Photonic Frequency Hopping and De-Hopping System by Ultra-Fast Wavelength Tunable Laser for Secure Terahertz Wireless Communication

To address eavesdropping risks in terahertz (THz) wireless communications, we developed a photonics-based THz carrier frequency hopping (FH) system. Our system employed an electro-optically wavelength tunable laser (WTL), enabling pseudo-random hopping by photomixing across three carrier frequencies in the 230-310 GHz range with a 40 GHz interval. Leveraging the ultra-fast wavelength tunability of the electro-optically WTL, nanosecond-level carrier frequency transition time is achieved, which is four orders of magnitude faster than conventional thermo-optically WTL-based THz FH systems. The demonstrated hopping rate of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {2.5 \times 10^{7}}$</tex-math></inline-formula> hops/s is more than 20000 times higher than conventional systems, significantly reducing eavesdropping risks. Moreover, we demonstrated real-time THz de-hopping using a photonics-based local oscillator (LO) at the receiver, where the LO frequency hopped from 228 to 308 GHz with a 40 GHz interval synchronously to RF. The system down-converted THz signals spanning 80 GHz to a constant 2 GHz intermediate frequency within 1 GHz tolerance, reducing the signal processing device's bandwidth by 40- fold at the receiver. Additionally, we demonstrated FH frequency shift keying (FSK) communication at 500 Mbit/s with a bit error rate of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\mathbf {2.5 \times 10^{-3}}$</tex-math></inline-formula> only driven by the electro-optically WTL without external modulator. Notably, the proposed THz FH/FSK system not only enhanced security against eavesdropping but also minimized the cost of peripheral electronic device, facilitating the practical deployment of THz wireless networks.