A 262-GHz Wireless IFoF Uplink With Remote Down-Conversion Using Optically Generated Sub-THz LO

We experimentally demonstrate the feasibility of a 262-GHz wireless intermediate frequency (IF)-over-fiber (IFoF) uplink with frequency down-conversion at a remote antenna unit (RAU). To distribute many RAUs for the coverage of terahertz (THz) wireless communications, it is important to simplify the RAU for the THz uplink. The remote down-conversion with a subharmonic mixer and a uni-traveling carrier-photodiode (UTC-PD) is driven by two optical tone signals from the central office (CO). This can reduce the high-frequency and wideband devices of the networks. Instead of coherent detection, the RAU can be simplified with optical transmission and direct detection (DD) by using a conventional optical modulator and a photodiode (PD). We measured the phase noise of the system and compensated for it with blind phase recovery. Then, the error vector magnitudes (EVMs) of the received signals were measured as a function of THz Tx power, optically generated local oscillator (LO) power, and THz wireless link distance. Single-channel 45- and 30-Gb/s data transmission was achieved over a 5-km fiber and 1-m THz wireless link based on soft- ( $2\times 10^{-2}$ ) and hard-decision ( $3.8\times 10^{-3}$ ) forward error correction (FEC) thresholds, respectively.