3D printed hollow core terahertz Bragg waveguides with defect layers for surface sensing applications

Abstract

We study a 3D-printed hollow core terahertz (THz) Bragg waveguide for resonant surface sensing applications. We demonstrate theoretically and confirm experimentally that by introducing a defect in the first layer of the Bragg reflector, thereby causing anticrossing between the dispersion relations of the core-guided mode and the defect mode, we can create a sharp transmission dip in the waveguide transmission spectrum. By tracking changes in the spectral position of the narrow transmission dip, one can build a sensor, which is highly sensitive to the optical properties of the defect layer. To calibrate our sensor, we use PMMA layers of various thicknesses deposited onto the waveguide core surface. The measured sensitivity to changes in the defect layer thickness is found to be 0.1 GHz/μm. Then, we explore THz resonant surface sensing using α-lactose monohydrate powder as an analyte. We employ a rotating THz Bragg fiber and a semi-automatic powder feeder to explore the limit of the analyte thickness detection using a surface modality. We demonstrate experimentally that powder layer thickness variations as small as 3μm can be reliably detected with our sensor. Finally, we present a comparative study of the time-domain spectroscopy versus continuous wave THz systems supplemented with THz imaging for resonant surface sensing applications.

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

“…A 3D-printed kagome-lattice THz waveguide with average propagation loss of 8.7 dB/m over three antiresonance windows in the frequency range from 0.2 to 1.0 THz has also been presented [18]. In addition, using 3D stereolithography, a hollow core Bragg fiber with propagation loss of 52.1 dB/m at 0.18 THz [19] was recently reported. In 2011, two rolled large air-core Bragg fibers were reported which exhibited propagation losses of 18 dB/m at 0.69 THz and 12 dB/m at 0.82 THz, respectively [20].…”

“…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].…”

“…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]. 3D printing is also ideal for the fabrication of highly porous structures, which is a challenge for other techniques, such as molding, drawing, rolling, and extrusion, owing to the deformation encountered during processing [7].…”

Ultra-high Q terahertz whispering-gallery modes in a silicon resonator

“…To the best of our knowledge, the achieved Q factor of 1.5 × 10 4 exceeds by far any other reported resonant structure in the THz frequency range [13][14][15][16][17][18][19][20][21][22][23]. Amongst the resonant structures with the highest Q factors reported in literature are, e.g., a bragg grating in a parallel plate waveguide (Q= 436) [13], a silicon photonic crystals slab (Q= 1020) [15], a plasmonic Fano metamaterial (Q= 227) [14], a 3D-printed hollow core bragg waveguide with defect layer (Q= 55) [16], and a HDPE disc WGM resonator (Q= 3000) [7]. The ultra high Q factor achieved with the Si sphere is a significant step towards the realization of THz photonics technologies based on WGM resonators as they are already well established in the optical regime.…”

Circular hole ENZ photonic crystal fibers exhibit high birefringence

“…These free-space propagation-based systems usually suffer from unwanted absorption losses, difficulties in integration with other devices, and high sensitivity to the surrounding environment. Consequently, several types of THz waveguides have been proposed to replace free space propagation, including solid stainless wires [3], dielectric metal-coated tubes [4], and Bragg fibers [5]. However, they are all based on metallic wires and subwavelength dielectric fibers.…”