This PDF file contains the front matter associated with SPIE Proceedings Volume 11349, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

One of the most important advantages of optical manufacturing by 3D printing is the high degree of freedom in geometry and optical design. This is especially true for fabrication methods like stereolithography which, in contrast to jet or extrusion based methods, usually enable true 3D geometries with undercuts and buried cavities. In case of multiphoton lithography such complex designs can additionally be manufactured with sub-wavelength feature sizes in all three dimensions. This enables optical designs with unmatched complexity combining reflective, refractive and diffractive surfaces as well as structures like photonic crystals in all 3 dimensions. In this work we introduce different strategies to show how the barely restricted design space can be used to realize compact 3D-printed micro-optics with strong optical performance. Different types of concentration and beam shaping devices for non-imaging purposes are introduced and refractive, diffractive, reflective and hybrid variants are discussed. While these devices serve to transfer one light distribution into another they are not suited for direct imaging. In order to image extended objects, lenses or lens systems are commonly optimized for a maximum space-bandwidth product which is connected to the product of imaging numerical aperture and image height. The space-bandwidth product is also correlating with the number of distinguishable image points which are transferred through a system. We demonstrate how maximum space-bandwidth product multi-lens optical systems can be designed and realized. Different variants of refractive, purely diffractive and hybrid imaging systems with lens barrel diameters below 500 µm are demonstrated and compared in terms of optical performance and manufacturability.

Photonic Integrated Circuits have made it possible to decrease the footprint of traditionally bulky optical systems and they create opportunities for various new and fascinating applications. One of the limiting factors for the widespread adaption of PICs is their connection to the outside world. As the mode field diameter of optical modes in waveguides tends to be an order of magnitude smaller than in their fiber counterparts, creating an efficient, robust and alignmenttolerant fiber-to-chip interface remains a challenge. In this work, we investigate the optimization of the fiber-side of the optical interface, whereas the chip itself remains untouched and makes use of spot-size convertors. Optical fiber tips can be functionalized using two-photon polymerization-based 3D nanoprinting technology, which offers full 3D design freedom and sub-micrometer resolution. We present a down-taper design strategy to match the mode-field diameter of single-mode optical fibers to the modefield diameter of waveguides with spot-size converters on PICs. The 3D printed down-tapers are characterized towards their geometry and mode shape, and we experimentally demonstrate their use for coupling towards a Silicon-On-Insulator chip with spot-size convertors. Furthermore, the performance of these down-tapered fibers is compared to conventional lensed fibers in terms of optical coupling efficiency.

There is an increasing demand for highly integrated optical and optoelectronical devices that provide active laser emission, adaptability and low optical losses. A well-established production technology for customized structures with high functionality and geometrical flexibility is additive manufacturing (AM). It enables new constructional degrees of freedom to overcome the limitations of substractive material processing such as milling and drilling. Commercial AM systems for metals and polymers are ubiquitous; whereas glass AM systems almost exclusively exist in scientific environments. Laser glass deposition welding allows the AM of waveguides by fusing coreless fused silica fibers with a diameter of 400 µm and a 50 µm thick polymer coating onto a fused silica substrate. The deposition process is performed with defocused CO₂-laser radiation (10.6 µm). Based on laser deposition welding, the fiber is fed laterally into the processing zone and is melted or fused by the incoming laser beam. In order to achieve a sufficient coupling of laser radiation into and out of the fibers, a proper cleaving process for the end faces has been established. The cleaving is performed with a CO₂-laser based process for optimized and reproducible results. In this contribution, the focus is on the manufacturing of bended waveguides and the feasible bending radii, which can be accomplished during the deposition process. The influence of the bending radius on the guiding efficiency is investigated. Therefore, the light transmission and beam profile of the deposited fibers is measured and compared with an untreated one. Furthermore, the appearance of the cleaved end faces and the internal stress in the glass substrate are characterized. Functional, nearly stress-free curved and straight waveguides for light transmission with high position stability are achieved, which opens a wide range of applications for optical system integration.

The combination of hybrid interconnection technology on ceramic as a carrier for the RF-electronics with excellent heat management and stereolithographic printing for 3D structures is a novel approach to achieve 3D-Opto-MID parts and, furthermore, to include mechanical properties. By directly printing polymers onto aluminum-oxide substrate (including an electrical circuit), brings together the advantages of both technologies. Using additive manufacturing makes this process suitable for small- to mid-scale productions with a very high design freedom. To analyze the adhesion between Al2O3 substrate and printed polymers, we compare six different resins according to the minimal structure length and the adhesion on the substrate. A longer exposure time of the first layer (burn-in time) leads to sufficient adhesion of the print on the ceramic substrate. To realize smaller adherent structures, longer burn-in times are needed. In a shear test, the forces to lift off the prints from the substrate are measured. The experiments reveal correlation between shear force and contact area with little variance. Based on this evaluation, choosing materials for future applications is easier and design rules can be determined. Furthermore, we present the application of flexible optical waveguides onto the 3D substrate (which will be directly printed in the future), as well as the passive alignment of laser and photodiode in this article. In a first test, we were able to prove the functionality of the 3D-Opto-MID package by launching the waveguide with the applied laser and measuring the current at the photodiode.

Metallic microstructures often are the key components in many applications, e.g. in wireless communication. While these components usually are planar, a number of benefits result from being able to fabricate 3D structures – broadband antennas being an example. Here, we show that direct laser writing enables the fabrication of 3D silver microstructures via photoreduction. A number of sample structures are presented to proof the versatility of this method. Since material properties, e.g. conductivity, of 3D printed structures often differ from their counterparts fabricated by subtractive methods, we furthermore throughout characterize these properties for our 3D printed samples. Fabrication of metallic structures by direct laser writing is based on the following mechanism: a photoreducing agent is two-photon excited by a focused laser beam and in its excited state has a higher reduction potential. Alternatively, the reducing agent may undergo a chemical reaction after excitation and its products have a higher reduction potential. In either case, this leads to the reduction of a metal precursor to neutral metal. If sufficient metal atoms are in close proximity, they nucleate and grow by adding further atoms to finally form the fundamental building block of the final structure. The complex nature of these chemical and physical processes usually limits this method to rather robust structures with large feature sizes. Here, we present how filigree silver micro-structures with feature sizes below 1 micron may be achieved using the described technique but we also show the current limits. Furthermore, the mechanical and electronic properties of these structures are characterized.

The joint project GROTESK investigates the application of additive manufacturing for the generation of optical, thermal and structural components using the example of a laser system. This includes multi-material connections of metallic and non-metallic materials with laser metal deposition, e.g. mountings for solid-state laser materials like neodymium-doped yttrium aluminum garnet (Nd:YAG), and the related material development for wire-based as well as powder-based processing. The contrary material groups require an exact consideration of the thermal and physical properties. In particular, the melting point of the alloy must be as low as possible, preventing thermal destruction of the Nd:YAG. Furthermore, this reduces the thermal gradient in the crystalline structure of the YAG and improves thermal shock resistance. Besides, a sufficient thermal conductivity is important to ensure a targeted heat dissipation. Another crucial aspect is the induced stress due to different thermal expansions of the connected materials leading to structural damage. Therefore, the thermal expansion coefficient of the alloy has to match the coefficient of the optical component. The recent approach is the application of copper-molybdenum pseudoalloys. The idea is to combine the low thermal expansion of molybdenum with the high thermal conductivity of copper. State-of-the-art are sintered molybdenum powders that are infiltrated with molten copper resulting in promising physical properties exceeding the requirements of the intended purpose and allowing the application in high-power laser systems. During first practical experiments with these powders, promising results have been achieved with a 680-Watt diode laser by solely melting the copper. The structure of the generated object contained unaffected molybdenum grains embedded into a copper matrix and therefore successfully forming a pseudoalloy. Effects of the adjusted powder composition, the laser parameters and the resulting thermomechanical properties are investigated. With the help of microsections, the additive manufactured pseudoalloys are evaluated and characterized.

In this paper we are exploring the possibilities of 3D printing in the fabrication of mirrors for astronomy. Taking the advantages of 3D printing to solve the existing problems caused by traditional manufacturing, two proof-of- concept mirror fabrication strategies are investigated in this paper. The first concept is a deformable mirror with embedded actuator supports system to minimise errors caused by the bonding interfaces during mirror assembly. The second concept is the adaption of the Stress Mirror Polishing (SMP) technique to a variety of mirror shapes by implemented a printed thickness distribution on the back side of the mirror. Design investigations and prototypes plans are presented for both studies.

Ceramics play an important role in today’s science and industry as it can withstand immense thermal, mechanical, chemical and other hazards. In recent years, the interest in 3D printing micro- or even nano-structures out of ceramics has been growing rapidly. Therefore, direct laser writing by two photon polymerization together with calcination have been proved to be a powerful tool for the fabrication of fully 3D glass-ceramic objects in micro- and nano-scale [1]. However, producing such structures with unique properties at meso scale (features from nm to cm overall size) is one of the greatest challenges [2]. In order to overcome it the composition of the starting materials and as well as conditions of calcination have to be fully understood and enhanced. We synthesized a series of organic-inorganic polymer precursors via sol-gel method varying the molar ratio of silicon (Si) and zirconium (Zr) complexes (Si:Zr, where Si=9; 8; 7; 6; 5 and Zr=1; 2; 3; 4; 5) [3] and investigated 3D processing of these materials. The study shows that the “glassy” phase structures retain their shape without any distortion. Furthermore, calcination provides a route for the continuous size control and formation of a variety of phase transformation for free-form nano-/micro-objects. It is shown that due to the isotropic nature of the shrinkage during calcination fabricated 3D objects retain complex geometry. Nano-woodpiles, bulk-woodpile hybrids and full bulk structures are formed. The sizes of single features in these objects vary from 120 nm to 800 nm with overall size going to 30 µm. Finally, changes in focused ion beam machining rates between standard and calcinated materials are shown proving enhanced resiliency of the final product (up to 50%). [1] Gailevičius, D., et al., Additive-manufacturing of 3D glass-ceramics down to nanoscale resolution. Nanoscale Horiz.; 4, 647-651; (2019) [2] L. Jonusauskas, D. Gailevicius, S. Rekstyte, T. Baldacchini, S. Juodkazis, M. Malinauskas, Mesoscale Laser 3D Printing, Opt. Express 27 (11), 15205-15221 (2019) [3] Ovsianikov, A., et al., Ultra-Low Shrinkage Hybrid Photosensitive Material for Two-Photon Polymerization Microfabrication. ACS Nano; 2(11), 2257-2262; (2008)

In this study, we use a hybrid mode-locked external cavity diode laser with subsequent amplification and pulse compression. The system provides laser pulses of 440 fs width (assuming a sech² pulse shape) and 160 mW average output power at a repetition rate of 383.1 MHz. The laser oscillator consists of a double quantum well laser diode with a gain segment of 1080 μm length and an absorber element of 80 μm lengths. The chip’s back facet is covered with a high reflective coating, the front facet with an anti-reflective coating. The resonator itself is operated in a collimated geometry and folded by two dielectric mirrors. The used output coupler provides a transmission of 20 percent, which is coupled into a tapered amplifier. Two Faraday isolators are used to decouple the laser and the amplifier from any back reflections. Subsequently, the pulses are compressed using a single pass Martinez type pulse compressor. Experiments on Two-Photon Polymerization were conducted on a conventional setup consisting of a 2D galvo-scanner system with an attached microscope objective. The oil immersion objective (NA =1.4) focusses the light pulses through a cover glass into a droplet of the photosensitive material. Process monitoring can be achieved by observing the image on a camera placed behind a semi-transparent mirror in front of the galvo-scanner. Using this experimental setup, test structures that consist of free-hanging lines supported by cuboids were produced. In addition, a procedure for automated linewidth measurements is outlined and used for analyzation of the generated structures. This work shows that mode-locked diode lasers can be used for the fabrication of microstructures by Two-Photon Polymerization. Typically used Ti:Sapphire or fiber lasers can be replaced by mode-locked diode lasers for Two-Photon- Polymerization. This allows for much cheaper Two-Photon-Polymerization systems and therefore, may open this field for more application-based research groups.

Silicon nanoparticles possess unique size-dependent optical properties due to their strong electric and magnetic resonances in the visible range. However, their widespread application has been limited, in comparison with other (e.g.,metallic) nanoparticles, because their preparation on monodisperse colloids remains challenging. Exploiting the unique properties of Si nanoparticles in nano- and microdevices calls for methods able to sort and organize them from a colloidal suspension onto specific positions of solid substrates with nanometric precision. We demonstrate that surfactant-free silicon nanoparticles of a predefined and narrow (σ < 10 nm) size range can be selectively immobilized on a substrate by optical printing from a polydisperse colloidal suspension. The size selectivity is based on differential optical forces that can be applied on nanoparticles of different sizes by tuning the light wavelength to the size-dependent magnetic dipolar resonance of the nanoparticles.

There has been a rapid technological development in the field of polymer-based photonic devices in recent times due to advanced fabrication techniques. Though, effective way to couple the light into the polymer devices is a difficult task. In this paper, we propose a novel technique to overcome the challenges in coupling the light from an optical fibre to a polymer-based photonic device. Unlike in silicon photonic devices where usually grating couplers are used to couple light, the same technique is quite ineffective to couple the light in polymer-based photonic devices due to small refractive index contrast and poor confinement. The proposed device has been theoretically analyzed using Lumerical MODE Solutions in the wavelength range of 1520-1580 nm. The proposed structure consists of a conventional 4-port, add-drop, racetrack resonator with a high-quality factor of 5316.7 for the notch at 1527.8 nm on top of cylindrical pillars of radius 6 μm. The free spectral range of the device is 11.42 nm. Two-photon polymerization based direct laser writing technique has been used to fabricate the device, using IP-DIP polymer. The micro-pillars provide a degree of freedom and lift the entire resonator structure to the desired height, thereby relaxing the vertical mismatch between fibre and the resonator. This method provides a simple method to couple light without using grating couplers or etching the fibre.

Many industrial and research applications benefit from laser beam profiles which are non-Gaussian but rather tailored to that specific application. For example, shaping the beam profile and footprint holds great potential for beam delivery in laser-assisted manufacturing processes. In particular, top hat beam profiles of different shapes and size would enable speeding up additive manufacturing while increasing the resolution of the 3D printed parts. In this paper, we present the design of different beam shapers for high power CO₂ lasers used in laser sintering, which are able to generate respectively square and circular top hat beam profiles. The size of the spot is controlled by using additional lenses to reduce or enlarge the beam size as necessary after the beam shaping optics. A spot size of 0.5 mm or 5 mm diameter can be achieved by switching between different lenses and adjust the distances accordingly. The designed beam shaping optics were subsequently fabricated in-house using ultra-precision diamond tooling in zinc sulfide material which is tolerant to high laser power and transparent at a wavelength of 10.6 μm. This beam shaping optics can form the basis for dynamic beam shaping in which the spot size, spot shape and/or intensity profile can be actively controlled by moving the optical components in the laser beam path.

Additive manufacturing (AM) has provided a new aspect of manufacturing 3D objects in the past few decades. The use of AM for the production of 3D objects has accelerated the rate of designing and manufacturing. These AM techniques can be utilized in manufacturing optical, mechanical and electrical prototypes. The manufacturing of optical prototypes involves the production of spherical lens prototypes and special forms of aspheric and concentrator lenses such as fresnel lens prototypes. Different designed fresnel lens prototypes are manufactured using a transparent clear resin material and stereolithography apparatus (SLA) process. It uses a photochemical process to develop 3D structures. These manufactured fresnel lens prototypes are difficult to postprocess using hand polishing, hence they are post-processed using lacquering to get more transparency. These prototypes are tested using a laser source to evaluate the attenuation of light and focal length of manufactured fresnel lens prototypes. Similar tests using a commercially available convex lens of the same focal length are carried out. The results of these tests show that the difference between the mean of attenuation of light beam when passed through a fresnel lens prototype and the convex lens is 1 dB. The focal length of manufactured fresnel lens prototypes has a 10 mm deviation. Therefore, it is feasible to manufacture complexity and cost reduced fresnel lens prototypes using SLA and lacquering.

Two-photon polymerization is a photochemical process usually initiated by tightly focusing an ultrafast laser pulse into a volume of photosensitive photoresists with a high-numerical-aperture objective. Scanning a write voxel" in 3D enables near free-form fabrication, but at a limited speed which is a critical factor for industrial purposes, because generally only a single writing-beam is used. Several strategies have been implemented to improve the fabrication speed, one such strategy is massive parallelization which is the approach used in our PHENOmenon H2020 European project. Massive parallelization can be realized by beam splitting diffractive optical elements which allow simultaneous fabrication with thousands of beams, decreasing the overall fabrication time. A major unexpected obstacle is encountered in massively parallelized fabrication: using several spots simultaneously to polymerize, local changes in the 2PP threshold have been observed. We linked this to the proximity effect. The aim of this study is to understand the proximity effect in parallel microfabrication using simulation to predict its behaviour and different systematic experiments to reduce the proximity effect such as changing photoresist, using thinner photoresist layers to increase oxygen penetration or using higher Numerical Aperture Objectives.

The paper represents a study on the characteristics and biocompatibility of tissue-engineering structures with nanocarbon scaffolds in the bioorganic matter for various bioengineering applications, including biomedical devices for the heart treatment and neurostimulation. These structures were obtained via a laser formation method. Structures were printed using previously developed laser setup and had a cellular structure in accordance to the cell monolayer formation. It was established that SWCNT bind to amino acids through oxygen atoms. It was observed that the SWCNT diameter increased due to their wrapping by a bioorganic matter. Moreover, electrical conductivity values of such structures exceeded the heart tissue conductivity (0.1 S/m) and reached 8.5 S/m. The proliferation of fibroblasts and endothelial cells on the studied structures was demonstrated via the fluorescence microscopy and the MTT assay. The density of proliferated cells on structures was higher than in control samples. Finally, the biodegradation rate of tissue-engineered structures during the implantation to laboratory animals was 75-90 days, the samples promoted neovascularization of the affected tissue.

Magnetic material is the key component in lot of electromagnetically-based optical to microwave applications. In the case of radio-frequencies/microwave applications, passive components are developed using planar design to facilitate their fabrication while 3D geometries are the best shapes to improve components properties. But nowadays, 3D printing technologies are coming up in industries and 3D design of passive components grows in interest. But 3D shaping of magnetic material remains a problem which has to be solved before considering industrial implementation. In this work, we demonstrate the possibility of 3D shaping ferrite magnetic powder using Selective laser melting/sintering in ambient air. A ferrimagnetic powder of Yttrium Iron Garnet (YIG) was used to form a 10-layers stack of magnetic material. A simple method for small surface (10x10mm²) deposition of powder was developed by dispersing the YIG powder into ethanol. A drop is then deposited on top of a substrate. Ethanol evaporates and an homogeneous layer is obtained. A 1064nm-nanosecond laser combined to a scanning lens is used to irradiate the powder layer and induce melting/sintering of the powder at ambient temperature and in ambient air. Chemical and structural changes induced by the laser process were studied using Raman spectroscopy. Results show that a part of the YIG was decomposed into a weakly magnetic phase of Fe₃O₄. Vibrating Sample Magnetometry was then used to compare the magnetic behavior of the YIG multilayer and the YIG powder. The multilayer always exhibit a magnetic behavior whatever the substrate is: YIG powder, YIG bulk or Al bulk.

Compared with traditional electronic materials (metals and semiconductors), electrically conductive biopolymers have improved compatibility with biological cells and human biological tissues. This allows creating new bioelectronic devices, for example, biosensors, drug delivery devices, 3D tissue-engineering matrix et al. A new laser method has been developed for the 3D manufacturing of electrically conductive nanocomposites with a given architecture. The architecture may be similar to the microelectronic component base (for example, the creation of microchannels between nanocomposite regions for designing transistors). A pulsed ytterbium fiber laser connected to a galvanometric scanner (laser wavelength - 1064 nm, pulse duration - 100 ns, frequency - 100 kHz, irradiation power up to 10 W) was used to form nanocomposites. By the galvanometric scanner, the focused laser beam moved along the trajectory (XYZ) specified in the software. As a result, the samples had the desired geometric 3D shape. Homogeneous dispersions of carbon nanotubes and biopolymers (albumin, collagen and chitosan amino sugar) were used as raw materials on a flexible substrate. The phase transition of the liquid dispersion of nanotubes into a solid was the main mechanism for the nanocomposites formation process. With focused laser irradiation, the temperature in the region of defects in carbon nanotubes increased, in contrast to other regions of nanotubes. As a result, the nanotubes were connected in an electrically conductive scaffold. Nanocomposites had high conductivity values of ~10 S/m, as well as high hardness of 300-500 MPa. The biocompatibility of nanocomposites has been proven in vitro и in vivo.