Spectral characterization of porous dielectric subwavelength THz fibers fabricated using a microstructured molding technique

Abstract

We report two novel fabrication techniques, as well as THz spectral transmission and propagation loss measurements of subwavelength plastic wires with highly porous (up to 86%) and non-porous transverse geometries. The two fabrication techniques we describe are based on the microstructured molding approach. In one technique the mold is made completely from silica by stacking and fusing silica capillaries to the bottom of a silica ampoule. The melted material is then poured into the silica mold to cast the microstructured preform. Another approach uses a microstructured mold made of a sacrificial plastic which is co-drawn with a cast preform. Material from the sacrificial mold is then dissolved after fi ber drawing. We also describe a novel THz-TDS setup with an easily adjustable optical path length, designed to perform cutback measurements using THz fibers of up to 50 cm in length. We fi nd that while both porous and non-porous subwavelength fibers of the same outside diameter have low propagation losses (alpha <or= 0.02 cm(-1)), the porous fi bers exhibit a much wider spectral transmission window and enable transmission at higher frequencies compared to the non-porous fibers. We then show that the typical bell-shaped transmission spectra of the subwavelengths fibers can be very well explained by the onset of material absorption loss at higher frequencies, due to strong confinement of the modal fields in the material region of the fi ber, as well as strong coupling loss at lower frequencies, due to mismatch between the modal field diameter and the size of the gaussian-like beam of a THz source.

Low-Loss Asymptotically Single-Mode THz Bragg Fiber Fabricated by Digital Light Processing Rapid Prototyping

“…Various fabrication techniques, such as drawing [26]- [29], extrusion [16], stacking [23], [24], [31], drilling [26]- [28], [30], molding [29], rolling [19], coating [25], and 3D printing [17], [18], have been used in the fabrication of THz microstructured fibers. As a cost-effective, fast, convenient fabrication technique, 3D printing is able to produce devices accurately with good repeatability, and hence it has attracted much attention for the fabrication of functional THz components, such as waveguides [17], [18], [38], fibers [39], lenses [40], antenna horns [41], and sensors [19].…”

Silk Foam Terahertz Waveguides

“…As it is detailed in our prior work, [ 24,31,35 ] a circular micro porous step-index fi ber operates in the subwavelength regime if the operation frequency is smaller than a characteristic value of…”

“…[ 31 ] . Cutback measurements were performed using conical shaped samples (see Figure 1 ) as obtained directly from the lyophilisation setup.…”

“…[ 31,32 ] , for example). In our analysis we neglect multiple refl ections within the sample (Fabry-Pérot effect) as spectral intensity oscillations associated with this effect are not discernible in the measured data.…”

“…[ 31,34 ] In general, the normalized transmission through the fi ber is given by: Fiber transmission spectra are presented in Figure 6 (a) for four different fi ber lengths. If all the spectra are to be used in the interpretation of the cutback results, then our analysis has to be limited to a narrow frequency range THz v THz 0.2 0.4 < < , where intensities of all the spectra are above the noise level.…”