Spectrally Efficient PDM-Twin-SSB Direct-Detection THz System Without Active Polarization Control

This Letter proposed a spectrally efficient polarization division multiplexed (PDM) twin single-sideband (twin-SSB) transmission scheme for direct-detection THz communication systems. The optical carrier of the twin-SSB is added at the optical THz converter, rather than being generated at the optical transmitter as in traditional SSB scheme. Hence the direct detection of each polarization branch of the PDM-twin-SSB signals at the THz receiver can be achieved, without active polarization control. Moreover, the SSB field recovery enabled by Kramers-Kronig algorithm can effectively eliminate the signal-to-signal beating interferences and contributes to better polarization de-multiplexing. The feasibility of the proposed scheme is verified with 5.75-GBd 16-quadrature amplitude modulation PDM-twin-SSB signals transmission over the 300-GHz direct-detection THz communication system by simulation. This scheme can not only significantly improve the spectral efficiency of direct-detection THz communication systems, but also effectively enhance the system's operability and robustness.