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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.

Novel hollow‐core THz waveguides featuring hyperuniform disordered reflectors are proposed, fabricated, and characterized. The reflector comprises aperiodically positioned dielectric cylinders connected with dielectric bridges. The proposed waveguides are fabricated using a 3D MultiJet printer. Optical properties of the fabricated waveguides are investigated numerically using finite element method, as well as experimentally using terahertz time‐domain spectroscopy. The results confirm that proposed waveguides exhibit sizable photonic bandgaps (21%) even with relatively low refractive index contrast (resin/air). Position of the bandgaps can be easily tuned by varying reflector geometrical parameters.

Taming the Terahertz waves (100 GHz-10 THz) is considered the next frontier in wireless communications. While components for the ultra-high bandwidth Terahertz wireless communications were in rapid development over the past several years, however, their commercial availability is still lacking. Nevertheless, as we demonstrate in this paper, due to recent advances in the microwave and infrared photonics hardware, it is now possible to assemble high performance hybrid THz communication systems for real-life applications. As an example, in this work, we present design and performance evaluation of the photonics-based Terahertz wireless communication system for the transmission of uncompressed 4K video feed that is built using all commercially available system components. In particular, two independent tunable lasers operating in the infrared C-band are used as a source for generating the Terahertz carrier wave using frequency difference generation in a photomixer. One of the IR laser beams carries the data which is intensity modulated using the LiNbO3 electro-optic modulator. A zero bias Schottky detector is used as the detector and demodulator of the data stream followed by the high-gain and low-noise pre-amplifier. The Terahertz carrier frequency is fixed at 138 GHz and the system is characterized by measuring the bit error rate for the pseudo random bit sequences at 5.5 Gbps. By optimizing the link geometry and decision parameters, an errorfree (BER<10 -10 ) transmission at a link distance of 1m is achieved. Finally, we detail integration of a professional 4K camera into the THz communication link, and demonstrate live streaming of the uncompressed HD and 4K video followed by analysis of the link quality.

In this review we evaluate recent experimental and theoretical progress in the development of wire-based waveguides used for practical low-loss and low-dispersion delivery of terahertz radiation. Waveguides considered in this review utilize plasmonic modes guided in the air gap between two parallel wires. The two parallel wires are, in turn, encapsulated inside of a low-loss, low-refractive-index micro-or nano-structured cladding that provides mechanical stability and isolation from the environment. We describe two alternative techniques that may be used to encapsulate the two-wire waveguides while minimizing the negative impact of dielectric cladding on the optical properties of the waveguide. The first technique uses low-density foam as a cladding material, while the other uses air-filled microstructured plastic claddings to support metallic wires. Additionally, we offer a detailed analysis of the modal properties of wire-based waveguides, compare them with the properties of a classic two-wire waveguide, and present several strategies for the improvement of hybrid waveguide performance. Using the resonant dependence of the confinement properties of some hybrid plasmonic modes also allows us to propose their use in terahertz refractometry. Finally, we demonstrate that wire-based porous waveguides can have a very large operational bandwidth while supporting tightly confined, air-bound modes at both high and low frequencies. This is possible as, at higher frequencies, hybrid fibers can support ARROW-like low-loss air-bound modes while changing their guidance mechanism to plasmonic confinement in the inter-wire air gap at lower frequencies.