http://www.acsu.buffalo.edu/~jmjornet/papers/2014/j1.pdf

Full length article: Terahertz band: Next frontier for wireless communications

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

https://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001/pdf

The 2017 terahertz science and technology roadmap

The 2016 terahertz science and technology roadmap

When two resonant modes in a system with gain or loss coalesce in both their resonance position and their width, a so-called exceptional point occurs, which acts as a source of non-trivial physics in a diverse range of systems. Lasers provide a natural setting to study such non-Hermitian degeneracies, as they feature resonant modes and a gain material as their basic constituents. Here we show that exceptional points can be conveniently induced in a photonic molecule laser by a suitable variation of the applied pump. Using a pair of coupled microdisk quantum cascade lasers, we demonstrate that in the vicinity of these exceptional points the coupled laser shows a characteristic reversal of its pump dependence, including a strongly decreasing intensity of the emitted laser light for increasing pump power.

/pdf/reversing-the-pump-dependence-of-a-laser-at-an-exceptional-268hmn9a8e.pdf

Reversing the pump dependence of a laser at an exceptional point

The field of terahertz integrated technology has undergone significant development in the past ten years. This has included work on different substrate technologies such as III–V semiconductors and silicon, work on field-effect transistor devices and heterojunction bipolar devices, and work on both fully electronic and hybrid electronic–photonic systems. While approaches in electronic and photonics can often seem distinct, techniques have blended in the terahertz frequency range and many emerging systems can be classified as photonics-inspired or hybrid. Here, we review the development of terahertz integrated electronic and hybrid electronic–photonic systems, examining, in particular, advances that deliver important functionalities for applications in communication, sensing and imaging. Many of the advances in integrated systems have emerged, not from improvements in single devices, but rather from new architectures that are multifunctional and reconfigurable and break the trade-offs of classical approaches to electronic system design. We thus focus on these approaches to capture the diversity of techniques and methodologies in the field. This Review Article examines the development of terahertz integrated electronic and hybrid electronic–photonic systems, considering, in particular, advances that deliver important functionalities for applications in communication, sensing and imaging.

Terahertz integrated electronic and hybrid electronic–photonic systems

A grating-gated field-effect transistor fabricated from a single-quantum well in a high-mobility GaAs–AlGaAs heterostructure is shown to function as a continuously electrically tunable photodetector of terahertz radiation via excitation of resonant plasmon modes in the well. Different harmonics of the plasmon wave vector are mapped, showing different branches of the dispersion relation. As a function of temperature, the resonant response magnitude peaks at around 30K. Both photovoltaic and photoconductive responses have been observed under different incident power and bias conditions.

/pdf/single-quantum-well-grating-gated-terahertz-plasmon-55aau0cnoh.pdf

Single-quantum-well grating-gated terahertz plasmon detectors

Thermophotovoltaics (TPV) is the process by which photons radiated from a thermal emitter are converted into electrical power via a photovoltaic cell Selective thermal emitters that can survive at temperatures at or above ∼1000°C have the potential to greatly improve the efficiency of TPV energy conversion by restricting the emission of photons with energies below the photovoltaic (PV) cell bandgap energy In this work, we demonstrated TPV energy conversion using a high-temperature selective emitter, dielectric filter, and 06 eV In068Ga032As photovoltaic cell We fabricated a passivated platinum and alumina frequency-selective surface by conventional stepper lithography To our knowledge, this is the first demonstration of TPV energy conversion using a metamaterial emitter The emitter was heated to >1000°C, and converted electrical power was measured After accounting for geometry, we demonstrated a thermal-to-electrical power conversion efficiency of 241±09% at 1055°C We separately modeled our system consisting of a selective emitter, dielectric filter, and PV cell and found agreement with our measured efficiency and power to within 1% Our results indicate that high-efficiency TPV generators are possible and are candidates for remote power generation, combined heat and power, and heat-scavenging applications

High-efficiency thermophotovoltaic energy conversion enabled by a metamaterial selective emitter

Tamm states on subwavelength, reconfigurable plasmonic crystals are studied in the terahertz regime. By introducing an independently controlled plasmonic defect, an electromagnetically induced transparency phenomenon is revealed.

Induced transparency by coupling of Tamm and defect states in tunable terahertz plasmonic crystals

Recent advances in microfabricated terahertz quantum cascade lasers have achieved coherent power and frequency performance previously possible only with much larger gas- or vacuum-tube sources. A significant advantage offered by terahertz quantum cascade lasers lies in the potential to integrate them with other components on the same chip. Such terahertz photonic integrated circuits would help close the terahertz technology gap between microwave electronics and infrared photonics. Here, we describe the first successful monolithic integration of a terahertz quantum cascade laser and diode mixer to form a simple but generically useful terahertz photonic integrated circuit—a microelectronic terahertz transceiver. We show that this terahertz photonic integrated circuit performs all the basic functions (for example, transmission of a coherent carrier, heterodyne reception of an external signal, frequency locking and tuning) of discrete-component terahertz photonic systems, but at a small fraction of the size and in a robust platform scalable to semiconductor fabrication production. A terahertz quantum cascade laser and diode mixer are monolithically integrated to form a simple microelectronic terahertz transceiver. The performance of this system — the transmission of a coherent carrier, heterodyne reception of an external signal, frequency locking and tuning — is as efficient as that of discrete component terahertz photonic systems.

Monolithically integrated solid-state terahertz transceivers

A multi-gate high electron mobility transistor coupled to a log-periodic antenna was engineered to detect sub-terahertz radiation through resonant excitation of plasmon modes in the channel. The device was integrated with a silicon hyper-hemispherical lens in order to enhance radiation collection and eliminate parasitic substrate modes. The continuous detector response spectrum from 185 GHz to 380 GHz indicates the presence of distinct collective plasmonic cavity modes resulting from the quantization of the plasmon wavevector. In a bolometric detection mode, a noise equivalent power of less than 50 pW/Hz1/2 and a responsivity exceeding 100 kV/W have been measured at 11.5 K.

Albert D. Grine

Papers

Single-quantum-well grating-gated terahertz plasmon detectors

High-efficiency thermophotovoltaic energy conversion enabled by a metamaterial selective emitter

Induced transparency by coupling of Tamm and defect states in tunable terahertz plasmonic crystals

Monolithically integrated solid-state terahertz transceivers

Enhanced performance of resonant sub-terahertz detection in a plasmonic cavity