Guest Editorial TTA Special Section on Terahertz Devices

Lying between the microwave and infrared frequencies,the electromagnetic spectrum band,normally defined as^0.1 THz to 10.0 THz,was often referred to as a“terahertz（THz）gap”due to the difficulties in efficiently generating,manipulating,and detecting THz radiation.However,driven by the promising applications ranging from non-destructive imaging,spectroscopic sensing,to ultra-high bit rate wireless communications,

Guest Editorial—TTA Special Section on Terahertz Functional Devices

In the past decades, terahertz technology has a great development and steady improvement, which has kept discovering and developing a series of potential applications in terahertz sensing, imaging, spectroscopy, security, and communication. After the recent technical breakthroughs in reliable sources and sensitive detectors, terahertz functional devices, such as waveguides, switches, filters, splitters, isolators, modulators and sensors, are indispensable for the construction of compact application systems and have become a worldwide supreme issue in research.

Guest Editorial TTA Special Section on Terahertz Devices

Recent advances of artificial structured materials, including photonic crystals and metamaterials, have greatly broadened the functionalities of terahertz （THz） devices and provided more degree of freedom in manipulating THz waves beyond traditional constraints. These materials are usually constituted by periodic or aperiodic sub-wavelength elements, showing significant electromagnetic responses during the wave matter interaction, thus enabling the modulation of amplitude, phase, or propagation direction of incident waves as a result. So far, a variety of applications have been proposed and experimentally validated, such as the THz filters, polarizers, modulators, and biosensors with the advantages of ultrathin profile, easy integration, and simple geometry. By incorporating novel materials like graphene, vanadium dioxide, and liquid crystals in the element design, we are allowed to adjust the characteristics of the THz radiation dynamically, which brings additional flexibilities toward the construction of novel THz functional devices.

Guest Editorial——TTA Special Section on Terahertz Materials and Devices

Lying between radio frequency and infrared radiation, terahertz （THz） wave encounters lots of difficulties to produce, detect, transmit, and modulate. Great efforts have been made to construct THz devices, including sources, detectors, switches, modulators, lenses, and filters. However, only moderate progresses have been made in THz generation and detection. Furthermore, the devices and techniques to control and manipulate THz waves are still in its infancy. Therefore, it is still a challenge to date to develop sophisticated THz application systems such as communication, sensing, safety inspection, imaging and medical diagnose systems. This difficult position of THz wave is essential due to the deficiency of THz materials having a suitable THz electromagnetic response, as compared to its neighboring microwave and infrared regime. Practicable material will largely push the THz technology to real-world applications. The GaAs/AlxGa~_xAs material system, for example, is the heart of THz quantum cascade lasers. High quality NbN films, again, set the basis of THz hot electron bolometer.

Guest Editorial TTA Special Section on Terahertz Sources and Devices

The terahertz wave is considered to have great values and plentiful applications, such as in material science, analysis of molecular spectra, information and communication technology, biology and medical science, nondestructive evaluation, and national security. High-power widely tunable terahertz sources are required in the above practical applications of terahertz technologies. A promising approach for monochromatic terahertz generation is based on second-order nonlinear optical effect, e.g.