224-Gbit/s PM-IM/DD transmission using hybrid optical-electrical polarization tracking with SiP polarization controller.

We propose and demonstrate a hybrid optical-electrical polarization tracking scheme for a 224-Gbit/s polarization-multiplexing intensity modulation and direct detection (PM-IM/DD) system using a silicon photonics (SiP) polarization controller. Optical polarization tracking is first employed at the receiver front-end to suppress polarization crosstalk and reduce mixed polarization beating interference (MPBI) to an acceptable level, enabling blind low-complexity electrical multiple-input multiple-output (MIMO) equalization. Compared with optical tracking alone, the proposed scheme achieves nearly an order-of-magnitude reduction in both average and maximum BER under a polarization scrambling rate of 200 rad/s. As a result, the maximum tolerable polarization tracking speed under the hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10-3 is doubled from 100 rad/s to 200 rad/s without upgrading the SiP polarization controller. These results demonstrate that electrical-domain compensation effectively relaxes the requirement on optical tracking speed for PM-IM/DD transmission in scale-up/scale-out short-reach optical interconnects for artificial intelligence (AI) data centers.