Suspended core subwavelength fibers: practical designs for the low-loss terahertz guidance

TL;DR

This paper presents practical designs of suspended core subwavelength polymer fibers for low-loss terahertz wave guidance, demonstrating broadband transmission, effective single-mode behavior, and low propagation losses suitable for imaging and sensing.

Contribution

The work introduces novel fiber designs with suspended cores that are easy to handle, hermetically sealed, and exhibit low-loss broadband terahertz guidance, advancing practical terahertz fiber technology.

Findings

Broadband transmission from 0.10 to 0.27 THz and 0.25 to 0.51 THz for different cores

Propagation losses as low as 0.02 cm^-1

Effective single-mode behavior confirmed by near-field imaging

Abstract

In this work we report two designs of subwavelength fibers packaged for practical terahertz wave guiding. We describe fabrication, modeling and characterization of microstructured polymer fibers featuring a subwavelength-size core suspended in the middle of a large porous outer cladding. This design allows convenient handling of the subwavelength fibers without distorting their modal profile. Additionally, the air-tight porous cladding serves as a natural enclosure for the fiber core, thus avoiding the need for a bulky external enclosure for humidity-purged atmosphere. Fibers of 5 mm and 3 mm in outer diameters with a 150 \mu m suspended solid core and a 900 \mu m suspended porous core respectively, were obtained by utilizing a combination of drilling and stacking techniques. Characterization of the fiber optical properties and the near-field imaging of the guided modes were performed using a terahertz near-field microscopy setup. Near-field imaging of the modal profiles at the fiber output confirmed the effectively single-mode behavior of such waveguides. The suspended core fibers exhibit broadband transmission from 0.10 THz to 0.27 THz (larger core), and from 0.25 THz to 0.51 THz (smaller core). Due to the large fraction of power that is guided in the holey cladding, fiber propagation losses as low as 0.02 cm-1 are demonstrated. Low-loss guidance combined with the core isolated from environmental perturbations make these all-dielectric fibers suitable for practical terahertz imaging and sensing applications.