Cost-Effective Photonics-Based THz Wireless Transmission Using PAM-N Signals in the 0.3 THz Band

We investigate the feasibility of pulse amplitude modulation-N (PAM-N) signal transmission over a photonics-based cost-effective THz wireless link. A direct detection-based THz wireless link was established by using commercialized optical and electrical components designed for the WR 3.4 frequency band (220-330 GHz). At the THz signal transmitter, a uni-traveling carrier photodiode (UTC-PD) was used as a photomixer. The maximum output power of the UTC-PD was ~47 μW when it was supplied with +17 dBm of optical power. At the THz signal receiver, the Schottky barrier diode was used as a diode detector; an offline digital signal processor (DSP) with a decision feedback equalizer was also used to mitigate the inter-symbol interference penalty. In the back-to-back configuration (i.e., antenna of Tx and Rx are placed at a distance of ~1 cm), the driving condition of the optical modulator was optimized to obtain the best transmission performances of the PAM-N signal. A carrier frequency of 300 GHz is carefully selected considering the bit error rate (BER) dependency on the carrier frequency. After the optimization procedure, the BER performances were analyzed by varying the PAM order, baud rate, and wireless transmission distance. Finally, a 90 Gb/s PAM-8 signal is successfully transmitted over a wireless distance of 1.4 m, in which the measured BER is below the 20% soft-decision forward error correction threshold (2.0 × 10
^-2
).