Frequency comb measurements for 6G terahertz nano/microphotonics and metamaterials.

Next-generation 6G communication holds the potential to revolutionize data transfer, enabling the realization of eXtended Reality (XR) with enhanced sensory experiences. To achieve this, advanced components such as high-performance intensity/phase modulators, waveguides, multiplexers, splitters, combiners, and filters operating in terahertz (THz) regime, specifically within the frequency range of 0.1-1 THz, are essential. However, existing microwave equipment and vector network analyzers designed for this frequency range suffer from limitations in resolution, stability, and accuracy when evaluating the intensity and phase responses of critical 6G THz devices. In this comprehensive review, we delve into the critical device requirements and emerging trends in next-generation 6G communication, essential performance evaluation parameters, comparisons between microwave and nano/microphotonic devices for testing, and the application of high-resolution THz sensors in 6G Internet-of-Things (IoT) scenarios. Notably, a frequency comb in the photonic regime emerges as the prime candidate for achieving precision evaluations of 6G networks and devices. Consequently, this review highlights the latest research in frequency comb measurements in the 6G THz frequency regime, with a particular emphasis on nano/microphotonic devices and metamaterials. The integration of frequency comb measurements into 6G and THz photonic devices and networks promises to accelerate the realization of high-density next-generation 6G communication.