Flexible Polymer Waveguides for High-Speed Short-Reach Links

This dissertation presents a detailed study of flexible polymer waveguides for used in short-reach communication links. Flexible polymer waveguides enable a wider range of applications as compared to the rigid polymer waveguides, especially for the rack-to-rack links and data bus systems in autonomous car and avionic industry. However, their optical performance including bending and twisting loss, crosstalk, bandwidth and mode coupling behaviour hasn’t been studied in detail when the flexure is applied to the waveguide. This research quantifies those performances when flexible polymer waveguides are being flexed and provides a useful guideline when designing those flexible polymer links in the real world. In addition, some suggestions have been discussed, which can be used to improve waveguide loss performance. A lot simulation work has been done to support the observations from the experimental results. The flexible polymer waveguides are proven to be robust and have low propagation loss (0.03 dB/cm) and high temperature resistance (up to 350 °C). They can be bent down to 2 mm without cracks and the resultant excess bending loss can be less than 2 dB. The excess twisting loss is also shown to be very low, around 0.02 dB for 4 × 360° full twisting turns as long as lateral tension is carefully reduced. The crosstalk results reveal their values are < -25 dB under any launch conditions when waveguides are flexed. The dynamic behaviour study shows that flexible polymer waveguides are robust and can work dynamically for a long-time horizon. In addition, a new design of flexible polymer waveguides has been proposed which can reduce the excess bending loss to around 0.5 dB at 2 mm bending, which is a big improvement. As for the mode coupling behaviour, both simulation and experimental works have been done to investigate how optical modes will evolve due to the small bends, micro bends and rough sidewalls. A better understanding of propagation mechanism inside waveguide is given and discussed. Then, the ultra-short laser pulse measurements are carried out to get the bandwidth length products (BLP) of the waveguides under flexure. The results indicate polymer waveguide can support over 100 GHz×m BLP and small bends have the ability of improving bandwidth performance further. At last, a 40 Gbps transmission over 1-m spiral flexible polymer waveguides under different bending radius has successfully been demonstrated