High-performance and Scalable Four-mode Cyclic Mode Converter Enabled by Semi-inverse Designed Directional Couplers

We present a high-scalability, wide-bandwidth, and high-performance four-mode cyclic-mode converter based on efficient semi-inverse design with variable-length segments. The measured insertion loss is $(\lt)1.8 \mathrm{~dB}$, the crosstalk is $(\lt)-15 \mathrm{~dB}$, and 110 Gbps -PAM4 signal transmission is experimentally achieved. © 2025 The Author(s)