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In this article, we give an overview of the development of an asymmetric optical bus coupler (AOBC) from the theoretical basis, the optical continuous wave, and bit rate performance to the implementation in a 3-D-Opto-MID package. The coupler allows for an interruption-free and bidirectional connection between two multimode waveguides, with different coupling ratios at the same node up to an aspect ratio of 5:1 depending on the coupling direction. For the first time, data transmission up to 12.5 Gbit/s is demonstrated with the AOBC, as well as the full implementation of the coupling element into a 3-D-Opto-MID package including an electrical test circuit.

This article presents an innovative way for additive manufacturing of optical multimode waveguides for short range data transmission. By the use of aerosol jet printing between conditioning lines on flexible foils, low cost, and low weight polymer optical waveguides can be easily fabricated. The main advantages – compared to other waveguide manufacturing techniques – are the maximum fabricable waveguide length (not limited by panel- or wafer size), technology costs and 3D-ability. Furthermore, the printing allows for very long structures, which are not limited to wafer or panel sizes. In order to classify the new manufacturing approach and compare it to other technologies such as photolithography, imprinting, dispensing and ion-exchange, results on the mechanical (shear strength) and optical performance (transmittance, near field and attenuation) are presented. In addition, the experimental results on the data transmission performance are important to prove the suitability of the waveguides for high-speed communication applications. In this context, nearly error-free transmission up to 10 Gbit/s was achieved at a wavelength of 850 nm.

This paper describes simulation, technology- and process development for the manufacturing of single mode polymeric waveguides by photolithography. Simulations for single mode operation in O- and C-band are carried out. Waveguides are directly patterned with UV-photolithography using Ormocere®-material. Fiber to waveguide coupling and near field are characterized.

In this paper we investigate the long-term stability and reliability of a 3D-Opto-MID package for multimode waveguide bus coupling. Preliminary works proved an interruption-free coupling approach with asymmetric coupling rates depending on the coupling direction for optical bus systems. This is possible thanks to a coupling at the side-faces of the waveguide cores where one coupling partner has a defined bending to achieve the asymmetric coupling. Crucial for this defined bending are three-dimensional assemblies. For this, we developed a mixed-material package based on ceramic thick-film substrates combined with stereo-lithographic printed polymers. Because of the different material parameters, we analyzed the package behavior in a high temperature storage, a temperature humidity and a temperature cycle test. The results of the reliability tests enable specific further development of the package and thus make an important contribution to the intended series production of the 3D-Opto-MID technology.

Printing polymer optical waveguides by means of combined printing processes has proven to be a challenging but effective way of producing waveguides with a loss less than 0.3dB/cm. In order to evaluate the optical performance of the produced waveguides, optical simulations have been carried out. In this work we show the influence on the optical performance by simulating droplets and enclosures in multimode waveguides with a proprietary raytracing algorithm. Critical waveguide parameters such as width and height variation will be evaluated. Finally, experimentally achieved optical performance is presented and compared with the simulation result.

In order to meet the increasing demand for data transmission over short distances of up to 100 m, the Optical Assembly and Connection Technology for ComponentIntegrated Bus Systems (OPTAVER) research group, funded by the German Research Foundation (DFG), developed a process for the additive manufacturing of three-dimensional optical waveguides. The research group focuses on design and modeling, simulation, and manufacturing polymer optical waveguides to produce 3D-Opto-Mechatronic-Integrated Devices (3D-Opto-MID). Inside 3D-Opto-MID, an optical coupler is presented based on an asymmetrical coupling principle. This paper reviews the entire process chain and the corresponding research results of the OPTAVER process.

A novel coupling approach with specific coupling ratios depending on the coupling direction (optical bus to electro-optical device and vice versa) is presented. According to that, an asymmetric optical bus coupler (AOBC) is obtained, where a high amount of light is coupled from a device/module into the optical bus, whereas the ratio in the opposite direction is significantly smaller to keep enough energy in the bus for later coupling. This is realized without any filters by a specific bending of the waveguides. Hence, an up to four times higher coupling ratio in the module-to-bus direction is achieved compared to the opposite direction at the same junction. In contrast, current coupling schemes have a 1:1 coupling, waveguides are interrupted or filters are used. In this paper, we investigate the influence of temperature on the AOBC. For that, we constructed a special measurement setup, which allows for a controlled temperature change only at the coupling point. With this setup, we investigated the influence of temperature (up to 80°C) on the bus coupling over 48 hours. The measurements revealed, that the coupling power rises with increasing temperature and vice versa. With an additional vision system, we observed the enlargement of the contact area of the waveguides (coupling area), because of thermal expansion, which leads to the change of the coupling power. Besides this variation, the coupling point is damaged at 20°C/80°C cycles because of the high mechanical load. However, at 20°C/60°C cycles, the AOBC is stable over the measuring period.

The development of easy-to-use optical bus-systems without the need for waveguide interruption is one important step to establish optical interconnects in short- to midrange networks. The challenge from the packaging side of view is the three-dimensional integration of optical parts and waveguides to a novel kind of package, called 3D-Opto-MID. In this article, we present an approach for stereolithographic printed, three-dimensional polymer structures on ceramic thick-film substrates. Thus, we are able to combine the design freedom of 3D printing with the excellent RF- and heat-management properties of the thick-film technology, especially important for electro-optical (e/o) converters. On the three-dimensional structures, the waveguides for the bus-coupler are applied, while the ceramic holds the electro optical converters. Furthermore, the 3D printing allows for easily manufactured alignment- and fixing structures for the coupler with a high accuracy. The results section shows the analysis of the adhesion behavior of the printed polymer on the ceramic, as well as the obtainable tolerances with the printed alignment structures. The average accuracy of the alignment was measured with 31.1µm, which is sufficient for the used 200 µm multimode waveguides. Furthermore, we demonstrate the functionality of the optical path of the module assembly, as well as the coupling to a bus waveguide, which proves the success of the 3D-Opto-MID integration.

This paper discusses a novel packaging approach for electro-optical (E/O) co-integration of IC-chips to realize hetero-integrated transceivers for optical chip-to-chip (C2C) communication. For an integration of chip-components into optical transceivers a polymer package fabricated using additive manufacturing methods are applied. Based on two optical transceiver assemblies - VCSEL-based and Si-photonic-based - different requirements on the package are discussed. For the Si-photonic chips measurements on the lateral and angular misalignment requirements have been performed. The results of the characterization of grating couplers show that the maximum lateral misalignment for 1dB-loss vary between ± 1 µm and ± 3.5 µm. For the angular sensitivity the 1dB-tolerances of +/- 2° at the in-coupling interface and of about +/- 0.4° at the out-coupling have been measured. The simultaneous IC-device embedding and chip-carrier fabrication using casting method is proposed. By subsequent build-up of dielectric/metal multilayer stack an electrical and optical redistribution network for routing of both optical and electrical signals can be realized. A hybrid polymer Ormocer® material has been applied as optical and dielectric material enabling the E/O co-integration using one material class. The performance of this material in both domains optical and RF has been proven. Based on attenuation measurements of multimode optical waveguides low-loss transmission of < 0.05 dB/cm at 850 nm wavelength has been shown. Based on transmission-line (TL) measurements in the frequency range of 140 GHz to 220 GHz the superior dielectric properties with TL-losses of about 1.1 dB/mm have been achieved.

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.

This contribution discusses technology development for the realization of chip-to-chip interconnection based on flexible optical waveguides. Two approaches for optical coupling between waveguides and active devices are presented. Both approaches built on the planar polymeric optical multimode waveguides integrated on flexible substrates (PEN-foil). This waveguides structured using UV-photolithography and Ormocere-materials feature low optical attenuation below 0.05 dB/cm. The first approach for coupling between optical waveguides uses a bidirectional interruption-free waveguide coupler. The principle bases on directional core-core-coupling and allows for adjustable coupling ratio by tuning the overlap area. In addition, an asymmetric coupling behavior depending on the coupling direction due to a bending of one of the coupling waveguides is achieved. This coupling method shows supremacy for optical bus systems where tunable, asymmetric coupling ratios are desired. The second optical coupling approach for waveguide-to-chip coupling bases on out-of-plane optics. Direct integration of 45° micro-mirrors into polymer waveguides using dicing process is investigated. Two approaches for optoelectronic (OE) subassembly with flexible optical waveguides are considered one with flip-chip bonded and one with embedded OE-devices. Using optical characterization the influence of fabrication parameters on the optical performance of diced mirrors with insertion power loss measurement is derived and presented.

In this paper, we present a bidirectional interruption-free multimode waveguide coupler for optical bus systems on board and module level. The principle is based on directional core–core coupling and allows for adjustable coupling powers by tuning the overlap area. By adding a bending to one of the coupling partners, it is possible to obtain specific asymmetric coupling rates depending on the coupling direction (module to bus or vice versa). The proposed approach is extensively analyzed by optical simulation (beam propagation method) and measurements including experiments on the attenuation, the coupling rate, and the bit rate performance.

The reduction of frictions losses in the drivetrain of modern internal combustion engines is one of the main development paths to lower fuel consumption and thus the CO2 emission.

In order to build high performance 3D-Opto-mechatronic integrated device packages, we demonstrate the direct stereolithographic printing of polymeric resins onto ceramic substrate. The effects of adhesion are examined, the lower size limit for structures is found and the adhesion strength is measured. With the results a suitable combination of materials can be chosen for creating a hybrid package for a 3D-Opto-mechatronic integrated device. A prototype of an optical coupler is printed successfully and shows one possible application.

A novel coupling approach with specific coupling ratios depending on the coupling direction (optical bus to electrooptical device and vice versa) is presented. According to that, an asymmetric optical bus coupler (AOBC) is obtained, where a high amount of light is coupled from a device/module into the optical bus, whereas the ratio in the opposite direction is significantly smaller to keep enough energy in the bus for later coupling. This is realized without any filters by a specific bending of the waveguides. Hence, an up to four times higher coupling ratio in the module-to-bus direction is achieved compared to the opposite direction at the same junction. In contrast, current coupling schemes have a 1:1 coupling, waveguides are interrupted or filters are used. In this paper we investigate the influence of the waveguide manufacturing technology on the coupling performance. The standard photolithographic waveguides with rectangular cross-sections are compared to Aerosol Jet printed waveguides with circular segment cross-sections. Furthermore, we monitored the coupling for several days to get results on the stability. The results show a fluctuation of about ± 20 % for the printed waveguides and about ± 5 % for the photolithographic ones.

In this article, we present a coupling concept for an interruption-free asymmetric bidirectional optical bus coupler for board and module level. With this approach, it is possible to connect several electro-optical devices to a single waveguide. A core-to-core connection principle is used, where the cores get into physical contact at their side faces. The coupling ratio can be tuned by adjusting the overlap area of the two cores with different contact pressures. Because of a bending in one of the waveguides, it is possible to achieve a specific asymmetric coupler design, where the coupling ratio depends on the coupling direction (bent waveguide to rigid one or vice versa). To derive design rules for prototyping, a simulation is performed using two different independent approaches for cross-checking. With a ray tracing simulation, coupling ratios and energy distribution within the bent core are analyzed. In addition, a simulation with the beam propagation method is used to take wave optical effects into account as well as to establish a holistic view on the coupling concept.

To improve printing results, a printing form can be functionalized and the material transferring behavior can be adjusted. In this work, a flexographic printing form is divided into three different areas: first the elevated, material transferring structures (1); second the rising edges between the printing form substrate and the elevated structures (2); and third the transition area (3) between (1) and (2). These three areas are laser functionalized by inserting a defined micropattern. Subsequently, the printing results are investigated and categorized into groups. The groups indicate which functionalized surfaces (1, 2, and 3) have what kind of influence on the printing result. As part of a low cost and efficient approach to manufacture polymeric optical waveguides, a way is presented to show how the waviness of printed conditioning lines can be reduced significantly by laser functionalizing to improve the quality of the waveguides.

This paper shows the modeling, simulation and production of polymer optical waveguides using the OPTAVER process. The additive manufactured multimode waveguides with their typical cross-section of a circle shape are of low cost and high-performance.

Recent fabrication methods print polymer optical waveguides (POWs) on three-dimensional carriers. The special geometry of the POWs enables the realisation of an optical ray splitter which is simulated by raytracing using a new bisection-algorithm.

This paper presents a simulation approach, with which results on multimode bending couplers are obtained much faster than with traditional methods. This is achieved by a two-stage simulation combining ray tracing and beam propagation method. Using this approach, design rules can be obtained faster with a simultaneous cross-check of the results. Hence, a more reliable prediction is achieved. The main challenge in the presented example is the exact ray tracing simulation of curved waveguides with program-own methods without selfprogrammed routines, which is solved by interlaced cylindrical volumes. Prior to the simulation approach, upcoming requirements for photonic networks for internet of things and industry 4.0 applications are discussed. Due to that, a paradigm shift – away from the traditional packaging levels to the new definition of device communication – is proposed in this work.

In this work we present the additive manufacturing of optical multimode waveguides on flexible foil by aerosol jet printing. In order to obtain higher aspect ratios for the waveguides, the foils are conditioned by a flexographic printing step in advance. This technique is used to manufacture asymmetric bus couplers, which allow for coupling without waveguide interruption. They follow the working principle of directional core-core-couplers but have different coupling ratios depending on the coupling direction, due to a bending of one of the coupling partners. The latest results on the printing process are shown, especially the laser structuring of the flexographic printing form to optimize the condition lines. Also the attenuation of the printed waveguides is measured as well as the coupling results of the asymmetric bus coupler. Especially the coupling powers and the strength of the asymmetric effect are shown.

In this work we discuss optical coupling technologies for the manufacturing of out-of-plane optics integrated in planar waveguide for interposer-and board-level. Each technology is evaluated on a silicon interposer with optical dielectric through silicon vias (TSV) with SU8 (core) and SiO2 (cladding). First, applying a nanoimprint technology a polymer waveguide has been created with round-shape curvatures to realize focusing of the light, which enhances the coupling efficiency. Furthermore due to the round shape the light is focused in the waveguide to reduce the transmission losses. Additionally as a second technology a moving mask method is shown to achieve a tilted mirror face by this special exposure procedure for better compability of mirror fabrication with lithography processes. As a third technology the mirror fabrication by dicing into a polymer waveguide has been applied, which results in a V-groove mirror. The feasibility of all fabrication technologies have been performed on rigid substrate. For enhanced yield of electro-optical system implementation of out-of plane optics on flexible substrate has been performed. In this case diced mirrors have been manufactured on polymeric waveguides with Ormocere® on a flexible PEN-foil. The influence of dicing blade on optical losses caused by the scattering on rough diced mirror surface has been analyzed. The min. power losses of the diced mirror of 0.22 dB have been measured.

As a tribute to the continuously increasing volume of data traffic, optical waveguides have become a serious alternative to electrical circuitries. The potential of precise spaceresolved strain measurements or the capacity to transmit very large amounts of data are two examples of the beneficial use of optical systems. Apart from the general advantages of the optical signal line, like high electromagnetic compatibility, usage in explosive atmosphere or the reduced weight compared to copper cables, modern technologies make use of the possibilities to integrate optical waveguides into structural components. The printing of polymer optical waveguides is part of the current research in functional printing technology. Optimizing the transmission quality and the resolution are key objectives to establish integrated optical data transmission in industry. The manufacturing of multimode waveguides presented in this work is accomplished by a combination of two printing processes. Before producing the optical waveguide itself, using Aerosol Jet Printing, pre-conditioned areas with either hydrophobic or hydrophilic behavior are generated on flexible substrates with an adapted flexographic printing mechanism. This two-stage process allows for the fabrication of step index waveguides featuring parabolic cross sections with minimum widths down to 10 μm and aspect ratios of about 0.3. Conditioning the substrate, which itself forms the bottom cladding, provides a low surface roughness of the optical core. This paper shows the latest results of printing polymer optical waveguides, focusing on actual challenges and optical transmission quality.

Goal of the presented work is the development of an optical bus-coupler, which enables easy connection between two waveguides without interrupting the bus. It is possible to realize optical bus systems by connecting several modules onto one waveguide with a core-core-coupler. In this paper we present the concept of a bus-coupler, which is suitable for a bidirectional coupling with a definable ratio. In order to tune the coupling efficiency bended flexible planar waveguides are used, which are pressed onto the bus with a defined force adjusting the overlap area of the two coupling waveguides. We will introduce the manufacturing of the multimode waveguides on flexible substrates by photolithographic structuring. Furthermore, we present results of our investigations on the behavior of planar waveguides under bending in terms of optical losses and power distribution within the waveguide core. Based on the experimental results we will derive the requirements and design rules for the coupling element.

In our work an optical bus-coupler is proposed, which enables easy bidirectional connection between two waveguides without interrupting the bus using a core-to-core coupling principle. With bended waveguides the coupling ratio can be tuned by adjusting the overlap area of the two cores. In order to ensure large overlap areas at short coupling lengths, the waveguides have rectangular cross sections. To examine the feasibility of this coupling concept a simulation was performed, which is presented in this paper. Due to multimode waveguides, used in short range data communication, a non-sequential ray tracing simulation is reasonable. Simulations revealed that the bending of the waveguide causes a redistribution of the energy within the core. Small radii push the main energy to the outer region of the core increasing the coupling efficiency. On the other hand, at excessive lowered bend radii additional losses occur (due to a coupling into the cladding), which is why an optimum has to be found. Based on the simulation results it is possible to derive requirements and design rules for the coupling element.

Research for new production chains in the field of waveguide fabrication is a challenging task. Realizing a cost efficient manufacturing process allows integrating optical data communication in arbitrary structures, for example, the wing of an airplane or the body of a car. The production chain described in this paper contains the design, simulation, and fabrication process of printed polymer optical waveguides (POWs).

For sensor systems and data communication, electro optical integration technologies are an auspicious alternative to conventional electronic system integration. To make the photonic integration more attractive compared to electronic integration technologies, packaging concepts are required which are suitable for mass production using standard processes of the electronics packaging. In this paper, a photonic transceiver integration technology is proposed. To take advantage of the development environments and processes commonly used in electronics packaging, a planar assembly strategy is preferred. That is why the concept uses glass substrates with planar lightwave circuits (PLC) and passive fiber chip coupling. By the use of flip-chip VCSELs and photodiodes, standard pick-and-place assembly becomes possible. Hence, a wafer-level manufacturing in high quantities is feasible. Additionally, the development processes for the photonic integration are of special interest in this paper. Until now, there is no development environment available to model or simulate entire optical devices in one workflow. Every sub part of the model requires a single tool instead. By using 3D-CAD, this work proposes to merge several sub-models into a single tool and achieves largely a simplified development of planar optical devices.