Bending loss improvement and twisting loss studies of flexible multimode polymer waveguides

© 2020 SPIE. Multimode polymer waveguides have attracted considerable interest for use in high-speed on-board communication links as they provide low loss (40 GHz×m) and can be cost-effectively integrated onto standard PCBs. The fabrication of such waveguides on flexible substrates can provide additional advantages: shape flexibility, lightweight and reduced thickness which are particularly important in the aviation and automotive industries. Such flexible and lightweight optical connections will play an important role in next-generation airplanes and driverless cars connecting the multitude of peripheral sensors with the central processing unit at high speed and low latency. However, in such applications, flexible polymer waveguides are required to be bent to meet their stringent space requirements and twisted or stretched when connecting movable parts. Under sharp flexure, the bending or twisting loss dominates the waveguide loss limiting their practical use. In this work therefore, we present a new waveguide design for flexible polymer waveguides with improved bending performance and derive useful layout rules for minimizing twisting losses in such samples. The proposed waveguide structure only requires one additional fabrication step and achieves bending losses below 0.5 dB for a 3 mm bend. In comparison, the conventional waveguide design yields a 2 dB loss under the same bending radius and launch condition. Additionally, useful equations relating the maximum allowed number of twisting turns for low excess loss with sample thickness and width are proposed. Bending and twisting measurements on flexible waveguide samples are presented validating these methods and demonstrating the potential of this technology