In this work, we present a 3D-printed waveguide that provides effective electromagnetic guidance in the THz regime. The waveguide is printed using low-cost polycarbonate and a conventional fused deposition modeling printer. Light guidance in the hollow core is achieved through antiresonance, and it improves the energy effectively transported to the receiver compared to free space propagation. Our demonstration adds to the field of 3D-printed terahertz components, providing a low-cost way of guiding terahertz radiation.

We demonstrate experimentally nonvolatile, all-optical control of graphene's charge transport properties by virtue of an Fe:LiNbO photoconductive substrate. The substrate can register and sustain photoinduced charge distributions which modify locally the electrostatic environment of the graphene monolayer and allow spatial control of graphene resistivity. We present light-induced changes of graphene sheet resistivity as high as ∼370 Ω/sq (∼2.6-fold increase) under spatially nonuniform light illumination. The light-induced modifications in the sheet resistivity are stable at room temperature but can be reversed by uniform illumination or thermal annealing (100 °C for 4 h), thus restoring graphene's electrical properties to their initial, preillumination values. The process can be subsequently repeated by further spatially nonuniform illumination.

We report the use of a terahertz (THz) transparent material, cyclic olefin copolymer (COC or TOPAS), for fabricating a hollow-core antiresonant fiber that provides an electromagnetic wave guidance in the THz regime. A novel fabrication technique to realize a hollow-core antiresonant polymer optical fiber (HC-ARPF) for THz guidance is proposed and demonstrated. The fiber is directly extruded in a single-step procedure using a conventional fused deposition modeling 3D printer. The fiber geometry is defined by a structured nozzle manufactured with a metal 3D printer, which allows tailoring of the nozzle design to the various geometries of microstructured optical fibers. The possibility to use the HC-ARPF made from TOPAS for guiding in the THz region is theoretically and experimentally assessed through the profile of mode simulation and time-frequency diagram (spectrogram) analysis.

Terahertz time-domain spectroscopy (THz-TDS) is a proven technique whereby the complex refractive indices of materials can be obtained without requiring the use of the Kramers-Kronig relations, as phase and amplitude information can be extracted from the measurement. However, manual pre-processing of the data is still required and the material parameters require iterative fitting, resulting in complexity, loss of accuracy and inconsistencies between measurements. Alternatively approximations can be used to enable analytical extraction but with a considerable sacrifice of accuracy. We investigate the use of machine learning techniques for interpreting spectroscopic THz-TDS data by training with large data sets of simulated light-matter interactions, resulting in a computationally efficient artificial neural network for material parameter extraction. The trained model improves on the accuracy of analytical methods that need approximations while being easier to implement and faster to run than iterative root-finding methods. We envisage neural networks can alleviate many of the common hurdles involved in analyzing THz-TDS data such as phase unwrapping, time domain windowing, slow computation times, and extraction accuracy at the low frequency range.

Terahertz (THz) technology has witnessed a significant growth in a wide range of applications, including spectroscopy, bio-medical sensing, astronomical and space detection, THz tomography, and non-invasive imaging. Current THz microstructured fibers show a complex fabrication process and their flexibility is severely restricted by the relatively large cross-sections, which turn them into rigid rods. In this paper, we demonstrate a simple and novel method to fabricate low-cost THz microstructured fibers. A cyclic olefin copolymer (TOPAS) suspended-core fiber guiding in the THz is extruded from a structured 3D printer nozzle and directly drawn in a single step process. Spectrograms of broadband THz pulses propagated through different lengths of fiber clearly indicate guidance in the fiber core. Cladding mode stripping allow for the identification of the single mode in the spectrograms and the determination of the average propagation loss (~ 0.11 dB/mm) in the 0.5-1 THz frequency range. This work points towards single step manufacturing of microstructured fibers using a wide variety of materials and geometries using a 3D printer platform. Terahertz (THz) waves or T-waves occupy a window of electromagnetic waves with frequency ranging from ν ~ 0.1 THz to ν ~ 10 THz (corresponding to the wavelength range from λ ~ 30 µm to λ ~ 3 mm). Over the last decade, THz waves have been exploited in many applications owing to their unique characteristic such as ability to penetrate in most of dielectric materials and provide improved resolution when compared to micro-or millimeter waves. Security scanning, non-destructive testing and imaging are some of the most noteworthy application of THz technologies 1,2. Because of their non-ionizing nature, THz waves can be used to detect organic tissue without causing damage, and can be safely applied for medical and biomedical sensing 3,4. THz waves have great potential to be exploited for detecting chemicals, pharmaceuticals and biological agents, as the main rotational modes of many macromolecules have a strong absorption in the THz region 5,6. They can also be used in wireless communications to increase data transmission, due to the large bandwidth of the THz band 7 , and in astronomy, to locate cold matter in space or for imaging applications in deep space 8,9. Although THz waves have shown strong potential for imaging and sensing, most of the THz systems are based on free-space optics that are quite delicate. Hence, a significant amount of research has focused on achieving low-loss and low-dispersion THz waveguiding. Metal wires were the very first material used in THz waveguides due to their low material absorption 10,11 : square and circular metallic waveguides have been demonstrated at the beginning of this century for very dispersive and low loss THz propagation 12. In 2001, two thin metallic strips were used to construct a parallel plate THz waveguides for low loss and low group velocity dispersion 13. The combination of metallic and polymer for fabricating THz waveguide was pro...

Terahertz time-domain spectroscopy (TDS) is a powerful characterization technique which allows for the frequency-dependent complex refractive index of a sample to be determined. This is achieved by comparing the time-domain of a pulse transmitted through air to a pulse transmitted through a material sample; however, the requirement for an independent reference scan can introduce errors due to laser fluctuations, mechanical drift, and atmospheric absorption. In this paper, we present a method for determining complex refractive index without an air reference, in which the first pulse transmitted through the sample is compared against the “echo”, where the internal reflections delay the transmission of the echo pulse. We present a benchmarking experiment in which the echo reference method is compared to the traditional air method, and show that the echo method is able to reduce variation in real refractive index.

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Coherent laser arrays compatible with silicon photonics are demonstrated in a waveguide geometry in epitaxially grown semiconductor membrane quantum well lasers transferred on substrates of silicon carbide and oxidised silicon; we record lasing thresholds as low as 60 mW of pump power. We study the emission of single lasers and arrays of lasers in the sub-mm range. We are able to create waveguide laser arrays with modal widths of approximately 5-10 µm separated by 10-20 µm, using real and reciprocal space imaging we study their emission characteristics and find that they maintain their mutual coherence while operating on either single or multiple longitudinal modes per lasing cavity.