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 SU-8 (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.

I. Introduction

It is widely known that the global communication traffic is growing exponentially within the next decade. Optical communication can attenuate the increase of the electrical energy consumption by its superior energy efficiency compared to electrical communication [1]. Optical waveguides have already replaced electrical waveguides in wide and medium range connections. It is marginally predicted that optics will have their commercial market entry for short range and chip to chip interconnection by 2025 with bandwidth above Tb/s [2].