Advancing High-Capacity Communication: Low-Loss and High-Data-Rate Terahertz Fiber Link

The rapid proliferation of data-intensive technologies, such as Web3, applied artificial intelligence, and immersive realities, has created a demand for higher data rates and uninterrupted transmissions. However, the current fifth-generation wireless communication technology faces challenges in meeting these requirements due to bandwidth limitations. To overcome these limitations, researchers have explored multilevel multiplexing techniques. However, these solutions pose practical challenges. In this context, terahertz (THz) and sub-THz-band frequencies have emerged as a promising solution for future communication networks.

The THz frequency range, spanning from 100 GHz to 10 THz, remains largely unexplored but holds great potential for high-data-rate communication without the need for spectral enhancement methods. The use of higher frequencies in the THz range aligns with the Shannon theorem, which suggests that higher frequencies generally result in greater channel bandwidth and capacity. The THz frequency range has already proven useful in diverse applications, including enhanced imaging, range finding, and wireless communications.

In a new study published in the peer-reviewed Journal Optics Express presents a low-loss and high-data-rate THz fiber link using an efficient dielectric-waveguide interface. The study conducted by Dr. Ratmalgre Koala, Kei Iyoda, Dr. Weijie Gao, Prof. Masayuki Fujita, Prof. Tadao Nagatsuma from Osaka University and Prof. Yuji Matsuura from Tohoku University focused on developing a THz fiber link with low loss and high data rates. The researchers employed a silica glass tube with an inner silver coating and a hollow core as the fiber structure. Modal analysis was conducted, assuming a circular waveguide with a hollow circular cross-section, to ensure a broad transmission bandwidth and minimize signal distortion. The results showed that a 1-mm core fiber exhibited a larger dispersion bandwidth compared to a 0.7-mm core fiber, making it more suitable for high-capacity communication applications.

In addition to the fiber investigation, the authors also focused on developing a silicon waveguide interface for use in the THz fiber link. The selection of an unclad silicon waveguide was based on its low loss and broad bandwidth characteristics. To achieve a refractive index between silicon and air, the design incorporated an electromagnetic section and an array of through-holes. Impedance matching between the silicon taper and the fiber was crucial, and a tapered structure was implemented to enhance coupling efficiency. The waveguide coupler interface design ensured a good modal match between the fiber and silicon waveguide.

The research team conducted experiments to evaluate the loss and performance of fiber optic cables with different lengths and core diameters for high-data-rate communication. The results demonstrated that the 1-mm core fiber outperformed the 0.7-mm core fiber, exhibiting better transmittance and lower losses, particularly as the fiber length increased. Through transmission power measurements, propagation and coupling losses were estimated, showing that the 1-mm core fiber had lower losses compared to the 0.7-mm core fiber.

Furthermore, communication experiments revealed that the 1-mm core fiber achieved error-free data transmission at rates up to 22 Gbit/s, while the 0.7-mm core fiber achieved a maximum error-free rate of 14 Gbit/s due to dispersion phenomena. The successful transmission of high-definition video over a 1 m-long fiber highlighted the practicality and versatility of the THz fiber for various applications.

In conclusion, the researchers successfully developed a low-loss and high-data-rate terahertz fiber link using an efficient dielectric-waveguide interface. The use of a 1-mm core fiber demonstrated superior transmittance, lower losses, and achieved error-free data transmission at rates up to 22 Gbit/s. These findings hold promise for high-capacity communication applications in the future, addressing the limitations posed by current wireless communication technologies. The advancement of THz frequencies and the successful implementation of the fiber link contribute to the progress of data-intensive technologies, opening up new possibilities for Web3, applied artificial intelligence, immersive realities, and other emerging fields.