THz phase-shifted waveguide Bragg gratings built on modular 3D-printed two-wire plasmonic waveguides are used experimentally for gas sensing. The physical parameters of a gas flowing along the grating are then monitored in real time by detecting the spectral position of a narrow transmission peak. The sensor sensitivity was found to be 133 GHz/RIU near 0.14 THz, with a theoretical sensor resolution of 7.5.10-5 RIU. The detection of glycerol vapors in air generated by an electronic cigarette was shown experimentally. The developed THz gas sensor can find its practical applications in environmental pollution monitoring and leak detection.
Terahertz (THz) near-field imaging promises new advances in medical diagnostics and material characterization. However, its spatial resolution is limited by the light diffraction on lenses/mirrors, which limits the optical resolution of a standard free-space imaging system to ~λ/2 (Abbe limit). Alternatively, super-resolution imaging can be achieved by employing a solid immersion lens (SIL) as the spot size of the focused THz beam is further reduced by a factor of 1/n, where n is the refractive index (RI) of the lens material. In this work, we present the design and fabrication of hemispherical THz SILs using powder mixes of titanium dioxide (TiO2) and polypropylene (PP) having nTio2≈10 and npp≈1.51 at 1.0 THz. We present two different lens fabrication strategies that are simple and cost-effective. The first one uses pressing the TiO2 powder with a PP powder at the Vicat temperature of PP while controlling the concentration of TiO2 and the resultant lens porosity. The second one uses pressing the TiO2 powder in a hollow hemisphere that is 3D printed using PP. The fabricated lenses are then characterized optically, and their RIs are compared to predictions of the Bruggeman model of the effective media. From the experimental characterization of the composite SILs, a resolution λ/5 was achieved at 0.09 THz (λ≈3.3 mm), which is one of the best resolutions for THz SILs reported in the literature. We believe that further improvements in material processing can reduce the resolution of the TiO2-based THz SILs to their fundamental λ/20 limit .
Imaging at terahertz frequencies (0.1-10 THz, wavelengths 3 mm-30 µm) has proven to be useful in the biomedical field. Still, the acquisition time is an important hurdle. Here, we discuss recent developments toward achieving real-time THz imaging. First, we demonstrate a spectral encoding algorithm to reconstruct a 4500-pixels image with 45 measurements. Second, we improve the image resolution using a super-resolution algorithm specifically developed for the THz. Third, we discuss our most recent work on the fabrication of an THz photoconductive antenna array for imaging. These works pave the way for future applications of THz imaging in biomedical science.
In terahertz (THz) communications, most of the research work is focused on wireless systems, while waveguide/fiber-based links have been less explored. Although wireless communications have several advantages, the fiber-based communications provide superior performance in certain short-range communication applications with complex geometrical environments. In this work, we present an in-depth experimental and numerical study of the short-range THz communications links (carrier frequency:128 GHz) that use subwavelength dielectric fibers of varying diameters (0.57-1.75 mm) and up to 10 m for information transmission (up to 6 Gbps) and define main challenges and tradeoffs in the link implementation.
In this work, a low-loss near-zero dispersion polypropylene fiber is designed for signal transmission at the carrier frequency of 128 GHz. An infinite 3D printing technique is explored to continuously fabricate the proposed fiber without length-limit. The in-depth theoretical and experimental comparisons between the two fibers printed using standard and infinite 3D printers are introduced in detail. Particularly, transmission losses of 2.39 dB/m and 5.57 dB/m have been experimentally demonstrated for the two fibers at 128 GHz. Furthermore, for the two fibers with the corresponding lengths of 2 m and 1.6 m, signal transmission with bit error rates far below the forward error correction limit (10-3) was clearly observed. Error-free transmission is realized at the bit rates up to 5.2 Gbps for the standard 3D printed fiber at the length of 1.5 m.
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