The successful fabrication of several freeform optical elements by ultraprecision micromilling is presented in this article.
We discuss in detail the generation of the tool paths using different variations of a computer-aided manufacturing
(CAM) process. Following a classical CAM approach, a reflective beam shaper was fabricated. The approach is based
on a solid model calculated by optical design software. As no analytical description of the surface is needed, this
procedure is the most general solution for the programming of the tool paths. A second approach is based on the same
design data. But instead of a solid model, a higher order polynomial was fitted to the data using computational methods.
Taking advantage of the direct programming capabilities of state-of-the-art computerized numerical control units, the
mathematics to calculate the polynomial based tool paths on-the-fly during the machining process are implemented in a
highly flexible CNC code. As another example for this programming method, the fabrication of a biconic lens from a
closed analytical description directly derived from the optical design is shown. We provide details about the different
programming methods and the fabrication processes as well as the results of characterizations concerning surface quality
and shape accuracy of the freeform optical elements.
The performance of optical systems is typically improved by adding conventional optical components which is
automatically connected to an increasing system size and weight. Hybrid optical freeform components can help to
overcome this traditional tradeoff by designing a single complex optical surface that performs several optical functions at
once. In this article we present the synthetic design and integrated fabrication of a reflective hybrid beam shaper offering
beam deflection, transformation and splitting capabilities. The shape accuracy and surface quality of the component are
demonstrated with profilometric measurements. Experimental investigations of the optical performance verify the
suitability of the applied fabrication methods and design approach.
Fluorescence detectors are applied for various applications in biomedical research, e.g. for pH-sensoring or single-cell
detection. Free space optical systems offer the advantage of compact and efficiently integrated systems with benefits in
the terms of systems alignment and optical functionality. On the other hand, due to the lab-on-a-chip character many
fluidic systems, such as segmented flow systems, are very compact and thus compatible with integrated optical systems.
We discuss the potential of the integration of the segmented flow approach in complex free space optical microsystems.
The design and realization of a highly integrated fluorescence detector is demonstrated. The system is fabricated by ultra
precision micromilling which allows one to monolithically integrate freeform optical elements for optimized optical
The application of multi-axis micromilling and flycutting is investigated for the fabrication of complex optical microsystems
incorporating different classes of aspherical and freeform optical elements. Such elements provide the necessary
degrees of freedom for aberration correction in integrated optical microsystems and are specifically interesting for
applications like beam shaping or computational imaging. Especially for elements with small radii of curvature, high
aspect ratios and spatial frequencies, micromilling and flycutting are interesting alternatives to the more established
diamond turning technology. We present the results of the fabrication of a monolithically integrated optical microsystem
consisting of two tilted flat surfaces used as coupling prisms and a freeform imaging element. On the resulting surfaces
the average roughness height without subsequent polishing was found to be Ra = 18.2 ... 25.5 nm (depending on the
fabrication technique) with an overall shape accuracy < 0.5 ... 2.9 μm (based on the determination of the radii of
Planar microoptical systems integration is a powerful approach for the fabrication of optical systems and has been
demonstrated for a large variety of applications. The folded optical axis in combination with planar fabrication
technologies enables highly integrated and rugged optical systems. In this geometry, however, specific care is necessary
to avoid aberrations resulting from the oblique optical axis. A purely diffractive implementation of these systems
generally leads to an efficiency of only a few percent. Combining classical refractive optics with diffractive correction
elements increases the overall efficiency. However, the purely refractive implementation suffered from the lack of
fabrication technologies for freeform microoptical elements. We present the results of the first fabrication of freeform
refractive correction elements combined with standard off-the-shelf refractive microlenses to form a completely
refractive planar integrated optical system using ultraprecision micromilling. Experiments confirm the increased optical
performance of the systems by integrating two micromachined reflective correction elements. Both elements have a size
of 2.4 x 2.4 mm2 with a peak-to-valley surface profile depth of 2.6 μm. They are fabricated with an average roughness
height < 40 nm and a surface tolerance < 400 nm.
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