Lukas Lorenz

Analysis of Bending Effects for Optical-Bus-Couplers

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.

Simulation of bended planar waveguides for optical bus-couplers

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.

Integration of polymer optical waveguides by using flexographic and aerosol jet printing

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.

3D Optical Coupling Techniques on Polymer Waveguides for Wafer and Board Level Integration

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.

The future of short-range high-speed data transmission: printed polymer optical waveguides (POW) innovation, fabrication, and challenges

One of today’s megatrends in the industrial environment is additive manufacturing. Faster prototyping, customized products like hearing devices, integrated functions like heatsinks and many other opportunities are offered by this technological development. The opportunity of using different materials and build up 3-D structures is virtually infinite. Another one is the digitalization of almost any product to build up a smart world. This trend leads to a tremendously rising amount of data to be transferred from one place to another. If a wireless transmission is not possible and if the distance is over 100 m glass fiber is the fastest and most secure way for these requirements. In case of most short-range applications up to 100 m primary copper cables or circuit paths are in use because the electrical data transfer is well known. The limited bandwidth of copper asks for new inventions to meet the demands of tomorrow. Regarding both megatrends, the solution for this upcoming bottleneck could be 3-D printed photonic packages. This paper shows a new and innovative way for the customized fabricating of short-range data transmission networks. By Aerosol Jet Printing (AJP) the so called polymer optical waveguides (POW), it is possible to build up 3-D printed light guiding structures with low attenuation on almost any three-dimensional surface. The main advantages of the here presented research are high flexibility, low weight and low costs. After three years of intensive studies the most important key facts (machine settings, geometry, performance) are summarized in this publication.

Optical coupling with flexible polymer waveguides for chip-to-chip interconnects in electronic systems

Abstract 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.

Asymmetric Optical Bus Coupler for Interruption-Free Short-Range Connections on Board and Module Level

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.

Approach for the production chain of printed polymer optical waveguides–an overview

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).

Development of a wafer-level integration technology for photonic transceivers based on planar lightwave circuits

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.