Optical loss and crosstalk in multimode photolithographically fabricated polyacrylate polymer waveguide crossings

Abstract

Complex interconnection patterns in electrical PCBs have to use multiple layers of copper tracks. However, the same interconnections can be made in a single layer using optical waveguides as they cross on the same layer. Waveguide crossings where two waveguides intersect in the same optical layer are particularly important components as they offer OPCB layout designers additional flexibility to solve layout problems such as routing around cutout areas, electrical components and other obstacles on an OPCB. Use of waveguide crossings can also help to avoid sharp bends in the design as these bends are an important cause of optical loss. Despite all of the advantages of waveguide crossings, and although most of the light travels along the intended waveguide, a proportion of the optical power in one waveguide will couple into the crossing waveguide at each intersection point or couple out of the original waveguide and into the cladding. This coupling phenomenon causes optical loss and crosstalk in the system. In this paper, the results of an investigation of the optical loss due to the crossing of multimode polymer waveguide, fabricated on FR4 printed circuit boards, PCBs, as a function of crossing angles are presented theoretically and experimentally. The results from ray tracing simulation is compared with the experiment results and the contrast is discussed.