A hybrid metallic waveguide with meta-holes for long-distance terahertz field enhancement

High-intensity terahertz (THz) field is crucial for various practical applications. Several structures have been used to achieve THz field enhancement, but the propagation distances of the high-intensity field can only be maintained at the wavelength or sub-wavelength scale. Here, a hybrid metallic waveguide with meta-holes (HMWMH) based on the combination of waveguide technologies and wavefront control methods is proposed to achieve THz field enhancement over a much longer propagation distance. By the phase modulation of meta-holes, THz waves incident on the waveguide can be converted into a guided mode and further focused at the center. To achieve the second field enhancement, the enhanced THz field at the focus is coupled into a triangular single ridge waveguide, which supports surface plasmon polaritons (SPPs) with deep-subwavelength mode widths and ultra-low loss. When the radius of the ridge tip and the gap between the tip and metallic plate are 15 and 100 μm, respectively, a hot spot area of 19.2 × 3.3 μm² (1.38 × 10^-5 λ²) and a field enhancement of 689 times are achieved simultaneously in the simulation. Theoretically the high-intensity THz field can propagate over a distance of 1.8 m due to the ultra-low loss of the SPPs, which is several orders of magnitude larger than the wavelength. According to the design, an HMWMH prototype is fabricated, and the simulated and measured results are consistent with each other. By realizing long-distance THz field enhancement, the HMWMH can greatly enhance light-matter interactions, which can promote the development of integrated THz photonic devices, THz biophotonics, and THz nonlinear photonics.