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arXiv2018

Voltage-induced strain clocking of nanomagnets with perpendicular magnetic anisotropies

Nanomagnetic logic (NML) has attracted attention during the last two decades due to its promise of high energy efficiency combined with non-volatility. Data transmission in NML relies on Bennett clocking through dipole interaction between neighboring nanomagnetic bits. This paper uses a fully coupled finite element model to simulate Bennett clocking based on strain-mediated multiferroic system for Ni, CoFeB and Terfenol-D with perpendicular magnetic anisotropies. Simulation results demonstrate that Terfenol-D system has the highest energy efficiency, which is 2 orders of magnitude more efficient than Ni and CoFeB. However, the high efficiency is associated with switching incoherency due to its large magnetostriction coefficient. It is also suggested that the CoFeB clocking system is slower and has lower bit-density than in Ni or Terfenol-D systems due to its large dipole coupling. Moreover, we demonstrate that the precessional perpendicular switching and the Bennett clocking can be achieved using the same strain-mediated multiferroic architecture with different voltage pulsing. This study opens new possibilities to an all-spin in-memory computing system.

physics.app-ph↗

arXiv2018

High efficient solar evaporation by airing multifunctional textile

Solar evaporation is important for many applications such as desalination, power generation and industrial drying. Recently, some studies on evaporation reported obtaining high energy efficiency and evaporation rate, which are based on floating evaporation setup (FES) with nanomaterials. Here, we proposed a new cheap and simple setup, named as airing evaporation setup (AES). It shows that the energy efficiency of AES reaches up to 87 % under 1 kW/m2 of solar irradiation, which is 14% higher than that of FES. Meanwhile, the total evaporation rate of AES is about 20% higher than that of FES. The theoretical analysis reveals that the main reason for a better performance of AES is the increasing evaporation area. More interesting, AES could be used for designing portable systems due to its simplicity and flexibility. Furthermore, we show that AES and the corresponding wick material can be used in solar desalination, textile quick-drying and warm-keeping.

physics.app-ph↗

arXiv2018

Gate-tunable near-field heat transfer

Active control over the flow of heat in the near-field holds promise for nanoscale thermal management, with applications in refrigeration, thermophotovoltaics, and thermal circuitry. Analogously to its electronic counterpart, the metal-oxide-semiconductor (MOS) capacitor, we propose a thermal switching mechanism based on accumulation and depletion of charge carriers in an ultra-thin plasmonic film, via application of external bias. In our proposed configuration, the plasmonic film is placed on top of a polaritonic dielectric material that provides a surface phonon polariton (SPhP) thermal channel, while also ensuring electrical insulation for application of large electric fields. The variation of carrier density in the plasmonic film enables the control of the surface plasmon polariton (SPP) thermal channel. We show that the interaction of the SPP with the SPhP significantly enhances the net heat transfer. We study SiC as the oxide and explore three classes of gate-tunable plasmonic materials: transparent conductive oxides, doped semiconductors, and graphene, and theoretically predict contrast ratios as high as 225%.

physics.app-ph↗

arXiv2018

Current-enhanced broadband THz emission from spintronic devices

An ultra-broadband THz emitter covering a wide range of frequencies from 0.1 to 10 THz is highly desired for spectroscopy applications. So far, spintronic THz emitters have been proven as one class of efficient THz sources with a broadband spectrum while the performance in the lower frequency range (0.1 to 0.5 THz) limits its applications. In this work, we demonstrate a novel concept of a current-enhanced broad spectrum from spintronic THz emitters combined with semiconductor materials. We observe a 2-3 order enhancement of the THz signals in a lower THz frequency range (0.1 to 0.5 THz), in addition to a comparable performance at higher frequencies from this hybrid emitter. With a bias current, there is a photoconduction contribution from semiconductor materials, which can be constructively interfered with the THz signals generated from the magnetic heterostructures driven by the inverse spin Hall effect. Our findings push forward the utilization of metallic heterostructures-based THz emitters on the ultra-broadband THz emission spectroscopy.

physics.app-ph↗

arXiv2018

Terahertz hyperspectral imaging with dual chip-scale combs

Hyperspectral imaging is a technique that allows for the creation of multi-color images. At terahertz wavelengths, it has emerged as a prominent tool for a number of applications, ranging from non-ionizing cancer diagnosis and pharmaceutical characterization to non-destructive artifact testing. Contemporary terahertz imaging systems typically rely on non-linear optical down-conversion of a fiber-based near-infrared femtosecond laser, requiring complex optical systems. Here, we demonstrate hyperspectral imaging with chip-scale frequency combs based on terahertz quantum cascade lasers. The dual combs are free-running and emit coherent terahertz radiation that covers a bandwidth of 220 GHz at 3.4 THz with ~10 μW per line. The combination of the fast acquisition rate of dual-comb spectroscopy with the monolithic design, scalability, and chip-scale size of the combs is highly appealing for future imaging applications in biomedicine and in the pharmaceutical industry.

physics.optics↗

arXiv2018

Suspended single mode microdisk lasers

Miniature semiconductor lasers have attracted a large amount of interest owing to their potential as highly integrated components in photonic circuits or in sensors. Particularly, microdisk lasers exploiting whispering gallery modes have been regarded as an important candidate because of their relatively small footprint and low threshold. However, it has been challenging for microdisk to operate under single mode operation and to lase in a preselected mode. We report subwavelength microdisk resonators suspended in air with connecting bridges and propose a simple method using the number and symmetry of bridges to enhance or reduce wave confinement in the whispering gallery cavity. Moreover, a suitable choice of bridges increases the quality factor of microdisks compared to microdisks resonator without bridges. Using this method, we demonstrate single mode lasing of preselected modes at telecommunication wavelength.

physics.app-ph↗

arXiv2018

Broadband, Temperature Tolerant and Passively Biased Resonantly Enhanced Mach-Zehnder Modulators

We describe a resonantly enhanced Mach-Zehnder modulator (MZM) that can be operated over a wide temperature range of 55C without being actively biased, while providing a significant resonant enhancement of 6.8 at the nominal wavelength / temperature compared to a linear MZM driven with a distributed driver. More importantly, it enables a ~20X improvement in power consumption compared to a 50 Ω matched linear traveling wave modulator with comparable phase shifter technology, drive voltage and output optical modulation amplitude. Passive biasing of the Mach-Zehnder interferometer is further implemented by replacing a splitter element in the MZM with a novel device combining splitting and fiber coupling functionalities in a single, multi-modal structure, that converts permanent fiber placement into a phase correction. Both concepts are combined in a single modulator device, removing the need for any type of active control in a wide temperature operation range.

physics.app-ph↗

arXiv2018

Ultrasensitive hybrid optical skin

Electronic skin, a class of wearable electronic sensors that mimic the functionalities of human skin, has made remarkable success in applications including health monitoring, human-machine interaction and electronic-biological interfaces. While electronic skin continues to achieve higher sensitivity and faster response, its ultimate performance is fundamentally limited by the nature of low-frequency AC currents in electronic circuitries. Here we demonstrate highly sensitive optical skin (O-skin) in which the primary sensory elements are optically driven. The simple construction of the sensors is achieved by embedding glass micro/nanofibers (MNFs) in thin layers of polydimethylsiloxane (PDMS). Enabled by the highly sensitive power-leakage response of the guided modes from the MNF upon external stimuli, our optical sensors show ultrahigh sensitivity (1870/kPa), low detection limit (7 mPa) and fast response (10 microseconds) for pressure sensing, significantly exceeding the performance metrics of state-of-the-art electronic skins. Electromagnetic interference (EMI)-free detection of high-frequency vibrations, wrist pulse and human voice are realized. Moreover, a five-sensor optical data glove and a 2x2-MNF tactile sensor are demonstrated. Our results pave the way toward wearable optical devices ranging from ultrasensitive flexible sensors to optical skins.

physics.app-ph↗

arXiv2018

Single-Multi-Single Fibre Optic Structure Based Water Depth Sensor

We propose and demonstrate a technique easy to fabricate and measure water depth based on selective mode excitation using single-multi-single (SMS) mode structure. The high extinction ratio has been achieved by equally exciting preselected modes of the multi-mode fibre (MMF) by optimizing the core offset at both the input/output splices of the SMS structure, and a wavelength shifting has been achieved by varying the ratio of major to minor axis of the MMF loop. A theoretical analysis of the observed behaviour is also presented showing an excellent agreement between the theoretical and experimental results.

physics.app-ph↗

arXiv2018

Carbon nanotube/metal corrosion issues for nanotube coatings and inclusions in a matrix

Corrosion is an inevitable phenomenon that is inherent in metals and even though there has been significant research on this subject, no ideal protection has been discovered to fully prevent corrosion. However, methods such as using protective coatings, and modifying the structure or composition of the material have been used to slow down gradual corrosion and fortunately they proved to be quite beneficial. The research focus has shifted to integrating novel materials and structures to improve the corrosion resistance of composites. Carbon nanotubes (CNTs) are an attractive and promising filler due to their chemical inertness and high mechanical, electrical, and thermal properties. CNTs can fill the gaps of metals and polymer-based composites by forming a passive layer on metals and promoting sacrificial protection in zinc rich polymer (ZRP) coatings, and can therefore function as an anti-corrosion filler. This paper reviews the research that has been performed to better understand the influence of CNTs on corrosion resistance in composites. Accordingly, in metal matrix composites (MMCs), most of the work has been carried out on electrodeposited coatings, namely Ni-based-CNT composites, which show improved corrosion resistance by CNT addition. On the other hand, there are a few papers that have studied the corrosion resistance of Mg-based-CNT composites and their corrosion results contradict those obtained from other metal-CNT composites. For ZRPs or polymer-based coatings there are a few papers that studied the effect of CNTs on the corrosion of said composites. It is believed that CNTs can strengthen the adhesion between the coating and the substrate and facilitate sacrificial protection by Zn particles by forming a conductive network, hence the improved corrosion resistance.

physics.app-ph↗

arXiv2018

A monolithic frequency comb platform based on interband cascade lasers and detectors

Optical frequency combs enable all-solid-state spectrometers that will trigger a breakthrough in miniaturization and on-chip integration of mid-infrared sensing technology. Interband cascade lasers (ICLs) are an ideal candidate for practical implementations due to their low power consumption and zero-bias detection functionality. Here, we demonstrate the generation of self-starting ICL frequency combs. We show that the gain is fast enough to respond to beating of the intracavity field, which hinders the formation of short pulses. Instead, the ICL operates in a comb state, where the phases of the fundamental intermode beatings are splayed over a range of $2π$. This state appears to be general to self-starting combs based on the inherent gain nonlinearity and minimizes oscillations of the population inversion. Using the same epi-layer material, we demonstrate efficient detector operation at room temperature up to several GHz bandwidth and thereby provide a complete and unmatched platform for monolithic and battery driven dual-comb spectroscopy.

physics.optics↗

arXiv2018

Graphene oxide membranes: on the absence of "graphene capillaries", "ultrafast flow" rate and "ultraprecise sieving"

The data by Q.Yang et al suggest absence of "ultrafast flow" of solvent across graphene oxide (GO) membranes. The "ultrafast flow" is result of using unrealistic geometrical model with close packed hole-free micrometer sized GO flakes providing only 0.1 % of area in each layer available for permeation. The data by Q.Yang et all demonstrate that at least 3-5 % of total layer area are available for permeation in real GO membranes due to holes between irregularly shaped flakes. At least 2-3 percent of area also needs to be added to the permeation cross section due to holes and cracks in GO flakes, especially abundant due to prolonged sonication of dispersions. Permeation of solutions mostly through pinholes penetrating tens of GO layers suggests that "graphene capillaries" are not required to explain water flow across the membrane. Taking into account realistic packing of GO flakes with holes between the flakes and across the flakes, 2-3 orders of magnitude shorter permeation path should be formed. Considering shorter zigzag permeation path between GO sheets and 5-10 % of area in each layer available for permeation due to holes across and between GO flakes, permeation rates across GO membranes can be explained by trivial diffusion. In absence of "graphene capillaries", the "ultra-precise sieving" related to "cutoff" value of 4.5 Å (hydration diameter) provided by "graphene capillaries" has little meaning. As it is well known from earlier studies and now demonstrated by Q.Yang et al using their own samples the swelling of GO membranes is different for different solutions, depends on concentration of solutes and results in delamination in many solutions. Q.Yang et al provide controversial data for stability of their GO membranes in water citing use of surfactant to prevent dissolving. Oxidation state of GO membranes remains to be unknown due to incorrect analysis of XPS spectra.

physics.app-ph↗

arXiv2018

The TT-PET Data Acquisition and Trigger System

This paper describes the data acquisition and trigger system of the Thin Time-of-flight PET (TT-PET) scanner. The system is designed to read out in the order of 1000 pixel sensors used in the scanner and to provide a reference timing signal to each sensor in order to measure time differences of better than 30 ps. This clock distribution is measured to have a jitter of less than 4 ps at the sensors. Collected data is locally processed before being forwarded to storage. Data flow as well as control, configuration and monitoring aspects are are also addressed.

physics.ins-det↗

arXiv2018

THz-to-Optical Conversion in Wireless Communications Using an Ultra-Broadband Plasmonic Modulator

Future wireless communication networks have to handle data rates of tens or even hundreds of Gbit/s per link, requiring carrier frequencies in the unallocated terahertz (THz) spectrum. In this context, seamless integration of THz links into existing fiber-optic infrastructures is of great importance to complement the inherent portability and flexibility advantages of wireless networks by the reliable and virtually unlimited capacity of optical transmission systems. On the technological level, this requires novel device and signal processing concepts for direct conversion of data streams between the THz and the optical domains. Here, we report on the first demonstration of a THz link that is seamlessly integrated into a fiber-optic network using direct terahertz-to-optical (T/O) conversion at the wireless receiver. We exploit an ultra-broadband silicon-plasmonic modulator having a 3 dB bandwidth in excess of 0.36 THz for T/O conversion of a 50 Gbit/s data stream that is transmitted on a 0.2885 THz carrier over a 16 m-long wireless link. Optical-to-terahertz (O/T) conversion at the wireless transmitter relies on photomixing in a uni-travelling-carrier photodiode.

physics.app-ph↗

arXiv2018

Laser writing of scalable single colour centre in silicon carbide

Single photon emitters in silicon carbide (SiC) are attracting attention as quantum photonic systems. However, to achieve scalable devices it is essential to generate single photon emitters at desired locations on demand. Here we report the controlled creation of single silicon vacancy ($V_{Si}$) centres in 4H-SiC using laser writing without any post-annealing process. Due to the aberration correction in the writing apparatus and the non-annealing process, we generate single $V_{Si}$ centres with yields up to 30%, located within about 80 nm of the desired position in the transverse plane. We also investigated the photophysics of the laser writing $V_{Si}$ centres and conclude that there are about 16 photons involved in the laser writing $V_{Si}$ centres process. Our results represent a powerful tool in fabrication of single $V_{Si}$ centres in SiC for quantum technologies and provide further insights into laser writing defects in dielectric materials.

cond-mat.mes-hall↗

arXiv2018

T-A homogenized and multi-scale models with real-time simulation capabilities for large-scale HTS systems

The emergence of second-generation high temperature superconducting tapes has favored the development of large-scale superconductor systems. The mathematical models for superconductors have evolved from simple analytical models to complex numerical models. The available analytical models are just capable of estimating electromagnetic quantities in single wires or small arrays. The numerical models like the H formulation finite element models are useful for the analysis of more medium-size systems, but their application in large-scale systems is problematic due to the excessive cost in terms of memory and the computation time. Then it is necessary to devise new strategies to tackle this challenge. The homogenization and the multi-scale approach are methodologies that have successfully simplified the description of the systems allowing the study of large-scale systems. Recently, efficient calculations have been achieved using the T-A formulation. In this manuscript, we analyze the adequate order of the elements used in the T-A formulation. More importantly, we propose a series of adaptations to the homogenization and multi-scale methodologies in order to allow their implementation to the T-A formulation models. The proposed strategies are validated by means of comparing them with the H reference model of a racetrack coil. The computation time and memory demand are substantially reduced up to a point that makes it possible to perform real-time simulations for slow ramping cycles. At the same time the comparison demonstrates a very good agreement with respect to the reference model, both at a local and global level, is achieved.

physics.app-ph↗

arXiv2018

Higher Order Nonlinear Dynamics in AlGaAs Doped Glass Photonic Crystal Fibers at Sub Pico-Joule Energy

In the present paper, a unique semiconductor doped glass photonic crystal fiber has been designed which is suitable for soliton propagation at sub pico-Joule energy. The fiber promises to yield low and uniform anomalous dispersion profile and very large optical nonlinearities 25211 W^(-1) km^(-1) at telecommunication wavelength, thus facilitating soliton formation at ultralow energy. The observed magnitude of nonlinearity is the highest reported ever till date in AlGaAs doped glass. The soliton dynamics has been investigated taking into account of higher-order dispersions and nonlinearities. Propagating solitons breadth and experience large frequency shift, which decreases with the increase in the initial pulse width and increases with the increase in pulse energy. Temporal width of solitons oscillate, the frequency and amplitude of oscillations increase with the increase in the value of pulse energy.

physics.optics↗

arXiv2018

Design and Analysis of a multiple quantum-well plasmonic Germanium/Silicon-Germanium nanolaser

There are many researches reported in using Germanium in Silicon based lasers but acquiring this potential for a nanolaser may also be important for development of a CMOS compatible plasmon source. In this paper, a Ge/SiGe multiple quantum well waveguide integrated nanolaser is introduced and theoretically investigated. This structure is simulated and by means of a semi-classical rate equation model, its performance is studied. The proposed nano laser has a tiny footprint of 0.07um^2, room temperature performance and CMOS compatible fabrication process. The output performance of the proposed structure as estimated, is noticeable. These simulated results, compared with some experiments and redundant software double checking, show acceptable compatibility. In 1550nm output wavelength, it provides 3.83uW output power with 1uA injection current while maintaining its performance in a wide modulation bandwidth of 24.5GHz. This remarkable performance is achieved thanked to a Purcell factor equal to 2208.

physics.optics↗