Showing papers by "John F. O'Hara published in 2019"

A Perspective on Terahertz Next-Generation Wireless Communications

Abstract: In the past year, fifth-generation (5G) wireless technology has seen dramatic growth, spurred on by the continuing demand for faster data communications with lower latency. At the same time, many researchers argue that 5G will be inadequate in a short time, given the explosive growth of machine connectivity, such as the Internet-of-Things (IoT). This has prompted many to question what comes after 5G. The obvious answer is sixth-generation (6G), however, the substance of 6G is still very much undefined, leaving much to the imagination in terms of real-world implementation. What is clear, however, is that the next generation will likely involve the use of terahertz frequency (0.1–10 THz) electromagnetic waves. Here, we review recent research in terahertz wireless communications and technology, focusing on three broad topic classes: the terahertz channel, terahertz devices, and space-based terahertz system considerations. In all of these, we describe the nature of the research, the specific challenges involved, and current research findings. We conclude by providing a brief perspective on the path forward.

Broadband tunable terahertz cross-polarization converter based on Dirac semimetals

Abstract: We have investigated a single-layer metamaterial based on bulk Dirac semimetals (BDSs) that features tunable, broadband terahertz cross-polarization conversion in transmission mode. This effect can be actively tuned by changing the Fermi energy of the BDSs with no change to the geometry of the resonators. Tunability of the broadband polarization conversion is observed in the 3.82–7.88 THz range, over which the polarization conversion rate mostly remains above 80%. The proposed design offers a potentially effective approach to developing active terahertz polarization control devices for terahertz imaging, sensing, and communications.

Controllable broadband asymmetric transmission of terahertz wave based on Dirac semimetals.

Abstract: We present a dynamic metamaterial based on Dirac semimetals and capable of realizing broadband and tunable asymmetric transmission in the terahertz region. The Dirac semimetal resonators have a chiral structure patterned with double-T resonators that results in partial polarization conversion of waves incident upon the material, leading to asymmetric transmission across a wide frequency range. We show how the gradual shift of the semimetal Fermi energy permits a method of control over the asymmetric total transmission.

Light Scattering from Solid-State Quantum Emitters: Beyond the Atomic Picture

Abstract: Coherent scattering of light by a single quantum emitter is a fundamental process at the heart of many proposed quantum technologies. Unlike atomic systems, solid-state emitters couple to their host lattice by phonons. Using a quantum dot in an optical nanocavity, we resolve these interactions in both time and frequency domains, going beyond the atomic picture to develop a comprehensive model of light scattering from solid-state emitters. We find that even in the presence of a low-Q cavity with high Purcell enhancement, phonon coupling leads to a sideband that is completely insensitive to excitation conditions and to a nonmonotonic relationship between laser detuning and coherent fraction, both of which are major deviations from atomlike behavior.

Remote N2O gas sensing by enhanced 910-m propagation of THz pulses.

Abstract: We modified our 910-m long path THz system to increase the signal-to-noise ratio (S/N) with a nanostructure plasmonic THz transmitter (Tx) chip and a seven-mirror array reflector with 1 m diameter. When the THz pulse propagates the 910-m distance in the atmosphere, the S/N is up to 1170:1, which made the THz pulse measurable at a high water vapor density (WVD) of up to 25.2 g/m3. The time shift of the THz pulse according to the WVD measured for each meteorological season was matched well with the theoretical result. Due to the modified long-distance THz system, we were able to measure for the first time the resonances of N2O gas, which is located 455 m away from the Tx and receiver (Rx) chips and contained in a 1.5-m diameter rubber balloon under atmospheric pressure. Seven resonances can be detected except for one overlay of resonant frequency by water vapor.

Compensating Atmospheric Channel Dispersion for Terahertz Wireless Communication.

Abstract: We report and demonstrate for the first time a method to compensate atmospheric group velocity dispersion of terahertz pulses. In ultra-wideband or impulse radio terahertz wireless communication, the atmosphere reshapes terahertz pulses via group velocity dispersion, a result of the frequency-dependent refractivity of air. Without correction, this can significantly degrade the achievable data transmission rate. We present a method for compensating the atmospheric dispersion of terahertz pulses using a cohort of stratified media reflectors. Using this method, we compensated group velocity dispersion in the 0.2-0.3 THz channel under common atmospheric conditions. Based on analytic and numerical simulations, the method can exhibit an in-band power efficiency of greater than 98% and dispersion compensation up to 99% of ideal. Simulations were validated by experimental measurements.

Aerobic septic system health monitor and maintenance device, system, and method of its use

Abstract: Embodiments of an aerobic septic system health monitor, and a method of its use, incorporate a microcontroller, with associated software, in communication with an aerobic septic system (electro-mechanical) controller that, in turn, is connected to at least one aerobic septic system component and component sensor. By using the microcontroller and software, highly specific monitoring and feedback is available to a user. This approach also offers a clear and easily accessible interface between the user and the aerobic septic system, whereas no such interface exists on prior art systems. The monitor also offers multiple redundancy to address system failures, unlike prior art. Finally, it enables several forms of preventative maintenance that simply don't exist in prior art systems. In some embodiments, the monitor may serve as the aerobic septic system controller, either overriding or supplementing the installed controller or replacing it.