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Abundant available spectral resources in terahertz (THz) bands enables opportunities to develop next-generation mobile communications. However, devices with large operating bandwidths are required to exploit the benefits offered by the THz band, which significantly increases the cost and complexity of implementation. In addition, THz frequencies experience a relatively large propagation loss, which inevitably reduces network coverage; thus, numerous antenna sites are required to provide reliable mobile services. Therefore, implementing antenna-sites for a THz-band 6G mobile network may be limited by various design restrictions, such as the high power, complexity, and cost requirements. A photonic-based approach for a THz communication system can offer an efficient solution for simplified antenna-site architecture. THz-wave generation using optical heterodyne can reduce the implementation burden on the antenna-site through the use of complex electrical signal up-conversion. When combined with radio-over-fiber (RoF) technology, the benefits of analog-waveform transmission can be achieved, such as bandwidth-efficient transmission in a mobile transport link. This study presents a comprehensive investigation of design guidelines for implementing an RoF-based photonic THz communication system. We investigate a major performance-limiting factor by analyzing noise contribution in a fiber-wireless link through theoretical and experimental verifications considering the quality of an RoF-based analog photonic link. Furthermore, we demonstrate the THz-band fiber-wireless transmission of an aggregated mobile signal using multiple intermediate frequency (IF) carriers to confirm the technical feasibility of the RoF-based photonic THz system for a 6G mobile network. The experimental results show that a mobile signal of 32 IF carriers with a total occupied bandwidth of 12.8 GHz was successfully transmitted over a 5-m free-space wireless link at a frequency of 0.3 THz, which satisfies the 16-quadrature amplitude modulation requirements. We also discuss the design issues related to the optical-link budget considering potential architectures of the RoF-based photonic THz communication system.

We demonstrate the transmission of uncompressed 4K videos over the photonics‐based terahertz (THz) wireless link using a directly modulated distributed feedback laser diode (DFB‐LD). For optical heterodyne mixing and data modulation, a DFB‐LD was employed and directly modulated with a 5.94‐Gb/s non‐return‐to‐zero signal, which is related to a 6G‐serial digital interface standard to support ultra‐high‐definition video resolution. We derived the optimal frequency of the THz carrier by varying the wavelength difference between DFB‐LD output and Tunable LD output in the THz signal transmitter to obtain the best transmission performances of the uncompressed 4K video signals. Furthermore, we exploited the negative laser‐to‐filter detuning for the adiabatic chirp management of the DFB‐LD by the intentional discrepancy between the center wavelength of the optical band‐pass filter and the output wavelength of the DFB‐LD. With the help of the abovementioned methods, we successfully transmitted uncompressed 4K video signals over the 2.3‐m wireless transmission distance without black frames induced by time synchronization error. Photonics‐based terahertz (THz) bands, having large bandwidths, are promising candidates for next‐generation wireless communication systems. They can transmit data at rates high enough to live‐stream uncompressed 4K videos. However, existing THz communication systems are complex and expensive. Now, researchers from Korea have developed a simple and cost‐effective photonics‐based THz wireless communication system. Utilizing a directly modulated distributed feedback laser and negative frequency detuning method, it successfully transmits 4K video signals over 2.3 meters.

Large bandwidths at terahertz (THz) frequencies higher than 100 GHz have been garnering significant attention as key enablers for future wireless networks to provide data rates in the range of terabits per second, which is approximately one hundred times higher than the transmission rate of millimeter wireless systems. To fully utilize the merits of THz frequencies, devices with large operating bandwidths are highly desired. From this perspective, promising choices are photonic devices developed for fiber-optic communications, which have been commonly used since the early stages of THz communications research with different architectures and parameters. However, the factors limiting the performance of photonics-based THz systems have not yet been investigated thoroughly in terms of general system aspects. Here, we comprehensively analyze and compare various potential THz communications systems with a photonics-based THz transmitter. Based on modulation and optical light sources, we characterize the three most typical architectures and theoretically and experimentally analyze the impact of optical and phase noise on system performance.