510-Gbps 322-GHz Photonics-Aided Terahertz Wireless Transmission System With MIMO Embedded Adaptive Phase Recovery Equalizer

Photonics-aided terahertz (THz) technologies in capable of supporting large signal bandwidths are promising in future ultrahigh-speed wireless communication systems, especially the THz-over-fiber (ToF) indoor applications. $2 \times 2$ multiple-input-multiple-output (MIMO) architecture for polarization-division multiplexing (PDM) can further double the system capacity with polarization dimension, while bringing more crosstalk and impairments to signal recovery. In this article, we propose to apply a MIMO equalizer with embedded adaptive phase recovery (eAPR) and independent channel processing (ICP) (MIMO-ICP-eAPR) digital signal processing (DSP) to better compensate for the crosstalk and impairments in a $2 \times 2$ MIMO PDM THz transmission system. With the novel MIMO-ICP-eAPR and photonics-aided THz-wave technologies, we experimentally demonstrate 60-GBaud probabilistically shaped (PS)-64QAM signal transmission over 20-km fiber and 3-m THz wave at 322 GHz in the air, empowered by a $2 \times 2$ MIMO antenna array for PDM technologies. The adaptive phase recovery (APR) integrated with MIMO equalizers can provide a better performance compared to separately applying MIMO equalizers followed by APR. Compared to the APR-separated counterpart, the proposed MIMO-ICP-eAPR can improve the input power sensitivity by 0.6 dB. Furthermore, even without ICP for mitigating IQ crosstalk, the MIMO-eAPR approach still shows performance enhancement compared to MIMO followed by APR. To the best of our knowledge, a record-breaking net rate of 510 Gbps per wavelength for a THz-wave transmission system with PS signals is reached. This work can provide fiber-THz architecture as well as a solution for future THz applications.