Hybrid photonic integration exploits complementary strengths of different material platforms, thereby offering superior performance and design flexibility in comparison to monolithic approaches. This applies in particular to multi-chip concepts, where components can be individually optimized and tested on separate dies before integration into more complex systems. The assembly of such systems, however, still represents a major challenge, requiring complex and expensive processes for high-precision alignment as well as careful adaptation of optical mode profiles. Here we show that these challenges can be overcome by in-situ nano-printing of freeform beam-shaping elements to facets of optical components. The approach is applicable to a wide variety of devices and assembly concepts and allows adaptation of vastly dissimilar mode profiles while considerably relaxing alignment tolerances to the extent that scalable, cost-effective passive assembly techniques can be used. We experimentally prove the viability of the concept by fabricating and testing a selection of beam-shaping elements at chip and fiber facets, achieving coupling efficiencies of up to 88 % between an InP laser and an optical fiber. We also demonstrate printed freeform mirrors for simultaneously adapting beam shape and propagation direction, and we explore multi-lens systems for beam expansion. The concept paves the way to automated fabrication of photonic multi-chip assemblies with unprecedented performance and versatility.

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Three-dimensional (3D) nano-printing of freeform optical waveguides, also referred to as photonic wire bonding, allows for efficient coupling between photonic chips and can greatly simplify optical system assembly. As a key advantage, the shape and the trajectory of photonic wire bonds can be adapted to the mode-field profiles and the positions of the chips, thereby offering an attractive alternative to conventional optical assembly techniques that rely on technically complex and costly high-precision alignment. However, while the fundamental advantages of the photonic wire bonding concept have been shown in proof-of-concept experiments, it has so far been unclear whether the technique can also be leveraged for practically relevant use cases with stringent reproducibility and reliability requirements. In this paper, we demonstrate optical communication engines that rely on photonic wire bonding for connecting arrays of silicon photonic modulators to InP lasers and single-mode fibres. In a first experiment, we show an eight-channel transmitter offering an aggregate line rate of 448 Gbit/s by low-complexity intensity modulation. A second experiment is dedicated to a four-channel coherent transmitter, operating at a net data rate of 732.7 Gbit/sa record for coherent silicon photonic transmitters with co-packaged lasers. Using dedicated test chips, we further demonstrate automated mass production of photonic wire bonds with insertion losses of (0.7 ± 0.15) dB, and we show their resilience in environmental-stability tests and at high optical power. These results might form the basis for simplified assembly of advanced photonic multi-chip systems that combine the distinct advantages of different integration platforms.

Miniaturized integrated optical coherence tomography (OCT) systems have the potential to unlock a wide range of both medical and industrial applications. This applies in particular to multi-channel OCT schemes, where scalability and low cost per channel are important, to endoscopic implementations with stringent size demands, and to mechanically robust units for industrial applications. We demonstrate that fully integrated OCT systems can be realized using the state-of-the-art silicon photonic device portfolio. We present two different implementations integrated on a silicon-on-insulator (SOI) photonic chip, one with an integrated reference path (OCTint) for imaging objects in distances of 5 mm to 10 mm from the chip edge, and another one with an external reference path (OCText) for use with conventional scan heads. Both OCT systems use integrated photodiodes and an external swept-frequency source. In our proof-of-concept experiments, we achieve a sensitivity of −64 dB (−53 dB for OCTint) and a dynamic range of 60 dB (53 dB for OCTint). The viability of the concept is demonstrated by imaging of biological and technical objects.

Glassy carbon is a graphenic form of elemental carbon obtained from pyrolysis of carbon-rich precursor polymers that can be patterned using various lithographic techniques. It is electrically and thermally conductive, mechanically strong, light, corrosion resistant and easy to functionalize. These properties render it very suitable for Carbon-microelectromechanical systems (Carbon-MEMS) and nanoelectromechanical systems (Carbon-NEMS) applications. Here we report on the fabrication and characterization of fully operational, microfabricated glassy carbon nano-tips for Atomic Force Microscopy (AFM). These tips are 3D-printed on to micro-machined silicon cantilevers by Two-Photon Polymerization (2PP) of acrylate-based photopolymers (commercially known as IP-series resists), followed by their carbonization employing controlled pyrolysis, which shrinks the patterned structure by ≥98% in volume. Tip performance and robustness during contact and dynamic AFM modes are validated by morphology and wear tests. The design and pyrolysis process optimization performed for this work indicate which parameters require special attention when IP-series polymers are used for the fabrication of Carbon-MEMS and NEMS. Microstructural characterization of the resulting material confirms that it features a frozen percolated network of graphene sheets accompanied by disordered carbon and voids, similar to typical glassy carbons. The presented facile fabrication method can be employed for obtaining a variety of 3D glassy carbon nanostructures starting from the stereolithographic designs provided by the user.

Coupling of light into multi-core fibers (MCF) for spatially resolved spectroscopy is of great importance to astronomical instrumentation. To achieve high coupling efficiencies along with fill-fractions close to unity, micro-optical elements are required to concentrate the incoming light to the individual cores of the MCF. In this paper we demonstrate facet-attached lens arrays (LA) fabricated by two-photon polymerization. The LA provide close to 100% fill-fraction along with efficiencies of up to 73% (down to 1.4 dB loss) for coupling of light from free space into an MCF core. We show the viability of the concept for astrophotonic applications by integrating an MCF-LA assembly in an adaptive-optics test bed and by assessing its performance as a tip/tilt sensor.

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realized as a sharp tip with nanometersize apex attached to a micrometer-scale cantilever. In current SPM systems, tip and cantilever are usually structured in a dedicated microfabrication process before being manually mounted and aligned to a macroscopic optomechanical system for piezoelectric actuation and optical detection of sub-nanometer movements. This concept leads to rather bulky implementations and requires laborious operation, given that the tip is a wear part that has to be regularly exchanged and re-aligned to the read-out system. In addition, tip-cantilever geo metries are currently restricted by the underlying fabrication techniques, relying on 2D lithographic patterning and subsequent anisotropic etching. These techniques usually result in pyramidal tips with rather low aspect ratios, and the dimensions of the cantilever are often subject to fabrication tolerances that lead to variations of the resonance frequency of 30% or more. [10] Moreover, current SPM systems are often limited in scanning speed, which inhibits high-throughput characterization of large sample areas. This may be overcome by arrays of SPM cantilevers for parallel scanning, [11,12] but the scalability and integration density of current SPM schemes is limited by the fact that each cantilever must still be individually addressed by a dedicated actuator and sensor element of macroscopic dimension. Chiplevel integration of individually addressable cantilevers has been Scanning-probe microscopy (SPM) is the method of choice for high-resolution imaging of surfaces in science and industry. However, SPM systems are still considered as rather complex and costly scientific instruments, realized by delicate combinations of microscopic cantilevers, nanoscopic tips, and macroscopic read-out units that require high-precision alignment prior to use. This study introduces a concept of ultra-compact SPM engines that combine cantilevers, tips, and a wide variety of actuator and read-out elements into one single monolithic structure. The devices are fabricated by multiphoton laser lithography as it is a particularly flexible and accurate additive nanofabrication technique. The resulting SPM engines are operated by optical actuation and read-out without manual alignment of individual components. The viability of the concept is demonstrated in a series of experiments that range from atomic-force microscopy engines offering atomic step height resolution, their operation in fluids, and to 3D printed scanning near-field optical microscopy. The presented approach is amenable to wafer-scale mass fabrication of SPM arrays and capable to unlock a wide range of novel applications that are inaccessible by current approaches to build SPMs.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.