Research On Ultra-wideband Terahertz Transmission Lines Based On Silicon Photonic Crystals

• High-Efficiency Optimization at Target Frequencies: A systematic study and optimization of six photonic crystal waveguide geometries were conducted. Using an external matching method, the transmission efficiency at a specific target frequency (140 GHz) was enhanced to exceed 99%, providing a clear pathway for designing highly efficient transmission lines at desired operational points. • Realization of an Ultra-Wideband Device for Practical Systems: Through a combined approach of the plane-wave expansion method (for bandgap analysis) and the finite element method (for performance simulation), an optimal waveguide design was identified from 12 candidates. The final structure achieves an exceptional absolute bandwidth of 125.23 GHz (80–230 GHz) with a relative bandwidth of 80.52%, whose passband fully covers the operational ranges of standard waveguides (WR-4,5,7,8), making it a readily applicable solution for broadband systems. • Demonstrated Robustness for Harsh Environments: Simulation analysis confirms the design's flat transmission and stable group delay in its passband. Crucially, it exhibits minimal performance degradation under extreme temperature fluctuations (200–400 K), with a bandgap center frequency shift of only 1.692 GHz, proving its potential reliability for real-world applications like space-air-ground integrated communications. An ultra-broadband waveguide based on two-dimensional silicon photonic crystals was intensively investigated in this short paper, aiming to provide a low-loss and easy-to-integrate terahertz transmission line design solution. By using the finite element method, the transmission efficiencies of the triangular and square lattice photonic crystal with only one straight line defect were optimized up to 99.90%, which also considered various structural differences including circular, square, and hexagonal dielectric-pillars, as well as three air-hole-arrays. The ultra-broadband characteristics of photonic crystal waveguide was specifically analyzed, which consists of two square lattice hexagonal dielectric-pillar-arrays. The transmission efficiency can maintain above −3 dB (50%) in the frequency range from 92.92 to 218.15 GHz, and the relative bandwidth is up to 80.52%. Compared with existing transmission line, its ultra-broadband and low-loss characteristics have potential applications in future space-air-ground integrated communication systems.