Experimental Demonstration of 224 Gbit/s PM-PAM4 IM/DD Transmission System Using TFLN Polarization Controller

In this paper, we experimentally demonstrated 224 Gbit/s polarization-multiplexed (PM) PAM4 intensity modulation and direct detection (IM/DD) transmission system using a thin-film Lithium Niobate (TFLN) polarization controller. We proposed and implemented a pilot-tone-assisted and calibration-free polarization tracking algorithm in an FPGA, achieved a record convergence time of 0.2 ms and polarization tracking speed of 2 krad/s for PM-IM/DD systems. The proposed scheme enables stable dual-polarization demultiplexing under fast polarization perturbations and represents a step towards practical high-speed, low-complexity PM-IM/DD systems with robust polarization tracking performance.