With optical technology and design advances, larger freeform optics are increasingly sought after by consumers for an expanding number of applications. Many techniques have been developed to meet the challenges of producing these nonrotationally symmetric optics, which cannot be fabricated via traditional manufacturing and metrology processes. In the past, methods were established to create smaller freeforms. With demands for more and larger freeforms, manufacturers must scale up existing processes. This paper will present some of the challenges and solutions of extending freeform polishing capabilities from approximately 150 mm diameter parts to a component of over 500 mm in diameter. In fabricating the 500 mm freeform, Optimax has addressed many of the manufacturing and metrology challenges using some proprietary techniques as well as some novel methods. Some of the approaches explored in this paper include acquisition of a substrate blank of sufficient dimensions, material handling logistics, polishing strategies, and metrology. Earlier freeform polishing projects at Optimax utilized a smaller pick-and-place style, 6-axis robotic arm. The route to design, build, and program a scaled-up polishing robotic arm is discussed. Considerations for polishing path planning and metrology are explained. In addition, deflectometry, a non-interferometric measurement method using fringe reflection and ray tracing, has been developed in parallel to help measure mid-spatial frequency error on a part surface faster and more safely than traditional methods, as it can be done in-situ.
Freeform optics have emerged as a new tool for optical designers and integrators. Manufacturing innovations are gradually increasing availability of precision freeform optics. As optics manufacturers strive to improve quality and decrease cost, some focus is placed on improvements in the challenging metrology requirements for freeforms. One relevant technique to be discussed here is the use of deflectometry to measure mid-spatial frequency error in-process or in-situ during the manufacturing of freeform parts. Deflectometry can measure the mid-spatial frequency error on freeform parts orders of magnitude faster than traditional tactile metrology tools at similar or better accuracy.
Freeform optical components are gaining popularity with designers due to their ability to improve optical and aerodynamic performance for many applications. The challenges involved with the manufacturing and metrology of these shapes, which have little or no symmetry, has been discussed at previous talks and conferences. This paper will focus on the challenges that Optimax faced as we scaled up our freeform polishing process from parts with approximately 150 mm diameters, to polishing components with diameters over 600 mm. The large format platform, designed, built, and programmed at Optimax, utilizes a pick-and-place style, 6-axis robotic arm for the polishing motion. In order to scale up the platform from our existing robotic polishers, a larger robotic arm was used. The associated challenges include: timing considerations for both the polishing and metrology, obtaining sufficient material removal for reliable measurements, and difficulties modelling robot joint positions for collision prevention. These issues have been investigated and mitigated through proprietary techniques and novel solutions, some of which will be explored in this paper. One such technique currently under development at Optimax is deflectometry; which is a noninterferometric method involving fringe reflection and ray tracing to calculate the mid-spatial frequency (MSF) error on a part surface. Deflectometry is able to measure MSF error two orders of magnitude faster than the current method, and has been implemented in-situ, mitigating another challenges involved with larger freeform optics: the logistics of moving them around a shop floor safely.
Systems like TESS require specialized components that challenge all involved. These systems consist of many sub-components, but we are focused on the refractive and reflective optical components. One purpose of this talk is to introduce optical system designers to application specific manufacturing processes. We, as manufacturers, need to tailor our processes for the optic’s specific operational environment. In addition, we want to introduce some of our more unique manufacturing capabilities to allow system designers to widen their design space. It is now feasible to manufacture a wide range of sizes, shapes, and materials for many different applications.
Recently the use of freeform surfaces have become a realization for optical designers. These non-symmetrical optical surfaces have allowed unique solutions to optical design problems. The implementation of freeform optical surfaces has been limited by manufacturing capabilities and quality. However over the past several years freeform fabrication processes have improved in capability and precision. But as with any manufacturing, proper metrology is required to monitor and verify the process. Typical optics metrology such as interferometry has its challenges and limitations with the unique shapes of freeform optics. Two contact metrology methods for freeform metrology are presented; a Leitz coordinate measurement machine (CMM) with an uncertainty of ± 0.5 μm and a high resolution profilometer (Panasonic UA3P) with a measurement uncertainty of ± 0.05 μm. We are also developing a non-contact high resolution technique based on the fringe reflection technique known as deflectometry. This fast non-contact metrology has the potential to compete with accuracies of the contact methods but also can acquire data in seconds rather than minutes or hours.
Improvements to sensing hardware and image processing for airborne optical systems have inspired designers to propose new optics and windows which may be any of: more precise, conformal/freeform and multi-functional. Manufacture of these optics has required innovations in machining, polishing and metrology. The performance requirements and manufacturing methods demand more from conventional optical materials, while also driving development of new formulations with tailored optical and mechanical properties. We describe innovations in manufacturing and adaptations for optical materials selected for end-use performance, though some such materials may present unusual challenges related to their composition, how they are produced, and/or the design geometry. Our desire is to share some observations with the optical designer, who may be able to incorporate some tips into parts “designed for manufacture.”
Optical systems must perform under environmental conditions including thermal and mechanical loading. To predict the performance in the field, integrated analysis combining optical and mechanical software is required. Freeform and conformal optics offer many new opportunities for optical design. The unconventional geometries can lead to unconventional, and therefore unintuitive, mechanical behavior. Finite element (FE) analysis offers the ability to predict the deformations of freeform optics under various environments and load conditions. To understand the impact on optical performance, the deformations must be brought into optical analysis codes. This paper discusses several issues related to the integrated optomechanical analysis of freeform optics.
Freeform and conformal optics have the potential to dramatically improve optical systems by enabling systems with fewer optical components, reduced aberrations, and improved aerodynamic performance. These optical components differ from standard components in their surface shape, typically a non-symmetric equation based definition, and material properties. Traditional grinding and polishing tools are unable to handle these freeform shapes. Additionally, standard metrology tools cannot measure these surfaces. Desired substrates are typically hard ceramics, including poly-crystalline alumina or aluminum oxynitride. Notwithstanding the challenges that the hardness provides to manufacturing, these crystalline materials can be highly susceptible to grain decoration creating unacceptable scatter in optical systems. In this presentation, we will show progress towards addressing the unique challenges of manufacturing conformal windows and domes. Particular attention is given to our robotic polishing platform. This platform is based on an industrial robot adapted to accept a wide range of tooling and parts. The robot’s flexibility has provided us an opportunity to address the unique challenges of conformal windows. Slurries and polishing active layers can easily be changed to adapt to varying materials and address grain decoration. We have the flexibility to change tool size and shape to address the varying sizes and shapes of conformal optics. In addition, the robotic platform can be a base for a deflectometry-based metrology tool to measure surface form error. This system, whose precision is independent of the robot’s positioning accuracy, will allow us to measure optics in-situ saving time and reducing part risk. In conclusion, we will show examples of the conformal windows manufactured using our developed processes.
The blistering pace of recent technological advances has led lens designers to rely increasingly on freeform optical components as crucial pieces of their designs. As these freeform components increase in geometrical complexity and continue to deviate further from traditional optical designs, the optical manufacturing community must rethink their fabrication processes in order to keep pace. To meet these new demands, Optimax has developed a variety of new deterministic freeform manufacturing processes. Combining traditional optical fabrication techniques with cutting edge technological innovations has yielded a multifaceted manufacturing approach that can successfully handle even the most extreme freeform optical surfaces. <p> </p>In particular, Optimax has placed emphasis on refining the deterministic form correction process. By developing many of these procedures in house, changes can be implemented quickly and efficiently in order to rapidly converge on an optimal manufacturing method. Advances in metrology techniques allow for rapid identification and quantification of irregularities in freeform surfaces, while deterministic correction algorithms precisely target features on the part and drastically reduce overall correction time. Together, these improvements have yielded significant advances in the realm of freeform manufacturing. With further refinements to these and other aspects of the freeform manufacturing process, the production of increasingly radical freeform optical components is quickly becoming a reality.
Spectroscopy diagnostic techniques have applications in such diverse areas as mechanical and aerospace engineering, physical chemistry, optics, food and pharmaceutical industries. However, the technological state-of-the-art spectrometers do not allow very fast processes to be evaluated or controlled. This ability is crucial in the optimization of industrial processes (welding, burning flames, spark ignition, pulsed radiolysis…) where more theoretical-experimental analysis should be performed. The INSCAN project aims to overcome this technological limitation, to satisfy needs in academia and industrial markets, by developing a compact spectrometer with focal lengths less than 200 mm, taking into account three important aspects: acquisition rate of approximately 10 kHz spectra, spectral resolution on the order of 0.1 nm and operating in the spectral range 200 nm to 700 nm. Initial work is described on the optical design of the device and several possible approaches to achieve the specifications are considered. To guide the first order design, we relate the optical linewidth, spectral bandwidth and imaging properties to component characteristics. The symmetrical Czerny-Turner optical mount was chosen for its flexibility and elaborated using ZEMAX. Predictions made based on the simulated system are compared with calibration and characterization measurements on an experimental test bench used to refine the model assumptions.
Holographic elements have several unique features that make them attractive for solar collector and concentrator
systems. These properties include the ability to diffract light at large deflection angles, Bragg selectivity, grating
multiplexing, and angle-wavelength matching. In this presentation we review how these properties can be applied to
solar collection and concentrator systems. An algorithm is presented for analyzing the energy collection properties of
holographic concentrators in specific geometries and is applied to a planar collection format. Holographic elements are
shown to have advantages for low concentration ratio solar concentrator systems.