Flexible Multimode Polymer Waveguide Arrays for Versatile High-Speed Short-Reach Communication Links

Optical interconnects play an important role in enabling high-speed short-reach communication links within next-generation high-performance electronic systems. Multimode polymer waveguides in particular allow the formation of high-capacity optical backplanes and cost-effective board-level optical interconnects. Their formation on flexible substrates offers significant practical advantages and enables their deployment in environments where shape and weight conformity become particularly important, such as in cars and aircraft. However, bending and twisting of flexible multimode waveguides can have a significant effect on their optical transmission performance due to mode loss and mode coupling. Moreover, the magnitude of the induced effects strongly depends on the launch conditions employed. In this paper, therefore, we present detailed loss, crosstalk, and bandwidth studies on flexible multimode waveguide arrays for different launch conditions regarding their use in real-world systems. The minimum radius to achieve a 1 dB excess bending loss is obtained for each launch condition as well as the crosstalk degradation due to bending. It is shown that for a 50 μm MMF input, a 6 mm bending radius is required for excess losses below 1 dB, while crosstalk below -35 dB is obtained in adjacent waveguides even under strong bending. Moreover, it is found that twisting has a small effect on the loss and crosstalk performance of the samples. Excess twisting loss less than 0.1 dB and crosstalk of -40 dB are obtained for three full 360° turns under a 50 μm MMF launch. Finally, the bandwidth studies carried out on the samples indicate than no significant bandwidth degradation is induced due to sample bending, with bandwidth-length product values larger than 150 GHz × m obtained for restricted launches. The set of results presented herein specify the deployment of this flexible polymer multimode waveguide technology in real-world systems and demonstrate its strong potential to implement low-loss high-bandwidth optical interconnects.