Purely Photonic Wireless Link at 120 GHz With a Photoconductive Antenna as Heterodyne Receiver

Optoelectronic generation and detection of THz signals are well-established in THz-sensing. Beyond sensing, there is great potential for using these photonic devices for wireless communication at (sub-)terahertz carrier frequencies. While photodiode-based emitters are often used in broadband wireless links, receivers based on photoconductive antennas are rarely found due to their limited electrical bandwidth of the intermediate frequency (IF). To demonstrate the potential of fully photonic wireless links, we have developed an efficient photoconductive antenna (PCA) that is integrated with a passive radio frequency (RF) circuit to support high IFs. The PCA is based on iron-doped indium gallium arsenide (InGaAs:Fe) and is packaged in a compact fiber-pigtail module. The RF transition from the antenna to coaxial output provides an IF bandwidth of 11 GHz enabling wide data channels. With this receiver, we report on a purely photonic wireless communication link over a distance of 1 m using a PIN photodiode as the transmitter. Using quaternary quadrature amplitude modulation (4-QAM), we achieved error-free data transmission at net data rates of up to 10 Gbps. This successful demonstration is an important step towards realizing the full potential of photonic technology in (sub-)THz communications.