Ultra-wideband photonic frequency-hopping waveform generator enabled by optical injection locking for secure terahertz wireless communications

Terahertz (THz) wave technology has garnered significance in various cutting-edge applications in recent years, including 6G communications, high-resolution imaging, and non-destructive detection. The challenge of generating wideband THz signals has catalyzed significant research efforts. This paper focuses on the advancement of wideband frequency hopping technology and its use in THz systems to enhance the robustness and security of information transmission, thereby mitigating the potential impact of interference and eavesdropping. We propose a scheme for generating ultra-wideband frequency hopping THz signals based on optical injection locking, which is capable of automatically and precisely selecting specific frequencies from an optical frequency comb based hopping set, and also simultaneously providing power amplification. This scheme offers both flexible tunability and narrow-band filtering compared to traditional methods, enabling dynamic management of THz frequency coordinates within the optical domain following optical beating. Rate equation modeling of semiconductor lasers under optical frequency comb injection conditions is elaborated to investigate the nonlinear dynamics, and thereby determine the optimal conditions for injection-locking state through numerical solutions. Experimental validation confirms operational functionality in the 115-140 GHz range with a 5 GHz hopping interval across six channels, resulting in a total hopping bandwidth of 25 GHz. Additionally, high-speed wireless transmission of Quadrature Phase Shift Keying (QPSK) signals at a 5 Gbps rate are successfully achieved, with a bit error rate (BER) of ${\bf 2.5\times 10^{-3}}$ . This will be a viable solution for secure terahertz frequency-hopping wireless communications.