Current lens systems are restricted in size, shape and dimensions by limitations of manufacturing. Multi-lens elements with non-spherical shapes are required for high optical performance and to correct for aberrations when imaging at wide angles and large fields. Here we present a novel concept in optics that overcomes all of the aforementioned difficulties and opens the new field of 3D printed micro-and nano-optics with complex lens designs. We demonstrate the complete process chain, from optical design, manufacturing by femtosecond two-photon direct laser writing and testing to the application of multi-lens objectives with sizes around 100 µm, and validate their high performance and functionality by quantitative measurements of the modulation transfer function and aberrations. The unprecedented flexibility of our method paves the way towards printed optical miniature instruments such as endoscopes, fibre-imaging systems for cell biology, new illumination systems, miniature optical fibre traps, integrated quantum emitters and detectors, and miniature drones and robots with autonomous vision.A dditive manufacturing enables new and unprecedented engineering and production possibilities that are predicted to have an enormous impact in the twenty-first century. The technology allows for the simple three-dimensional (3D) printing of volumetric objects directly from a computer-aided design 1 . So far, additively manufactured objects are mostly fabricated from metals, ceramics and opaque plastics. There are a number of different fabrication methods to manufacture small and high-performance micro-optical systems 2-10 ; however, these technologies suffer from drawbacks such as limited miniaturization, inability to combine multiple elements, restrictions in designing the surfaces 2-4,11 and problems with the alignment 12 .Multiphoton lithography is one of various 3D printing technologies that realize the fabrication of 3D objects 13-15 . Using femtosecond laser pulses and two-photon absorption, this manufacturing method takes 3D printing down to submicrometre feature sizes and therefore pushes the ongoing trend of miniaturization forwards. Direct laser writing with highly transparent photoresists enables 3D printing to enter the realm of manufacturing optical elements at the micro-and nanometre scale [16][17][18][19][20][21][22] . Thus the precise fabrication of complex optical elements on demand becomes possible.We demonstrate that 3D direct laser writing is a suitable tool for fabricating complex multi-lens optical systems that show high optical performances and tremendous compactness. Until now multi-lens optics that have comparable performances are considerably larger 12,23 and at the same time do not show the manifold compound structures and possibilities presented here. Our optical devices consist of several different free-form lens elements with air in between. This work is right at the interface between microand nano-optics and represents a paradigm shift for micro-optics. It takes only a few hours from lens desig...

Micro-optics are widely used in numerous applications, such as beam shaping, collimation, focusing and imaging. We use femtosecond 3D printing to manufacture free-form micro-optical elements. Our method gives sub-micrometre accuracy so that direct manufacturing even on single-mode fibres is possible. We demonstrate the potential of our method by writing different collimation optics, toric lenses, free-form surfaces with polynomials of up to 10th order for intensity beam shaping, as well as chiral photonic crystals for circular polarization filtering, all aligned onto the core of the single-mode fibres. We determine the accuracy of our optics by analysing the output patterns as well as interferometrically characterizing the surfaces. We find excellent agreement with numerical calculations. 3D printing of microoptics can achieve sufficient performance that will allow for rapid prototyping and production of beam-shaping and imaging devices.

A highly miniaturized vision system is realized by directly 3D-printing different multilens objectives onto a CMOS image sensor.

Preclinical and clinical diagnostics increasingly rely on techniques to visualize internal organs at high resolution via endoscopes. Miniaturized endoscopic probes are necessary for imaging small luminal or delicate organs without causing trauma to tissue. However, current fabrication methods limit the imaging performance of highly miniaturized probes, restricting their widespread application. To overcome this limitation, we developed a novel ultrathin probe fabrication technique that utilizes 3D microprinting to reliably create side-facing freeform micro-optics (<130 µm diameter) on single-mode fibers. Using this technique, we built a fully functional ultrathin aberration-corrected optical coherence tomography probe. This is the smallest freeform 3D imaging probe yet reported, with a diameter of 0.457 mm, including the catheter sheath. We demonstrated image quality and mechanical flexibility by imaging atherosclerotic human and mouse arteries. The ability to provide microstructural information with the smallest optical coherence tomography catheter opens a gateway for novel minimally invasive applications in disease.

Highly efficient counter-propagating fiber-based optical traps are presented which utilize converging beams from fibers with 3D printed diffractive Fresnel lenses on their facet. The use of a converging beam instead of diverging beam in dual-fiber traps creates a strong trapping efficiency in both the axial and the transverse directions. Converging beams with a numerical aperture of up to 0.7 are produced by diffractive Fresnel lenses. These lenses also provide a large focal distance of up to 200 μm in a moderately high refractive index medium. Fabrication of such diffractive lenses with microsized features at the tip of a fiber is possible by femtosecond two photon lithography. In comparison to chemically etched fiber tips, the normalized trap stiffness of dual-fiber tweezers is increased by a substantial factor of 35−50 when using a converging beam produced by diffractive Fresnel lenses. The large focal length provided by these diffractive structures allows working at a large fiber-to-fiber distance, which leads to larger space and the freedom to combine other spectroscopy and analytical methods in combination with trapping.