A simple independent triple-sideband THz signal generation and detection scheme based on delta-sigma modulation and heterodyne detection

This paper proposes a scheme for the transmission and generation of independent triple-sideband (TSB) terahertz (THz) signals based on delta-sigma modulation (DSM) technology. The method converts multi-sideband high-order quadrature amplitude modulation (QAM) signals into a low-order quadrature phase shift keying (QPSK) signal, enabling the transmission of independent TSB 256/512QAM signals. Compared to directly transmitting high-order QAM signals over the standard single-mode fiber (SSMF), the signal after the DSM modulator reduces the average energy and enhances the system's noise resistance. The system achieves an improvement in optical signal-to-noise ratio (OSNR) gain of at least 2.5 dB. The receiver sensitivity gain for back-to-back (BTB) transmission and 60 km SSMF transmission is at least 1.5 dB and 2 dB higher, respectively. Additionally, at the receiver end, the original signal can be restored by simply eliminating out-of-band quantization noise through low-pass filtering, without the need for an additional digital-to-analog converter (DAC), which contributes to cost reduction. Simulation results demonstrate the successful transmission and detection of independent TSB 256/512QAM signals over SSMF at 320 GHz frequency, achieving a maximum transmission distance of 60 km. The bit error rate (BER) remains below the hard decision forward error correction (HD-FEC) threshold of 3.8 × 10^-3, confirming the feasibility and effectiveness of the proposed scheme.