Single-Mode Terahertz Bragg Fiber Design Using a Modal Filtering Approach

This paper proposes a single-mode Bragg fiber design method based on a modal filtering technique and applies it to the design of a hollow-core single-mode Bragg fiber, which can achieve low loss by avoiding material loss. The proposed method exploits the Brewster phenomenon to filter out the TM₀₁ mode so that only the fundamental HE₁₁ mode exists. Consequently, this proposed method maintains a balance between single-mode propagation and low-loss propagation so that it is specially suitable for terahertz single-mode Bragg fiber design. An explicit relationship between the first bandgap width and the layer thickness is derived. As a result, for a certain design bandwidth requirement, the Bragg fiber parameters can be determined. The proposed design strategy is applied to a hollow-core single HE₁₁-mode Bragg fiber operating in the 0.65-1.35-THz range with a calculated loss ranging from 0.2 to 1 dB/m.