviewed. Some new developments, in the Hartmann test, deflectometry, and phase retrieval, as representatives of non‐interferometric areal measurement, are then presented. Overall, the focus is on single‐point‐probe‐based profilometry categorized into coordinate measurements and slope‐ or curvature‐based measurements. Innovative measurement technology is trying to bridge the gap between high accuracy and high dynamic range as freeform optical surfaces are finding more applications in visible and shorter‐wavelength optics.
Nearly every commodity imaging system we directly interact with, or indirectly rely on, leverages power efficient, application-adjustable black-box hardware image signal processing (ISPs) units, running either in dedicated hardware blocks, or as proprietary software modules on programmable hardware. The configuration parameters of these black-box ISPs often have complex interactions with the output image, and must be adjusted prior to deployment according to application-specific quality and performance metrics. Today, this search is commonly performed manually by "golden eye" experts or algorithm developers leveraging domain expertise. We present a fully automatic system to optimize the parameters of black-box hardware and software image processing pipelines according to any arbitrary (i.e., application-specific) metric. We leverage a differentiable mapping between the configuration space and evaluation metrics, parameterized by a convolutional neural network that we train in an end-to-end fashion with imaging hardware in-the-loop. Unlike prior art, our differentiable proxies allow for high-dimension parameter search with stochastic first-order optimizers, without explicitly modeling any lower-level image processing transformations. As such, we can efficiently optimize black-box image processing pipelines for a variety of imaging applications, reducing application-specific configuration times from months to hours. Our optimization method is fully automatic, even with black-box hardware in the loop. We validate our method on experimental data for real-time display applications, object detection, and extreme low-light imaging. The proposed approach outperforms manual search qualitatively and quantitatively for all domain-specific applications tested. When applied to traditional denoisers, we demonstrate that---just by changing hyperparameters---traditional algorithms can outperform recent deep learning methods by a substantial margin on recent benchmarks.
We proposed a method for the design of a freeform lens for light emitting diode (LED) light source based on intensity distribution curve. The energy mapping rules are considered in this design. The freeform lens achieves the optical requirements of the element and the geometrical requirements of the surface continuity. The method simplifies the design process of the freedom surface to avoid the repetitive optimization design and increase the design efficiency. In this paper, the modeling and optical simulation of freeform lenses for LED light source with 45°and 30°intensity distribution curves are performed. The simulation results prove the accuracy of the proposed method.
In this section, we list examples of head-worn display architectures organized by the field-of-view (FOV) parameter. Low-FOV designs (<40°), suitable for integration into an eyeglass form factor, are reviewed along with mid-FOV (between 40° and 60°) and wide-FOV (>60°) designs. Eyeglass-based displays are particularly interesting because they are well suited for mobile applications, and such displays are more likely to enjoy higher social acceptance due to esthetics.
In this section, we list examples of head-worn display architectures organized by the field-of-view (FOV) parameter. Low-FOV designs (<40°), suitable for integration into an eyeglass form factor, are reviewed along with mid-FOV (between 40° and 60°) and wide-FOV (>60°) designs. Eyeglass-based displays are particularly interesting because they are well suited for mobile applications, and such displays are more likely to enjoy higher social acceptance due to esthetics.
This paper proposes an efficient and uniform illumination system with a freeform mirror for a color-sequential LCOS pico projector based on LED. The novel homogenizer is composed of a micro lens array and a freeform mirror. A freeform mirror with XY polynomial profile is adopted for the reshaping of light pattern, the correction of keystone distortion and the folding mirror for the reduction of volume. Typically, the design of micro lens array, the aspect ratio of the lenslet is corresponding with that of the panel. However, the crosstalk phenomenon occurs due to each lenslet with different collecting angle in horizontal and vertical direction, especially when the aspect ratio of the panel in our study is 16:9. The crosstalk phenomenon not only reduces efficiency but also generates stray light on the panel. Therefore, we use a micro lens array with square lenslet to eliminate it. Subsequently, the square light pattern on the panel needs to be reshaped to fit the aspect ratio of the panel. A cylindrical mirror with a fixed power is used to compress the light pattern first. However, for the requirement of different focal distances from the cylindrical mirror to the panel on entire surface, it generates severe keystone distortion. A freeform mirror with progressive power variation is employed for the correction of keystone distortion with high overfilled efficiency and the reshaping of the light pattern fitting the ratio of the panel. In the results of optical simulation, JBMA uniformity on the panel is 98 % and the coupling efficiency from LED to the plane of the panel is 85 %. Furthermore, the alignment tolerance of the freeform mirror has also been discussed. Finally, the freeform mirror is fabricated by ultra-precision diamond milling process. The form accuracy and surface roughness of the freeform mirror are less than 0.5 um and 5 nm, respectively.
In the last years the requirement of special illumination optics increased in the course of developing specific optical systems for wide range of applications in industries and science. Standard components become continuously substituted by more complex freeform surfaces with higher effciency. Therefore, other methods in evaluating optical systems are of special interest. In illumination design the classic way to check the performance of a system is to trace a huge number of rays through the system and analyze the radiance and irradiance distribution on the target surface. Another access to the most important illumination quantities like radiance is to look at the transformation of etendue in phase space. This offers a new perspective for the optical designer onto illumination systems. Another interesting aspect is the analysis of aberrations also for freeform elements where standard aberration theory for rotational symmetric systems fail.
Diamond tuning lathes augmented with fast tool servo technology are an efficient and accurate means of producing precision optical and mechanical surfaces. In this paper, a comprehensive approach to the fabrication of freeform surfaces with diamond tools is presented. A variety of fast tool servos have been developed at the Precision Engineering Center (PEC) over the past 25 years. The latest system, FLORA II [1], has a 6 mm range and has demonstrated 2 nm RMS surface finish and 31 nm RMS figure error machining a 50 mm diameter titled flat with 1 mm peak-to-valley excursion at 600 rpm. This is comparable to the best results obtained from the base diamond turning machine, an ASG2500. FLORA has its own DSP based controller and is fully integrated into the machine. Matlab" software has been developed to generate tool path data for machining complex surfaces with the FLORA system. This software can also create design data for the spherical coordinate measuring machine, Polaris3D [2], "closing the loop" from design to fabrication to metrology. Finally two examples are discussed. One is a 100 mm aperture far off-axis segment of a biconic mirror for an infrared spectrometer and the other is a small, multi-element collimating optic for a diode laser.
Fast tool servo is increasing applied to manufacture optical freeform surfaces, which are adopted in aerospace, imaging, bioengineering, energy fields to improve the performance of the system, simplify the structure of the system and lower cost. The existing FTS have limited stroke and bandwidth. FTS driven by electromagnetic force is discussed. The analysis of the magnetic circuit, the requirements of the system and the corresponding design parameters are studied. The designed FTS can realize the bandwidth of 0-100kHz with a special designed driver.
With the development of new concepts and principles over the past century, helmet-mounted displays (HMDs) have been widely applied. This paper presents a review of avionic HMDs and shows some areas of active and intensive research. This review is focused on the optical design aspects and is divided into three sections to explore new optical design methods, which include an off-axis design, design with freeform optical surface, and design with holographic optical waveguide technology. Building on the fundamentals of optical design and engineering, the principles section primarily expounds on the five optical system parameters, which include weight, field of view, modulation transfer function, exit pupil size, and eye relief. We summarized the previous design works using new components to achieve compact and lightweight HMDs. Moreover, the paper presents a partial summary of the more notable experimental, prototype, fielded, and future HMD fixed-wing and rotary-wing programs. (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.
Freeform surfaces enable imaginative optics by providing abundant degrees of freedom for an optical designer as compared to spherical surfaces. An off-axis two-mirror–based telescope design is presented, in which the primary mirror is a concave prolate spheroid and the secondary mirror is freeform surface-based. The off-axis configuration is employed here for removing the central obscuration problem which otherwise limits the central maxima in the point spread function. In this proposed design, an extended X−Y polynomial is used as a surface descriptor for the off-axis segment of the secondary mirror. The coefficients of this extended polynomial are directly related to the Seidel aberrations, and are thus optimized here for a better control of asymmetric optical aberrations at various field points. For this design, the aperture stop is located 500 mm before the primary mirror and the entrance pupil diameter is kept as 80 mm. The effective focal length is 439 mm and covers a full field of view of 2 deg. The image quality obtained here is near diffraction limited which can be inferred from metrics such as the spot diagram and modulation transfer function.
Diamond turning assisted by fast tool servo is of high efficiency for the fabrication of freeform optics. This paper describes a long-stroke fast tool servo to obtain a large-amplitude tool motion. It has the advantage of low cost and higher stiffness and natural frequency than other flexure-based long-stroke fast tool servo systems. The fast tool servo is actuated by a voice coil motor and guided by a flexure-hinge structure. Open-loop and close-loop control tests are conducted on the testing platform. While fast tool servo system is an additional motion axis for a diamond turning machine, a tool center adjustment method is described to confirm tool center position in the machine tool coordinate system when the fast tool servo system is fixed on the diamond turning machine. Last, a sinusoidal surface is machined and the results demonstrate that the tool adjustment method is efficient and precise for a flexure-based fast tool servo system, and the fast tool servo system works well on the fabrication of freeform optics. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
The concentrated photovoltaic (CPV) can be employed to improve the efficiency of solar cells and reduce the system cost of power generation, which is the primary part of the CPV system. Based on the demands for the concentrators to have an ultrathin and ultralight design, a design of ultrasmall aspect ratio concentrators is proposed. The concentrator is formed by a lens array and a freeform reflector to precisely control the light. The solar cell is placed at the side of the concentrator, which greatly reduces the overall thickness of the concentrator. The design can reduce the aspect ratio of concentrator by a considerable amount. The freeform reflector can shape the light beam and achieve a uniform distribution of light energy. © 2014 Society of Photo-Optical Instrumentation Engineers (SPIE).
The radial spiral feed of the tool and the tool nose radius compensation are taken into consideration for the tool position trajectory (TPT) generation in diamond turning of freeform optical surfaces. Using the coarse sampling and the fine interpolation, a novel approach based on singular spectrum analysis (SSA) is presented to decompose the generated TPT into a slowly varying trend and a quickly varying quasi-periodic oscillation. The numerical experiments of the TPT decomposition of toroidal surfaces have been carried out. The results verify that the proposed approach is very effective for the TPT decomposition.
The advent and rapid development of efficient high power LED sources with their unique emission characteristics
enables the development of illumination systems that meet very strict requirements concerning light distribution
and efficiency. Most of the algorithms used to design the necessary optical freeform surfaces rely on the point
source assumption. As long as the distance between LED and those surfaces is sufficiently large, this is a good
approximation. One further important design goal is to make the optical components as small as possible, which
makes the point source assumption less accurate. The existing design algorithms thus have to be accompanied
by methods to treat the finite-sized LED sources. We examine the limits that are set by the finite size of the light
sources and present algorithms to optimize optical freeform surfaces up to these limits. Point source results are
iteratively improved to get the desired illumination pattern employing finite sized LEDs. At each iteration step
the illumination pattern used in the point source computations is adapted so that the real illumination pattern
of an LED approximates the originally desired pattern.
Long stroke Fast Tool Servo (LFTS) with maximum stroke of is designed, manufactured and tested for fabrication of optical free-form surfaces. The large amount of stroke in LFTS has been realized by utilizing the hinge and lever mechanisms which enable the displacement amplification ratio of 4.3. In this mechanism the peculiar shape was devised for maximizing the displacement of end tip in LFTS and special mechanical spring has been mounted to provide the sufficient preload to the piezoelectric actuator. Also, its longitudinal motion of tool tip can be measured by capacitive type displacement sensor and closed-loop controlled to overcome the nonlinear hysteresis. In order to verify the static and dynamic characteristics of designed LFTS, several features including step response, frequency response and cut-off frequency in closed-loop mode were experimentally examined. Also, basic machining result shows that the proposed LFTS is capable of generating the optical free-form surface as an additional axis in diamond turning machine.
In this paper, a design method based on a construction and iteration process is proposed for designing freeform imaging systems with linear field-of-view (FOV). The surface contours of the desired freeform surfaces in the tangential plane are firstly designed to control the tangential rays of multiple field angles and different pupil coordinates. Then, the image quality is improved with an iterative process. The design result can be taken as a good starting point for further optimization. A freeform off-axis scanning system is designed as an example of the proposed method. The convergence ability of the construction and iteration process to design a freeform system from initial planes is validated. The MTF of the design result is close to the diffraction limit and the scanning error is less than 1μm. This result proves that good image quality and scanning linearity were achieved.
The unique optical system of the folding single-lens-reflex viewfinder used in the Polaroid SX-70 Land camera has required novel approaches to design and manufacture. The camera uses an unusual short-barrel taking lens with front-element focus, two plane mirrors, an eccentric reflective Fresnel focus screen, an aspheric aperture element, an aspheric concave mirror, and an aspheric eye lens. All the viewing components are tilted or decentered, and two aspheres are not figures of revolution. Beginning with J. G. Baker’s computer design, special technology has been needed for producing millions of replicas of this system and controlling their quality.
Challenges in fabrication and testing have historically limited the choice of surfaces available for the design of reflective optical instruments. Spherical and conic mirrors are common, but, for future science instruments, more degrees of freedom will be necessary to meet performance and packaging requirements. These instruments will be composed of surfaces of revolution located far off-axis with large spherical departure, and some designs will even require asymmetric surface profiles. We describe the design and diamond machining of seven aluminum mirrors: three rotationally symmetric, off-axis conic sections, one off-axis biconic, and three flat mirror designs. These mirrors are for the Infrared Multi-Object Spectrometer instrument, a facility instrument for the Kitt, Peak National Observatory's Mayall Telescope (3.8 in) and a pathfinder for the future Next Generation Space Telescope multi-object spectrograph. The symmetric mirrors include convex and concave prolate and oblate ellipsoids, and range in aperture from 92 x 77 mm to 284 x 264 mm and in f-number from 0.9 to 2.4. The biconic mirror is concave and has a 94 X 76 mm aperture, R-x = 377 mm, k(x) = 0.078, R-y = 407 nun, and k(y) = 0.127 and is decentered by -2 nun in x and 227 mm in y. The mirrors have an aspect ratio of approximately 6:1. The fabrication tolerances for surface error are < 63.3 nm RMS figure error and < 10 nm RMS microroughness. The mirrors are attached to the instrument bench using semi-kinematic, integral flexure mounts and optornechanically aligned to the instrument coordinate system using fiducial marks and datum surfaces. We also describe in-process profilometry and optical testing.
The Design, Manufacture and Metrology of contact lenses is a field heavily dependent on the existence and advancement of Precision Engineering. Astigmatic lenses (also called torics) are used to correct vision when the ocular system needs one power of correction along one direction (axis) and a different power along another. In Astigmatic lenses, the two powers are generally orthogonal to each other and the corrective lens must be held in place to prohibit excessive angular rotation thereby keeping the respective powers in the proper angular orientation. On astigmatic lenses, and other higher order aberration lenses, the central 4 to 8 mm contains the power correction (also known as the Optic Zone, or OZ) and all, or part of the remaining portion of the lens, provides the angular stabilization (Stabilization Zones). Stabilization zones use gravity and/or blinking forces of the eye to hold the lens in place. Solid modeling and the mating of dynamic FEA taking into account variables such as tear film thickness, viscosity and the velocity and direction of eyelid movement, have opened new avenues to design procurement. Contact lenses for correcting astigmatism can have a back surface toric, a front surface toric, or both, but all types all need stabilization zones. Manufacturing Manufacturing techniques of contact lenses include spin casting, cast molding, and direct lathing of contact lens material (un-hydrated state) known as buttons. In direct lathing, the base curve (concave) side is machined first. The button is then mounted, using wax, on to an arbor that has a profile similar to the base curve as seen in the figure below. Once the wax has hardened, the front surface is machined. The toric optic zone can be achieved either by a toric generator, or by crimping (pinching) a button while on the arbor and machining a spherical optic zone. When the crimped button is released, a toric surface remains.
A turning machine includes a controller for generating both aspherical and non-symmetrical shape components defining the predetermined shape, and a controller for controlling a spindle and a positionable cutting blade to thereby form a predetermined non-rotationally symmetric shape in a workpiece surface. The apparatus includes a rotatable spindle for rotatably mounting the workpiece about an axis, a spindle encoder for sensing an angular position of the rotating workpiece, the cutting blade, and radial and transverse positioners for relatively positioning the cutting blade and workpiece along respective radial and transverse directions. The controller cooperates with a fast transverse positioner for positioning the cutting blade in predetermined varying transverse positions during a revolution of the workpiece. 14 figs.
Current techniques for manufacturing off-axis paraboloids are both expensive and insufficiently accurate. An alternative method, turning the workpiece about its axis on a diamond-turning machine, is presented, and the equations describing the necessary tool movement are derived. A discussion of a particular case suggests that the proposed technique is feasible.
Challenges in fabrication and testing have historically limited the choice of surfaces available for the design of reflective optical instruments. Spherical and conic mirrors are common, but, for future science instruments, more degrees of freedom will be necessary to meet performance and packaging requirements. These instruments will be composed of surfaces of revolution located far off-axis with large spherical departure, and some designs will even require asymmetric surface profiles. We describe the design and diamond machining of seven aluminum mirrors: three rotationally symmetric, off-axis conic sections, one off-axis biconic, and three flat mirror designs. These mirrors are for the Infrared Multi-Object Spectrometer instrument, a facility instrument for the Kitt Peak National Observatory"s Mayall Telescope (3.8 m) and a pathfinder for the future Next Generation Space Telescope multi-object spectrograph. The symmetric mirrors include convex and concave prolate and oblate ellipsoids, and range in aperture from 92 x 77 mm to 284 x 264 mm and in f-number from 0.9 to 2.4. The biconic mirror is concave and has a 94 x 76 mm aperture, Rx = 377 mm, kx = 0.078, Ry = 407 mm, and ky = 0.127 and is decentered by 2 mm in x and 227 mm in y. The mirrors have an aspect ratio of approximately 6:1. The fabrication tolerances for surface error are < 63.3 nm RMS figure error and < 10 nm RMS microroughness. The mirrors are attached to the instrument bench using semi-kinematic, integral flexure mounts and optomechanically aligned to the instrument coordinate system using fiducial marks and datum surfaces. We also describe in-process profilometry and optical testing.
In this paper the equations that describe off-axis conic surfaces for a four axis approach to non-axisymmetric surface generation are derived. In addition considerations that minimize the fourth axis range of motion are reviewed. An example using a well known segmented astronomical mirror is used to illustrate these considerations.
A Diamond Turning Machine (DTM) can fabricate components with extremely high precision and high quality surface finish characteristics. Existing commercial controllers are limited in their ability to support high performance machining and related advanced control algorithms. Evolving enhancements to the functional capability and control algorithms of a DTM require increased performance and flexibility from the computer system controlling it. To provide this capability the Precision Engineering Center at North Carolina State University has developed and implemented a high performance control system for such a machine tool. The control system is based on a heterogeneous hierarchical multiprocessor computer architecture. This provides the capacity to apply advanced control concepts to the DTM, resulting in improved precision and quality of machined parts. Additionally, the ability to machine non-rotationally symmetric components has been made possible by application of multiprocessor capability.
We present highlights from the American Society for Precision Engineering's 2004 winter topical meeting entitled Free-Form Optics: Design, Fabrication, Metrology, Assembly. We emphasize those papers that are most relevant to astronomical optics. Optical surfaces that transcend the bounds of rotational symmetry have been implemented in novel optical systems with fantastic results since the release of Polaroid's first instant camera. Despite these successes, free-form optics have found only a few niche applications and have yet to enter the mainstream. The purpose of this meeting is to identify the state of the art of free-form optics design, fabrication, metrology and assembly and to identify the technical and logistical challenges that inhibit their widespread use. Issues that will be addressed include: What are free-form optics? How can optical systems be made better with free-form optics? How can designers use free-form optics? How can free-form optics be fabricated? How can they be measured? How are free-form optical systems assembled? Control of multi-axis systems.
Off-axis biconic mirror fabrication
- K P Garrard
- A Sohn
- R G Ohl
- R Mink
- V J Chambers
Garrard, K.P., A. Sohn, R.G. Ohl, R. Mink and V.J. Chambers. Off-axis biconic mirror fabrication. Proceedings of
the Third International Meeting of the European Society for Precision Engineering and Nanotechnology (EUSPEN),
277-280, (2002).
Need for precision engineering in astigmatic contact lenses
- M Heinrich
- C Wildsmith
Heinrich, M. and C. Wildsmith. Need for precision engineering in astigmatic contact lenses. Proceedings of the
ASPE Topical Meeting on Freeform Optics, 31, 18-22 (2004).
Benefits of freeform mirror surfaces in optical design
- M Rodgers
- K Thompson
Rodgers, M. and K. Thompson. Benefits of freeform mirror surfaces in optical design. Proceedings of the ASPE
2004 Winter Topical Meeting on Freeform Optics, 31, 73-78 (2004).