The manufacturing of optical freeform surfaces offers a high potential for optical approaches in the future, since they can make new optical systems lighter and more compact or even enable completely new functions, compared to conventional optics. However, the expanded possibilities go hand in hand with higher complexity in production of freeforms for precision optical applications. This leads to high prices and long delivery times. This paper shows an approach to improve manufacturing of freeforms in small batch sizes with a high degree of customization, by a process chain consisting of (ultrasonic-assisted) pre- and fine grinding combined with ultra-fine grinding using resin bond tools. The process chain is suited for efficient fabrication of optical surfaces. A main focus of the experiments is on reduction of low- and mid-spatial frequency surface deviations, as well as surface roughness. Several different influencing factors in a 5-axis CNC grinding process of fused silica freeforms are investigated and their effects on the resulting surface topography (from the low to the high frequency range of surface deviations) are observed using white light interferometry measurement principles. Various optimization approaches can be concluded.
We provide a review of the latest research findings as well as the future potential of plasma-based etching technology for the fabrication of micro-optical components and systems. Reactive ion etching (RIE) in combination with lithographic patterning is a well-established technology in the field of micro- and nanofabrication. Nevertheless, practical implementation, especially for plasma-based patterning of complex optical materials such as alumino-silicate glasses or glass-ceramics, is still largely based on technological experience rather than established models. Such models require an in-depth understanding of the underlying chemical and physical processes within the plasma and at the glass–plasma/mask–plasma interfaces. We therefore present results that should pave the way for a better understanding of processes and thus for the extension of RIE processes toward innovative three-dimensional (3D) patterning as well as for the processing of chemically and structurally inhomogeneous silicate-based substrates. To this end, we present and discuss the results of a variety of microstructuring strategies for different application areas with a focus on micro-optics. We consider the requirements for refractive and diffractive micro-optical systems and highlight potentials for 3D dry chemical etching by selective tailoring of the material structure. The results thus provide first steps toward a knowledge-based approach to RIE processing of universal dielectric glass materials for optical microsystems, which also has a significant impact on other microscale applications.
The production of complex glass components with 2.5D or 3D-structures involves great effort and the need for advanced CNC-technology. Especially the final surface treatment, for generation of transparent surfaces, represents a timeconsuming and costly process. The ultrasonic-assisted grinding procedure is used to generate arbitrary shaped components and freeform-surfaces. The special kinematic principle, containing a high-frequency tool oscillation, enables efficient manufacturing processes. Surfaces produced in this way allow for application of novel smoothing methods, providing considerable advantages compared to classic polishing. It is shown, that manufacturing of transparent glass surfaces with low roughness down to Rq = 10 nm is possible, using an ultra-fine grinding process. By adding a CO2-laser polishing process, roughness can be reduced even further with a very short polishing time.
The fabrication of high-quality optical components involves great effort. Polishing often functions as the final step in a manufacturing chain. To reduce the conventionally time-consuming, complex polishing process with loose grain, an interesting approach with novel resin bond grinding tools is presented for surface smoothing. Various processing-experiments were carried out, regarding different silicate materials such as BK7® and fused silica. Among other results it is shown, that good surface qualities with low roughness down to Ra = 8 nm or Rq = 10 nm can be achieved so far, a quality that already allows speaking of “ultra-fine” grinding. This results in remarkable possibilities to reduce conventional fine-machining procedures with loose abrasives. The fine grinded components can directly be polished to finally smooth the surface and remove remaining defects. Total-processing-times can be strongly reduced, involving significant economic advantages.
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