Negative Curvature Hollow Core Fibers for Terahertz Wave Guidance via 3D Polymer Printing

Utilizing 3D printing to fabricate optical waveguides is a versatile approach for developing sophisticated structures to efficiently guide the light. The terahertz (THz) region is significant for telecommunication, imaging, and sensing applications, and developing high-performance THz waveguides is critical to successfully demonstrating its importance for the applications mentioned above. This study introduces the design, optimization, and fabrication of a THz guiding negative curvature hollow-core fiber (NCF) realized via the 3D printing technique. The fiber is designed as a hollow-core structure surrounded by four sets of tubular elements with bars as nest elements at the center of the tubes. The fibers are modeled using cyclic olefin copolymer (COC, or commercially known as TOPAS), which has low absorption losses in the THz region. The fiber's geometry is systematically optimized for outstanding optical performance, and iterative simulations are performed to define the design parameters. The calculated confinement and total losses are found below 1 dB/m across a wide THz frequency region with periodic high absorption peaks occurring naturally in every NCF structure. The optimized 4-tube design is later fabricated using the fused deposition modeling (FDM) 3D printing technique and commercially available COC filaments. Fibers with a 3 mm core diameter, an 11.6 mm outer diameter and 150 mm length are realized with a minimum feature size of 400 µm. The optical performance of the fibers will be investigated using a THZ frequency domain spectroscopy (FDS) device in the frequency region ranging from 0.1 to 1 THz. This innovative approach opens up possibilities for developing customized and sophisticated NCFs tailored for various THz applications, thereby accelerating advancements in this rapidly evolving field.