Hybrid optoelectronic I/Q integrated down-conversion system for terahertz wireless–fiber communications

Fiber-wireless systems offer a promising way to enhance high-capacity wireless services and extend transmission distances by leveraging the low loss and broad bandwidth of optical fiber. They depend on efficient electro-optic receivers in millimeter-wave (mmWave) and terahertz (THz) fiber-wireless systems to convert high-frequency wireless signals into the optical domain. However, traditional down-conversion relies on real-valued IF processing using a balanced mixer, which can generate conjugate spectra that appear as image interference during optical modulation. To address this, we introduce a hybrid electro-optic receiver design that directly connects an electrical I/Q mixer with an optical I/Q modulator, enabling direct electro-optic conversion of complex IF signals. By preserving the inherent I/Q orthogonality, the proposed approach allows optical single-sideband modulation without optical filtering and avoids image components associated with conjugate spectra. Building on this innovative hybrid optoelectronic communication system, we have successfully demonstrated the transmission of 16 Gbaud QPSK signals over a 2-m wireless link and a 5-kilometer single-mode fiber at 142.8 GHz with error-free performance.