Terahertz-wave detector on silicon carbide platform

We developed a novel terahertz-wave detector fabricated on a SiC platform implementing an InP/InGaAs Fermi-level managed barrier (FMB) diode. The FMB diode epi-layers were transferred on a SiC substrate, and a waveguide coupler and filters were monolithically integrated with an FMB diode. Then, fabricated detector chip was assembled in a fundamental mixer module with a WR-3 rectangular-waveguide input port. It exhibited a minimum noise equivalent power as low as 3e-19 W/Hz at around 300 GHz for a local oscillator power of only 30 microwatts.

Reflective and transmissive cross-polarization converter for terahertz wave in a switchable metamaterial

Utilizing the phase transition characteristic of vanadium dioxide, we present a metamaterial configuration to achieve both reflective and transmissive cross-polarization converters. When vanadium dioxide is metal, the design behaves as a reflective cross-polarization converter. It consists of metallic grating, topas spacer, and vanadium dioxide film. Polarization conversion ratio is more than 90% in the frequency range from 4.80 THz to 13.13 THz. When vanadium dioxide is insulator, the design behaves as a transmissive cross-polarization converter using cascaded metallic gratings with rotation angle . High-efficiency broadband cross-polarization wave conversion is achieved in the frequency band of 0.50-4.75 THz. The effects of oblique incidence on reflective and transmissive modes are studied on polarization conversion. The results tell that cross-polarization conversion is better when incident angle is in the range of -. The designed metamaterial may have a certain inspiration for the research of terahertz multifunctional polarization converter.

Multi-function terahertz wave manipulation utilizing Fourier convolution operation metasurface

We propose a novel metasurface based on a combined pattern of outer C-shaped ring and inner rectangular ring. By Fourier convolution operation to generating different predesigned sequences of metasurfaces, we realize various functionalities to flexible manipulate terahertz waves including vortex terahertz beam splitting, anomalous vortex terahertz wave deflection, vortex terahertz wave splitting and deflection simultaneously. The incident terahertz wave can be flexibly controlled in a single metasurface. The designed metasurface has an extensive application prospect in the field of future terahertz communication and sensing.

Photonics-Assisted Terahertz-Wave Beam Steering and Its Application in Secured Wireless Communication

Beam forming and beam steering are inevitable technologies for the practical application of high-frequency electromagnetic waves. Specifically, beam control technology using a phased array for terahertz waves above 100 GHz is necessary to realize the future of high-speed wireless communication. By photomixing, which is a promising method for generating terahertz waves, the phase of the generated waves can be tuned in the optical domain, so that the beam from the phased array can be controlled by photonics technologies. Directing the beam of a terahertz wave enables wireless communication to be improved not only via an increase in power efficiency but also in security in the physical layer of the wireless transmission. By utilizing this advantage and using coherent detection at the receiver, a secured wireless communication system is proposed, and the fundamental mechanism is demonstrated in a feasibility experiment.

Terahertz-Wave-Plethysmography (TPG): A New Principle of Radar Based Pulse Detection

This study presents findings at Terahertz (THz) frequency band for non-contact cardiac sensing application. For the first time, cardiac pulse information is simultaneously extracted using THz waves based on the two established principles in electronics and optics. The first fundamental principle is micro-Doppler (mD) motion effect, initially introduced in coherent laser radar system 1, 2 and first experimentally demonstrated for vital sign detection 3. This motion based method, primarily using coherent phase information from the radar receiver, has been widely exploited in microwave frequency bands and has recently found popularity in millimeter waves (mmWave). The second fundamental principle is reflectance based optical measurement using infrared or visible light. The variation in the light reflection is proportional to the volumetric change of the heart, often referred as photoplethysmography (PPG). PPG has been a popular technology for pulse diagnosis. Recently it has been widely incorporated into various smart wearables for long-term monitoring, such fitness training and sleep monitoring. Herein, the concept of Terahertz-Wave-Plethysmography (TPG) is introduced, which detects blood volume changes in the upper dermis tissue layer by measuring the reflectance of THz waves, similar to the existing remote PPG (rPPG) principle 4. The TPG principle is justified by scientific deduction, electromagnetic wave (EM) simulations and carefully designed experimental demonstrations. Additionally, pulse measurements from various peripheral body parts of interest (BOI), palm, inner elbow, temple, fingertip and forehead, are demonstrated using a wideband THz sensing system developed by Terahertz Electronics Lab at Arizona State University (ASU), Tempe. Among the BOIs under test, it is found that the measurements from forehead BOI gives the best accuracy with mean heart rate (HR) estimation error 1.51 beats per minute (BPM) and stand deviation (std) 1.08 BPM. The results validate the feasibility of radar based plethysmography for direct pulse monitoring. Finally, a comparative study on pulse sensitivity in TPG and rPPG is conducted. The results indicate that the TPG contains more pulsatile from the forehead BOI than that in the rPPG signals and thus generate better heart rate (HR) estimation statistic in the form of empirical cumulative distribution function (CDF) of HR estimation error.

Terahertz interface physics: from terahertz wave propagation to terahertz wave generation

Terahertz (THz) interface physics as a new interdiscipline between THz technique and condensed matter physics has undergone rapid developments in recent years. Especially, the developments of advanced materials, such as graphene, transitional metal dichalcogenides, topological insulators, ferromagnetic metals, and metamaterials, have revolutionized the interface field and further promotes the development of THz functional devices based on interface physics. Moreover, playing at the interface with these advanced materials could unveil a wealth of fascinating physical effects such as charge transfer, proximity effect, inverse spin-Hall effect, and Rashba effect with THz technology by engineering the charge, spin, orbit, valley, and lattice degrees of freedom. In this review, we start from the discussion of the basic theory of THz interface physics, including interface formation with advanced materials, THz wave reflection and transmission at the interface, and band alignment and charge dynamics at the interface. Then we move to recent progresses in advanced materials from THz wave propagation to THz wave generation at the interface. In the THz wave propagation, we focus on the THz wave impedance-matching, Goos–Hänchen and Imbert–Fedorov shifts in THz region, interfacial modulation and interfacial sensing based on THz wave. In the THz wave generation, we summarize the ongoing coherent THz wave generation from van der Waals interfaces, multiferroic interfaces, and magnetic interfaces. The fascinating THz interface physics in advanced materials is promising and promoting novel THz functional devices for manipulating the propagation and generation of THz wave at the interfaces.