4096-QAM Signal Transmission by an IM/DD System at THz Band Using Delta-Sigma Modulation

The transmission of high-order quadrature amplitude modulation (QAM) signals in a low-cost intensity-modulated direct detection (IM/DD) THz-band communication system at 300 GHz is experimentally demonstrated in this letter. The system employs delta-sigma modulation (DSM) technology to encode the baseband waveform of the high-order QAM signal into a one-bit quantized on-off keying (OOK) signal and utilizes a low-cost envelope detector (ED) for signal reception. Compared with high-order QAM or multi-level PAM signals, transmitting OOK signals can effectively alleviate ED saturation effects and reduce nonlinear impairment. After 1-m wireless transmission, the bit error rate (BER) of the 4096-QAM is below the 20% soft decision forward error correction (SD-FEC) threshold of
$2.4\times 10 ^{-2}$
. To the best of our knowledge, this is the first application of DSM technology in the IM/DD THz-band wireless transmission system.