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Femtosecond direct laser writing is a key enabling technology for complex microoptics. Imaging and illumination applications have impressively been demonstrated in the past. Here, we take 3D-printed microoptics one step further and assess the feasibility of complex microoptical systems: From a pinhole camera to a spectrometer.
The first step in successful realization of complex microoptical systems are specialized measurement techniques that match both fabrication and simulation methods. Different setups are presented to reach stray light control, isolate topographic effects, and measure the efficiency of diffractive structures with small lateral extensions. All methods are easy to implement and can be key to targeted optimization of complex systems.
In a second step, the spectrum of corresponding fabrication methods to fsDLW is extended by the microfluidic addition of a functional substance. We show that the incorporation of microfluidic channels into the 3D-printed mounting structures can be used to absorb a non-transparent fluid to create aperutres. Thus, a 3D-printed micro-pinhole camera can be demonstrated.
Finally, all learnings and methods from these studies are combined to create complex microoptical systems. Multiple concepts of ultra-compact 3D-printed wide-angle cameras are examined. A special focus is laid on optical and mechanical design, measurement and optimization of highly tilted refractive and catadioptric freeform surfaces. An iterative correction mechanism is developed to improve shape fidelity to realize first implementations of 180°×360° field of view multi-aperture imaging.
The highest complexity of a 3D-printed microoptical system is finally reached by the realization of an entire measurement system. The feasibility of a monolithic spectrometer in a volume of only 100 × 100 × 300 μm³ is theoretically and experimentally demonstrated. The results represent the first direct spectrometer in this miniature size range and unclose a new era of complex 3D-printed microoptical (measurement) systems, enabled by novel methods for charactarization, optimization and aperture fabrication.
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